1990 (ish) Yamaha 3 HP only runs on choke

[tpenfield]

I inherited a 3 HP Yamaha OB a couple of years ago from a relative. The engine had been purchased at the end of the 1990 boating season, winterized and then never used. Single cylinder 3 HP, internal tank. . . . spotless :thumb:

When I first got the engine, it was a bit cranky for having been woken up after 28 years in storage, but after some carb cleaner and a little bit of seafoam in the cylinder to loosen things up, it ran very well. I have been using it on my dinghy to get out to my mooring.

Fast-forward to just recently - all of a sudden the engine would not start . . . no matter what. It seemed like it was flooding . . . Thinking it might have been some contaminated fuel messing up the float valve, I took the carburetor apart and cleaned it out, although it was spotless inside. Nothing really that I could see, but I poked all the little orifices with wire, blew things out with compressed air, etc. and put it all back together.

The engine ran fine . . . I ran the engine in gear in a barrel for about 30 minutes and all seemed good, it now could hold an idle speed in gear, and also would increase in throttle (as much as you can really do in a barrel

I put the engine back on my dinghy, and it initially seemed OK, but very quickly it only wanted to stay running with full choke (or nearly so). It will go to mid-range speed, powering the boat, but that's about it. If I try to back-off the choke, the engine dies . . . whether in gear or neutral.

So, at this point, I think that something happened to the motor (carburetor) that I am overlooking or not realizing that caused the initial problems. Not sure what it could be :noidea:, but having to run on choke tells me that there is air getting in somewhere other than via the throttle plate. Of course this latest issue seems like the opposite of the initial issue . . . initially getting too much fuel, now not getting enough . . . . :noidea: I adjusted the idle air screw to no avail . . .

Since I'm at a loss for next steps, I thought I would post the issue to see if anyone has some ideas or similar experiences and possible causes.

 

[dingbat]

Describes perfectly the symptoms of both my chain saw and string trimmer when the fuel line in the tank went bad.

The line was soft and would collapse on anything above fast idle. Would run most of the way up with choke on.

Similar symptoms on the golf cart turned out to be a failing fuel pump.

 

[tpenfield]

Thanks, I'll have to check the fuel line while the engine is operating . . . the tank is a bit of a gravity feed and there is a fuel pump that is built into the carb.



Anyway . . . I think I found something that would explain the issues, and it is quite bizarre actually.

I took a closer look at the carb this morning and noticed 2 areas where there should be those little balls or plates covering a passageway. They are open


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The 2 holes/passageways are supposed to be plugged as shown above One must have fallen out initially and maybe the second one fell out when I was working on it (although I did not notice it and accounted for all the parts when putting it back together.

I'm thinking I should just buy a new carb . . . wondering if it is too late to take it back on the warranty 30 year old motor, but hardly broken in

 

[Scott Danforth]

easy to check Ted...... put some plumbers putty in the holes as a temporary test plug. if the problem goes away, then get a few stake-plugs to replace the temporary plug

 

[tpenfield]

Thanks Scott . . . I was thinking putty of some sort might gunk up the innards or passageways. What's a "stake-plug"? are they also known by another name?

Not sure what the little beads/balls that are used to plug passageways in carburetors are called . . . welch plugs :noidea:

 

[tpenfield]

After a bit of research it looks like the plugs in question are known as "EIS ball expansion plugs" . . . just wondering if I can get a few and fix the carburetor.

I did order a new carb (aftermarket $60), but it would be nice to fix the OEM carb . . . which lists for about $200

 

[tpenfield]

I found some of these 'plugs' on McMaster and ordered them yesterday . . . they arrived today !!!


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I measured the holes in the carburetor body at about 4mm . . . these are 3/16" since McMaster did not have the metric sizes. Hopefully they will be a good enough fit.

If that fails, I do have a replacement carb on order.

 

[Qwazert]

Maybe a BB and a dollop of JB weld to hold it in place?

