DBD34 Mikuni carb problem

[chrisf-1]

Hi everyone I am having a problem with this carb and cannot get past it, the carb is a VM36 and supplied by Phil Pearson Jnr to the previous owner the problem I am getting is firstly the float keeps sticking and secondly it will only run and rev on choke, the carb has been in a sonic cleaner twice the pilot jet has been replaced and was not blocked or worn anyway bigger pilot jets have been tried but it runs worse with those, this was only done because I could not think of another solution and just do not know what to try next suggestions please

[V500]

Maybe contact Pearson?

[scifi]

Number one gotcha...?
The choke is On when the plunger is pulled out.
Normal running is when the plunger is pressed In.

[chrisf-1]

Choke on is when lever that operates the plunger is down and choke off when it is up

[cornishbob]

have you looked at needle, valve and seat? the right needle can make all the difference
is it a mikuni mikuni or the american copy (cant remember what theyre called). the yankie ones arent finished as well so i'd check for bad cleaning up on the bowl.

look up motocarb.com they are brilliant

[cornishbob]

should have said motocarb recommends a VM38. might be a /4 but i'm not sure about that

[scifi]

Have you tried a larger Main Jet..?  The sizes are different to Amal, so you need to experiment.  I found that a good way of carb tuning was to partially cover the inlet with a thumb, if it went faster you needed a bigger jet.    ( Obviously running with no air filter.)

[chrisf-1]

Honestly I have given up and sent the carb back to Allen's Performance for them to sort out but many thanks for your reply

[cornishbob]

i would have said the right meedle was imperayive but its all academic now

[chrisf-1]

As far as I know the carb was running correctly as the milometer was zeroed when it was rebuilt and it now has 384 miles on it but it has gone back to Allens performance for thorough ivestigation and I have asked them to give me a list of the spec and sizes of everything

[V500]

That's why I love Amals...

[Mike40M]

Exactly what do you mean with float sticking? Is fuel dripping?
Has it correct fuel level in the float bowl?
Have a couple of bikes with VM carbs, Velocette, Honda and Suzukis. All running great.

[chrisf-1]

Yes but not all the time just when it feels like it and yes I have changed the fuel cut off valve for a new one and it still does it when it wants

[cornishbob]

VM's are brilliant. they have to be set up right and its a bit of a faff. once they are though you'll never looh back

[DAVE BRADY]

Hi,

I have a Mikuni on an A65 and when it was new the fuel would come out of the overflow tubes when the fuel was left on.  Not every time but annoyingly frequent. I think in the booklet that came with the carb it did imply that the float needle is not meant to act as 'fuel tap' and that the fuel should be turned off when not in use.  Turning off the fuel at the same time as stopping then engine solved the problem.
However over time, if I leave the fuel on, there does not seem to be a problem any more.

Dave.