Overflowing float bowls

[jackstraw]

I cleaned, rejetted and rebuilt carbs using new bits from David Silver and left them on the bench for a week with the remote fuel tank 3 foot above carbs, fuel tap on & no leaks!!!

Put on the bike and on some starts from cold I get overflow from float bowls, not sure if its all of them-I need to put some clear tubes on to check which are overflowing, which isn't as easy as it sounds, bloody awkward position.

Even more bizarre is its not consistent. It mostly happens on a cold start, but not every cold start, if left for about 5 days between starts, then the issue seems most common. Once the engine has warmed up and heat gets around the carbs-a few minutes-they all hold fuel, and I can leave the tap on. ( I don't obviously) . But as the engine cools down, there appears to be a capillary effect-I think this overrides the vacuum tap- which I now think puts too much fuel in the carbs and makes the next cold start, especially after a few days difficult because the plugs get very wet, so it floods. Hence me binning the vacuum valve so I can control the flow from the fuel tap.

A friend has just rebuilt his carbs on his Triumph TR4-with new components and he has identical issues. He reckons its modern fuels with crystals forming on the valve needle tips. Another engineer I spoke with has heard similar and reckons when the carbs are cold, and the air is cold carb icing forms, just enough to disrupt the needle valve tips.

So I am still conducting tests using the remote fuel tank, had the remote plastic tank at various height levels above and parallel with carb bodies, get the same result whatever position. I haven't put the fuel tank back on yet, will do so and see what happens on a ride. I guess I need to wait for spring temperatures to tell. My other thinking is if the float valves hold when warm or hot there seems little point in taking off the carbs to reduce the float height as I won't get sufficient fuel in the float bowls in normal use.

Always assuming that the David Silver spares I used are the best items one can buy, genuine items obviously not available.

1. Has anyone experienced anything similar, if so is there a work around?
2. I Have disconnected the vacuum tap, is this wise?
3. Are the spare parts from David Silver (UK) generally good?

Many thanks

[daves79x]

Did you use genuine Keihin float valves? Did you polish the brass float valve seats? Did you carefully check every brass standpipe for tiny cracks? The two most common causes of leaks.

Dave

[wessi]

First thing to do in this case, some soft hits with a mallet on right and left side of the mounted carb-assembly helps to let things "sat" on the right place.
In my case , it works perfect. No overflow again since then, even after one year

[Larry Zimmer]

First thing to do in this case, some soft hits with a mallet on right and left side of the mounted carb-assembly helps to let things "sat" on the right place.
In my case , it works perfect. No overflow again since then, even after one year

So very true, Wessi. Works on 4-wheel things (cars!) just as well. I learned that one many years ago. (1967 as I recall)) Never put a carb together since then that didn't get a little tap. And, yes, has to be done AFTER installation. Doing it on the bench doesn't count.