Polaris Mutt Mod
- Thread starter skiroule
- Start date
skiroule
Well-known member
Good progress on the cabin project has allowed me to spend a short amount of time in the shop with the Mutt. I knew the belt was waaaay too tight but I was pressed for time and I just wanted to see if it would fire. It’s a little boggy on the low end but perks up when the mains kick in. I’m sure that is at least partly due to the tight belt. If it’s still boggy when the belt is adjusted, I’ll have to look at jetting/clutching changes but it’s making smoke and the track goes around. I’ll take it for now.
I was just going to ask the same LOL don't remember finger throttles back in the day LOL. SOUNDS GOOD skiroule!!! that sound brings back many memories! and again...a true master at your craft!!
skiroule
Well-known member
Nothing gets past you guys!
I had to do several modifcations to the throttle lever to get the slides to bottom out, even with the cables adjusted all the way down in the caps. I had flipped ithe lever over to drill the cable seat deeper and I guess that, in the frantic activity of getting it firing, I forgot to flip it back over. Looking at it now, it does look pretty silly.
Funny thing is, back in the day we used to do that intentionally because the heavy throttle pull really took a toll on the thumb. Guess that created a fairly significant safety hazard because if you were thrown backward with a death grip on the throttle, you usually pegged the throttle. But then, safety wasn't a big concern back then.
I had to do several modifcations to the throttle lever to get the slides to bottom out, even with the cables adjusted all the way down in the caps. I had flipped ithe lever over to drill the cable seat deeper and I guess that, in the frantic activity of getting it firing, I forgot to flip it back over. Looking at it now, it does look pretty silly.Funny thing is, back in the day we used to do that intentionally because the heavy throttle pull really took a toll on the thumb. Guess that created a fairly significant safety hazard because if you were thrown backward with a death grip on the throttle, you usually pegged the throttle. But then, safety wasn't a big concern back then.
FWIW, my current sled, the Doo Blizzard, has a throttle lever that rotates, thumb or finger pull but I seldom us it.
Years ago I broke my right wrist which needed to be reconstructed with pins and screws. I spent about 6 months in a cast so it would heal and be somewhat functional. I would have lost a snowmobile season had I not found an aftermarket conversion throttle from thumb to fingers. Worked well for me and like Gary, my Skidoo Renegade has a movable throttle which I use frequently when the thumb gets tired.
skiroule
Well-known member
The rotating throttle feature is new to me. Just shows how out of touch I am with modern sleds.
Something you sharped-eyed guys probably noticed is that I did get the pan trim and bumper installed. The “bumper” is basically cosmetic but hopefully I won’t be running into any trees. A few more things to clean up on the chassis and then it will be on to finishing the hood.
Something you sharped-eyed guys probably noticed is that I did get the pan trim and bumper installed. The “bumper” is basically cosmetic but hopefully I won’t be running into any trees. A few more things to clean up on the chassis and then it will be on to finishing the hood.
skiroule
Well-known member
Thanks for the vote of confidence guys! Speaking of which, mine took a bit of a hit this weekend. After loosening the belt more and making some carb adjustments, it became obvious that the low rpm issues I’m having is bigger than simple adjustments.
In my (limited experience) opinion, that leaves two primary possibilities: A: The motor is just not happy with the tuned pipe or B: there is a mag side crank seal leak. I never thought I’d say this, but I’m rooting for the seal issue. I don’t have a Plan-B for another pipe, the fit is just too tight to replace it without major mods to another pipe.
The reason I’m suspecting a seal is that the mag side cylinder is the one that is not firing as it should. It doesn’t really come on strong until the RPM’s get up to around 3000 and the mains start pushing more fuel. The PTO side (which has a new seal) seems to run fine up through the RPM range. If it were a pipe issue, I would think it would idle fine but have issues on both cylinders at the same point(s) in the power curve. It definitely won’t idle at normal idle RPMs.
I’m going to try to start eliminating suspects later this week and maybe find the guilty party a little later this month and I'm sure the culprit will eventually be found. You’d think by now I’d know that you can pay now or pay more later when it comes to these engines. I should have replaced the seal when the engine was on the bench.
There are a lot of small engine mechanics on this site that are much more knowledgeable than I and if you have any suggestions, feel free to chime in with your thoughts.
In my (limited experience) opinion, that leaves two primary possibilities: A: The motor is just not happy with the tuned pipe or B: there is a mag side crank seal leak. I never thought I’d say this, but I’m rooting for the seal issue. I don’t have a Plan-B for another pipe, the fit is just too tight to replace it without major mods to another pipe.
