Suddenly my '67 runs like crap! Can you help?
05-29-2017, 04:51 PM
#22
Instructor
My 2 cents
After reading what everyone has said it's all good advice, but I think Dans Yellow is on the right track. My 67 does the same thing and it's always the carb,you know they don't make good old gas like they used to( before the tree huggers got involved). The one thing that has always worked for me was carb cleaner with the long straw nozzle, I removed the inspection screw the one that you check the float level and spray into the float chamber. That seemed to work for me good luck lots of good info on this thread.Tom
05-29-2017, 05:47 PM
#23
Pro
Thread Starter
Update - Memorial Day
I spent some time today trying to diagnose the poor running problem on my '67 using the suggestions you guys offered.
First I checked the choke mechanism. The flap was open from the last time I ran the car. When I depressed the gas pedal it closed shut. I think that's normal, isn't it?
The next check I made was to see if gas was being fed to the two back barrels of the carb when I actuated the throttle. Indeed, two jets of fuel were delivered each time I moved the throttle rod. So far, so good.
I noticed what appeared to be evidence of a small amount of fuel leaking onto the intake manifold, below the front two barrels, on both sides. I cleaned that up, to check if the leak(s) re-appeared after the road test.
I cranked the engine, which started readily. But soon the idle dropped below 500 rpm, causing the engine to want to stall and die. So, I turned the idle speed screw in a couple of turns to increase the idle, which kind of solved that problem. But now the idle is too high, and I suspect this way of fixing the problem is only a band-aid for now.
I took the car out on the road. But, the same symptoms as before were present: rough-ish running, and a bog upon acceleration. If I accelerate gradually there is no problem, but any sharp application of throttle results in a momentary 'bog' followed by a whoosh of acceleration as the extra fuel gets fed to the engine.
I didn't see any black smoke which would indicate an over-rich condition. However, after starting the car again after it was shut off for 10 minutes I noticed an initial puff of blueish smoke which went away quickly.
I checked again for fuel leaks on the intake manifold after I ran the car for about 20 minutes on the road, but could not see any obvious leaks.
For your info, I had this Holley carb rebuilt last year and have driven the car less than 500 miles since then.
So, here are my latest questions:
Thanks for your help!
First I checked the choke mechanism. The flap was open from the last time I ran the car. When I depressed the gas pedal it closed shut. I think that's normal, isn't it?
The next check I made was to see if gas was being fed to the two back barrels of the carb when I actuated the throttle. Indeed, two jets of fuel were delivered each time I moved the throttle rod. So far, so good.
I noticed what appeared to be evidence of a small amount of fuel leaking onto the intake manifold, below the front two barrels, on both sides. I cleaned that up, to check if the leak(s) re-appeared after the road test.
I cranked the engine, which started readily. But soon the idle dropped below 500 rpm, causing the engine to want to stall and die. So, I turned the idle speed screw in a couple of turns to increase the idle, which kind of solved that problem. But now the idle is too high, and I suspect this way of fixing the problem is only a band-aid for now.
I took the car out on the road. But, the same symptoms as before were present: rough-ish running, and a bog upon acceleration. If I accelerate gradually there is no problem, but any sharp application of throttle results in a momentary 'bog' followed by a whoosh of acceleration as the extra fuel gets fed to the engine.
I didn't see any black smoke which would indicate an over-rich condition. However, after starting the car again after it was shut off for 10 minutes I noticed an initial puff of blueish smoke which went away quickly.
I checked again for fuel leaks on the intake manifold after I ran the car for about 20 minutes on the road, but could not see any obvious leaks.
For your info, I had this Holley carb rebuilt last year and have driven the car less than 500 miles since then.
So, here are my latest questions:
- I hear you guys refer to an "accelerator pump" and a "power valve" - are these the same thing?
- Could a defective power valve be the cause of both the idle and flat spot on acceleration problem? Would a stuck power valve cause some fuel to leak onto the intake manifold?
- Lastly, how difficult is it to replace a power valve, if you're inexperienced as I am in these things?
Thanks for your help!
05-29-2017, 05:52 PM
#24
Race Director
That really sounds like a filter problem to me. I'd replace the power valve (easy and cheap) and then the filter.
You might want to pull each plug and check its condition and see if there is any variation between cylinders (for example if one plug is black and sooty - that may point to an ignition problem in that cylinder - e.g. rich condition)
Do you run points?
You might want to pull each plug and check its condition and see if there is any variation between cylinders (for example if one plug is black and sooty - that may point to an ignition problem in that cylinder - e.g. rich condition)
Do you run points?
