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  #1  
Old 02-17-2008, 07:53 AM
EvoFatboy EvoFatboy is offline
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Default Mikuni HSR 42

Hope one of you can help me(at least with my ?) I installed a Mikuni HSR 42 a few weeks ago. The bike runs ok but I have a problem with coughing thru the carb. It happens excessively when it's cold and after it warms up it happens when I gently roll on the throttle. It came with a #25 slow jet and a # 160 main. I installed a 27.5 & 165, adjusted the mixture screw and it helped a little. It still acts as if it's a little lean but my plugs are starting to soot at the base. I also checked for air leaks at the intake and can't find any.

#2- After the bike warms up the throttle return seems sluggish. The CV carb had a crisp return. The cables are not bent tightly or pinched anywhere and I did lube them.

Should have bought an S&S!

Robert
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  #2  
Old 02-17-2008, 12:00 PM
wadejesu wadejesu is offline
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Default RE: Mikuni HSR 42

Lower the needle 1 notch, If that don't work get a smaller needle. JY7
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Old 02-17-2008, 12:08 PM
Greybeard Bob Greybeard Bob is offline
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Default RE: Mikuni HSR 42

Check the accelerator pump delivery so it gives a good shot right off idleand it is aimed down the center of the throat of the carb. Make sure where the pump rod runs thru the casting is free, dab a bit of lightweight grease on there if needed. The manual for those carbs is pretty good about troubleshooting them. One you get the carb set up properly, they run good, I like mine. JMHO, YMMV, etc.

Bob
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Old 02-17-2008, 12:32 PM
FXSTCHEWY FXSTCHEWY is offline
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Default RE: Mikuni HSR 42

I second what Bob says, You want almost no gap on the accel pump.
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Old 02-17-2008, 03:01 PM
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mentor70 mentor70 is offline
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Default RE: Mikuni HSR 42

I want to know more about your bike...
engine displacment, and mods if any...what type of exhaust?

When it pops when cold is the enricher being used?

as for tuning, If it is a stock EVO, I would put a 150 main in it and put the stock pilot jet back in unless you have drag pipes or a large 2 to 2 system.

then leave the needle it came in it, and move the clip down one notch. and try again. This willraise the needlegive more fuel just off idle and enrichin the fuel though the mid range.

My bike is a 95 ci, with cams and head work and a 2 to 1 exhaust, and the bike wants a 150 main and Im using the 25 pilot now, and it is just a tag rich!

your bike may want more fuel, all bikes are a little different, but I think you may be going the wrong way going rich, Ive been though all of this before and I wanted to give it more gas all the time, and I was wrong....ALL the time!

my cables were binging up a bit to after the instal and I had to route them very carfully to keep the thottle working right, your cables may need aditional fineadjustments to keep them from binding, reference you service manual for the proper procedure.
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  #6  
Old 02-17-2008, 08:04 PM
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cruiser85257 cruiser85257 is offline
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Default RE: Mikuni HSR 42

Evo:

The HSR 42 is a beautiful carburetor. You violated the most important rule of tuning your carb. Only make one change at a time, this way you know where to go back to if you have a problem.

Mikuni has a nice tuning manual that comes with the Carb. If you didn't get one, you can download one of their site. It is loaded with good info and can be a great help in tuning.

Don't mess with your needle height, at least not yet in this early stage of tuning.

Accelerator pumps are rarely needed in larger displacement engines. All it will do is make your fuel mileage worse.

You should be looking at two things right now. Your pilot jet size, and air screw setting. Main Jets have zero affect up to the throttle opening that your seeing problems right now. Up to a quarter throttle your running on the Pilot circuit, and air screw setting. If you have to turn your air screw out more than 2 and 1/2 turns your pilot jet is too big. 1 turn out or less and your pilot is too small. Your goal is around 1 1/2 to two turns out.

HSR tuning manual : http://www.mikuni.com/fs-carburetor.html
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Old 02-18-2008, 12:06 PM
Tucker99 Tucker99 is offline
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Default RE: Mikuni HSR 42

I agree with Cruiser. I used mine right out of the box. A comon misconception is that you unscrew the air screw to richen it. That is incorrect. When you loosen the air screw you let in more air hence leaning it.
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Old 02-18-2008, 01:00 PM
Greybeard Bob Greybeard Bob is offline
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Default RE: Mikuni HSR 42

Quote:
ORIGINAL: cruiser85257

Accelerator pumps are rarely needed in larger displacement engines. All it will do is make your fuel mileage worse.
I get 45 - 50 MPG with my Mikuni equipped FXSTS. Good enough for me. Just out of curiosity, what do you consider a "larger displacement" engine? If they weren't needed, why do most carbs of any kind come with them? Although I am sure that your fuelie twinkie runs great without one.........JMHO, YMMV, etc.

Bob
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  #9  
Old 02-18-2008, 04:16 PM
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cruiser85257 cruiser85257 is offline
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Default RE: Mikuni HSR 42

GreyBeard apparently Mikuni has changed their manual. I bought mine back in 1999. They had a side note that said adjusting the accelerator pump on larger engines wasn't necessary. I followed the book and never had mine adjusted. Bike ran just fine. Or should I say my Twinkie ran just fine.

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  #10  
Old 02-23-2008, 07:52 AM
EvoFatboy EvoFatboy is offline
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Default RE: Mikuni HSR 42

My engine is a stock 80" Evo, my current exhaust is 100% Screamin Eagle(headers,mufflers,etc)The enrichener is not on at the time, this popping happens all the time cold or hot. Carb adjustments out of the box were lean. Just got my bike back from the garage(annual inspection)and my mech. had installed a # 30 pilot jet and made some other adjustments, Runs worse! Guess I'll have to go back to square 1.

Robert
Quote:
ORIGINAL: mentor70

I want to know more about your bike...
engine displacment, and mods if any...what type of exhaust?

When it pops when cold is the enricher being used?

as for tuning, If it is a stock EVO, I would put a 150 main in it and put the stock pilot jet back in unless you have drag pipes or a large 2 to 2 system.

then leave the needle it came in it, and move the clip down one notch. and try again. This willraise the needlegive more fuel just off idle and enrichin the fuel though the mid range.

My bike is a 95 ci, with cams and head work and a 2 to 1 exhaust, and the bike wants a 150 main and Im using the 25 pilot now, and it is just a tag rich!

your bike may want more fuel, all bikes are a little different, but I think you may be going the wrong way going rich, Ive been though all of this before and I wanted to give it more gas all the time, and I was wrong....ALL the time!

my cables were binging up a bit to after the instal and I had to route them very carfully to keep the thottle working right, your cables may need aditional fineadjustments to keep them from binding, reference you service manual for the proper procedure.
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Old 02-23-2008, 07:52 AM
 
 
 
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