276 carb flooding?

[cmfalco]

I'll have a go at lapping the needle into the seat with fine grinding paste and then tapping and rotating the needle.

Lapping my float needle completely cured the problem for me. But, use very fine paste and limit how much you lap because, to some extent, lapping results in the effect shown at the right, exaggerated here for visibility.

I would be reluctant to try to improve things by tapping, since it will be extremely difficult to have the needle and seat precisely perpendicular to each other when you tap it, which only will make things worse. Actually, there's a good chance tapping will make it irreparable. If lapping alone doesn't cure the leaking it already may be beyond salvaging, since some previous owner might already have distorted the seat and/or needle by tapping.

[nevhunter]

Relating to fuel level...Fuel does not come out of that hole. When you tickle the float the fuel runs out of the hole at the side of the Bowl lid if you do it longer than I usually do. A low fuel level makes starting and idling less regular. Nev

[cmfalco]

Relating to fuel level...Fuel does not come out of that hole.

Fuel should not come out of that hole. It won't If the level is correct, which is well below the top of the needle jet. If it does, it means the float level is too high.

[MarkO]

cmfalco - I like your thinking and the illustrated explanation. On mine, fuel ran out from what looked like the base of the mixing chamber, suggesting it originated from the hole in the jet block as you suggest. Hence the reason for the level to be at - or probably just below - the top of the Union nut which would seem to correlate to just below that hole. That said, if fuel was suspected to be passing from the float valve, then I guess that is the first thing to investigate as likely that would be the root cause rather than the fuel level.

I have now lapped with fine paste and lightly tapped - rotating the valve each time - in much the same way as lapping cylinder head valves. The needle seems to seat better, offering a wee bit of resistance to push it up out of the seat. Bowl cap recess lightly polished with wet and dry and blown clean with carb cleaner. I screwed the cap in all the way and backed off about half a turn. Needle was very free to move within it beforehand. Tested it this afternoon. No leaks and a hot start twice from first kick. We'll see how it goes......

[cmfalco]

if fuel was suspected to be passing from the float valve, then I guess that is the first thing to investigate as likely that would be the root cause rather than the fuel level.

Quite right. Since most of us lack x-ray vision to see what is happening inside the carburetor, that hole serves a very useful diagnostic function. If no fuel is coming from the hole, it doesn't necessarily mean all is OK, but if it is coming from that hole, something definitely is wrong.

A runny nose is a symptom that tells you something is wrong. But, knowing that, it is then important to determine whether the cause is a cold, allergies, or Covid, each of which would require a different treatment to address the problem. Fuel running from that hole tells you the fuel level is too high, possible causes of which could be the float being partially filled with fuel, the float sticking, the float chamber somehow mounted at the wrong level with respect to the carburetor, the float valve not sealing, etc.

[MarkO]

A further thought. A new plug was installed last week. Since then I have racked up about 150 miles. Removing the plug and it is black and sooty and also a wee bit oily. This seems to indicate rich running.The pilot air screw is about right, cutaway is what it is, main jet is whatever is standard, but first thoughts would be to lower the needle. However, needle is already on the highest notch. Do I therefore need a new needle and jet? I think Burlen supply?

[simon.holyfield]

How old is the needle and needle jet? Needle jets are sold in one thou increments (0.106, 0.105 etc.) so you can see that it doesn't take a lot of wear in the needle or the jet to make a big difference to the mixture strength. Recently I removed a needle which was showing three to four thou wear in some areas.

The bike persistently fouled plugs until I changed the needle.

[MarkO]

Simes - yes agreed. No idea how old the jet is, but it looks decades! Needle looks recent and I may have replaced it within the last 5 years - cannot remember. Main jet is 170 not 160 so changing that too. 0.106 needle jet, needle for 276 carb, and 160 main jet ordered from Dragonfly anyways....

Kick start arm also fell off somewhere! Loctite for the replacement beckons....

[cmfalco]

Removing the plug and it is black and sooty … The pilot air screw is about right, cutaway is what it is, main jet is whatever is standard, but first thoughts would be to lower the needle.

This sounds very much like the symptoms of a worn needle jet, since most riding is done at fairly low throttle settings where the taper on the needle doesn't even come into play, nor does the size of the main jet make much of a difference. The needle itself is a less likely suspect but, as noted by others, the needle jet is a wear item. Ones on my Gold Star Catalina only last ~1200 miles before they are completely worn out (enlarged by 0.0005").[*]

[*] several years ago I measured 22 NOS Amal needle jets ("original" Amal, not Burlen) and found 77% of them were fine. However, two were more than a full size smaller than marked, and three were a full size larger. A half size (0.0005") changes the fuel flow by over 6%, which is enough to cause a bike to run very lean or very rich. Anyway, I have a special micrometer I use to measure the diameter of needle jets when I install them, and record the values so that I can later check on their "progress."

[MarkO]

Some fine metrology going on here. Mind, this is a VB, so as long as there is a hole in the jet then who cares

The old jet is stamped AMAL and I don't think is brass plated, certainly not brass colour, rather some faded silver/grey coloured alloy of some description much like the one in the photos in the previous post. It certainly looks old. Needle looks OK, but a new one ordered.

I'm thinking a cleaner plug may also improve my hot starting issue.