S U Carbs Leaking

Pocket rocket · Post by **Pocket rocket** » Sat Jan 13, 2007 12:41 pm

A friend (yes, really

) has an SD!-derived 3.5 RV8 in his Cobra. After only a few hundred miles he decided to do something about the blue smoke so stripped the engine. Bores were scored necessitating a rebore, new pistons & rings, new cam bearings etc. Engine now rebuilt with Viper (or Hurricane, I'm not sure) cam installed. He has SU carbs on the original Rover manifold.

Before the car was SVA'd he had difficulty starting - found that the sump was full of petrol

so carbs were stripped and the opportunity taken to put in the correct jets etc. Float levels were set by a man who knows what he's doing. After that the car ran, was driveable with reasonable power but the blue smoke problem eventually got worse.

Obviously the scored bores led to conclusion that the carbs may still be leaking fuel - bench testing (carbs fitted to the manifold) reveals that the fuel does indeed go straight through. I have suggested that he test each carb separately to see if one or both are at fault. he did say that petrol was coming out of both sides of the manifold

My thought is that there is relatively little to go wrong on these carbs and that the problem is with the floats. he also thinks possibly damage to the (new) jets or seats.

Any advice/thoughts?

ian.stewart · Post by **ian.stewart** » Sat Jan 13, 2007 1:31 pm

Sounds more like too much fuel pressure, what pump are you using and what, if any, is the pressure reg set at??

Pocket rocket · Post by **Pocket rocket** » Sun Jan 14, 2007 9:40 am

I'll have to check but I think he's got an interrupter pump fitted.

That said, I'm not sure if the pump is the problem. When he tested the carbs off the car, he used an oil can to feed fuel to the carbs/manifold and still had leaking fuel

davemgb · Post by **davemgb** » Sun Jan 14, 2007 10:24 am

Check whether the fuel is coming out of the main jet or the choke system. If it is the choke system then fairly obvious the chokes are wrong. If it is the main jet the check the float heights and check that the float chamber breathers are not blocked. If the carbs have been cleaned by bead blasting then my money is on blocked breathers and the man who alledged know what he was doing should be shot!

Manuals and spares are available online from www.burlen.co.uk

Dave

john 215 · Post by **john 215** » Sun Jan 14, 2007 11:51 am

Make sure floats are not punctued by floating them in warm water,when resetting the hight,i always invert the carb (i am assuming you are using HIF type) then slip a paper clip over a steel rule,they are normaly 40 thou thick (1mm for the converted!) and then place rule on base of inverted carb, side paper clip along the rule to check the hight of the float.
The other things i have seen is when incorrect fuel hose is used ie.not lead free resistant,and what can be described as tiny flakes of hose break away and get trapped under of foat valve and seat,when you remove carb they get dislogged and the mystery starts!If not already installed fit a filter/regulator and monitor.
Another fault can be the float chamber breathers esp if the type fitted to SD1 set up,green plastic tubes,become blocked with crud ect.They run down the front of the block and when we had winters even use to freeze up!
Hope this helps,spent years working on these carbs and as you say they are reasonably reliable.
John