stumped and need help bad

[jmac]

72 Johnson Seahorse Model# 25E72R 25hp<br />At WOT it has a miss, for want of a better word.<br />Rebuilt carb, set points .020, hard spark on both plugs, plugs gaped .030. Haven't tested compression. Starts easy. Idles fine. OK to about 1/2 throttle, then it coughs a bit evens out and starts to "miss" at anything over 3/4 throttle. What is causing this? Replaced fuel pump about 4 yrs ago. Pumping bulb makes no difference. I'm in a bind and need some expert advice. Help

 

[Hooty]

Re: stumped and need help bad

After trying to run above 3/4 throttle for a while, to a quick plug check and see if one is wetter or drier then it should be. To wet, ignition problem. To dry, look for a fuel deliviery problem.<br /><br />g'luck & c/6<br /><br />Hooty

 

[aeronutt29]

Re: stumped and need help bad

Compression is probably not causing this, but it wouldn't hurt to check it. The only things that you didn't mention are the ignition timing, carburetor syncronization, and condition of the reeds. <br /><br />In spite of just rebuilding the carburetors, it's still possible that they aren't mixing correctly if the high speed jet didn't get thouroughly cleaned or are the wrong size. Pull the spark plugs and look for dry brown deposits. Two cycle motors shouldn't have dry spark plugs.

 

[jmac]

Re: stumped and need help bad

This motor has a fixed high speed jet in the carb. bowl so it is not adjustable. I did make sure it was clear. Don't know how to check the timing/carb sync. Both plugs are brown and a little moist. Both cylinders are making power at idle. Removed plug wires to test this. adjusted low speed idle screw. Leaned it out and richened it up and it acted the way it should have. reved up or bogged down. tried at wot and didn't notice any change in missing. need help on that timing/carb synchornization.

 

[sloopy]

Re: stumped and need help bad

I bet you a dollar its the timing

 

[jmac]

Re: stumped and need help bad

oh yeah reeds look to be in real good shape, not broken and are laying flat against the orifices. Do reeds get fatigued and open more than they should? If so can you reverse them?

 

[jmac]

Re: stumped and need help bad

alright sloopy how do I check/set the timing. I know I need to pull the flywheel then what?

 

[aeronutt29]

Re: stumped and need help bad

The carb sync is nothing more than adjusting the linkages to ensure that each carb on a multi-carb engine starts to open at exactly the same time. Ignition timing is highly engine-specific, so without the manual it's hard for me to guess how to set it. You might find the specications printed on the motor somewhere and then just use a timing light to verify the correct setting. Since you have slightly wet plugs it's likely that you don't have a fuel delivery problem unless the engine was idled for a while before you pulled the plugs. We know for certain that the idle mixture is correct so maybe running the motor hard for a little while and then just cutting the key off and pulling the plugs would give a better reading of "under power" plug condition.

 

[aeronutt29]

Re: stumped and need help bad

One more thing that might sound silly but has bit me in the bee-hind before is simply replacing the plugs. I've actually installed brand new plugs before that made the engine run WORSE. Even if the plugs you are using are new, try a different brand just for kicks and see if it makes any difference.

 

[loganmallory]

Re: stumped and need help bad

hey jmac<br />i have the exact same motor you do. mine idled/trolled awesome, and wot was excellent as well. EVERYTHING in between stinked. it "missed", coughed, etc etc. after trying a million things, i figured out that it was the stator plate. it was worn so badly against the plates that it sat on/bolts onto that it was way too floppy. i couldnt tighten it any more. i tried shims, washers, etc. nothing. i ran it that way all year until yesterday when i bought a parts motor and replaced the stator. now works like brand new. something to think about anyways. grab the plate and see how much play it has up/down. it souldnt have hardly any. <br />LM

 

[slow_boat]

Re: stumped and need help bad

Get a manual to show you the way to set timing. It is an issue of synchroizing the fuel delivery system with the ignition system, assuming this is a magneto system (I know the '70 model used a magneto system). On older johnudes this involves aligning a notch or mark on the 'pick-up' below the flywheel with the cam follower (a small roller assembly) associated w/the carburetor linkage. These marks MUST coincide with the particular engine model's specs at the instant the throttle shaft in the carburetor starts to move during throttle increase for the engine to run efficently.