Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing SU carburetor advice needed

I've been chasing a ghost for a while trying to solve a low speed skip problem on a '61 +4DHC (triumph engine)

I thought at first that it was an ignition problem, but I replaced the ignition system (I have spares) and re-timed and had no success. Compression checked out (150-155 on all 4), so I started looking for vacuum leaks. The only vacuum leak I can find is on the throttle shaft bushings on the carburetors. I pulled the shafts out, and measuring with calipers there's about .006" clearance between the shaft and the bushing. I don't know SU's very well, but this seems like too much clearance. It looks like the shaft is supposed to be .3100" diameter, but I don't know what the spec is supposed to be for the bushing bore.

What's considered acceptable before parts need to be replaced? Anyone re-bush one of these carbs?

It's a long time since I stripped down an SU carb but you should be able to tell visually if the shaft is worn.

I can't remember if rubber or neoprene seals were used but there's the possibility that these may be leaking given their potential age. Have you tried running the car and dropping some oil over the spindle end to seal out the vacumn leak?

Have you thought about contacting Burlen Services, Shaftesbury as they manufacture SU carbs, stock spares and will rebuild if required.

The bodies can be drilled to take bushes but must be done with the right tool to ensure perfect alignment or it will be scrap. Not sure of spindle tolerances but they have to be well worn before you'll experience any running issues. I'd check everything else first.

There's visible wear on the shaft, but it's the bushings that seem to be the worse for wear. I measured .3085" on the shaft and .3155" on the bushing

No seals, just bushings... I was surprised by this. I shot some carb cleaner at the end of the shaft and almost stalled out the engine. There's obviously air getting by, but without shaft seals I figured some loss must have been accounted for. I'm on the US East Coast. We've got a few places around that I'm sure will service it, but I can probably do it faster myself if 1) I figure out the problem and 2) know what the specs are.

.006 seems too much. If you can spray WD40 on the bush and the RPM goes up than they probably need rebushing. To do this job one must have a reamer for that size. Expensive. As You live in Massachusetts I would call Linda at Morgan Spares. She probably has somebody that does this job and will get it done. I have had good results working with Morgan Spares.

Button
Seattle

I tried to do this myself and it was a disaster. But I have not tried installing a new bush. Might be a solution and a better solution than re-reaming the aluminum (whatever). The suggestion to contact the folks that make them looks to be a good idea.

Button
Seattle

Try sucarb.

Em

I seem to recall that older type SU'S didn't have spindle seals.

Contact http://joecurto.com/ in New York. Very highly regarded carb service

http://www.su-stromberg.de/HTML/content/pages/index.php

...highly recommended (but in Germany..)!

(no connections, just a satisfied customer)