Twin SU plumbing and throttle

satancom · Post by **satancom** » Mon Sep 22, 2008 3:10 pm

ChrisJC wrote:Yes. I did that too.

Thats good enough for me,

Cheers

ewokracing · Post by **ewokracing** » Tue Jan 11, 2011 9:00 am

satancom wrote:
One question. The fuel inlet on the carb. Currently it has a mistery fitting on. The pipe under the fitting has a ridge as a normal push fit system would. Can I just dremel the screw fitting off, push a hose over and use a small jubilee clip to hold it in place?

The reason I has is I have loads of clips and none of these fittings, and don't really know where to get them anyhow? Surely this would be the same and secure ? The pump is only 4psi so shouldn't blow the jubilee clips off!

bumping up an old thread as it has 90% of the answer that I need.

I've got a 1976 p6b that has a slightly different fuel setup, mine has the fuel filter on the drivers side rocker cover and it has the two screw in nuts+olives to hold the fuel filter in place. To replace a fuel filter is 20 pounds from the UK, whereas a normal fuel filter here in Australia with the push on barbed ends is about 5 dollars.

ChrisJC: you mentioned that you had cut off the screw fitting on your carbs, what size rubber fuel line do you need to use? 8mm or 10mm?

Mine has a 90 degree screw fitting, so I want to cut it off and down the pipe slightly so that I can curve the rubber hose toward the filter

ie slightly right of where my fingertip is:

ChrisJC · Post by **ChrisJC** » Tue Jan 11, 2011 1:00 pm

I can't recall what pipe bore it was, just measure the OD of the metal pipe with some calipers.

Chris.

ewokracing · Post by **ewokracing** » Wed Jan 12, 2011 5:07 am

ChrisJC wrote:I can't recall what pipe bore it was, just measure the OD of the metal pipe with some calipers.

Chris.

yeah um, I've kinda lost mine!

ewokracing · Post by **ewokracing** » Wed Jan 12, 2011 9:08 am

All good, chanced it with some old spare fuel line I had from a 70's Mazda and 8mm line fitted perfectly.

Tonycougar · Post by **Tonycougar** » Thu Nov 28, 2013 12:28 am

Pocket rocket wrote:Another if it helps

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Thought I'd bump this up.
Been reading through it and examining the pics.......looks like mine, except the 2 pipes going to the front of the SU's are not there on mine......the big pipe from the top RH rocker cover just goes straight over board.......could that be the cause of my high idle problem?

Tonycougar · Post by **Tonycougar** » Thu Nov 28, 2013 2:37 pm

Here's a pic of the breather pipe I mentioned (the one I'm pointing at) which just dumps straight overboard.[/img]

Tonycougar · Post by **Tonycougar** » Thu Nov 28, 2013 2:40 pm

Here's 2 pics of the carbs. Pipework looks different, and wrong to me.
Could this be the cause of my high idle?

ChrisJC · Post by **ChrisJC** » Thu Nov 28, 2013 6:49 pm

It looks like the pipes from the rear of the air filters into the carb are effectively bypassing the throttle plate, so yes, I expect that they would make the idle high (and unaffected by the idle screw!).

You might need to do a bit of experimentation as there are a ton of variations, but the general idea is to keep the crankcase at a slight vacuum.

So I fitted an aftermarket PCV valve between the two pipes on the carbs (T'd together) and one of the rocker covers (so that always keeps a small amount of sucking on that side), and then vented the other rocker cover to atmosphere. That way, it draws in on one side and out into the carbs on the other with the total suck controlled by the PCV.

Chris.

kiwicar · Post by **kiwicar** » Thu Nov 28, 2013 9:42 pm

Hi
the tapping at the back of the carb should be connected to the crank case evacuation system or blanked off.
best regards
Mike

Tonycougar · Post by **Tonycougar** » Thu Nov 28, 2013 10:02 pm

Looks like I need to do some tinkering.

Tonycougar · Post by **Tonycougar** » Fri Nov 29, 2013 7:39 pm

kiwicar wrote:Hi
the tapping at the back of the carb should be connected to the crank case evacuation system or blanked off.
best regards
Mike

Had a little tinker today. Got it running to temp where it was fast idling. Then pulled those pipes off. No difference. Put my fingers over the holes on the carb (effectively blanking them), and it died.
Put it all back the way it was and ran it, now it wants to die without a bit of throttle. Seems there is some play in the linkage and the cable which I need to sort, but I'm not sure that was causing the high idle. Ran out of tinker time, had to go to work.
More tinkerage required.

kiwicar · Post by **kiwicar** » Fri Nov 29, 2013 7:50 pm

Hi
Then pulled those pipes off. No difference. Put my fingers over the holes on the carb (effectively blanking them), and it died.
yup that would figure, the idle mixture must be set very rich for it to run at all with the pipes bypassing the ventury like that, cover them up ypu are probably running (or not!) an AFR about 6 or 7 to 1, unless it was stone cold I would think it would not want to fire.
Best regards
Mike

Tonycougar · Post by **Tonycougar** » Fri Nov 29, 2013 11:39 pm

It is more difficult to start when hot. Starts easy when cold.

ChrisJC · Post by **ChrisJC** » Sat Nov 30, 2013 6:23 pm

Sounds like the idle is shut right off, and it is just idling on the pipes you unplugged.

So plug the pipes up, then increase the idle speed a lot until it will idle without any throttle pedal. Finally adjust the idle down to a sensible level.

Chris.