[Black fingernail]

Went to Paignton this morning, (a very British, bucket & spade seaside town, in Devon), for a coffee, in my favourite coffee shop.
No problems at all, she normally starts first time, except, of course, if people are watching!
Today though, she had a hissy fit, I turned her over once, with no ignition to prime, ignition on, BANG, back fire, not a big one, but after that, no start, Bugger!
Checked points,(have they closed up a bit), all good, put a spare plug in, good spark, compression blew my thumb off plug hole, all good.
Scratched my head for a bit, looked at the carb, THERE IT WAS, just off it's rubber mounting! loosened clamp, pushed back on, tightened back up, BOOM, running like a ten bob watch again!
This little escapade lasted @ twenty minutes, in this time, I fielded seven, stupid, fat, smirkey remarks, like, "that's the beauty of a British bike", et al, I think my reply of, "doesn't yours do this from time to time?" seem to make them waddle off and make a nuisance of themselves somewhere else.
The clamp that holds the carb in place, is a bit careworn, and doesn't seem to tighten as much as it should, so, a couple of replacements seem a good idea.
All in all, an eventful morning.

[ace.cafe]

Check the rubber intake hose for small cracks or leaks.
They fail regularly from modern fuels, and a small leak causes lean mixture, which can in turn cause a spitback that blows the carb off.
Ask me how I know!

[Black fingernail]

Check the rubber intake hose for small cracks or leaks.
They fail regularly from modern fuels, and a small leak causes lean mixture, which can in turn cause a spitback that blows the carb off.
Ask me how I know!

Yes, I checked that, I think it is the clamp that doesn't seem to do-up very well.
I fitted a new rubber this spring, and at the time thought the clamps were a bit dodgy.
I don't know if it is me, but after lockdown, the quality of regular unleaded petrol seems to be a bit rubbish. I haven't touched the timing or mixture screw or anything, but hill climbing, two up, causes a bit of 'pinging', I ran the tank down as low as I dared, and filled up with Vpower zoom juice. No more 'pinging', I have run this for a bit, there is no other difference, performance wise, so I've filled up on regular, just to see if it is my imagination, there is just a bit, barely detectable, 'pinging' two up, and it's just popped the carb off. So... I know these are supposed to run on the most rubbish fuel imaginable, but, I think I'll just use the allegedly good stuff from now on.

[AzCal Retred]

As Ace says the factory spigot rubber is rubbish. Mine is showing cracks (again) at 3 months. I keep seeing radiator hose mentioned as a spigot rubber substitute. What's a good place to look, NAPA Auto? Any part number references? -ACR-

[ace.cafe]

As Ace says the factory spigot rubber is rubbish. Mine is showing cracks (again) at 3 months. I keep seeing radiator hose mentioned as a spigot rubber substitute. What's a good place to look, NAPA Auto? Any part number references? -ACR-

You just have to go into the store like Autozone or whatever, and get a piece of straight generic hose that they sell by the foot.
1.25" I.D. should fit the stock system.

[Black fingernail]

The rubber failed on mine in spring, I fixed it with a piece of car radiator hose, to get me home. There was a cone air filter fitted with no support, so I ran about a bit using the piece of radiator hose that got me going again. I then fitted the British made (better quality) rubber from Hitchcocks, I have also fitted a proper filter box that supports the other end of the carb. I still keep the hose in the tool box though, just in case.

[Adrian II]

I had a BSA B40 that would do this with aftermarket carbs fitted in rubber mounts!

A.

[DavidGraves]

Not Embarrassing in the least...I distinctly remember a young man who would bend over the petcock and motor of his 750-4 as if to doodle around with the timing on his friends duo-glide.

IT was just something one did if you wanted to impress the onlookers outside the saloon (nah...McDonalds)....

Besides the behavior there were all the requisite devices like the tiny little slip lock pliers that would fit in your watch pocket.

I can't remember that kids name.....

[axman88]

IT was just something one did if you wanted to impress the onlookers outside the saloon (nah...McDonalds)....

My buddy told me that the coolest thing to do when he was riding his Jawa, back in Poland in the late 70s, was to sit astride your machine, smoking a cigarette.  As you took the last puff, you'd casually reach down, take off the gas cap, and with a flourish, toss the smoldering butt into the tank.

[AzCal Retred]

Ace - any advantage to making the connector stub longer? How about upstream of the carb, should there be 4" - 6" of intake tract? Or maybe none of it really matters until you pump-up the motor a bit?

I run a clamp-on K&N because I had dirt intrusion from the standard air box and it was bulky. I rejetted/lower # slide using the Hitchcocks guide. It seems about the same, performance wise, but a bit better off idle. I recall lots of Japanese machines are very unhappy with clamp-ons and stock carbs, but those were usually making 1 1/2 - 2 BHP/cu. in. or so.  -ACR-

[Black fingernail]

In my opinion, if you fit a cone type air filter on a 500, you leave all the weight of the carb on the rubber mounting, this will cause the rubber to split.
Some sort of supporting bracket must be fitted on the filter side of the carb to prevent this, better still, do what I did and fit an airbox, but open up the inlet hole to try and make it less restrictive, I made a filter from a car flat, 'waffle' type k&n cut and rolled to fit, (Jaguar X type).

[ace.cafe]

Ace - any advantage to making the connector stub longer? How about upstream of the carb, should there be 4" - 6" of intake tract? Or maybe none of it really matters until you pump-up the motor a bit?

I run a clamp-on K&N because I had dirt intrusion from the standard air box and it was bulky. I rejetted/lower # slide using the Hitchcocks guide. It seems about the same, performance wise, but a bit better off idle. I recall lots of Japanese machines are very unhappy with clamp-ons and stock carbs, but those were usually making 1 1/2 - 2 BHP/cu. in. or so.  -ACR-

No, keep the carb where it normally is. If you want to add intake length like a stack, add it between the carb and the filter/housing.

I concur with the above recommendation to have a bracker to support the filter end of the carb.

[Royal Stargazer]

I'm sort of glad I'm not the only one who's had this happen... I'd just fueled up sometime last year, happy as a clam that my bike had been performing so well. Kickstarted at the pump and got a couple good thumps, then this really weird noise, and my bike died.

A bracket to support the carb was on my "to bodge" list for this year. Probably a short trip to the hardware store and an hour or so of wrenching would have done, but this year went very south.