Carb queries

[Phil C]

Hello all,
I'm taking apart my Concentric carb in order to check the pilot jet is clear, having been advised that a pilot jet blockage is probably the reason for my bike conking out about one second after starting. I've never done this before, so am seeking help please! So far everything looks generally pretty clean, although there was a little bit of gooey muck in the bottom of the drain plug. I've found the pilot jet underneath the pilot air screw, and I see two holes in the carburettor bore which I believe are the outlet holes. So I need to check that the passageways through the jet and through to both those two holes is clear. Please forgive this basic question: how do I check it? ( I have a can of carb cleaner. I have not got compressed air but have a foot pump if that's any use.) How do I actually do it?
Phil

[Phil C]

Looking to answer my own question, I did a bit of carb-cleaner squirting. First I squirted some into the pilot jet hole, and it came squirting up through both the tiny holes in the carb bore. So I guess that's clear (and maybe the idea that the engine is stopping because of stale fuel blocking the pilot jet now appears wrong?) I then squirted some into what I think is the pilot air hole, ie the left hand one of three as you look from the rear of the carb, it came squirting out of one of the two tiny holes in the bore (the one nearest the centre of the bore) but little or none through the other (the one nearest the carb flange.) Is that what should happen?  Phil

[Stubaker58]

Hi,
Have you seen "Bushman's Carb Tuning secrets"?  It's very informative and easy enough to folllow.

http://www.ntnoa.org/carb_secrets.htm

Click on the link to the pdf and print it off for some bedtime reading!

[Phil C]

Thanks very much for the link, but it's not secure so I'm a bit reluctant to use it. When I say insecure, I mean it has an exclamation (warning) mark at the top left corner rather than a padlock sign.

[berniej]

You're just downloading data from the site not submitting any sensitive data back to it.
A secure connection is not necessary for that.

Cheers,
Bernie

[Phil C]

But doesn't it mean my computer would be susceptible to hacking? (unlikely, I know, but...)

[Pete C]

I downloaded it several years ago and haven't had any problems. If you are that worried I can send you direct my copy.

Cheers
Pete

[AdrianS]

Just download it.
I've down loaded many articles, manuals etc over the years. Never had any problems. You are not giving out any personal info, only downloading. I assume your computer has some anti viral program and if you are running the latest version of windows 10 there is some built in antiviral software.
Apple Mac systems rarely get any problems.

[berniej]

But doesn't it mean my computer would be susceptible to hacking? (unlikely, I know, but...)

No

[Phil C]

I downloaded it several years ago and haven't had any problems. If you are that worried I can send you direct my copy.

Yes please Pete.

[Phil C]

Thanks very much everyone. Pete emailed me the Bushman's stuff -  really useful and interesting info.     Phil

[Phil C]

Interesting: I thought the two tiny holes in the bore were one for the pilot air and the other for pilot fuel, but no, they both take both, the fuel and air having been mixed just below, in the pilot mixing chamber.  So I guess, unless I'm mistaken,  any carb cleaner squirted into either of the pilot passageways should come up out of both those tiny holes.    Phil

[Phil C]

Ah, I might have been premature when I said the theory that the pilot jet was blocked might be wrong. Looking at the Bushman's information, and at other stuff, it appears the route that the pilot fuel takes begins near the rear of the carb, at a threaded hole where (pre-1968) there used to be a threaded jet. From 1968, in order to place the jet closer to the outlet holes, it was placed (pressed) in the gallery behind the pilot air screw. So the thread at the start of the pilot fuel's journey from the bowl is now redundant. As I understand it, the pilot fuel is drawn through the threaded hole, and along towards the front of the carb, and through the jet, near the outlet holes. So the holes I squirted carb-cleaner into a couple of days ago (as described in my previous post) were both part of the pilot air route. The pilot fuel route is different. And when I now squirt carb-cleaner into the threaded hole, ie the fuel route, none seems to appear at the tiny outlet holes. Which I guess might mean the route is blocked, as I was told! ( by Paul, I think - thanks again.) My bumbling efforts continue. Watch this space (well, if you're easily entertained and/or very patient!). Phil

[Phil C]

Me again. Update: gave it a bit of a blow with a foot pump, and then squirted carb- cleaner onto the threaded hole and watched for it coming out of the two tiny outlet holes in the carb bore. It came out of one ( the one nearest the centre of the carb, but not the other. I think it should come from both? I've seen a diagram of the carb (Concentric) which labels that hole (the one I get carb-cleaner through) as "pilot by-pass" and the other as "pilot outlet". What's that all about? All help appreciated!   Phil

[Phil C]

By the way, the reason the carb-cleaner didn't come out of either hole first time was that I'd forgotten to refit the pilot air screw, so the carb-cleaner would just have shot out of there. Anyway, as I say, it's now coming out of one hole but not the other. Why are there two holes anyway?