Hitchcocks Forum

I followed the instructions, but it didn't do what it said on the tin!...........

List of mods:
Raise comp; 7.5:1
Opened exhaust (by punching out rear baffle)
Jetted up; 30 pilot, 117.5 main. P4 needle jet
And the cruncher; 19 tooth G/B sprocket.

The intention was a good cruising speed without flogging the engine.
THE RESULT: Like shite off the proverbial up to 60mph. but after that it went like shite, in fact massive pre-ignition, horrible metallic rattle and engine failure/cut-out.

I reckon the 19 teeth are confusing the engine, and and I can't get the throttle open far enough to work the main fuel jets.
Any experience here anyone, and any ideas please.

Sounds like the carb settings to me. The 19 tooth sprocket will only change the revs at any given speed if the bike is too highly geared it will simply run out of puff. The terrible rattling sounds like pinking on the full throttle so I would suggest you check the plug to inspect for signs of leanness and increase the main jet size accordingly. Remember the main jet only kicks in at the upper end of the throttle so it shouldn't effect the lower speed running which sounds quite good from your description. Be carefully about thrashing the motor in any fettle if it is an iron one as they will tune up beyond the metallurgical abilities and seizing at high speed can be dangerous and costly. The Bullet Whisperer is the man to advise on the main jet you require although he will need more info about what sort of Bullet and carb. Good luck S.

How do I call the Bullet Whisperer Simon?

It also occurs to me that my 350 which is similarly warmed over and also goes like shit of shovel to 65-70 depending on the wind will go faster but does start to pink and get hot if held at this sort of speed for any length of time. I improved it by putting in a cooler plug B7HS rather than the B6HS and I now run it on premium fuel which here is 96 or 98 octane depending on the provider. My feeling is to get any long term high speed I'm going to need to change to an aluminium barrel. There is a fascinating story about WO Bentley when rebuilding the Le Rhone Radial during WW1 where he unveils the aluminium piston for the first time and then goes to steel lined Aluminium barrels in order to stop engine failure killing more men than the enemy.

Hopefully he'll be reading this.

Hi AL ---- Your own description is telling you a weak top-end. Give us some more, precise details of your machine --- I'm assuming a Classic 500 Iron Barrel ? and Carb type & size & filter system ?? I suspect you are still using the VM28 ?? I personally think that to pull a 19t sprocket you may well have to go up to a 30 or 32mm carb. in order to get the full benefit. Remember Hitchcocks jetting guide is only that---a GUIDE. They say as much themselves. First, try going up to the 120 main and see how that feels. I do my carb. testing with an engine at full temp. and on a slight hill and in 3rd gear. You don't need to actually be going at a fast road speed----but do need a load to pull against. Also it's quicker to stop when doing a plug chop---- you HAVE been doing these, haven't you ???? Yes, it won't do what it says on the tin because this isn't a "quick-fix, bolt-on, go-faster, press-button" scenario--alas !!! If only it were--we would all be Master Mechanics then. One change at a time and be accurate with your observations--not emotional. Keep your chin up !! and keep us informed, eh ??

Hi Al,
I think the 19t sprocket may be a bit much, you have raised the gearing by over 10 percent in fitting that and the engine will labour hard in top gear, inducing pinking. One Bullet I tweaked a few years back and still resides and runs locally, was fitted with a 28 mm Mikuni [just like the Mikarb copy] and it had a 120 main jet which I opened out to an estimated 130 to just about lose the pinking and put enough fuel in. This machine runs at about 9.5 :1 compression, with ported head, standard cams and trials exhaust, it does many long distance trips and returns about 70 mpg at legal 'A road' speeds and tops out around 90 mph on 17 / 38 gearing with 4.00 x 18 rear tyre.
Try gearing down and jetting up!
Regards,
Paul.

Simon; a bit like Banksy then? Maybe i could just no-Face book ? I'm getting a message tho.

If you have the standard 500 Bullet it is more than capable of using a 19 tooth sprocket. The first thing I do to a 500 is fit this size sprocket if it has a free flowing exhaust system fitted and the Micarb has been correctly rejetted. It sounds like a carb or ignition problem to me.

Well, hello Mr. Whisperer. I genuinely thought you were an etherial wish list the way Simon dropped you in it.
This is all unveiling nicely now. Thanks for the details, and valued experience.
Before I melt the piston, I will need to either dump the 19T,maybe 18, and or get more fuel into the cylinder. It is definately running weak. Brilliant advice.