Help with Mikuni carburetor tuning

[jim_himself]

Well I just finished building my new honda clone. I added and aluminum flywheel, , billet rod, 265m cam and a 22mm mikuni. I finally got around to bolting it up to my doodlebug, and tried to start it, after a little bit of playing with it i was able to have it run, and man was it fast. When I came to a stop, it shut off and wouldn't start again. I then went to my garage and after messing with it for a I was able to get it running again, but as soon as I give it any gas it would shut off. I now cant get it running at all. P.S I am running a 125 main jet. Any and all help is appreciated.

 

[125ccCrazy]

you may need to go up to a 17.5 or a 20 pilot jet.. where is the needle clip? did you swap out the stock clone sparkplug?

 

[roccosbike]

Look at the color of the spark plug...if its black you need a lower number jet if its light colored you need a higher number jet.when its a light brown like coffee with creamer in it...that's what your looking for.

 

[jim_himself]

Well it is pretty black so i need to lean it out. I the only other jet i have is a 95 though. I also switched the sparkplug to a new one. I will look at it again tomorrow and start fiddling with it.

 

[Karterdan]

A good starting point is 12.5 Pilot & 130 Main Jets, that's where we usually ended up with the 22mm Roundslides.

Dan,
GX200 Tuning Store UK

 

[jim_himself]

At the moment the carb has a 125 main jet and whatever the stock pilot jet is. I tried again to start it today and it will only run with the choke on. So I leaned out the mix then it would run well until i gave it throttle then it would die immediately. It is also extremely hard to pull. It will be easy 5 or so times in a row, then it will about rip your arm off. I am not sure what to do. Right now I think I will order several main and pilot jets and start experimenting. I am not sure why it wont work with the current set up since it ran fine at first.:shrug:

 

[TheRealDeal]

just a thought here, but is the fuel clean and are you useing a fuel filter, may just be a dirty jet if it ran fine the first time out

 

[collinsdad]

i would recheck the lashes,as for myself i have had to use a 130 main with a pilot jet 22.5 during some of my testing,my motor has the 22mm mikuni also and was a real pain in the ass to get it jetted right,but like you said you will need a bunch of jets to keep tuning,and one more thing do you have a fuel pump?

 

[jim_himself]

Well I can't get it to run at all today. Gonna try some fresh gas and put in a new fuel filter since I was using an old one. I do not have a fuel pump as the engine is on a mini bike and the tank is above the carb. Gonna order a bunch a jets in a few days, assuming the fresh gas and such doesn't work. I plan on installing a 14cc head I bought for 20$ from a buddy, so I will have the whole thing apart and redo the lashes then. I had set them at .004 intake and exhaust but that may not be ideal.

 

[saychz316]

nothing wrong with an .004 lash. i just like mine a bit tighter. i run with .002" -.003" intake and exhaust. they tend to loosen up a bit on a stock type rocker arm.

make sure you are not hanging a valve open. also, make sure the choke is not on. if this is the case, you will fight forever to make the engine run.

i know this sounds foolish, but make sure the main jet is where it is supposed to be. my friend came to me with a non running motor, and his main jet had rattled out, and was sitting in the bottom of the float bowl.

with a 125 main and a 15 or 17.5 pilot, it should start and idle fine. i am guessing you have the choke on, and are fighting it in opposite directions.

 

[jim_himself]

Well I took apart the cab and took the head off, I am going to install the 14cc head this weekend. I'll make sure I check the choke once I have it all back together:laugh:

 

[graygoose420]

Well I took apart the cab and took the head off, I am going to install the 14cc head this weekend. I'll make sure I check the choke once I have it all back together:laugh:

Remember the choke is on if its in the downward position. One thing to try , cover the opening to the carb and pull the pull start slowly untill your hand gets gas on it. It should start next pull.
Another thing if your motor is yanking the pull start out of your hand the your compression release on the cam is getting stuck.
Let us know how everything turns out.

 

[jim_himself]

Hmmmm the compression release getting stuck... it is a brand new cam. Could the compression release getting stuck be caused by the crankcase being overfilled with oil?
:shrug:

 

[jim_himself]

Put on the new head, set lash, rechecked it after turning the engine over a few times, and still can't get the thing too run at all. :censure: Went through the whole engine, it is getting a spark and everything is rotating smoothly. The carb also has a new issue, whenever I open my fuel valve gas just flows right out the drain hole at the bottom of the carburetor. I may just suck it up and buy a different carburetor at this point, but I would prefer to make this one work

 

[jim_himself]

Still can't make the clone run... guess I am going to have to take the who god darn thing apart again:censure: I put the stock carb on just for kicks to see if it would even start but no dice. It is getting spark, gas is going through, and it has plenty of compression. I have no idea what is wrong with it at this point...

 

[mmisterbungl]

have you taken the flywheel off to see if you might have sheared the flywheel key? if your timing has slipped, you'll never get the thing started/running correctly.

 

[jim_himself]

I hadn't thought of that. I feel like there is no way it would have started in the first place if that was the issue, but I may as well check it out when I take the thing apart again.

 

[mmisterbungl]

I hadn't thought of that. I feel like there is no way it would have started in the first place if that was the issue, but I may as well check it out when I take the thing apart again.

You'd be surprised. All it takes is one good kickback or backfire and the key will go bye-bye. It's happened to me a few times and it was always the last thing I wanted to check. I run all my flywheels now without keys on built hondas/clones. I just lap it and tighten the balls out of it.

 

[collinsdad]

this sounds juse like the problem i had when i did my build on my sons motor,although my motor wouls start it would not rev up,i went nuts with the carb and thought for sure that it was the problem,went through the same crap you did,in the end the coil was the problem,had spark but it was not hot enough?????that solved my problem if its any help:shrug:

 

[jim_himself]

I will take the motor apart again this weekend and check the key. I wonder if I set the gap between the flywheel and the coil incorrectly. I believe I set it to .015.