Rev limiter? '88 Johnson 30 HP

Hezekiah

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Feb 23, 2015
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Hello everyone!

I am running a 1988 30 HP Johnson, Tiller short shaft. I have a 13 pitch prop on it. The boat it's on is a 1963 Richline 14' - Deep V-Hull. Normal load is around 500 lbs with boat, batteries, gear, gas, and me and my son.

When I get going, once I get around 5300-5500 RPM, the motor cuts out. The problem I question is this: I have a lot of throttle left in the tiller handle. Is this normal? When I say it cuts out - it doesn't die...it just stops accelerating and drops the RPMs down.

It runs great as long as I don't get near that high RPM range, when I do - it cuts out....I drop the RPMs back down and it's back to running great again.

Is this some sort of safety feature?

If I re-propped with a higher pitch, would that help? It seems I'm maxing out RPM's too early.

Does anyone have any advice? Thanks.

Hez
 

Hezekiah

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Feb 23, 2015
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Have you looked into an overheat problem ??

Thanks for the response Racerone.

When I purchased the motor 2 months ago, my mechanic came over and rebuilt the carbs, replaced the impeller, and replaced the thermostat - cleaned out some salt water build up that was in the water passages, and put a new gasket on there. The motor pees good and the water coming out is only warm...never hot.

Based on that...I don't believe it's an overheating issue. It only happens at those high RPM's, and as soon as it happens - I back out of the gas and it runs normally, once it has dropped RPMs.

What are your thoughts now?
 

sutor623

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I would say to take the cover off the motor, and the airbox off the carbs and twist the throttle grip and look at the butterfly's in the carb throats. My guess is that your carb WOT stop is set incorrectly. What would happen in this case is the throttle body butterfly opens up fully and then begins to close in the other direction. This will limit air flow and the engine will die down.
 
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Hezekiah

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I would say to take the cover off the motor, and the airbox off the carbs and twist the throttle grip and look at the butterfly's in the carb throats. My guess is that your carb WOT stop is set incorrectly. What happens is the throttle body butterfly opens up fully and then begins to close in the other direction. This will limit air flow and the engine will die down.


Thanks Sutor,
That seems to be a very logical explanation for the symptoms I'm experiencing.

Could the WOT stop be set for a heavier vessel? Possibly a prior application?
 

sutor623

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No, the WOT stop is the WOT stop, regardless of what boat it is on. Even being set a little bit off can turn the rpm curve in the other direction.

Check it and check back in. If its not the issue you may have an upper RPM fuel delivery problem.
 

Hezekiah

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No, the WOT stop is the WOT stop, regardless of what boat it is on. Even being set a little bit off can turn the rpm curve in the other direction.

Check it and check back in. If its not the issue you may have an upper RPM fuel delivery problem.


Ok, I will check it when I get home from work, and post the findings in about 2 hours.
 

Hezekiah

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No, the WOT stop is the WOT stop, regardless of what boat it is on. Even being set a little bit off can turn the rpm curve in the other direction.

Check it and check back in. If its not the issue you may have an upper RPM fuel delivery problem.


Ok, I was able to check it a bit quicker than I thought.

Below is a link to the picture I uploaded that I just took of the carb and it seems that the butterfly is stopping in the right spot.

http://s32.postimg.org/4whnnckjp/Car...fly_at_WOT.jpg

Picture is sideways, top to the right
 
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sutor623

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Yea, looks good to me. Try having a friend pump the fuel bulb while running at or near WOT. If the engine runs good doing this then you either have a fuel restriction or a bad fuel pump.
 

Hezekiah

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Ok, I will try to get it out on the water this weekend and see if that helps.
 

Hezekiah

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Yea, looks good to me. Try having a friend pump the fuel bulb while running at or near WOT. If the engine runs good doing this then you either have a fuel restriction or a bad fuel pump.

When the carbs were rebuilt, the following was also done:

New Fuel Pump
New Fuel Tank
New Line
New inline fuel filter
new thermostat
new gasket

I know that doesn't necessarily mean it can't be the fuel pump, but as I said - I just wanted disclose the full list of what had been done, as the fuel pump had not been mentioned in the post yet.
 
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sutor623

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What was the reason all of
This work was done? What was the motor doing before these items were replaced?
 

Hezekiah

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What was the reason all of
This work was done? What was the motor doing before these items were replaced?

I purchased the motor from a mechanic at a local shop here. Upon purchase, it had been serviced, and the final step was putting the new fuel pump on. We tested it on the hose, it ran good - then put it on my boat and went out and did a lake test on it.

On the lake, it had trouble getting passed half throttle. So the mechanic bought the carb rebuild kit, and when he came over to do the carb rebuild kit - I installed all the new gas tanks, lines, filter - and at the same time he wanted to check thermostat, which we did - and that's when he cleaned the water passages and put new gasket on.

We did a water test immediately after this work, and it was bogging down at full throttle...and the guy let it sputter for a few seconds and that cleared it up. Ran like a scalded ape after that. Has ran good ever since, except as those high RPMs. Like I said, I thought it was a rev limiter until i recently installed the tachometer this last weekend, and saw it was cutting out at only 5300-5500 RPMs, and wasn't consistent each time.

Now I question the mechanics ability, so I didn't want to take it back to him without getting some information for myself....and possibly fixing it in the process. I'm hesitant to mess with it, because the motor runs great...except at those high RPMs.
 
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boobie

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Nov 5, 2009
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Put a timing light on it and run at the rpm where it misses. Look into the timing light for black spots and if you see them you have an ignition miss.
 
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