CR33's

[Steve H]

Ok, I ve got the CR33's working reasonably well. The only problem I have is a slight hesitancy when opening the throttle, typically this is when you start to roll the throttle open at the apex of a bend. Ive found that I'm compensating by dipping the clutch slightly which isnt ideal. It runs slightly rich when on the throttle, the idle circuit is still rich but weaker than when on the throttle. Should I richen the idle circuit or weaken it to improve the transition. I can try both but I have to strip the tank off to make adjustmenets so would rather take it in the right direction the first time.
The other thought I had was to purposely put the two throttles out of balance, this might smooth out  the transition between closed and open, this would be similiar to the original carbs which has the slide opening prior to the CV. I suspect Yamaha however did this for other reasons
Any thoughts ?

[andy230]

Hi Steve,

I'd try for a little weak low down, and richer up top.  Am assuming you wont be going hard on small throttle openings, thus lower risk of seizure (the bike, not you!)

Don't like the idea of 2 carbs out of balance, as its never going to be just right...  ie.  at "full bore" on the "open" carb, the other will be slightly sub-optimal.  But maybe tahts ok for road use?

This is by no means scientific!!  For info, the racer is 'orrible in the paddock, often not wanting to idle, run low down etc.  But she's lovely when opened up- ie. pembrey, once I'd ironed out the fuel pipe kinks!   

But am not bothered about tootling round the paddock, so didn't care too much about making it nice in this area.

I think the 2 carbs were originally used to make a big lumpy single, with reasonably good performance, easy to ride for people who didn't grow up on britbikes.  Ie, it tends to allow gentle delivery rather than great thumps of torque to make chains snatch and motors stall in traffic when opened up.

Suck it and see I think!!

a

[Steffan]

Rich on throttle says that your main jet is too big,
If it OK at idle but running out of juice as you roll on then you need to raise your needle.

idle jet - needle - slide - main  in that order

[Steve H]

My original post was proabaly a bit confusing. I'm using a Lambda sensor in the exhaust to judge mixture, based on that I am slightly on the rich side of ideal, (but not really rich) dropping the needles causes it to bog when the throttles opened quickly, so my next step will be smaller mains (Andy do you have any 115's I could borrow to try out).
My main problem is the transition from closed throttle to slightly open. I have set the mixture so it is just about ideal based on the lambda sensor. I was intersted in whether people thought I should richen or weaken this (using air screw) to cure the hesitancy. I'm going to try richening to start with and go from there.

[Steve H]

For info, the racer is 'orrible in the paddock, often not wanting to idle, run low down etc.  But she's lovely when opened up- ie. pembrey, once I'd ironed out the fuel pipe kinks!   

Whats was it like on the road when you were using it ?. Preumably teh bottom end ran reasonably well then

[andy230]

For info, the racer is 'orrible in the paddock, often not wanting to idle, run low down etc.  But she's lovely when opened up- ie. pembrey, once I'd ironed out the fuel pipe kinks!   

Whats was it like on the road when you were using it ?. Preumably teh bottom end ran reasonably well then

Yes, it was pretty usable on the road.  I think it had been set up on a dyno.  It had 118's in to start with (airbox, modd'd lid, no filter), then I put a K&N filter in and didn't change the jets- a bit rich, but ok.

And yes, I have 115s, 118s, 120s, 125s.  No probs, can post them on  (see my post in chatter tho steve...!!)

andy

[J Hop]

EDIT: I have copied and pasted this directly from a jetting expert on a four stroke off-road forum :


how to confirm your pilot circuit setting

seems like the most common jetting issue that comes up are pilot circuit related.the following is a sure method to choose the needed changes.

with the bike warm and idleing turn the fuel screw in till the idle drops/misses.then go back out till the idle peaks/smooths.

this should happen between 1 and 2.5 turns on a fcr carb and 1 and 3 turns on a cv.

if you end up at less than 1 turn you need a smaller pilot jet.more than 2.5 (or 3 turns on a cv) you need a bigger pilot jet.

choose the appropriate size and retest.