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engine miss at idle in gear

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carlv

New member
Here goes, hope someone can help. 2003 150hp, carbureted with 525 hours. Recently when coming to idle after a long run I noticed a miss while idling in gear. The miss isn't noticeable in neutral. New plugs didn't help. Compression was good on all cylinders. I'm a retired auto mechanic so I have a lot of experience, but mostly on 4 cycle engines. Thank you , in advance , for any suggestions. Oh yeah, the problem has progressed to where now I need to get above 1700 rpms for the miss to go away. No problem in neutral.
 
Possibly time to strip and clean those carbs. Have you got a water seperator/filter in the fuel line? The other thing to check is the low pressure fuel pumps. They are a known maintenance item on that engine and can cause running issues. If you unbolt them from the side of the block and then squeeze the primer bulb they should not leak. If they do leak they need replacing or a new diaphragm/seal kit. If you do end up cleaning the carbs make sure you do a complete and thorough clean using lots of compressed air.
 
aliboy said:
Possibly time to strip and clean those carbs. Have you got a watein seperator/filter in the fuel line? The other thing to check is the low pressure fuel pumps. They are a known maintenance item on that engine and can cause running issues. If you unbolt them from the side of the block and then squeeze the primer bulb they should not leak. If they do leak they need replacing or a new diaphragm/seal kit. If you do end up cleaning the carbs make sure you do a complete and thorough clean using lots of compressed air.[/QUOTE

Thanks for the advice, since posting, an acquaintance has mentioned the primary circuit in one of the carbs. Fortunately I'm very comfortanble with carbs, and rebuilding, ( a dead skill with the advent of injection). Especiall appreciate the pump advice, I'll act on it.
BTW, yes on the seperator, and I've owned the boat since new, and I've topped the boat off after every trip to minimize seperation. I've used Star tron since it's introduction.
Click to expand...
 
Carbs are the most likely, but the fuel pumps are a 15 minute check for someone with mech skills so worth having a look at anyway.
 
Just giving you the courtesy of an update/conclusion to the "miss" problem. I used an old , not in any repair manual , solution. Years ago, before electronics, we used the engine vacuum to clear clogged primaries (when we were lucky). Simply put you raise the engine rpm above idle, and suddenly choke the engine hard. Depending on the size of the throat, you could use the palm of your hand, or a sturdy cloth. It didn't work every time, but often enough. It worked this time. I was surprised at the difference, it must of been slowly fouling because I hadn't felt it run that smooth in some time. Two hours on the water, and it still purrs. If nothing else it verifies the problem, and I won't hesitate cleaning the carbs if the problem returns anytime soon. Thanks again for your input.
 
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