KH Carburation Saga

[David Smith]

My original Carb, a 15/16 379 monobloc bored out to 1" would never pull full throttle despite jetting the main jet down and down, but idled very well and was good up to 1/2 throttle. So fitted a second hand 1" item which unfortunately idled badly due to a loose fitting slide, but was good when run without the air pipe connected. So refitted the original carb with a 1" jet block just in case I had altered the venturi effect,on standard settings, fuel level checked with a perspex float cover and perfect with an old nylon float needle, too high with a rubber tipped item, ran great all the way through with the air pipe off. Reconnected air pipe and original burgess air filter. ran like a bag of spanners above 1.2 throttle. so I presume the villain of the piece is the burgess air filter not flowing enough air. Have ordered a gauze fitted clamp on bell mouth from Hitchcock's as my carb does not have the more standard threaded end but is a plain boss off who knows what. Have also ordered a generic clamp on cone air filter in case I want to ride on the beach! This has taken a while as am earlier carburation test run dumped me on the deck with a broken arm when an errant horse shoe nail found its way through the front tyre!

[will_curry]

For what it's worth 375 monoblocs without the threaded inlet were fitted to Arrows and Leaders
with the 376 fitted to Sports Arrows.

[tony.barnett]

Jetting would be different for a carb with or without an air filter. A carb jetted for an open mouth will be chucking far too much fuel in if you then put an air filter on it.

[Simon.Gardiner]

The two-stroke monobloc often has an angled spray tube in the jet block and different needle jets (with no cross-hole?), If you've been trying to get a two-stroke carb to run on a four-stroke engine it might be troublesome....

SG

[David Smith]

Simon, definitely a four stroke carb, The jetting is standard, but clearly with the burgess filter running rich at higher revs as it seems unable to flow enough air and must be strangling the carb.

[Roger Gwynn]

I would be surprised if a burgess air filter made any difference, itvus not very good at filtering air socwould offer little restriction