05-29-2017, 06:01 PM
#25
Drifting
No matter that it was rebuilt a year ago as Holleys are famous for failing after long periods of inactivity...In addition to the power valve I would check for a vacuum leak on a small vacuum line...They habitually miss at idle and clean themselves up as you accelerate...Pull them off (1) one at a time and check for cracks or cuts.
Greg
Greg
05-29-2017, 06:16 PM
#26
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Take the sight plugs out of both fuel bowls and check the fuel level to make sure a needle valve is not hanging open. If it is, fix it. If it isn't, a power valve could be your problem.
Check this before spending your sawbuck.
Check this before spending your sawbuck.
05-29-2017, 06:28 PM
#27
Drifting
It's pretty obvious that you know nothing about a Holley...Take it back to the person that rebuilt it and let him heal it.
Greg
Greg
05-29-2017, 08:32 PM
#28
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Last edited by JohnZ; 05-29-2017 at 08:34 PM.
05-29-2017, 09:21 PM
#29
Team Owner
Do you know what material the float is made of?
The power valve hasn't failed completely, but sometimes they deteriorate and the symptoms can come and go for a little while!
I dont like running carbs carbs without a sight plug, but that is a dead argument with you stock wanting guys. The needle shut off could be slightly deteriorated and gas still siphoning past it and overfilling the bowl and as the float rises, it isn't shut off completely.
I would say it is flooding at lower rpms and idle and will clean out as you give it throttle! So it runs smooth at cruising or in mid-range rpms? Sometimes the fuel pump gasket rubber is deteriorating and leaking past! Raw fuel dripping to your manifold came from somewhere! Also I have zero port vacuum anything connected to my carbs! So PCVs and other things are never a fracture to troubleshoot in my cars and related that cause vacuum leaks!
Sounds like the car ran better under choke which would be holding it to a higher running idle rpm, but then when it came off of choke it started to stall or drop rpms!
Power valves are an enrichment circuit and different than the accelerator pump or pump shot circuit! The power valve changes the vacuum in the carb, so it is more of a when running device issue! They are easy to change, but you have to be careful to not nick the little sealing surfaces on the metering blocks by scoring or scratch with a wrench or socket! But easy to change with that one precaution! They don't stick!
Whatever issue you have is minor since the idle mixture screws had an effect on idle! Those only essentially change idle gas volume and the carb when running transitions out of those circuits to essentially other circuits internally!
Did you blow out the top little air breeds inside the horn! Best to do that at high choked idle and rap the throttle some as you spray! It will load up your mixture lessening the air flow inside the carb, and cleaning those will almost stall the car, even just giving one a shot at a time! The carb spray straw usually fits perfect in one of those bleeds to clean them! The need to clean those would rare because most of you guys have air cleaners, but some crud could build up eventually as they are sucking air!
if it was ignition, you would have other run issues at other running in the power band rpms! At idle is the easiest parameter for the ignition system to operate in, because you should be at a fixed rpm and the vacuum advances and such should not be coming in yet!
The power valve hasn't failed completely, but sometimes they deteriorate and the symptoms can come and go for a little while!
I dont like running carbs carbs without a sight plug, but that is a dead argument with you stock wanting guys. The needle shut off could be slightly deteriorated and gas still siphoning past it and overfilling the bowl and as the float rises, it isn't shut off completely.
I would say it is flooding at lower rpms and idle and will clean out as you give it throttle! So it runs smooth at cruising or in mid-range rpms? Sometimes the fuel pump gasket rubber is deteriorating and leaking past! Raw fuel dripping to your manifold came from somewhere! Also I have zero port vacuum anything connected to my carbs! So PCVs and other things are never a fracture to troubleshoot in my cars and related that cause vacuum leaks!
Sounds like the car ran better under choke which would be holding it to a higher running idle rpm, but then when it came off of choke it started to stall or drop rpms!
Power valves are an enrichment circuit and different than the accelerator pump or pump shot circuit! The power valve changes the vacuum in the carb, so it is more of a when running device issue! They are easy to change, but you have to be careful to not nick the little sealing surfaces on the metering blocks by scoring or scratch with a wrench or socket! But easy to change with that one precaution! They don't stick!
Whatever issue you have is minor since the idle mixture screws had an effect on idle! Those only essentially change idle gas volume and the carb when running transitions out of those circuits to essentially other circuits internally!
Did you blow out the top little air breeds inside the horn! Best to do that at high choked idle and rap the throttle some as you spray! It will load up your mixture lessening the air flow inside the carb, and cleaning those will almost stall the car, even just giving one a shot at a time! The carb spray straw usually fits perfect in one of those bleeds to clean them! The need to clean those would rare because most of you guys have air cleaners, but some crud could build up eventually as they are sucking air!
if it was ignition, you would have other run issues at other running in the power band rpms! At idle is the easiest parameter for the ignition system to operate in, because you should be at a fixed rpm and the vacuum advances and such should not be coming in yet!
