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I can’t get my 94 exc 300 to run right. Stumped! Please help

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I recently picked up a 94 ktm 300 exc supermoto (yes it’s a 94, newer plastic). It has the stock pwk39 carb, fmf gnarley and good dual stage reeds.

 

It runs really poorly and I have tried many jetting combinations. Stock jetting is 180 main, 50 pilot, n85a needle.

 

Most recommend 172 main, 45 pilot, and n85d needle in second from top position, 40:1 mix, 1.5 turns on mixture as a starting point.

 

The bike as I got it had a 148 main, 58 pilot, and n85d in middle position, no air filter.

 

Which seems too lean up top and too rich everywhere else, it would run strong in high rpms but would spit and sputter everywhere below and was basically unrideable. I added a notoil air filter and have tried close to a dozen jetting combinations with no luck, in fact it may be worse. I tried the recommended jetting and it was too rich, I’ve been slowly leaning it out with no luck. Now it will start and idle but as soon as I hit the midrange it bucks badly and won’t even reach the power band.

 

I currently have a 158 main, 38 pilot, and needle in second from top position. Plug is rich. Something isn’t adding up, it shouldn’t need to be jetted this lean. The odd thing is in neutral or with the clutch pulled in it revs very cleanly all through the rpms, but under load it bucks like crazy as soon as I reach mid rpms. I’ve tried middle position on needle and it didn’t help. I also adjusted the float correctly. I’m running a br8eg plug, which is for newer 300s because the oem ngk b9egv is discontinued. Can anyone shed any light? There is not a lot of info online about the pre-internet KTMs. Thanks so much!

 

-Calvin

 

 

IMG_1326.thumb.JPG.74209e80b86f3026433011a8a310bbe7.JPG  

 

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I'm guessing that is not true fuel line coming off your petcock. That plastic stuff is susceptible to being eaten from the inside out by todays ethanol fuel and that debris makes it into the carb, clogging things up. It doesn't take long before you start see crazing in it, telling you it's compromised and is about to fall apart. Put real rubber fuel line on it meant for ethanol.

Those stubby gas cap vents are problematic too.

What's your elevation?

 

 

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I'm guessing that is not true fuel line coming off your petcock. That plastic stuff is susceptible to being eaten from the inside out by todays ethanol fuel and that debris makes it into the carb, clogging things up. It doesn't take long before you start see crazing in it, telling you it's compromised and is about to fall apart. Put real rubber fuel line on it meant for ethanol.
Those stubby gas cap vents are problematic too.
What's your elevation?
 
 

Elevation is 2,000 ft. I tried running it without the gas cap vent and it did not change the way it ran. Also the carb is very clean (I’ve had it apart many many times). That is actually true fuel line, I buy it from a local motorcycle shop and have been running it on my bikes for years without issue. After about 2 years it begins to yellow but I’ve never had a problem with it, it’s nice to see the flow of fuel when troubleshooting.

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"Now it will start and idle but as soon as I hit the midrange it bucks badly and won’t even reach the power band."

Has the engine had any work done to it? I think next thing I'd do is check the power valve. Take the PV covers off and check the linkages and everything there.

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The SEM ignition takes some of the blame.  in 97 they went to jap. kokuisan ing.  and jetting was way better. 

So you telling us the bike was ran with no air filter???

Check reeds.

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"Now it will start and idle but as soon as I hit the midrange it bucks badly and won’t even reach the power band."
Has the engine had any work done to it? I think next thing I'd do is check the power valve. Take the PV covers off and check the linkages and everything there.


I will check and report back, at this point I expect that the top end has been done multiple times. It has great compression and the clutch has been replaced so im sure ttr top end has been as well.

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The SEM ignition takes some of the blame.  in 97 they went to jap. kokuisan ing.  and jetting was way better. 
So you telling us the bike was ran with no air filter???
Check reeds.


I have checked the reeds they are aftermarket dual stage and are in good condition, no cracks or noticeable gap. I disassembled them, cleaned and reassembled myself and checked for air leaks. I have a spare coil from a 95, maybe I’ll try that. I haven’t checked the coil that’s in it with a multimeter yet so maybe that’s in order.

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did you replace the crank seals?  They have to be crusty after all these years.

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did you replace the crank seals?  They have to be crusty after all these years.
.

No I have not, it does smoke but not excessively so I did not think they were to blame but they could be leaking and causing a rich condition.

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I had the same problem on a 1994 exc what is was on the top on the float bowl you can take it apart has tamper prof Allen’s the gasket was bad letting gas from bowl into the carb what I did was take it apart and reseal with permatex gasket bike could not be jetted

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I had the same problem on a 1994 exc what is was on the top on the float bowl you can take it apart has tamper prof Allen’s the gasket was bad letting gas from bowl into the carb what I did was take it apart and reseal with permatex gasket bike could not be jetted

That is very interesting. I flipped the bowl with the gas on and confirmed that the needle valve (point valve) wasn’t leaking, but maybe it’s leaking above this point. Where exactly is that tamper proof hex located, I don’t recall seeing one. Thanks in advance!

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You are using an air filter now, I assume?  A boggy-rich mid to lower range could easily be a float level issue. 

Edited by Russell Dp
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The screws on the top of the bowl there’s a second part to it that where mine was leaking did the same thing call me 209 603-2038 or buy a new carb

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On 8/27/2019 at 3:53 PM, firechicken93 said:

I tried the recommended jetting and it was too rich, I’ve been slowly leaning it out with no luck. Now it will start and idle but as soon as I hit the midrange it bucks badly and won’t even reach the power band.

A bike that age, surely needs a new jet block gasket in the carb.  

https://www.jetsrus.com/individual_parts/021_532_su.html

Might as well get a carb rebuild kit and replace the needle and all of the other gaskets while you're at it.

https://www.jetsrus.com/individual_parts/020_110_su.html

Edited by redrider144
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The carb suggestions are good.

I’d also clean every electrical connection including the grounds. A bad connection will really mess up how an engine runs.

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Take the float off and turn the body upside down there should be some tamper prof screws take them out and reseal the part mine was doing the same thing gas was seeping through

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The screws on the top of the bowl there’s a second part to it that where mine was leaking did the same thing call me 209 603-2038 or buy a new carb


Thank you Louis. I took the carb apart as described and put a little rtv on the seal and reinstalled it. It did look pretty wet as if it was leaking. I then took the bike for a spin, it’s running the best it has so far but still pretty rough. It’s still “bucking” and “breaking up” but now if I stay on it I can get through to the power band. I’m currently running a 158 main and it still feels too rich. I tried a 168 and it wouldn’t even rev past half throttle, with the 158 it’s closer but still too rich. I’m going to go buy some new plugs as the one in it, though new. probably isn’t any good after these test runs. To the person who suggested I grease the wiring harness and check the grounds, that is the first thing I did [emoji106]. Also I noticed a couple drops of oil dripping from the air box drain, is that a reed issue?

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Opps take it apart again n get the RTV out of there,gas dose funny things to RTV n soon it will desolve n be all over in your fuel passages.

Dont beleive me take a small dab wipe it flat on a piece of steel ,let it drie n then wet it with gas.

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2 hours ago, firechicken93 said:

I took the carb apart as described and put a little rtv on the seal and reinstalled it.

I gave you the links to that gasket and a full rebuild kit.  Use them, not RTV nonsense.

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I dont know if rtv would work what I used was permatex gasket maker black-brown not rtv and you did take the screws out right you have you take it apart to fix it right jetting around 2000 -4000 ft Ithink was 148/42 or 45 I don’t remember the needle

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