Supercharger Stalling

I’m trying to get my Eaton m45 suck through supercharger set up so I can get it to the rolling road, the car will Idle fine around 14 on the wide band gauge but when I Rev it will stall straight away and go to around 9 on the afr gauge.

I’m running a Hif 44 carb with a 12oz green spring and a vmax spec carb needle with 2.5 psi of fuel.

I’m in the process of getting the static ignition timing sorted to 9 degree ( vmax electronic distributor ) but would this cause the car to go rich and stall if not set correct ?

I’ve got a few other needles I can try which include a BCA or a BDK.

Any suggestions please ?

Edited by sam138, 29 August 2021 - 07:26 AM.

Could be ignition, if it fails to ignite properly it'll could chuck unburnt fuel at your lambda sensor.

 

I don't think it'd be the needle if it's the carb, sounds more like something is stopping the piston from rising creating lots of depression over the jet & sucking too much fuel in. Sticking piston or damper, inlet elbow/ filter housing gasket obstructing the communication port to below the piston?

Thanks for the reply, could you advise how to best test the carb for these issues ? Can I take the cone air filter off and run the car to see if the piston rises ?

Sure, may not move much if there's no load though. Just lift it with a finger to check for physical obstructions, how smoothly it drops back will be more telling.

 

You'd see lack of clear hole here: (Good job MG enthusiasts aren't as lazy as me)

 

http://www.mgb-stuff...images/su3d.jpg

 

Thanks, does the Hif44 have the same hole layout that could be blocked as per the pic ? If my air filter gasket is covering the hole do I simply trim gasket ?

Edited by sam138, 30 August 2021 - 08:19 PM.

I’ve checked the carb as per above and changed the dash pot oil from 20w/50 back to the SU oil as it wasn’t very smooth the thicker oil.

Even with two fingers you still have to put some pressure on the piston to lift it up, is this because of the 12oz spring ?

I started the car again and I’m still having the same issue, if I rev the car slightly it will almost stall but revs then pick back up to idle, almost as if the car is hunting. If I press the accelerator fully the car will stall.

Bump

Thicker oil will make the mixture richer under acceleration. The damper is what an SU uses in place of an accelerator pump - it slows the piston rising, so the air has to flow faster through the narrower gap above the jet. That creates a bigger pressure drop that sucks more fuel in.

 

Afraid it's going to be difficult to track down if it's not something obvious or broken....

 

The place to start is with the ignition as you can measure the timing against simple specifications with a strobe. How the fuel burns is dependent on the ignition, so you'll chase yourself in circles if you try to set up the carb with dodgy ignition.

 

A carb will be like a stopped clock that must be right once in 12hrs, so if everything else is ok you should at least be able to get it running even if it goes rich or lean when you start making power.