83 250r.
Was running like a bear. Rebuilt everything.
Stopped all of a sudden. Now will not start. After a couple of kicks, it might backfire through the pipe.
Compression is 185, has good blue spark and the plug is new and wet.
Air filter is new.
Pipe and silencer...new.
Piston...new.
Rebore (by non-douche)...new
Bottom end.....new
reeds new
carb...rebuilt

Only parts that are not new are ignition system, but the spark appears good?

Also - almost felt as though it was hydro-lock from TOO much fuel after a few kicks?????

I am just a stupid Porsche mechanic...please help.

 

Good spark, good compression, wet plug. It's getting gas, but is it good gas ? That's the only logical thing I can think of under the specific set of circumstances. Maybe you got water in it somehow.

 

Even the gas is new. LOL

Are the pulse generators in these such that the timing can exist, but be WAY out of time??

 

I don't know dude, I was just giving a suggestion based on a general knowledge not your bike specifically. I had a dirtbike that seemed to have good spark with the plug out, but under compression the spark was not good enough. That sounds like another possibility. It's apparently firing occasionally and burning the un-burnt fuel in your exhaust. Also, did you try more than one plug ?
Did this start suddenly ? What led up to the symptoms ? Was it doing this before carb rebuild and did it ever run right after carb rebuild ? Now this ones pretty far out there, but the equivelant of cam timing on 2 strokes is accomplished by port sizing and placement. Is it possible you have a gasket blocking part of a port ? I know that ones really far out, but just trying to rack your brain.

 

When you are trying to kick it over, are you getting fuel running out of the bowl overflow tube?
Just want to ask, because my YZ did all the same things as yours, and all new.............and I kept changing the float height because I was flooding the cylinder with fuel, but it ended up being the O-ring that holds the needle seat in, was bad. If your getting fuel out of that tube at all then check that of the float height.

Other than that, I think Sparky covered it [img]i/expressions/face-icon-small-happy.gif[/img]

 

Thanks guys - I am going to test the entire ignition system. I am sure it is possible that the spark is being blown out.
Floats and valve are good.
I did, however, use a mix of xylene to raise octane - now I am wondering if there aren't any soft plastic parts in these Keihin carbs that I have melted with my turbo dyno knucklehead fuel................
I will report back after I fix it and let you guys know if it is okay to use aromatics over 33% LOL.

 

Have you tried to put fresh gas directly in the plug hole (cylinder) , then tighten spark plug back and kick it? You might be getting gas, but too much or not enough could cause it to backfire.........

 

Well - it was a combination of things.
My fuel mix was 20:1 (like it says in the damn manual - why write a manual if you are stupid, Clymer?)
the plug was fouled because of it.

I had tried to clean the plug several times, but evidently, if you can't clean the insulator nose, the plug is junk on a 2-stroke.
I popped in a new BR8ES, and it fired right up. Mix is now 40:1.
It was probably better to break in the total rebuild on 20:1 anyway, in hindsight.
Plus, I bought myself a brand new PWK 35MM flatslide in my diagnosis quest as a bonus!!

Now its .060 over, Wiseco, CR250 reeds, PWK 35MM, 190 psi cold, Uni, DG front/back - runs pretty good.
Gonna take it to the Mustang dyno just for a laugh.

 

Sounds like a sweet R. I use to have an '83, I loved that thing. Blew the engine and gave it away. STUPID STUPID STUPID. I wouldn't mind seeing some dyno numbers from that thing, just for ***** and giggles. Let us know. Got any pics??