Follow up to my L71 overheating issue
03-22-2016, 05:52 PM
#21
If your vacuum at idle gets back to the stock specs then you will need this can:
12" B26, NAPA VC1765 or equivalent in another brand.
I would recommend the one above with the stock cam.
If your vac at idle is around 10 (non stock spec) Both GM and NAPA have discontinued the vacuum advance can. GM D1312C - B28 and NAPA VC1810. I read that rock auto may have them. Be aware that this one starts advancing at 5" and is all in at 8"@16 degrees advance.
Either one may be found on EBay as well.
12" B26, NAPA VC1765 or equivalent in another brand.
I would recommend the one above with the stock cam.
If your vac at idle is around 10 (non stock spec) Both GM and NAPA have discontinued the vacuum advance can. GM D1312C - B28 and NAPA VC1810. I read that rock auto may have them. Be aware that this one starts advancing at 5" and is all in at 8"@16 degrees advance.
Either one may be found on EBay as well.
Last edited by babbah; 03-22-2016 at 06:15 PM.
03-22-2016, 06:19 PM
#22
Drifting
When the car was new (and the radiator in good shape), it didn't overheat in normal driving. If you got stuck in heavy stop/go traffic on a warm day, it would overheat. Typical of the L71 with ported vacuum.
I haven't had a chance to try it out since a new DeWitts radiator, changing to manifold vacuum, and the B28 vacuum can.
03-22-2016, 06:21 PM
#23
Le Mans Master
Airtex Distributor Vacuum Advance 4V1053 supposed to be same as B28.
Check out this thread. Airtex and Standard Ignition parts are available at most parts stores. You may have to order the part and wait a day for delivery.
https://www.corvetteforum.com/forums...er-source.html
Check out this thread. Airtex and Standard Ignition parts are available at most parts stores. You may have to order the part and wait a day for delivery.
https://www.corvetteforum.com/forums...er-source.html
03-22-2016, 06:42 PM
#24
Melting Slicks
I've been reluctant to change the timing, due to the fact that I neglected to bring my timing light with me, and I really didn't want to buy another one, but it looks like I may have to. As I asked before where would one go about buying a new vac canister? I have this adjustable one that I was going to try but I would rather have a stock looking one if I could get it.
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Dave Cunningham (03-22-2016)
03-22-2016, 07:33 PM
#25
Racer
Thread Starter
It looks like Duke says the B28 comes in at 8" vacuum. I think that is an AC Delco part.
I would hit the traditional loca Auto Parts store. There is a chain of Warehouses in LA locally owned. Hanson Distributors. Call Hanson, tell them where you are and ask for the number of their closest store to you. They sell most independent stores in your area and deliver parts from the WD to these stores every day giving you access to all parts they sell.
I would think Napa could have offered the same service but your guy chose not to put in the effort.
You might also find the part on Amazon and get it next day delivery.
I would hit the traditional loca Auto Parts store. There is a chain of Warehouses in LA locally owned. Hanson Distributors. Call Hanson, tell them where you are and ask for the number of their closest store to you. They sell most independent stores in your area and deliver parts from the WD to these stores every day giving you access to all parts they sell.
I would think Napa could have offered the same service but your guy chose not to put in the effort.
You might also find the part on Amazon and get it next day delivery.
I took it out for a test ride and though I didn't go too far, it never got over about 170 or so on the gauge. But if I try to get on it at all it knocks like crazy. I went and bought a timing light, and haven't checked it yet, but I noticed that the new vac pot looked like it would pull a couple more degrees of timing than the stock unit, I should have took a picture of it before I installed it , but here is a pic of the stock one. The Accel unit has a slightly longer opening, which allows it to pull further than the old one.
03-22-2016, 07:37 PM
#26
Sounds like you are getting too much total advance. Check the timing with your light at idle and then rev the engine to see what your total advance is. Then go from there.
Set your initial timing advance back in small increments until you don't ping and get back within specs.
Your vac at idle now should be more normal for your engine so be careful that the B28 can gives you too much advance too soon. If so go to the 1765 can.
Then You should be in good shape
Set your initial timing advance back in small increments until you don't ping and get back within specs.
Your vac at idle now should be more normal for your engine so be careful that the B28 can gives you too much advance too soon. If so go to the 1765 can.
