• Husqvarna Motorcycles Made In Sweden - About 1988 and older

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Need advice on performance 83 250 XC

cgmjr

cgmjr

Husqvarna
C Class
Today I got my old 83 250 XC back on the trail, after 26 years :) I've just started the restoration, got a long way to go.

But on the trail today the power was awful. The engine bogged under throttle, and in some cases would barely make take-off in 1st gear. I've put on some weight, but not THAT much.

She starts easily, and idles fine, seems to rev fine in neutral. She has the stock jetting: 440 main, 45 pilot, 6DH20 needle, 166 R-4 needle valve. 38mm Mikuni, of course. The slide, however, appears to have been modified by hand from a 2.0 to a 2.5. I bought it from a racer back in 1985, so I guess he did that.

I've cleaned the bejebbers out the carb, but I have not touched any of the mixture screws except the idle.

Ideas? Are there any tell-tales signs about the piston or rings that might cause such poor performance?

Thank you in advance.

-cgm
 
A bit more data: I have the stock pipe, but no silencer. Gears are 13T/56T at the moment, but I have a 53T on its way from Husqvarna-parts.com. If she will hardly move with that 56T, she'll die on the 53T I suspect.

Any ideas much appreciated.
 
Set the mixture screw at 1-1/2 turns out for baseline.
I know this is basic but did you check the fuel flow to the carb, cap vent could be plugged. Also pull the air cleaner out, make sure its getting plenty of "clean" air (if you don't have a new filter yet).
A kicking pressure check, will tell you if the top-end is up to snuff. Should read 140 to 160 psi. Give it 5 or 6 good kicks with the throttle wide open and read the pressure.
 
Thanks Ron. I'll do all that tomorrow. Filter-wise, I have a new K&N (RU-1760) that is the closest I could find to what I had back in the day. It has about a 1/2" smaller diameter than the old one. But I'll pull it off as you suggested while I diagnose.

I'm a decent wrench, but this is my first time working on a Husky; what is the cap vent? I have a clear fuel line on right now with no filter, just to ensure that fuel is flowing. I think fuel flow is good.
 
Gas cap ;)

K&Ns dont work well on 2 strokes
It will fell like less power with a 53t sprocket thats for better top end speed.
56 will give it more snap out the gate.
 
86 400 XC said:
Gas cap ;)

K&Ns dont work well on 2 strokes
It will fell like less power with a 53t sprocket thats for better top end speed.
56 will give it more snap out the gate.
Click to expand...

I remember those filters, and you are right they rob power
the airbox was designed to flow still air into the carb, and to have the volumn for acceleration without turbulent airflow
where is your original airbox?
 
@86400XC Ah! Doh, thanks! I was thinking carb cap or somesuch.
@2premo I am using the original airbox, but I do not have the boot or wire cage (pn 15 14 151-01). Back in 85 she ran strong with the old K&N, but that was then. Perhaps I should get the original setup again.

What are you guys using, filter-wise?
 
uni filter

I had a 81 250 that had a bog and no low end power.
I replaced the main jet, it was worn out to a slightly larger hole and was really rich.


Steve
 
@86 Sweet! Got one of those too. By next weekend I should have that part redone.

Thank you for the help!
 
If you have a hose off your gas cap, then you are most likely venting the gas tank adequately.
What I was referring to is with a standard style gas cap, the vent hole could be plugged (not venting) causing a capillary effect on the gas flow to the carb.
Think of holding your finger on the end of a straw and seeing liquid held in the straw. When you release your finger, the liquid flows out. The same thing can happen if your gas tank doesn't vent properly.
 
Report #1: compression tested twice, 125-130; a bit lower than @Ron suggested. Also, and I'm a bit embarrassed by this, I have an Acerbis gas cap and gasket, but was running with it plugged by a small cap (size of a toothpaste cap), no hose :/ I guess I never thought about the air-tightness of the tank and its effect on fuel flow. Phew, I got a lot to learn...

Anyhoot, is 130 compression too low? Is it ring/piston time?
 
The bike should run a 130 psi, but may start getting harder to start when cold. Were you holding the throttle wide open while kicking?
I just put a new piston and rings with a fresh bore in my 250 today. I'm getting 165psi.
Next thing I might check is to make sure your exhaust pipe is clear. No telling what may have built a nest in there.
After that, verify the timing is correct. Should be 2.55mm BTDC for your 83 250XC.
Ditch the toothpaste cap. If the carb is not filling properly, the float level will be drawn down making the engine run leaner and leaner until it starts running like its running out of gas.
But worse than that, if your motor was fresh you most likely would have siezed it.
 
@Ron, I was indeed holding the throttle open. Toothpaste cap is gone :) Pipe is clear. The plug was light tan coloring, but not too lean looking. But I think that cap vent was a big part of the problem.

I have some service manual-like pdfs, and replacing the ring / piston looks pretty easy. But I'm curious about the sleeve/liner. Do they wear like a car's cylinder? If one bores the jug, must you get a larger liner? Or is it the liner itself that gets bored?
 
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