Carb problems

[JEAN-NOEL]

Hello Gents,
I have carburetion problems on my 650 CSR.
1°/ I got a steady idle at 900 RPM, but the air screw adjustment is not sensitive. From the basic setting (1 1/2 turn) I can close almost completely or unscrew several turns without change.
2°/ At circa one third throttle the engine misfires badly.
The carb has been refurbished with the suitable repair kit.
The settings are : main 390 (I am living at 3200 ft elevation, but with a 450 the problem is the same, and the mixture seems to be too rich), pilot 20, needle 0.106, throttle slide 4 (checked vs an other, brand new) needle 4th notch - Float level checked, OK No air leaks on the intake.
Full advance 34 on left, 31 on right. Mag newly refurbished. - Rockers well setted at 8 thou.
Sparking plugs : Champion N4C, gap 20 thou.
I rinsed the tank and poured in fresh gasoline, Total Excellium, ethanol free.
I would like to dispense with changing the carburetor.
The next step will be to deal with needle for two notch to see the result ?
That's what I planned this morning, but now it's raining cats and dogs !
Your advices welcome.

[Mick D]

Hi

Your air screw not having any effect suggests you are controlling the idle on the throttle stop and that there is a blockage in the pilot air system - presumably you have checked the pilot jet so look to the internal galleries in the carb, get the compressed air gun out if you have one.

With regard to your misfire, have you considered it could be timing related / sticky ATD? - loss of spark on one cylinder?

Regards Mick

[1608]

If I may piggy-back this post, my new carb is running too rich. Lowering the needle makes it too weak. What to do.

[JEAN-NOEL]

No blockage in the pilot air system : checked with brake cleaner and compressed air gun. I have mag ignition with manual advance. Checked an re checkeck with a timing disc...Misfires only at some apertures (1/3) of the throttle...It runs perfectly on small apertures, but there is flat spot towards 3000 rpm. Engine is new, and I don't run it full trotthle ! At 3000 RPM in top gear I am above speed limits on our lanes...My gearing : 24*42 + 17*42, with 18' rear Wheel and K82 3.50 tyres. Exhaust pipes and silencers sealed with special stuff, and new clips.

[les ward]

I had a similar problem on my csr with a brand new carb and going to a 3 1/2 slide cured it for me.

[JEAN-NOEL]

So, I have fitted split copper washers on the mag wires, with the copper core splayed ! I hope I have done everything possible to get a decent result ! But...

[Drunclej]

Perhaps not related, however since rebuilding the engine ('49 mod18), I was struggling to get the bike running right... timing/points seemed ok. Stripped carb down, cleaning all jets and passages in carb and jet block. Replaced carb, and was plagued with even worse running... frequently breaking down completely. Stripped carb again, ensuring correct jets were in place, and noticed the thin paper washer under the jet block was missing. On replacing this, the transformation was immediate; with a bit of pilot jet tweaking, it's running bloomin luvverly. Presumably p.o. had perhaps used some sealant instead, I disturbed the joint when cleaning the jet block, giving me the run of problems that were hard to diagnose.....parts diagram was very useful...
https://accessories.hitchcocksmotorcycl ... rburettors. ......as was this website.

[1608]

Would the absence of the jet block paper gasket cause rich running and if so is it from leakage at that joint or because the block sits that bit lower.

[Drunclej]

That's what I assumed...fuel could leak up past that joint, although I could be clutching at straws. I have found a real transformation since replacing what appeared to be such an insignificant looking paper gasket. My original symptoms led me to think it was a blocked pilot circuit, which it may well have been, but by disturbing the un gasketed joint, I served myself with a new set of tasty symptoms! The link I posted discusses this gasket.

[JEAN-NOEL]

hello,
Thank you all for your advices.
I had never dismantled the jet block. So I will check if the gasket is in place. Fortunately I have some kits of carb. gasket. If the weather is good, I hope to have a rod test on next wednesday.
Fingers crossed !