V8 on SU carbs, fueling issue

[Soren Frimodt]

Now, I have always been a petrolhead and hated diesels, but having to cover a lot of miles to get to work have made me drive a boring and noisy 200tdi.

Now though my job is much closer so I've just bought meself a good old 3,5 rangie with 3 speed auto.

The previous owner had fitted K&N's and modified the exhaust so it was running way too lean on the Strombergs.

Some years ago I acquired a pair of SU's from an SD1, they look good, both on the inside and outside, so I thought I'd rather fit these and tune them in, now that I have them anyways.

BUT I've run into a problem, they seem to be seriously over-fueling the engine, and starting it is very hard, requires full throttle and both of the damped pistons fully open.

If you keep the gas on it runs well enough, but with a lot of black smoke, and Idle is nowhere to be found,

So clearly over-fueling.

Obviously there must be something wrong with the floats or valves, but I can't seem to find any issues, so I was thinking if there was something that I might have missed? could it be a restriction problem in the fuel return? could it be a fault in the choke? Or is there somebody out there who just happens to know that little thing that I just haven't thought off?

Any input whatsoever would be really appreciated! Thanks chaps

[Quagmire]

My 3.5 is on SU's and did this a little while ago. I normally run on LPG but ran out and so switched to petrol for the first time in ages. It was throwing out black smoke and would not idle. Giving it throttle it would bog down and stutter until the revs got pretty high and then it would take off like a scalded cat!

I ended up taking the tops off, cleaning the dashpots throughly and refitting. New oil in the dashpots and all was well again. I think I had a piston sticking on one of the carbs.

[Quagmire]

One more thing was when I took the tops off I deliberately turned on the ignition to run the fuel pump. With the top, spring, piston and needle removed you can see the jet orifice. I was able to verify that there was not a float problem as you would either expect to see fuel coming out the overflow, or pumping up out the jet hole. I had neither of these things happening.

Also - how did you set the mixture up? With the top removed you should set the jet height to be flush with the body, then wind it down 2 turns. This will get you running and you can go from there. I use the bottom end of a set of vernier calipers to make sure each jet is set equally at first. You will probably need to lean off a lot from this initial setting to get through emissions...

[Soren Frimodt]

Very good info there Quagmire, will have a look at this tomorrow, haven't had the tops off, so there could be something there since I'm only able to start it up with these open. I could try switching off the fuelpump too I suppose, then I would know if it's too much fuel delivery. Haven't really set the mixture screws anything specific, but will try your tip, thanks mate

[GW8IZR]

Make sure rocker breathers are clear,

[smokinv8]

I had the same problem on a series 3 hybrid i once owned, turned out my fuel pump was pushing way too much fuel through. Changed it for a pump from a Diesel and all was fine then, no more petrol shooting out the overflows onto the floor!

[Bowie69]

One stupid thing I did recently when sticking an SU on my 2.25, was to forget which was the petrol in, and which was the overflow, needless to say it showed the same symptoms as above

May be worth checking, we all do something silly from time to time

[Soren Frimodt]

Had a look at it today, and found that obvious thing that I had completely overlooked When inspecting the pistons and cleaning them I suddenly noticed that one of the needle jets was sitting way low in the carb, and the other much higher, despite having turned the screws equal turns out. So obviously you can't just wind them all the way in and undo them, say 4 turns and think everything is good and in sync. So lesson learned, and it now runs considerably better. Though I still haven't adjusted the butterfly's to match each other yet, so idle is very rough, but it's there! So now I just have to sort throttle linkage and so on, but now I have a new bag-full of motivation and energy for this Though too little time..

[Burnsinbarnsley]

I had this fun a few weeks ago!!!

ended up with full rebuild kit for carbs, rotor arms, dizzy caps, leads, plugs, points, condensers, a new timing gun, comp tester, rocker covers off and finally a new electronic points distributer!!!

Problem sorted!!

Could do with a carb balancer though to tweak it correctly!!

I remember the motivation!! Shame I've lost it!!

[Burnsinbarnsley]

A crypton synchro would help you!(and me!!)

[Soren Frimodt]

Bringing you guys up to date. Today I found the real culprit, the O-rings at the Choke valves, they where harder than a rock, and needless to say, not to much use. This caused too rich a mixture. So with this fixed she actually was starving fuel when I first fired her up!