Hunting and Adjusting Carbs

Hi All,

Just completed a overhaul of the engine. 73 750. Overhaul included Jounal Bearings, new conrod nuts & bolts, cyclinder hone, new valves, seats and springs, carb slides have been re sleeved and bodies bored with original jetting settings. K&N air filter instead of the normal setup.

After start up, it took me a whle to get it to run on its own. But when it did it seemed to hunt around and i have had to raise the idle adjustment screw to run. I have checked for air leaks on inlet side and tried to play around with the air mixture screw. I will set the timing properly this afternoon using a strobe but is there somewhere else i should be looking.


Cheers
Ross

If your needles and needle jets are original, they are likely worn out and in need of replacement. Mine were 2 years newer than yours and I couldn't get it to run cleanly until I replaced them. Stay-up floats and Viton-tipped float needles are good updates, too.

Hello Ross
This sounds similar to faults I had with rebuilt Mk1 Concentric carbs on my 73 Roadster.
The carbs had been cleaned, bored and new brass sleeves fitted to the thottle slides by a recommended restorer.
I found that one of the slides was sticking - there is a trend for machinists to fit and bore to tolerances that are too fine - so worth checking for slide sticking and ease with some metal polish and clean if necessary.
Also have you cleared the pilot jet circuit?
On mine the pilot jets were clear but the two tiny holes where the fuel goes into the intake were partially blocked.
See this link to Amal info and section on Pilot Circuit.
http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
My bike now starts, runs and ticks over sweetly. I'm sure you'll get it sorted.
Good luck
Andy

Did you flatten the carb body and float bowl faces ? Did you use a 1/4" drill bit as a gauge to set the slides as a starting point ? How far out are your idle screws ? If they are not ~1 1/2 turns out you could have a bit of crud in the idle jets. Original jetting and K&N air filters might not be a good match especially if you have different mufflers.


Greg