Then You should be in good shape
Last edited by babbah; 03-22-2016 at 07:47 PM.
03-22-2016, 08:33 PM
#27
Racer
Thread Starter
Sounds like you are getting too much total advance. Check the timing with your light at idle and then rev the engine to see what your total advance is. Then go from there.
Set your initial timing advance back in small increments until you don't ping and get back within specs.
Your vac at idle now should be more normal for your engine so be careful that the B28 can gives you too much advance too soon. If so go to the 1765 can.
Then You should be in good shape
Set your initial timing advance back in small increments until you don't ping and get back within specs.
Your vac at idle now should be more normal for your engine so be careful that the B28 can gives you too much advance too soon. If so go to the 1765 can.
Then You should be in good shape
03-22-2016, 08:42 PM
#28
Yes, that is exactly what I have on my BB, just Revving it past 3000 RPM. No load. Under load you should have around 36 degrees total. Under load vacuum is nill. 14" of vacuum at idle now sounds normal for your setup so I'd get the 1765 can or if you've dialed the one in that you have use it.
Then set your initial timing correctly and you should be good to go. You may set the initial timing a bit higher than 4 degrees advance. and then adjust idle accordingly.
Last edited by babbah; 03-22-2016 at 08:52 PM.
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Dave Cunningham (03-22-2016)
03-23-2016, 02:34 AM
#29
Le Mans Master
The distributor advance curve is unique for each engine and for perfect tune will need some tweaking. The most important number to avoid engine damage is not exceeding the max number for your engine while under load. This can be checked by disconnecting the vacuum from your distributor, plug the vacuum and then set your total timing.
Rev the engine with a set back timing light attached and make sure you don't have more than 36 degrees when your mechanical advance is fully engaged. You should also record at what RPM your distributor stops advancing. This is normally set to be around 3,000 RPM. Some come in a little earlier and some come in a little later but this number is very important both for performance and durability so record it. With 34-36 degrees total at 3,000 RPM you may run perfect but at 38 degrees total you could damage pistons and at 32 degrees total it will feel sluggish, so this number is your most important number to be accurate with.
By setting your distributor timing so it is accurate at 36 degrees at 3,000 RPM your timing at idle is done and you live with the number it comes out to be at idle. This is determined by how much mechanical advance is built into your distributor. If you have 22 degree's of mechanical advance built in, measured with the previous test your idle timing reading will now be 14 degrees initial timing at idle now 14 degrees plus 22 mechanical = 36 total at 3,000 RPM.
Drive it now with the vacuum disconnected. Make sure it is not pinging while accelerating with these distributor settings. If it pings at this point your mechanical advance is coming in too soon and you will need change internal springs in the distributor to slow this mechanical advance introduction.
Now you play with the vacuum advance to fine tune drive ability.
Check your timing while testing the vacuum advance and see how much timing the vacuum can adds fully engaged. If you are pinging after adding the Vacuum advance you will need to slow down the introduction of the vacuum advance till your engine is happy and your pinging goes away. Lars has a great article describing this in detail on this forum. There are shops that can dial in known good advance curves for you if you take them your distributor or you can dial it in to your liking by playing with it and experimenting but never exceed the Total timing at 3,000 of 34-36.
You will get it dialed in to your liking if you are patient and you have already proven you are patient. The good news is your internals are perfect and your vacuum is perfect now that proper advance is there at idle. Congratulations.
Rev the engine with a set back timing light attached and make sure you don't have more than 36 degrees when your mechanical advance is fully engaged. You should also record at what RPM your distributor stops advancing. This is normally set to be around 3,000 RPM. Some come in a little earlier and some come in a little later but this number is very important both for performance and durability so record it. With 34-36 degrees total at 3,000 RPM you may run perfect but at 38 degrees total you could damage pistons and at 32 degrees total it will feel sluggish, so this number is your most important number to be accurate with.
By setting your distributor timing so it is accurate at 36 degrees at 3,000 RPM your timing at idle is done and you live with the number it comes out to be at idle. This is determined by how much mechanical advance is built into your distributor. If you have 22 degree's of mechanical advance built in, measured with the previous test your idle timing reading will now be 14 degrees initial timing at idle now 14 degrees plus 22 mechanical = 36 total at 3,000 RPM.
