Yamaha F8 top Plug Fouling

Misguided · 10-17-2009, 08:31 AM

It happenened the other day while trolling, it's the top plug only that is fouling & when pulled out it's black & sootie lookin & smells like gas.

I replaced both plugs the next morning, perfect running like B-4, then after 4 hrs into the trool it started running rough again, same results as above.

I fear it may be in the ign. system & that sounds ilke money!!!

Any help appreciated. Jim Sr.

Highmark · 10-17-2009, 08:45 AM

How does the bottom plug look ?? and what is the comprission on that cylinder ???

Misguided · 10-17-2009, 09:06 AM

Quote:

Originally Posted by Highmark

How does the bottom plug look ?? and what is the comprission on that cylinder ???

Bottom plug is fine, as far as compression, I don't know. Don't have a Comp Tester.

This motor has between 100 & 150 hrs & have never had a problem starting or running

Highmark · 10-17-2009, 09:19 AM

Is the slow trool at idle or just above it...? it's not carb thing it would
be doing on both plugs. one other thing, is it heating up..?
if it not heating up. that could foul it. running to cold..
I would test the compression on that cylinder and the thermistat.

Misguided · 10-17-2009, 09:32 AM

It is just above slow idle (the sweet spot is what I call it on a slow trool). What if it was... heating up? (overheating?) I don't remember smelling it at the time it started the rough idle.

It has the same BR6HS10 plugs, which are the hotter plug.

Misguided · 10-17-2009, 11:02 AM

I was advised on another forum (http://www.boatdoctor.com/) to swap the coils & see if the problem follows to the bottom plug, I have not recieved a reply from him on this, so is he refering to swaping the plug wires?

Highmark · 10-17-2009, 11:39 AM

It could be plug wires. if it's not heating up enough to open the
swtich in the carb it may get to much gas and do the same thing
this has been talked about before. I'm remembering bits and
peices of that. it has something to do with after it heats up
to a temp range it trips something and cuts back on gas.
Now to much gas will do what you are seeing..
that is why I said that... now it if the coil voltage is low
it will not have enough spart or a weak spark and do the same...

Quote:

Originally Posted by Misguided

I was advised on another forum (http://www.boatdoctor.com/) to swap the coils & see if the problem follows to the bottom plug, I have not recieved a reply from him on this, so is he refering to swaping the plug wires?

Misguided · 10-17-2009, 12:55 PM

I just got the reply on the other forum & he checked the manuals & it only has 1 coil so no go on that.
I need to get the valve adjustment checked next week & will have tech do some checking.

Thanks for your time to all who replied.

Jim Sr.

Gundog · 10-18-2009, 11:44 AM

Do you have a hot hands connected on this motor? I have heard the hot hands can make the motor run cold in very cold water.

Mike

Misguided · 10-18-2009, 07:03 PM

Quote:

Originally Posted by Gundog

Do you have a hot hands connected on this motor? I have heard the hot hands can make the motor run cold in very cold water.

Mike

No, but it was tapped by the factory. It has been in the 60's when it happened.

Misguided · 10-27-2009, 08:26 PM

I got the motor back, mech. tuned the carb,said it was running rich(they sometimes do this). All is well now, runs like a DEER (champ).

I love my little sewing machine, that's what it sounds like to me.