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Spark Plug Fouling

  • Thread starter Thread starter Hoomgar
  • Start date Start date
H

Hoomgar

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What would cause a spark plug to foul after sitting? Let me explain. I've had my #3 plug foul out on me about a half a dozen times now. Every time it is after sitting at least over night. Twice it did it first fire of the morning. But every time after that it will only do it if the bike sits for two days or more. If I ride it everyday it won?t foul. If I let it sit more than a day then #3 will foul when I fire up. What is taking place while the engine sits that makes it foul out when I fire it after a longer sit? Maybe has something to do with some of the other issues I have been having with this thing?
 
oil slowly seeping past intake valve seal.
when it sits long enough, enough oil gets sucked in to coat the plug.
 
RacingJake said:
Do you think it's oil or fuel fouled?
Click to expand...


hmmm... :-k not really sure? How can you tell?

The two comments above make a lot of sense huh?

What should I look for jake?
 
I would think fresh plugs would have that wet look if fuel fouled and oil residue on oil fouled. Smell test may be required.

I'd swap 2 & 3 leads around just to make sure it's not electrical.

Check float fuel level on #3 carbs

Check valve clearance

Compression test and leak down test, then spray some oil in cylinder to see it's worn rings causing a problem

Replace valve seals

???????
 
28 years takes it's toll on intake seals. The recent drubbing it has received during the jetting project might have torn a seal.
Guides could be worn but even good guides need a seal at the top, unless they are brass knurled and new and that is not the case here.

The seals MIGHT be replaceable on the bike if you pressurized the cylinder or stuffed rope in the cylinder and held the valve that way. But the design of the head makes reinstalling the retainer and keepers pretty tough. They can be popped easy enough with a large socket but reinstallation will be a real Hillary.

This weekend I can drag my spare cylinder head out and see if I can get the retainers back on with the engine togethjer. If I figure out a way to do it I will let you know. I want to replace mine and I do not want to pull the head so this is a good way to find a way.
 
Could be what the others say about the seals. Do you get a puff of whitish smoke at start up?
By fouling, do you mean when you first start the bike it obviously runs on 3 cylinders, then as it warms up it pops a few times and starts firing correctly? This can also be a high fuel level in the bowl caused by a leaking float valve. Usually accompanied by some fuel smell. Some leaks can be slow enough to take a couple days to show up. I've seen new aftermarket float valves leak, if you've replaced them with these.
To test for this, you can drain the bowl of the problem carb/cylinder before starting and then prime. If the fouling continues, it's not because of a high fuel level.
If it's oil fouling, you can start the bike and immediately turn it off and check the plug for oil. Should be easy to tell from fuel. Oil is stickier and won't dry in the air like fuel will.
 
Hoomgar, what did you find out? I have a very similar problem with my 850. Mine is fouling with fuel. Once fouled, it won't clear itself. I all ready swapped plugs and then later the plug wires for 2-3. Still foul #3 plug.

Anxious to hear what you found out.

Rick
 
Yeah i just had the same problem with the EF, I think it was due to having a low charged battery, ( I swiped the Battery to get the GS750, MISTAKE)I stuck in a new set of plugs and took it for a long ride and it seems to have cured it, before the 1-4 plugs fouled, the I cleaned them and the next day 2-3 fouled, I thought here we go, Charged Battery and the new plugs, after a plug chop seem to be running a little lean now, but still ok
 
Considering your bike is a 78 I would check the petcock first. Block the petcock vacuum line Turn the petcock to prime to run the bike & turn to on just before shutting off. DO it for a few days & see if it still fouls the plug
 
Considering your bike is a 78 I would check the petcock first. Block the petcock vacuum line Turn the petcock to prime to run the bike & turn to on just before shutting off. DO it for a few days & see if it still fouls the plug
 
Thanks Lynn. (I think that was directed to me:) That is an easy check.

Will do that this morning after work.

Rick
 
Mark
if you need a tool to pressurize the cylinders. My long lost in the forest buddy in Carmichael california ((daveo)made me one last year. If you need it i will look for it and lend it to you.
dom
 
After my carb rebuild my bike was running richer, even with the same fuel pilot settings, and would foul the plugs occasionally.

If you have the VM carbs, try closing up the pilot screw a bit (1/4 turn to start) and see if it improves.

~Adam
 
Oh geez, a thread from the dead! Sorry guys, I forgot to update this. Yeah I found out it was my rich jetting in those carbs back in June/July. Now that I have the bike jetted correctly it runs great and no more fouling.

Sorry, I always like to close a thread with a solution or at least something. I simply forgot all about this one months ago and moved on.
 
Thanks Hoomgar. I haven't messed with my jetting. But I did adjust the air mixture screws just prior to the carb synch a few weeks ago. The fouling has been since the synch job. I'll try backing that screw off 1/4 at a time.

Have been hunting ebay for the used Katana coils too. My wires are cracked all over the place. This should also improve the overall performance.

Thanks a bunch.

Rick
 
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