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M20 Carb

Hi every one

The carb on my m20 seems to be starving petrol to the plug , the plug is bone dry when attempting starting the bike .

i have stripped the carb down and given it a good clean but still the same

Any ideas guys ?

Re: M20 Carb

Assuming a fuel supply & that the carb is clean & in reasonable nick, did you press the plunger to get fuel into the float bowl?

Re: M20 Carb

yes , i have removed the float bowl top and checked , it seems to be filling with petrol

Re: M20 Carb

Ray
Would it be an idea to recheck the jets & needle?

Re: M20 Carb

Hi have you fitted an inline fuel filter to rubber hosing as most sold these days are for motorcars and need pressure from a pump to operate. If standard copper piping have you a blockage in the piping or new taps that are greased with thick grease and blocking the flow. If you have the original pre mono carb with seperate float bowl being a 276C/1B do you have the correct throttle needle marked 6 and being 81.32 mil long as a longer needle can starve the carb. Do you tickle the float bowl to start the bike? If so if you press it for long enough does fuel flow out. Are the two small holes in the knurling on the opposite side of the float bowl top clear. Is small hole in fuel cap clear.

email (option): ukcarbsathotmail.com

Re: M20 Carb

Hi

i have the original copper pipe , nothing seems blocked on the pipes and holes ect and fuel is reaching the carb ok

The carb fitted is model number 276 AW / 1BB with a Number 6 needle

With tinkering today i have got it started but seems to not rev and stales after a very short time

Re: M20 Carb

When you say that you stripped the carn, did you remove the jet block and clean the pilot airways ?

Does the tickover respond to the pilot air screw ?

Sorry if it's a Grandmother egg-sucking question :relaxed:

Re: M20 Carb

I did completely strip and cleaned the carb including the block ect , the bike only runs for a very short while with no time to adjust the pilot screw and does not respond to the throttle

Re: M20 Carb

Will it run with the choke applied or partially applied?

email (option): Edwards

Re: M20 Carb

Hi,

Perhaps the flange is warped? You can test that by smearing grease all around the edges of the join to the cylinder. If the bike runs reasonably well for a short time (until the grease melts) then you know you have a warped flange and air is leaking into the cylinder. You can dress it flat using a piece of plate glass and rubbing compound, and lots of patience.

Allan

email (option): allanmatchless@yahoo.com

Re: M20 Carb

A 276AW/1BB is off a BSA B31 1946 to 1948 and may have the bowl on a 3 degree or 7 degree angle or has it got the proper M20 bowl of 1B which is no angle. If you have a 7 degree angle bowl you may find it will play up on bendy roads as too rich on some bends and too lean on other bends but should not upset the starting. If the bike is starting and then stopping real quick has it got stale fuel?

email (option): ukcarbsathotmail.com

Re: M20 Carb

And have you pulled the choke lever to off? Sounds silly but I have met a few guys who think the choke is off by pushing it away:thinking_face:

Ron

email (option): ronpier@talk21.com

Re: M20 Carb

This might sound a bit daft but it's happened to mne when restoring older bikes.

A rat or mouse family makes a home in the silencer and they bring in enough bedding material to block the pipe. Successive generations bring in more material. The bike will start eventually but will not rev above idle. Worth checking...

email (option): cas.vanderwoude@gmail.com

Re: M20 Carb

The carb has the 1b float bowl

It is possible a bit more rubbish has entered the carb from the tank , so i will strip it again

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