Last edited by TCracingCA; 05-29-2017 at 09:51 PM.
05-29-2017, 10:07 PM
#31
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Hi Alex,
I had this identical problem on my 63 with 300hp and 4160. Drove me nuts for about three weeks but ended up being a sticky choke. When it was cold, I could hit the throttle and hear the choke snap shut, so I thought it was ok. Turns out that it wasn't closing completely, which caused it to run like crap. As soon as I sprayed the crap out of the choke plate and linkage and manually worked it while spraying it...it started running perfect. I usually don't pipe in on these threads, but thought I'd share what worked for me when I faced the exact same problem with the same setup you're running. Good luck!
PS- might want to pull a plug for inspection too.
I had this identical problem on my 63 with 300hp and 4160. Drove me nuts for about three weeks but ended up being a sticky choke. When it was cold, I could hit the throttle and hear the choke snap shut, so I thought it was ok. Turns out that it wasn't closing completely, which caused it to run like crap. As soon as I sprayed the crap out of the choke plate and linkage and manually worked it while spraying it...it started running perfect. I usually don't pipe in on these threads, but thought I'd share what worked for me when I faced the exact same problem with the same setup you're running. Good luck!
PS- might want to pull a plug for inspection too.
Last edited by Dannoman; 05-29-2017 at 10:13 PM.
05-29-2017, 10:42 PM
#32
Race Director
Do you know what material the float is made of?
The power valve hasn't failed completely, but sometimes they deteriorate and the symptoms can come and go for a little while!
I dont like running carbs carbs without a sight plug, but that is a dead argument with you stock wanting guys. The needle shut off could be slightly deteriorated and gas still siphoning past it and overfilling the bowl and as the float rises, it isn't shut off completely.
I would say it is flooding at lower rpms and idle and will clean out as you give it throttle! So it runs smooth at cruising or in mid-range rpms? Sometimes the fuel pump gasket rubber is deteriorating and leaking past! Raw fuel dripping to your manifold came from somewhere! Also I have zero port vacuum anything connected to my carbs! So PCVs and other things are never a fracture to troubleshoot in my cars and related that cause vacuum leaks!
Sounds like the car ran better under choke which would be holding it to a higher running idle rpm, but then when it came off of choke it started to stall or drop rpms!
Power valves are an enrichment circuit and different than the accelerator pump or pump shot circuit! The power valve changes the vacuum in the carb, so it is more of a when running device issue! They are easy to change, but you have to be careful to not nick the little sealing surfaces on the metering blocks by scoring or scratch with a wrench or socket! But easy to change with that one precaution! They don't stick!
Whatever issue you have is minor since the idle mixture screws had an effect on idle! Those only essentially change idle gas volume and the carb when running transitions out of those circuits to essentially other circuits internally!
Did you blow out the top little air breeds inside the horn! Best to do that at high choked idle and rap the throttle some as you spray! It will load up your mixture lessening the air flow inside the carb, and cleaning those will almost stall the car, even just giving one a shot at a time! The carb spray straw usually fits perfect in one of those bleeds to clean them! The need to clean those would rare because most of you guys have air cleaners, but some crud could build up eventually as they are sucking air!
if it was ignition, you would have other run issues at other running in the power band rpms! At idle is the easiest parameter for the ignition system to operate in, because you should be at a fixed rpm and the vacuum advances and such should not be coming in yet!
The power valve hasn't failed completely, but sometimes they deteriorate and the symptoms can come and go for a little while!
I dont like running carbs carbs without a sight plug, but that is a dead argument with you stock wanting guys. The needle shut off could be slightly deteriorated and gas still siphoning past it and overfilling the bowl and as the float rises, it isn't shut off completely.
I would say it is flooding at lower rpms and idle and will clean out as you give it throttle! So it runs smooth at cruising or in mid-range rpms? Sometimes the fuel pump gasket rubber is deteriorating and leaking past! Raw fuel dripping to your manifold came from somewhere! Also I have zero port vacuum anything connected to my carbs! So PCVs and other things are never a fracture to troubleshoot in my cars and related that cause vacuum leaks!
Sounds like the car ran better under choke which would be holding it to a higher running idle rpm, but then when it came off of choke it started to stall or drop rpms!
