Hitchcocks Forum

Hi All,

Need your help lads, My 1959 250cc Clipper has started to spit back, thru the exhaust then cuts out, any idea's

Tried all the normal stuff, checking for air leaks, made sure everything is nipped up tight etc, carbs where never my strong point boys so you it's up to you to pull me out please!

Any help as to setting up a 375/16 with a 7/8 bore from scratch would be great! your ways, not tech notes.

Cheers.

P.S. has all the rights jets etc, and main neddle set on 3rd notch.

Sounds like pilot jet blockage. This download may be of use to you - http://www.britcycle.com/Manuals/MonoblocTuning.pdf

Hi Howzie. As Bryan says, it's most likely to be the pilot jet becoming blocked. I would suggest you remove the carb from the engine for a complete clean up....it'll take about 2 mins. (No need to disconnect cables just remove the slide assembly complete)......BEFORE you start you really should buy the Monoblock gasket set and perhaps fit the VITON float needle, and also buy some Iso-Propyl Alcohol or Acetone or carb cleaner fluid to be able to dissolve the lacquer or gum that builds up inside the carb and the jets. Remove the main jet assembly, the pilot jet, air screw, float bowl cover, float and float needle. Soak the jets and pieces in the fluid to soften the gung and brush clean with old toothbrush or the like. Check the jets and airways by blowing through them. Even the pilot jet should have the hole clear enough to allow you to view light through the hole when held up to a bright source. Clean out the debris from the bottom of the pilot-hole cover nut and main jet nut...there is usually a big build up in there…get every bit out. After EVRYTHING has been cleaned immaculately, reassemble making sure all jets and nuts are tight and new gaskets/washers fitted. The fuel filter in the float bowl banjo needs to be removed and washed clean too. Set the air screw one and a half turns from fully screwed in (Closed) Refit carb and slide in slide and connect fuel pipe to banjo and tighten bolt. Turn fuel on very slightly tickle carb no more than 2 secs shut, choke completely, turn engine over a couple of times, leave throttle shut, and kickstart...engine should fire first kick....LOL!
You will now find that turning the air screw makes a big difference to the slow speed running and once warmed up the tickover can be set very accurately with just slight adjustments of throttle stop and air screw....Just as an extra note; check you tappet clearances you might them a touch tight.

AMMENDED & CORRECTED VERSION-----------------------------------------------------------Remove the carb from the engine for a complete clean up....it'll take about 2 mins. (No need to disconnect cables just remove the slide assembly complete)......BEFORE you start you really should buy the Monoblock gasket set and perhaps fit the VITON float needle, and also buy some Iso-Propyl Alcohol or Acetone or carb cleaner fluid to be able to dissolve the lacquer or gum that builds up inside the carb and the jets. Remove the main jet assembly, the pilot jet, air screw, float bowl cover, float and float needle. You can leave the throttle adjusment screw in or make a careful note as to the exact position it is in, by counting the turns out to remove it...This will make the first restart so much easier!... Soak the jets and pieces in the fluid to soften the gung and brush clean with old toothbrush or the like. Check the jets and airways by blowing through them. Even the pilot jet should have the hole clear enough to allow you to view light through the hole when held up to a bright source. Clean out the debris from the bottom of the pilot-hole cover nut and main jet nut...there is usually a big build up in there…get every bit out. After EVRYTHING has been cleaned immaculately, reassemble making sure all jets and nuts are tight and new gaskets/washers fitted. The fuel filter in the float bowl banjo needs to be removed and washed clean too. Set the air screw one and a half turns from fully screwed in (Closed). Refit carb and slide assembly (This might be easier before fitting the carb if the fuel tank is still in position). Connect fuel pipe to banjo and tighten bolt. Turn the fuel on (Ignition off)... very slightly tickle carb no more than 3 secs...shut the choke completely, turn engine over a couple of times with throttle slightly open. Then switch on ignition...Close the throttle and kickstart the engine...it should fire first kick....LOL! ....You will now find that turning the air screw makes a big difference to the slow speed running and once warmed up, the tickover can be set very accurately with just slight adjustments of throttle stop and air screw....Just as an extra note; check you tappet clearances you might have them a touch tight.

Thanks Beezabryan & Les H for your swift reply, will take carb off tomorrow & make a start, let you know how I get on later in the week!

Cheers.