Yamaha 20 horse problem?HELP

[chris63]

1989 20 horse 2 stroke starts idles and trolls just fine.When powering up past 1/3 throttle it bogs out and will only get up to 5.5 to6 mph.I tried sea foam new plugs different tank/gas.Where is a good marine mechanic in the west metro?(By Mound preferably)Thanks for your time.c63

[chris63]

No ideas?Today I'm going to try Deep Creep carb cleaner.If that fails it's off to the motor Doctor!c63

[Surface Tension]

Could be one of a lot of things.

What did the plugs look like?

Was there a wet one, did they look dry?

Check for spark, it could be your running on one cyl.

Could be a dirty carb but usually the the low speed circuits(because of the smaller die) will show signs of being dirty before the high speed.

That would mean it wouldn't idle well and it wouldn't start well.

It could be that your not getting enough fuel to the carb.

That would be a leak in the fuel line anywhere between the tank and carb.

Could be a weak fuel pump as well.

A dirty fuel filter could be restricting the fuel.

Is the primer bulb hard?

If it is soft your leaking air or the fuel pump is weak.

If it soft squeeze it up and then go to full throttle.

Did it build the RPMs but then start to bog?

If so your back to the air leak, weak pump, bad filter, improper float drop(not enough fuel in the bowl).

You can drain the bowl on the carb by backing out the drain screw on the bottom. Sometimes that'll get the float to drop enough to open the inlet valve all the way and debris can pass .

[chris63]

Frank,fuel lines ok,put sea foam in the fuel tanks(2 different ones)soak carbs down twice with deep creep with engine warm and running.Tried new fuel filter.How much pressure should the fuel pump produce?6to8 psi or more?Primer bulbs (both tanks)hard no issues with air leaks.Is the drain screw the one at the bottom corner of the carbs?(Side of the float bowl?)...........too many questions not enough mechanics!c63

[boatfixer]

When you say you soaked the carb, how so? In order to effectively clean the carburator, it needs to be disassembled.

Have you verified good compression?

Have you been able to verify good spark on both cylinders? A timing light works well for checking it through all rpm ranges. You dont need to direct the light towards anything, just watch for the light to consistantly flash.

One other tip is to try activating the choke/cold start primer, while its bogging. If it "picks up" that indicates a carb issue.

[chris63]

I sprayed deep creep into the carbs when the engine was running.I didn't technically "soak" the carbs.If the engine starts and idles fine but will only power up to about 1/3 throttle then bogs what does this sound like to you?c63

[chris63]

Both cylinders have spark.I don't have a timing light to check through rpm ranges.I don't have a compression tester either but when pulling the engine seems to have compression like it always has had.(I know this is backwoods marine mechanics no-no rule #1.c63

[boatfixer]

I would check to see if the throttle is actually opening up all the way.

I would do a compression check

Then I would verify spark

Once those check out, I would focus on fuel.

Does is just kind of bog down? or want to die? Does it shake?

[chris63]

Thanks Bruce,if I was in your neck of the woods I would bring it to you!c63

[chris63]

It doesn't want to die unless I use manual choke which I think is normal.Kill off the air and the motor starts to flood right?Engine runs smooth.No shaking or vibrations.c63

[boatfixer]

Can you see if the the throttle is opening all the way?

[chris63]

I checked compression today checked for spark took all fuel lines off.All checked out OK.Is the small square assembly on the lower right of the bottom carb the fuel pump?I assume the fuel pump is mechanically driven.How do I check for proper fuel pressure?Yes the butterfly's for both carbs are opening all the as both chokes are closing freely.Frustrating to say the least.c63

[delcecchi]

I checked compression today checked for spark took all fuel lines off.All checked out OK.Is the small square assembly on the lower right of the bottom carb the fuel pump?I assume the fuel pump is mechanically driven.How do I check for proper fuel pressure?Yes the butterfly's for both carbs are opening all the as both chokes are closing freely.Frustrating to say the least.c63

Can you put a timing light on it and see if the spark advance is moving with engine speed like it is supposed to? Just a guess, but if you have a timing light it would be easy to check.

[boatfixer]

Yes the fuel pump is located on the bottom carburator. It uses pulses from the crankcase to pump the gas. In order to test for pressure, you would need a fuel pressure/vacuum tester.

I really think there is a restriction in one of the carbs. Once you get over idle, it sounds like its only running on one cylinder. I wouldnt keep running that way. If it is starving for gas on one cylinder, its not getting any lubrication to that cylinder and you could make things worse.

If you are uncomfortable doing anymore troubleshooting, take it to a shop and have them do further testing or you could always tackle rebuilding the carbs and the fuel pump yourself.