Hey everyone. As some of you might be aware I've just got my new engine going in the car. Just trying to finalise the tune at the moment before Warwick next weekend.

Engine is 2054cc, Scat C20 cam, Los Pachitos heads with 1:1.25 ratio rockers. I'm running twin 40mm Kadron carbies.
009 Dizzy set around 30-32° with Petronix electronic points kit.

The carbies currently have 55 idles and 130 mains.

I've set the idle and synced them up. It idles around 1000rpm at the moment. When I drive it it's a little stumbly and has some hesitation. I think this is mostly due to the dizzy.

The issue I'm having is when I go to set the mixture screws. When I wind the LHS carby mixture screw in the carby just keeps running. It doesn't start to drop of at all, even when the screw is all the way in. What could be causing this?? The RHS carby works as it should and starts to drop off and dies so I give it 1/4 back out.


The other issue I'm having is she seems to be fouling the plugs at idle.
I drove down the Gladstone today, 300km round trip. Before I left to come back I stopped at Red Rooster drive through to get some lunch, was sitting there probably 5-10 minutes with the car idling. When I left and was driving though town the car was missing and backfiring. I think I fouled the plugs up. Got her out on the highway and it wasn't long before the plugs cleaned out and she was running sweet again. Same thing happened as I was driving through Rockhampton, just from stopping at the lights. Must be running quite rich to do this so quickly.

Is this because of the idle jets being too large? Or something to do with my not being able to set the mixture screw?


Help would be much appreciated, I only have a few days to sort this before the drive to Warwick.



Smiley

mmm........ new carbs??
blocked idle on the LHS would be my guess.
Pops and backfires when idling - runs good on the mains

What pressure you running?
Stock fuel pump?
Kads like 1.5lbs?

Have you had a read of http://www.lowbugget.com/help_section.html 

Your running on the rh only. You need to back down the rh carb idle speed and raise the lh, untill they both respond equally. The fouling will sort itself out once the carbs are running better, depending on what plugs are in there.

Hi

What Matt said, I wouldn't leave your motor idling for that long, particularly a new motor.

You can check your synchronization by pulling #2 & #4 leads of the dizzy cap in turn until you get an equal drop in revs each side.

Steve

Hi

What Matt said, I wouldn't leave your motor idling for that long, particularly a new motor.

You can check your synchronization by pulling #2 & #4 leads of the dizzy cap in turn until you get an equal drop in revs each side.

Steve

Won't that mess up the syncronisation?

It mustn't be right by your description. How did you sync them? Post a pic of your gear, we know you like posting pics

Quote:

Originally posted by matberry It mustn't be right by your description. How did you sync them? Post a pic of your gear, we know you like posting pics

I've just triple checked the carbies again. According to the tooling they are syncronised spot on perfect. At idle they are both on 7 on the gauge on the tool.

But if I wind the mixture screw in on the LHS carby the same issue occurs. The revs pick up slightly as it's nears the sweet spot then the crew bottoms out in the hole. No more adjustment and the revs don't start to drop off.


Smiley

Maybe give this a read:

http://www.lowbugget.com/main_page.html

and downlaod the tuning guide:

http://kaddieshack.com/

I just do it by ear , I would turn both idle screws out so that the motor idles about 700 ,
I always use the 10 heat spark plugs not the 8
then check the timing try about 7deg

By ear for me, sync tools are for 'I don't know who'

Check the idle jets because you can, and you want to confirm your sync by pulling plug leads (or shorting them to earth pref). All cylinders will make equal rpm drop when tuned correctly. The rh carb may give you a clue as to where the mixture screw should be. If it responds as you'd expect, sus out where the mix screw is from bottom (careful not much pressure onto the seat), and compare to lh. set l roughly similar and again kill cyl's and compare if one side is stronger than the other. The stronger side is running faster idle than the weaker side so adj idle screws to compensate. You want each idle screw to make the same idle speed change, just like your mixture screws. Dial em in and sync the linkages after all carb adjustments done and go for a spin.....the linkages are equally if not more important to get just right. It's all about getting both carbs to start moving off idle at EXACTLY the same time.

Sweet. Thanks to everyone for the replies.

I know about setting the linkage right, very important

Should I fit the balance tube between the manifolds too??



Smiley

^ personally, tune with it blocked, but run it the rest of the time

I would fit the balance tubes between the manifold, if you read into Kads a bit mroe they are a plenum carb just like a holley 4 barrel and the like.

You need them to balance each other up because you have the 1 carb feeding both cylinders,