Still won't run past 1800 RPM

[5150abf]

1981 Rude 50

I am totally baffled here, went through some more stuff, changed a few more wires that were in ? shape, ran it today, ran like a scalded dog for 100yrds,on plane and almost 30MPH then dropped back to 1800RPM again.
Took the carb cover off the front and shined my spot light into the throat at WOT and it has a really heavy fog so I don't think it is high speed jets, has the correct timing low( 2BTDC) and high(22BTDC) and it advances as it should, nothing wrong with the lnkage ect. ect. I have pretty much ruled out a fuel problem.

Another clue, I replaced the fuses with breakers and one of them was shorted against the engine housing,standard marine breaker with 2 blades, forgot to tape it up, it would have been the small black wire from the engine wiring harnesss coming from the binacle,whether this happened before or after it started screwwing up i don't know but if that fried something what would it have fried???
What electrical could be bad but still allow the engine to start, idle and run up to a certain speed.
I am utterly clueless.
Thank you in advance.

 

[lexkyboater]

Re: Still won't run past 1800 RPM

Did you check plug wires and do a spark test per http://forums.iboats.com/showthread.php?t=213548&highlight=spark+tester? Did you ohm out your plug wires and wiggle them to make sure there's no open circuit? How's your fuel lines? Tank vent open? Is there an anti-siphone valve in the tank? Is the bulb staying hard? Does it help when it drops rpms to pump bulb? Could be trash in carb, but just need to isolate electrical first before tackling carb issues. Need to find out if it's fuel or fire.

 

[5150abf]

Re: Still won't run past 1800 RPM

No I haven't checked plug wires, thought that was something that worked or didn't.
I get a small pump on the bulb but I already tried that, pumping it while it's running has no effect one way or the other.
I have run the fuel system from the tank to the lines that go in the carbs and there isn't anything blocking them or restricting flow.
I am definately leaning towards electrical the way is was fine one second then riight to this.
Also the way it runs fine for the first couple minutes then nothing.
My friend has a similar engine so I may start swithing parts out and see if I can stumble onto it but I will check the plug wires, they are 26 years old so they probly need changed anyhow, certainly can't hurt.
Thanks

 

[5150abf]

Re: Still won't run past 1800 RPM

Just ran a spark check and I got it to throw a spark 3/4 inch so that rules that out.
Should post a picture,my checker involes a piece of cardboard ,2 long screws,a large straight screw driver,a wire I found on the floor and 2 feet of tape, not pretty but it works and it only took 4 minutes to make.
Unfortunately that rules out an easy fix.
I took apart and cleaned (again) my fuel pump and even checked the pickup in the gas tank,still clueless.

 

[kenmyfam]

Re: Still won't run past 1800 RPM

Just a thought and without a doubt not a diagnosis......but,
I know some motors go into "slow" mode if there is a problem with cooling system.
Just a thought. There are plenty of experts out here that will help you further.

 

[5150abf]

Re: Still won't run past 1800 RPM

thanks for the idea, at this point I will take anything. this seems to happen before the motor even warms up though.
Launch, start the motor get it to where it will idle and it will take full throttle for a 100 yards then BLAAAAAHHHHHH.

 

[lexkyboater]

Re: Still won't run past 1800 RPM

Just some more ideas, but I'm not familiar with that motor. Did you try pulling the choke when it goes to 1800 rpm and see if it runs better or worse? If worse, you know you're getting gas, if better, you've probably got a carb problem. You can also remove the gas line from the carb and crank it over to make sure the fuel pump is pumping gas. It could be electrical. Possibly a power pack heating up? Seems I've read similar problems from powerpack problems. I would think a bad stator would give you low rpm problems, I don't think I've heard of high rpm issues with stators, but maybe that's possible. I had a yz 125 that had a bad stator and it wouldn't fire when kick started but would start when roll started because it had enough rpm to get the stator to work. Apparently low rpms didn't give it enough to fire.

Have you tried running at night to see if you see any arcing from wires? I've read of guys that couldn't find electrical issues till you see them sparking at night. Hopefully some other guys familiar with this motor can chime in. I don't have my manual with me at work. When it's running bad, have you tried pulling plug wires to see if it runs the same when one is pulled, indicating a problem with that cylinder?

 

[5150abf]

Re: Still won't run past 1800 RPM

Haven't checked back for awhile, too busy building boats for other people to work on my own oddly enough.
I asked my bro-in-law,one time marine mechanic, and he said he thought it was a"switch box" (?) or high speed side of stator, sound feasible?
And what is a switch box, never heard of such a thing.
Mechanical stuff I can handle but electrical I am pretty clueless.
I have rebuilt 3 lower units sucsessfully but once wired a main power cut off switch with + on one terminal and - on the other,as I diapeared in the cloud of smoke I figured I did something wrong.
Is there a way to test a stator, even on Ebay they are over 100 so I don't want to go there if I don't have too.
thanks for the help, I am in northern indiana and the crappy weather is coming, I want to get this sorted out before it is 45 and raining

 

[lexkyboater]

Re: Still won't run past 1800 RPM

My understanding from an expert here is that the manual gives you specific instructions for checking stator, and all are specific to that particular model.

 

[HighTrim]

Re: Still won't run past 1800 RPM

If your motor has SLOW , check it this way.

ENGINE WILL NOT ACCELERATE BEYOND 2500 RPM:
1. Use a temperature probe and verify that the engine is not overheating.
2. Disconnect the tan temperature wire from the pack and retest. If the engine now performs properly, replace the temperature switch.
3. Make sure the tan temperature switch wire is not located next to a spark plug wire.
4. Check the stator resistance. If it reads approximately 900 ohms, replace it with the 500 ohm design.

Check the DVA output on the orange wires from the power pack while connected to the ignition coils. You should have a reading of at least 150V or more, increasing with engine RPM until it reaches 300-400 volts. A sharp drop in voltage right before the miss becomes apparent will normally be caused by a bad stator. A drop on only one orange wire will normally be the power pack.

 

[5150abf]

Re: Still won't run past 1800 RPM

Got my new CDI today put it on and went to run the boat, it made no difference whatever,I am very dissapointed.
So my next purchase would be coils and plug wires yes?
Worst case senario all this stuff is 26 years old and could use replacing but I would really like to fix this.
Oh, my engine doesn't have the SLOW system.