Johnson gt150 acceleration issue.

[Jduq12]

I rebuilt my 89 johnson GT150 last year, everything is great besides a slight acceleration issue. Engine fires up and idles flawlessly.. tons of power, planes in seconds and gets to max speed at 5300rpms very quickly. My issue is a slight/major acceleration hiccup.

After initial launch start up, with primed bulbed and carbs full, i can punch throttle and it takes off with minor hesitation. A hesitation that i would like to blame the prop. Its a hesitation i could deal with. I can continously cruise at any speed with the motor running as it should. The problem starts once i bring it down back to idling speed for a minute or so and then try to take off again.. the hiccups begin.

Slight hiccup= as long as I feather into punching the pedal, she gets out of the hole as it should.. (split second hesitation usually, occasionally no hesitation.)

Major hiccup= romping on the pedal immediately creates it to bog.. and die if i dont let off the throttle.

To counter these issues, If I squeeze the primer bulb until its full and then immediately punch full throttle.. (usually still has the slight hesitation, but occasionally just rips right out of the hole with absolutely no hesitation..

It seems likely to pinpoint the issue at the pick up tube, maybe a dirty screen. I possibly wouldnt have had to write this post if I replaced it, but ive tempted to remove it a couple of times and had quite the fight with it.. and lost.

Im looking to get a confirmation on the tube being the problem before i burn another few hours trying to get it out. Or if it could be something else?

Thanks, Jason

(In return, ill upload pictures of my %95 fully restored/custom 1989 ranger 375V)

[ELGIN]

Did you replace the six recirc valves in the intake?
They will cause the engine to bog on acceleration.

Recirc valves.jpg

#7 is the recirc valve, they are available in Atlanta and Beloit, they are about 40 bucks each.

[Jduq12]

Yes, all of them were replaced last year.

[ChampioNman]

I'd try a portable tank just to eliminate the fuel tank. It won't take long to tell, before jumping into the tank.

[316jughead]

Are you using the VRO? The slight hesitation may be eliminated by setting the idle timing pick up at 10 degree's, before the carbs start to open. Follow your service manual for the sync and link.

[Jduq12]

I'd try a portable tank just to eliminate the fuel tank. It won't take long to tell, before jumping into the tank.

Ok. I dont know why i didnt think of that.. oh thats right, i didnt think any portable tank was big enough for my thirsty horse. Lol. Ill give it a shot. Thanks

[Jduq12]

Are you using the VRO? The slight hesitation may be eliminated by setting the idle timing pick up at 10 degree's, before the carbs start to open. Follow your service manual for the sync and link.

Yes, bought a new vro alast year. I tried the 10 degrees. No luck. Sync and link completed and double/tripple/ quadrupled checked...

[Jduq12]

Ok. I dont know why i didnt think of that.. oh thats right, i didnt think any portable tank was big enough for my thirsty horse. Lol. Ill give it a shot. Thanks

No difference with the portable tank..

[ELGIN]

Just to test, move the throttle roller as far back in the slot as it will go away from the cam, see if the engine still hesitates, if not, move it back towards the cam until it does hesitate then find a happy medium. Its just a thought.

[316jughead]

You might want to check the all the timing and throttle linkage, to make sure nothing is binding up, like the big arm that opens every thing. If that makes any sense, I just woke up. Might want to check for air in the fuel line, does the motor smoke a lot at idle? After up and running for a while and shutting down is there a noticeable drop in idle RPM?

[omcforever]

Was this a problem you where chasing when you replaced the VRO (prior to rebuild/why was it rebuilt)or has it happened since it was replaced? Was the new VRO a true new BRP/OMC manufactured unit? When you say it gets better when you pump the ball is a big clue. If it where me, I would perform a fuel pressure test per your OMC manual staring on page 2-8 and also verify all hoses and clamps are good as is the tank check valve and no air leaks..insure you bulb is a BRP/OMC unit and works properly and installed right and like the others say,,re-check your link and sync.

[omcforever]

Also verify recirc hose routing is correct..

[omcforever]

[Jduq12]

I happened to catch some intermittent spark while timing. checked all cylinders.. the missing sparks seems to jump around but foucused on 1 and 3. I tested it today and it seems to be the culprit.. as far as squeezing the primer bulb and or feathering into the full throttle, id still think there's a fuel issue. Unless intermittent misfires allowing fuel build up in bottom end, resulting in poor combustion until the timerbase magically starts working. Maybe some magic for the primer bulb squeeze as well.. idk. Do you have a timerbase for sale?.. my friend owned my boat many years ago and it would always bog when he tried to load it on the trailer.. this was before it was rebuilt.. and it always does the same to me.. would a timerbase be a problem that would stick around with problems and still allow the boat to work for so many years.. that would mean this boat hasn't been getting solid consistent spark for at least the last 10 years.

[Jduq12]

Also verify recirc hose routing is correct..

Checked out

[Jduq12]

Was this a problem you where chasing when you replaced the VRO (prior to rebuild/why was it rebuilt)or has it happened since it was replaced? Was the new VRO a true new BRP/OMC manufactured unit? When you say it gets better when you pump the ball is a big clue. If it where me, I would perform a fuel pressure test per your OMC manual staring on page 2-8 and also verify all hoses and clamps are good as is the tank check valve and no air leaks..insure you bulb is a BRP/OMC unit and works properly and installed right and like the others say,,re-check your link and sync.

Yes, unfortunately i tend to chase problems with money rather than time.. but its a 30year old motor. And i use it a lot. So these spare parts are a good thing to have.. i save every single part that comes out of the engine. Once i get new timer base in(other post response) ill start with the pressure test.

[Jduq12]

You might want to check the all the timing and throttle linkage, to make sure nothing is binding up, like the big arm that opens every thing. If that makes any sense, I just woke up. Might want to check for air in the fuel line, does the motor smoke a lot at idle? After up and running for a while and shutting down is there a noticeable drop in idle RPM?

Evrything seems free as it should be. Found some issues with timing base. Hoping that fix EVERYTHING! Ha ive hoped that with the last 20 hours of tinkering and $$ out the pocket.. good thing the timer base is cheap.

[Jduq12]

Will do.

[Jduq12]

Ok... soo, ive been going in circles here. This motor has been nothing but a mystery.. when i rebuilt the carbs, the looked very clean. So i cut corners, one being not pulling the offices.. well tonight i took them apart again due to crappy black float bowl gaskets..and i didn take the offices out. one of the 3 offices didnt match up with factory.. the idle air bleed i took out is .038, and factory is .035.. is this whats causing my problem.. i dont really know

[omcforever]

Bowl gaskets should be brown and torqued properly and cant be re-used....dont use anything other than OMC kits. Idle orifices should all be .035. All orifices need to come out and clean passages. Round idle bypass covers inside carb bowl need to come out and insure area and passages clean and new covers pressed back in.