Hi-
I need to get a new 140 and 145 main jet for my mk3 carb (so I can finally get the mixture correct) and also a needle for it- do I need a different needle for each jet and do the jets come in standard screw sizes? Are they specific to each model of CRM? Does anyone have a part number or know who stocks needles and jets?

The jets are common across many MX bikes in particular. What you want are jets for a PE series Keihin carb. Any good MX dealer should have them and the jets are independent of the needles.

Here is a link to an exploded drawing with the part no. the site has given me top service in the past on jets for various carbs

http://www.allensperformance.co.uk/exp-pe.html

Thanks for the info guys- gold dust!! ;-)

Nick

Any idea what needle jet size I should be using, if I swap from a 150 to a 143 main jet?? -Would the same needle do, or should I get a newbie? My current jetting is way too rich and I can't ajust it anymore.

My current needle doesn't end in a point (like most normally do), but rather an inverted point- it this normal, or has someone changed it?

You don't ned to change the needle if you change jets. However I'm not sure what you mean by 'inverted point'. A previous owner may have changed the needle or worse bocken off the end .

I'll look up the needle part number but you might find it more difficult to get hold of.............

I had my carb apart recently, and because I couldn't find the number written down any where, I jotted down the number I found on mine, which was, J3R.
Mike

Excellent- thanks for that!! My needle, rather than having a sharp point on it, goes upwards- into the needle, like a cone shape...never seen this before!?

Can only get the needle (in the parts book) with 2 clips and the plate that it fits to. No. - 16012KAE740

Currently in stock at Lings for £22.96 ex VAT and Postage.

I have recently bought a Mk3 road legal bike and a "spares" Mk3 bike. So far I've only ridden the legal bike a few times, acceleration seemed poor with flat spots so I have just stripped carb and to my surprise found a 158 main jet, 50 pilot jet and needle clip in mid slot. I thought that I would check the carb on the "spares" bike and found that that had a 160 main jet , 45 pilot jet and needle on mid slot.
My exhaust expansion box is what looks like the "normal" black box that I see on many photos - there does not seem to be any manufacturer mark on it and I have a Honda silencer. I have checked the spark plug and it is dark brown to black in colour which I guess indicates it is running rich. I am wondering why someone would have increased the main jets so significantly.

I presume it is ok to go back to spec sizes - any advice/comments please?

Thanks

Andrew

Should be OK to go back to original jets (150/45) but do do a plug chop test. Maybe they put different exhaust, air filter etc... on and changed back to the original

Do check your power valve is working.

Thanks. I have checked the power valve servo and it seems to be working but not as smoothly as the You Tube video of the power valve. I will check the power valve itself.
What reed would you recommend?

Boyesen No.1.

Thanks, Where's best to purchase from?

Any MX shop. Racespec online............