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Bike-Doc
Bike-Doc, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 671
Experience:  I have fixed & modified bikes for 35 yrs I'm now THE Mobile Bike Mechanic for S.LONDON since 1990
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I have a ktm 300xc. I just had the motor rebuilt and in the

Customer Question

I have a ktm 300xc. I just had the motor rebuilt and in the process the guy (Dicks Racing) modified it. Bored the carb and ported the head. I ran it twice and never reved it out for a breakin. Just roled on power up to bout 3/4 throttle for bout 15 minutes each time. When I started to romp on it it would not run at full throttle. I could floor it at once and kill the motor. It would also do it exiting turns at full throttle. I've gone larger on pilot and main jets and lower needle setting and seems to be getting worse. I first thought is was to lean. im stumped..
Submitted: 1 year ago.
Category: Motorcycle
Expert:  Bike-Doc replied 1 year ago.

Hi Don
Welcome to JustAnswer

My name is***** am a professional here at JustAnswer.com
I noticed that your request has not received a response yet and thought I would see if you still want the problem diagnosed.

My info is somewhat limited on your exact model but as no one else has responded I will try to help you.
I understand that you ran the engine in statically at various revs but at WOT (wide open throttle) she dies, correct?

Is this when going WOT straight from idle, gradually increasing revs or both?

Is this a 'race bike'? or why the boring, porting & jetting?

Thanx

Ride Safe

Bike-Doc

Sorry to have to ask what may seem like stupid questions, but it is obviously difficult diagnosing problems remotely, I cannot hear, see, touch or smell anything so I have only what a customer tells me to make a correct diagnosis.
Also I dont know how proficient a customer is or what they may have done already. So I need to ask stuff which may seem obvious or unrelated

Customer: replied 1 year ago.
It will stall at wot from idle or gradually increasing revs (both). It is a race bike for off road racing. Did the mods to give it more ppower and it did. However it will not run at full throttle. It usually does not just die immediately at wot but starts to cut out really bad and will die if I don't reduce throttle.
Customer: replied 1 year ago.
Boring the carb increased it from a 36mm to a 39mm. (think that is the correct specs). gives it more fuel. The head (head only not cylinder) was modified to give it more torque and rev.
Customer: replied 1 year ago.
I only started changing jets because of the stalling problem
Customer: replied 1 year ago.
This is a two stroke dirt bike
Expert:  Bike-Doc replied 1 year ago.

Was the bore increased?

Has any other work been done?

Did you run her @ WOT before the mods?

Has the head just been skimmed &/or was the squish band altered?

Customer: replied 1 year ago.
Bore is stock. It was recoated because of some scarring and it was just time to do it. It has a nakisil coating and was put back at stock size. Squish is not altered as far as I know. Prior to mods it ran fine at all throttle positions. FYI< I run amsoil sabre premix at 80/1.
Expert:  Bike-Doc replied 1 year ago.

Is fuel fresh?

How does the plug look?

Has the rev limit been altered?

Customer: replied 1 year ago.
Fuel is fresh, plug is brand new and I haven't checked it yet for fuel burn. I don't think two stroke has rev limiter does it?? If so it shouldn't have been changed
Expert:  Bike-Doc replied 1 year ago.

I meant to ask if the ignition system is std & have you checked the exhaust wadding & air intake filter?

Do she have a tacho? at what revs does this occur?

& just to clarify, is it as soon as the throttle is opened wide or do the revs build up & then quit ?

Customer: replied 1 year ago.
Exhaust is new, Air filter is freshly cleaned. No tach. I quits at both rev build up or quickly opening throttle.
Customer: replied 1 year ago.
Ignition is stock and un-altered also. Kick start.
Expert:  Bike-Doc replied 1 year ago.

Can you check the plug pls?

Customer: replied 1 year ago.
Not now. Bike is at parents house. Im not with it right now and wont be till Wednesday
Expert:  Bike-Doc replied 1 year ago.

Have you tried altering the amount of wadding, if the exhaust is stock it may be restrictive to the increase of the intake

When you say it kills the motor, do you just mean she stalls suddenly?

Do the engine quit completely?

Customer: replied 1 year ago.
It begins stalling pretty quickly at full throttle. If I don't back off throttle it will kill the motor. The exhaust is a aftermarket FMF pipe. It is for improved performance over the stock unit. It improves throttle response and rev and torque. Don't think its anything to do with Exhaust
Expert:  Bike-Doc replied 1 year ago.

Sounds Trick!

Then I need you to pull the plug for a burn diagnosis

I can keep this open for you to get that info

Keep me informed pls

If I have already helped you then please press accept as that is the only way that I am compensated for my input, your question will stay open for its 7 day (or more) lifespan!

Please take the time to rate my service to you, I hope it has been favourable
Thanx

Ride Safe

Bike-Doc

Please dont rate my service before giving me a chance to help you, negative (low) ratings are taken seriously here & I will try my best to help you as much as I can (for both our sakes)

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Customer: replied 1 year ago.
You have made a great effort but nothing that is helpful at all. I'll check plug and let you know. I wont give you a bad rating but It doesn't seem you are going to be of any help. I don't think you have much dirt bike experience. I'll get back to you after I check plug. tks
Expert:  Bike-Doc replied 1 year ago.

No but I have a lot of 2 stroke racing & drag racing experience with solos & combos from modern going all the way back to my Yam '73 TZ350B altered for road use & my old Suzi 3cyl GT750 with Barton Racing engine

Your problem seems to be jetting or air related & a good look at the plug is needed - unless you have a colour-tune set?

But if you like I can opt-out & open this question up for others if you want