Drive it now with the vacuum disconnected. Make sure it is not pinging while accelerating with these distributor settings. If it pings at this point your mechanical advance is coming in too soon and you will need change internal springs in the distributor to slow this mechanical advance introduction.
Now you play with the vacuum advance to fine tune drive ability.
Check your timing while testing the vacuum advance and see how much timing the vacuum can adds fully engaged. If you are pinging after adding the Vacuum advance you will need to slow down the introduction of the vacuum advance till your engine is happy and your pinging goes away. Lars has a great article describing this in detail on this forum. There are shops that can dial in known good advance curves for you if you take them your distributor or you can dial it in to your liking by playing with it and experimenting but never exceed the Total timing at 3,000 of 34-36.
You will get it dialed in to your liking if you are patient and you have already proven you are patient. The good news is your internals are perfect and your vacuum is perfect now that proper advance is there at idle. Congratulations.
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Dave Cunningham (03-23-2016)
03-23-2016, 05:28 AM
#30
Dave,
I would be very careful sticking a timing light and hand close to a running engine at any elevated RPM, you may end up with more than timing specs to worry about.
Sounds like you are getting the idea about timing. Give some thought to placing a 36-38* mark on the harmonic damper, this can be done by rotating the engine at 12* intervals using the timing cover tab while marking the damper. Make sure the ignition key is off and put the engine in third gear to rock the tires as this will move the crankshaft so you can get your marks.
Remove the centrifugal springs and start the engine and at approx 900-1000RPM you can time the engine for total WOT advance at that 36-38* mark you made. The initial timing will fall where it will, if at that point you decide to run more initial timing you will need to shorten the total WOT timing, you get the idea.
At that point you can tune the V/A to provide additional full manifold 10-15* timing.
I would be very careful sticking a timing light and hand close to a running engine at any elevated RPM, you may end up with more than timing specs to worry about.
Sounds like you are getting the idea about timing. Give some thought to placing a 36-38* mark on the harmonic damper, this can be done by rotating the engine at 12* intervals using the timing cover tab while marking the damper. Make sure the ignition key is off and put the engine in third gear to rock the tires as this will move the crankshaft so you can get your marks.
Remove the centrifugal springs and start the engine and at approx 900-1000RPM you can time the engine for total WOT advance at that 36-38* mark you made. The initial timing will fall where it will, if at that point you decide to run more initial timing you will need to shorten the total WOT timing, you get the idea.
At that point you can tune the V/A to provide additional full manifold 10-15* timing.
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Dave Cunningham (03-23-2016)
03-23-2016, 10:26 AM
#31
Racer
Thread Starter
The distributor advance curve is unique for each engine and for perfect tune will need some tweaking. The most important number to avoid engine damage is not exceeding the max number for your engine while under load. This can be checked by disconnecting the vacuum from your distributor, plug the vacuum and then set your total timing.
Rev the engine with a set back timing light attached and make sure you don't have more than 36 degrees when your mechanical advance is fully engaged. You should also record at what RPM your distributor stops advancing. This is normally set to be around 3,000 RPM. Some come in a little earlier and some come in a little later but this number is very important both for performance and durability so record it. With 34-36 degrees total at 3,000 RPM you may run perfect but at 38 degrees total you could damage pistons and at 32 degrees total it will feel sluggish, so this number is your most important number to be accurate with.
By setting your distributor timing so it is accurate at 36 degrees at 3,000 RPM your timing at idle is done and you live with the number it comes out to be at idle. This is determined by how much mechanical advance is built into your distributor. If you have 22 degree's of mechanical advance built in, measured with the previous test your idle timing reading will now be 14 degrees initial timing at idle now 14 degrees plus 22 mechanical = 36 total at 3,000 RPM.
Drive it now with the vacuum disconnected. Make sure it is not pinging while accelerating with these distributor settings. If it pings at this point your mechanical advance is coming in too soon and you will need change internal springs in the distributor to slow this mechanical advance introduction.z
Now you play with the vacuum advance to fine tune drive ability.
Check your timing while testing the vacuum advance and see how much timing the vacuum can adds fully engaged. If you are pinging after adding the Vacuum advance you will need to slow down the introduction of the vacuum advance till your engine is happy and your pinging goes away. Lars has a great article describing this in detail on this forum. There are shops that can dial in known good advance curves for you if you take them your distributor or you can dial it in to your liking by playing with it and experimenting but never exceed the Total timing at 3,000 of 34-36.
