starting sequence

Head

Head

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Jan 26, 2021
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well folks,

i have a vm34 carb on my Norton,
i have 260 mains and 40 pilot
air screw is set at 1 and a half turns out

last month i cleaned the carb and i could not get the pilot out so had to drill it out without much issue
replaced the 40 pilot and cleaned the whole carb
before i went near her she used to start first kick hot with no choke and choke only when cold first kick
now after rebuild she wont start cold with choke i kick 2 or 3 times turn off choke and then add little throttle she fires up but until warm im on and off choke
when hot she is first kick everytime any ideas folks thanks
 
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You need to tune the pilot circuit, 1.5 turns on an air screw is only a starting point. Tune the pilot circuit when the engine is fully up to temp, adjust the air screw for highest revs then reduce revs using throttle stop screw, then adjust the air screw a second time in case the lower revs affects the mixture before final throttle stop adjustment. Now the mixture will be tuned for fully warm running and you will need choke when cold starting.
 
kommando said:
You need to tune the pilot circuit, 1.5 turns on an air screw is only a starting point. Tune the pilot circuit when the engine is fully up to temp, adjust the air screw for highest revs then reduce revs using throttle stop screw, then adjust the air screw a second time in case the lower revs affects the mixture before final throttle stop adjustment. Now the mixture will be tuned for fully warm running and you will need choke when cold starting.
Click to expand...
you are a legend i will try this this evening , when you say throttle screw is this the idle screw on carb which controls the tickover revs ?
 
You will have to get info on the VM, never worked on one, the throttle stop screw is the one that sets the revs during normal running. If the VM has a seperate idle revs screw then that gets set during a cold start. On my Amal B44 I screw the main throttle stop screw in 1/2 a turn for cold starts which keeps the revs higher until the engine warms up.

Read this

 
The smallest single carb I've tried on a commando was a 34 MK II...it must be economical :) throttle = Idle speed screw
 
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When you "rebuilt, drilled & cleaned" , did you VERIFY flow visually, using aerosol liquid, EVERY passage, both fuel & air?
I've repaired hundreds of VMs.
 
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What ye thinking folks sounds bit rough to me pulling like a train plenty of go in her seems little rough 1 to 2k revs , starting first kick when warm , will try cold start again tomorrow, done the air screw setting , will keep ye posted
 
Head said:
What ye thinking folks sounds bit rough to me pulling like a train plenty of go in her seems little rough 1 to 2k revs , starting first kick when warm , will try cold start again tomorrow, done the air screw setting , will keep ye posted
Click to expand...
Did you find any debris/ swarf when you stripped and cleaned/flushed out the carb.?
When the motor is warm and on the stand does she cough or hesitate if you quickly open the throttle ...to get the motor to rev to say 3500 ?
 

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