Poor starting / running.

[Kramer]

Good evening chaps.
AR's been laid up since about September. Tried to start it but got nothing till I put some petrol in the cylinder and then won't run off choke till its been running for ten minutes. Idle when warm is erratic and sounds very lean running.... if I turn the mixture screw fully in it helps. Poor throttle response unless I have the choke on.
Carb is DEFINATELY clean and set up correctly.
In the 8 years I've had this bike it has always been a poor starter from cold if left for more than a few days but over the last couple of years I have noticed it getting worse and a "lean" idle when the bike is very hot. Seems to smoke a lot when idling as well.
I'm thinking possible crankshaft seals here but want to be sure before splitting cases.
What do you guys reckon?

[gregorious77]

you could do a leak down test to check.

[fallenmikethebike]

^^^^+1 also,a compression test. Carb clean, and replace the idle jet.
Is the oil level dropping in the gearbox between services? Or is pushing oil out of the breather?
Mike

[Kramer]

Understand the leak down test but don't have the gear to do it, have a compression tester though.
I'll check the box oil tomorrow.
Cheers.

[helisupp]

fmtb

A serious technical question:

How can a duff crank seal cause oil out of breather, and cause low gearbox oil by letting oil into crank, which means its leaking both ways.

I thought (maybe wrongly) the crank sucked oil in with a duff seal as per my IT175 last year, does it also pressurise the gearbox.

We have an engine here that is breathing oil out of the breather, is it a crank seal.

Mark

[knackeredMk1]

Seals can go both ways depending how bad and where the damage is. If the generator side seal goes you only generally notice this as the engine running lean as air is sucked in and unless the damage is bad it is only a small amount of intake and unburnt gases that come out, which you might not notice. If the same fault applied to the drive side you would notice compression in the gearbox as the gases would go through the oil/gearbox and exit through a narrow pipe.

[fallenmikethebike]

I would imagine it would be something like, the down stroke of the piston will pressurise the crankcase, and if it's badly sealed to the gearbox, that pressure will leak into there, thus pressurising the gearbox and it's contents.
Conversely, the upstroke, sucking the ignition charge, above the piston, will create a partial vacuum, thus pulling gearbox contents through the same ill fitting crankcase joint, or something like that .
Mike

[helisupp]

I had better order a couple of crank seals from LT this week then and put them in.

[fallenmikethebike]

I had better order a couple of crank seals from LT this week then and put them in.

Possibly, it may still be the case though that the seals are fine, but the crankcase faces, at the gearbox/ crank housing juncture are poorly machined,or badly mated, or indeed even porous, thus allowing the afore mentioned phenomenon, this is however very rare.
Mike

[Kramer]

Well. the gearbox level is ok.
Question for knackered; if I whip the generator off do you think there might be any leaking evidence around the seal or should I be looking at the carb again? I've had the carb off twice and blown through every airway with an airline.
About replacing the pilot jet; how much low rpm does the pilot system deal with? After the initial low rpm flat spot the bike actually runs fine and has plenty of power. Can the pilot jet wear out?.... the bike was running fine when I laid it up.

[gregorious77]

All jets can wear out. and for a few quid its worth replacing them.
Pilot circuit affects up to 1/4 throttle.
http://twostrokemotocross.com/2009/12/c ... nd-tuning/
http://justkdx.dirtrider.net/printcarbtuning.html
http://www.kawtriple.com/mraxl/carb/carbadj.htm

[Kramer]

Thanks for the links. I reckon I've got enough stuff lying around the garage to make that homemade leak tester in the third link.

[fallenmikethebike]

I've heard " cocoa cola " can be used to soak the carb in and makes a good alternative to ultrasonic cleaning.
The pilot jet can get a dried emulsion on the surfaces.
Is it running lean, or reluctant to start.
Mike

[Kramer]

Ok, found a guy near me with a F-reg CRM who is going to let me try his carb. This will potentially save me a bit time [which I don't have at the minute] and take a bit of the guess work away. Am I right in assuming his carb is the same as mine?

[knackeredMk1]

AR carb is completely different from the other Mks