The reason I’m suspecting a seal is that the mag side cylinder is the one that is not firing as it should. It doesn’t really come on strong until the RPM’s get up to around 3000 and the mains start pushing more fuel. The PTO side (which has a new seal) seems to run fine up through the RPM range. If it were a pipe issue, I would think it would idle fine but have issues on both cylinders at the same point(s) in the power curve. It definitely won’t idle at normal idle RPMs.
I’m going to try to start eliminating suspects later this week and maybe find the guilty party a little later this month and I'm sure the culprit will eventually be found. You’d think by now I’d know that you can pay now or pay more later when it comes to these engines. I should have replaced the seal when the engine was on the bench.
There are a lot of small engine mechanics on this site that are much more knowledgeable than I and if you have any suggestions, feel free to chime in with your thoughts.
hybrid
Active member
seal up the intake and exhaust and do a pressure test
skiroule
Well-known member
I don’t know about answering my own questions but I often argue with myself and still manage to lose the argument. I’ve been eyeballing it and I might be able to pull everything with the motor still in the chassis. If not, removing the motor is about a one-hour job. Would suck to have to re-align everything though.
This is really the right way to diagnose the condition of the seals without tearing down the engine. The trick is getting a perfect seal on the intake and exhaust ports so the leak-down test is accurate. Even a tiny leak in the test setup will give a false result. Not having a setup already, I’m not real confident I could build something that I could guarantee is accurate.
I guess that now I’m looking at it from the perspective that I should have replaced the seal in the first place so it needs to be changed anyway.
First order of business this weekend will be to pull the pipe and see how it runs. If there is no change, I’m thinking the seal is the most logical source of the problem. I did run this motor on a spray bottle a few years back and thought it ran OK but with spray you’re pushing in a lot of fuel and might have masked the issue.
One easy way to determine seal leak is with starting fluid, carb clean or wd 40, spray it around seal while running and see if the idle changes or not. I highly doubt it would be the tuned pipe. Im sure you have checked the obvious as well...intake leak...properly adjusted choke. In my experience a seal leak will affect more than just up to 3000 rpm's which leads me to think the issue may lie in the carburetor itself, namely the pilot circuit which will considerably affect the idle and up to that rpm range. are both carburetors jetted the same? I only ask because some engines have a richer jet on the PTO side. if jetted the same try switching the carburetors and see if the problem follows by disconnecting one plug wire at a time and see which cylinder is affected. I could be wrong but doubt it is a crank seal or a tuned pipe issue as I dont think either one would only affect that idle and rpm range. Those carbs looked like you could drink from them but its what you cant see that causes issues. If you can I would first try swapping carbs and see if problem follows, I may be wrong but I'm betting on fuel delivery. in my experience the seal that would only affect the idle zone of the machine and would not only affect one side was a center crank seal
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mezz
Well-known member
Now that is sound advice. No harm, no foul.
skiroule
Well-known member
Good to get some input from someone who knows small engines. I agree that a seal or the pipe just doesn’t make sense, especially since these engines are not prone to seal failure, center or otherwise but at this point I’m still in the dark.
Here’s where I’m at so far. When I first got it running, I had installed a new set of carb boots but a set of used carbs. It was obvious that it was only firing on one cylinder so I assumed a carb problem. I ordered a set of new VM34’s, figuring I could go through the first set eventually and use them on another sled.
When I started it with the new carbs, at first it seemed a little better but eventually I concluded that it was basically the same. I had swapped out the mains to 310’s but kept the 30 pilots that came with the new carbs. As much as I’d like it to be a carb problem, it now seems unlikely. The choke thing is something to be checked out though, as I used the same set of plungers on both carb sets.
After running, the mag side cylinder is noticeably cooler, which seems consistent with it sounding like it is running on one cylinder a lot of the time.
It’s hard to spray anything on the mag side seal because of the rewind cover and flywheel but tomorrow night I’m going to start by swapping the carbs. If nothing changes, I’ll swap plugs and then plug wires. I do have another CDI box but it seems like they should either work on not. If all these things have no effect, I’ll pull the pipe. If I’m still where I started, I probably have no choice but to check the seal.
I did have a Fuji engine on a Chaparral that ran poorly and would not idle and the problem turned out to be a mag side seal. The tension spring had broken and dislodged from the seal so it was sucking major air though the seal. The Polaris version of th Fuji uses an entirely different seal design so it would suprise me if it was a major seal failure but I guess you never can say for sure.
