Engine develops a "miss" after warm up?
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Engine develops a "miss" after warm up?
I got the timing down to +16, vacuum = 22, idle = 900, oil pressure 20@idle, temp 190.
After the engine warms up, it starts to miss. It keeps running but gets choppy.
Any ideas? I already checked for vacuum leaks...neg.
After the engine warms up, it starts to miss. It keeps running but gets choppy.
Any ideas? I already checked for vacuum leaks...neg.
Pro
Joined: Dec 2002
Posts: 560
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From: Mooresville NC
Try to isolate the problem. I usually put a timing light on each spark plug wire to see if I can see the "miss". Then I can pull that plug or wire or check the distributor cap. If you find nothing, start looking at the carb for fuel float adjustments, reset idle mixture screws, etc.
Pro
Joined: Sep 2002
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From: near Memphis TN
Originally Posted by Jughead
I got the timing down to +16, vacuum = 22, idle = 900, oil pressure 20@idle, temp 190.
After the engine warms up, it starts to miss. It keeps running but gets choppy.
Any ideas? I already checked for vacuum leaks...neg.
After the engine warms up, it starts to miss. It keeps running but gets choppy.
Any ideas? I already checked for vacuum leaks...neg.
Thread Starter
Senior Member since 1492
Joined: Aug 2000
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by SpyderD
First thoughts - something wrong with choke/choke not opening completely after warm up and your car is running too rich.
No choke on carb.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by yellow 72
Is the vacuum reading steady at idle when it's missing?
At idle the vacuum is pretty steady, maybe if at all, twitching between 21-22.
At idle miss is barely noticeable. Only when I increase rpm's does it become apparent.
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Advanced
Joined: Jun 2004
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From: North Canton Ohio
Spark plug wire grounding out? I remember having trouble with an engine miss on a 79 L82 that got progressively worse with RPM. Tried all kinds of things - no luck. When I went to replace the cap and rotor that were nearly new, I found a hairline crack on the rotor near one of the attachment screws. When I changed that, the miss went away! I couln't believe it!
Race Director
Joined: Mar 2001
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From: Living in the Hartland
Did you recheck your valve lash now that you have some run time on the motor? You can pull one plug wire at a time and see which causes the least change in idle quality to try to determine which cyl might the culprit. Once good thing about a Chilton's manual is that it has a section on eng diagnosis with a vac gauge, very handy. I can scan and e-mail it to ya if you like.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by Fevre
Did you recheck your valve lash now that you have some run time on the motor? You can pull one plug wire at a time and see which causes the least change in idle quality to try to determine which cyl might the culprit. Once good thing about a Chilton's manual is that it has a section on eng diagnosis with a vac gauge, very handy. I can scan and e-mail it to ya if you like.
Run time???
I think I maybe have 40 min of run time. Most of that was spent looking for leaks. 
Chilton's? But then I'd have to take time to read a book.
No I didn't re-check valve lash, just retorqued the head bolts. 
Thanks, I'll check on some of those ideas.
I do have another carb, but it's brand new and you know how finicky new parts can sometimes be. I was hoping to get all the bugs worked out with this carb since it has worked flawlessly on my SB....its a 750 Holley 3310.
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You also need to seat the rings properly on a new motor, not saying that is the problem just reminding you
Last edited by MotorHead; Sep 30, 2004 at 12:27 PM.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by MotorHead
Reset lash when running if hydraulic cam, check to see if any plug wires are touching headers and shorting.
Le Mans Master
Joined: Apr 2000
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From: cincinnati ohio
St. Jude Donor '09
Originally Posted by Jughead
I was hoping to get all the bugs worked out with this carb since it has worked flawlessly on my SB....its a 750 Holley 3310.
I would look at wires, plugs etc first. Pull the plugs and see if any are significantly different to track down the offending cylinder.
Instructor
Joined: Jun 2004
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From: algonac michigan
Originally Posted by Fevre
Did you recheck your valve lash now that you have some run time on the motor? You can pull one plug wire at a time and see which causes the least change in idle quality to try to determine which cyl might the culprit. Once good thing about a Chilton's manual is that it has a section on eng diagnosis with a vac gauge, very handy. I can scan and e-mail it to ya if you like.
id like to see that.
orcrest@sbcglobal.net
thanks
R.
Melting Slicks
Joined: May 2002
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From: Florida
After it warms up, put it in drive while holding brakes on and apply a little throttle. If engine misses under the load it usually has been a defective plug wire from my experience. As mentioned by others, a crack in the insulation or boot allowing the fire to jump to a ground. For some reason the problem is usually worse when hot or under engine load, probably because of higher resistance. I have also had luck with looking at the wires while the engine is running in complete darkness, such as in the garage. Just remember to leave the garage door open. Good luck...let us know what you find.
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by MotorHead
You also need to seat the rings properly on a new motor, not saying that is the problem just reminding you
Thread Starter
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Originally Posted by jimvette999
After it warms up, put it in drive while holding brakes on and apply a little throttle. If engine misses under the load it usually has been a defective plug wire from my experience. As mentioned by others, a crack in the insulation or boot allowing the fire to jump to a ground. For some reason the problem is usually worse when hot or under engine load, probably because of higher resistance. I have also had luck with looking at the wires while the engine is running in complete darkness, such as in the garage. Just remember to leave the garage door open. Good luck...let us know what you find.
Guess I'll have to put the driveshaft back in first.
Safety Car
Joined: Jul 2002
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From: St Louis MO
Originally Posted by Jughead
Guess I'll have to put the driveshaft back in first.
Just kiddin, of course. Some tuning you will have to do after a road test. Especially after you get rid of that 3310.
Brett
