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Hey everyone, I just bought a used shifter kart that wasn’t running when I got it. I went through and cleaned out the carb and put in all new jets and it starts up great and runs good in all situations except full throttle. No mater what rpm I’m at it will completely cut out as though it’s getting no fuel. If I keep it floored it will cut out and decelrate until I let out to 75% at which point it will pick back up immediately and pull hard like nothing ever happened.
What size main jets are people using for 40-50 degree temps at our altitude. There is a 180 in it right now. Could that still not be a rich enough main or should I be suspecting my fuel pumps. It’s a cr125 with an rs piston, mikuni carb and pump around setup. 110 octane with redline 32:1 mix. 180 main, 37.5 pilot, stock needle on middle setting. Any help would be great!ill check that out but i would think that if it were a magneto problem that it would be a little more of a rpm based problem not throttle based and cut out on me at high rpms whether i was full throttle or not. i also lowered my plug gap in the beginning because i thought i was blowing out spark too but that had no effect either so im still leaning towards it being a fuel problem. its acting like its going very lean only at full throttle.
But either way i would still like toget an idea of main jets everyone uses at this altitude.My mistake, Derrick, I missed your “no matter what RPM I’m at” quote…. it does sound more like fuel.
We have nothing but great shops in Colorado if you need help.
I never ran a shifter, so no thoughts on jetting.
My first thought is it’s too rich. When too lean at full throttle generally it will rev well till it sticks the piston. Plus I remember running main jets in the 150’s- 160’s range. Reading the plug and piston top after running it in the poor full throttle condition might confirm rich or lean. Or put in a richer jet and see if the condition happens even sooner in the rpm band.
@Rodney Ebersole wrote:
My first thought is it’s too rich. When too lean at full throttle generally it will rev well till it sticks the piston. Plus I remember running main jets in the 150’s- 160’s range. Reading the plug and piston top after running it in the poor full throttle condition might confirm rich or lean. Or put in a richer jet and see if the condition happens even sooner in the rpm band.
for weather this cold i would not expect anyone would be running a jet that small. but hey thats the kind of info i was looking for. the problem with reading the plug is that itwould not be accurate at this temperature. the plug could read rich but its not actually running rich as it explains in this article
http://srsengines.com/technical-library/shifter-kart-engines/honda-cr125-cold-weather-jetting
im starting to lean more towards the fuel pumps now, but ill check it all out tomorrow at the track. hopefully its just a matter of changing the main jet or rebuilding the fuel pump.
@[email protected] wrote:My mistake, Derrick, I missed your “no matter what RPM I’m at” quote…. it does sound more like fuel.
We have nothing but great shops in Colorado if you need help.
I never ran a shifter, so no thoughts on jetting.
oh no problem, thanks for the input though!
If you want me to I would be glad to check the main jet I have in this CR125 after running well @ 10,000 ft in freezing temps.
http://i967.photobucket.com/albums/ae157/Freezeman_photos/iceracing054.jpg@Rodney Ebersole wrote:
If you want me to I would be glad to check the main jet I have in this CR125 after running well @ 10,000 ft in freezing temps.
http://i967.photobucket.com/albums/ae157/Freezeman_photos/iceracing054.jpglol yeah id say if it worked in those conditions it will eliminate my question of jetting issue. that would be great if you could check that for me! that way i can be sure whether i need to go richer or leaner and if that still doesnt help then i can point the finger at the pump setup. thanks for the help
hi derrick, not sure what size carb you are running or if you have a pump around system, pull your float bowl off and tell me if you have a float still installed or a sponge like material in place of the float bowl, and check floatbowl needle for wear if applicable, but you are certainly starving for fuel at the upper end. next time you are at the track pull the choke plunger up when it cuts out and see what the engine does that will tell you which way to go on your jetting.
Ken@Ken Arellano wrote:
corection to my post, check to see if there is a float still installed in the float bowl..
kenno, i mentioned towards the end of my first post that it is a pump around system so its just the sponge like material in the bowl. the carb is a mikuni and im pretty sure it is their 38mm carb. i think we’ve narrowed it down to either the main jet or pumps starving it, but heck, if i knew for sure i wouldnt be asking for help lol. thats why im trying to figure out what main jets people are using for similar conditions or colder because if i have similar jets as they do then i know its not a jetting issue and its probably the pump starving the bowl at full throttle.
@[email protected] wrote:
Haven’t karted in a while, and many here are more qualified, but my first thought was magneto.
A bad coil or spark plug could miss-fire at high cylinder pressures when at full throttle. I would not rule out either. Does your rpm gauge still give you a reading when it cuts out?
@Les Prins wrote:
@[email protected] wrote:
Haven’t karted in a while, and many here are more qualified, but my first thought was magneto.
A bad coil or spark plug could miss-fire at high cylinder pressures when at full throttle. I would not rule out either. Does your rpm gauge still give you a reading when it cuts out?
Yeah the rpm still reads even during the cutout.
You more than likely have sludge in the fuel pump, take it apart and clean it and if able orient the pump so the pulse line drains back into the crack case. Pump a rounds require frequent cleaning or the balance between supply and return gets out of whack.
Rick
Sorry for the double clutch post here. Must be a bit rusty?
You more than likely have sludge in the fuel pump, take it apart and clean it and if able orient the pump so the pulse line drains back into the crack case. Pump a rounds require frequent cleaning or the balance between supply and return gets out of whack.
Cr’s are very forgiving as far as the main jet is concerned, you might try to rev it on the stand and in gear to see if it will build rpm’s in a quick and clean manner. If it wont rev or it takes quite a bit to get it cleaned out, you’re probably a little fat.
The range of jets we used on a pwk is 142 to 165 main, the needle however is very critical for transitioning to the WOT circuit. If you find it difficult to deliver a smooth application of throttle through corners, it’s probably your needle selection and / or clip setting. This can really create a hand full to drive.
If you forward me your e-mail address, I’ll send you some (more than you ever bargained for) very useful tuning information to absorb.
Also, if you haven’t gone through and replaced the fuel lines, do so. it is cheap insurance. Take a photo of the plumbing before you disassemble and make sure you route the lines properly.
Cr’s also have an inherent potential for the coil wire to fail or become intermittent, keep an eye on this and possibly upgrade the spade connector to a good quality unit and run your wiring so it has no pretension on it.
As a long shot, make sure there is no obstruction in your pipe, a forgotten rag in the exhaust manifold can be a very frustrating problem to trouble shoot.
Good luck and have fun with it.
Rick
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