Comet Crankcase Breather

[Howard]

David

25mph up a 1 in 8 is just a bit inconsiderate to other pedestrians, innit?

Phil

I haven't got a lot of experience of road going Comets, but I'm pretty sure that is considerably worse than "slow going" - John's 60 mph from Waterworks sounds more like I'd expect. I don't think that's anythig to do with the breather (unless you've got a compressed air line attached to it ), and I don't think that much power loss is down to silencer.
I seem to remember you've had this problem for a few months, so you've probably checked the usual suspects. Is your ATD working? Are your fuel filter(s) or petrol taps blocked? Carb jets blocked? Float level too low?
Diagnosis by email isn't easy.

H

 

[Phil Baker]

Morning, Howard

ATD seems OK - it's a reconditioned one kindly supplied by Stumpy Lord during the Rob Minivin day of Comet glory! Plenty of fuel getting to the carb as far as I can tell. I've got one extra fibre washer on the bottom of the carb/float chamber union to stop the infernal dripping. The bike is happy to rev up and do 65+ on the straight - good power in 2nd and 3rd and then 4th is a sort of overdrive gear, or so it feels. Compression is OK now - I can stand on the kickstart on the compression stroke and it will very slowly drift over. I haven't been out on it since retiming the breather and I'm working today so don't know when I'll get the chance but I'll post when I've tried it out again.

Phil

 

[nkt267]

What rear sprocket have you got..If you had a twin one on by mistake it will seriously overgear you and that may be worth checking..John

 

[Howard]

What rear sprocket have you got..If you had a twin one on by mistake it will seriously overgear you and that may be worth checking..John

Yep. It sounds like gearing from that description. Should be 48 tooth on the wheel - worth checking the gearbox sprocket is 18 tooth too. But, it ought to rattle up hills quite happily in 3rd.

While I was looking up the sprocket sizes, I found my racing days additions and noticed the clutch sprocket I used was 42 tooth (AMC clutch) not 40 tooth as standard. It may be worth checking that too - primary drive should be 23T - 40 T.

H

 

[Phil Baker]

Definitely 48 tooth rear sprocket - just counted (used all my fingers and toes and it came to just the right number). I'll find an original silencer - a couple of the chaps have something old - and give that a go next.

Phil

 

[Howard]

Definitely 48 tooth rear sprocket - just counted (used all my fingers and toes and it came to just the right number). I'll find an original silencer - a couple of the chaps have something old - and give that a go next.

Phil

What about the gearbox sprocket, 1 tooth out on that can make a big difference.

H

 

[Phil Baker]

I can't see the gearbox sprocket, Howard, please don't make me take more things apart!!!

 

[Phil Baker]

Well, Len has kindly lent me a Burgess original silencer with a tiny tease of coarse gauze inside to act a a baffle and I have bolted it on. Can't take it for a buzz, though, 2 glasses of wine spells trouble..... The only comment that I would make at this stage is that, having taken my silencer off, there is a 10mm hole that I can see through all the way from one end to the other so I'm not expecting miracles with the Burgess.
Phil

 

[Howard]

I can't see the gearbox sprocket, Howard, please don't make me take more things apart!!!

Take the plug out, put it in top, turn the back wheel 1 rev, the engine should turn 4.6 revs. take the mag cover off, the mag should turn 2.3 revs, if that's easier to see.

H

 

[Phil Baker]

Trust you to have a clever tehnical way of doing it!!! I'll give it a try when next I can swim to the garage....

Phil