top of carb loose

chrisb · Post by **chrisb** » Tue May 22, 2012 2:19 am

Hi All,
After a bit of spluttering and stalling my 1949 18 500, stopped on the side of the road, still with 10 miles to go. After 15 minutes of trying to act like nothing was wrong to all the passing motorists, I found that the top threaded ring on the Amal carby was ajar. If I tighten it too much it tends to jump over the thread. Any fixes for this , or is it new carb or slider chamber or what?, someone suggested loctite? any ideas appreciated,
Regars Chris

wilko · Post by **wilko** » Tue May 22, 2012 3:13 am

You could try belling out the top with a hammer and some round ended stock or a big ball peen hammer. Loktite should work though. Do you have a spare top to try?

en7jos · Post by **en7jos** » Tue May 22, 2012 4:13 am

Would wrapping some PTFE tape around the thread help, although I guess this could desolve with the petrol fumes and make a mess? My old carb had a similar problem around the top of the float bowl. I found a previous owner had wrapped string round the thread to give it more bite, although this wasn't that effective really.

Loctite is surely going to get a bit messy isn't it?

A replacement carb (or at least the offending components) is probably the only real long-term solution. Is is the top or the body that is worn or just the ring itself? The latter would be an easy and cheap replacement and may do the job.

Regards, James

chrisb · Post by **chrisb** » Tue May 22, 2012 5:12 am

Thanks , for your reply's, with my luck it will be the body worn not the ring, ( wonder if you can buy this bits ). Will remove the tank and have a good look this weekend. By the way James your website looks great, who designed it? Regards Chris

en7jos · Post by **en7jos** » Tue May 22, 2012 9:37 am

Mckorkins · Post by **Mckorkins** » Tue May 22, 2012 10:24 am

I had exactly the same problem with my Model 18: the top of the carb came off three times during the VMCC's Spring run in Somerset this last March. The amazing thing was that the bike still ran, although backfired considerably when shutting the throttle. I made quite a noisy and spectacular entrance at the rendezvous point and everyone looked up to see what it was making all that row!

The spring that holds the top of the carb was worn and unable to do its job and therefore allowed the cap to unscrew.

I ordered replacements from Amal for just over a tenner + P&P. The part numbers you want are:
4/235 Cap Retaining Spring
389/065 Cap Top Ring

http://www.amalcarb.co.uk/ (Burlen Fuel Co Ltd)

Hope this helps.Edited by - Mckorkins on 22 May 2012 09:34:43 AM

Rob Harknett · Post by **Rob Harknett** » Tue May 22, 2012 10:35 am

Years ago it seemed all the old bikes suffered this fault. Quite often found they held on better having checked the top fitted nicely in the carb body cutout. With that firmly held down tight, screw the ring on with the spring clip wedged open, they seemed to go down that extra thread.
trying to screw the ring on with the spring doing the job intended, they seem to cross thread easy, jump out the cut out and never seem to go down tight. So common was this problem with the old bikes we rode mid 50's , you got in the habit of checking the carb top each time you turned the petrol tap on. Nothing was ever used on the worn threads, parts were never replaced, you just lived with the fault.Edited by - Rob Harknett on 22 May 2012 09:36:30 AM

petert120r · Post by **petert120r** » Tue May 22, 2012 10:52 am

I've successfully used the PTFE bodge in the past

ianselva · Post by **ianselva** » Tue May 22, 2012 10:54 am

Martin Bratby used to be able to supply an undersize ring and re-machine the top of the carb to suit. I dont know if he still does it though as I have just cut the ring and silver soldered it back together again ,ensuring the thread lines up either side of the cut.

IanEdited by - ianselva on 22 May 2012 09:55:43 AM

1608 · Post by **1608** » Tue May 22, 2012 11:08 am

I think the best idea is to swage the top of the carb body and have the threads re-cut. But, make sure the threads are ok on the ring first and also replace if needed. I think a new carb body for this reason alone is a bit excessive, but I'm very much of the mend and make do mould I'm afraid. And tight fisted!