keeps fouling plugs

[BROOKSIE]

Well I'm back again.
I bought this bike a month ago (1980 midnight special)
after riding 35 to 40 miles all four plugs are sooty black and they foul out.

I cleaned and adjusted the carbs, no changes 35 to 40 miles black plugs. all jets are stock sizes air cleaner is new

Then with the help of this site I fould out I had the wrong TCI had a 4R0 needed a 2H7. found one and put it on the bike.

Checked the coils, the resistor (volt meter while riding) the battery, charging system, all wires and conections, checked the wires to the pick-up coils, all good

Mecanic friend of mine checked the pick-up coils on a scope and found them to be acting erratic (Have not replaced them yet)

Between my friend and I we have checked and rechecked everything we can think of.

Any thoughs, I'm about to throw in the towel any good xs guys around Bellingham Wash?

Thanks, Pulling my hair out and don't have much left

[mason79]

you didn't mention how it ran,in all rpm ranges


make sure they are the right heat range plugs since all four are running the same, or maybe the needle jet is one notch too low.

[petejw]

Did you check your float levels
when you had the carbs apart?


pick up coil wires have a known
problem of breaking wires, theres
several posts about checking and fixing
sorry i dont kno how 2 post a link.

[TADracer]

Sounds like you checked out everything except perhaps your plugs. Might be that your PO had put automotive plugs in your bike. Some will work but it is really hard to find the right heat range that suits an air cooled motor. The correct heat range can cure a host of problems. I think the stock plug for your machine is NGK BP-6ES. Perhaps a set of these might cure your problem.

[mitch]

Wires

http://www.xs11.com/forum/showthread.php?threadid=543
Try this
Doug

[thewiz]

There seems to be a bit of a contradiction here ???

."....checked the wires to the pick-up coils, all good
...Mecanic friend of mine checked the pick-up coils on a scope and found them to be acting eratically... "


Now the PU coils themselves are hard to kill .... all they do is send a little magnetic pulse to the TCI. Seems unlikely that one would ever go bad on it's own.

The wires that connect them to the harness ..... now that 's a whole 'nother story. These wires wear so thin that you can pull 'em apart with your fingers and there is seldom any indication superficially ... sooo .....

Try this ... with the bike running as best as it can, wiggle the wires at the PU coils and see in you can cause a change. There are TONS of threads on this site about this subject.

IMHO, this PU coil/wire thing must be sorted out first before moving on to carbs .....

[TopCatGr58]

Hey there Brooksie,

Okay, first we need/want to know about any mods to the bike, like Individual filters, or K&N air filter in OEM airbox, drilled bottom of box, as well as STOCK pipes, or 4-1 or other aftermarket pipes vs. the OEM black Chrome ones?!

Secondly, the bike is new to you, but you don't know what the PO has done to it before hand, including what brand of jets were put into it?? Folks have gotten carb kits with what were marked as the right size/# of jets, but due to different brand of manufacture, they were actually way too rich, causing all sorts of problems, similar to what you've described with overly rich condition, black sooty plugs! BTW, what ARE the sizes of the jets you currently have, both pilot and mains?

Getting a set of genuine mikuni Pilot and main jets will go a long way towards solving the problem. ALso, what height did you set the floats, the 80 uses 23mm vs. the 78-79 that uses the 25.7mm setting, yours should have had the newer plastic floats vs. the old brass ones.

ALso, Yamaha put out some funky carbs with mixed bag of parts in 80 due to the transition from the earlier model to the later model....so....did yours have the rubber plugs over the pilot jet towers, or were they open? Also, check to see IF there is a small tunnel linking the pilot jet and Main jet towers! And then check to see IF the Main Jet NOZZLE/emulsion tube has a matching small hole in the end/side of the nozzle that would match up with the TUNNEL between the main and pilot jet tower.

The earlier model carbs use the pilot jet rubber plugs/caps because they are supposed to get their supply thru that Tunnel from the Main Jet, and IF the caps are not there, then they are getting fuel directly from the bowl which can make them much richer!!
T.C.

[Ken Talbot]

Re: There seems to be a bit of a contradiction here ???

Originally posted by thewiz
Try this ... with the bike running as best as it can, wiggle the wires at the PU coils and see in you can cause a change. There are TONS of threads on this site about this subject.

There's a little technical article here that I have referenced once or twice while diagnosing and repairing problems with the pick-up coil wires....

[BROOKSIE]

Topcat,

I know the PO he rode the bike back and forth to work and had no problem, never fouled a plug or in my case plugs.

Only mod I have seen was a K&N air filter (should I try stock?), exhaust is stock.

This seems to have been a sudden problem that affected all 4 cylinders at once.

It has plastic floats and they were set at 23mm. I find it hard to believe all four carbs would fail at the same time. Gas tank is free of rust and carbs appeared spotless but I cleaned them anyway.

As for the pick-up coils I have pulled on the wires untill I thought they should break but, I'll try again.

Think I may try new coils from mikesxs and see if that changes things. (caps are good and I have tried hotter plugs)

Thanks for the information.