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Old 07-27-2006, 06:23 PM
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Misfire at low RPM

I've been having trouble with a misfire at low RPM on my 200 straight 6. I had a bad flat spot in acceleration, but I got it cleared up by getting my accelerator pump working real well. Now I'm having some misfires at low rpm. I've got my timing set real nice, and it idles real nice. Once it gets to higher RPM, it really smoothes out and the misfire goes away. Doesn't seem to be a miss at idle. What are some reasons for low RPM misfires? Thanks guys, I wanna clear this up so I can get a smooth acceleration. The miss is really noticeable especially when you barely give it gas in drive. I appreciate it.

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Old 07-27-2006, 09:40 PM
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low rpm miss

I have been down this road before and I would say that you are still having an accelerator pump problem or passage from the pump blocked.
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Old 07-27-2006, 11:50 PM
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I'll pull it tomorrow and clean it up better than. Thanks. I'll post results.
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Old 07-28-2006, 05:59 AM
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carbs are cool

A blow gun with a rubber tip works great on the passages. GOOD LUCK!!!!!
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Old 07-28-2006, 06:34 AM
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Are you sure it is an ignition misfire and not the inherent vibration factor of these engines (144-170-200) to lightly vibrate at low RPM's? It has something to do with the way they are balanced due to the length of the crankshaft.
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Old 07-28-2006, 03:52 PM
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low rpm miss

From what i gathered from the first post on this problem it sounded like he has a dead spot when coming off idle until it gets past part throttle.BUT I have been wrong before!!!!!!!!!
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Old 07-28-2006, 08:57 PM
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I got rid of the dead spot. It was a clearance issue on the host that runs through the carburetor spacer with coolant. The clamp that was holding the hose down was sticking the linkage on the acceleration pump, and not letting it move. I got that cleared up. Now it seems as though there's a misfire. Instead of vroooooooooom it goes vroothumpooothump thumpoooothump until a higher rpm where it goes WAHHHHHHHHHHH real smooth. It might be the vibration though. I got it idling real nice and it hardly vibrates in the car at all. I'm going to clean out the pump and see if that helps any and report back. I haven't had time due to my girlfriend's birthday party I've been setting up for her. Thanks for the input guys. Maybe I'll take a video of it so you can watch and hear. =)
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Old 07-29-2006, 07:37 AM
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Low Rpm Miss

If it still pops back through the carb when you take it off of idle it sounds like you may be running to lean.You might want to check for vacuum leaks.GOOD LUCK!Let us know what you find.
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Old 07-29-2006, 08:02 AM
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check your #5 and #6 sparkplugs, and switch them with the #2 and #3 plugs. these engines have a tendency to foul those plugs, could be missing them at the low RPM under load but burning at high rpm. my '67 will compleatly foul the #5 if I flood it up accidently, couse I switch it with #3 and all is well. I run Autolite 46's
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Old 07-29-2006, 02:08 PM
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It's not popping through the carb, it's thumping. Nothing's shooting out of the carb. I'm going to check the plugs today.
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