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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #1  
Old 15th December 2006
Tommy_Gunn's Avatar
Tommy_Gunn Tommy_Gunn is offline
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Default Fuel / oil spit back help

Hey Guys,

Hope this hasn't been covered somewhere else on the forum at length, but couldn't find it.

Ok, I've had sportys before and oil has been known to blow back through the air filter filter or pipe dependant on the breather setup.

On my 06MY 883L I have the S&S Quick Set-up that has a long pipe that guides any oil expelled through the breather safely away from the bike.

I was therefore shocked when I started seeing the tell-tale signs of oil 'droplets' on the outside of my oil tank and drops on the case.

I have since realised that the substance is not infact oil but fuel !

I realised this when I took off the air filter cover and it was dripping in stinking fuel.

I assume the carb must be spitting back or something?

Any ideas what could be wrong?

Cheers

TG
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  #2  
Old 15th December 2006
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Tommy_Gunn Tommy_Gunn is offline
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Out of interest the problem seems to be similar to that described by BASSBOY311 when he had his special HD air cleaner cover on with his Big Sucker -

http://xlforum.net/vbportal/forums/s...t=41408&page=2
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  #3  
Old 15th December 2006
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Quote:
Originally Posted by Tommy_Gunn
Hey Guys,

Hope this hasn't been covered somewhere else on the forum at length, but couldn't find it.

Ok, I've had sportys before and oil has been known to blow back through the air filter filter or pipe dependant on the breather setup.

On my 06MY 883L I have the S&S Quick Set-up that has a long pipe that guides any oil expelled through the breather safely away from the bike.

I was therefore shocked when I started seeing the tell-tale signs of oil 'droplets' on the outside of my oil tank and drops on the case.

I have since realised that the substance is not infact oil but fuel !

I realised this when I took off the air filter cover and it was dripping in stinking fuel.

I assume the carb must be spitting back or something?

Any ideas what could be wrong?

Cheers

TG
What exhaust are you running?
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  #4  
Old 15th December 2006
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Tommy_Gunn Tommy_Gunn is offline
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Quote:
Originally Posted by cantolina
What exhaust are you running?
Hey Cantolina,

S&S Slip-Fits - They come standard as part of the S&S Quick Setup kit.

Cheers

TG

Last edited by Tommy_Gunn; 15th December 2006 at 18:21..
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  #5  
Old 15th December 2006
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Quote:
Originally Posted by cantolina
What exhaust are you running?

are you thinking reversion
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  #6  
Old 15th December 2006
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Tommy_Gunn Tommy_Gunn is offline
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Quote:
Originally Posted by grizz420
are you thinking reversion
So what's reversion then Grizz420?

TG
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  #7  
Old 16th December 2006
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Quote:
Originally Posted by grizz420
are you thinking reversion
I was, but I don't know d**k about that S&S setup, so I can't comment....
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  #8  
Old 16th December 2006
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Quote:
Originally Posted by Tommy_Gunn
I realised this when I took off the air filter cover and it was dripping in stinking fuel.

I assume the carb must be spitting back or something?

Any ideas what could be wrong?
Yes, it's reversion. Reversion occurs on every motor, but with a stock air cleaner your don't see it since the fuel/oil is contained in the air cleaner assembly by the stock backing plate. When you open up the air cleaner, you open yourself up to seeing the fuel/oil mess. You took care of the oil by routing that separately. Now you are seeing fuel (which is probably mixed with air filter oil) blowing out of the carb. Also, this is more apparent with oiled air filters than dry paper filters, since the gas washes the oil out. On a dry filter, the gas just saturates the filter for a while, until it's supersaturated.

When I say it happens on every bike, I mean it CAN happen on every bike. At some RPM, the length of the intake track (not normally changed on an XL, so that's pretty constant except for air cleaner configuration) the timing of the cams, the type of exhaust and the RPM you are riding at all conspire to blow the intake charge back out of the carb. On some bikes it's not visible because you never ride in that RPM range for it to be a problem.

There is an exhaust wave that heads out of the engine via the exhaust valve, gets to the end of the exhaust pipe (or some point in your specific exhaust system) then heads back toward the cylinder. Based on the timing of the close of the exhaust valve, at some RPM, the exhaust wave is going to arrive at just the right time to make it in the exhaust and out the intake and all the way back to the carb, blowing the fuel charge right into your air cleaner.

People who don't see this: it's only because you're not riding at the RPM where it would happen on your bike. If you don't believe me, pull the air cleaner off and run the bike, carefully looking for the ball of fuel hanging in the mouth of the carb. Play with the RPM and watch the ball of fuel move in and out of the mouth of the carb. At some RPM, it will move all the way out of the carb, and that of course is where it would wash the oil out of your air filter.

I did this on a dyno, at night, with fans blowing on the bike, and used a strobe (timing light) to observe. It was like stop motion photography with the timing light. It was also scary to see the ball of fuel get blown back by the exhaust fans right on to the glowing rear exhaust head pipe.

About 8 years ago, I made a post over at sportster.org about the night I did this. The one word I recall from the thread (Maurice Riggins wrote it, not me) was Nomex (like "put on the Nomex suit" or something) but I can't find it now. I will try searching the archives or something.

--Chris
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  #9  
Old 16th December 2006
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Tommy_Gunn Tommy_Gunn is offline
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Quote:
Originally Posted by cantolina
I was, but I don't know d**k about that S&S setup, so I can't comment....
Hey Cantolina,

The S&S Quick set-up is nothing special.

Very similar to stage 1 set-ups.

It's just -

Jet kit
Chrome teardrop cleaner cover
Free flow filter
Slip fit mufflers

The breather kit uses rubber pipes rather than a metal type. It has a long pipe that allows the excess gases / oil to clear the bike safely.

TG
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  #10  
Old 16th December 2006
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Tommy_Gunn Tommy_Gunn is offline
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Quote:
Originally Posted by chrishajer
Yes, it's reversion. Reversion occurs on every motor . . .
Hey Chris,

Thankyou very much for the detailed explaination. That makes perfect sence.

Does this mean however that I just have to 'live with it'?

The reason I ask is that I'm about to spend out on a 883/1200 conversion (or similar) but don't want to carry on tuning the bike if this 'reversion issue' is incureable or at least I can reduce the amount of fuel on my bike!

For info, we do ride most journeys at 70mph+ once the motors are warmed through.

Most of the bikes are 1200's (Sportys and Buells) so I'm obviously on the throttle more than most.

TG

Last edited by Tommy_Gunn; 16th December 2006 at 11:29..
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