stromberg balancing

[Steve P]

Anyone give me any pointers on the following:

Trying to balance my carbs to make it tickover better,at the moment it `hunts` between about 750 and 1100 revs,once going it revs and pulls fine.I put a flow tester on each carb with the link slackened off and the rear carb will read say 5 and the front one 0 unless you wind the front one open until the tickover is up at 1500-2000 revs,this is with the rear  carb throttle screw right out not even touching the carb body.i think either the spindles aren`t sealing or an air leak.The carbs are recon from Andrew Turner with under 2k miles on them.
Thoughts appreciated.
Steve

[Lord Sorbington]

The procedure in my car handbook worked quite well for me -  I'd never touched a twin carb set up prior to this.

Just ensure that each throttle is open an equal amount at idle and fully open at full throttle. If your set up is like my 150CDSs, once the throttle spindles are clamped together any further idle adjustment affects both carbs equally.

Took me a while to get the mixture right, I didn't find the lifting pin method very helpful but it did serve as a starting point for fine tuning.  Initially my rear carburettor was a bit too rich which caused a lumpy idle and a rather sooty exhaust, checking the colour of the spark plugs confirmed this (the rear 3 were a bit black) so leaned it off a little, now all 6 plugs are spot on!

Things like valve clearances / condition and of course any air leaks will also affect the airflow through the carbs so could be worth checking these if you still have problems.

[Clive]

Could be a butterfly not closing fully? And the butterfly is fitted the correct way round, I think it has a chamfer on the edge so it seats nicely in the closed position.

Can you apply mild pressure to the throttle linkage to try and close it fully? see if that helps.
It is usually something simple.......

For air leaks apray carb cleaner or WD40 around the joints, see if it affects idle speed.

[Deleted User]

Definitely sounds as though either the back throttle isn't closing properly or you have an air leak between the front carb and the inlets. Like Clifty said, see if the back throttle will close further manually, and spray WD40 around the front manifold to see if the idle rises.

When you say the idle "hunts", that suggests to me that there's an air leak, which is more likely if they've been reconditioned.

[willcolumbine]

Not had much experience with Strombergs myself but 99% of people who have a problem with them seem to have knackered diaphrams. How did the problem happen? These types of carb are pretty simple and dont usually go out of tune in 2000 miles! Were they okay when fitted originally or did they go out of tune gradually or were they okay one minute, rubish the next?

[Steve P]

To be honest they`ve never been right since reconditioning,i took the tops off after 100 or so miles and found one diaphragm split,i`ve had problems getting the linkages to stay in sync as the front one slides on the centre bar if you open them right up and they both flooded when first refitted,not impressed really.

I will take the rear one off and check the butterfly is the right way round as it doesn`t seem to close fully and you can close it slightly more by hand.
Cheers
Steve