TWIN HS4 VERY HIGH TICK-OVER-NOW FIXED :)

[lambrettalad]

Hi Just stripped and refurbished a pair of SU HS4 carbs for the MGB.BUT

Got it started despite loads of backfiring thru the carb

Both chokes are opening and closing smoothly

When ticking over ,(when up to temperature ),revs at 2500, both chokes off:all adjustments backed off fully.

if I restrict the air flow into the rear carb revs drop ,(NO AIR FILTERS FITTED)

also when lifting the pistons the: front revs drop , and then :rear revs drop,oil in the pots
any thoughts very welcome

yours Frozen solid ,tired ,man flu, on the way,totally pis**** off,wife doesn't understand , brain scrambled,Villa lost ,can't feel my toes ............

[ian.mcdougall]

Did you replace ths butterflys are they correctly fitted, do you have a vacuum leak, if this link works it may help or go on su burlen site see if there is a trouble shooting page, I think I got a set up guide when I refurbed my series mm carb
Regards ian

http://www.wihealeyclub.org/.../Trouble ... 0Carbs.pdf

[mike.perry]

Slackened off cables? Pistons dropping fully?
Read page 40-41 Burlen's SU Workshop Manual?

[mogbob]

A few thoughts.
Both carbs kept separate and parts not mixed up.Suction chambers marked ..relative to their respective bodies ( i.e.not rotated 180 degrees )
Using lift pin do both pistons drop freely against the bridge.
Jet needles, straight when rolled on a flat surface and no wear ridges.Needle guides flush with the underside face of the
piston.Jet flush with the bridge and both carbs at the same height relative to each other.
Throttle operation OK and no signs of sticking.

If you don't have any carb balancing kit, use a short length of tube you can hold to your ear to listen to the air being sucked into the carbs.The induction noise as the air is sucked in should be the same in each carb, keep switching back and forth whilst adjusting the mixture.
Blip the throttle every now and again to clear unburnt fuel and resume tuning. With carbs disconnected from each other you will need to lift both throttles manually. Use the lifting pins to establish the effect of adjustments.When you are happy with each carb tighten up the connecting linkages.
You'll be a new man in the morning.. hope you have greater success with your efforts.

[bmcecosse]

First question - was it all ok before you fiddled with it? Obviously there is an air leak - engine can only run if air is getting in... Was the manifold off - and if so - is now back on correctly and tightened up? Servo connected? Suction hoses to the crankcase connected? And - are the throttles closed..? Did you have the throttle plates out - and if so - put back in right way round? Are they the type with a little valve in the throttle plate - designed to ensure some air goes through the engine on overrun ?

[lambrettalad]

thanks everyone f the time and effort

everything spot on ish (timing points etc,was crypton tuned) before the rebuild except for sticking chokes and worn carbs,

all new parts fitted to the empty carb shell.

I just want to get it drivable to the tuner ,approx 8 miles

I shall return to my shed in the morning,and start again from scratch using the helpful guide lines you have given me.

[Trickydicky]

Have a look at this video, it may help. http://m.youtube.com/watch?v=4nvGLgO6pj0

[lambrettalad]

cheers Tricky ,not done a thing today ,too cold

I tink we need a smilie for Frozen Stiff

[lambrettalad]

Well I walked away yesterday and thought s*d it

went back today and within 5 mins fixed it could have sworn I had done it correctly

I had not done the basic check i.e..fully separating the carb connecting rod ,It took one full turn of the locking nut

now running sweetly

My brain does not work too well in the cold ,if at all

sometimes it's best to leave a problem overnight and go back fresh the next morning.

thank you for your support

[bmcecosse]

Non essential jobs like that are best kept for warmer weather! Well done getting it fixed.

[lambrettalad]

cheers Roy ,but it had to be done ,it was running like a drunken sailor in a force 10 gale It ran at about 85% and I no patience at all (except for house work)