Plug colour

[jfligg]

Hi Guys
  I am in the midst of tuning a PWC carb I installed on my 61 Super Rocket.  I have dropped two main jet sizes and the plugs are still black.  I am hesitant to drop another size.  I have a friend and he says with this modern fuel the plugs are always black.  What colour are your plugs.  anyone got brown plugs?  Jeff

[nagrod]

My 60 Super Rocket has 50 miles on a rebuilt engine. I pulled the plugs after a 5 mile ride this morning (no plug chop) and they are greyish white at the insulators. I know in the good old days this would indicate a lean mixture and I am thinking of raising the needle a notch to see. It's been starting and running so well I hate to change anything!

Rick D

[BSA_54A10]

Our bikes can not burn modern fuel properly at idle.
It is not all that much better at speed but if you do a plug test after idleing they will be black, & usually wet.
If you do the plug chop properly ie kill the spark &  declutch coasting to a stop then they should be a reasonable colour.
Remember the engine must be at it's usual operating temperature which will take at least 15 minutes on the road.

[Triton Thrasher]

My 60 Super Rocket has 50 miles on a rebuilt engine. I pulled the plugs after a 5 mile ride this morning (no plug chop) and they are greyish white at the insulators. I know in the good old days this would indicate a lean mixture and I am thinking of raising the needle a notch to see. It's been starting and running so well I hate to change anything!

Rick D

No harm in raising the needle height as a trial, but if it's running well without pinking, the needle height probably isn't wrong.

 There is a procedure for getting all the carburettor settings right.

[nagrod]

Thanks for the reply - I did notice a little pinking yesterday which made me check the plugs. I dug out the sheets I have accumulated on tuning the Monobloc. I am thinking since most if not all of my riding is below wide open throttle the needle position is the place to start. I am not so concerned with the plug color as I am with the pinking.

Rick D

[fido]

Yes, the modern fuel is not very good and plugs are more likely to soot up. Some people on Velocettes have improved matters by using a different grade of plug

[muskrat]

 G'day Jeff,
               those carbs are good but can be a bugga to tune. I run a pair of 30's on the cafe and had to change everything from the stock settings. The needle is the hardest to sort out, there must be about 30 to choose from  . Also went to 3 1/2 slides (cost nearly as much as the complete carb).
Most of normal riding (wots that) is on the slide or needle. Hope the attached chart is readable.
Cheers

[jfligg]

Hi Muskrat
  Should I go back to the original main jet and try the needle position.  Were do you think the most logical place is to start with tuning these carbs.  Should I tune with the air filter on or off.  Thanks Jeff

[A10Boy]

I have a "std" A10 with a std set up in the amal 376 and std exhausts. The plugs are a nice brown just like you would expect. So it is possible with modern fuel.

My problem is an irregular tick-over due I think to wear on the slide.