'84 Johnson 30HP - Power Up Problem

[Doolin]

Hi All,

I've had this motor on a 16' Valco Runabout for 2 years now. It's always had this problem and I've tried just about everything. I'm hoping for a hint or two to point me in the right direction.

Current Condition:
It starts easy and idles well. Once up on a plain... it runs WOT well.
When I increase throttle from idle, it boggs and can even die. To get throttle increased, I have to nudge up the throttle then bump the choke injector. At all speeds, the engine seems to run better when I bump the choke. It'll sound better and the rpms will increase for about 3 seconds then it'll come down again.

Where I've been:
I've always thought this was a 'fuel starved' condition, so I started with the fuel pump. That seemed to make a little improvement... but the primary problem didn't go away. I thought that maybe it was a venting problem since there was a big 'sucking noise' when I opened the tank after running the motor, so I replaced the tank with one that had a manual vent. No improvement. I thought maybe the carb was dirty... so I removed, cleaned, reassembled & reinstalled. The motor did run better (more power) but it still had the need for the choke to be bumped to get the RPSs up. Still thinking it was a 'fuel starved' condition, I followed the fuel lines and found a fitting that was too small. Thinking that maybe this was a choke point... I replaced it with a larger fitting & replaced the lines inside the hood. No improvement.


What's left:
I havent' replaced the lines from the tank to the motor. The bulb will pump up hard and since it runs WOT ok, my guess is that the line isn't the problem.

There is a 'cam adjustment' on the throttle linkage that I haven't played with yet... but I'm not sure how to adjust that one. It seems like it could be related as it looks to be tied to the throttle plate and could impact the air/fuel ratio through the throttle range.

I've also considered trying a bigger main jet as my guess is that this is still a 'fuel starved' condition and if I get a big enough jet... at some point the dang thing will get enough fuel.


Thanks in advance for any suggestions!


Ben

 

[crxess]

Re: '84 Johnson 30HP - Power Up Problem

You should have a service manual for reference.

The Throttle cam under the flywheel should be set to just start opening the Carb butterfly at the point where the Line on the cam aligns with the follower on the carb.

It is also possible you are chasing shadows on the fuel and the timing might be off. That can give the same results.

 

[Doolin]

Re: '84 Johnson 30HP - Power Up Problem

Thanks for the suggestions.

I do have the service manual... it says the timing is automatic and not adjustable.

I'm only assuming that the issue is fuel because the electric choke is just pumping in more fuel... which seems to correct the problem... at least for about 3 seconds.

The throttle cam I mentioned is a secondary linkage attached to the side of the carburator (not under the flywheel). The manual does mention it... but it wasn't really clear on how it should be set. I'll take another look and see if I can figure out what it's trying to say.


Thanks,

Ben

 

[shipwreck]

Re: '84 Johnson 30HP - Power Up Problem

i had problem like that today out on lake
no power at WOT i actual end adjusting make cam on butterfly valve and went
from 7- miles an hour to 24 miles hour and less fuel
weird what the right air / fuel mix will do.

i with other guy check your manual and butterfly cam link timing.

 

[Doolin]

Re: '84 Johnson 30HP - Power Up Problem

I went back to the manual. In searching the web for more info... I found that the manual I 'should have' is the OMC OEM manual as it'll be more detailed and specific to my motor.

The lack of detail is exactly the problem I was dealing with. After a lot of studying of the text, 'poor quality' photos and looking at my motor I was able to figure out what they were trying to say.

In case anyone else comes across this same problem... here's what I did:

1: Release the stop on the throttle advance (the one with the set screw that slides along the throttle linkage on the side opposite the throttle plate linkage). On my motor... it was holding the cam folower off of the cam even with the throttle lever in neutral.

2: loosen the lock screw holding the cam folower to the throttle lever.

3: Center the cam follower between the two cam marks on the cam.

4: Adjust the throttle plate to be closed at this point.

5: Move the throttle lever to Wide Open.

6: Adjust the throttle stop so that the throttle plate is level. NOTE - The throttle plate will adjust to 'past level', reducing air flow.


Following those steps, my motor reved right up like it hasn't done since I've owned it. The final test will be under load. I'll post a follow-up in about a week.

Thanks much,

Ben

 

[ISLAND1000]

Re: '84 Johnson 30HP - Power Up Problem

I'm waiting for your final results. I have the same engine and some of the same symptoms.

 

[Doolin]

Re: '84 Johnson 30HP - Power Up Problem

I still don't have it running perfect. It's better but not there yet. I still need to hit the choke to get the motor to speed up under load.

I bought a compression tester but the part that screws into the plug hole is too long. It actually hit the piston on my 4hp kicker. Fortunately it's a pull start and it didn't hit the piston hard.

Without screwing it in all the way, it doesn't seal. I think I'm going to try to cut that adapter in half... so it doesn't stick down so far.

I also ordered a spark plug tester that screws out so you can see just how far the spark will jump. I have the 'in line' light tester... but I already knew that both pistons fire... they could be firing weak though.

Anyone know how far the spark should jump on this motor?

I'll post again if I am able to make more improvements.

Still open to suggestions if anyone has an idea as to why it won't speed up without hitting the choke. Thinking maybe a bigger main jet?

 

[Doolin]

Re: '84 Johnson 30HP - Power Up Problem

SOLUTION:

I purchased a spark plug 'gap jump' tester that screws out so you can measure just how far your spark will jump. Although... I'm not sure how far my spark should jump... anyone know?

I also purchased a compression tester. Fortunately, I tried the compression tester on my pull-start 4HP motor first. The 14mm adapter is way too long and actually hits the piston. Had I hit that with the starter motor instead of the pull rope, things might have gotten real bad. I think I might have to cut that adapter in half with my die grinder... not sure how else to make it work.

Anyway, to the point, I didn't get the opportunity to test either before finding the problem. Again, the problem appeared to be a fuel starved condition that would be significantly improved by hitting the electric choke which just squirts more fuel into the carb. This on a motor with a freshly rebuilt fuel pump and cleaned carbs.

My throttle linkage was way out of whack and it did run a little better once I figured that out and correctly adjusted it. The 'real' fix to the fuel starved problem though, was the low idle adjustment. I had adjusted it based on a recommendation I read here. In all fairness, it may not have been a recommendation for my motor. I came across another suggestion recently that made a lot more sense.

I had followed the original advise which was to run the motor and close the low idle needle until the engine starts to 'lean sneeze', then back it out 1/2 turn. I did this and never touched the needle again.

I read another suggestion a couple days ago that said to find the 'lean sneeze' point then the 'rich sputter' and start with the needle in the middle of these two points. Then try to power up. If it's still lean (choke improves the power up) richen up the mixture (counter clockwise to move the needle out) by 1/8th turn then try again.

I made a couple adjustments and now the motor will power up on its own without choke 'shots' to get it to accelerate and hitting the choke under power just kills the motor (too rich at that point).

Hope that helps some others... it was a real pain for me... but I did learn a lot about my motor