Carburation

[hendred]

Arthur is quite right, there Ignition topic has gone off topic and some very useful information could be lost.  I have taken the liberty to start a new topic and copy across the relevant information (the Forum Administrator may be able to move posts?)
First off many thanks to Fredvincent for posting the following on an original Amal 2038 carb.

"My 2038 has Main Jet 480, Needle Jet 108, Needle 2F1 on second groove from top, Slide 3, Pilot 25 in top of float bowl. This is as the manual for my bike states, except needle in middle groove. The needle was dropped one notch in service. The bike has done 12000 miles so it was running OK up to 2012. May need a bigger main jet now with current fuel available.

I checked my manual for ignition timing. It states 37.5 degrees, 0.3 in BTDC at full advance. This is for a late bike built in February 1979 which is I assume a Peter Green ported bike.

The engine data listed on the forum states 7mm BTDC for Mk 1, 5mm BTDC for Mk2 and 7.6mm BTDC which is 0.3 in for late Mk2’s."

This is slightly different to the settings in the Technical Section on this site and provides a good benchmark for sorting out carburation problems.  The manual supplied with my Silk only gives the needle and pilot jet positions with no information on the size of carb or original jetting.

[Dirk]

thank you, i should have done that when i startet talking about carbs

[hendred]

While checking the pilot jet position this morning I checked the other settings of the 2038/302 carb:

Main jet 490
Pilot jet 20
Needle jet 108
Needle 2F1
Throttle slide cutaway 3

The bike has had several owners so not in a position to say if original.

I also found the throttle slide was only opening about 3/4 - 7/8.  Discovered there is a throttle stop in the twist grip and this was screwed right in.  Adjusted to get full slide fully open.  I didn't realise there was a stop in the twist grip, been like it for at least the last 12 years!

[Dirk]

.......isn‘t that ultra cool ?!!!
those findings / experiences with old bikes, tryin‘ to find the „stock“ settings (or maybe better settings)....
that is fun ! i just love those „problems“ and people like you, that inspire me every time 👍👍👍

[hendred]

Resurrecting an old topic but relevant I hope.  My Silk 4 stroked badly at small throttle openings - about 30 mph or less so town riding was not pleasant.  I thought it would be a throttle slide cut out problem, turned out to be a worn needle jet. New 108 needle jet fitted and problem solved.  I was surprised how worn the needle jet was, the hole was quite oval, a lot of wear for 17,000 recorded mileage.