K&B 3.5 NEED HELP WITH A FEW QUESTIONS.

[Rokieboater]

I have a new guy setting up a .21 mono and he has a K&B 3.5. Was wondering if anyone remembers if that motor ran a short or long plug. Maybe a ggod starting point on head clearance. Without shims it is .032.

 

[Kez]

The K&B 3.5 runs a short reach plug.
I can't remember the head clearance. But I will try to measure mine

 

[Tom Foley]

I would run no more than .015 head clearance . Less is even better down to .006 but if he is new stay a little conservative . run a little rich for the rod life .

 

[Al Hobbs]

The early K&B 21 engines used a short plug. Later versions used a long plug.

I think that you would want 0.006' head clearance.

The weak point in that engine is the connecting rod.

 

[Wasted wages]

Non idle bar ....

 

[Stevegross]

What % nitro is everyone using? I have a gold head to try next year.

 

[brad nichols]

! ran mine on 50% but 60 is good to but that's up to you and how long you want it to last.

Brad

 

[Wasted wages]

I've seen people run them on 25% to 65% with various degrees of success..
Higher percentage, and needles start to get finicky... 40-50% seems to work well..

Just check the rod and bearings often..

 

[Mike Hughes]

12mm cranks ran the short plug, 13mm changed to long. But both head buttons fit the same motor so there is a possibility that it could have change. If you see the side of the head and its about 1/8 showing then it is the short plug. More would be the long one.
Mike