Johnson 30 problem - fuel starvation or ??

northernmerc

Chief Petty Officer
Joined
Apr 6, 2009
Messages
401
This 2000 model year Johnson 30 two stroke starts fine. It also runs well at half or at full throttle, but only for a minute or so. It then loses power but does not stall. If the throttle remains wide open, it surges and momentarily tries to speed up but then again slows. It does this surging thing over and over until one eases up on the throttle. When it does this, it will idle fine, but won't move beyond an idle without surging.

After idling for a minute or so, or after turning the motor off for about thirty seconds, it again runs well - for a minute or two.

The fuel tank vent is wide open, the hose is new, and the fuel is fresh. Squeezing the primer bulb when it is acting up does not help.

Does this sound like a problem with the fuel system? What are the most likely things to check?
 

HybridMX6

Senior Chief Petty Officer
Joined
Oct 22, 2008
Messages
676
Re: Johnson 30 problem - fuel starvation or ??

If it's not the fuel line/bulb, and pumping it didn't help, when's the last time the carbs were rebuilt with new kits? Could be a bad float and you're running the fuel out of the bowl. I'm not sure the primer bulb and fuel line being "pumped" would rule that out or not, but it should rule out most other possibilities. You may need someone to help ya with this one, but I'm wondering if you had someone with a spray bottle with some premix fuel in it, spray some into the crabs when it starts to do this, and see if it goes away (while spraying).
Seems like you've already taken the parts before the motor out of question (assuming the new line and bulb are good, ya never know), so it's got to be down to the motors fuel system. I'd think the fuel pump is fine since "pumping the primer bulb" didn't help any, which really only leaves the carbs, or maybe a fuel leak somewhere around them.
 

northernmerc

Chief Petty Officer
Joined
Apr 6, 2009
Messages
401
Re: Johnson 30 problem - fuel starvation or ??

Thanks for the reply, Hybrid. Could you or someone else give me more detailed instructions on how to disassemble and clean or rebuild the carbs? And what settings do I need to watch for when reassembling it? Thanks.
 

kellyisu

Petty Officer 3rd Class
Joined
Oct 3, 2007
Messages
75
Re: Johnson 30 problem - fuel starvation or ??

I have the same problem right now. Do you know what it ended up being OR does anyone else have any experience with the same problem with resolution?
Thank You
Kelly
 

northernmerc

Chief Petty Officer
Joined
Apr 6, 2009
Messages
401
Re: Johnson 30 problem - fuel starvation or ??

Nothing yet. I'm still looking for more info on how to take apart, clean, and set the carburetor before tackling this.

Anyone, please?
 

northernmerc

Chief Petty Officer
Joined
Apr 6, 2009
Messages
401
Re: Johnson 30 problem - fuel starvation or ??

After a few hours of running, the problem with surging improved a little. Instead of only running a minute or so without the problem happening, it now runs a few minutes at full or half throttle. Then the surging starts and it will only run well at an idle for the next minute or two. Then it's good to go again for a few minutes.

Any other comments? Is a carb kit likely to fix this? Or should I be looking elsewhere for the solution? Thanks.
 

cdn-pk

Petty Officer 2nd Class
Joined
May 20, 2009
Messages
162
Re: Johnson 30 problem - fuel starvation or ??

i have a 1977 140HP johnson and had a similar problem. Except it would only run WOT for a few seconds, the problem got worse then better, it kinda really ticked me off. It stalled once on me in the middle of the lake so i took some time and found the fuel line into the lower card was pinched. i tried keeping it round with my fingers and getting my bud to give it WOT. fixed the problem. Hauled it out and replaced all the fuel line so far so good.
 

northernmerc

Chief Petty Officer
Joined
Apr 6, 2009
Messages
401
Re: Johnson 30 problem - fuel starvation or ??

The surging problem on this Johnson 30 continues. It runs fine for a minute or two at full throttle and then cuts back and surges repeatedly until I ease up on the throttle. Then after idling for a minute or so, it's fine again, but only for a minute or two.

I took the carb apart and cleaned it - twice - and installed a carb kit, including float. No improvement. Then I took the fuel pump apart and checked it; all seems fine there. Also tried a different tank and hose.

Any ideas? Does the 2000 model year Johnson 30 have an overheat sensor? Would an overheat sensor cause a surging condition by cutting the fuel supply? There is no alarm. It seems that it has a reasonably strong stream from the little black tube.:confused:
 
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