Stalling at low rpm

[Carl]

I have my engine set to idle around 1K rpm. I had turned it up from 850 rpm since the engine would stall as soon as I shifted into gear. I still have a stalling issue, but not quite as bad. My problem is more shifting from fwd to reverse or reverse to fwd especially trying to get the boat back into my slip. The rpms drop to 400-500 and then stalls out. It typically starts right up again, but it gets frustrating and a bit dangerous trying to manuever in and out of a small marina.

My first step is to run off a small portable tank to see if that makes a difference. That will also bypass the racor filter as well. Then I was going to pull a wire off 1 cylinder at a time to see if a cylinder is not firing. I also thought to rebuild / replace the fuel pump

The engine runs strong at anything at or above 1000 rpms.

Am I on the right track, what else should I do?
Thanks

Carl

[THEFERMANATOR]

When was the last time the plugs and wires were done? How about the carbs? That engine should be able to idle down to around 700-750 in neutral or so without stalling when shifting. My old 150 idled at 700 out of gear and 650 in, and my really old 150 idled at 600 in neutral and 500 in gear and never stalled. Sounds to me like a fuel problem with the carbs in the fuel pick-up jets for the idle circuit.

[steplift20]

i had a problem like yours and it was the stator

[Carl]

The plugs are new this season. Wires have not been changed in the 5 years I have had the engine. I have not done anything to the carbs except use some carb cleaner on them at the end of last season. The carb cleaner did not seem to have any effect.

I will keep trying

Thanks

Carl

[spareparts]

wires generally don't give a lot of problems, I'd guess a carb job and a good synk&link after you get the carbs on.

[Carl]

So,

I did some diagnosis this afternoon. Here is what I did. I ran on a separate fuel tank with new fuel bypassing the racor - No change

I pulled a wire off one at a time starting with 1-3-5. Pulling 1 and 3 made the idle slow and almost stall. Pulling 3 did nothing - no change. I did the same on the port bank 2-4-6. #2 wire was broken at the coil, but the coil was sparking like crazy without the wire attached (the only coil that did that). #4 wire was the only wire that provided some volts into my fingers as I pulled it off, but did affect the idle. #6 wire also affected the idle.

Since I have at least 1 bad (broken wire) I will replace all 6 and re-test. Could there also be some coil issues?

Spare - I'm confident I can rebuild the carbs, but what does a "good sync and link" mean? Is that something in a manual or more of a feel and hear of a good mechanic?

[spareparts]

sounds like you proved me wrong about the wires

a sync and link is setting teh carburator linkages all in sync with the timing linkages. Getting everything set up right is the key in making an outboard run well.

first things first, do a compresion test, repair the wire(s) and check spark with a spark tester. Once you have determined you have compresion and spark, then pull the carbs off and go thru them. See if you can locate a factory manual for the sync and link set up

[Carl]

I did a compression check and found all cylinders are within a few #'s of each other. Here are the averages
1= 112
2 = 112
3 =110
4 = 115
5 =115
6 = 110

I rebuilt the fuel pump yesterday which helps the overall performance, but it does not help at all in the low rpms. I did not yet pull the carbs. That will be next after these two questions.

1 - Per the wiring diagrams, there is a idle control module identified, but the engine does not have one installed. Could this be part of my idle problem?

2. - Since the engine runs great at mid and high speeds, could this be as simple as just an idle jet replacement, and if so, can that be changed without removing and disassembling all the carbs?

Thanks for all the help

Carl

[BRIELLY]

Lots of people remove the idle control module because when it goes bad it causes problems and the engine can run fine without it. When you remove it you need to make some slight adjustments to the timing. If this was done by the previous owner and the motor ran well before you had this problem I wouldn't worry about it. Before getting into the carbs did you make certain that you were getting spark on all cylinders? Stators have low speed and high speed windings so its possible to run ok a higher rpms but poorly at low rpm. I had a similar problem earlier this summer and wound up needing a stator and switch box.

[breastman569]

Have you checked for a vacuum leak around the carb or the intake manifold? At a higher RPM this would not effect the performace but it will for sure at lower RPM's. it is easy enough to check with some starting fluid.