1975 Mark 3 Poor Starting

I recently purchased a pair of new Amal Mark one concentric carbs for my 1975 Electric Start 850. After 600 miles of running great I decided to replace the valves in the head with Kibblewhites. Reassembled and I decided to change needle settings. There are three grooves on the needles that were supplied with the carbs I bought which are 932/35 and 932/36. Main jets are 260 slide 3.5 and needle jet 106. My question is which needle position are the carbs normally in when they are supplied. I dismantled the carb tops and have forgotten how they came. Clip in top groove, middle or bottom ?????? I am having major starting problems however when started she runs great.clips presently in bottom groove (3)
I have checked valve clearances /fuel flow from gas taps. Breather hole in gas cap etc. tried tickling both sides to excess and also choke. I am running Boyer and timing is at 31 deg. Battery is new and fully charged. Spark seems a little weak. I am wondering whether it could be an electrical issue which is intermittent. will check filter later today as I am running standard big plastic airbox

thackero said:

There are three grooves on the needles that were supplied with the carbs I bought which are 932/35 and 932/36. Main jets are 260 slide 3.5 and needle jet 106. My question is which needle position are the carbs normally in when they are supplied. I dismantled the carb tops and have forgotten how they came. Clip in top groove, middle or bottom ??????

Click to expand...

"Top (weakest notch)" according the Mk.3 manual (Section A): http://britmoto.com/manuals/Manuals/850_man.pdf
(standard 928/104 needle) however, where peashooters and/or non-standard air filters have been fitted this needle setting may not be correct?

If I'm reading you correctly, the problem started after you changed the valves.

Were the carbs adjusted properly before you made this change? Air jet settings, idle stop, etc.

Some change may have occurred with valve work, requiring readjustment of carbs.

If it runs okay once started then likely not electrical, but the weak spark could be a suspect. Have you tried new spark plugs?

The Carbs were adjusted correctly and all was well before the valve change. The reason for the valve change was that the exhaust valve stems were worn causing oil to enter the combustion chamber which resulted in oil travelling into the exhaust downpipes and weeping from the exhaust collar /cylinder head port joint. I have new plugs. Once started she runs well. I will take a look at the air filter element and maybe remove and inspect the pilot jets. Ethanol fuel could have blocked the jets which may be contributing to the difficult starting.

Needle clip position will have no effect on starting.

The weak spark must be explored... kill switch? Connections disturbed taking head off? Perform a compression test.

1975 Mark 3 Poor Starting - FIXED !

I checked the air filter and dismantled the right-hand switch gear as the spark seemed to be a little weak then it would be strong blue. Gas tank off again and checked all connections. I have the original spade connections which do seem to be slightly better quality than the replacement parts from Boyer etc. The earth connection seemed a little sloppy so I will change out for a permanent ring connecter soldered to the earth wires. Assembled everything and tickled carb till just overflowing ,no choke and ignition on ,hit start button and she fired up straight away. Took her out for a spin and rides like a dream. It seems like the sloppy earth connection was the culprit. Thanks for all your help and Happy Thanksgiving to all !