Does anyone have the dimensions for the C15 375 Monoblock throttle slide return spring? The throttle action on my bike is very light - but the engine is also slow to return to tick-over when the twist grip is closed. I am thinking that one possibility is that the return spring is no longer fit for use. Google is giving me two lengths (2.5" and 1 7/8") for this spring, whilst the dealers seem to only have one spring that fits all. If anybody has their carb in bits I'd be grateful for the length of one that works perfectly.
Ring Burlen in Salisbury for the definitive dimensions.
They're helpful and knowledgeable , they make Amal bits.
Hi,
Does the cable need some lubrication? Providing that the cable and the twist grip are not offering any resistance, then the throttle should 'snap' shut.
Dave.
Brand new cable (carefully routed), brand new twist grip. It snaps shut with the engine off, and I can clearly here it hit the throttle stop. But it is in no hurry to hit the stop when the engine is running. The twist grip action is much lighter than on a pal's monobloc equipped Ariel.
Hi,
Assuming that this is probably the original carb., there will be wear on the slide and the bore of the carb body. It is possible that the suction of the engine is causing the slide to 'stick' against the body. Try spraying some WD40 on to the closed slide and work it in a bit by opening and closing the throttle. Make sure it gets to the engine side of the slide. It may work but eventually the affect of the WD40 will fade but at least it may indicate a solution.
Dave.
I'm also thinking its suction, clean up the slide and look for wear ridges.
If indeed the slide and body are worn then that will allow air past which will cause air and fuel to enter the engine which will slow the return to tick over down . They can be realigned and a new slide fitted but probably cheaper to renew .
I forgot to mention that I had put a new brass slide in. I must have been happy with the fit of the slide in the bore. The carb hasn't seen a lot of action - the bike was in bits for 44 years. This business with the throttle arose on my first ride out with the bike (Wednesday)- about fifteen miles in total. Further checking today has revealed that the 'sweet spot'(established during the ride) was with the choke 3/4 on. I had the needle on the middle groove. I was about to lower the needle one groove - but suspect this won't be enough. All the jets /needles etc are precisely as per the book.
I guess the other possibility is I have a leak at the manifold'O'ring. Has anyone tried the 'squirting something' (WD40?) at it with the engine running test?
OK, this could be a completely different problem. You will find any number of threads on bikes that don't slow down when the throttle is shut. This could very well be a carb set up issue, perhaps with a bit of ign timing in the mix. Check the float level first as this affects everything, (tube, idle jet, dot etc) and get that right. The idle mixture on the air screw matters more than you may expect, try just a fraction on the rich side first and set the idle stop low. And double check the timing and movement of the auto a/r unit back to its full retard stops.
Quote from: Tigerfeet on 18 Jun, 2026, 07:43 Brand new cable (carefully routed), brand new twist grip. It snaps shut with the engine off, and I can clearly here it hit the throttle stop. But it is in no hurry to hit the stop when the engine is running. The twist grip action is much lighter than on a pal's monobloc equipped Ariel.
If it has a mid length adjuster in the cable try wiggling it and holding it in perfect line with the cable so there is no curve at that point.
I had a similar niggle when l put my B44 together . The seemingly negligible friction was enough to affect smoothness.
I think the end cups in pattern adjusters are too shallow and too slack.