Hitchcocks Forum

I was suffering with my bike stalling when I shut the throttle when warm, so I adjusted the idle screw to speed up the tickover a bit. However, the 'idle' is now racing and adjusting the throttle screw down (or up) seems to make no difference. In fact, the screw can be adjusted up or down through its entire range without affecting the speed.

I have checked the slider, which seems to move freely, and I don't think there are any air leaks. Does anyone have any suggestions about the cause of this problem?

Hi Mate,
When you close the throttle does the slide hit the adjuster screw, audible click should be apparent. If not is throttle cable to short, it can be adjusted on top of carb.
Is the carb a Monoblock?
Make sure you are not adjusting the air /mixture screw instead of the idle stop screw. I believe the idle stop adjuster is the one at about 45 degrees to the body.Sorry to give out basic info as I am unaware of your experience.
rgds Roy

Sorry to say this but yet again, someone has posted too little information to be able to give an answer. James, I realise you are new so you are forgiven but you must fill in the blanks: Model? Year? Recent history of bike? Type of carb? And probably some more! My guess would be worn out carb body and/or slide (throttle valve). Give us more info and we'll crack it...
REgards, Mark

As said,my idle screw is big and 90 degrees to the carb body,with the colder weather coming it does need turning a tweek.

The idle screw on the standard Micarb has a knurled head and can be turned with your fingers even wearing gloves; if you have to use a fine screwdriver to turn a small screw which is flush with the body, it`s the wrong one, that is the idle jet screw.

Apologies for lack of info. I am new to Enfields and it is about 40 years since I last owned a motorcycle. The bike is a 250 Crusader, year uncertain, with an Amal monobloc carb. I have been adjusting the vertical screw with the spring at the base of the carb, which can be easily turned by hand. I have had the air filter off and checked the slider, which seems Ok.

When I first had the stalling problem I was able to adjust the screw upwards to speed up tickover until it seemed 'just right'. However, now it is racing and adjusting the screw downwards doesn't make any difference. It may also be relevant that the choke lever makes no difference (ie not needed for starting and when engine is warm moving it to the 'choke' position doesn't affect the engine at all).

I am thinking of taking the carb off to give it a thorough examination, it could be just knackered I guess!

Sorry, should also add that I have recently bought the bike and I believe it has been off the road for about 4 years. It was got back in running order by the seller and it does run OK apart from this carb problem.

Cable come out of the top of the carb, frayed cable cable, come out of throttle end and stuck?

For the avoidance of doubt: if you go to the Parts Book online on this site and have a look at 1960 Crusader Sports, page for Monobloc carburettor, you'll see an inset picture of the carb body with adjustment screws. The mixture screw (not the throttle stop screw,) is item no 25. The standard setting is 1.25 to 1.5 turns out from completely closed, this setting is for fine tuning when you've got the throttle stop about right. I tend to Norm's suggestion that something seems to have suddenly changed and a stuck or hung up cable or throttle slide sounds like the explanation. Be aware that the Monobloc body can distort if the flange fixing nuts are overtightened so be careful!
REgards, Mark

Thanks for the advice. I have had another look at the carb and checked over all the throttle linkage from twist grip back and I can't see anything wrong. I have noticed that occasionally, when I shut the throttle and disengage the clutch, the tickover does drop to slow, almost stalling, but just for a few seconds then it speeds up and races. Does that give any clues?

Is it worth taking the carb off and checking the throttle slide? Is it replaceable or, if it is worn, is the carb beyond repair?