Mikuni Carb question about tuning

[mrsg]

Well last night i installed my performance cf muffler and my flat slide mikuni 28mm carb. I fired it up and it sound great!!!
Problem is i am getting smoke out the muffler. I tried adjusting the idle speed screw(green arrow from picture) got the idle where i want it. Then i tried adjusting the Red arrow screw, which i thought it was the air mixture screw. I am still getting smoke. The jets i use was 35 pilot and 120 main i think(ya i never wrote it down so now i am tearing it apart tonight to figure out what i have).
My thoughts for the smoke are, new exhaust might smoke a bit till it burning off what ever it is burning off(might be totally wrong on that one)

Other though is i am too rich or lean.
I been reading up and not really finding information to explain it. What are signs of rich and lean. If i have smoke is it rich/lean?
If i am rich, Adjust air mixture screw? If i am still smoking change jet size up or down?
I have read you adjust needle for bogging issue up or down. They say needle is for throttle levels from 25%-75%.

Yes i know very little about carbs. I am willing to learn and have fun while doing it. If anyone could help me out explaining it great. If you do not want to type it out to me PM your number and i will call you!

On the bright side i love how it is sounding and when i get my pannels back from the paint shop i will be test riding it!!!




Thanks once again for all your help!

Ray

[mrsg]

Thanks for the info.
The smoke is more white or grayish smoke.
Ya i need to put in my stock plug for this instead of iridium.

Thanks
Ray

[mrsg]

www.mikuni.com/pdf/vmmanual.pdf

Is the best write up i have found. For who ever bought one.
Before you buy one i would read this thread
www.kiwibiker.co.nz/forums/showthread.php?t=65422

I just prey i can fine tune mine enough to go from idle to wot with no bogging but does no look like i will be able too.

From the first link i think it might be running too rich, that would be the excessive gasses coming from the exhaust.

Thanks
Ray

[Rocketdog]

Good luck with your tuning MRSG. A Mikuni flatside can be tuned to work and work well within certain parameters, Temp, Elevation, Humidity, and such. However if your in an area of the country where the temperature varies, like here in Tennessee 95-25, you might want to rejet for winter and summer. The flatsides with the accelerator pump works better in my opinion. Don't get discouraged. Change one thing at a time and see how it runs. Start with the main jet at WOT, high rpm, and work your way down the idle Circuit. We will all help as much as we can.

[Rebel]

Daddy always told me that white/blue smoke was oil (also could be coolant on a water cooled motor), black smoke was gas. so I guess that would mean your smoke is most probably from the oil used to prevent rust during shipping, it should clear up, if not, more work ahead.

[mrsg]

K, the smoke is gone, had 130 jet in it and changed it to 110. When i give it throttle it cuts out.
Have to tinker with it some but ran into a new problem, my regulator is gone again. What a pos mr.gasket regulator. I think i am going to byte the bullet on it and go back to my vacuum fuel pump.
I tried running it with no regulator, gas coming out every hose lol and flooded engine.

Does anyone know max amount of fuel for these mikuni's? Like if i bought Mikuni Fuel Pump #DF44-211-D with the 14 LPH flow rate be the right amount?

I will be using stock petcock but want something better. Only problem going back to the vacuum pump is i only have one vacuum line from the intake so i will have to use a splitter, which i wanted to avoid. The other line goes to the canister i think for emissions. I think i can just kink the hose going to the valve cover and get rid of the rest?

Only other problem i am getting now is a back fire. Not all the time and wonder if it is because of fuel/carb. I will get a gasket made up for it, and hope it fixes it. I bought a performance muffler where you connect the pipe to the muffler with a spring. I did not weld the 2 pieces together. Maybe i will have to do this.

Thanks for all the help.

Ray

PS
Yes JR you are right again, go back to the vacuum pump!!!

[mrsg]

Well Jr i went back to the factory petcock for now and put back on the emission with a "y" connector. Still running way too rich on a 110 so i will be buying a 100. Almost thinking of buying a 90. But if the 100 is too rich i will be soldering them and making them smaller. Now i have a 35 pilot, could this be causing it to be too rich? My understanding is 35 pilot was for acceleration or higher speeds, but more i read on carbs it sounds like it is for idling.
Once i had the petcock on it i have had no back fires. I am wondering can u do serious damage with running rich?
Hope not but will up date progress tomorrow.
If i had to do it all over again i would of stayed with or got a high performance cv carb. Best part is cv carbs are way cheaper too.

