Having Performance Problems (CR250)

[razorboy]

Hey Fellas,

Well, this CR250 is still not running right and I am getting to my wits end with it.

The bike has no power. I have replaced all the top end gaskets and resurfaced the head. I did have a coolant leak problem with the head but solved that with a little copper sealant spray.

The bike ran decent before I worked on it. The problem was that it was a bee-atch to start. Now I can get it started in 2-3 kicks where it used to take 10 or more. I discovered that the base gasket was leaking and decided to replace all the topend gaskets. After replacing the gaskets, I discovered the leak on the head and had the head resurfaced. It still leaked a little but now it doesn't.

There are 2 things. The first is that the bike has no power. Get on the throttle and it farts out and goes nowhere. It jumps off the line but then loses all gusto. The second is what sounds like it could be detonation after running it for a little while. When I pull the clutch in and coast after a few minutes of running it, I can hear it making popping sounds which stop after I idle for a 10 seconds or so. I am not sure what detonation on a 2-stroke sounds like so any help here is appreciated. C'mon guys, someone here has to know what the heck is going on with this thing? Is it possible that the head has been milled out of spec and my compression is now too high? Could this cause both detonation AND the loss of power or could it be two unrelated problems.
I have cycled through every needle position and I have also messed with the airscrew (I keep it 2 turns out as a start reference)

Its my kids birthday this weekend and I had hoped to get out riding with him but not if this piece of c**p doesn't come together.


:bang:

Cheers
Bernie

 

[nickyd]

does that bike have a powervalve? did you touch the carb at all when you did the rebuild?

 

[razorboy]

Hi,

Yes, it has the power valves which oddly enough were not working when I tore the topend down due to coking seizure. I cleaned everything out and now they work perfectly. I watched them opening through the exhaust port.
I did clean out the carb when I had it off. I don't remember removing anything outside of the float and needlevalve. Then sprayed out the rest with carb cleaner. The carb was very clean to begin with and I doubt I did anything positive or negative.

The bike jumps off the line and then bogs. If I keep the throttle on, it will build power as it approaches the topend. It appears to be brutal in the low / midrange.

 

[Morvo]

Have you changed the reeds yet?

 

[razorboy]

yes, it has brand new reeds....

 

[Wyld Bill]

I feel for ya man. I've been rebuilding a 1990 CR250 since this spring. The whole engine is all new basically & now I'm having trouble getting things back together right. Especially the power valve parts.
Anyways with your are you SURE the power valves are opening all the way on they're own or is the exaust pressure just pushing them open? When you put the jug back on did you make sure the linkage for the power valve cam & rack lined up correctly?
Sounds stuipid but have you checked your air filer?

 

[razorboy]

Thanx for the reply,
The HPP system is definately working properly. The valves open and close completely under throttle.
I haven't "checked" the airfilter per se? I know it is still there....lol
It was clean before I began the work so I am assuming it is still in good shape. Maybe I will clean it anyway, gawd knows I've cleaned everything else!
I may actually have to take this thing to a shop if DRN can't figure out what's happening......... :(

 

[bleeds]

Hey there. I have a much older CR250R without a PV, but mine was doing this after I repacked my silencer. It idled fine. It reved great. Great response then BAM. Fall flat on its face when you tried to spin out, or drive sudden and hard. BOG BOG BOG>> DIE>. I had tried to put the end of a pop can in there with holes in it to make it a little bit quieter without getting another silencer. Sadly, it didnt work. Too much back compression. The engine couldnt breathe. I took that out and damn was it fast! Check to make sure you silencer and muffler isnt clogged. dunno.. worth a try. If your carb istn adjusted right it will fall flat too. Take the air screw and turn it "OUT" until you start to hear the engine rev up. Then back in till it starts to go down. Then back out again, listening closly to it until it just starts to rev and leave it. Then ride it and see if it is better. Fixed mine. Also if you are using pump gas, make sure to use the high octane stuff, and you might want to mix it 32:1. One more thing, you had the head resurfaced, I am wondering if you might have raised the compression ratio enough that regular pump gas isnt going to run in it very good anymore. Just ideas, as I am new to 2 stroke and learning alot from these pros here!!!
Bleeds
PS one more thing, when you said you replaced the gaskets, I am assuming that you did the top end as well. (rings, piston..etc)

 

[razorboy]

Hey Bleeds,
Well, I have not done anything to the exhaust at this point. I had run the bike initially without the exhaust on and it did the same thing. I was assuming that the lack of an exhaust was what was causing the problem but it remained after I installed it.
The compression and octane you mention is where I am going next. I am going to mix up some 32:1 today and use high octane gas to see if it improves things at all.
I'll post back if anything changes.......

Cheers
Bernie

 

[twpgummi1]

cr250 problems

what color is the plug when it comes out of the head . also when you kick the bike does it feel like it has good compression

 

[_JOE_]

what color is the plug when it comes out of the head . also when you kick the bike does it feel like it has good compression

He's probly gonna have trouble remembering, it was 3 years ago.

 

[lsxtrkiller]

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