You will get it dialed in to your liking if you are patient and you have already proven you are patient. The good news is your internals are perfect and your vacuum is perfect now that proper advance is there at idle. Congratulations.
Rev the engine with a set back timing light attached and make sure you don't have more than 36 degrees when your mechanical advance is fully engaged. You should also record at what RPM your distributor stops advancing. This is normally set to be around 3,000 RPM. Some come in a little earlier and some come in a little later but this number is very important both for performance and durability so record it. With 34-36 degrees total at 3,000 RPM you may run perfect but at 38 degrees total you could damage pistons and at 32 degrees total it will feel sluggish, so this number is your most important number to be accurate with.
By setting your distributor timing so it is accurate at 36 degrees at 3,000 RPM your timing at idle is done and you live with the number it comes out to be at idle. This is determined by how much mechanical advance is built into your distributor. If you have 22 degree's of mechanical advance built in, measured with the previous test your idle timing reading will now be 14 degrees initial timing at idle now 14 degrees plus 22 mechanical = 36 total at 3,000 RPM.
Drive it now with the vacuum disconnected. Make sure it is not pinging while accelerating with these distributor settings. If it pings at this point your mechanical advance is coming in too soon and you will need change internal springs in the distributor to slow this mechanical advance introduction.z
Now you play with the vacuum advance to fine tune drive ability.
Check your timing while testing the vacuum advance and see how much timing the vacuum can adds fully engaged. If you are pinging after adding the Vacuum advance you will need to slow down the introduction of the vacuum advance till your engine is happy and your pinging goes away. Lars has a great article describing this in detail on this forum. There are shops that can dial in known good advance curves for you if you take them your distributor or you can dial it in to your liking by playing with it and experimenting but never exceed the Total timing at 3,000 of 34-36.
You will get it dialed in to your liking if you are patient and you have already proven you are patient. The good news is your internals are perfect and your vacuum is perfect now that proper advance is there at idle. Congratulations.
Also if you have 36 degrees of total mechanical advance, and then add back in the vacuum advance , which I think is only around ten degrees, how do you end up with the total of , I think someone said 55 or so?
This is going to be my project today, so hopefully I can get her dialed in, and I no longer have any cooling issues.
03-23-2016, 10:54 AM
#32
Dave,
Three types of engine advance to consider.
The first is idle advance, initial timing and full manifold vacuum advance.
The second is WOT advance, initial timing and full centrifugal advance.
Third is total advance, this is the sum of all variables and includes initial,centrifugal and vacuum advance. This changes while driving because many times the engine RPM is not high enough for the centrifugal advance weights to be fully extended. Rule of thumb is total advance in the low 50's max for best economy.
Many times the vacuum advance can provide 10-15* additional advance and sometimes this can be to much given the initial timing setting and how fast the centrifugal advances so it can be reduced to the lower number (10*) to keep the motor from ping at certain load conditions.
It all depends on what makes the engine happy and it's a trial and error because many engine build factors effect what works best.
Don't be afraid to experiment, when you get happy with that you can start to tune the carburetors. :-)
Three types of engine advance to consider.
The first is idle advance, initial timing and full manifold vacuum advance.
The second is WOT advance, initial timing and full centrifugal advance.
Third is total advance, this is the sum of all variables and includes initial,centrifugal and vacuum advance. This changes while driving because many times the engine RPM is not high enough for the centrifugal advance weights to be fully extended. Rule of thumb is total advance in the low 50's max for best economy.
Many times the vacuum advance can provide 10-15* additional advance and sometimes this can be to much given the initial timing setting and how fast the centrifugal advances so it can be reduced to the lower number (10*) to keep the motor from ping at certain load conditions.
It all depends on what makes the engine happy and it's a trial and error because many engine build factors effect what works best.
Don't be afraid to experiment, when you get happy with that you can start to tune the carburetors. :-)
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Dave Cunningham (03-23-2016)
03-23-2016, 12:08 PM
#33
Race Director
Member Since: May 2000
Location: Redondo Beach USA
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The L-71 OE centrifugal curve is 0 @ 900, 30 @ 3800. Of course, who knows what it is on a nearly 50 year old car. You have to measure the curve with a dial back light to verify what it really is, which establishes the baseline. Start the process by determining the start point, then take readings every 500 RPM and determine the RPM where it achieves maximum advance. Of course, record all the data, and this test must be done with the VAC disconnected and the signal line plugged. A golf tee works very well.
