Perfectmix

Noticed port engine idling higher than normal while in neutral. Happens more after a run. Idle is normally around 800rpm. It is running 1100 or so. When I put into gear it drops off and wants to stall. I actually have to feather the throttle to keep running. Runs great in gear when I get it over 1000rpm. It has Holley 750 with performer rpm intake. I checked the linkages to make sure they were returning. I does have pcv valve it is working correct. I am thinking vacuum leak? Wondering if anyone else had any ideas?
Thanks
PM

RumRunner

If it was running fine, and then the problem started, (without making any other changes or adjustments) you most likely either have a vacuum leak, or some dirt in your carburetor. First check for vacuum leaks, if not go through and clean out the carb.

Perfectmix

RumRunner--
No adjustments were made. I will have the carb checked and cleaned. That is a start. Unfortunately winter is upon us and engine is filled with red pop so I can't run. Just want to fix what I can before spring.
Thanks
PM

Wobble

What would be a safe way to check for a vacuum leak in a boat? Carb cleaner?

Mark

Lmarth

I'm with Doug on this one. Carefully check the carb and intake mounting bolts. I'd put a vacuum guage on it. One neat trick I learned is to put light oil in a squirt can. Start the engine and aquirt it around the base of the carb and where the intake gaskets are. If you've got a leak, the vacuum will suck the oil in and the idle speed will drop. Good Luck!

KAAMA

iTrader: (1)

A vacuum leak sounds like the problem. Not trying to hi-jack "Perfectmix's" thread, but I also usually have noticed the similar kind of idling problems on BOTH of my engines as well only they do NOT stall while going into gear. Actually, I have seen this kinds of problems happen on several hi-perf boat engines over the years. It always happens after a run. Once I come off plane and keep the engines in gear it is fine, and will idle low if I desire--no problem. However, if I happen to take either the port or starboard engine out of gear it wants to idle (in neutral) at about 150-200rpm's higher than what it normally idles at (800rpm or so). I don't know why, but it always wants to idle higher---this is only if it is taken out of gear and set in neutral. If I shut the engine down and immediately start it back up it still wants to jump up around 1000rpm or so. If I remember correctly, it does NOT seem to want to die after putting it back into gear though. After a while of cruising at idle speeds it seems to calm down and will idle in neutral at it's normal idle of 800rpm. Not sure really what's going on, but maybe it's a way of the engine catching it's breath after an on plane run.(???)

Perfectmix

Thanks Guys. Most likely a vacuum leak. Not that it makes any difference but the carbs were completely rebuilt last year. I still will check for foreign objects that may have found there way into my carb.
Kaama--I have noticed this on my boat before the only difference is this time it is isolated to the port side and it wants to stall after putting into gear at 1100 rpm. The other side may idle a little high after a run but doesn't want to stall when put back into gear. I always though it was normal.
PM

John B

Generally after a hard run, the oil is hot and has less viscosity. Most motors (carb) will idle faster until the oil cools down. My 572's pick up 2-300 idle rpm after a run.

If only one does this, it could be something else. Is one hotter than the other?

Perfectmix

John B

It just started happening. It idles higher at start up so I believe it to be a vacuum problem. And it wants to stall going into gear, also pointing to vacuum.

RumRunner

You can use carb cleaner, or propane to check for leaks. I generally just use carb cleaner, or WD-40. If the engines idle changes raises once the engine is up to temp. the carburetor is most likely too lean.