I think my butterfly is stuck open - pic
06-17-2014, 07:35 PM
#1
Heel & Toe
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I think my choke is stuck open - pic
So, I just got a 73 with the standard 350 engine the other day. Yesterday it started idling rough and actually quit on me twice.
It would crank then immediately die. Would not run again until I let it sit for about 10 minutes.
It had (guessing) old fuel in it so I siphoned that out and added fresh. The guy that had it before me only drove 4,000 miles in 10 years (83k on the car)
I also changed the spark plugs and ignition wires today. Driving down the road it seems to be OK.
At idle, the gauge shows the engine bouncing between 500-700RPM and the engine sounds rough & it occasionally dies.
One thing I noticed is the butterfly on the carb never closes. Could that be the cause?
None of the rods that are holding it open will move.
I have no idea if it was stuck open when it was running ok.
How can I release it?
I just did a vacuum test (hopefully I connected it the right spot). The needle was fairly stable at 14 & went to zero then higher when I revved it, then back to 14. I believe that is correct and shows I have no vacuum leak.
Thanks,
Chris
It would crank then immediately die. Would not run again until I let it sit for about 10 minutes.
It had (guessing) old fuel in it so I siphoned that out and added fresh. The guy that had it before me only drove 4,000 miles in 10 years (83k on the car)
I also changed the spark plugs and ignition wires today. Driving down the road it seems to be OK.
At idle, the gauge shows the engine bouncing between 500-700RPM and the engine sounds rough & it occasionally dies.
One thing I noticed is the butterfly on the carb never closes. Could that be the cause?
None of the rods that are holding it open will move.
I have no idea if it was stuck open when it was running ok.
How can I release it?
I just did a vacuum test (hopefully I connected it the right spot). The needle was fairly stable at 14 & went to zero then higher when I revved it, then back to 14. I believe that is correct and shows I have no vacuum leak.
Thanks,
Chris
Last edited by cdsinfla; 06-17-2014 at 08:12 PM.
06-17-2014, 07:59 PM
#2
Safety Car
Most like Chris you're looking at a carb rebuild or at least a good cleaning. A second option would be a new carb as they are pretty cheap nowadays. The butterfly's you are referring too I think ......is the choke flap. That only needs to be closed on a cold engine and then opened after warmed up.
06-17-2014, 08:14 PM
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Most like Chris you're looking at a carb rebuild or at least a good cleaning. A second option would be a new carb as they are pretty cheap nowadays. The butterfly's you are referring too I think ......is the choke flap. That only needs to be closed on a cold engine and then opened after warmed up.
Would it all of a sudden run like crap? It ran much better when I bought it & I am thinking I may have knocked something loose.
Is 14 enough vacuum?
Thanks
Last edited by cdsinfla; 06-17-2014 at 08:17 PM.
06-17-2014, 09:03 PM
#4
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Correct me if I'm wrong, but that looks like it's a manual choke setup. It's not going to close until you manually close it to start the engine.
First and foremost, if this car sat a lot, you need to get the carb rebuilt. I did mine just to be sure and I found more problems and issues with it then I would have ever guessed. It run so much better now. Lars is a good option if you don't want to mess with rebuilding it.
The vacuum line in the pic, the one in the front of the carb, is that hooked to your gauge or your distributor?
14 is not bad depending on the build. Adjusting the idle mixture after the carb it rebuild might give you a bit more.
First and foremost, if this car sat a lot, you need to get the carb rebuilt. I did mine just to be sure and I found more problems and issues with it then I would have ever guessed. It run so much better now. Lars is a good option if you don't want to mess with rebuilding it.
The vacuum line in the pic, the one in the front of the carb, is that hooked to your gauge or your distributor?
14 is not bad depending on the build. Adjusting the idle mixture after the carb it rebuild might give you a bit more.
06-18-2014, 01:38 AM
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Correct me if I'm wrong, but that looks like it's a manual choke setup. It's not going to close until you manually close it to start the engine.
First and foremost, if this car sat a lot, you need to get the carb rebuilt. I did mine just to be sure and I found more problems and issues with it then I would have ever guessed. It run so much better now. Lars is a good option if you don't want to mess with rebuilding it.
The vacuum line in the pic, the one in the front of the carb, is that hooked to your gauge or your distributor?
14 is not bad depending on the build. Adjusting the idle mixture after the carb it rebuild might give you a bit more.
First and foremost, if this car sat a lot, you need to get the carb rebuilt. I did mine just to be sure and I found more problems and issues with it then I would have ever guessed. It run so much better now. Lars is a good option if you don't want to mess with rebuilding it.
The vacuum line in the pic, the one in the front of the carb, is that hooked to your gauge or your distributor?
