fuel/oil pouring out of air box breather. Ahhhhhh

[twowheellover]

Hi everyone, I have a very poorly GSX750F.
She fires up fine but after about 20 seconds a mixture of fuel & oil start to pour out of the air box breather. The crankcase is full of this mixture.
This all started after she wouldn't fire up one day & after trying several times to start her she eventually did the loudest backfire I have ever heard, I couldn't hear for 15mins.
My question to you all is what is going on ? I think, but I could be wrong, that one set of rings at least has gone thus allowing fuel into the crank & pressurising it, this in turn is blowing the mixture through the breather into the air box. Does this sound reasonable or am I way off.
Any help would be appreciated as I would love to get her up & running again soon.
____________________
baza

[Stalk]

Fuel tap / float needle leak, or if vacuum operated tap, possible leak down vacuum hose, into cylinder, leak past rings into crankcase dilutes oil. Unlikely rings are knackered as petrol is thin and will get past. Check for fuel leaks in the areas suggested. Change oil and filter. Maybe check if the level has gone up. Remove plugs and spin engine on starter, does petrol get spat out? Will narrow it down to one carb. Or fuel tap if it takes vacuum from that cylinder. Don't let so much fuel in the bore that you have hydrolock. Bends rods in some cases. Buy a manual, worth its weight in gold

[Pol Anorl]

take breather pipes off and check for umulsified oil which youll probably find, then blow it out refit and ride it.
____________________
GOOD GAME BODYGUARD: https://i.imgur.com/8WePGgf.jpg
20:30:37 Pyro.: I don't sort of like men, I take every advantage to choke on dick.
Jewlio Iglesias: You live in Liverpool - Chances are, the front door has already been kicked off the hinges

[Casper]

OK. Where is the oil/fuel coming from? Think you have a rubber pipe from the top middle rear of the head going into the airbox. Pop that out the airbox end and run to see if it stops. No then its coming through the carbs and they need an overhaul and/or the fuel tap is fucked. You will get some smoke from said pipe but not lots of oil/fuel unless your tap/carbs have been letting fuel flow when the bike is off and its now in the engine. Its the oil level high and take the filler off ans sniff.

Your profile says this is your late brothers bike. Had it been of the road for a while and you have just started to ride it?

[temeluchus]

Float needles are fudged/dirty.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[misscrabstick]

Ethanol in the fuel has eaten your float needle tips probably, try some new ones, around 40 pounds on ebay for 4, clean your carbs, fuel lines while your at it, if there's any filters clean/ replace as needed, finish up with a balance if you have gauges and your problem will be gone, incidently ethanol eats fuel tap insides as well, getting a rebuild kit for the tap is worthwhile too, decent float needles will hold back fuel even if the tap leaks so the issue is bigger than just a leaking tap.

[twowheellover]

Thanks for the advice guys, here is what I've already done.
The bike was stood for 5 years as my brother had motor neurone disease so couldn't ride. I started her up with the old petrol that was in the tank about 3 years ago, didn't mean to I was just seeing if she would turn over & she fired up within seconds. There were a number of issues to sort out prior to taking her for MOT. Seized brakes front & rear, damage indicators, no oil in forks & seal stuffed, various lamps stuffed & battery screwed. I don't have a garage next to the house mine is rented from the local council so is a little way from my house so progress was slow. So all the above issues were eventually sorted & I thought I was ready for MOT, by the way I have put new fuel in every so often & I've had a cheeky ride round the block to check everything was ok.
Then the huge backfire happened & the problem with fuel getting into the crank was discovered, which is probably what caused the backfire to start with.
I took the carbs off, stripped & cleaned them, refitted them & tried again. Still pouring fuel into the engine.
My next job will be to check the fuel tap (vacuum operated) & compression in each cylinder.
I may need to remove the carbs again & check more closely the float needles. I will let you know what I find, as you can see this might take me a little while with the garage being away from the house & work & other stuff also taking up time.
Cheers
____________________
baza

[twowheellover]

Hi GPZ750.
The oil/fuel mix is pouring out of the airbox drain pipe that hangs down just in front of the rear shocker. It looks like this mixture is getting blown through the breather from the head into the airbox. I will take the breather off next time I go round to the garage.
I will need to drain the engine oil & renew as it definitely has fuel in it.
Cheers
____________________
baza

[Casper]

In that case its only coming from one place mate. The Carbs. The needle jet is designed to cut the fuel off when the float hit a certain height. (Same principal as your toilet cistern) Your jets or jet is worn or blocked with shit letting the fuel continue flowing. Now the tap is designed to not let fuel flow unless its on prime or engine is running. Are you leaving the bike on prime. If yes then dont. If no then the tap may want an overhaul kit (around £15) However the tap may be fine and your getting the fuel from over time with what is the fuel hose from tap to carbs. Carb overhaul will cure this.

The Ethanol idea is worse case scenario. I am yet to hear anyone who has had major issues with it in this country. Think people with plastic tanks are having problems but yet to hear about it eating carbs. Mind and do the float height as well as the needle jets and if you can afford the carb kits a new gasket would not go amiss.

Good luck. Hope you get it running sweet as that bike means more to you than any other old GSX750F

[twowheellover]

Hi all,
Went round to my garage this evening & all of you who suggested the problem was the vacuum fuel tap were
spot on.
I disconnected the 2 out going fuel lines & turned the tap to reserve & fuel poured out. So I have ordered a repair kit & a set of float needles.
Here's hoping.
____________________
baza

[twowheellover]

OK so part 1 of the repair. I have repaired the fuel tap & put fuel in the tank - no leaks. Part 2 I have installed new float needles, filled the bowl with fuel & tried to blow down the fuel lines. No air getting through so floats & needles now OK.
Time for tea now so after tea I will go to my garage & refit carbs, air box & tank. Here's hoping.
____________________
baza

[kramdra]

Sticky float needles are often caused by the aluminium shaft sticking in the brass seat - rather than the tip (of course you have already cleaned both). I find this is always fixed by rubbing the shaft on some wet, scrunched up aluminium foil. It has worked on 3 bikes (6 cylinders between them)

Carbs are great but I strongly dislike the amount and frequency they can leak:

Floats and needles, they depend on gravity and will not work as intended when bike is on its side or if for any reason they stick (contaminated fuel, or just old, dirty), which is common. You wouldn't know if they started to leak when riding, until your bum catches fire.

The result is any crash, fuel will piss out, good chance of fire. A working vacuum fuel tap will limit this a bit, but there is still plenty in carbs to leak out..

Would like to see an aftermarket kit of an electronic solenoid fuel tap, electronic carb level sensor and valve

[temeluchus]

[twowheellover]

So fuel tap repaired & new float needles in, 1 gallon of fuel in the tank & no issues at all. Fantastic.
Thanks to everyone for the advice, as you can tell I've never had a bike with a vacuum fuel tap before so it threw me a little.
Just need to bleed the brakes & replace rear lamp then it MOT time & out on the road.
A little jaunt round the block & how different she is to my GS500E, wow really quick.
Thanks everyone.
____________________
baza