200cc clone losing power

[mark123]

This is not go kart related but I couldn't get any responses in the sled forums so I thought I would ask here. I recently put a 200cc clone into my young fellas arctic cat 120 mini snowmobile and when I did it it had tons of power, it would spin the track with me (200lbs) and take me to 20mph. Now after approx 10 hours of use it will barely take my son (50lbs) to 14mph and won't make it up hills with him. Throttle is operating fully and the choke is off completely and I also tried removing the air cleaner with no change. I did a compression check and it is only showing 70psi and with 2 teaspoons of oil in the plug hole it is showing 85-90psi. There is no burning oil smell at all. Could this be a valve clearance issue? When I removed the govenor I made up some shims for the valve springs from washers approx 0.70" thick for more spring pressure and re-adjusted them to factory specs, could 1 or both of them come out of adjustment or something. I assume if the rings were bad I would be smelling burning oil. Thanks for any help

 

[OzFab]

Since you've already played around with the valve clearance, that would be my first guess: they could now be out of adjustment as a result (not saying you did it wrong but, the may have moved).

Also, did you follow the run-in procedure?

 

[Doc Sprocket]

And while we're at it, let throw some other food for thought into the mix. Any chance of a bad or contaminated clutch? Excess friction in the driveline like a dragging brake? Maybe the throttle is no longer going wide open? Carb jet part clogged? Fuel delivery issue?

 

[mark123]

Well I took the engine out and the valves were both approx. 0.10" so I readjusted them to 0.03" ex and 0.02" intake. Then I rechecked compression and it fell to 40psi ????? I removed head and everything looks good, no burnt valves, everything nice and smooth, no scuffing etc.... I then noticed the decompression system on the cam gear, will this give me false readings when checking compression? I am using the electric start while checking and it is turning over fairly fast. It always needs choke to start no matter how warm it was and it idled good just didn't have the take off or top end it did. Plug is nice and tan color, I will check carb for dirt and clean it, there is only a total of 10 hours or so on this engine.

 

[OzFab]

All that & you didn't answer my question regarding run-in...

Valve clearance should be 0.006" in & 0.008" ex

 

[machinist@large]

Contrary to popular belief, any engine at that price point has a definite break in procedure; having stated that you already tore it down, you've pushed the rest of us into no man's land. We weren't here, and we didn't see just what you did.....

Then there is the usual; .

 

[Doc Sprocket]

The compression relief mechanism is notorious for throwing compression readings out. Two ways to handle this-

1)Remove recoil mechanism and use a rope to spin engine backwards (defeats the mechanism

2)Steal a page from the Briggs manual- ignore straight compression numbers and perform a leakdown test.

 

[mark123]

All that & you didn't answer my question regarding run-in...

Valve clearance should be 0.006" in & 0.008" ex

If you mean proper break in procedure then I have to admit no I didn't. I bought the engine, did the modifications and basically ran it wide open. Anyway today I got it all back together and it seems to be running stronger but I am going to check with GPS to see if I got the speed back. As for the valve specs, I am seeing everythoing from 0.002"in 0.003" ex to 0.006"in 0.008" ex, it seems there are many opinions out there.

 

[OzFab]

If you mean proper break in procedure then I have to admit no I didn't. I bought the engine, did the modifications and basically ran it wide open.

Well, there's your problem

As for the valve specs, I am seeing everythoing from 0.002"in 0.003" ex to 0.006"in 0.008" ex, it seems there are many opinions out there.

The simple thing to remember is too little clearance & your valves may not close completely

 

[exenos]

Well, there's your problem

I wouldn't be so quick to jump on that. Think about how many tools that are equipped with industrial engines that never get a proper break in. Lawn mowers, compressors power washers ect. I highly doubt that most people will read the manual and do a break in.

Have you checked to see how freely the track spins? Will the engine hit full rpm's and act normal when the back is held up.

 

[mark123]

Well I took the engine out and apart and the cylinder is perfect, cleaned carb, no dirt whatsoever in it. no burnt valves, valves seat are perfect. The only thing I noticed was that the part of the valve stems that rest on the retainers were very slightly mushroomed, just enough that I could not pull the valves out of the head, I mean very very slight. Is this occurring because of the shims I made? with the valves adjusted to 2 and 3 thou there was no improvement at all, still 14mph. I loosened the track a bit too. All bearings are good, brake is not draging. It just seems not to have the RPM and power it did. Alos throttle is operating fully and choke is off completely. I am stumped. It is actually slower than it was with the stock 120cc govenor removed engine.

 

[Poboy kartman]

What have you been eating lately?

A few musing ramblings: .....you did check to make sure it had WOT from the pedal, correct?

Valve lash that is too tight can kill power two ways- as already mentioned it can keep the valves from closing completely- but it can also rob compression and power by opening the valve on the exhaust cycle before the combustion charge has had time to deliver full burn and power on the way down and closing the valve on the intake cycle before the cylinder is full. Does that make sense?

While keeping the valve open longer is the goal- and a tighter valve lash will achieve that- unless the timing is adjusted to match it can be detrimental. JMHO.....

 

[KartFab]

just swap it out at harbor freight within 30 days of purchase?

 

[exenos]

Any chance the govenor is messed up? Otherwise, if its still within the warranty/return period I'd just package it up again and bring it back.

EDIT: Ninja'd.

 

[mark123]

Valves were approx 9 and 10 thou and now they are 2 and 3 and the performance is the same. Can't return engine, as it is hacked up, govenor has been removed, muffler pipe has been cut and rewelded at a different angle (no obstruction, free flowing) . Hand throttle is operating the throttle linkage to it's fullest. One other thing, after running wide open for a bit and then let to idle and the shut off it back fires.

 

[Half-breeder]

.... guessin youll remember to 'break-in' the motor before you go to improving it... nexttime.

 

[Doc Sprocket]

The whole "break-in" thing is the topic of MUCH debate... MUCH. I have had men much smarter than I tell me that modern engines constructed of modern materials do not require an old-fashioned break-in period. This one could probably be debated until the cows come home. I'm not convinced that this is the issue at hand, but one way or the other, don't attempt to return the engine. Totally dishonest.

With the lash going out of whack and the stems mushrooming, I really find myself wondering about the metallurgy and it's implications. Shimming the valvesprings shouldn't have added THAT much spring tension! A pound, maybe? Two?

I wonder if swapping in some Honda valvetrain components might help here, but I'm not sure of compatibility. The predator is commonly known as a clone, but I'm also pretty sure it's not a "true" clone.

 

[mark123]

If break in is the problem, what exactly do you think went wrong? I had the engine apart, cam lobes/lifters look perfectly shiny and smooth, cylinder is perfect, valve seats are like mirrors. There is no obvious signs of abnormal wear that I can see. I am going to do a Leak down test next

 

[Half-breeder]

... may be ring positioning... did you remove the piston at any point in time? I know theres an order/direction those things are suppose to be in...

 

[mark123]

No I didn't remove the piston. A leak down test should tell me if the rings are leaking either from working their way around each other and lining up their gaps or if for some reason they wore. If rings were the problem though I assume I would smell burning oil?