Author Topic: Fuel getting into crankcase  (Read 2979 times)

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dirtbag

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Fuel getting into crankcase
« on: September 17, 2017, 02:48:22 PM »
Have a problem with my 1980 Kawasaki Invader 440 Liquid.

Put my sled away in the spring running great. Didn't drain the gas and next winter I have a crank case full of gas. Removed the pipes and carbs and then started the sled to let it run off the gas in the crank until most was burned out/off (yes it would start and run w/o carbs) .

Between the carbs and tank is a stand alone Mikuni fuel pump that runs off crank vacuum. Took pump apart and it looks great. Had a local shop check my float needles (checks them with a vacuum gage or some set up). He says they're fine. Not surprising they're only a few years old.

How can that fuel be making it into the crank??

Any suggestions or thoughts appreciated.

Boomologist

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Re: Fuel getting into crankcase
« Reply #1 on: September 17, 2017, 03:20:09 PM »
Fuel is getting past the fuel pump or the primer pump. Most likely the fuel pump.
The diaphragm in fuel pump may have a hole or crack allowing fuel to run into crank case through vacuum tube. Some pumps also have an internal fuel shut off which sometimes fails. I always put a manual shutoff valve between the tank and pump to stop this from happening.
It is also possible fuel could be siphoning past the primer pump if the valve in it is stuck or damaged.

rminier

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Re: Fuel getting into crankcase
« Reply #2 on: September 17, 2017, 04:13:18 PM »
 Exactly what Boomologist said.
 My Invader is sitting in an enclosed trailer, but here is a picture of a $12 shut off valve in my '82 Blizzard....I installed the same thing in my Invader.
You will NEVER have your engine fill with gas if you have one of these.
I should qualify my use of the word "never". It only works if you remember to close it when you're done riding.. ;)
 I usually remember....I sometimes forget to open it....the sled will tell you. It may start and run for 30 seconds or a minute....then....DOH! It dies. ::)
75 SnoJet Astro SS, 79 Kawasaki Invader 440 (two of them), 81 Scorpion Sidewinder, 82 Blizzard 9500, 83 Yamaha Vmax 540, 97 MXZ 670....and holding...for now.

jskal

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Re: Fuel getting into crankcase
« Reply #3 on: September 17, 2017, 07:27:08 PM »
New needles & seats (even though they check out) and fuel pump rebuild will go a long way to avoiding frustration down the road.  Nothing worse than trying to start a motor that filled with gas overnight or because you trailered it forgetting to hit the shutoff valve.

Boomologist

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Re: Fuel getting into crankcase
« Reply #4 on: September 18, 2017, 06:52:31 PM »
I install shutoff's between tank and pump not only to keep crankcase from filling but from a fire safety standpoint. If it leaks into the engine long enough it is possible to have gas run out the exhaust. If sled is inside and leaks gas near a source of ignition it could take out your shop, house,......

jimvw57

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Re: Fuel getting into crankcase
« Reply #5 on: September 21, 2017, 11:23:31 AM »
If you look at the Kawasaki Invader, you will notice the fuel tank sits higher than the crankcase (and carbs) which makes it possible for the fuel to siphon in through the carbs and fill the crankcase. The fuel pump  (stock) looks taller than a normal Mikuni pump because it has and anti siphon valve incorporated in it. thus the fuel pump will not work until the engine creates enough vacuum to open the valve, which makes it hard to start if there is no fuel in the carbs.  Thus the need for a primer...

However, since the primer bypasses the fuel pump. there is a check valve in the primer to keep fuel from going into the carb (which is lower than the tank)  unless it is under pressure. If the check valve fails, you get gas in the crankcase, and the engine will draw fuel in through the primer and you get a high idle. Seems lately primers only last about a year or two.

Once the engine gets flooded with fuel, it strips the oil off the surface of the crankcase and crankshaft, and of course the bearings. This causes everything to run dry and damages bearings and most importantly the crankseals. after the engine dries out and runs a bit, you could end up with a blown motor from a damaged crank seal. 

To help this, I always packed the seals with grease to give them a little more protection fro drying out. Also new needle and seats every year.  And make sure you have the correct fuel pump.

Sorry just some rants from an old guy.
« Last Edit: September 21, 2017, 11:26:23 AM by jimvw57 »

jimvw57

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Re: Fuel getting into crankcase
« Reply #6 on: September 21, 2017, 11:29:17 AM »
A better way to drain the fuel would be to remove the spark plugs, tip the sled on it's side (recoil side) and pull over the motor. that will push the fuel out the plug hole. It will spray all over so protect the hood, your eyes, the dog, etc. When it stops shooting out, the crank is empty.  Then make sure you dry out the exhaust pipe and mufflers. One spark and it could go boom!