SU Carb advise

[Rob]

Hi , I have a set of triple HS4 that i have rebuilt , pulled apart again and checked several times. No air leaks , butterflys are sealing correctly , piston drops as it should etc.
I know my ignition is all good along with my timing , I have fitted a fuel reg and rechecked it is working also , checked vaccum lines from manifold and everything else i can think of.

I set the carbs as per numerous forums , needle flange level with bridge then 12 turns down choke stop off , fast idle screw etc. Now i can start the car fine ... my problem is as soon as i increase the revs above somewhere around idle by trying to sync the carbs the engine stalls regardless if i try adj rich or lean on the needle adj nut , double checked for leaks , the damper piston moves etc the only way i can restart the car is to back the idle adj screws back to zero again.. going mad ... any ideas

[doc1965]

sounds like your not using the correct the oil in the chamber and allowing the pistons to lift to fast which is flooding the carbs
or not enough oil in the chambers, you have to be pretty precise with the right type and weight of oil

[Rob]

Thanks Doc , i will try changing to engine oil , im using singer general pupose at the moment. There is a fair bit of talk on this on various forums suggesting atf or engine oil. Going to check the floats one more time & i will change the damper oil as well to a heavier wieght .. thanks for the advise Doc will let you know the result.

Cheers , Rob

[Rob]

Well tried heavier oil , checked and rechecked the carbs ... so in frustration i pulled off the lot with the view to put the stromy and original manifold back on.
Had a closer look at the redline manifold and the casting is pretty bad .. didnt allow the head intakes and the manifold outlets to line up nice and straight in fact you could also rock from side to side by about 2 mill as stud cutouts are also wrong so that will be job number 1 ... grinding.

I also noticed on the side of the block below the inlets but only 3&4 5&6 there was oily fuel type streaking like the inlet manifold wasnt sealing coorectly against the head. After measuring the landings between the headers ( old two piece cast type ) and the landings on the red line ( where washers push both against head ) they are about 0.75 mm different thickness ... even though both exhaust and inket seemed hard against head ... was the intake actually leaking at the mating surfaces ? why couldnt i hear it leaking .. could this be the problem , a poorly made intake manifold ?.

Remember original problem was i could start the car and it would idle ( with idled adj completly off ) but as soon as i attempted to adjust the idle screws the engine would just stop .. no stutter no rough idle but just stop.

Next job try and find something to tighten both manifolds evenly against head given different thicknesses ,, i dont want to machine the landings on the headers as they are original cast iron units , not skilled enough to build up the redline landings with welding .. so some sort of shim between the nuts that hold both manifolds ... any ideas ?

[mgyates61]

Well tried heavier oil , checked and rechecked the carbs ... so in frustration i pulled off the lot with the view to put the stromy and original manifold back on.
Had a closer look at the redline manifold and the casting is pretty bad .. didnt allow the head intakes and the manifold outlets to line up nice and straight in fact you could also rock from side to side by about 2 mill as stud cutouts are also wrong so that will be job number 1 ... grinding.

I also noticed on the side of the block below the inlets but only 3&4 5&6 there was oily fuel type streaking like the inlet manifold wasnt sealing coorectly against the head. After measuring the landings between the headers ( old two piece cast type ) and the landings on the red line ( where washers push both against head ) they are about 0.75 mm different thickness ... even though both exhaust and inket seemed hard against head ... was the intake actually leaking at the mating surfaces ? why couldnt i hear it leaking .. could this be the problem , a poorly made intake manifold ?.

Remember original problem was i could start the car and it would idle ( with idled adj completly off ) but as soon as i attempted to adjust the idle screws the engine would just stop .. no stutter no rough idle but just stop.

Next job try and find something to tighten both manifolds evenly against head given different thicknesses ,, i dont want to machine the landings on the headers as they are original cast iron units , not skilled enough to build up the redline landings with welding .. so some sort of shim between the nuts that hold both manifolds ... any ideas ?

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[mgyates61]

You Could try 2 Extractor Gaskets to maybe make up that difference.Good Luck but stick with it


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[claysummers]

What about modify some mounting washers. Build up one side with mig and grind flat so you have a 0.75 mm step. In any case sounds like you are on to the problem. Huge lean out straight off idle.
Cheers
Clay


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[Harv]

In any case sounds like you are on to the problem. Huge lean out straight off idle.
Cheers
Clay

Agree. Sound like you have a big air leak on the manifold. By adjusting the idle screws right out (extra fuel), you can get a decent enough fuel/air mix even with the throttle plates shut. As soon as you open the throttle plates, more air flows and the mixture goes lean enough to not fire. Strommies are a little less susceptible than SUs, as Strommies have an accelerator pump circuit that gives an extra fuel squirt as you open the throttle plates.

One way to confirm is to put the leaky manifold back on, fire it up to idle, then carefully spray WD40 around the gasket joints. If it is leaking air, the idle will jump up as it sucks in (and burns) WD40. Be careful with WD40 near hot exhausts though.

Cheers,
Harv

[Rob]

Thanks Harv , i tried that exact exercise with wd40 .. admitedly i did not try around the bottom of the intake manifold face but every where else , i also pinched the brake booster hose , trans mod valve hose etc and the manifold appeared to be on .. nice and tight al be it a little missaligned if looked at the top edge of the manifold against the too edge of the manifod gasket .. so im thinking it wasnt sitting flat on the face coupled with the gasket not quite taking up the difference ... some one most have had this before .. i cant be the only one to fit a redline manifold with x2 cast headers ?. Anyway going to investigate further today.
Bottom line is ive spent a lot of money on this set up and dont like not knowing .. so lets see

cheers all

[Rob]

Finally solved , three problems the first being i had to rework a new redline manifold as the head landings did not allow the manifold to sit level with the exhaust / intake gasket at one end it sat high on the studs the other end low ... Second i made stepped washers out of mild steel with a mill to cater for the difference in thickness between the landings on the carby manifold and x2 headers , this was harder than youd think as every landing on the carby manifold was a different thickness ... almost 2.5 mm difference between thickest and thinest .. now i can torque the both exhaust and intake manifolds evenly, i tested this by using some cardboard and carbon paper between the head and manifolds then tightened to see any high spots .. luckily now there are none.
Finally a brand new gt40 coil .. car would not rev over 2000 rpm without stopping dead .... went to the wrecker and got a second hand one as my original was for a points distributor ... moral of all this never trust new as being good.

New REDLINE MANIFOLD ... two days to fix
New BOSCH GT40 coil ... faulty

Now you mite say warranty ... sadly like a lot of us i by parts months ahead over several months as i cant afford to by them all in one hit ... so no warranty