Thanks again for the advice!
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does the engine have a starter cup on it that you can wrap a rope around and start the engine with the recoil removed? if so, start the engine that way and spray along side flywheel if there is a seal leak where it is drawing air you should know instantly, without having to pressure test the engine. I would still try swapping the pto side carb with mag just to eliminate the carburetor possibility even though they are new. I still highly doubt the pipe possibility especially since its isolated to one cylinder. Do you possibly have an inductive or in line spark tester where you can see the pulse of the light to compare to other side to see any difference or interruption in ignition in case it is an ignition issue?
skiroule
Well-known member
It’s hard to believe how many things can go wrong with a motor and yet they run most of the time. I did check the compression on both cylinders after I first got it running – 135 in both cylinders. Not great, but not bad for a 45 year-old motor. Also took a peek at the pistons back when I had the Y-pipe and carb boots off. Thought the pistons looked pretty good.
First thing I did tonight was to check something I thought I’d seen with the first set of carbs and wanted make sure it wasn’t my imagination.
I started it and held the idle just low enough to keep it running on one cylinder. Then I gave the mag side carb a couple of shots of gas. Bam - that cylinder started firing and the RPMs jumped by a couple of thousand. So it wasn’t my imagination. Next thing was to swap the carbs and run the test again. Same result, only started firing on the mag side at idle when I gave it a shot of gas.
I guess what this tells me is that I can rule out some kind of ignition problem and it suggests that there is a fuel/air ratio issue that is not providing the proper ratio to fire the cylinder at idle. After seeing the same result with three different carbs, it’s probably safe to say it’s not the carb. It could still be a boot issue but the boots are new so that’s a long shot.
I should have tried to run it without the pipe but after removing the pipe I figured I might as well tear into the seal because I wanted to change it anyway. Even for a hack mechanic, it’s less than an hour job to get it out. I love the seal design of these Fuji engines. The mag and pto sides are slightly different but the concept is similar. Rather than drive the seal into the case, the seal is mounted in a plate which is fastened to the case with four bolts/screws.
This is what it looks like on the mag side before removal and after replacement.
I was hoping the seal would look visibly bad but it didn’t have any obvious flaws, no tears or chunks missing. It seemed a little spongy but maybe that’s wishful thinking.
Anyway, the seal is in and stator plate re-mounted.
I put the flywheel back on but don’t have the right size socket to snug down the flywheel bolt (I cheated on the socket taking it off but didn’t want to torque it down without the right one).
We’ll see if it makes a difference tomorrow night but I have this uneasy feeling Euphoric1, that you’ve been right all along, it really wasn’t the seal after all.
Thanks for letting me think out loud about this!
First thing I did tonight was to check something I thought I’d seen with the first set of carbs and wanted make sure it wasn’t my imagination.
I started it and held the idle just low enough to keep it running on one cylinder. Then I gave the mag side carb a couple of shots of gas. Bam - that cylinder started firing and the RPMs jumped by a couple of thousand. So it wasn’t my imagination. Next thing was to swap the carbs and run the test again. Same result, only started firing on the mag side at idle when I gave it a shot of gas.
I guess what this tells me is that I can rule out some kind of ignition problem and it suggests that there is a fuel/air ratio issue that is not providing the proper ratio to fire the cylinder at idle. After seeing the same result with three different carbs, it’s probably safe to say it’s not the carb. It could still be a boot issue but the boots are new so that’s a long shot.
I should have tried to run it without the pipe but after removing the pipe I figured I might as well tear into the seal because I wanted to change it anyway. Even for a hack mechanic, it’s less than an hour job to get it out. I love the seal design of these Fuji engines. The mag and pto sides are slightly different but the concept is similar. Rather than drive the seal into the case, the seal is mounted in a plate which is fastened to the case with four bolts/screws.
This is what it looks like on the mag side before removal and after replacement.
I was hoping the seal would look visibly bad but it didn’t have any obvious flaws, no tears or chunks missing. It seemed a little spongy but maybe that’s wishful thinking.
Anyway, the seal is in and stator plate re-mounted.
I put the flywheel back on but don’t have the right size socket to snug down the flywheel bolt (I cheated on the socket taking it off but didn’t want to torque it down without the right one).
We’ll see if it makes a difference tomorrow night but I have this uneasy feeling Euphoric1, that you’ve been right all along, it really wasn’t the seal after all.
Thanks for letting me think out loud about this!