I need to install a heat spacer between the carb flange and engine to reduce petrol boil-off. Mine has the short carb studs, about 1/4" protruding from the nut. I've read that 1/8" thick cork can be used as a heat spacer, more effective than the usual Tufnol. Has anyone ever tried this?
Thanks, John
email (option): John.childs1@btopenworld.com
Gasket set, Amal 276/289 GS276
https://www.draganfly.co.uk/index.php/component/hikashop/product/20058-
Includes 2 heat insulators/gaskets for 5 pounds sterling.
I have used 1, and 2 in the past - I cannot tell if there is an impact in performance.
I should add, in my experience, in stop n go traffic where you just cannot cool the bike off (and high heat like in Canada) - there is just no winning. Lane split, shoulder ride or take a break.
Hope this helps. Brad
email (option): You can look me up in past posts :)
I imagine cork would be too soft and squidge up with the heat. A Tufnal spacer with a standard gasket each side of it is all that is required. These bikes were used prolifically in hot African and eastern countries. If your bikes are overheating and boiling petrol in the carb? Then I would suggest there is another problem! (Timing, mixture?)
Hitchcock's have a full range of spacers.
https://accessories.hitchcocksmotorcycles.com/Amal-Carburettors/Heat-Insulators/13313
Ron
email (option): ronpier@talk21.com
Thank you both for the suggestions. I've managed to find a 5mm Tufnol spacer which should just fit.
This has been puzzling me, aware that fitting a spacer is treating the symptom not the cause. This bike has previously run fine for many thousands of miles in all weathers and conditions without such a problem, except on the hottest of summer days. The carb has always been mounted directly to the engine with just a paper gasket. Now, recommissioned after a 27-year lay-up, the boiling has started. It will start fine from cold, first or second kick every time, and ticks over solidly. The timing is as good as I will ever get it, and a subject that I have spent hours upon and check frequently. The exhaust doesn't have the flat note of being retarded and there are no obvious pre-ignition sounds. Runs nicely at road speed. Spark plug is a nice chocolate brown and there are no usual symptoms of lean running, spitting back or popping in the exhaust. But once fully warm, after several miles, it stalls at tickover and won't restart until cool. If I raise the throttle slide I can see little spits of petrol fizzing up into the bore. The carbs settings are exactly as per back in the good ol days, in fact I didn't even take the carb off the engine during the recommission, just flushed it through and sprayed with cleaning solvent. My only theory is that over the years petrol has become more volatile, something to do with the ethanol perhaps, or optimised for modern fuel systems with electric pumps and injectors? So now it boils at a lower temperature.
This weekend I will strip and clean the carb properly, then try again with just a paper washer. If it still boils I'll try the spacer.
John
email (option): John.childs1@btopenworld.com
The one thing that has changed is the specification of the fuels we are currently running compared to those in the past...Perhaps this is making the difference in terms of engine temperatures...Ian
email (option): ian@wright52.plus.com
Just a quick update. Fitting a 5mm Tufnol spacer (from Feked.com) seems to have solved the boiling problem. I can now get a tickover when hot. Starting from hot is still a complete sod though, even though the mag has been overhauled and gives a good spark when hot. The throttle slide is so worn that it visibly rattles back and forth at tickover with an audible tat-tat-tat. Also the revs momentarily die as the throttle is lifted from rest, so all in all it's time for a replacement slide, I think.
email (option): John.childs1@btopenworld.com
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
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
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
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
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.
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.
Good to see some one contributing as to what solved their problem. Cheers. Bonza.
email (option): ukcarbsathotmail.com
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
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
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
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.
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
Bruce, do not drink and drive. 🥴
John 👍
email (option): john.kater@chello.nl