Carb/Jetting Problem?

[SemiSaneSteve]

I've finally got around to starting work on my mk.3 project bike and obviously the first job is to find out exactly what needs sorting. Chassis-wise it's OK, all the bearings and seals are sound. The first thing I did was replace the air filter and plug and clean the carb out. However, it's still a bugger to start and won't idle. Apart from that, it runs fine up to half throttle then bogs badly. There are no discernable air leaks on either the intake or manifold sides.

The bike has an FMF fatty header pipe and a Mugen silencer. It's currently jetted 45 pilot and 165 main (which seems excessively large, even for the header/silencer combination). First of all, can anyone recommend a jetting setup? Secondly, is there anything else I should be looking at? I have many years experience with trials bikes but almost exclusively trials bikes and I'm finding all of the powervalve and autolube gubbins on the CRM a tad intimidating (why the hell is there a coolant feed to the carb?? To prevent icing?)

Anyway, all advice gratefully received!

[Gwyn]

I've finally got around to starting work on my mk.3 project bike and obviously the first job is to find out exactly what needs sorting. Chassis-wise it's OK, all the bearings and seals are sound. The first thing I did was replace the air filter and plug and clean the carb out. However, it's still a bugger to start and won't idle. Apart from that, it runs fine up to half throttle then bogs badly. There are no discernable air leaks on either the intake or manifold sides.

The bike has an FMF fatty header pipe and a Mugen silencer. It's currently jetted 45 pilot and 165 main (which seems excessively large, even for the header/silencer combination). First of all, can anyone recommend a jetting setup? Secondly, is there anything else I should be looking at? I have many years experience with trials bikes but almost exclusively trials bikes and I'm finding all of the powervalve and autolube gubbins on the CRM a tad intimidating (why the hell is there a coolant feed to the carb?? To prevent icing?)

Anyway, all advice gratefully received!

Hi Steve. Yes, the coolant feed to the carb is to prevent icing.
Has the engine had a re-bore? If not, i would set all the carb settings back to standard, as a base point, and take it from there. If you haven't got the standard settings, let me know and i will sort a copy out for you 165 main jet does seem a bit excesive To give you an idea, this is what i have done to my MK2, and it has had a re-bore, bearing in mind that the standard carb settings are not the same for MK2's and MK3's.

RE-BORED----1st OVERSIZE.
FULL RSV PIPE.
AIRBOX----STANDARD, WITH BAFFLE AND RESTRICTOR PLATE REMOVED.

SPARK PLUG----B9EGV----(BR8ES IS STANDARD).

PILOT JET-50----(48 IS STANDARD).
MAIN JET-135----(128 IS STANDARD).
NEEDLE POSITION----MIDDLE----(MIDDLE IS STANDARD).
AIR SCREW----1 1/4 TURNS OUT----(1 1/4 IS STANDARD).

[knackeredMk1]

Starndard Mk3 - 150 main 45 pilot.

Usual FMF pipe is 'Gnarly' made specifically for the CRM. I may be wrong but the 'Fatty' is for CR?

Usually FMF 'Gnarly' requires leaning the main jet.

[SemiSaneSteve]

Thanks guys. As far as I know (which means I'm not 100% certain because the previous owner of this bike has emigrated), it hasn't had a rebore. I'm pretty sure that the header is a Fatty although I'll double-check tomorrow. Hmmmm, wonder if that accounts for the bucket-sized main jet? Although the bike was *supposed* to be running fine before going into storage but again, my information about the bike's history is somewhat unreliable.

I think I'll but a selection of jets and have a play until something works and take it from there. Where's the best place to buy from? Leisure Trail? Allen's?