Erratic Low Speed

[buckaroo]

Its a 98 2 cycle 60HP. Problem is at start it smokes real bad and seems not to be running on all three cylinders until about 1500rpm. After that it runs flawlessly as far as WOP. Carbs were removed and thoroughly cleaned three times with little results. It seems to run best at factory carb settings except below 1500 rpm. Engine has only about 150 hours on original engine. Am I looking at something electrical or what?

[boats.net]

Start with a compression test to see if all cylinders are even and a spark test to see if firing on all cylinders. If it's an oil injected model the back seal in oil pump may be leaking. Check the fuel pump, may have ruptured diaphram in it.

[buckaroo]

Erratic Low Speed

Thanks, we did compression and spark and everything is up to par. It is not an oil injected engine . The fuel / oil ratio is right on. We are stll perplexed.

[robert graham]

Check to see if spark plugs are wet with gas, check for broken fuel pump diaphragm causing very rich mixture, fouling, smoke, rough running.

[buckaroo]

Yep plugs are wet, and engine displays all the problems that Robert cited. I had disassembled the fuel pump a few days ago but did not find a problem with either diaphram or any part of the body. No fuel is leaking out so air must be leaking in I think. Rather than play with the pump I m going to replace it over the weekend. Beyond that, what else should I be looking at? The ball is always hard throughout operating range and filters are clean. Thanks again

[99yam40]

have you checked the timing with a timing light?
Did you do the sync and link procedure on the carbs after they were reinstalled?
If the compression is good and it is getting good spark at the right time then it would have to be the fuel/air mixture.
If the pump is good then it is back to the carbs.
Does it have the Prime Start System or chokes?

[buckaroo]

Erratic Slow Speed

Installed new fuel pump. No change in problem. Double checked sync & linc. Everything lines up good. Compression 120 and equal in all 3 cylinders. I don't have time light so I brought #1 cyl to top. The time mark on the timing plate = the timing pointer at TDC. It starts as soon as the key is turned. I drained all gas and replaced it with fresh fuel. No change. However, now I cannot run past 2800rpm. I don't think it is the result of what I have done since it has been a couple of weeks sitting on the trailer. I'm not a mechanic. I did all the weekend warrior stuff I could think of. Am I now getting in over my head or is there a guru with the answer. If not, thanks to you all for your help.

[99yam40]

The timing is con*****ed by the CDI and you have to check if it is setting the timing properly with a timing light at all RPMs.The CDI limits RPM by changing the timing if the motor has a problem.
Have you checked the spark with a spark tester on all cylinders? An inductive timing light will also show a loss of spark at different RPMs
Do you have a manual that you are following the sync and link procedure out of? If not get one for your motor, it will give a lot of testing procedures.
You never said what your motor model # was or if it has choke or prime start.
My thoughts are it is the carbs. but I am not looking at it or know what all has been done and how well