zbuck
New member
Was there oil in the engine upon purchase? If not what did you use, Dino/Syntnetic? When you had the head off, was the crosshatch in the cyl. still there?
200cc clone losing power
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Was there oil in the engine upon purchase? If not what did you use, Dino/Syntnetic? When you had the head off, was the crosshatch in the cyl. still there?mark123
New member
No oil when purchased. The first fill was with cheap 10W-30 for an hour or so and then I switch to 100% synthetic 10W-30 and have changed it twice . As for cross hatch I didn't really look for that, I just rubbed my finger all around with the piston all the way down and it was very, very smooth.
OzFab
Well-known member
You could've gone from one extreme to the other, set them somewhere inbetween & see what happens; it can't be any worse...
That sort of backs up poboys theory about the vavle clearance...
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zbuck
New member
Using 10w30 and then switching to synthetic, with both being slicker than 30w, you may have glazed the piston rings. An that maybe the reason why you have 40psi compression. Along with the valves and 40psi= loss of power. Do a leak down test and let us know the results.mark123
New member
Will do. Thanks again everyone in participating in this thread.
firemanjim
Just kartin' around....
Take the washers back out from under the springs. You might be bottoming out keeping your valves from doing their job......
mark123
New member
I thought of doing this as well but can't understand why it worked great for approx 10 hours and then gradually lost power. I ordered proper 18 lb springs. I wonder if maybe the shims + possible inferior materials + higher than stock RPM have caused the springs to lose a lot of the original pressure
mark123
New member
One other thing, the last time I took this apart I was able to remove the spring retainers and put them back on with my fingers, I don't have a lot of experience doing this but how hard should it be. Is it typically fairly easy or does it require a lot of force.
OzFab
Well-known member
Stock springs are 10lb (IIRC) so, no, not a lot of force is necessary.
mark123
New member
I just did a leak down test and am showing approx 10% leakage and the air is coming back up through the carb. When I do this it is impossible to hold the crankshaft in position so while the air is blowing I just rotate the crank so it becomes as hard as possible indicating the valves are both shut and the air pressure builds up to 90 max which is 10% less than the 100 I set the gauge at.I assume it has to be an intake valve issue. I removed the valve cover and there is clearance there so the valves are completely closed. I removed the head and the seats look OK to me but to be sure I am going to lap them anyway. After I lap them and put a plug in the head I was going to tip it upside down with the valve spring on and pour some gas in so the valve are submerged and see if the gas stays there for a few hours. Is this a good way to check if they are sealing properly. Anything else I should check while it is apart.
OzFab
Well-known member
Put a tiny thin smear of lapping paste on the valve seating surface, drop the valve into place & apply a bit of pressure (as much as the spring would provide). Now use a sharpie or similar & place a reference mark on the valve & head.
Lift the valve & check the seat; wherever there's lapping paste on the seat, it sealed; if there is a void in the paste, well, I think you can figure it out...
Lift the valve & check the seat; wherever there's lapping paste on the seat, it sealed; if there is a void in the paste, well, I think you can figure it out...
Poboy kartman
Senior Moments Member
Sorry- but WHY? The OP has already stated he was going to lap the valves- the very best way to determine valve seat. The only merit I see is possibly to determine a bent valve. ....Is that it?
OzFab
Well-known member
Op stated
That means the inlet valve is not sealing; why not? It's a new engine...
Lapping the valves won't show anything, only that one point of the valve is contacting the seat at one point...
To answer you question simply, yes, that test shows if a valve is bent or possibly burnt
Poboy kartman
Senior Moments Member
I see but I don't see. A lap with coarse grit will show a difference in surface sheen. A perfect seat between both will show a complete ring on both, while a bent/ burnt valve will make a circle on the seat- the valve wont have a perfect circle, correct?
mark123
New member
I lapped them today and can see even wear marks all around the seat and valve. After I installed the spring I filled cumbustion chamber with varsol and then blew compressed air into the intake with the nozzle of blow gun about an inch away from opening, there is one particular spot that bubbles, I tried rotating valve with same results. I removed valve and there is nothing in that are that looks any different than the rest. Is this too be expected or should it be sealing better. I tried exhaust as well with similar results. It has been hoding the varsol for a couple of hours now with no leaks. Should I put it back together or get the valve ground?
Update, it slowly leaking into the intake port. I am going to get them ground today.
Update, it slowly leaking into the intake port. I am going to get them ground today.
OzFab
Well-known member
A valve not sealing in a particular spot usually indicates either a slightly bent valve (depending on the size of the leaking section), a slight burn (which doesn't usualy affect intake valves) or simply a bad grind.
If you take them to an engine shop, they can tell you which one is the problem...
Remembering that those engines are manufacturered in China & their manufacturing processes & machinery aren't exactly the best; If a valve is fed into the grinding machine even slightly off centre, the whole head is affected, 0.005" off centre means the valve is off by 0.010"...
If you take them to an engine shop, they can tell you which one is the problem...
Remembering that those engines are manufacturered in China & their manufacturing processes & machinery aren't exactly the best; If a valve is fed into the grinding machine even slightly off centre, the whole head is affected, 0.005" off centre means the valve is off by 0.010"...
mark123
New member
This is going to drive me crazy, I just got everything back together, leakdown is much better, only around 4% BUT it is even slower now than before 13mph. Where as it was getting 20 when the engine was new 10 hours of use before. It just feels like the throttle is not opening all the way or something. I varified that the butterfly inside is opening fully when the hand throttle is depressed. It idles perfect. I also took out the valve spring shims and set valves to 0.004"in and 0.006"ex. I tried going WOT and slowly pulling out choke it just gets worse, tried removing air cleaner all together and no change. Any other ideas.
happy_8637
New member
i had a similar problem with an old flat head briggs 5 horse... we did a complete rebuild on it and it ran perfect.. gave it to him he tilled his garden and he was complaining of power lossage so we took it back lapped and adjusted the valves again still nothing.. so we did a leak down test same thing. had a bright idea lets shave the head about .0020 thousands of and inch and see what happens and it straighten the thing right up had better compression he never complained any more about loss of power
Poboy kartman
Senior Moments Member
Ummmmm- maybe what was suggested a while back- check for WOT from the PEDAL? Maybe you have done that, but you haven't posted so.... Just get a stick- push on the gas pedal and make sure that the butterfly is fully open that way.......
mark123
New member
A snowmobile does not have a pedal, as I said I did verify that by squeezing the handle throttle and the butterfly is fully opening. I just ran it wide open with a new plug for 1/2 hour and the plug remained perfectly clean, is this a sign it is running lean?
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