Hitchcocks Forum

Hi all

Following my fairly well documented rebuild I am having no end of bother getting the bike to run for more than a minute or so... I'm fairly convinced that it is a Carburation problem... Carb is a mk1 900 series concentric with 220 main and 106 needle jet..Carb has standard nylon float at the moment so not adjustable and the needle jet is working fine. I've thoroughly checked and cleaned the carb and blown through all fuel ways.. Are there any other checks I can do to ensure the carb is ok

Hi matey !!--------I feel the pain, Brother !!......been there, done that etc--etc......Questions for you}-- a) What convinces you it's a Carb problem ??.........b) What size pilot jet is fitted ??.........c) Is a "minute or so" an actual measured time or just a turn of phrase ??..........d) When the engine does run can you get it to rev cleanly or does it splutter and is reluctant to increase with throttle demand ??............e) What's the history of the carb ( new or s/hand ??)...........f) Can you fit a substitute carb that's known to be OK ??

Hi Alan...... The carb was fine prior to the rebuild... The engine was standard 500 and jetted 210 105... I may be wrong but don't think there is a changeable pilot jet in the carb..

I literally removed the jet carrier via the drain plug and changed the jets..

A minute might be an over estimation.. It seems to tick over OK for "about a minute" and the engine just starts to warm.. I blip the throttle and booooore (I think that's how you spell the sound) engine death... Ignition is a Mk3 boyer.. Again was fine prior to the rebuild.

I don't have a spare carb..

Tom

Hi Tom. Next time you start the engine, as it catches and runs, get your thumb on the tickler quickly and see if it keeps running with fuel spilling from the tickler button, if it continues to run and then splutters and dies if you release the tickler, your problem is definitely fuel [or rather lack of] related. Regards, Paul.

Hi Alan /Paul.. Just checked and yes there is no pilot jet..

Carb is 28mm

Tom

Hi Guys-------- yes, I know that sound you so eloquently described there-------certainly has the hallmarks of an engine gasping for fuel..........I've posted this image just as a point of reference

Mr Spock ( He of the ears and logical mind ) might say}---"The carb worked fine ---- then you changed some jets ----- now it doesn't work fine.....ergo something you did / or didn't do on rebuild has caused this problem....." At this point I'm going to suggest that you remove the carb, strip it in stages ( with photographs ) and post on here so we can all see what's what .....It'll be something silly like the float getting nipped in position etc.............Incidentally Paul's mention of the tickler prompts me to ask}---Using the tickler can you feel the float rising and falling ??-

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Hi Alan

Thanks for the photos of the carb fitted with a pilot jet, which mine does not have... Your photo has confirmed that 100% for me.. As I said originally I changed the jets without removing the float bowl, via the drain plug hole... The float moves freely... You can hear it if you shake the carb... Yes it's off of the bike at the moment as I've checked everything I can think of..