 

[tpenfield]

Maybe a BB and a dollop of JB weld to hold it in place?

Already got the 'Push plugs' . . . so that will be the first thing I will try. If I do use a BB, it will be to put it out of its mystery

In other news, I received the new carburetor . . . so that will be my 'Plan B' in case the plugs don't bring the engine/carb back to life.

 

[tpenfield]

Update . . .

I must have been off in my measurements . . . the holes seem like they are 3mm not 4 mm and the 3/16" plugs would not fit. :facepalm:

No worries, I took the 'ball' out of the plugs and just used the ball, which seemed to fit fine. A little dab of JB Weld to hold them (as suggested) and I should be in business. Just waiting for the JB to cure. :thumb:

 

[tpenfield]

Update. . . (fixed :noidea: )

I tried out the 'repaired' carburetor this morning, and it did not seem to run any better than before. So, something else must be messed up . . . I'm thinking the float or fuel pump.


.

Anyway, enough fussing with that . . . bring on the new carburetor ( $57 aftermarket variety ) .

Instantly the engine seemed to run better. I am currently giving it a tank test and later will try it out on the dinghy.


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I am not a fan of the single cylinder outboards though. . . very hard to hold an idle with single cylinder (unless it has a heavy, heavy flywheel, which most don't)

I think I'll search for a 4-6 HP 2 cylinder engine as a go-between for this engine and my Merc 7.5 hp.

 

[tpenfield]

Another Update . . .

After running well for a while, the motor started having fits . . . not running right, then running fine for a while . . . stupid thing

So, I replaced the fuel line that leads from the shut-off valve to the fuel pump with a clear hose to see if gas is making its way to the fuel pump/carburetor. It appeared that the shut-off valve was not letting a decent amount of fuel flow.

I then disassembled the rest of the fuel line and the integral tank. There was no fuel filter at the tank outlet, but there appears to be a filter of some sort on the input side of the shut-off valve. I cleaned the valve with acetone and in the process realized that the valve itself was intermittent . . . sometime when I turned it on, I'd get a nice stream of liquid . . . other times, I'd get a few drops, not really flowing.

So, perhaps the problem has been the shut-off valve all along . . . of course, I took the valve apart, but did not see anything obvious, other than its 30 years old Maybe the sealing material within the valve has become too soft. I'll order a new one and see how that goes.

In the meantime, I added an inline filter. . . the red thingy.


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[tpenfield]

I ordered a new shutoff valve, but it looks like it may take a week or so to get here. Since I plan on using the motor this coming weekend, I put a temporary fuel shutoff in there . . . the kind for lawnmowers
.

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I'll just be opening the engine cover to turn it on/off.

One thing I have noticed about this type of fuel system is that the fuel line leading to the pump/carb never seems to prime very well. It has more air than fuel in it, regardless of the filter or not. This filter is designed for gravity feed tanks, so you would think it would put up very little resistance. The air in the line just seems like it's got nowhere to go . . . I even tilted the motor up to see if the fuel would prime the line, but it did not want to . . . maybe if I leave it tilted for a while :noidea:

Any thoughts on that?

 

[QBhoy]

Hi there.

couldn’t help but reply with something on this. Mainly because I have two of these wonderful engines. One running and one almost complete for parts. Not sure about over there, but here these are regarded as one of the best and most sought after small motors ever. Command crazy prices here and still rising. They are caked a Yamaha Malta over here in Europe. Much larger displacement than your normal 3hp and made to last.
my engine at first had similar issues and took me 3 goes at taking the carb off. In the end, an ultra sonic clean did the trick and a new fuel pump diaphragm at the same time.
Amazing wee engines and extra robust over built things with sea water use in mind.
I run mine on 50-1 now, despite the original 100-1 idea.

 

[QBhoy]

Ps. If you want any pics of mine or the one in bits..let me know. Happy to help.

