Monoblock 376/5 - O Ring

[chappers1962]

Ive just purchased from Ebay an original 376/5 Monoblock to replace the non standard concentric which came with the bike. The flange on the carb does not have a slot for the O ring as did the Concentric. I'm assuming I still use the 'thick' section O ring, i.e hold it in position and then tighten, or for carbs with no O ring slot, should I be using the gasket supplied in the rebuild kit?

[ajscomboman]

What you have is a very early 376 that was used when the manifold had the groove for the o-ring. You cannot use the o-ring with an plain manifold as it will simply bow the carb flange. As you have no provision for an o-ring best solution is some nice thick flexoid gasket paper.

[chappers1962]

Many thanks. The Carb was from an AFS bike - which the seller stated had only done 4k miles. Stripped the carb and had very little evidence of ware, and still had the original brass float. Cheers

[chappers1962]

More trouble I'm afraid. I replaced the float and needle valve which were provided in the major repair kit. When I put it all back together, a constant drip of petrol came out of the carb opening. Checked the float by pushing it to the top of the float chamber, but there was still a few thou gap between the float and the float needle, thereby not sealing properly. Unfortunately, I can't find the old float needle to check size (somewhere in the garden - doh!). Question is were there different lengths of needle valve between the various versions of the 376, or am I missing something?

[1608]

Might seem a bit obvious but, check the float isn't upsidedown. However, I have found different length tickler buttons, so who knows

[alanengineer]

You may have put in an extra fibre washer under the needle valve assembly, lots of people do. Their should not be one

[chappers1962]

You may have put in an extra fibre washer under the needle valve assembly, lots of people do. Their should not be one

Only got a fibre washer under the needle seating as per the repair kit diagram. Found the original needle valve and size is the same as the new one. Put the original needle valve and brass float in and same problem, so could either be the washer is too thick or needle seating is wrong (which is a bit surprising as apparently the carb came off a 'working bike').

Float is the right orientation ( new one has 'Front' showing).

Will do some more investigation in the morning.

Marking on the carb is 376/5, but as per earlier post is an early monoblock version (i.e. no O ring slot).

[ajscomboman]

No fibre washer fitted to the needle holder on an original monobloc so if you have fitted one remove it, they are only fitted to new ones.

[chappers1962]

No fibre washer fitted to the needle holder on an original monobloc so if you have fitted one remove it, they are only fitted to new ones.

brilliant - many thanks, will remove tomorrow and report on progress.

[Rosy]

Worth checking the float for leaks as well.