New plugs every 800 miles

Tom Willis · Post by **Tom Willis** » Mon Sep 10, 2007 1:41 pm

Could use some help with this one. 74 750 GT restored 4 years ago & 14,000 miles. Electronic ignition, new needles when carbs rebuilt, stock coils and new (then)

non resistor wires. Always starts 2nd kick with full choke when cold and runs great until plugs need changed. Plugs have some carbon build up but not the heavy carbon buildup I expect to see. The bike will begin to either start poorly or pop more than normal at cold or even loose fire to the rear cylinder. Needles are dropped to the top notch on the rear and middle on the front. When weather is 40-50 degrees I have to limit how long I stay on choke as it shortens the life of the plugs to less than 800 miles. Plugs are NGK B7ES. Timing, valve adjustment, float levels and carb sinc are all good. Further investigation shows K-3 needles, AB 265 atomizers, 120 main jet front soldered and drilled to a 115, 120 main jet rear soldered and drilled to a 110. When running fresh plugs the rear is charcoal colored and the front, if you use your imagination, has a slight color of brown.

I am thinking maybe a worn atomizer assembly, wrong plug wires, or maybe it just needs hotter plugs.

Post by **BevHevSteve** » Tue Sep 11, 2007 10:19 am

try BP7HS plugs, always leary about soldering and re drilling and recommend just buying new jets. I also recommend when you replace needles to also replace the atomizers as they rub against eachother and are the same material....... If 1 is worn, so is the other.

What does a leakdown test tell?

Check valve guide seals....... worn?

Compression?

Tom Willis · Post by **Tom Willis** » Tue Sep 11, 2007 11:14 am

Steve,
The main jets were already drilled but I was trying to establish whether I was close or not. The Haynes manual says 118 front and 112 rear so after measuring I think I am "in the county" as far as sizes go. I am sure a new atomizer, needle and main jet would help but I am not convinced it is just a carburation problem. It starts and runs too good to be too far off. I will try different plugs. Will wire core plug wires work OK with stock coils and electronic ignition? I checked compression 14,000 miles ago when I restored the bike. Do you think I should do another check? Just kidding! I plan on doing another after I reassemble the carbs. Are you thinking maybe some oil fouling versus too rich a fuel mixture?
Thanks
Tom

Post by **BevHevSteve** » Tue Sep 11, 2007 11:53 am

yep, that was what I was gettin at

Tom Willis · Post by **Tom Willis** » Tue Sep 11, 2007 1:36 pm

I will let you know what I come up with...my problem is I don't stop riding it long enough to fix it!

Tom Willis · Post by **Tom Willis** » Thu Sep 13, 2007 5:49 am

125# rear, 127# front. Don't know how to do a leak down test. I have valve guide seals in the top end gasket set I bought from you. Can they be put in without pulling the heads? I think if the plugs were wet looking when I pulled them and it was just fuel wet they would dry out. These still look wet and do feel of oil.
Thanks

wdietz186 · Post by **wdietz186** » Thu Sep 13, 2007 9:14 pm

Tom, I had the same symptoms with my 75 GT years ago. While you could be running too rich and pushing some oil I suspect you have low battery voltage and tired coils. The stock coils were pretty weak to start with and unlike wine they don't improve with age. I would suggest fitting some Dyna coils. You state you have elect. ign. most systems are pretty sensitive about supply voltage it seems 10volts is about the lowest voltage they will tolerate. If you run with your lights on and at lower revs the charging system won't be able to keep up and available voltage will drop off. I've used the Dyna ign. and coils in my bike for 20yrs. with no problems at all. But I do have to keep the battery charged.

Tom Willis · Post by **Tom Willis** » Fri Sep 14, 2007 6:03 am

Thanks for the input, very interesting! I had to convert my charging system to a Detronics because I (self inflicted) shorted my stock voltage regulator while cleaning terminals several years ago. Recently my battery needed replaced so I put the 2 year old Oddessy battery from the Guzzi in until I get a new one. It charged at first but now won't hold a charge very well. With my charging system I am lucky to run between 12.0 volts and 12.4 at the most. After a 25 mile highway speeds run the other day it actually went down from 11.9 to 11.0 so I know it's time for a new battery. Tail light bulb burned out on the ride also which could be a sign of low voltage. The bike now has 26k on the stock coils so maybe it is time for some new spark!