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Re: Carb Heat Insulator. Cork?

A new slide will only partially cure the problem as I suspect that most of the wear is in the carb body. So better to find another good carb or a new one or get yours re-sleeved. Ron

email (option): ronpier@talk21.com

Re: Carb Heat Insulator. Cork?

Hello Ron,
Yes, I'm working towards that conclusion. I really just want to make it reasonably rideable for a bit of summer pootling and will almost certainly go for a resleeve over the winter. I have a second hand slide that's less worn than mine, not best practice but if it keeps me going through the next couple of months it will have earned its rations.
Can anyone recommend a trusted supplier for resleeving a 276?
Regards,
John

email (option): John.childs1@btopenworld.com

Re: Carb Heat Insulator. Cork?

Following problems with some reconditioned carbs I'm more inclined to have new ones personally, unless that's not an option....I fitted a new one on my M20 at least 15 years ago and have never really looked at it since apart from giving it a clean up every so often..
If you have a used slide that's not TOO rattly it should run OK on it, you'll just be using a bit more petrol to get the mixture right....There's a lot of M20s running about with worn carbs!!....Ian

email (option): ian@wright52.plus.com

Re: Carb Heat Insulator. Cork?

Continuing the saga:
Yesterday installed a substitute throttle slide from the old spares tin, second hand but considerably less worn than the original. Adjusted carb to factory settings. Bingo, started first kick from cold, no rattling from the slide. Solid tickover. Runs nicely on the road. Ticks over when hot, a bit lumpy on full advance but sound enough on retard. Stop engine and try to immediately restart. Does so on third or fourth kick after a tickle. So far so good. Leave for a 5 minute soak with engine off. No fuel boiling, good. Refuses to start. Seems to be no spark. Very puzzling as the bike has only done about a hundred miles since the mag was overhauled. Leave for half an hour. Spark now present and starts nicely but cuts out suddenly after a couple of minutes on tickover. Does this three times in a row.
I'm now feeling that despite it's complete overhaul there is a problem with the mag when hot. Runs fine on the road with an airflow but after a standing soak the heat works into the mag and kills the spark. Very annoying if so. Investigations continue.....

email (option): John.childs1@btopenworld.com

Re: Carb Heat Insulator. Cork?

Don't know if this has anything to do with your problem, but when I rebuild an engine i take great care to remove ALL the mud/crap/crud from the cilinder and head.

The crud can sometimes be so hardend that it looks like metal itself..

A highspeed multitool with a long drill to get between the fins works good for this.

Think this has great influence on the cooling ability of these parts.

Re: Carb Heat Insulator. Cork?

Prompted by John Parker's request for problem solvers, this is my solution for hot carbys. I machined a shallow groove on each side of the insulating spacer to take a 1/8inch viton O-ring sitting slightly proud of the spacer to be compressed/squeezed into the groove & against the barrel on one side & the carby flange on the other side to give a air tight seal. No other gasket is required. You do of course have to make longer studs to suit. My bike is 600cc & running Goldie touring cams & in Queensland (OZ) with summer temps of 30plus I have had no problems over a couple of years. I pulled it down recently & could have used the O-rings again but hang the expense, new ones went in.

20200729-091129
20200310-093844

Re: Carb Heat Insulator. Cork?

Good to see some one contributing as to what solved their problem. Cheers. Bonza.

email (option): ukcarbsathotmail.com

Re: Carb Heat Insulator. Cork?

John,

The starting issues you seem to have now when hot seems point to a condenser problem. Maybe ask you mag guy if he changed the condenser or did he just rewind the coil. Maybe ask what type of condenser he used if he changed it. NOS Lucas condensers are still around but due to their age will be more or less useless, but your mag guy should know this.

Tim W

Re: Carb Heat Insulator. Cork?

Thanks Tim.
The magneto engineer diagnosed a dud condensor as the original problem when I had it overhauled back in 2013. He replaced the condensor and rewound the armature. It took me several years to get round to refitting it, during which time the mag was dry stored indoors so I wouldn't expect the elapsed time in itself to be a problem. I'm continuing to do short local rides in an attempt to build up a consistent pattern of behaviour, basically now to build confidence that it's not the carb at fault. I've so far solved the ignition timing slippage (cracked pinion boss) and boiling petrol (tufnol spacer) in this area, and my bones are telling me that despite the replacement this is a condenser fault. Next, I might pop the mag off and bench test it after a heat-soak it in the warming oven at say 60-70 C. Anyone tried this before?

email (option): John.childs1@btopenworld.com

Re: Carb Heat Insulator. Cork? Update.

Just to round off this tale.
Having suffered problems with hot starting and weak tickover, and convinced myself that the carb was not to blame, I bit the bullet and sent the mag off to be looked at. Even thought it had supposedly been reconditioned it was diagnosed with a faulty armature. With the overhauled mag fitted the bike now starts and ticks over nicely, hot or cold. The overhaul was done by Chip Capponi, an excellent service with quick turnaround.
John

Re: Carb Heat Insulator. Cork? Update.

I don't think those in the UK do much riding in temperatures over 100 degrees (38 degrees C) and don't have any big hills or mountains to climb on their M20 when it is this hot.

My M21 will on a very hot day be very difficult to start in these temperatures unless the carb has cooled down. The bike will run fine but once parked the carb will boil over in a few minutes, squirting fuel out the float bowl vents on top until it has no fuel left. If you turn the fuel tap back on, it boils out of the carb also.

I rode my M21 last year in a temperature of 118 degrees up a small mountain to 4000 feet. The bike ran perfect but once I parked it, the carb immediately boiled over. I measured the cylinder head temp at 580 degrees. After lunch and a few pints of beer it had cooled down enough to start on the first kick. Fitting insulating gaskets to the carb helps a little but not a lot when it is this hot.

In the winter, no problems at all.


By the way has any one else noticed that other than the cylinder and head, the rest of a M motor runs much cooler than and overhead valve bike. Even after long rides the oil tank never gets all that hot. My pre-unit Triumphs in the summer, you can't touch the oil tank.

Re: Carb Heat Insulator. Cork? Update.

These BSA singles, both SV and OHV are very 'cool running' in terms of heating up the oil...OHV models in particular are known for it...Ian

email (option): ian@wright52.plus.com

Re: Carb Heat Insulator. Cork? Update.

Bruce, do not drink and drive. 🥴

John 👍

email (option): john.kater@chello.nl

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