I have a racy outboard!!

[yarcraft91]

The motor- 1991 Johnson 120 V-4. This motor has been great, needing nothing but routine maintenance since I bought it new, until last season. Then it began coughing at idle. I found a broken fuel line clamp on the fuel pump inlet and another further upstream on the fuel supply line. Once I replaced those clamps, the coughing stopped last season. Now I have a different problem.

I just took the boat out of storage and started it on a flushing muffler (40 degrees outside). It started right up, but, once it warmed up, the idle speed seemed higher than it should be- 1400 rpm. I expect a high idle in neutral on a flushing muffler, but not this much. Periodically, the engine speed would race up to 1800 rpm for 10 seconds or less, then drop back to 1000 briefly, then go back to 1400 for as much as a minute, then race to 1800 again, back to 1000 and on and on. The rpm's wandering up and down is a new behavior.

I have not put the boat in the water to test the in-gear idle speed.

I checked the throttle cable adjustment- that seems to be correct. The throttle cam follower does not touch the cam at idle- also correct. The throttle plates are closed at idle. None of the timing adjustments have been tweaked since new.

Ideas?

[Hot Runr Guy]

There's an old saying, that goes something like,,,,,, a 2-stroke runs it's best, right before it seizes up! Are you sure it's getting oil, if it's on a VRO system?
HRG

[yarcraft91]

There's an old saying, that goes something like,,,,,, a 2-stroke runs it's best, right before it seizes up! Are you sure it's getting oil, if it's on a VRO system?
HRG

Yes, I've heard that one, too, hoping it doesn't apply in this case. The motor is on a VRO system, oil consumption was normal right through last season. Judging from the smoke out the exhaust today, I'd say the motor is still getting oil.

[Flip Silverlake]

You migh have a restriction in carb circuts. 2 stroke engines will run like mad when you lean them out, but that is only for a brief time then it's boom and its all over. I remember guys that would lean the snot out of their snowmachines in warm weather only to find out when it got cold they would start scoring pistions and jugs becasue you get more air in colder weather. More air less fuel equals trouble.

One other thing is that muffs do not create any back pressure on the motor and sometime let them get into a run away condition. I've always been nervous about running on muffs. I know sometimes you just have to do it but it can be scarry.

[yarcraft91]

I found some "extra parts" lying in the bottom of the powerhead housing- a white plastic ball, a spring and a yellow plastic part- looks like a check-ball seat. It appears the check valve (OEM Part 0986534 ) in the aspirator system fell apart, since there are no parts inside it now. It's hard to imagine that's the cause of changes in how the motor runs...

[yarcraft91]

OK- think I found the problem(s).

Re-assembled the aspirator check valve. How that thing fell apart is beyond me- it takes some real force to snap the ball seat into the housing . Of course, it had nothing to do with the racing behavior- I think it's just there to pump out the lower motor housing in case the engine springs a water leak.

Inspected all the engine hoses and clamps- all OK. It shows how good modern materials can be- 18-year-old fuel hoses are all still soft, pliable and crack free.

Torqued the carburetor main body-to-throttle body screws to spec (48 in-lb). Most were loose (as much as 3/4 of a turn)! Hmm. Pays to check these things and have a good, small torque wrench.

Torqued the throttle body mounting screws and nuts to spec (120 in-lb). Several of them were loose, most less than 1/4 turn. Hmm, again.

Put boat in the lake and ran it- idle is still too high- 950 rpm in gear. Checked the idle timing- it was 4 degrees ATDC (spec is 8 degrees ATDC). Adjusted to spec- now I have a stable idle just under 700 rpm in gear- just as it should be. Idle speed on the flushing muffler is higher (900-1000), but the racing-up behavior is gone.

The idle timing hasn't been touched since the boat was new- I'm wondering why this wasn't an issue before now. Something to watch- if it drifts away from this adjustment, it may be time for a new power pack.

This is what I get for running an antique... :o

[perchjerker]

thats good to know

hopefully that manual helped you out in this

[yarcraft91]

thats good to know

hopefully that manual helped you out in this

Thanks again for giving me a copy of that manual. I just sent you an e-mail on that subject.