 

[tpenfield]

I have the motor running and use it on my tender. I am generally favorable on Yamaha motors, and had an 8 HP that was bullet proof. This little 3 HP is not a thoroughbred by any means. Although it has some good moments, it has not run well in a consistent fashion. I think being a single cylinder, puts it at a disadvantage in a marine application for low speed operation.

I'm now considering to get a twin cylinder 4-6 hp engine as a back-up to my almighty Mercury 7.5 hp I'll probably keep the 3 hp, becuase it was given to me by an extended family member, and you know how that goes

 

[QBhoy]

I have the motor running and use it on my tender. I am generally favorable on Yamaha motors, and had an 8 HP that was bullet proof. This little 3 HP is not a thoroughbred by any means. Although it has some good moments, it has not run well in a consistent fashion. I think being a single cylinder, puts it at a disadvantage in a marine application for low speed operation.

I'm now considering to get a twin cylinder 4-6 hp engine as a back-up to my almighty Mercury 7.5 hp I'll probably keep the 3 hp, becuase it was given to me by an extended family member, and you know how that goes

I know what you mean. I also have a 93 and a 2001 8hp Yamaha 2 Stroke. Incredible things. But if lightweight and other limitations are a factor...there isn’t a better small engine out there. If you get fed up with it...stick it in the post to Bonnie Scotland!

 

[Lou C]

Had a similar problem on a Suzuki DF2.5 (four stroke) but with the difference was it was brand new! The dealer replaced the carb but it was only marginally better. Then the factory rep took a look at it and removed a tin cover over the idle mixture screw and adjusted it slightly then filled the recess with some kind of sealer. It was definitely better but not 100%. After the warrantee expired that sealer mysteriously disappeared and the idle mixture screw turned about 1/2 turn out ...all by itself ....then...it was 100%...

 

[tpenfield]

Almost 1 year to the day since I started this thread and I am still battling with the Yammy 3HP kicker engine that I use for the dinghy. I used it for about 6 weeks this year while my Merc 7.5 HP was laid up.

The Yammy has gotten progressively worse at staying running, particularly below 1/3 throttle. The best that I have figured . . . after all of the carb replacement, etc. that I did last year . . . is that the engine runs too lean at low throttle. The symptoms are high speed revving and then dying out (stall)

Now with my Mercury back in action, I brought the Yammy home to the test tank and did some 'work' on it while I watched T.S. Henri slide by. there is what looks to be a low speed adjustment screw on the carb, (not sure if it is fuel or air . . . usually it is air), so I played with that cranking it all the way closed and then backing it out 1/2 turn at a time to see if it would find a nice place. . . . nada. Did not seem to make much difference.

The only thing that seems to get the engine to idle at a decent and constant speed was to run it at about 1/2 choke.

I'm thinking that maybe the carbs on these things are just set too lean . I know from my snowblower tinkering, many of the new carbs are set very lean and the machines do not have the gusto that they should. I'm also wondering since this is a single cylinder engine, it needs to idle at a higher RPM, like my single engine snow blower stuff?

Should I ream out the main jet? TIA for any advice . . .

 

[Lou C]

Not sure Ted if that will work but we had a similar problem with a 2012 Suzuki DF2.5 I bought for my son. Even from new. They replaced the carb, same issue. Then they removed a tin cover over the idle mix screw and adjusted it; better but not perfect. So when the warrantee ran out I removed the epoxy they put over the screw (horrors, an owner might choose to adjust their own fuel mix, a real threat to life on earth) and gave it a half turn out which was all it needed not to stumble. There are in the Suzuki catalog different jets that can be used. You might check that for the Yam before drilling anything out.
PS how’d you do in the storm? We were predicted to get a direct hit on LI by the news (around Patchouge LI about 30 miles from here) but the Windy app (excellent by the way) predicted it passing over Montauk LI and it actually went to the east of there & went right over Block Island. We got lucky I saw pix of New London Ct and Westerly RI and there was a lot of damage.