Author Topic: Fuel In Crankcase...Guru Needed!!  (Read 1694 times)

pimpdaddydog123

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Fuel In Crankcase...Guru Needed!!
« on: October 17, 2013, 02:38:36 PM »
Hi Guys, I have been reading this forum all night and wow...it is fascinating.
I live in the UK and 125s are very popular here because they can be ridden by anybody with a car license, you have to take a test to ride a bigger bike.
Anyway I buy a lot of non runners to repair an re-sell and today I bought a Sym HD125 (watercooled 4 stroke).
I suspected the bike was seized so paid very little for it, the starter motor wouldn't crank the engine despite a new battery being fitted by the previous owner.
I took the transmission cover off and realised that the bike wasn't seized it was hydralocked.
After reading sevferal posts on this forum I decided to check the oil to see if it smelt of gas and as soon as I removed the oil filler cap a mixture of gas and oil literally flooded out, I am guessing there was at least 2-3 litres in there.
I have read posts on this forum describing similar problems but having looked very closely at my bike I cannot really work out how gas is getting into the crank case.
There is a vent pipe from the gas filler which goes to a "T", from the other side of the T it goes to a check valve but the other side of the check valve is just an open pipe.
The 3rd side of the T goes down to the fuel cock so even if fuel were travelling along the filler neck vent it would only get as far as the fuel cock.
If the float was stuck in the carb (and it isn't at the moment) excess fuel would surely just be vented from the carb overflow.
If the fuel cock had failed (and it seems to be fine), again fuel would just stay in the carb.
How on earth is this excess fuel getiing into the crank case?
My plan is to fill the engine with the correct level of oil and run the engine and see what happens but any help would be much appreciated.

Keep up the good work guys

Marcus

skootz

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Re: Fuel In Crankcase...Guru Needed!!
« Reply #1 on: October 28, 2013, 10:11:53 AM »
Resolved yet?

pimpdaddydog123

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Re: Fuel In Crankcase...Guru Needed!!
« Reply #2 on: October 28, 2013, 12:39:29 PM »
Yes it is resolved thanks!

I think writing my original post helped me to think through the problem so the following day I took another look.

I discovered that as I originally suspected the only way fuel can get into the crankcase on this particular bike is via the carb so I set the carb up on my bench with a temporary fuel tank and sure enough fuel was pouring out of the carb.

This particular carb has an oveflow cast into the float bowl but it hadn't been drilled, I suspect that due to emissions regulations manufacturers are no longer allowed to have a float bowl with a vent which is open to atmosphere.

Anyway I took the float needle out and discovered a small ball of compacted cotton fibres (possibly from a Q Tip) preventing the needle from sealing against it's seat.

Cleaned the carb, drained the oil sump, filled with fresh oil and it now runs perfectly.

I took the precaution of making a careful note of the oil level then measured it again after a ten mile ride to make sure it hadn't risen.

It hadn't, so I drained the oil again to get rid of any fuel remnants then filled with fresh oil.

The bike is now ready to sell.

When I initially looked at the carb it did look like it had an overflow pipe connected to the float bowl but that was in fact just a drain tube which allows you to drain the carb via a small screw if you need to.

I was tempted to drill the overflow casting to prevent a future problem but decided to leave it stock.

I hope this helps somebody else with a similar problem.

skootz

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Re: Fuel In Crankcase...Guru Needed!!
« Reply #3 on: October 28, 2013, 07:07:32 PM »
Glad t hear you have a fix on that leaking gasoline.

However.......if the vacumn operated fuel line shut off valve was working, it should have shut off and prevented any gasoline from flowing after the engine is shut down.....no vacumn on intake port at carb means closed valumn valve and no gas flow......this type device was placed on most gravity feed fuel systems for the past 30 years to avoid this very problem.....many folks see it as a problem system and remove the vacumn valve and lines to run straight from tank to carb....ok if you are racing and watching things very closely after engine shut down....but for the casual rider, the vacumn system is a no brainer intended to replace the old fashioned manual fuel shot off valves that we all would either forget to turn on.....sputter...sputter sputter... as we cross the four lane !!!!!! yikes.....
Or......just forget to turn off after riding......park in garage next to gas water heater....gas leaks...you take a bath and the next thing you know .....well you get the picture.

Anyway...sounds like you got a winner there...have fun......i'd look into that fuel line....for a couple of bucks you can get a plastic quick inline fuel shutoff....just got to find a convenient place on the SYM to set it....and I can't think of where you might situate that.....best to see if the vacumn valve is functioning....

Regards.

SKOOTZ

pimpdaddydog123

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Re: Fuel In Crankcase...Guru Needed!!
« Reply #4 on: October 29, 2013, 09:15:59 AM »
That's an interesting point you raise re: the fuel shut off valve Skootz.

The lady who sold me the bike originally did tell me that her husband had replaced the valve at some point and sure enough it did look new.

I did test the valve and it seemed to function properly so I can only assume that either the old valve was stuck open or the engine was only filling with fuel whilst it was running.

She did say that the bike was running one minute then slowed down, stopped then appeared seized so possibly a bit of both.