gas in crankcase problem

[Guest]

Hi Guys, new GS owner and 1st bike. I need some advice on next steps to troubleshoot the issue I am having which is I am getting gas into the crankcase after riding for a short time,, maybe 5-10 miles.

I have a 1981 GS650 GL shaft drive with about 12,000 miles. It had been sitting for awhile when I purchased it and would only start and run with the choke fully on. So I have completely disassembled the carbs,, soaked them,, cleaned the passages,, blown them out,, replaced the float needles,, purchased from Z1-- replaced all o-rings from GS resource recommended source. cked float measurements,, did not make any adjustments to them. Reassembled everything,, also have paper filter on gas line. also I have not synced them yet,, need to get the tool? its on the list of things to do.

Bike runs great.. but after riding a short distance,, gas in crankcase. Petcock appears to be working properly,, have a clear vacuum line and do not see any gas going through it, and not getting any overflow via the carbs or air filter .

I just wanted to get some advice before I tear into it again.

should I ck the plugs and see if any plug is fouled and then suspect that float level is off for that carb or the float needle is stuck or possible blockage?


Possibly rebuild the petcock just to give me peace of mind.

Any other suggestions or steps would be appreciated

I have enjoyed getting this bike running and the site has been very helpful,,so far I have replaced the brake lines,, rebuilt the rear brake master cylinder, replaced back brakes, replaced clutch springs, speedometer that goes on front wheel, clutch cable, added clubman bars, changed plugs, replaced air filter and resealed air box replaced O rings for carb boots, and getting very good at changing the oil but would like to ride it a little more,, but need to get this fixed.

thanks again
Mark

[Octain]

Faulty petcock.
But I dont understand how fuel would make it into the crankcase with the bike running?

Welcome to GSR!

[Mharal]

thats what I do not quite understand,, the oil level was between the Full and low mark when I started the ride,, but was completely full when I cked it,, after about 5 - 10 miles and smelled of gas.

also I can disconnect the gas tank and it does not leak..so I would think the petcock is working properly.

[Mharal]

side note,, where did you get your seat for your bike,, I am thinking of getting something like that.

thx

[tom203]

Faulty petcock.
But I dont understand how fuel would make it into the crankcase with the bike running?

Welcome to GSR!

Yeah, strange- that much gas would likely foul plugs on its way to crankcase.
Mharal; run bike for 10-15 miles, stop and pull all spark plugs and see if any or all look wet. But first, before you ride, remove that clear vac line from #2 carb and suck on it- any gas headed your way?

[Nessism]

It's not possible for gas to fill the crankcase while riding the bike.

Oil expands when it gets hot. Maybe you are misreading the oil level?

[Mharal]

hmm,, emptied the oil,, filled to mid-level,, started the bike,, ran it for a few minutes,, turned it off,, let it sit for about 15 minutes,, rechecked and filled oil to mid level,, which was between the F and the L,, not sure how i could mis-read that,, then took a short ride,, stopped and let the bike sit again for about 10 minutes,, cked the oil and the oil level was completely full. removed the oil filler cap and there was a strong smell of gas from the oil filler opening.

Is there another way for the gas to get to the crankcase while running?

only other thing i can think of is after I turned off the bike,, fuel kept flowing from the petcock,, but if the tank is removed there is no leakage from the gas tank.

any suggestions?

thx for the reply.

[Mharal]

if the float adjustment was not correct for some reason,, and they were not shutting off,, fuel would flow out the overflow vents.-- correct?

so that would lead me to suspect the petcock is not closing all the way after the bike is running and flooding the crankcase.

does that make sense? just trying to take next steps,, which I will check,repair or replace the petcock.

thx
Mark

[cowboyup3371]

Where is your petcock pointing - down for on or to the rear for prime?

[Mharal]

the petcock is pointing down,, I only used the prime postion once after i had cleaned the carbs and reinstalled them. After that I moved the lever to the down postion and have not changed it.

[cowboyup3371]

Have you verified your float settings? What are they set at?

Are you positive your petcock is working correctly? Pull the fuel line off your carbs and watch what happens? If it flows freely without the engine running, you have a bad petcock. If it works like it should, apply suction to the vacuum line such that fuel will flow. If it doesn't stop when you stop sucking then you have problems there too.

[Mharal]

Float levels were measured during the carb rebuild and looked good so i did not change them.

i will ck the petcock tomorrow,, I know it does not leak with the tank disconnected,, but think the issue may be it is not closing off all the way after running,, hopefully that will be the issue. Will let you know how that goes.

[cowboyup3371]

Looked good means what? How did you measure them - with a caliper or by your eyeball? Even if you did the rebuild properly, it is possible they moved ever so slightly when you either took them off or put them back on. Were they done as written up in Nessism's guide so that they are at 22.4mm +/- 1.0 mm above the gasket surface (without the gasket in place)?

[Mharal]

float level measured with caliper per the service manual specs,,

if the floats were allowing too much fuel, it would go out the overflow vents right? if so,, that is not happening so I am going to hold out that the petcock has some sort of problem and will ck that tomorrow.

thanks for all the suggestions,, helps to cover ever possibility.
Mark

[Mark Harrop]

Petcock...

Had the same thing happen on my 82 750....it would fill the crankcase with gas. Eventually you will ruin the crank/rod bearings, starting with #1 (its the lowest when the bike is leaned on the kickstand)...it washes the oil off the bearing surfaces.
I installed a manual fuel valve...problem solved....and the bad bearing gave me an excuse to yank the 750 and replace it with an 1100.

Ran like a scalded dog though...