Thread: These carbies are drivin me crazy!!!

If you can't find a mechanic, likely over 55-60 years old, who is skilled with setting up multiple SU's, then buy "The SU Carburettor High-performance Manual", by Des Hamill, Veloce Publishing 2006. Pit Stop Bookshop have it. This has a full section on initial set-up of multi-carburettor engines. Also, have a look for "Tuning S.U. Carburetters including full needle charts", Speedsport Motobooks 1975. This may be out of print and could possibly be found on the second-hand market, swap meets, e-bay.


Now, the world is full of self-appointed SU experts. When you get them properly set up, surround them with a ball of barbed wire, and do not let anyone, including yourself, touch them. Fiddling produces failures.

You can try getting a kit and rebuilding them yourself, I paid a fortune to a recomended shop to have my stage 1 3.5 refurbished & balanced and they only made them worse. So I was stranded west of Kununurra, in the wet. Organized a kit through the local repco, rebuilt both carbies (learnt alot ) roughly retuned by eye and ear (limited facilitys on station) only had genuine manual to read and had them vac balanced when able to get to town.
Also changed all the linkage balls to metal ones, to remove any slack.

These set-ups are notorious for causing grief when people start "hit-and-miss" tuning. Try getting everything back to stock standard, including the dizzy. Sometimes these engines don't get along with aftermarket stuff. Carbies should be the last thing you adjust during a tune. You have to know your ignition is sorted first, which should include replacing the coil so that you know you have a good one. (In fact, it helps to have a few parts on hand in case you got a dodgy one.)

I would also check the fuel pump and return and get them back to standard if necessary.

As recommended above, you should also get a kit and rebuild the carbies yourself - just so you know it's been done. After that, you can then go through the handbook for setting up.

The thing with these setups is that if you aren't methodical, working through the job in steps, then you never really know what the problem could be. Ignition and fuel problems have been known to impersonate each other and cause people to go running around in circles until they buy a diesel Toyota!

It sounds to me that you have a fuel supply problem. Agree with others to try and put everything back to where it was, but that is often hard. The key here is she splutters under load.

If it was an ignition problem it would probably always splutter under load, but you say a short pause and you can put her under load again....and she goes for a short period and then splutters. Sound like she uses all fuel available and then sucks air.

First check all fuel filters from tank to Carbie. One blocked filter will cause this syndrome. If you find a filthy one...thats it.Dont forget some tanks have a filter built into the bottom, but start from the Carby and work back to pump, and then tank.

Second check the Carbie fuel bowls for crap. eg rust from tank. That can block jets. How it bypasses filters is beyond me, but I have suffered from it.

If filters are clean, then check the pump is delivering a good steady stream (into a bucket). No hazards eg smokes, static electricity, electrical connections etc. If the pump is good, then next is carby tune.

I have triple SUs on my E-Type which would sound like a nightmare to balance, but it is really quite simple. If we get to that, we can use the manuals referenced in replies, the LR manual, or my triple instructions.

If it still splutters...I am wrong, it must be ignition.

I am assuming there IS plenty of petrol in the tank..

Jim

SU carbys = nightmare best thing you can do is unbolt them and toss them into the nearest river!!!this should stir up a bit of ****,but my experiance with SU carbys is unbolt and throw away ,i like strongbergs personally some people put holleys on but i am not a fan of holley carbys either,i have had many experts rebuild my Su carby but never did i get it running good and i am a mechanic!! .

Thanks for your responses, the carbies will go eventually but for now I have to put up with them - I have even read of a few success stories with them.
I do have good fuel flow and pressure (fuel pressure reg fitted and 2ltrs of fuel gettin to carbies every minute), as far as I am aware the ignition is as good as it can be (new coil, dissy, plugs and leads) - need to make sure the supply voltage is good though.
Only leaves the carbies, it seems like an obvious fuel supply problem to me but as I said it's good; so it's gotta be the carbies!! it's just gotta be...) I am ordering the book as sugested although previously I have looked at these manuals and thought they are like computer manuals - if you can read them, ya don't need them.
Question's - Once the carbies are balanced should the fuel mixture screw affect the balancing, if so would it be a big change? I have them balanced really well but when I touch the mixture screw the balance is affected severely and I have to readjust the balance.

Thanks again.

I have twin SU HIF's on my V8.

I had a very similar problem which turned out to be the seal in the choke poppet valves. They dont use a butterfly for the choke, but a dribbler system which will run very rich if the seals are gone. The previous owner had it looked at by many mechanics and no one could solve the issue.

I ended up removing the choke valves altogether and sealing up the external recess with JB Weld. - this solved all the issues. I give it a shot of lpg when starting on petrol on a cold morning which works well.

I'd also suggest checking the slide by removing the three screws holding the top cover on and checking the slide is not binding in the housing. The best way to check it is to hold it horizonatally and spin in it in different positions. If it is binding , some careful of use of very fine wet and dry (1500 or finer) should free things up.

They are actually very simple and reliable carbs and I prefer them to Strombergs because there are no diapragms to split and they dont tend to lose the damper oil like the strombergs do.

Do I need petrol in there?? aahhhh - wish it was that easy, when I first got the car it ran out of fuel ewvery twenty minutes even though there was fuel in the tank....took me 6hrs to work out the hose had come off inside the tank and the pick only went down about 40 to 50mm..... been an interesting journey with this car and I haven't been anywhere yet...lol