Engine not coming to full speed

[Swampmouse]

Guys,
Many of you have helped me over the last year on doing a rebuild opn my 1983 Johnson 115. Thank you for all the help you have given me!

Last Saturday I finally got it on the water - I was trying to get a working tach so I could do a link and sync, but could not wait any longer. So, I got the boat to the lake, engine idled well.

When I got out of the no wake zone and let her rip, it would not come up to speed. Since my speedometer does not work, I would guess that I was going probably about 10-12 mph. Not quite fast enough for the boat to plane out. When running, the speed was indicative that I should have had about 80% more throttle.

I should note that I recently replaced the throttle cables.

My guess is that somehow I did not have the cables adjusted properly, but they SEEMED right.

Is this a timing problem - remember the engine idled good and in neutral would rev up very high if I moved the lever all the way.

Any suggestions?

Thanks,
Sm

 

[JB]

Re: Engine not coming to full speed

Well, s-mouse, I agree that the first things to check are that the carb throttle plates are opening fully and that the ignition timing (stator position) is advancing fully.

What a 2 stroke does with no load can be very misleading. Don't believe it.

If she passes muster on the above you need to test for one or more dead cylinders. Side by side dead ones suggest a carb problem, over-under dead ones suggest a powerpack problem.

Good luck.

 

[kenmyfam]

Re: Engine not coming to full speed

What kind of hull are you pushing ??? What is your set up like ???? are you trimmed where you should be ??? Is the motor set high enough ???
Just a few thoughts before you dig into the motor.
Before the rebuild did it run better ???

 

[Jacob645]

Re: Engine not coming to full speed

How do your coils look? Any cracks? Do a good check of those. Sometimes they cause problems like you're describing.

 

[Yamajoe]

Re: Engine not coming to full speed

Sounds like the main jets are blocked, pull the carbs off and give it a clean out and blow dry with air. The bottom carbs tend to play up, at least this was the problem with a recent 115 hp i worked on.

 

[Swampmouse]

Re: Engine not coming to full speed

I have a 1981 Procraft bass boat that used to run close to 60mph at WOT. So, this is definitely not a trim issue.

So, could this be a carb problem even though it idles good and revs up high on the muffs and in the water?

I did have the carbs off for several months during the rebuild. How and where am I cleaning and blowing the carbs out???

ONE THING I forgot to mention was that when running at the top speed she was giving me, every now and then I would get a clunk like a cylinder missing. I guessed spark plugs, because I haven't replaced them yet. IS this related or outside issue altogether?

I will check stator position and also power packs, although power packs were fine before the rebuild.

I will check in the next few days and let you know what I see (wish I weren't moving - otherwise I could do this tomorrow)

Thanks for the input,
SM

 

[Willyclay]

Re: Engine not coming to full speed

When you removed the carbs for the motor rebuild there may have been enough fuel in them to clog up your main jets needed for high speed. Before you start pulling things apart, you can check for this problem by making an in-the-water test, not on muffs. After warm-up and in forward gear, try WOT and activate your choke/primer switch. If the engine RPM and boat speed increase substantially, you have clogged main jets. If not, you have to continue trouble-shooting. Trying the same procedure except substitute pumping the fuel primer bulb for "activating the choke/primer switch" will tell you there is a restriction in the fuel flow to the carbs such as leaking hoses/clamps, bad fuel pump, bad anti-siphon valve in fuel line, blocked pickup screen in the tank, etc. Good luck!

 

[Swampmouse]

Re: Engine not coming to full speed

Thanks Willy. I will try in 2 weeks once I am done moving.

I appreciate the input.

SM