Running on 2 cylinders with bike carbs, 2.0 pinto - advice needed.

[rread97]

Hello all, 

 

so I’m after some desperate advice with some bike carbs on my 2.0 pinto, I’m running a vacuum dizzy with 1 vacuum outlet per manifold tube on the carbs and then the brake servo also on the 4th tube, these are all connected via t pieces and 6mm tube. 
 

the problem I’ve got is it only seems to run on 2 cylinders, I know this is a carb / vacuum issue as I’ve swapped back to the original 32/36 carb and it runs a treat. 
 

Any ideas what could be causing this? It’s only on cyl 3&4, if you rev the car above 3k then it seems to run normal / better, it’s only on low revs / idle.

also if I disconnect the vacuum pipe from 3&4 on the manifold then it runs much better. 
 

Could it be because I haven’t got a proper vacuum chamber and I’m only using 6mm pipe?

Could the carbs be faulty?

Could I have an air / vacuum leak?
 

any help is much appreciated!

 

[Peter Bell]

Personally I would do away with the vacuum advance on the dizzy, it’s only there really to improve fuel consumption, sounds like there are lots of possibilities for leaks, just leave one line for the servo. What fuel pump are you using, have you got a pressure regulator? 
Sounds like possibly carbs 3&4 are just flooding, are the needle valves ok in them?

[HAWKNORTH]

I have a 2ltr pinto on Yamaha R1 carbs. The vacuum dizzy is connected to the carbs via tube only. 1 to each cylinder and 1 for brake servo. All "T"d into 1 tube to the dizzy. No chamber at all. Pressure regulator set at 1.5psi. everything works fine throughout the rev range. I would think it's a carb problem on the lines of Peter Bells suggestions.

[rread97]

On 8/12/2023 at 11:35 AM, HAWKNORTH said:

I have a 2ltr pinto on Yamaha R1 carbs. The vacuum dizzy is connected to the carbs via tube only. 1 to each cylinder and 1 for brake servo. All "T"d into 1 tube to the dizzy. No chamber at all. Pressure regulator set at 1.5psi. everything works fine throughout the rev range. I would think it's a carb problem on the lines of Peter Bells suggestions.

This is exactly how mines set up, might need to strip the carbs down I think 

[rread97]

On 8/11/2023 at 10:51 PM, Peter Bell said:

Personally I would do away with the vacuum advance on the dizzy, it’s only there really to improve fuel consumption, sounds like there are lots of possibilities for leaks, just leave one line for the servo. What fuel pump are you using, have you got a pressure regulator? 
Sounds like possibly carbs 3&4 are just flooding, are the needle valves ok in them?

I’m using a genuine zx6r electric fuel pump, think it’s max 3psi, I’m not using a regulator no, which needle valves do I need to check? I’ve just started stripping the carbs down 

[Peter Bell]

Sorry just saw your reply so the pump should be fine, its the float needle valves in the carbs that may not be seating correctly.