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although this thread has gone off on a tangent i figured i would post the resolution in case anyone else searches about the same problem lol
well i finally figured it out this weekend… it was the simplest mistake in the world. Mikuni jets are on a different scale…everyone that i was asking for help had a keihin carb, so people were telling me jet sizes like 165-175 depending on the weather is what works for them so thats what i should run. i would tell them that i have a mikuni carb but most people dont know much about them, so nobody told me that keihin jets are waaaay bigger than mikuni jets. a keihin 168 main jet is huuuge compared to a mikuni 168. so i eyeballed it and made a guess. i put a 360 main in it and it ran great. 100% throttle pulls like crazy now so i must be in the ballpark, now i just need to find the range so i can compensate for weather. got my times from 58’s to 54’s this weekend too 🙂 getting there ! ill post some video from this weekend later tonight. BTW Ken thanks for all the help this weekend. i had an awesome time finally getting to ride up against Chris and his Kart. looking forward to getting back out there next weekend.hopefully i wont be going off that much more lol, but yes im playing around with limits of the current tires and setup so inevitably im going to end up in the dirt from time to time 🙂 what better time to make my mistakes than when we have the track to ourselves and there is no grass to ruin when i go off track lol.
Yeah the video exposed lots of stuff for my driving and my girlfriends driving lol. Just seems so much different while you are actually out there. I won’t be riding without it anymore 🙂
Yeah thanks Ken and everyone else for the help. Chris and I got it running much much better after making small adjustments in the right direction. I have a good starting point now, so I should be able to make small changes with the weather from here on out to keep it running well. Plenty of work to be done in the alignment, tire pressure, and driving department…. Especially in the driving department. Here is a quick and crappy iPhone quality video of the first lap I was able to do at a decent pace after we got it working.
http://www.youtube.com/watch?v=lyyWalZYuwY&feature=youtube_gdata_player
now cut me some slack. There are a lot of areas of improvement but I’ll dial it in by this summer for sure. What times should I be shooting for in this kind of kart?@Ken Arellano wrote:
Like I said, when you are at the track and you are on the the back stretch pull your choke lever up when it cuts out that alone will give you good info and dont change the plug gap they are pre gaped, very unlikely it is the coil, you are starving for fuel. Cold temps = rich jets warm temps = lean, the weather is looking better for sunday testing, start with a 170 main high temp for sunday is 41. If it were the coil it would cut out all over the rpm range.
P.S. I’m the guy that got your mychron to work
Yeah chris told me you were going to reply. Thanks again for giving the micron your magic touch btw! I’ll give that a try on the back stretch today. Two weeks ago I knew absolutely nothing about carbs or two stoke operation. I feel a lot more comfortable now about how it all needs to work that Ill be able to solvethe problem today. I’ll let ya know. I’ll check on that cdi to could distance too.
Thanks a ton for the input. Reving it on the stand it’s almost as if there is no problem. It revs normally even at full throttle. It’s only when load is applied like when I’m actually driving it on the track that it acts up at full throttle. I’ll give the pump a look tomorrow. I’m going to go ahead and rebuild it anyway just to get it out of the way. It must ne the fuel pump because I tried a number of jets fom 150 to 180 and the problem was consistant so if you guys use 140-160 during the warmer months then one of those many jets should have cleared the problem up if that were the problem. I’ll pm you my email for that info, thanks again for the help. Hopefully I will have good mews to post tomorrow when everything works well 🙂
@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.
@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.
@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
@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!
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.
