Seeking Advice on 1986 ATC 250R Not Pulling on Top

[EE-Honda]

I have a 1986 ATC 250R that I am having problems with getting it to pull on top. It has an FMF fatty pipe and FMF silencer, 36mm keihn carb, reed spacer, uni-filter, dial-a-jet, and runnng with an open air box lid.

The engine will pull extremely hard through mid range, but right around the point where it should really take off, it flattens out. I have verified that it is not a jetting problem through hours of trying different combinations of jets and eventually installing a dial-a jet.

I bought this engine approximatley 1 year ago, the individual that I purchased it from tried ( stress the word tried) to do some porting on the motor. Really all he accomplished was removing what I will call the "diffusers" from the auxillary intake ports. I tried to smooth them back out the best I could.


I am trying to get some opinions on where to start looking.........

Since the engine is failing to pull only on top(keep in mind it runs perfectly bottom-mid) I was going to start by replacing the stock reeds and removing the reed spacer. If I still see the problem after that then I will look at taking the cylinder to a shop and getting someone to look at re-working the auxillary ports, that is if mis aligned auxillary ports could even cause this problem???

Please give me your opinions on where to start looking to try and fix this problem.

Thanks!!!!!

[AZ250R]

Whats your compression @?

[EE-Honda]

Ratio (XX.XX/1) or actual psi?

[cliff2302]

Check your stator. I had the same symptoms on my T3. I guess when a stator is going bad, it will still work good at low rpms, but in the upper level is where it quits out. But your right about your reeds, they would have the same effect. Im not too sure about the ports though, im sure someone will touch on it soon. good luck

[Tri-Z Pilot]

Whats your compression @?
I think if the compression is down, he would be suffering from bottom-mid wouldnt he?
EE-honda, Az250r meant psi, not compression ratio, I.E. 180psi ex. not 12t01 ex.

[nate b]

get a new cyl.

[deathman53]

get a better pipe, the fmf pipe falls flat on top end

[jeswinehart]

kimmers 250 r was doing that and i asked a fella who has forgot more about 2 strokes then i'll ever know ,,, but anyways,,, i relayed the info i was told based on what kimmer had posted ( close to what you are describing ) and it was the crank seal was leaking at the higher r.p.m. range and kimmers r would just fumble + stumble instead of hit the power range.
if i remember right ,,, the tell-tale sign of the crankcase seal failure was oil on the stator or in the case on the left side.

okay ,,, that's all i know about it ( and i hope to hell it ain't your crank seal ! )

john

[Wickedfinger]

... I think you are on the right track by taking off that reed spacer first - I do have a question though - is it mounted before the reed cage or after it?. - It makes a big difference. Deathman was also correct about the FMF pipes and topend if its a "Gnarly" or the old "Fatty". An SST is a topender. Those intake runners on the side ports wouldn't cause it to loose top end - but - if he botched the porting really bad, especially by removing too much from the tops, he could have altered your port timing into the crapper.

[Dammit!]

I can tell you the FMF Fatty definitely does not cause a 250R to flatten out on the top end like EE-Honda is explaining. Not by any stretch. My old Paul Turner definitely pulled harder on the top end though. Even with the Fatty on there my R is still a very top-endcentric (I made up a word!) bike.

[HaggLE]

Repack your muffler. If its too restrictive or blocked it will behave exactly as you say. I would also be checking that left crank seal but i would think that would make it rough everywhere. Let us all know how it goes from there.

[sandpuppi101]

I agree with dammit,the fmf does not flatten out ,I have a fatty and a buddy has a Gnarly on his R .Something to think about would be to go with a Rad valve ,with a port job shabby or not the rad valve shoots the air right down the engine.But another thing to consider is the air flow,give it all the air she can handle.I bumped up to a 38pdk carb and removed my airbox altogether an put on a K&N and when I get on it you can hear the sucking.It could be alot of things hope that helps.

[gotballs 250r 82]

could very well be the stator i have had that problem to