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Tommy_Gunn
15th December 2006, 12:26
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

Tommy_Gunn
15th December 2006, 14:29
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/showthread.php?t=41408&page=2

cantolina
15th December 2006, 15:06
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?

Tommy_Gunn
15th December 2006, 16:26
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

grizz420
15th December 2006, 17:41
What exhaust are you running?


are you thinking reversion

Tommy_Gunn
15th December 2006, 21:19
are you thinking reversion

So what's reversion then Grizz420?

TG

cantolina
16th December 2006, 02:14
are you thinking reversion

I was, but I don't know d**k about that S&S setup, so I can't comment....

chrishajer
16th December 2006, 06:16
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

Tommy_Gunn
16th December 2006, 12:00
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

Tommy_Gunn
16th December 2006, 12:07
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

aswracing
16th December 2006, 15:30
Chris is exactly right, as usual.

The solution for this issue is with the exhaust system.

If you're riding at an rpm where the exhaust is pushing back, you're giving up both a lot of power and efficiency as well. Change the exhaust so that it pulls at the rpm tht matters.

If you look at the torque curve on a dyno sheet, reversions are pretty easy to spot, as a hole or dip in the torque curve. They also generally cause the a/f to go rich at that rpm, because the intake charge get's momentarily pushed back out before being sucked back in. So it goes through the carb 3 times: in, out, back in again, picking up fuel each time.

When the torque is peaking, it generally means you're getting a strong negative pressure wave during overlap instead of the positive wave that causes reversion. That's where you want to be. Negative waves help cylinder fill, positive waves kill it.

The reason that different types of waves arrive at different rpm's is that the wave travels at a constant speed in the pipe, the speed of sound, regardless of the rpm of the engine.

Without diffusion in the pipe, a given wave, positive or negative, tends to arrive over about a 2000 rpm range.

What you want from the exhaust is to time and diffuse the waves such that you get a broad negative wave that arrives over the range of rpm in which you ride.

Examples (look at the torque curves only):

http://www.nrhsperformance.com/images/drbrianjohnson.gif
reverting bad at 2700 rpm, pulling hard at 5000 rpm

http://www.nrhsperformance.com/images/drdannorlin82.gif
reverting at 4300 rpm, pulling hard at 6500rpm

http://www.nrhsperformance.com/images/drrobnoble.gif
two torque peaks, we see this with certain 2 into 1 systems. Actually works pretty well to widen the power band. This is a Samson Caliber system.

http://www.nrhsperformance.com/images/drbobkasper.gif
The 2 into 1 Supertrapp's tend to do this, pull real hard down low and then fall off slowly as rpm rises.


http://www.nrhsperformance.com/images/drrichmartinez.gif
Picture-perfect diffusion for a street motor, a wide parabola of a torque curve

cantolina
16th December 2006, 15:44
Chris is exactly right, as usual.

The solution for this issue is with the exhaust system.

<snip>Change the exhaust so that it pulls at the rpm tht matters.

<snip>

This is exactly what I was thinking....

Try experimenting with different slip-ons....or at least look into the baffling properties of the ones you have...

If they are TOO free-flowing, that can be a problem....

This is a matter of "exhaust tuning", which we really haven't covered much here, because its very complicated.....certainly too complicated for ME, anyway....I would modify the current slip-ons, or try another brand....

Tommy_Gunn
16th December 2006, 20:04
Hey Guys,

You 'rock'. Many many thanks for your responses. I really don't mind trying different exhausts / mufflers, infact it's fun :) Even better when I have a damn good reason to do so. (I can see my girlfriend will love me for this - not).

Perhaps I should look into buying a tunable or is that tunible (hmm doesn't look right either way) system such as Supertrapp. Used them in the 90s on Sportys and later Buells (S1's and X1's) and they were always pretty cool. I'll have to see if they make them for the 06 MY.

With a handful of spare 'rings' in hand we should, I guess, be able to set a Supertrapp up at a Dyno centre to reduce if not remove the drop as you showed on the dyno charts?

Are there other exhausts which have this tuning capability too? You mentioned the Samson Caliber too. Never used those before.

Again, I really appreciate everyones help on this . . .

TG

Tommy_Gunn
16th December 2006, 21:36
Actually it's quite funny looking at those Dyno charts. I'm having problems with a near stock Sporty that produces approximately 40 bhp and similar torque.

Each of the attached dynos are at least doubling the torque and nearly tripling the bhp.

At the moment I'd be happy to have my 40 breaker running nicely, but maybe one day . . . :smoke

Cheers

TG

:xlrocks

opiewontaylor
16th December 2006, 22:49
Anyone try an "air cuff"? I saw one in a JP Cycles catalog. It's a plastic shield that snaps on the end of the carb and is supposed to eliminate fuel reversion getting to the aircleaner. It probably doesn't do squat, but if I was getting my aircleaner soaked in gas, for $20, I'd give it a try. Cheaper than changing mufflers.

Tommy_Gunn
16th December 2006, 23:25
Anyone try an "air cuff"? I saw one in a JP Cycles catalog. It's a plastic shield that snaps on the end of the carb and is supposed to eliminate fuel reversion getting to the aircleaner. It probably doesn't do squat, but if I was getting my aircleaner soaked in gas, for $20, I'd give it a try. Cheaper than changing mufflers.


Good call Opiewontaylor.

Any clues anyone?

TG

cantolina
16th December 2006, 23:55
Good call Opiewontaylor.

Any clues anyone?

TG

Band-aids are exactly that....

Reversion is a symptom, not a problem....

The laws of physics are NOT suggestions... :D

Worst 20 bucks you might ever spend, IMHO....

Tommy_Gunn
17th December 2006, 01:52
Reversion is a symptom, not a problem....

The laws of physics are NOT suggestions... :D

Worst 20 bucks you might ever spend, IMHO....

Fair comment Cantolina

I'll be trying different exhausts and baffeling myself, but I could understand people trying the 'band-aid' approach if their decision was based purely on 'initial' financial out lay to 'reduce' the amount of fuel deposited on their bike.

Looking at the product in question, I can't see it doing anymore than reducing the quantity of fuel sprayed down the bike.

Actually it is interesting that until today, I'd never heard of reversion even though I'd riden HDs for over 18 years.

Now I see that nearly ever exhaust manufacturer 'claims' to produce exhaust systems which have a patented 'Anti-Reversion' system in it.

I think I'll let the dyno do the talking as ASWRacing says.

I'll update you all with any findings . . .

Tommy Gunn

Jimbo999
17th December 2006, 01:57
I get a small amount of reversion if I get on the throttle before she's fully
warmed up. After warm up never had a problem.