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[Trew Biker]

Hi All, I have a 2001 Bullet 500 Clubman S fitted with bellmouth on the carb and Goldstar style exhaust. Once started, it pops back through the carb if I try to give it any revs until its warmed up. Its ok then, just occasionally popping and stalling when I pull off. Any ideas on the cause and how to fix it would be greatfully recieved.

[papasmurf]

"They all do that Sir," Nature of the beast with those modifications. (It could also be running a tad weak, until warm.)
My wife's Suzuki VS800 with aftermarket pipes and aftermarket "silencers," needs leaving for a minute or so, until it will tick over with no choke. Not leaving it to warm up and it sounds like heavy gunfire if any throttle is applied.

[Bullet Whisperer]

I would retard the inlet cam by 1 tooth, if it were me, that will probably sort it and make it faster. I shall now wait for the flak ...

[PeteF]

No flak from me BW, I did this to my 350 and it was a definite improvement. A mate of mine has since done it to his 500 with similar results.

[Alan R]

Sounds like you're running weak overall---- you shouldn't be stalling when pulling away when warmed up..Have you fitted jets according to our hosts recommended settings ??

[Mark M]

Paul (BW) is this just for the Indian engines? I was thinking of doing it on my heavy flywheel (500 wheels) Redditch 350 Trials Works Replica, any advantage? Ta,

REgards, Mark

[Trew Biker]

Thank you all for your suggestions. I havent checked the carb settings but I have looked at what they should be so I will do that first. Ill try the cam retard if that doesn't help.

[Bullet Whisperer]

Hi Mark, you could try it - it certainly won't take long to do and won't cause any mechanical harm. On a machine which runs well, perhaps pulling hard from very low rpm through the mid range, but runs out of 'puff' at the top end, i would say give it a try. It may not be what you want for a trials type machine, although the firing pulses would be softer at low / medium engine speeds. Basically, you will lose a little at the lower rpm scale [not much] and gain more than you lose up at the higher end of the rpm scale. The 500 [Indian] Bullets respond well to this in fairly standard form, the 350's also rev more freely and will go faster overall with the change, but don't have the engine size to cope as well as the 500 with the slight loss lower down the rev range - raising the compression ratio on the 350 helps counter this. I tried a late valve timing on a pre war AJS 250 and this sounded the buisiness until I put it in gear and went for a test ride - the engine just didn't have the 'cubes' to cope and it became slower overall, in spite of revving higher in the lower gears, it couldn't quite catch the power band in top gear. Another thing a retarded inlet timing will help with is pinking in high compression engines - the reduced cylinder pressure when the piston is coming up on the compression stroke helps here, all due to the inlet valve shutting later, the engine will be easier to kick start and any electric starter would get an easier life. I think the Indian bikes have an early inlet timing because they seem to like to slog their machines and feel the 'thump' [not good for bottom end life] and it would seem their roads are pretty rough and crowded, so it might make sense to tune them that way. I have comparison videos of my own tuned 350 Indian Bullet and a couple of 500's, as well as that AJS 250 with before and after runs, also a tuned Electra X with Redditch 'S' cams running the inlet retarded by 1 tooth - might be of interest? All sorts of stuff here. Regards, Paul. ... https://www.youtube.com/channel/UCcxcOW ... RWg/videos

[Mark M]

Thanks Paul, I've just had the engine down and fitted a higher compression piston as it was a bit flat before so I'll see how that goes first.

REgards, Mark

[Tim NZ]

While the motor is still cold and prior to the engine reaching operating temps, the fuel is not fully atomised with the incoming air. The result is that the combustion process takes longer in a cold motor. Hence, the need for a 'choke' (Or a temp raising of the float level) en-richening function in the low speed carb circuit to provide additional fuel. Thus there is a temporary excess of fuel particles present to ensure consistent flame propagation and complete combustion.


It is this initial longer combustion process that is still occurring when the inlet valve opens that cause the hesitation, or in extreme cases 'Spitting' back even after the engine has reached operating temp. (In which even fit a smaller cut-a-way)


Retarding the cam timing to correct an otherwise normal situation (Lean when cold) carburettion process is akin to applying the hand brake when what is required is backing off the throttle.