Power valves are an enrichment circuit and different than the accelerator pump or pump shot circuit! The power valve changes the vacuum in the carb, so it is more of a when running device issue! They are easy to change, but you have to be careful to not nick the little sealing surfaces on the metering blocks by scoring or scratch with a wrench or socket! But easy to change with that one precaution! They don't stick!
Whatever issue you have is minor since the idle mixture screws had an effect on idle! Those only essentially change idle gas volume and the carb when running transitions out of those circuits to essentially other circuits internally!
Did you blow out the top little air breeds inside the horn! Best to do that at high choked idle and rap the throttle some as you spray! It will load up your mixture lessening the air flow inside the carb, and cleaning those will almost stall the car, even just giving one a shot at a time! The carb spray straw usually fits perfect in one of those bleeds to clean them! The need to clean those would rare because most of you guys have air cleaners, but some crud could build up eventually as they are sucking air!
if it was ignition, you would have other run issues at other running in the power band rpms! At idle is the easiest parameter for the ignition system to operate in, because you should be at a fixed rpm and the vacuum advances and such should not be coming in yet!
Seriously, great info there.
Last edited by TJefferson2020; 05-29-2017 at 10:42 PM.
05-30-2017, 12:08 AM
#33
Team Owner
It is so much better to troubleshoot eyes on, instead of off of someone else's descriptions of symptoms!
The dripping primaries, the whisp of blue smoke or black, the bog, the stalling at idle etc lead me to believe it is loading up on idle, affecting the initiation of transition from idle! Whether that be choke, vacuum, part failure, adjustment is difficult to diagnose not being there!
I have electric fuel pumps to a aeromotive expensive fuel log with a fuel pressure regulator and a fuel pressure gauge at the carb feeds! I have clear sight plugs even though they have to be changed often (they will fail, snap off from heat cycling or cloud). I run steel needles, not viton so they can leak a little inherently in street usage, but they are consistent . I run mechanical secondaries, anti slosh with bowl extenders, billet main bodies and metering blocks, power valve protection circuit, etc. Even my chokes are manual cable pulls! so going back to stock stuff requires having a memory and it is getting worse! Every post, I always feel I could have done a better job of writing them. But in therapy for my lack of writing skills!
Last edited by TCracingCA; 05-30-2017 at 12:27 AM.
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TJefferson2020 (06-01-2017)
05-30-2017, 07:27 AM
#34
Very difficult issue to solve without looking at the car but here is my .02 cents worth.
It's very possible the carburetor has a internal gasket leak, this can come from the power valve gasket or any of the other gaskets. Holley's are modular in design meaning the various parts need to seal together for the carburetor to work properly. If it was apart it could simply be a internal leak either air or fuel, the power valve gasket gets the highest torque of all the carburetor fasteners at 100 inch pounds.
Whenever I assembly a Holley I always use my miti-vac and pull a vacuum on the small power valve feed hole in the bottom of the baseplate. it will always leak down very slow but you will know right away if a valve did not seal or a gasket is not sealed. i
It's probably best to get it to someone with more knowledge about carburetors, remember you are fooling around with gas and a hot engine..
It's very possible the carburetor has a internal gasket leak, this can come from the power valve gasket or any of the other gaskets. Holley's are modular in design meaning the various parts need to seal together for the carburetor to work properly. If it was apart it could simply be a internal leak either air or fuel, the power valve gasket gets the highest torque of all the carburetor fasteners at 100 inch pounds.
Whenever I assembly a Holley I always use my miti-vac and pull a vacuum on the small power valve feed hole in the bottom of the baseplate. it will always leak down very slow but you will know right away if a valve did not seal or a gasket is not sealed. i
It's probably best to get it to someone with more knowledge about carburetors, remember you are fooling around with gas and a hot engine..
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Mr Fufu (06-19-2017)
05-30-2017, 10:39 AM
#35
Team Owner
Most guys don't even own a real, let alone inch pound torque wrench! Those are kind of on the expensive side!
05-30-2017, 10:48 AM
#36
Race Director
Also have two larger FT-LB wrenches as well.
Only thing I don't regularly torque is aluminum or the aluminum alloys.......mostly do these by "feel" unless in critical service.
Larry
05-30-2017, 11:52 AM
#37
Le Mans Master
If you are seeing fuel all of a sudden on the intake manifold, that would to me be a stong indicator to take a look inside the carb. My bet is you have some trash in there. Bad gas can also happen. A few months back, my 64 ran like crap one morning. Had filled up recently at a major station and got a bunch of small particles of trash in the fuel. It does not take much to screw up a needle and seat on one of these carbs. 
05-30-2017, 06:11 PM
#38
Race Director
05-30-2017, 09:09 PM
#40
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Torque wrenches are only as good as the last time they were calibrated.