turbo running rich

[Guest]

hello guys, was helping out andy today with his turbo re its running issues -

what i found so far was:

couple of carb hoses wrong way round and a split vac hose from carb to ecu. sorted this out and changed to a set of new plugs i had lying around.

Took it for a spin and it was much better - but is still running very very rich. The new plugs were sooty black after about 10 miles.

air filter is ok and ignition system looks good. car doesnt feel down on power but lumpy on idle with the mixture.

So, i was thinking fuel preesure reg - looks like the screw has been moved at some point? or is it possible for the auto choke to stick on? last thing could the incorrect needle valve do this?

I have a spare untested pressure reg i got with 251 - so maybe worth a try.

was even considering swapping the full carbs over Lol to try and narrow it down

cheers

chris

[Andy]

Cheers for taking the time to have a look over it Chris its much appreciated. The new needle I have bought seems to be a different size than the one currently in which we couldn't get out, its a 0.100" needle, is this the correct one? It was running much better on the way home shame its not going to start easily with the spark plugs been black. Hopefully get it sorted before I take it off the road for winter ha. TVR's a beast Chris me want one lol.

[Mike Brock]

I don't think its anything to do with the needle valve guys. Its likely the two rubber O ring on the choke mechanism have failed - easy fix though.

[E_T_V]

Do the stepper motor O rings on the carb. Then set the mixture to the default setting, and then tweak it as necessary to get a good idle.

If it still misbehaves then take it from there. It is easy for one of your changes previously to alter the carb tune a lot. Get back to square one before trying to tweak other things is my advice.

[Andy]

Do the stepper motor O rings on the carb. Then set the mixture to the default setting, and then tweak it as necessary to get a good idle.

If it still misbehaves then take it from there. It is easy for one of your changes previously to alter the carb tune a lot. Get back to square one before trying to tweak other things is my advice.

The carb has just been rebuilt with a proper SU carb service kit so I take it these were included and been changed. Dam thing cut out last night had to get the AA to take me home again started up straight away then would cut out every time I tried to move. The AA bloke found a screw sitting on a tray under the carb, didn't know what it was, didn't seem interested to find out and just towed me home.
Chris my mates been round today while I was at work and changed the needle in the carb, I forgot to tell him we found it was different and that screw was from the idles jet adjuster. I have been in the garage and fired it up and it more or less burst into life straight away which I was surprised at but I never took it for a drive as these defiantly something wrong with the auto choke and I cba waiting for the AA to take me home again ha. Ail try and get these choke o-rings as quick as possible and then take it from there as Dan said.

[Guest]

Did u say u found where that screw came from?

[mgdavid]

he did;
'and that screw was from the idles jet adjuster.'

[Guest]

Do the stepper motor O rings on the carb. Then set the mixture to the default setting, and then tweak it as necessary to get a good idle.

If it still misbehaves then take it from there. It is easy for one of your changes previously to alter the carb tune a lot. Get back to square one before trying to tweak other things is my advice.

OK this weekends update -

autochoke o-rings changed - old ones looked damaged.
but it was still the same, so i tested fuel pressure between the swirl pot and carb and it was showing 7.5 psi on idle. so i think there lies the problem.

I had a brand new reg with me - that came with 251 - so put that on, but the pressure has remained exactly the same...

so where to take it from here?
semi blocked fuel return?
wrong spec fuel pump?

im guessing i could rule out blocked fuel return by running a fresh piece of hose temporarily to a petrol can in the garage?

[Guest]

You can do that! and I fell for the exact same thing.
the problem is if you then go out for a run the car will run out of fuel on hard acceleration as the swirl pot will empty as no fuel flow is passing through the 4mm nozzle on the return that draws fresh fuel into it to keep a constant full swirl pot of fuel for the suction filter. The exception is if the fuel tank is 3/4 full as this is above the height of the swirl pot.
The 4 mm nozzle is critical to the system working correctly. I have found that if it is restricted it causes two problems, too much resistance to obtain a
4 psi fuel pressure on tickover, and too little flow to create enough of a venturi to draw fresh fuel into the swirl pot causing fuel starvation under heavy acceleration.
I only proved this by using a seperate 25 ltr tub as tempory fuel tank in the boot

[Guest]

You can do that! and I fell for the exact same thing.
the problem is if you then go out for a run the car will run out of fuel on hard acceleration as the swirl pot will empty as no fuel flow is passing through the 4mm nozzle on the return that draws fresh fuel into it to keep a constant full swirl pot of fuel for the suction filter. The exception is if the fuel tank is 3/4 full as this is above the height of the swirl pot.
The 4 mm nozzle is critical to the system working correctly. I have found that if it is restricted it causes two problems, too much resistance to obtain a
4 psi fuel pressure on tickover, and too little flow to create enough of a venturi to draw fresh fuel into the swirl pot causing fuel starvation under heavy acceleration.
I only proved this by using a seperate 25 ltr tub as tempory fuel tank in the boot

hello, the 4mm nozzle that you are talking about - is this at the tank end?

[Guest]

sadly it is in the fuel tank, at the end of the fuel retun line

[Guest]

ok :+(

but im guessing that as its high on idle - even disregarding on boost performance - I assume that running to a container should prove or disprove the theory to some extent?

[Mike Brock]

Hi Chris - is the fuel regulator not adjusting when you turn the screw?

[Guest]

hello mike - not tried that yet - but will do next time - I just assumed they came factory set at 4 psi...?

[Mike Brock]

Never assume anything when fault finding. Every time I read this thread I keep thinking about the idle screw that had fallen out - could be a reflection of how bad the carb was recently rebuilt?? I would take the carb off and check float height and if the float needle is seating correctly? Not sure what a blocked fuel return line would do to the fuel pressure - but no harm testing it.