34 replies to this topic

[petey81]

Hi all

I have installed a New head (recent posts about double valve springs)on and running but I cant get the afr gauge below 11.8 on idle! ( Usually sits at 14)I've checked the valve clearances, timing and for air leaks but nothing.
I have taken apart the carb needle valves and there are closing fine when blown through, I'm stuck lol
Also I have tried to lean out the carbs but making little difference- they have been leaned out as far as they go! Plugs are very sooty
I have a fuel pressure regulator which makes zero difference when adjusting.

Any advice? Cheers

[miniGTS]

What needles do you have in there?

What springs in the dashpot assembly?

Is there oil in the carb dashpot piston?

[petey81]

All the same as removed a few days ago. Car was running and carbs set up in Dec on a rolling road.
Needles were profiled years ago by AC

[Lplus]

Hi all

I have installed a New head (recent posts about double valve springs)on and running but I cant get the afr gauge below 11.8 on idle! ( Usually sits at 14)I've checked the valve clearances, timing and for air leaks but nothing.
I have taken apart the carb needle valves and there are closing fine when blown through, I'm stuck lol
Also I have tried to lean out the carbs but making little difference- they have been leaned out as far as they go! Plugs are very sooty
I have a fuel pressure regulator which makes zero difference when adjusting.

Any advice? Cheers

Presumably you mean you have screwed the jet adjusting nuts up until the springs are coil bound.  Are you sure the jets are following the jet screws upwards?  Since you replaced the head and thus removed and replaced the carbs, is the choke cable too tight and holding the jets down?

[petey81]

Hi I have yeah and wound down 12 flats, and it drops the afr to 9. Choke is fine as in testing with it connected and disconnected. The carbs were set at 12 flats down(from jet flat with the bridge)
I'm thinking it's the fuel pressure regulator...
The carbs were just removed and not replaced

[cal844]

Now you will need the carb reset. Phone AC Dodd and get him out to work his magic. Replace the fuel pressure regulator for a well known brand (not the Sytec push adjuster type)

[petey81]

Carb has been reset to what it was after the rolling road. I mark it up and measured it.
I've missed the last few tuning days with AC but happy to book in asap.

[timmy850]

Do the plugs have consistent colour on them? It could be only one carb is over fuelling

If the float level is too high it will also cause rich running

[68+86auto]

You haven't confirmed that the jets are actually going back to the normal position.

 

 

get rid of the fuel regulator entirely and fit the correct pump.

[petey81]

Do the plugs have consistent colour on them? It could be only one carb is over fuelling

If the float level is too high it will also cause rich running

Plugs are all sooty. The float height has been checked and is perfect

[petey81]

You haven't confirmed that the jets are actually going back to the normal position.


get rid of the fuel regulator entirely and fit the correct pump.

Jets are going back to the normal position.
I will look at fitting the correct pump but have used a pressure regulator for 10 years with no issues.

[petey81]

Update. I have reset carbs back to factory settings and checked float valves again plus fuel pressure regulator fitted but no change.
I have noticed that if I disconnect the carb breathers it runs fine and the afr gauge is at 13! All I did was change the head 😂 so stuck with ideas! Maybe I have a vacuum issue? Or I need to fit a pcv? Engine cannister goes straight to the carb connections. Very odd and frustrating lol
I do have quite a few bubbles in the fuel filter...

Edited by petey81, 17 April 2025 - 04:36 PM.

[timmy850]

Do the engine breather ports go to the side of the carb? Or do they go to the manifold port?

It could be something simple like the oil cap breathing hole being blocked, or a significant air leak somewhere that’s allowing too much or too little air to the carb ports

[petey81]

They go to the carbs. I have a spare oil cap which made no difference. I can't locate any air leaks.
I will do more checks tomorrow, all happened after changing the head which I've done many times on my cars and other people's. I will remove the carbs again lol

[Steam]

The pressure regulator has zero effect on mixture unless it is restricting the float bowl fill time so badly that the fuel level is too low. I would remove the regulator completely, it is just another restriction in the fuel line.