14 is not bad depending on the build. Adjusting the idle mixture after the carb it rebuild might give you a bit more.
How would I "manually close" the choke? Is there a hidden switch in the car I haven't found? I would think it would be closed when the engine was cold but it never moves.
I see the rebuild kit & that's probably more than I want to handle. I found out my intake manifold is an Edelbrock but the carb looks stock. I just want a daily driver & not a hot rod. Looks like I can get a rebuilt one for $250. What's a ballpark for Lars to rebuild? What do you guys recommend?
The vacuum line in the pic goes to the distributor. The other line with the yellow arrow is where I connected my gauge. I did some more research on using a vacuum gauge and another test run and it looked good.
Great info ->http://www.secondchancegarage.com/public/186.cfm
So after rechecking all the ignition wires, distributor and looking for other obvious issues it seemed to be running better than yesterday. I took it out for a spin and it ran fairly good until it heated up for about 10-15 minutes. It then turned to crap again. I even notice it driving now as well as idling. It's like it starts to miss. When I slow to a stop it chokes and wants to die until I throw it in neutral. Once the load is off, it idles up to around 900RPM but still sputters a bit. My VW did this exact same thing & I found a wire from my ignition coil to the choke was no good. As soon as the VW engine would heat up, it would cough, sputter and die. Once I fixed that, it ran like a top. This lead me to believe it had something to do with my choke being stuck in the vette.
Good thing I like to tinker
Chris
Last edited by cdsinfla; 06-18-2014 at 01:44 AM.
06-18-2014, 07:07 AM
#6
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I will be corrected if I am wrong, but I think all 73s came with Quadrajet carbs, so not only has the intake, but carb changed as well.
I can't help much with what you have going on except to get it tuned to stock specs as a starting point. Also check to make sure that the heat riser flap is opening correctly. ( right side exhaust between the manifold and pipe)
Also if you have not done it, there are some great reference books out there that you should consider.
You will want/need the AIM ( assembly manual), and the dealer service manuals are also reccomended. Haynes manuals are not the greatest help.
Welcome to the madness.
I can't help much with what you have going on except to get it tuned to stock specs as a starting point. Also check to make sure that the heat riser flap is opening correctly. ( right side exhaust between the manifold and pipe)
Also if you have not done it, there are some great reference books out there that you should consider.
You will want/need the AIM ( assembly manual), and the dealer service manuals are also reccomended. Haynes manuals are not the greatest help.
Welcome to the madness.
06-18-2014, 10:35 AM
#7
Racer
You can see the welding rod holding the choke open. Without changing the choke to a heat (or electric) there is no easy way to make that manual choke function. It really has nothing to do with your symptoms.
The first thing I would do is check ignition timing. I would verify that the vacuum and mechanical advance mechanisms are working. I'd verify no vacuum leaks. Holley carbs do not always fit manifolds designed for spread bores.
I'd check fuel pressure and then I'd buy a can of carb cleaner and make sure the idle air bleeds are clear.
The first thing I would do is check ignition timing. I would verify that the vacuum and mechanical advance mechanisms are working. I'd verify no vacuum leaks. Holley carbs do not always fit manifolds designed for spread bores.
I'd check fuel pressure and then I'd buy a can of carb cleaner and make sure the idle air bleeds are clear.
06-18-2014, 10:55 AM
#8
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Your choke is a manual choke, and it has been locked open with a piece of wire - it is completely non-functional. The open choke has nothing to do with your symptoms, however: It may cause some cold-start issues and difficulty maintaining idle when dead cold, but it will have no effect on operations once the engine has warmed up.
Suggest you check timing, total timing, and vacuum advance systems first: Make sure total timing is at 36, and that you have a resultant initial timing in the high-teen range. Make sure vacuum advance is operational and correctly hooked up - you have it hooked up to ported vacuum, which will not produce best idle characteristics - I suggest you fix that. Once done, make sure it's firing on all 8 and then verify carb setup - never do any carb work until all ignition and timing issues have been verified. 14 inches of vacuum at idle suggests that the engine may have a bit of an aftermarket cam in it, so you need to make sure you have at least 18 degrees of initial timing in it and that the vacuum advance control unit is a B26 or softer unit (you can't use a stock vacuum advance with 14 inches of vacuum). The aftermarket cam may also require some special carb tuning, and it's critical that you balance out the primary and secondary idle speeds to assure that the primary throttle blades are not exposing any more than .020" of transition slot in the throttle bores. With this setting, verify float levels and set idle mixtures correctly, and it will run well.
