I put this on my EVO Fatboy and according to the instructions the factory setup would be close if not right on for a factory/slightly modified engine. Had trouble starting the 1st time, now it is ok. Problem is keeping it running. Using the choke produces a nice even tone that gets faster as it warms but if I release the choke it dies. Turned the idle screw in and it helped but it is a rough idle. When running down the road it performs well as long as it's pulling. Normal acceleration causes it to pop, backfire, and carry-on out the carb. Also can any of this be caused by cables not set up correctly. I'm having trouble getting them where they should be. Doesn't want to return to zero quickly, let off the throttle and it hangs and then drops slowly. HELP PLEASE!
You are too lean. Most likely due to an air leak at the carb or manifold.
If that is not the problem you will need to increase the low speed jet or raise the needle. If you have an air leak you can find it by spraying wd40 around the joint and listen for the engine to smooth ou t for a few seconds.
Mik's are my favorite and will be yours after you get it dialed in..
They usually come with a 25 low-spd jet and a 97 needle installed.. If they included a 27.5 low-spd, try it.. Remember all motors are diff so do not hesitate to even try a 30.. I run a 30 in the 93" and the 80"..
The 97 needle is prob correct, heck I run a 97 in the 120".. However as wright said you may have to raise it..
All this of course after you eliminate intake leaks..
The cables are a diff prob that you must figure out..
__________________ "Fill your hands you son of a bitch"
Rooster Cogburn
I don't have any air leaks so I ordered some jets for it. Do I need a new bowl gasket each time I open it? Also ordered an adaptor for the Arlen Ness Big Sucker. The kit came with a cleaner for an Evo but it doesnt fit correctly. Can't attach the breather tubes correctly.
Hey Fatboy (no offense, couldn't help myself)
No you don't have to change the bowl gasket unless you somehow destroy it..
I've had both the top cover and bowls off my 3 Miks Lotsa times with no probs..
Tipper,,,, First off, you prob never get in the main cuz remember the Mik is a throttle position carb NOT an RPM carb for jetting-- and the main is NOT used till you are over 3/4 turn with the throttle.. Soo, just regular rolling you're prob NEVER in the main.. Did you do the tape marking on the throttle grip.? It works..
Do you have the directions with that 42.? They will tell you what you need to do.. All I would tell you is exactly what the directions say.. If you don't I'll be happy to send you some, or better yet just call Mik of USA, they'll send em..
I forgot what your sickle is----- 80" EVO or 88" TC---- stock.??????
I would GUESS that you might want a 20 and possibly move the needle DOWN, i.e. put the needle in the TOP slot.. Make one change at a time,, I would do the needle first.. Perhaps you need a 98 needle but man, that's the leanest so I wouldn't think so..
These have become my absolutely fav carbs but the operator must do a little work to get it right..
__________________ "Fill your hands you son of a bitch"
Rooster Cogburn
Hey Fatboy (no offense, couldn't help myself)
No you don't have to change the bowl gasket unless you somehow destroy it..
I've had both the top cover and bowls off my 3 Miks Lotsa times with no probs..
Tipper,,,, First off, you prob never get in the main cuz remember the Mik is a throttle position carb NOT an RPM carb for jetting-- and the main is NOT used till you are over 3/4 turn with the throttle.. Soo, just regular rolling you're prob NEVER in the main.. Did you do the tape marking on the throttle grip.? It works..
Do you have the directions with that 42.? They will tell you what you need to do.. All I would tell you is exactly what the directions say.. If you don't I'll be happy to send you some, or better yet just call Mik of USA, they'll send em..
I forgot what your sickle is----- 80" EVO or 88" TC---- stock.??????
I would GUESS that you might want a 20 and possibly move the needle DOWN, i.e. put the needle in the TOP slot.. Make one change at a time,, I would do the needle first.. Perhaps you need a 98 needle but man, that's the leanest so I wouldn't think so..
These have become my absolutely fav carbs but the operator must do a little work to get it right..
None taken, in fact I could probably stand to lose 50 or so. Figured I'd wait until all the modifications are done to the bike in case I need it to keep the front wheel on the ground. Now for the technical side, I also am experiancing terrible mileage, around 30mpg, was getting 45-50 with the CV. SHould I make adjustments to the needle first before putting in the slow jet you recommended? I am taping the throttle this weekend and trying that 1st, JP has yet to send my jets! Does the mixture screw adjust the same as the CV?
Hey Fat,,,, good one- keep the wheel on the ground..
I'm still guessing that you have a lean condition with that popping etc., but if you're also running bad mileage--- there's a confusion..!
OK, try this, since you have not said what intermediate(slow jet) is installed, I'll guess it's the stock 25.. Install a 30.. It might be too rich on the bottom but let's try to eliminate that popping and b'firin first.. Try a 27.5 later,, if it starts popping and such again you can always re-install the 30..
I've found the slow jet doesn't affect my mileage.. I run a 30 in the 45's on both the 93" and 80".. A 32.5 in the 120"s 48.. I like it a bit rich off idle..
BTW, I get 41mpg in the 120" and over 45mpg each with the 93" and 80".. That's half hiway and half city..
Take off the top cover as per the instructions and with a 2.5mm allen LOOSEN, do not remove, the allen screw that holds down the needle and pull it out with tweezers.. Careful, don't lose the nylon washer beneath the needle.. Move the needle clip to the top notch, that'll lean out cruising but be made up for with the 30's fatness.. I'm guessing it's a 97 needle..
As you run with the taped throttle you'll see where you need to fine tune the needle notch.. Remember you're in the needle till 3/4 throttle.. It takes a little work but you'll be glad you did it.. Remember to take up any throttle cable slack when you mark your throttle and barrel tapes.. The instructions are very clear and understandable.. They want you a little lean for political correctness---but You want it to run and start like a champ so if you do what you think it needs you might be richer than the instructions will lead you to believe.. The mixture screw SCREWS IN to fatten.. Gently screw in to bottom the mixture screw then screw out about 1.25 turns.. I bet a dime to a doughnut (you know how much I like doughnuts) that'll get you real close with a 30.. I am only Guessing cuz I'm not there so fill me in..
Love it when a guy does his own stuff-- Yeah Baby..
PS-- After you get it to run good you may have to make LEAN changes if you gotta go through annual emmisions tests,, once you pass,, change back..
__________________ "Fill your hands you son of a bitch"
Rooster Cogburn
Mikuni HSR-42 
Another Mikuni question 
Linear Mode
