32 replies to this topic

[Kevybmini]

Ok, here goes.

 

New engine build all running fine, head gasket goes so upgraded to stage 3. Since then soon as accelerate hard in say 2nd it’s as if the carbs run out of fuel. Vac gauge all over the place, 20 seconds later all is well and drive off again.

 

Done so far :

 

Cleaned out fuel tank and removed internal filter

Blew out petrol lines

4/5.5 PSI Facet (new) but had the same problem when using the mechanical pump, got 3 PSI at the carbs

Twin HS4’s

Checked and cleaned float bowls

Blew out the jets

Tried with and without fuel regulator 

I’m at a loss what to try next

 

[viz139]

Sounds like a fuel volume rather than fuel pressure problem. Check that you haven't squashed the fuel pipe under the car. I had this problem only when driving hard.

[Kevybmini]

Mmmm that’s not a bad idea

[nicklouse]

So if I read this right. You have greatly changed the engine spec and ability but not touched the needles?

[Kevybmini]

No haven’t touched the needles - currently has no6 needles and red springs. It seems to just run out of petrol when you rev out say 2nd gear - pull over just about running with vac gauge fluttering - 20 seconds comes back to life and off you go for another 1/4 mile

[Avtovaz]

try putting a new coil on it.

 

it could be something to do also with the advance? check the earth strap in the dizzy is ok if you still run a dizzy, and where the point go under the spring [the red or blue bit]  its on the right way, not earthing out on the body.

Edited by Avtovaz, 23 April 2024 - 05:44 PM.

[Kevybmini]

New Aldon electronic dizzy

[Lplus]

Upgraded to stage 3 from what?  cam change as well?

 

 

For twin HS4s I've found  blue springs and CP4 needles are a good compromise in lightly modded 1275.  Since you have no 6s in there, they must be fixed jet carbs, so the CP4s don't need modifying.

 

I'm asssuming a 1275...

[nicklouse]

No haven’t touched the needles - currently has no6 needles and red springs. It seems to just run out of petrol when you rev out say 2nd gear - pull over just about running with vac gauge fluttering - 20 seconds comes back to life and off you go for another 1/4 mile

So have you checked the float chambers when it stops? 
 

ie kill the engine when it “runs” out and then pop the covers off. 

 

if you have not done that you don’t really know if it is running out of fuel or if there is another issue.

 

you will need to do this a few times to get a consistent result. Unless it is totally without fuel.

[Kevybmini]

 

No haven’t touched the needles - currently has no6 needles and red springs. It seems to just run out of petrol when you rev out say 2nd gear - pull over just about running with vac gauge fluttering - 20 seconds comes back to life and off you go for another 1/4 mile

So have you checked the float chambers when it stops? 
 

ie kill the engine when it “runs” out and then pop the covers off. 

 

if you have not done that you don’t really know if it is running out of fuel or if there is another issue.

 

you will need to do this a few times to get a consistent result. Unless it is totally without fuel.

 

Not a bad idea 

[68+86auto]

Do you have a filter between the tank and pump? If so then remove it, unless it is a mesh screen type.

Edited by 68+86auto, 24 April 2024 - 06:01 AM.

[fatcatvera]

It is possible that the float valve is too small a diameter and is choking the flow into the fuel bowl. I'm aware if two tuned engines having this issue with HIF44 carbs fitted.

 

On both we fitted the 'Turbo' valve :- https://www.bullmoti...wzx1095/WZX1095

 

The diagnosis for each before the valve being changed was lambda going digitally high (engine going lean) and inspection of the float chamber showing empty of fuel.

 

If you're running an HS4 then I'm not sure whether larger diameter/bore valves are available or even whether this can be an issue on the HS4?

[Lplus]

It is possible that the float valve is too small a diameter and is choking the flow into the fuel bowl. I'm aware if two tuned engines having this issue with HIF44 carbs fitted.

 

On both we fitted the 'Turbo' valve :- https://www.bullmoti...wzx1095/WZX1095

 

The diagnosis for each before the valve being changed was lambda going digitally high (engine going lean) and inspection of the float chamber showing empty of fuel.

 

If you're running an HS4 then I'm not sure whether larger diameter/bore valves are available or even whether this can be an issue on the HS4?

The op has twin HS4s  I don't see how a pair of valves would be insufficient to fuel a 1275.

[Ethel]

Float chamber vents?

 

Float pivots?

[Kevybmini]

Latest conclusion following much much messing about. The fuel pressure is too high so going to turn it down to 2psi. Was chasing not enough fuel but think it’s too much and flooding the engine. Update to follow when it stops raining this weekend. Thanks for all the replies