Mikuni lean out of box?

[Kags]

Apearenty the HSR 42 is too lean for my build out of the box. I was almost sure these carbs tend to be on the rich side for most 95"? I need to get the motor broke in for the main but would you change the main or the needle to make it through the brake in? To recap my build KB-10.5:1, S&S 585 cams, 2>1 exhaust, S/E race igition.

Its running hot and the plugs are now lean. I doubble check & no air leaks.

[HDWRENCH]

I would try needle as you are not going to be really getting on the main for break in. If you cannot get enough fuel bump the main and return needle to stock postion. The Mik has a great booklet that comes with the carb and it is online as a down load.

[kgoose]

Originally Posted by Kags

Apearenty the HSR 42 is too lean for my build out of the box. I was almost sure these carbs tend to be on the rich side for most 95"? I need to get the motor broke in for the main but would you change the main or the needle to make it through the brake in? To recap my build KB-10.5:1, S&S 585 cams, 2>1 exhaust, S/E race igition.

Its running hot and the plugs are now lean. I doubble check & no air leaks.

As mentioned, Mikuni has a very good tuning booklet. If you did not get one with the carb, you can download from there site.

If you are not using a one range cooler plug, I would go that route before you start to re-jet.

You can get one range cooler champion and autolite plugs at most auto parts dealers. I get mine from advance auto.

Champion - RA6HC
Autolite - 4163

If the bike is detonating try plugs first. If this does not help then your timing & advance slope will need to be adjusted. No reason to waste gas to cover up the possible real problem.

My 95TC had a compression ratio of 11:1. Carb jetting (mikuni45) was 97 needle, 165 main, 25 pilot, 60 exc pump.

Even with the cooler range plugs, I had to have a custom ign map made to control detonation. I used a Zippers ign module (DTT private label) so Zippers made me a custom map for free. Solved the detonation problem. Not sure if they do that anymore.

Good luck

[Kags]

kgoose, I am running the 10 deg retard S/E race ignition and I was getting mild ping under light throttle with colder plugs. Mikuni's book said to change needle so I did. The bike is now running cooler. Pinging has stoped. Its now set up on the rich side I think so I feel good knowing its no longer running very hot. It now just a little hotter than it was with the 10.25:1 S/E pistons. Intill I get it broke in I will stay with the 165 main 96 needle and the 25 pilot air screw 2 turns. With the smaller needle I think I will be able to go with the 20 pilot, time will tell. Even under light throttle the bike is running very strong .Thanks for the input guys.

[kgoose]

Originally Posted by Kags

kgoose, I am running the 10 deg retard S/E race ignition and I was getting mild ping under light throttle with colder plugs. Mikuni's book said to change needle so I did. The bike is now running cooler. Pinging has stoped. Its now set up on the rich side I think so I feel good knowing its no longer running very hot. It now just a little hotter than it was with the 10.25:1 S/E pistons. Intill I get it broke in I will stay with the 165 main 96 needle and the 25 pilot air screw 2 turns. With the smaller needle I think I will be able to go with the 20 pilot, time will tell. Even under light throttle the bike is running very strong .Thanks for the input guys.

Kags, I am glad that worked for you. On only one occasion did I have to richen the jet needle on a Mikuni. Thats was on a 97 EVO I had. On my wifes stock 88TC Fatboy I had to but in a leaner needle 98 because it was running to rich. Run the stock 97 needle in the Mikuni 45 I use with my 107TC.

As they say, each bike is diff.

[AustinFXDWG]

That's pretty unusual. More typical is that it is a bit on the rich side down low, and maybe a tad lean on the main jet. Did you relieve the cylinder fins adjacent to the seam on the float bowl so the carb can seat fully into the intake manifold? that is something often overlooked which will cause an overlean condition. You need to carve out the corners of a single fin on each cylinder so the carb will go all the way into the intake.

[Kags]

Originally Posted by AustinFXDWG

That's pretty unusual. More typical is that it is a bit on the rich side down low, and maybe a tad lean on the main jet. Did you relieve the cylinder fins adjacent to the seam on the float bowl so the carb can seat fully into the intake manifold? that is something often overlooked which will cause an overlean condition. You need to carve out the corners of a single fin on each cylinder so the carb will go all the way into the intake.

Not only did I notch for the bowl, I notch so I could get a screwdrive in there. Thats 3 fins down, 2ed fin down 1/2 the size of the bowl notch 3rd fin 1/2 the 2ed.