spark plug fouled

[Bill Conquest]

Hi - I've been having a problem with my right side spark plug fouling after 100 miles or so & have noticed some dark soot deposits at the end of my ex pipe - where should I begin to look ? It's a '79 r65.
Thanks, Bill

[montmil]

Bill, What does the spark plug look like? Oil fouled or dry. Any other odd operational symptoms happening?

Perhaps try a swap of the ignition leads and see if the plug fouling changes sides.

Monte

[Barry]

Bill

First thing I'd check is that the right side choke is fully off i.e. both levers are hitting the stop at the same time.  If it's not that I'd look at idle mixture both the idle mixture screw setting and check that the idle jet O ring is sealing.

If mixture is OK could the right side be burning oil. Take a look through the spark plug holes and compare piston tops side to side. With the right light source and with the pistons at half stroke you should actually be able see oil along the bottom edge of the piston if it's getting into the combustion chambers.

[Bill Conquest]

Thanks guys.. the plug seems to be oil fouled -a dark,sooty deposit. I only have one choke lever, but I guess I should check the cable?And i'll take a look in the cylinder to see.How do I adjust the idle mixture screw? Also one thought - I have seen a bit of oil in the air intake area, could that be a factor?(I keep the bike on the center stand).
Thanks,Bill

[tvrla]

Do check the cable adjustment to make sure it returns completely.

But a good diagnostic approach is to swap plug wires side to side as advised. If the problem migrates then it's in the coils or leads. If it doesn't then it's either fuel delivery or a compression problem. You could do a compression check to see if that side is down.

When did this problem start? How long has this been going on?

[Barry]

Bill, You should have one choke lever on the air filter housing but it has two cables one to each carb both with cable adjusters at the carb end which should be set so that both choke operating arms hit the stops at the same time. There are stops on the carb body for fully open and fully closed.

Dark dry soot is not necessarily oil fouled.  Any carb related problems are going to be easier to fix than excess oil consumption so I'd eliminate carb issues first. If the engine is running well it's quite hard to have the running mixture settings so far out that it actually fouls the plugs and it's more likely to be excessive use of or faulty operation of the choke.

There is always going to be a little oil from the engine breather in the intakes particularly with short runs/cold weather.  If there is enough getting into the combustion chambers to foul the plugs surprisingly it does not all get burnt and you will be able to see it pool at the bottom edge of the piston and the piston top will be wet.

[Dizerens5]

On my 79 the choke cable inners are stiff wire, not the usual flexible stuff. Sometimes one or other sticks in the outer so the choke does not open correctly (for normal running) when you put the lever to normal. Then I have to push the outer down by hand. It was a while before I noticed what was happening and causing misfire with warm engine.

[Bill Conquest]

Thanks for the ideas...I put 2 new bosch plugs in & it fires right up..i'm beginning to wonder about the coils.I have replacements & just ordered new wires & caps & will replace everything. How can I test the coils? thanks, Bill

[Barry]

A basic test on the coils would be to measure the primary and secondary resistance.

Primary resistance between terminals 1 and 15 should be 1.5 Ohms and secondary resistance measured between the HT tower and terminal 15 should be approx. 7000 ohms.

Exact values are probably less important than both coils measuring the same as that would tend to indicate there were no internal shorts on one coil. Another reason for not worrying about exact values is most people are unlikely to a have a meter good enough to measure 1.5 ohms with any degree of accuracy much better than + or - 7%.

[Bill Conquest]

Thanks, Barry - i'll give that a try on the old ones when the wires come & the tank is off. Ran a check on the replacements & they run 1.9 each on the primary, secondary I couldn't quite read with my meter-doing something wrong... Thanks, Bill