81 250 has a funny bog ???

[86 400 XC]

Starts easy, good comp. new plug and installed a good used coil.
cleaned the carb, new air & fuel filters
new boot on coil wire, gap .025
runs and putts around good and it will rev out fine, but if you crack it open fast from low rpm it bogs like a spark blow out. If you go easy on the gas to mid rpm it hits good from there on.
Intake boot has cracks but it does not leak and got a new 1 coming.

any thoughts fellow Husky budds?


thx Steve

 

[speedcowboy]

The reed valves are probably cracked,hard or dirt is come inside so the can not close! I had a similar problem once...someone made the air filter out of some kind of furniture foam and it came apart in little pieces so the reeds could not cloce!

 

[86 400 XC]

Thanks speedcowboy, i will have a look at them.

 

[86 400 XC]

They look OK, so what else is there to check? weak spark, could a over oiled air filter create this bog?

Thx

 

[Ron]

Try adjusting the air screw on the carb. Screwing it in (clockwise) reduces air making it run richer, screwing it out (counter-clockwise) increases air and makes it run leaner.
If the pilot jet is correct, you should be able to improve the throttle response, when you whack the throttle open, by adjusting the air screw.
If the idle speed increases as you adjust the air screw, slow the idle down and adjust again.
In either case, if the air screw is more than 3 turns out the pilot jet is to large. If the idle cleans up at less than one turn out, your pilot jet is to small.

 

[86 400 XC]

420 jet.
It looks worn out, are they like car jets?
Is 420 a .042 hole size? its around .065 .070

 

[Ron]

Mikuni jets are rated for flow, they are calibarted in fuel grams/min. The higher the number the more fuel flow.
The main jet is not part of your bogging issuse though.

 

[86 400 XC]

I have reduced the bog with the screw but its still sort of there once in a while.

thanks for the help Ron!

 

[Ron]

Have you checked the floats? A high float level can make it get rich when riding.

 

[86 400 XC]

Been there, all is normal. Bike runs nice out of gear.
In gear it gets going easy, you can short shift into 3rd, 4th and putt.
When you let off and get back on it, its not there unless start riding it like a 125 and fan the clutch tons.
I dont remember the bike being a dog like that, but that was 20 years.

 

[Ron]

Okay, sounds like your issue is in the needle jet and needle.
Don't recall, is the 81 motor the new style (swingarm bolt goes thru the engine)?

If so I have an 83 250XC (same motor) that runs perfect at 1500 to 4000 ft elevation.
Compare my jetting to yours:

Pilot = 45
Main = 470
Needle jet = R2
Needle = 6DH3 (clip at 4th down from top)
Slide = 2.0

 

[86 400 XC]

Well Ron its working great at the moment , i could not get it to stumble/bog.

I did lower the float a hair and i put the clip down a notch on the needle, in the middle groove now.
Wants to pull the wheel when i crack it open hard now.

Thanks for all the advise!!


Steve