choosing the right jetting: Jaycee/Geers 62 Terminators

[Jonny Grigg]

Hi guys,

some quick advice if you don't mind to get me in the right ball park with jetting my 62s.

The motor is 2442, massively ported CB comp eliminator heads on 46*40 valves, 1.4 rockers with a WebCam 251 grind. Compression ratio is 14.1:1. Carbs have 48mm venturis. Oh, and the motor is also running a small(ish) shot of N2O.

Yeah, OK the carbs may be a bit big for the valve size and heads but they were a sound investment for a future engine or two 

The current engine is for drag racing only running C16 race fuel in the UK roughly at sea level (1013mb air pressure) Ballpark calcs give me the following:

Main jet: 190
air corrector: 240
idle jet: ?
emulsion tube: ?

I could do with some advice for the last two or any comments on all the jetting based on experience.

Thanks

J.

[ugly duckling]

just my suggestion but reg 51.5 would have been more than enough carb for that recipe. my two bits .  UD .

[Phil West]

Hi Jonny,

Sounds like things are coming together then!  I'd start with an F11 emulsion, 195 main/220 air and a 70 idle.  Are you running a/f sensor etc in which case that will reveal all.

And if you do ever decide you want to downcarb I bagsy them big jugs!

Cheers
Phil

[Roman]

The terminators have a very weak vacuum signal. The classic calculation with main=4 x vent size didn't apply on mine.
I would start with 220 or more for the mains.
Call Geers or JayCee, they will give you hint.

[JamieL]

So -  we made it to rolling road and a 240 main wasn't big enough - lean (c.15:1 AFR) and wouldn't pull past 5k rpm...

Any suggestions??

I think smaller vents for improved air velocity and therefore more effective pressure drop to make the jet stacks work properly ...?

[Jonny Grigg]

Does anyone here have any experience of tuning Terminator carbs? Given the data (and logical common sense) we are not getting enough fuel into the motor when it starts to come on cam. Fuel pressure is rock-steady at 4psi, and going from a 220 to a 240 main made a bit of a difference, but it still went lean and flat before we got to 5k rpm. Going 200 really was the wrong way, but just upping the jet size doesn't feel right. Ok, I know the motor is over-carbed, but I want to get these running right. Our next step s to get some 45mm venturis made this week and go again....

Any thoughts would be appreciated.

[dangerous]

With the very limited experience I have with the terminators,
you will likely need to use a smaller venturi being that you only have a 46 valve.

Which is why your mains-changes are not responding as they should.

We also found that the air corrector effected the curve very early,
but this assumes you have enough signal to initiate the main circuit the first place.

[blue bullet]

with my 58 berg is the same problem ...the solution is  reduct the air corrector .(210fuel/190 air for the base) .

[bedjo78]

engine 78 X 101.6 . Not quessing but I end up with  48 vent  230 main / 180 air / F2   and  75 idle.  .  .