Lars
Suggest you check timing, total timing, and vacuum advance systems first: Make sure total timing is at 36, and that you have a resultant initial timing in the high-teen range. Make sure vacuum advance is operational and correctly hooked up - you have it hooked up to ported vacuum, which will not produce best idle characteristics - I suggest you fix that. Once done, make sure it's firing on all 8 and then verify carb setup - never do any carb work until all ignition and timing issues have been verified. 14 inches of vacuum at idle suggests that the engine may have a bit of an aftermarket cam in it, so you need to make sure you have at least 18 degrees of initial timing in it and that the vacuum advance control unit is a B26 or softer unit (you can't use a stock vacuum advance with 14 inches of vacuum). The aftermarket cam may also require some special carb tuning, and it's critical that you balance out the primary and secondary idle speeds to assure that the primary throttle blades are not exposing any more than .020" of transition slot in the throttle bores. With this setting, verify float levels and set idle mixtures correctly, and it will run well.
Lars
Last edited by lars; 06-18-2014 at 11:05 AM.
06-18-2014, 10:58 AM
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Thanks
Last edited by cdsinfla; 06-18-2014 at 11:03 AM.
06-18-2014, 01:48 PM
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Lars,
I owe you a beer!
I tested the 2 vacuum ports. one only read above zero when I gave it throttle. The other was the constant 14. I now have the distributor connected to the constant port and it idles SO much better. Is the port in the pic below the one you recommended?
I drove it around for about 20 minutes and it did not run rough at all.
Could that have been the problem the whole time?
After the engine warms up, would that cause it to run like crap?
I am a bit of a computer nerd for a living & spend a lot of time on forums. I gotta say...this forum is great & everyone seems very helpful.
I have a timing light and I was looking for the notch on the harmonic balancer last night. It has no degree marks that I can see. I do see the arrow & a line on the flywheel but not sure if that's TDC - if that's it it should have been marked better. Next job is to find cylinder #1, pull the plug and verify.
I owe you a beer!
I tested the 2 vacuum ports. one only read above zero when I gave it throttle. The other was the constant 14. I now have the distributor connected to the constant port and it idles SO much better. Is the port in the pic below the one you recommended?
I drove it around for about 20 minutes and it did not run rough at all.
Could that have been the problem the whole time?
After the engine warms up, would that cause it to run like crap?
I am a bit of a computer nerd for a living & spend a lot of time on forums. I gotta say...this forum is great & everyone seems very helpful.
I have a timing light and I was looking for the notch on the harmonic balancer last night. It has no degree marks that I can see. I do see the arrow & a line on the flywheel but not sure if that's TDC - if that's it it should have been marked better. Next job is to find cylinder #1, pull the plug and verify.
06-18-2014, 02:00 PM
#11
Melting Slicks
Lars,
I owe you a beer!
I tested the 2 vacuum ports. one only read above zero when I gave it throttle. The other was the constant 14. I now have the distributor connected to the constant port and it idles SO much better. Is the port in the pic below the one you recommended?
I drove it around for about 20 minutes and it did not run rough at all.
Could that have been the problem the whole time?
After the engine warms up, would that cause it to run like crap?
I am a bit of a computer nerd for a living & spend a lot of time on forums. I gotta say...this forum is great & everyone seems very helpful.
I have a timing light and I was looking for the notch on the harmonic balancer last night. It has no degree marks that I can see. I do see the arrow & a line on the flywheel but not sure if that's TDC - if that's it it should have been marked better. Next job is to find cylinder #1, pull the plug and verify.
I owe you a beer!
I tested the 2 vacuum ports. one only read above zero when I gave it throttle. The other was the constant 14. I now have the distributor connected to the constant port and it idles SO much better. Is the port in the pic below the one you recommended?
I drove it around for about 20 minutes and it did not run rough at all.
Could that have been the problem the whole time?
After the engine warms up, would that cause it to run like crap?
I am a bit of a computer nerd for a living & spend a lot of time on forums. I gotta say...this forum is great & everyone seems very helpful.
I have a timing light and I was looking for the notch on the harmonic balancer last night. It has no degree marks that I can see. I do see the arrow & a line on the flywheel but not sure if that's TDC - if that's it it should have been marked better. Next job is to find cylinder #1, pull the plug and verify.
06-18-2014, 02:01 PM
#12
You now have the vacuum line correctly connected.
The harmonic balancer only has a line on it, after cleaning the spot where the line is take some white paint dab it on the line and wipe off the excess.
There should be a tab with lines and numbers attached to the timing cover, see the picture in the link.
http://www.hotrodders.com/forum/chev...to-178514.html
The harmonic balancer only has a line on it, after cleaning the spot where the line is take some white paint dab it on the line and wipe off the excess.
There should be a tab with lines and numbers attached to the timing cover, see the picture in the link.
http://www.hotrodders.com/forum/chev...to-178514.html