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Old 10-22-2007, 07:07 PM   #11
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Oh yeah the fuel pump would stop running if there is no ignition pulsing after a few seconds or it could be running all the time and flooding the engine when the car is moving and bouncing the carb float in the bowl. Either way you are not really saving a lot of gas if you only turn off the engine for a short amount of time and have it running rough after it starts again. Bump starting should be a quick clutch out and in again then let the engine run a few seconds and then get it up to speed all without giving it any gas then step on the gas to match rpm to speed and let the clutch out again normally. However if the engine is not running smoothly then you probably have some fuel leaking from the carb fouling the cylinders and will end up with gas in the oil and loss of lubrication in some cylinders that get flooded which will eventually cause ring and cylinder wear. The Cat runs at about 700 degrees and it will cool off pretty quick when you consider that you are moving at speed with no additional combustion heat being supplied to it. Not sure if it makes much difference if you just took your foot of the gas and kept it in gear though.
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Old 10-22-2007, 08:04 PM   #12
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I don't RPM match. Usually my idle isn't that much lower than my RPM when I am reengaging. Not sure I understand all that you are saying. I have fuel leaking while the engine is off? Or all the time? (That sure would explain a thing or two....) It only struggles after the first two flawless bump starts. The third and subsequent times is when it starts to have trouble.
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Old 10-22-2007, 11:26 PM   #13
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had that fuel pump issue with my 91 CRX, fixing it made all the difference. Try just sitting in your driveway and just turning the key to the "ON" position repeatedly, just make sure that you can hear the fuel pump humming behind you for a few seconds each time that you do so. If you don't hear the humming , or it varies each time, then it's time to pull out your DMM and test the wiring and the fuel pump to make sure they're all still in good working order.
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Old 10-27-2007, 01:39 PM   #14
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I bump start all the time, and have no problems at all. I use as high as gear as possible, at least 3rd
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Old 10-27-2007, 05:11 PM   #15
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Sometimes when you first turn the ignition to the on position the engine will squirt some gas into the intake to prime the engine - usually only for cold starting. Injectors can leak slowly and if the engine is off for a long enough time the fuel evaporates but if only off for a few minutes it may be enough to flood a cylinder or two. Carb engines have a float in the carb bowl that holds back the gas from the fuel pump - if the float bowl is bouncing around it can allow some of the fuel in the lines still under pressure to overfill the bowl and overflow into the intake. Plus with the key still on the fuel pump may still be pumping and maintaining pressure.
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Old 10-28-2007, 05:45 AM   #16
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I had a very similar problem in my now retired '92 Civic Si. First few bumps were always fine. Intermittently I would have difficulty bump starting after that. I never figured out why but it seemed to happen more frequently on hot days. After trying a couple times I usually wound up at the side of the road with the flashers on. After a couple of cranks it would start. The other manifestation was with engine off coasting to a stop. Then when the light changed I would crank but it wouldn't fire. After a couple more tries and a little embarrassment it would start.
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Old 10-28-2007, 06:40 AM   #17
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Yeah, sounds pretty similar. Sometimes I think it has more difficulty at slower speeds. Second gear and sometimes third often lurches the whole car before starting. It hasn't been so bad of late because I haven't been doing it quite as often. If I could fix my idle I'd be much less inclined to bump start altogether, but seeing as I have a high idle I feel that it has some savings.

Maybe I should start coasting with the key in the off position, and only put it to the on position right before I bump start to see if that makes any difference.
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Old 10-28-2007, 03:04 PM   #18
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Maybe let the engine spin a little more in gear after you turn the key off to pump some of the fuel and air out then push in the clutch and then when the engine stopped turning - turn the key on again. This way if the injectors are leaking a little after shutting off they have a change to clear the cylinders. I used to rev the engine in my Geo and then turn off the key to flush and hold the gas pedal down out the moisture from the exhaust in cold weather as I turned off the engine.
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Old 11-01-2007, 08:29 PM   #19
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Find our whats wrong with the car.

Bump or key start it should fire right up.... I bet when you find the problem your mpg will get better.
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Old 11-07-2007, 02:12 PM   #20
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Quote:
Originally Posted by JanGeo View Post
Oh yeah the fuel pump would stop running if there is no ignition pulsing after a few seconds or it could be running all the time and flooding the engine when the car is moving and bouncing the carb float in the bowl. Either way you are not really saving a lot of gas if you only turn off the engine for a short amount of time and have it running rough after it starts again. Bump starting should be a quick clutch out and in again then let the engine run a few seconds and then get it up to speed all without giving it any gas then step on the gas to match rpm to speed and let the clutch out again normally. However if the engine is not running smoothly then you probably have some fuel leaking from the carb fouling the cylinders and will end up with gas in the oil and loss of lubrication in some cylinders that get flooded which will eventually cause ring and cylinder wear. The Cat runs at about 700 degrees and it will cool off pretty quick when you consider that you are moving at speed with no additional combustion heat being supplied to it. Not sure if it makes much difference if you just took your foot of the gas and kept it in gear though.
When I bump start, I let the clutch out in order for the engine to come back on. I don't put the clutch back in again immediately after I bump start to let it warm up as you say, I just start driving. I only put the clutch in again immediately after bump starting if it starts doing the laggy business. But I have just been bump starting a max of 3 times per trip in order to prevent the problem since it seems to occur from excessive bump starting.

Is there a reason you put the clutch back in again after bump starting? Engine runs fine immediately after bump starting the first few times I do it.
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