91 3pg runs better in Reverse (video)

[treeguy27]

I have a 91 Marathon that is driving me crazy. It runs, but not as good as I believe it should. I want to put a small lift and larger tires on it, but am really worried it wont be able to turn them without difficulty. I've gone through this thing several times trying to figure out what's going on. Since I got the cart my seat of the pants feeling has always been that it runs stronger in reverse than forward. It has 115 lbs of compression in both forward and reverse. I put a new Ebay carb on it because the original one was worn and had a ton of play in the main throttle shaft and seamed to be making it run very lean. I put the one inch shorter belt on and a stiffer spring in the driven clutch.

Today I had it on jack stands and was spraying the crank seals again to check for leaks. I don't believe they are leaking. I can't tell any noticeable difference when spraying them. What I did notice was that it runs much smoother and revved quicker in reverse. In the video you'll see that the drive clutch quickly closes and stays there. It doesn't even take full throttle to get it there. When I put it in forward it doesn't rev up as fast and the clutch doesn't close completely even at full throttle. There is also some clattering in forward, I think from the engine. That doesn't happen in reverse. It's kind of hard to hear it in the video. I don't know if it's detonation or something mechanical. I don't know if it's a timing issue or maybe even something wrong with the drive clutch that only happens in forward. Any help would be appreciated. I'm frustrated with this thing.

https://www.youtube.com/watch?v=V0wUfk4fh08

Hopefully the link to the video works.

[Ron Benedict]

Try checking the voltage regulator. Most 2 strokes seem to run better backwards because the generator is not charging in that direction.
Hook up a volt meter to your battery and if it shows more than 14.5 volts running forward that probably is your problem.

[treeguy27]

Thanks Ron, I will try that.

Also wanted to add that it also has problems starting in forward occasionally. Sometimes when you push the pedal it will do nothing for a few seconds then finally begin to crank. Sometimes it will turn over very slowly for a second or two then start cranking at full speed. Never happens in reverse, only forward. I cleaned all of the cable connections on the FNR switch, but still does it occasionally. Don't know if that could be related to running better in reverse as well or not.

[treeguy27]

After more time spent working on it, I believe my crank seals are bad. I Had jacked it up and sprayed them several times before but noticed no difference. I was using carb cleaner and wd-40 which I have seen referenced as good to use. I still wasn't convinced so I bought some starting fluid and sure enough it picked up and showed bad seals.

I have 115-120 lbs of compression in forward and reverse. I'm trying to decide if that's good enough, or should I be redoing the top end while I have the motor out? What compression should I expect with a fresh top end?

Does anyone have a link for procedures for changing the crank seals, and a good source for the seals? This will be my first time tackling them. Looking forward to pulling the clutch and flywheel.

[cart around]

That's good compression. I would just change the seals.

[treeguy27]

After getting the flywheel off ( not fun) I noticed the timing seemed to be all the way advanced or retarded, not sure which. I would assume the screws should be more centered than all the way to the edge of the slots? I'm guessing that would be a possibility for running better in reverse and worse in forward. Can anyone give me an idea of approximately where the timing should be set?

I may have plenty more questions as I get farther into this thing. The crank bearings don't sound all that great when I turn it over by hand. Yeah!
I may have to keep tearing into it. If so, Ill be asking all kinds of questions.

[treeguy27]

Thoughts on the timing setting?

[racin161]

I'd try to set it in the middle and see what happens which is listed in the manual. If you look close at the plate you should see a marked line center the screw on that mark then tighten the screws. You should be good to go.

LOU

[treeguy27]

Thanks Racin.

I've discovered at least one crank bearing is bad. Found some little pieces of bearing when I removed the crank seals. I haven't got the case split yet to see how bad all the bearings and the crank shaft are. I don't have a press to do so. The connecting rod has a good amount of side to side play. How much is acceptable? I don't see any bluing or wear other than the side to side play. I'd really like to not have to buy a whole new crank assembly if possible.

Looking around on line at rebuild kits it seems most include everything including crank assemblies, piston, cylinder and the works. Is it not practical to hone or bore the cylinder and reuse the crank if it doesn't show much wear? I really didn't want to put $500 back into this motor. Any guidance would be appreciated.

[racin161]

Have been there !!! I would replace the crank bearings get a jug & piston kit (comes with rings,piston,gaskets needed and jug) Be sure to check the ring end gap before installing. When removing the crank bearing look close for a shim behind the bearing & crank maybe yes- maybe no. This is not a hard job. As for rod side play I wouldn't worry about it it's the up & down movement you would be worried about if none go for it.

Lou