Whats size needle and main on a BBK

[turbowrenchhead]

I had a customer bring me a 89 blasty with a vito's bbk on it. It had a lean burn down condition. It has fmf exhaust, air lid removed, stock carb with tors removed. I went through the carb and moved the needle to the richest setting (all the way down). It also has a 340 main in it. I ported the vito's cylinder a bit more too. I bored it over to 73mm and got it going again. I gave him a lot of info on jetting and warned him to let it warm up and get it jetted right with plug chops. Well he must not of done any of that and blew her up in a weeks time.
What should I be looking at for a needle and a main? Whats in there is not cutting it. The combustion chamber was grey in color and the piston was quite scored.

 

[Triple_B]

Start rich and work your way down. Go up like 4 sizes and then go down from there.

 

[turbowrenchhead]

Start rich and work your way down. Go up like 4 sizes and then go down from there.

On which one? The needle or the main?

 

[Triple_B]

On which one? The needle or the main?

The main. You really shouldn't need the needle other than fine tuning. Having it all the way down and it still being lean says that you need to go up in the main jet

 

[turbowrenchhead]

The main. You really shouldn't need the needle other than fine tuning. Having it all the way down and it still being lean says that you need to go up in the main jet

There is an aftermarket needle in there and its blue in color. It must of been from the vitto's kit. What size needle should I look for because I'm going to replace it this time around with a richer one.

My personal experience with my blaster tells me that the needle is more then just fine tuning. I had a 160 main jet in a 35 pwk with a modded motor. I kept having multipoint seizers and went through a couple of pistons in the process. I ended up going 4 needle sizes richer and now its gravy. Now I'm running a 158 main and its still a bit to rich. I could go to a 155.

 

[Blaaster]

That blue needle is a pretty rich critter, I would put it aside for future use and fit a stock on the middle clip.

#340 main seem to me to be big enough, and should have done ok.

Did you leak test the motor before you sent it back? It screams of air leak to me.

What oil ratio is being used?

You are so right when you say about the needle, you just cant guess where it is.

The float level should be correct, idle adjusted just right.

Plug chops should be done WOT, and on the needle at 1/2 and 3/3 throttle to get it right.

I would bet you a Dollar to a pound of crap that heat cycles and proper break in was not performed.

Did you inform him not to just ride but but to break it in properly?

 

[Awk08]

ding ding ding /\/\/\
i smell an airleak/improper break-in/warm-up aslo.

was the cause of the original seizure pinpointed before frying the second batch of eggs ?
i'm betting they were both airleak related ?

there's not much info available for jetting stock carbs on bbk cylinders, as most upgrade to a larger 34mm+ carb

maybe a call to vito's would help, i saw someone mention a toll free hotline with a bunch of info ???
but it has to be proven air tight before anything