12 replies to this topic

[087dave]

Hello how do you know if your carb bushes are gone
and how much is enough play on the spindle??
Cherrs

[Stevee]

there shouldn't be to much ive just rebuilt my carb and mines got a tiny bit but on a DTI theres a fair bit but theres just me being picky but they are fine but if it moves up and down loads there gone

[087dave]

THanks and is it hard to replace them???? and is it hard cherrs

[Big_Adam]

Not hard, just the right tools are expensive, be quicker and a bit cheaper to just taken them to a machine shop or send them to Burlen Fuel Systems if they still offer the service.

[Stevee]

i drilled my old ones out since my carb was ruined from people int he facotry by looks off it

but drilled and then used a press to get new ones in ^^ thank god i go college

[Brigbeale]

The carb on my 998 (HS4) seemed ok until I went to get the MOT'd.

The emissions went off the scale within 5 seconds.
I put it into a garage to get the engine/fuelling sorted as it kept stalling after the 'so called mechanic' I had employed previously left it on a condition where it would stall every time the throttle was released when stopping the car.
He told me the carb was very worn, But had set it up so that it would run continuously.
He also told me that the HS4's wear was in the spindle where it goes through the carb.
The car was still on the ramp and he showed me the wear.
I found that I could literally wiggle the spindle near where the throttle cable and return spring are mounted.
The mechanic (who is a mini fan - he had three and had just returned from a big mini event) told me that if I cold feel any movement, then it is too worn!
The problem was when the throttle was pressed, the spindle with the butterfly valve would move, but when it was released, it the spindle and butterfly valve would come to rest in a different position each time. This would affect the tick-over and the car would run rough or stall. Also, the wear would cause an air leak into the carb further upsetting the mixture.
Fortunately, I bought a stage 1 kit off ebay and a HIF carb was included.
He told me to bring the car back with that carb and he would fit it.
He also told me that he preferred the HIF as it has a return spring on both sides and reduced the 'stress' on one side of the carb as in the HS4, so wouldn't suffer as much.
He fitted the HIF and the car has run fine since.

I did enquire as to having the carb rebushed, but he told me that the carb would need to be sent off and was not going to be cheap as it was quite an involved job to do.
As I had another carb, I didn't go any further with HS4 rebushing.
Also the car was needed on the road ASAP.

Edited by Brigbeale, 10 January 2011 - 09:31 PM.

[tommy13]

SU still offer the rebushing service according to their website.
http://www.sucarb.co...tail.aspx?id=27

[Turbo Phil]

There should be hardly any noticable movement at all. The bushes are easy to remove & replace if you have the correct size drift.

[087dave]

Thanks for the replys, only i am setting up twin carbs and when i get the idle
sounding right the carbs die off and the engine stalls

so i was thinking are the bushes gone when i
or has somebody come across this problem before
Cherrs

[tommy13]

Sounds as though it may be down to mixture adjustment. There is a useful video here on you tube, made by a guy with an obvious love of SU's and MG's. The carbs shown are the HIF type but the principle is the same except the mixture is adjusted with a screw on these carbs.


Also check this

[087dave]

Thanks tommy,
i have richened the mixer because it backfires thru the carb
so do you think that i should lean off

[tommy13]

Thanks tommy,
i have richened the mixer because it backfires thru the carb
so do you think that i should lean off

Quite possibly, spitting back can be a sign of weak mixture. Have you filled the dampers with oil?
I would get it to running temp and try lifting the pistons as shown in the video. You only want to lift them about 0.8 mm which is difficult when using the lifting pin as its hard to tell when it contacts the piston and then gauge how far you have lifted it. This is why the guy in the video uses a small screwdriver. Stick at it, if the engine revs increase when you lift the piston then it is too rich, if they fall then you should richen some more.

[MRA]

Shaft movement should be barely noticeable, and using a drill will give you poor results as the surface finish and accuracy are not good enough

Be careful if using a drift as some SU's have moulded in bushes, drifting them out can result in damage to the carburettor body.
Also some of the bushes now available are not a direct replacement for the original sizes.

It really is best to ream out the old bush using a fixture to hold it all square and true, impossible to obtain with a hand reamer

The more slack you have around the butterfly spindle shaft the more air is drawn in which effects your mixture, this is bad enough, however if you have a "blow through" turbocharged or supercharged system this can allow fuel to leak out. Even with the Metro & ERA turbo carburettors seals fitted they can still leak if the shaft wear is excessive.