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fuel mist coming out of filters???
pickmaster - 5/2/14 at 11:22 AM

Ive fitted an ST170 engine on ZZ6R bike carbs with a pipercross 90mm depth dome filter
When under load and full bore fuel mist comes out of the filters
With it being a front engine car and the filters sticking out in the air this fuel mist sprays back on onto my visor
Anyone got any ideas
deeper filters 150mm?
longer intake tubes?
longer trumpets?

Any ideas anyone????

prawnabie - 5/2/14 at 11:27 AM

Is it misfiring under load or spitting back throught the carbs?

pickmaster - 5/2/14 at 11:29 AM

No misfire
Its pulling like a train

pickmaster - 5/2/14 at 11:37 AM

on the road you don't notice as its not often I give it that much as it wheel spins with it only being light (500kgs)
But I have fitted an LSD so now can give it more throttle and be under load, not spinning the wheels

Peteff - 5/2/14 at 11:45 AM

Fuel standoff, all to do with pulses and inlet lengths. Can you fit an airbox ? Watch this about 1 minute 20.

pickmaster - 5/2/14 at 11:54 AM

That's it
Here is mine with no filters on rolling road about 12 seconds in mist
http://youtu.be/Ppjy8rGHvZk
Any ideas on how long or short to make the intakes
plus 14"
plus 12"
plus 1"
Where would I start??????

britishtrident - 5/2/14 at 12:13 PM

The only real cure is an airbox.

Scuzzle - 5/2/14 at 12:20 PM

Fuel mist is normal on bike carbs at full throttle, never heard of it coming through the filters though, what filters are you using?

scudderfish - 5/2/14 at 12:30 PM

quote:
Originally posted by britishtrident
The only real cure is an airbox.


Is that curing it or hiding it? Are you going to end up with a puddle of petrol waiting for the next backfire for fun and chuckles?

v8kid - 5/2/14 at 12:46 PM

quote:
Originally posted by scudderfish
quote:
Originally posted by britishtrident
The only real cure is an airbox.


Is that curing it or hiding it? Are you going to end up with a puddle of petrol waiting for the next backfire for fun and chuckles?


I think the idea of the airbox is to reflect the pulses at the resonant frequencies so i guess thats a cure if you get the frequency right and hiding it if you get it wrong

Cheers!

PS can the OP lengthen the inlet tracts? Although it may seem counter intuitive by lowering the resonant frequency the pulse strength is also lowered and the added inertia of the gas may overcome the pulse - Whell something like that !

[Edited on 5-2-14 by v8kid]

Peteff - 5/2/14 at 12:49 PM

You get to suck the fuel back in when you let off the throttle instead of losing it to atmosphere

MikeRJ - 5/2/14 at 12:58 PM

quote:
Originally posted by scudderfish
quote:
Originally posted by britishtrident
The only real cure is an airbox.


Is that curing it or hiding it? Are you going to end up with a puddle of petrol waiting for the next backfire for fun and chuckles?


What do you think happens in the original plenum?

pickmaster - 5/2/14 at 01:12 PM

I don't think an air box is an option
I won't be able to see where I'm going with that in the way

pickmaster - 5/2/14 at 01:16 PM

It's a pipercross 90mm deep dome filter
I can't go any shorter on intakes because of the angles between carbs and cylinder head

[Edited on 5/2/14 by pickmaster]

MikeRJ - 5/2/14 at 04:21 PM

quote:
Originally posted by pickmaster
I don't think an air box is an option
I won't be able to see where I'm going with that in the way


Then the only way to work around this would be longer trumpets to try and contain the stand-off, but that may require the carbs to be rejetted, and you may sacrifice some top end for more mid range (which is often a good thing).

jacko - 5/2/14 at 07:22 PM

engine
engine
Why not i did with the filters out side
Jacko

pickmaster - 5/2/14 at 08:14 PM

That's a neat solution
But I'd like to spend a bit more time trying to cure the problem rather than contain it
I'm going to experiment with intake lengths and see how I get on
If not maybe a mesh baffle inside a larger filter
I'll try 3" longer then shorten 1/2" at a time see what happens

madteg - 5/2/14 at 08:28 PM

Have you checked the cam timing, just a guess but bet you have adjustable vernier wheels fitted.

pickmaster - 5/2/14 at 08:38 PM

Now that's a thought it's on that VVT thingy
I have full advance set at 1500 rpm
So at 4000rpm when it's spraying its on full advance
Maybe too soon?

madteg - 5/2/14 at 08:54 PM

Let me know what you find, thanks Kev.

Canada EH! - 6/2/14 at 12:01 AM

It was a common problem in the 70's when I raced, friends Volvo 122 was really bad, a longer set of air horns fixed the problem.

MikeRJ - 6/2/14 at 09:04 AM

quote:
Originally posted by pickmaster
That's a neat solution
But I'd like to spend a bit more time trying to cure the problem rather than contain it


You can't "cure" it, it's an inevitable part of engine operation. . Containing the stand-off is the only solution, whether it be in longer trumpets or within a plenum or air box.

pickmaster - 6/2/14 at 09:45 AM

I've been on the phone to pipercross today and they have said there is a carbon element in the filter to stop this
But I've been using K&N filter oil and they think its worth trying there's first as the two oils are for different materials
Watch this space!!!!

pickmaster - 9/2/14 at 06:04 PM

I've cleaned and recoiled filters with pipercross filter oil and been out this afternoon when it was dry
Still the same oil and fuel coming out at 4000 rpm and full throttle
Next time I get half an hour I'm going to extend the inlets an inch
See what happens

britishtrident - 9/2/14 at 08:14 PM

quote:
Originally posted by pickmaster
I've cleaned and recoiled filters with pipercross filter oil and been out this afternoon when it was dry
Still the same oil and fuel coming out at 4000 rpm and full throttle
Next time I get half an hour I'm going to extend the inlets an inch
See what happens


As others have aready said you can't stop it from happening only contain it so it gets sucked back in and not blown away in the slipstream
Although the. net flow into a cylinder is inward airflow into a single inlet tract pulses in both directions.
You can't rewrite the laws of physics the length of the inlet tract. has a major affect on power delivery and mixture.

[Edited on 9/2/14 by britishtrident]

pickmaster - 12/2/14 at 08:01 PM

Update
After a lot of checking through the wiring I've found the VVT solenoid staying retarded
So I spent the afternoon tracing the fault all the way back to the ECU trigger wire not earthing at revs so the solenoid not working and the timing being retarded at speed
Graham and Duncan at Chester Sports Cars were very helpful and had a test rig simulator for my ECU to double check the fault and help me rewire around the fault from another ECU output
I just need the weather to clam down to prove the theory on the road. It all adds up in theory in my mind now

Thanks for all your comments and help without which I would still be getting sprayed

pickmaster - 13/2/14 at 07:09 PM

Took the car out today for a run and it's cured now
So it was the timing out because the ECU wasn't triggering the VVT solenoid fitted to the ST engine
I was probably only running 100bhp at the crank as well as getting sprayed with fuel
The car is now back to its insane mental self thanks again