Gas/oil carb question

W

Woodfiend

New Member
I have a 78 Yamaha xs750 special and have the gas - oil issue. I know about the petcocks going bad and plan on getting some from Mikesxs but in the meantime I put two inline shut offs in the fuel lines...... I have changed the oil a couple of times in the last couple months (even though I haven't been riding much) But I can still smell a bit of gas in the engine oil.

I read that sometimes the floats can get holes or the float valve (not sure if that is what it is called) can stop functioning and allow fuel to pass into the engine. My carbs run fine and even with pods on the bike I don't have any issues with the carbs other than the fuel getting through. So I am reluctant to tear them all apart.

So my question is "Is there any way to narrow down which carb is the offending culprit? Or do you just have to assume it is all of them and fix them all?"

 
Sorry! I just realized I had multiple pages open on DTT and probably posted this in the wrong section. If a mod could please move it to a more appropriate one that would be appreciated. Thanks.
 
If you're getting gas in your oil then you're destroying your motor. You need to check float height on both carbs to make sure they're adjusted properly and, were it me, I would just get rebuild kits for both and make sure they include new float needles and seats.
 
Thanks Sonreir.


Rich: I am trying not to destroy my engine. I have only been riding maybe once a month for the 6 months I have had the bike....... and I change the oil each time before I ride (short rides too). So I think I am fine in that regard. But I don't want to run the risk of ruining it (plus it is expensive to operate in this manner! ) :) :eek:

But I was curious if it was possible to figure out which carb could be doing it? Or do I just have to bite the bullet and do them all at the same time?
 
I would not ride or run the bike at all until I figured out the issue. Doesn't take much gas in the oil to quickly ruin a good engine. Don't roll the dice, inspect each carb to ensure they are all done correctly and give you piece of mind.

Aren't the carbs all on a rack anyway? If so, they'll all have to come off even to work on one so it won't be too much additional work to bring all to spec.
 
Woodfiend said:
Is there any way to narrow down which carb is the offending culprit? Or do you just have to assume it is all of them and fix them all?"
Click to expand...

Pull the rack.

Look at the inside of the boots.

It will be obvious which one(s) are leaking fuel into the crank case.

-Deek
 
Thanks for the good advice everyone.

So what should I look for inside the boots when I pull them? I'm new to working on bikes and nervous about messing with the carbs because that is always what everyone seems to have issues with. I don't want to accidentally let the magic out.......
 
You're looking for any sign that gasoline has leaked into the cylinder head. A puddle is a dead giveaway but so is varnish (or a lack of varnish depending on when/how it leaks). Also, signs of a dried-up puddle is a dead giveaway.

If you have just one cylinder leaking fuel, it will be obvious. In general you'll see a relatively clean area leading to the intake valves in your head. If you see something different, it's likely a sign of gas.

Remember that what comes out of your carburetors is mostly air. Even pig rich smoke-em if you got-em mixtures are too light to puddle in a normal intake situation. A puddle of gasoline or really even "wetness" that's gas is not normal.

-Deek
 
Quick way to find out which carb is leaking is to pull spark plugs and crank engine.
It's a good idea to disconnect the coil primary wires, I've seen a few real good 'flamethrowers' by people who ignored the second part ;D
 
Crazypj can you elaborate for me please? Or I guess a more accurate request would be can you dumb it down for the less mechanically inclined? :-[ ;D

Do I just remove one plug at a time and turn the engine over with the kick starter? You aren't suggesting doing this by having the engine running are you? Sorry I am new to all of this.
 
Take all the spark plugs out, crank it over, excess gas comes out of the hole where it's leaking
 
crazypj said:
Quick way to find out which carb is leaking is to pull spark plugs and crank engine.
It's a good idea to disconnect the coil primary wires, I've seen a few real good 'flamethrowers' by people who ignored the second part ;D
Click to expand...

It does look pretty awesome though.
 
Any recommendations for where to get the carb repair kit from? Which one has the best parts for the money? I see some from K and L on Amazon for $17...

I will probably order carb boots and put new ones on while I have them off as well.
 
K&L are about as good or bad as anyone. Make sure you get the right set though
Yamaha use Hitachi and Mikuni carbs, the Hitachi are awful to try and modify
 
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