Sean

We put a pair of rebuilt 540s(crank polished and magnafluxed, new rings, bearings, block boiled, new lifters) in the boat using the same electronics, 1050 dominator, etc and now the port motor won't idle. We've replaced all the ignition components, the carb, checked the fuel pressure, checked for vacuum leaks and now, I personally, am out of options...the guys at the shop are still scratching there heads and I'm sure they'll figure it out, but does anyone have any ideas?

DOCTOR DAVE

Sean, need to be more specific on wont idle. does it stall or just wont idle down? if stalling at what rpm, or when putting into gear? i assume the other engine is ok, what ignition system are you running?

Sean

The ignition is the old style Mercruiser...it's Thunderbolt something...sorry I can't be more specific, but the boat is a 1987 and the original motors were 420s. The other motor runs fine(in fact, we took most of the accessories off of it to try and troubleshoot this problem) and the idle problem is in nuetral. We haven't even attempted to try and put it in gear.

The motor will not stay running at 1500rpm or below. It will stall unless you give her some gas. The fuel pump has been replaced as well and she appears to be getting plenty of fuel.

jspeeddemon

Spray the carb area with starting fluid and if the RPM's change you have a vacuum leak. Check you motor with it running with a vacuum gauge. My guess is that this will lead you to your problem. Possibly the intake is not matching the heads and you may have a vacuum leak from the underside, check you oil for water, if vacuum leaks probably the water ports will too.

NW_Jim

Sean, sorry to hear your having troubles with the new engines. Are your 540's tall decks? If so, what intake manifolds are you running. Just curious.

Good luck fixing the problem.

GregP

Check that you have enough initial ignition advance. My motors won't idle well below 14 degrees initial, and really are happier at current 18 degrees. I shortened the advance to keep 35 total. Bigger cams and bigger bore both want more initial advance (bigger bore but same flame front speed needs more advance).

Check that you don't have a bad power valve. Have had blown ones dump so much fuel that they won't idle, but will run once you open it up a little so it can absorb the extra fuel. Might try swapping carbs with the one that runs and see if the problem moves with the carb.

-Greg

Sean

Thanks for the suggestions. We swapped carbs from the good motor with the same result. The starting fluid idea sounds like a good idea.

The motors are tall decks and I'm running Team G manifolds...not tall deck manifolds, so there's a spacer in there to make up the difference. We took the entire intake assembly apart, cleaned and resealed...still won't idle...

The timing idea also sounds valid...I noticed the timing was "all over the place" but I'm not sure how advanced it was. Is it possible that the timing chain is off by one tooth or possibly 180 degrees?

DanB

Sounds like a vacum leak...intake spacers can be a pain. When you say the timing is all over the place...is that on the light?
One other thing that can cause a rough/poor idle is having a valve out of adjustment (too tight)
Dan

Sean

Dan,

Yes, on the light, the timing seems to be all over the place. I never thought about the valves though either.

Thanks for the suggestions guys, I'll let you know what the outcome is.

Sean

Audiofn

Maybe the cam a tooth off?

Jon