Best total WOT advance for big blocks is in the range of 36-40 deg., and the maximum you can run in this range is limited only by detonation, so it's best to start at the high end of the range and if it doesn't detonate, you're good to go. If it does detonate back down in two degree increments until the detonation goes away.
To set total WOT advance (VAC disconnected, line plugged), set the dial on the timing light at your total WOT advance target, rev the engine a few hundred revs above where you determined the centrifugal is all in and rotate the distributor to bring the balancer notch to zero on the timing tab.
The OE L-71 centrifugal curve is somewhere between the "lazy" ones that max out at 5100 and the most aggressive on the 365/375 HP engines, which is all in at 2350. Once you have established the most detonation-free total WOT advance the engine will tolerate, get a Mr. Gasket 928G spring kit and use the lighter springs to see if you can get it in sooner without detonation.
Once you complete the above tasks (including converting to full time vacuum advance with a B26 VAC) you have optimized the spark advance map for best performance and fuel economy.
If you end up with total WOT advance of 38 and the centrifugal is really 30 then the initial should be 8. Total idle advance will be about 24 (initial plus full vacuum advance of 16), and maximum cruise advance, above the max centrifugal advance engine speed will be 38+16 = 54.
The final task after the spark advance is optimized is going through the idle speed-mixture adjustment procedure as explained in the CSM. I recommend a target idle speed of 900. Idle vacuum should be in the 14-15" range with the OE cam, and there will be a slight lope.
The difference between the above setup and OE is dramatic - better idle quality, better low rev throttle response, less tendency to run hot in hot weather heavy traffic conditions, and better fuel economy.
Another check is to measure the exhaust manifold temperatures with an IR gun. With the above setup they should be no more than about 500F. With the OE setup expect about 900. As the exhaust gas traverses the head ports considerably more heat is transferred to the cooling system, which is why the OE setup can run hot, especially if radiator heat transfer performance is degraded from as new.
The reason EGT is higher with the OE setup is because the total idle advance is less than what is needed for peak idle efficiency, which is indicated by minimum EGT/manifold temperature. Adding full time vacuum advance gets total idle advance close to the optimum range of 25-30 for a high overlap cams, which means more of the fuel's energy is being used to overcome internal engine friction rather than being thrown out the exhaust, and this is why fuel economy, especially in around town stop-and-go driving improves.
Total parts cost is about 25-30 bucks (new VAC, spring kit, 1/8" tee and vacuum tubing) and a couple of hours of time.
Duke
Best total WOT advance for big blocks is in the range of 36-40 deg., and the maximum you can run in this range is limited only by detonation, so it's best to start at the high end of the range and if it doesn't detonate, you're good to go. If it does detonate back down in two degree increments until the detonation goes away.
To set total WOT advance (VAC disconnected, line plugged), set the dial on the timing light at your total WOT advance target, rev the engine a few hundred revs above where you determined the centrifugal is all in and rotate the distributor to bring the balancer notch to zero on the timing tab.
The OE L-71 centrifugal curve is somewhere between the "lazy" ones that max out at 5100 and the most aggressive on the 365/375 HP engines, which is all in at 2350. Once you have established the most detonation-free total WOT advance the engine will tolerate, get a Mr. Gasket 928G spring kit and use the lighter springs to see if you can get it in sooner without detonation.
Once you complete the above tasks (including converting to full time vacuum advance with a B26 VAC) you have optimized the spark advance map for best performance and fuel economy.
If you end up with total WOT advance of 38 and the centrifugal is really 30 then the initial should be 8. Total idle advance will be about 24 (initial plus full vacuum advance of 16), and maximum cruise advance, above the max centrifugal advance engine speed will be 38+16 = 54.
The final task after the spark advance is optimized is going through the idle speed-mixture adjustment procedure as explained in the CSM. I recommend a target idle speed of 900. Idle vacuum should be in the 14-15" range with the OE cam, and there will be a slight lope.
The difference between the above setup and OE is dramatic - better idle quality, better low rev throttle response, less tendency to run hot in hot weather heavy traffic conditions, and better fuel economy.
