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| Runs rough on acceleration when warm | Rate Topic |
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| Posted: 07-20-2009 07:46 pm |
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1st Post |
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Gary Martin JH 15371 Member
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My car runs fine when cold and for first few miles. After driving two or three miles, it will start to idle rough, then misses badly and occasionally coughs when talking off from a stop. Once it gets up to about 2300 rpm it smooths out and runs fine. It cruises fine. After slowing for a turn, it will buck and cough from 1500 to 2300 rpm again, then runs fine. It seems like a carburation problem to me. Engine is rebuilt, Strombergs are rebuilt, floats set correctly and carbs balanced. Carbs seem to tune fine and needle valves are set to datum. I run Chevron premium gas. Pertronix ignition with new wires and plugs. I thought it might have been the fuel pump, but I swaped the one from my spare JH and it made no difference. Currently timing is set to 5 deg BTDC and total timing at 3000 rpm is 30 deg. Dist does not have a vacuum advance unit. If I set timing any more advanced (say 10 or 12), I get a lot of spark knock on heavy acceleration. So I backed off the timing. One other wierd thing, every time the fuel pump clicks, the tach jumps up a thousand rpm and returns. Pump is stock SU type. Is there a fix for this ? Gary
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| Posted: 07-24-2009 07:36 pm |
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2nd Post |
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ozzadavies Member 
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Play in the distributor?
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| Posted: 08-01-2009 10:59 pm |
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3rd Post |
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Gary Martin JH 15371 Member
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I have advanced the timing from 5 deg back to standard 10 deg BTDC and this seems to have improved my coughing and bucking problem at lower RPM. So it seems having the timing too far retarded must have been causing this condition. However my other problem with spark knock has returned under medium to heavy acceleration. It will ping and knock from 1500 to 3500 rpm under med-heavy acceleration. I have not wound it up much past 4000 yet as I'm still sorting out the car. Does anyone know the correct mechanical advance curve ? With timing at 10 deg @idle, I'm getting about 35 deg total timing at 3000 rpm. Maybe the distributor has too light of advance springs, or too much total advance ? I bought this engine complete with dizzy and have not had dizzy out to inspect it yet. It has Pertronix ignition and it does not have a vacuum advance module. Not sure if is a complete Pertronix dizzy or if someone just added the Pertronix module and removed the vacuum module. Gary
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| Posted: 08-02-2009 03:25 pm |
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4th Post |
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Brett Gibson JH5 20497 Member
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A stromberg equiped engine was spec'd with a vacumn advance dizzy, could be an issue, also you say it runs better cold, I assume a choked engine extra gas, if thats the case maybe your running lean when warm. Setting the engine to factory specs is all well and good for a engine just out of the factory, but one that has seen some miles and differant driving styles really needs to be tweeked to what runs best for it. What do your plugs look like color wise, that is one of the best indicators of mixture, whats the compression readings, you say the engine was rebuilt. Just thoughts. Brett
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