Hitchcocks Forum

Just installed a Taiwan-made JRC PWK and so far it's quite a nice change from Mikarb. Better high range and easy starting. 2000 Bullet, tea caddy, short muffler with baffle. Main 130, pilot 40 needle at center notch, air needle 1.5 turns. Starts and runs clean, gray plug tip with surround of light soot, no pinging. As with the Mikarb I removed I have a wandering idle that has me fussing with the stop screw at stoplights. Sprayed WD40 at intake joint at idle with no effect.
Any ideas?

Hi FELIX-------- are these the carbs in question??}----- http://jrcengineering.com/portfolio-vie ... tructions/

You haven't given enough info. yet......I'm assuming that you've done all the basic checks such as making sure that at idling the throttle slide is actually resting on the stop screw rather than hanging off the cable ??... Is this a 350 or 500 ??...What size carb is it ??..( Your Main and Pilot jets would seem to indicate a 30mm carb on a 500 ).......What size needle jet have you ??....What No. cut-away is on the slide ??...Did you do a proper "Plug Chop" test to get that plug reading ? ..."Hunting" is usually associated with a weak mixture, so have you changed the intake rubber hose ( if not that might just be the common factor with the Mikcarb that was previously fitted ??)...Key to carb. fault diagnosis is to alter / change ONE-THING-AT-A-TIME !! .........Final thought}--- does it do this straight away or only after the engine has got to operating temperature ?? ( and was that the same answer for the Mikcarb as well ??)--- If the answer is "Only when hot" and "Yes, on both carbs " then you might repeat might have a fault on the Cyl. Head.....

PS---Forgot to say}-- Have a read of their download setting tips and you'll see that they say exactly the same that our hosts do in their tech. tips and that Amal do in their help notes...

Hi Felix, seeing as you say the problem of the erratic tickover was present with the previous carb, I would be looking at the auto advance mechanism - the springs may have stretched, causing sloppiness in the bob weights. also, make sure your pushrods can spin freely, with the engine cold. Regards, Paul.

Changing carburetors would not cure an air leak between the carburetor and cylinder head, and that can cause a wandering tickover.

Point taken papasmurf, but Felix mentions checking the inlet manifold for leaks already. As an aside, it amazes me the number of manifolds suspected of leaking in posts on here, I have honestly never encountered a faulty one! Regards, Paul.

I personally have not had problems with leaking manifolds but I have know others have the problem at motorcycle rallies which I have cured temporarily with some specialist duct tape which will stop air/water leaks up to 10 psi.

Gentlemen,
Yes that's the carb on my 14000 mile 500. It's flange-mounted and the seal is quite good. JRC provide no needle jet or cutaway specs, claiming they are a non issue for tuning the RE. They do provide an array of jets, just not the ones I needed.
I always change one thing at a time, and did cruising speed throttle plug chops on the roadside. The fast/slow idle issue is when the engine is hot. I went from a 38 to a 42 pilot because the best air screw setting was 1/2 turn out. Perhaps a 42 pilot would help if it's still too lean. The carb runs quite well other than idle.
The flange mount has new gaskets with as schmear of copper/silicone and WD40 tested for leaks while running.
I just received the advance extractor from our host, but I'm uncertain how to check the springs. If needed, they would take a week or two by post. I checked the pushrods cold and they stay set very well.
I plan to replace the stock piston in a few months as a preventive measure, and the valves will get attention as well.
I've never seen another IB in SoCal, so it's nice to have your help!

Ooops.
I went from a 38 pilot to a 40 pilot and now wonder if a 42 would help if it's still too lean.

Seems to me, if the problem existed before the carb change, it's not the carb's fault.