One thing i have noticed, sounds like i have a ton of power with my bike. I am in wow mode right now with the flat side set up and high performance exhaust. My neighbour asked me if i bought a harley lol.

Thanks for all the useful help JR and everyone.

Ray

[mrsg]

k i will try moving the needle tomorrow and if i am still smoking i think i will move from a 35 to next size down. If it is rich then moving up would make it more rich right? so moving down would lean it out some?
I though the same as you with the 110, but though well different type. I be ordering drill bits so i can do my own, get expensive fast buying them.
Ray

[mrsg]

Well the battle is still rich
I am using a 32.5 pilot and 100 main jet and black smoke still, when reving the engine. I have smoke at idle but not really black more grayish.
With the 32.5 and 110 in it i had fire shooting out the tail pipe so i think something is up.
I am going to drill smaller jets to try out and see if i keep blowing out smoke.
Right now i am even considering putting the old carb on and save this for a winter project.

I think i am going to try smaller pilot and jets. The smaller the number more fuel efficient i think. So maybe this is a good thing i am doing.
I also keep polishing my spark plug from soot.

Any ideas feel free to share i am all game!

Ray

[mrsg]

K i decided to put in the original pilot. No more idle smoke!!! Sweet!!! I think i would have to be on the lean side now with it, but very happy to see no smoke at idle. I still have smoke when i rev then engine so tomorrow project is to figure out what number bit i need to make a 90 main and 80 main.
Thanks for all your help guys. I have learned quite a bit tinkering with the carb and would recommend everyone have to go through this pain in the ass once.

One of my mistakes is i changed it all at once- performance exhaust, 30mm metal intake, carb, and air intake.

I also moved the needle to the bottom (closest to bottom of carb not top)
I just can not understand why i have to go with so small pilots/main then everyone else. i hear everyone going to 37/120 but i am going in opposite direction.

Thanks
Ray

[xs650]

Jul 10, 2009 20:04:18 GMT -5 mrsg said:

One of my mistakes is i changed it all at once- performance exhaust, 30mm metal intake, carb, and air intake.



Thanks
Ray

That is definitely not a mistake. You have a well balanced combinatiojn of parts and will only have to tune it once this way.

[mrsg]

Well getting better 90 main still has smoke. Going to try 85!!

WoW!!!!!
I had a bit of a break through. I am using a mikuni 15 pilot. I was going to test and see how high i can bring my pilot so i grabbed my 32.5 mikuni jet and started seeing what number bits it would go over.
It went over #75 drill bit therefore = 0. 5334mm!!! I was in shock, i though it was .325mm but it was not. I did the same for the 15 pilot i have in it right now and it comes out as a 79=0.3683mm=37 pilot. So i think the mikuni 15 is the right size for my bike, no smoke but i though since it was so small must be lean now, which i think is not the case from the measurements.
Maybe i am doing it wrong but to me it make sense now why i was so rich. I think the B&M is selling me oem ones, they do not have the mikuni symbol on them, but swear they are mikuni jets(they do fit and look 100% the same though and the 15 pilot is mikuni)

I will keep you posted

Ray

[mrsg]

K i have no more smoke!!!
I went with a #67=81mm main jet and a #79=37 pilot

New problem, back fires, Waiting for bike to cool going to pull muffler and use the gasket maker high heat on it and put it back on. I think the exhaust from ebay was not so great. The end was not completely flat so i might have to replace the end, if a gasket does not work.

Ray

[usfmarine]

Ray,

I use a 3.5psi electric Facet fuel pump with no regulator. The mr. gasket fuel pressure regulator was nothing but a pain for me. I removed it on a lark, just to see what would happen. What happened was 100% reliability and zero issues. The Mikuni flatslides can handle quite a bit of fuel pressure. Remember, they are usually used on applications with a lot more fuel flow! Of course a variety of vacuum fuel pumps could work too.

It's interesting how different your jetting is from mine. I have a pretty much wide open exhaust and UNI sock intake. Main jet is a 125, pilot 35.

Once dialed in, I have not had to rejet once. From 30 degrees to about 95 degrees. I'm glad you've experienced the flatslide throttle, aint it fun! Much different from grandma's CV

Keep us posted on your progress. Here's a little tuning diagram I try to post whenever possible.

[mrsg]

I live on the Great lakes. About 100m-200m above sea level max. Humidity here here is unreal. Taxes in the 120 heat would feel like a relief where i live!

Well i just put high heat gasket maker on and waiting for it to dry. So tomorrow i will give it a try and prey no back fire!!

Keep you updated then!

Ray