Bhoag6276

Need some help all.....86 Formula 357, twin mercruiser 400 cyclone engines with Holley carbs. One motor runs great all the time. The other one runs fine off the get go. I can cruise at 3200-4000 rpm for an hour (I don't beat on it). As soon as I back off to an idle or almost an idle and back on the gas the max rpm I can get out it is right around 4000, when the other will rev (in gear) to at least 4500. If I put it in neutral it will die, I will start back up and idle at 1000 rpm but nothing less. I can rev it up and revs fine, go to put it gear and it dies, start right back up and repeat the whole process. I got it to go once and it didn't sound right, almost like a backfiring (could have been in my head). I was checking the carbs today and one is dirtier that the other, almost seems to be running rich. Not horribly dirty but not as clean as the other. Something else I noticed was when I take the spark arrestors off the choke plate is almost completely closed (they have electric choke). This I assume is normal since the engines were cold. On the engine that runs fine, if I were to push on the throttle linkage, as to rev the engine, the choke plate didn't move. On the other when I do the same, the choke plate would completely close and would not allow any air in. I have to wonder if that is what is happening and its choking the engine out, but it revs fine in neutral just won't idle at normal idle rpm and dies if you put it in gear. Both fuel filter were just replaced last week. Maybe it just needs a good cleaning? Maybe rebuilt? The engines and carbs have 32 hours on them since full rebuild. Thanks in advance for any and all help!

ShortCircuit

Check to make sure you have 12v to the electric choke with the engine running, it gets power to heat the spring and open from the oil pressure switch. Second I would check to make sure the 3 screws that hold the choke cap are on tight and check the adjustment vs. the other motor.

Bhoag6276

funny you say that.....my oil pressure gauge doesn’t work, as soon as i hit the key (engine off) it pegs all the way to the high side. I’ve checked the choke adjustment versus the other engine and it’s the same. I haven’t checked for 12v with the engine running, i will do that next. You think the faulty oil pressure gauge is partly to blame?

Helmwurst

I sounds to me like you have an open ground on that side. Are other gauges for the motor in question working ok ?

Mbam

I don't think you need the choke at all. Easy to remove the shaft & butterfly

Just pump once or twice before starting when cold if needed.

Dose the gauge go to 0 once it starts? If so sounds like your gauge is connected to the audio alarm switch instead of the pressure sender.

Bhoag6276

All the other gauges work just fine. It does not go to zero once it starts. I agree about not needing the choke. Maybe it is best to unhook. Think that’s what’s causing my issue? The stalling when going into gear after being warm?

SB

No way for him to know without bring at your boat. Easy enough to check. Start engine without arrestor on and watch.

Could be dirty passage in your carb , sticking or leaking needle and seat/ etc.

So, time to check:go thru things one at a time. Report back for some help / guidance.

Bhoag6276

That's kinda what im thinking, go run it for a bit and wait for it to happen again.....then pull the spark arrestor and watch what is actually happening. I update again with my findings. Thanks!

Bhoag6276

Went out tonight, same result. Ran fine at anywhere from 3000-4000rpm. Soon as i idled down it stalled. Pulled the arrestor and started fine, will idle at 1200rpm but none less. Put it in gear and stalls. Choke was wide open. It looked pretty dirty in there, I’m hoping a good cleaning might do the trick? Maybe something in there is sticking or gummed up. Any other ideas?

SB

I find globules of e10 gas junk alot in carbs. More Holleys than webers/quadrajets...but then again more oeople with Holleys around me.

Have you gone thru one ? If not Real easy. but nice to have someone close who can show you thru one. I do this alot to. Last was a Gen X or Y? He’s early 20’s , wow I was happy some kids like this stuff.