Top end swap problem

[motorhead]

I've got this 2 stroke 50cc vento triton. I bought it with a seized piston and replaced the top end with a 70cc malossi kit. The problem is that it only goes 25mph tops, smokes a little more than a normal 2t. I have the stock airbox and 75 main 22 pilot jet mounted. What is weird is that I bought a new 50cc piston, honed the stock cylinder and when I install it the bike wont run, not even with starting fluid. It only runs with the 70cc top end. So, what do you guys think???

[lshigham]

What does your plug look like? Sounds like it's too rich to me.

[scootinbow]

That would be guess also that it is rich. I know my triton that still has the stock pilot in it is really rich until the autochoke cuts off the extra fuel.

[motorhead]

Here is a pic of the plug. Its a dry feeling, light gray color. I ran it Wide open up and down the street for a while before pulling the plug. The plug is an Autolite 4092 (which translates to NGK B7HS).

[lshigham]

That looks lean, strange.

You need a bigger main jet, probably a 85 or so.

[90GTVert]

I agree, start with a larger main and see what that does.

[reveeen]

I *wonder* if anyone determined the reason for the original seizure, and corrected it, because these things don't decide to just seize?

[motorhead]

Originally the wrist pin bearing seized up and got destroyed which then made the piston beat against the cylinder and head.

I put an 85 jet and it still ran the same. Then I took out the foam filter from the airbox and it hits 35mph max now. Once at 35mph it wants to go faster but then the acceleration cuts off keeping me at 35.

[90GTVert]

I would verify that the float level is correct and then play with main jets till I got something out of it, unless there are other symptoms. It quits at 35 now, but other than it lacks acceleration, are there other symptoms? (Sputtering, hollow wahh sound, very high revs, very low revs?)

[motorhead]

I should say that at 35 it wants to go faster but it hesitates. Produces a little more smoke than a normal 2 cycle. From a a stop it accelerates good, hits a dead spot around 20 and slowly goes up to 35.

[dude]

Check your reeds. You may even have a bad new plug. Check the CVT.

[troy1896]

Firstly, I think that if the original 50cc cylinder was buggered up too much and then honed, it might be too big of a bore now, and without an oversize piston, the compression might be too low.

On the 70cc, it sounds like a couple of things going wrong and combining into 35MPH. I think that your carb is not set up right. It kind of sounds like you are rich on the low end and lean on the top end (like when the autochoke disengages). Try to get the MJ right first, adjust air/fuel on idle next, get the needle clip dialed in, and then check the idle air/fuel and speed once more (at least that is how I do it.) There are links to some good instructions on the site.

As others have mentioned, there could be restrictions in the variator, the belt could be too short, the rollers could be the wrong weight, the reeds could be broken or restricted, the exhaust could be restricted, plugged up, not proper backpressure, the throttle might not be adjusted correctly, the brakes could be dragging, clutch could be slipping, etc., etc....which are adding to the problem.

When you get something used, and it is not running, you kind of have to check everything because you don't know what previous tinkering has been done on it. I never believe the previous owner (even if it is my friend). Try to make one change at a time and test it, otherwise it gets too confusing which change affected what.

I would try to get the carb straightened out 1st otherwise you risk damaging your new cylinder. If it is a high mileage scooter, try giving a couple of "light" kicks to the exhaust and see if that improves it, it may be plugged up with soot.

One last thing, a 7 plug might be a tad hot and I would use a 8 or 9 with about a .028 gap depending on the timings of your BBK.