Another check is to measure the exhaust manifold temperatures with an IR gun. With the above setup they should be no more than about 500F. With the OE setup expect about 900. As the exhaust gas traverses the head ports considerably more heat is transferred to the cooling system, which is why the OE setup can run hot, especially if radiator heat transfer performance is degraded from as new.
The reason EGT is higher with the OE setup is because the total idle advance is less than what is needed for peak idle efficiency, which is indicated by minimum EGT/manifold temperature. Adding full time vacuum advance gets total idle advance close to the optimum range of 25-30 for a high overlap cams, which means more of the fuel's energy is being used to overcome internal engine friction rather than being thrown out the exhaust, and this is why fuel economy, especially in around town stop-and-go driving improves.
Total parts cost is about 25-30 bucks (new VAC, spring kit, 1/8" tee and vacuum tubing) and a couple of hours of time.
Duke
Last edited by SWCDuke; 03-23-2016 at 12:32 PM.
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Dave Cunningham (03-23-2016),
Westlotorn (03-23-2016)
03-23-2016, 01:13 PM
#34
Racer
Thread Starter
Duke after our conversation last night, I ordered a vc1765 from Napa this morning, and it will be here at 11. I'm not sure how many degrees it adds but I think they are all in at 12" correct?
03-23-2016, 01:18 PM
#35
Racer
Thread Starter
The last line in your article states " and I am never going to talk about vac cans again, ever!" Lol
03-23-2016, 01:26 PM
#37
Originally Posted by Westlotorn
I did not realize a big block could tolerate that much timing. The 36 quoted is a small block number. Thanks Duke
03-23-2016, 02:50 PM
#38
Racer
Thread Starter
Ok , I set VAC to match the specs of the vac 1765, plugged off the vacuum advance set my timing light to 38 and adjusted it accordingly. Took some tools with my and headed out for a test drive. The car felt great and pulled real hard, but quite a bit of spark knock when bogged down. So I pulled over twice and retarded it a bit each time, and it's is pretty good now. It's probably about 80 degrees out and it cooled very well.
I have not set the idle mixture yet, and I am wondering if it is causing this other problem I am having. Once the car is good and warm if you come to a light it will idle ok for a few seconds and then start to falter, and will die if you don't I've it some gas. If I can solve that problem I think it is drivable now.
I have not set the idle mixture yet, and I am wondering if it is causing this other problem I am having. Once the car is good and warm if you come to a light it will idle ok for a few seconds and then start to falter, and will die if you don't I've it some gas. If I can solve that problem I think it is drivable now.
03-23-2016, 02:59 PM
#39
Le Mans Master
Just to verify, does your timing advance smoothly as you rev from idle to 3500 rpm?
It should move nice and smooth, consistent with RPM change.
Where does it max out. 3k,3.5k, 4K,5k?
Sounds like your getting close.
It should move nice and smooth, consistent with RPM change.
Where does it max out. 3k,3.5k, 4K,5k?
Sounds like your getting close.
03-23-2016, 03:10 PM
#40
Ok , I set VAC to match the specs of the vac 1765, plugged off the vacuum advance set my timing light to 38 and adjusted it accordingly. Took some tools with my and headed out for a test drive. The car felt great and pulled real hard, but quite a bit of spark knock when bogged down. So I pulled over twice and retarded it a bit each time, and it's is pretty good now. It's probably about 80 degrees out and it cooled very well.
I have not set the idle mixture yet, and I am wondering if it is causing this other problem I am having. Once the car is good and warm if you come to a light it will idle ok for a few seconds and then start to falter, and will die if you don't I've it some gas. If I can solve that problem I think it is drivable now.
I have not set the idle mixture yet, and I am wondering if it is causing this other problem I am having. Once the car is good and warm if you come to a light it will idle ok for a few seconds and then start to falter, and will die if you don't I've it some gas. If I can solve that problem I think it is drivable now.
Your getting there. :-) Consider leaving the total WOT advance (initial + centrifugal) near the 38* and think about reducing the V/A travel 4-6* +- to get the rattle out. This should get you 10-12* vacuum advance. The engine will respond better when you stand on the throttle because the V/A will go away but the timing will still be advanced more on the lower end to help light a momentary lean mixture. What I am suggesting is to retard the timing by limiting the V/A instead of retarding by turning the distributor.
I am fairly confident the emulsion screws need to be adjusted on the carburetor and that is your pudder out problem.