I have a problem with my Mikuni HSR42 spraying fuel back out into the air filter when the throttle is cracked and during acceleration. Any thought on how toi correct?

 

Sounds as if the accelerator jet is misaligned or has trash blocking it? The instances which you describe are both times when the accelerator jet would be spraying fuel into the carb. If it was misaligned or blocked it might cause fuel to spray backwards, i.e., towards the air cleaner. I may be off-base here, but that's my first thought...

 

Where's Doc's fuel standoff thread??????

 

Why is there fuel coming out my air filter? by Doc
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its called fuel stand off....and it gets little specks of oil all over the bike plus fuel drips out of the air cleaner.

"FUEL STAND OFF'....this is a characteristic of a internal combustion engine with a carb on it. It has nothing to do with your jetting or acceleration pump intake leaks or timing......it's a pulse wave that happens when a column of air(intake) traveling at 650 feet per second into a cylinder THEN the valve closes on this column of air. The column of air with a charge of fuel in it just doesn't stop, (who was it that said for every action there is a reaction?) any way when the valve closes the charged column of air traveling at a speed of 650 fts bounces off that valve and makes it's way to the other head where it bounces off that closed valve and the column makes it's way out through the carb....now here is where this gets interesting...the carb isn't too smart, It doesn't realize which way the air is traveling so as it goes over the venture it picks up more fuel in the column of air that already had a charge of fuel in it....when the column of charged air hits the atmosphere it's like hitting a brick wall so the air is reflected back into the engine as a little weaker pulse wave but since the fuel is much heavier than air the fuel continues out into the atmosphere soaking your air filter and the whole right side of the bike depending on how long you have the bike under a load at high throttle positions.
To witness this you can take off your air filter and do a few runs on the dyno and watch this STAND OFF happen before your eyes....a plumb of fuel will hover out side the mouth of the carb up to 8' away depending on the displacement of the engine, cam overlap, and exhaust system used.
Now when you take the time to set up 'Intake Track Tuning' this waisted gas can actually be pulled back into the engine and used instead of washing your air filter. Intake Track Tuning is using the pulse waves of the intake to assist in cylinder fill by timing the wave to hit the intake valve as it is starting to open.....these are the things you do on motors that need the the EDGE to be a winner.

Hope this helped you to understand whats going on with your bike, you don't see or smell this gas on a bike with a stock air filter because it's all tightly sealed, nor will you see STAND OFF in a EFI bike because there is no fuel to pick up on the way out.
If you continue to have a problem with the fuel on your bike and/or clothes take one of your wife's (or girl friends), light day pads and place it in the bottom of the football A/C cover....this will absorb all the fuel and oil from the breather, the fuel will evaporate and the oil will be trapped in the pad. Now one more piece of advice...........................change out the panty shield every 28 days.

Go on and laugh but this really works....don't use the pant shields with the WINGS.... the wing will stick out the cover and drip on the engine.

I got to take a nap now....but first here is how you figuer out intake tuning for those of you who have inquiring minds.

Intake track tuning is done by lengthening the distance from the middle of the intake valve to the atomosphere....ie if you add a 5 or 6' velocity stack to the end of your carb that would be extending your intake track. The intake track on My Pro Modified Drag Bike is 19 3/4' long, a stock [URL=http://www.*****************/f

 

If that doesnt answer your question i dont know what will...

Doc......you-da-man!!!!!

 

Well, like I said... I may have been a little off base... [&:]

 

Doc,

I have a 2004 EFI Road King. I cleaned my air filter last night and there was a light film of what looked like oil (??) all over the inside of the filter. I pulled off the back plate and there was a coating of oil all over everything stuffed behind there, too. I checked the breather tubes and they are not cracked or damaged. The throttle body looks nice and sealed, too. What might be going on here? Thanks.

 

Thanks Doc, You took the words right out of my mouth......Yeah.......Bldr

 

The oil is coming from the crank case breathers...there is always a fine mist going on there but if you ride the bike hard the oil will be more evident....if the oil is getting all over your bike, from the breathers, it's called 'oil carry over' and it needs to be addressed.

OIL CARRY OVER:

Oil pump alignment is aligning the oil pump with the ports in the cam plate. Its done with installing two tapered threaded pins in hole #1 and #2 in the cam plate while rotating the engine. If the pump isn't aligned it damages the pump body and the oil pump is no longer efficent. Now when you ride hard (80 mph) for40 min or so the cam chest fills up with oil because the pump can't pump it out fast enough so the oil is forced up the push rod tubes by the crank case pressure (from the pistons on the down stroke) filling the rocker boxes with oil and out the breather it comes as 'oil carry over'
A new way oil pumps are getting damaged causing Oil Carry Over is from flywheel shifting on the 07 and up bikes.

 

I have a problem with my Mikuni HSR42 spraying fuel back out into the air filter when the throttle is cracked and during acceleration. Any thought on how toi correct?

You did not explain your set up so I'll tell you about mine with the same problem andthe fix. This was on a1997 FLHR Road King (EVO) with a Mikuni HSR 42, Andrews EV-46 cam, Jim’s lifters, etc...PlusPorker slip-on pipes NOT BAFFLED. When riding hard and alwayswhen the air got thinner (high altitudes) I would get gas spray-back into the air filter. This would eventually soak the filter and the filter oil which then would get the right sidecover & saddlebag buggered. This was not anoil blow-by/crankcase breather system problem.

The fix: I baffled the pipes and did a re-tune on the Mikuni. Note: minor adjustment on the main jetting only: Jet Needle, Pilot Jetand Accelerator pump nozzles are stnd.;Main Jet:162.5 The problem went away. I also talked to the Mikuni Rep at a bike show and he confirmed the problem/solution.

I hope this helps but thereare so many "problems"/set-ups so to find your solutiontakes troubleshooting, trial-errorand doing your homework - like reading this forum.Hey, thanks to the folks that started this one!

- Jim


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