running problem M8

[red_dog49]

hi, I started up my restoration project (1960) for the first time in the week,but it will only run with full choke
it seems to be running ok but reduce choke and ease of the revs and it stops,could I have got the timing
wrong although I have followed all the advice going about setting up the timing
I am sure someone out there will know the answer before I start messing around with the timing again.
thanks
rob.

[Les Howard]

Hi Rob. My first item to check would be the carb. The symptom appears to be a partially blocked main jet this is easily checked by removing the bottom main jet cover and removing the jet. It is possible that the needle clip has come off the groove and allowed the needle to fall into the main jet and not move up with the throttle slide. Also check for a blocked pilot jet (Monoblock carb?) this blocks up with gum quite easily after a long storage on the bike. If the jets and needle are OK you can check that the float bowl if filling to the correct height and this can be felt by depressing the tickler...if the fuel is at the right height you can feel the float lever and fuel should wet the finger in around 2-3 seconds most. There is also a chance that there is a big air leak on the carb manifold too...Check all these these carb items first (very easy) and if still the same let us know......

[cbranni]

Hi Rob .............don't take this the wrong way but you are pulling the choke lever to open the choke not pushing it away from you to close if that makes sense, when engine is running the lever should be pulled towards you when sitting on bike. If the engine will not run with choke open then the mixture is weak, petrol level in float chamber too low, air being drawn in somewhere, dirt in jets.

Colin

[red_dog49]

thanks for the replies,
I have checked the carb and all seems good,yes I am moving the lever to the correct position, I tried
tried moving the needle down a notch but no change.

[Ozmadman]

thanks for the replies,
I have checked the carb and all seems good,yes I am moving the lever to the correct position, I tried
tried moving the needle down a notch but no change.

Should that be UP a notch? Moving the needle down will lower it into the jet making it weaker

http://oldthumpers.files.wordpress.com/ ... ricks.docx

Paul

[red_dog49]

hi, I thought if I went to a lower notch it would raise the needle ?
as an afterthought I checked the serial number of the carb...376-280 now this does not seem to be correct
in one list I have it states 389-42 but on amal website lists 389-68, could the carb type be wrong.
regards
rob.

[cbranni]

Rob 376/280 is inch and sixteenth bore and the 389/42 is inch and eighth so there is a difference, the 398/68 is the same as 389/42 I think.
I have a 389/42 you can borrow, I lent it to another member and I havn't put it back on the bike yet, pm me your address and I will post it to you, it is in perfect condition and if the engine doesn't run with this carb then its not the carb.

Colin

[Ozmadman]

hi, I thought if I went to a lower notch it would raise the regards
rob.

yes it would if you moved the clip down a notch but you said you moved the needle down a notch ?
Paul
And, that's a good offer from Colin.. helpful as ever, he has saved the day for me on more than one occasion, a real nice guy

[red_dog49]

hi, so fitted the carb colin sent me and yes runs nicely on tickover !!, stripped again my carb,put back on and it runs now without choke
but not so sweet as colins. will return colins carb asap.thanks for the help.
rob.

[SPRIDDLER]

it seems to be running ok but reduce choke and ease of the revs and it stops,

Although you seem to have more or less sorted it now Rob the following may be of help/interest......
The main jet is only feeding th'engine from about 1/2 to full throttle. Altering the needle will have virtually no effect at small throttle openings (i.e. tickover to 1/2 open).
At tickover to 1/8 open only the Pilot jet is feeding fuel. If it's blocked or partially blocked th'engine will stop when you close the throttle . In your situation operating the choke is just a bodge to increase the vacuum in the carb throat which will 'suck' a bit more fuel through from anywhere, especially in a carb with worn body or slide.
The Pilot jet drilling in the carb body is only 16 thou dia and easily blocked, especially since the intro of ethanol in petrol.
Squirt WD40 or brake cleaner through the drillings to ensure that they are clear.
Pilot drilling in carb throat shown here: