I'm having some issues with my Mikuni hsr42 and need some advice from the mikuni guys out there. My bike is a 98 FXDL stage 2 done by Hillside. 10 to 1, W8, stage 2 head porting, S&S pushrods and lifters, Dyna 2000 ign module with the voes on curve 3 (seems to run better with the voes, less pinging with premium gas) and timing set according to the dyna instructions, RB racing prostock 2-1 pipe with the baffle they provided. Iv'e been using a wego 3 and got the afr in the high 13's to the low 14's, jetting is 25 pilot, 97 needle in the middle and a 170 main. Its starts, warms up and runs pretty good except I have a stumble or a breaking up, if thats what you want to call it, if I'm going along, say about 60 (3000 rpm in 4th gear) and whack the throttle open then it cleans up and runs good. The air screw is adjusted so idle afr is 14-ish. I'm getting probably 40-42 mpg and the plugs look good. The accelerator pump is set to about a 1/16 gap at closed throttle and stops pumping at 3/4, it is the stock nozzle, 70 I believe. I was real close to replacing the mikuni with a super e but I have too much $$ into it to start over carb-wise. The decel popping is all but gone, very slight. This stumble or break up is the only thing that got me scratching my head. I had it dynoed back in November and got 87 hp 85 tq and the on the printout showed 14's and 15's which I think is too lean for this build, thats when I decided I'm going to do this myself and I think ?? I'm going in the right direction with it, I hope. I just can't seem to get rid of this stumble. The accelerator pump is the only thing I can think of, or maybe timing? BTW I did try a timing light with the clear timing plug and couldn't see a thing. I almost forgot to mention that I have and S&S air cleaner with the breather going external, It seems that one works the best. Once again I come before with a problem to be solved. Thanks again and the help is very appreciated.

 

What's the WOT a/f ratio? You might want to drop the nozzle on the pump to a 50 and take out the 1/16 gap. What's the needle position set at?

 

I've found it very helpful to put some white paint on the dot so that it is easier to see when setting timing.

I suggest you put some white paint on the dot and make sure your timing is set correctly before going any further with the carb.

 

I have a Mikuni but am not the Mikuni guy, have referred to this tuning sheet that might help you. If not, at least your back at the top of the page.
Good luck chasing this demon

 

Can't help you with the carb but the timing I can. Get neon paint. Follow the manual as far as which dots and RPMs as that effects the curve and voes. Rotate the engine using the back wheel in 5th off the ground until you see the dot and clean it with a qtip dipped in cleaner then let it dry and use another qtip to mark the dot with the neon paint. Then get a dual back light and with the bike running at the check rpm you can slowly dial the light until you see the dot. You'll see the tdc dot and the light setting dial should then correspond to what your timing is set at. So you can use a sis back light and the tdc mark or whatever the manual says and set the light to zero. I found it easier to dial the light to find the dot

 

Just make sure it's a bright colored neon!!!!

 

Ok the answers to your questions, the needle is in the middle notch, WO afr is in the high 13's, the timing was set on 0 tdc with the led as per the dyna instructions. My factory manual states to use the line on the flywheel for timing, should I be using the dot for a 98 evo?. Kp877 could you give a rundown on you use of the timing light. Thanks.

 

The line is for TDC of the front cylinder.
You should be using the single dot for your timing.

 

Give me a few minutes. I'll get details

 

No.... Set the tdc on the line for adjusting the Dyna ignition on the front cylinder. Turn the ignition module till the light just goes out and lock it down your done with that......

I don't have a mik but does the accelerator pump work the same as the S&S. If not i don't think there should be a gap......