1989 40hp 3 cyl Yamaha idle issues...

I believe there is only one fuel pump for all 3 carburetors. It goes from the filter to the pump, and then through a tube that splits into 3 to each carb. I'm going to take a look at all that and the bottom carburetor when I get some time this week. Thanks for the suggestions; hopefully I can finally get this all sorted out.

Quick question, the black plastic box that says Mitsubishi on it; is this the thing that controls the timing? What do the tick marks mean on it? There are 3 ticks toward the bottom and one at the top, and that linkage on the box is con*****ed by the throttle to change the timing as RPM changes. Thanks!

[jb123]

http://www.boats.net/parts/search/Ya...RTS/index.html

That is the CDI box & those black ticks are the timing reference marks.Did you do a sync & link on the carbs?just something to check.

That is the CDI box & those black ticks are the timing reference marks.Did you do a sync & link on the carbs?just something to check.

How do you do a sync and link? I advanced the timing a bit and it will idle, but the bottom cylinder is still having issues...

[dorf]

It is somewhat complicated(sync and link)depending upon the model. I purchased a Clymer Manual that is really helpful with lots of pictures and descriptions, better than the factory manual for my 2006 50 HP, 2 stroke.

See:http://clymer.com/Book.aspx?bid=650&...s%2c+1984-1989

Well, I got a Clymer manual and the only thing that you have to do to adjust the timing is to just adjust that lever on the CDI box (in the picture it is gray plastic connected to a piece of metal pointed to the CDI box).

What I'm going to do is just take it out on the water and put some load on it and just see what happens. This motor has been sitting so long it will probably help it to just run for a while on the water. I checked the bottom carburetor again and can't find anything wrong with it. They're all getting plenty of gas, and all the plugs are working. It idles fine with the way I have the timing adjusted, but the bottom cylinder is still having issues and doesn't seem to be firing. After replacing the crack seals, it runs a LOT better, but I'm not convinced that was the entire problem.

If running it doesn't help any I guess the next thing is to start troubleshooting the ignition/timing to make certain it's sparking correctly...

[dorf]

I re-read your original posts.

What are the compression readings on each cylinder? top, mid, bottom?(throttle plates full open)

My 2006 50 hp had similar problems and I researched the carb situation in both the Clymer and Yamaha manuals but it has the auto Prime start system.

The throtle plates need to be almost closed when starting. Idle is obtained by screwing the idle screw just until the throttle plates start to move and then all be in sync.Your engine has individual carb adjustments, mine does not. Maybe carb adjuistment is off.

Part of my problem was a closed/sticking Anti syphon valve (spring loaded ball valve) in the boat gas tank. It was removed and the fuel lines and the 10 micron fuel filter replaced.

So.......your engine might be sucking air somewhere along the way to the engine bottom carb or a restriction in the fuel lines. Or improper (high restriction)fuel filter installed. ???

Verify that the correct part number carb is installed the proper location.

Also check Margretiavilles post on this similar subject.

I don't remember exactly what the compression was, but I know they were all on-spot, like +/- 1%. I think they all read 120lbs. if I remember correctly.

My mechanic friend had already adjusted the carburetors and this helped a little but it didn't fix the problem. I did replace the filter and clean out inside the plastic cup, and I know I used the correct filter for my model.

My inclination is that it is sucking in air from somewhere. I know 2 strokes get cranky when their vacuum gets messed up, and this one is acting like that. I've all but ruled out everything else. Going through the carburetors and replacing the crack seals definitely helped a lot, but something still isn't right. I guess I just need to examine the parts diagrams in the Clymer's manual and double-check any places where air could possibly be getting in.

I'm not to sure on your model. But I know that on some engines Yamaha put diffrent sized jets in each diffrent carb. When you took them all apart and cleaned them. Did all the parts from each carb go back in same place??

I'm not to sure on your model. But I know that on some engines Yamaha put diffrent sized jets in each diffrent carb. When you took them all apart and cleaned them. Did all the parts from each carb go back in same place??

The jets were all replaced with the parts from the rebuild kit and they were all 3 the same shape/size and all of them fit OK. I did some more troubleshooting today and went through the bottom carburetor yet again, and also blew out the fuel line and tested each of the 3 outlets to the carburetors to make sure it was giving them all fuel and they were all pumping.

I'm just going to have to take it out next week sometime on the water and run it WOT to see what happens. If it still doesn't run right after running for a while, and if I still can't figure it out, it's gone off my transom and being replaced with an OMC...

I would stay away from running it WOT untill you put the timing back to spec. You also seem to think it's ignition related. Have you swapped coils over 1 to 3 or 2 to 3 and see if the problem is still with number 3 cyl?

Yes, I have tried swapping coils and the bottom cylinder was still having issues. Timing should still be within spec. I think the 3 tick marks on that box are just markers for where it should be at idle, and I have it inside those markers right now. That Clymer's manual is about worthless as it says nothing about those notches at all...

only way to set timing for sure is with a timing light. If it's set to far advanced at idle it only gets worse as you open the throttle and could cause a whole bunch of other issues. Have you inspected the reeds when you had carbs off? I know it's hard to see in there but you might see something obivous. When the engine is running above idle around 2500 or so does the bottom carb spit back at out a little. Thats the quick way of seeing if reeds are working correctly , It's by far not a perfect test but will tell you if somethings wrong. Have you tried spraying some fuel from spray bottle around intake while under some load to see if it picks up? Has the bleed lines been removed and put back in correct location? You can also check bleed lines check valves that are mounted on the block and intake. Can't remeber if your model uses a seperate trigger for each cyl. Does it have a multiple colored wired plug coming out from under the flywheel. Can't remember all the colors but it will have 3 white wires with diffrent colored strips on it one for each cyl. Disconnect the plug and check for ohm resitance between each white colored/striped and the black wire. Just make sure they are all about the same plus or minus 10% ish then check each white/strip wire for continiuty to engine ground, it should open Good luck

read this

i have a 89 40hp elg....when i bought the boat the first thing i did when i got it home was "fire it up" it ran good for 20 secs, then squeaked, then died!When it squeaked thats when it would misfire and then die! If it sounds like"metal on metal squeak or more like a chirp" Your problem is your rings are siezed! I pulled my powerhead...honed the #3 cylinder, put a new piston and rings.....i actually honed all 3 cylinders, new rings in all 3, and replaced #3 piston.....your compression will read good for the first 20 seconds, but after that it will drop off....the only way to check it , is to pull the block apart, i m sure that is your problem....got nothing to do with fuel or carberation...if it squeakes then die's its your #3 piston and ring....dont keep starting it if its still squeaking , your only do further damage...
regardzzzz
jesse