need help 1969 hurst olds coughs thru carb on acceleration
October 22nd, 2014, 07:04 PM
#1
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need help 1969 hurst olds coughs thru carb on acceleration
Have had her quite some time just recently started coughing once in a while thru the carb only does it on hard accelerations or in hi gear with full throttle will cough worst at hi gear full throttle. Checked timing ,dwell, new 850 performance carb, new fuel tank sock sending unit, plugs wires cap points also checked valve spring just completely puzzeled. Also adjusted air mixture every way possible looking for new ideas.
October 23rd, 2014, 01:08 AM
#3
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Join Date: May 2009
Location: Woodland WA
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I think coughing through the carb is more often caused by lean running or bad ignition timing setting off the mixture before the intake closes. But the things you have described doing should have eliminated those possibilities.
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
October 23rd, 2014, 07:04 AM
#4
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Thread Starter
Join Date: Oct 2014
Posts: 5
I think coughing through the carb is more often caused by lean running or bad ignition timing setting off the mixture before the intake closes. But the things you have described doing should have eliminated those possibilities.
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
October 23rd, 2014, 07:10 AM
#6
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Join Date: Oct 2004
Location: Forest Ranch Ca.
Posts: 7,731
I think coughing through the carb is more often caused by lean running or bad ignition timing setting off the mixture before the intake closes. But the things you have described doing should have eliminated those possibilities.
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
This is a long shot but if the car was 'coughing' before you did all the things described and they didn't cure it, you might look at the condition of the valves --not just the valve springs. Do a compression test.
Twice in my car owning life I've had those symptoms under similar full throttle and couldn't solve them until doing a compression check and finding valves didn't seal and contain combustion to the chamber.
Good luck with this and I do hope you don't have to go into the heads to solve your problem.
Jerry
October 23rd, 2014, 07:57 AM
#7
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Join Date: Mar 2007
Location: Northern VA
Posts: 47,451
Have had her quite some time just recently started coughing once in a while thru the carb only does it on hard accelerations or in hi gear with full throttle will cough worst at hi gear full throttle. Checked timing ,dwell, new 850 performance carb, new fuel tank sock sending unit, plugs wires cap points also checked valve spring just completely puzzeled. Also adjusted air mixture every way possible looking for new ideas.
Second, tell us about the engine? Is it stock? If not, what's been done to it?
Third, adjusting the IDLE mixture screws will have exactly zero effect on how the engine performs off of idle Put them back to where they were originally, as they are not the problem.
Fourth, You didn't mention the ignition coil, which is often the cause of problems under load.
October 23rd, 2014, 07:53 PM
#8
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Join Date: Oct 2014
Posts: 5
First, what is an "850 performance carb"? Since it's not the original carb, how is it set up to match your engine?
Second, tell us about the engine? Is it stock? If not, what's been done to it?
Third, adjusting the IDLE mixture screws will have exactly zero effect on how the engine performs off of idle Put them back to where they were originally, as they are not the problem.
Fourth, You didn't mention the ignition coil, which is often the cause of problems under load.
Second, tell us about the engine? Is it stock? If not, what's been done to it?
Third, adjusting the IDLE mixture screws will have exactly zero effect on how the engine performs off of idle Put them back to where they were originally, as they are not the problem.
Fourth, You didn't mention the ignition coil, which is often the cause of problems under load.
October 23rd, 2014, 08:07 PM
#9
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Join Date: Oct 2014
Posts: 5
Hey Joe it's a Smith street master Quadra jet stage ll the engine is stock no modification and I put air idle screws back to factory settings it has a stock coil . Replaced the distributor with a pintronics hei system also checked for slack in timing chain there was no slack. After New distributor was installed set timing at 10 degrees before TDC reset idle at 575 still pops when shifting in to 2nd gear and at hi rpms. Gonna pull valve covers tomorrow check valve springs a buddy said could be a cam shift starting to go flat. Any other ideas would be helpful also I normally run 100 octane but recently dropped down to 89 octane could gas be the problem? Didn't do it on 100 octane
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