I'm trying to work out why my Mont is over revving. It could be so many things so Im just going through each possbibility one at a time. Cable routed well and moving nicely. New carb rubber to cylinder. Throttle body moving well and not caught. Just taken carb apart. I've never had an amal carb before so Im not use to their seting up. The slide seems to have about 2mm gap at the bottom. This seems a bit excessive. Am I right ? I thought the idle jet alone would allow for it to idle with the slide shut. Does the slide require a gap and if so how much ? Also, Im worried that the slide may be worn. Should there be any play at all in the slide or not ?

gareth

The slide should not movement sideways in the body Concentric Amal carb bodys and slides wear Look round the bottom the slide for wear marks ( at the output side )If badly worn it can break wrecking the engine The two screws on the side the horizontal one is the mixture (idle) the other at an upword angle is the throttle stop You can get info onthe Amal web site www.amalcarb.co.uk

Edited August 8, 201214 yr by naichuff

The slide should not movement sideways in the body Concentric Amal carb bodys and slides wear Look round the bottom the slide for wear marks ( at the output side )If badly worn it can break wrecking the engine The two screws on the side the horizontal one is the mixture (idle) the other at an upword angle is the throttle stop You can get info onthe Amal web site www.amalcarb.co.uk

Thanks for that info. What about the gap at the bottom of the slide and the carb body ? Should it be as much as 2mm ?

Gareth

Yes..You still have to get air into the motor even at idle..

just had a look at the Amal on my 348.. theres easy 4 or 5mm

gap on the air cleaner side...

Edited August 9, 201214 yr by petenz

Yes..You still have to get air into the motor even at idle..

just had a look at the Amal on my 348.. theres easy 4 or 5mm

gap on the air cleaner side...

Thanks for that info. I suppose it will be trial and error with the throttle stop screw. Any idea how many turns out the air screw should be on a mont 123 amal carb ?

If you are starting from scratch in setting your carburettor check the jets, needle and slide are correct for your bike. The original Montesa owners manuals have details of the original settings. A new correctly oiled air filter is an advantage if the existing filter is getting a bit crumbly.

Start by adjusting the throttle stop screw by backing off the screw until the slide reaches the absolute bottom of its travel. Make sure there is a little slack in the throttle cable. Then lift the slide by 1.1/2 to 2 turns of the throttle stop screw. If the slide is too high the carburettor's pilot system will not work properly.

Now gently screw the pilot screw in till it stops then wind it back out 1.1/2 turns to begin with.

Start the engine and let it warm up fully. If it does not tickover screw the throttle stop screw gently in until a tickover is obtained. If it ticks over too fast wind the throttle stop screw out.

We finally set the pilot air screw by listening to the engine revs, turn the pilot air screw slowly in both directions until maximum revs are attained. Turning the screw out weakens the mixture and inwards richens the mixture. Too weak or too rich a mixture will cause the revs to drop or the engine to stop. When the point of maximum revs has been found the throttle stop screw will probably need adjusting to your preferred tickover speed. Once set a half turn of the pilot air screw in either direction should cause the revs to fall.

When the tickover is how you want it check the throttle cable for excess play.

Hope the above is of use.

Edited August 9, 201214 yr by tayld

If you are starting from scratch in setting your carburettor check the jets, needle and slide are correct for your bike. The original Montesa owners manuals have details of the original settings. A new correctly oiled air filter is an advantage if the existing filter is getting a bit crumbly.

Start by adjusting the throttle stop screw by backing off the screw until the slide reaches the absolute bottom of its travel. Make sure there is a little slack in the throttle cable. Then lift the slide by 1.1/2 to 2 turns of the throttle stop screw. If the slide is too high the carburettor's pilot system will not work properly.

Now gently screw the pilot screw in till it stops then wind it back out 1.1/2 turns to begin with.

Start the engine and let it warm up fully. If it does not tickover screw the throttle stop screw gently in until a tickover is obtained. If it ticks over too fast wind the throttle stop screw out.

We finally set the pilot air screw by listening to the engine revs, turn the pilot air screw slowly in both directions until maximum revs are attained. Turning the screw out weakens the mixture and inwards richens the mixture. Too weak or too rich a mixture will cause the revs to drop or the engine to stop. When the point of maximum revs has been found the throttle stop screw will probably need adjusting to your preferred tickover speed. Once set a half turn of the pilot air screw in either direction should cause the revs to fall.

When the tickover is how you want it check the throttle cable for excess play.

Hope the above is of use.

That is a fantastic bit of advice and many thanks ineed. I've got monday off work so I'm going to dedicate it to the carb and get the bike running.

gareth

^Upadate.

^{Stripped carb. Put airline through it. Rebuilt it according to above instructions. rerouted throttle cable. Bike runs sweet as a nut. Many thanks. Gareth}