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[Davie Hall]

Please bullet whisperer, tell me/ us more about this modified 350. I an intrigued with it and what you did to it

[Bullet Whisperer]

Hi Davie,
Basically, I shorten the cylinder barrels by 1.5 - 2.0mm, to help raise the compression ratios of both 350 and 500cc engines. I usually shorten them from the base gasket face, rather than the head gasket face and liner spigot end, to keep things simple, but if the ledge covering the tappet compartment is a bit too thin, I take it off the top face. Shortening from the bottom, it is wise to take the same amount off the bottom of the liner, to avoid any risk of the conrod and liner making contact, although it would be unlikely. Shortening a barrel by this amount won't give a massive increase in compression ratio, but it will have a noticeable effect on performance. If sporty cams are used, it might be necessary to enlarge the inlet valve cutaway in the piston crown, depending on what piston is to be used, but my point was that by literally just removing excess metal from these engines, be it by lightening the crank flywheels, porting the head, or shortening the barrel, or preferably all three, a Bullet engine can be made to really wake up ! Regards, Paul.

[Bullet Whisperer]

Here is my 350 in action, by the way -
https://www.youtube.com/watch?v=RBPg_Xj2X04

[wilf]

The bike sounds great in the video and looks to be going at a fair old speed, especially when overtaking. Presumably you completely rebuilt the engine whilst shortening the barrel and beefed up the bottom end. Are you using a K&N type air filter? What impact has the tuning had on MPG?

Oh yes! How the hell do you stop it?

Great stuff.

[simon]

I believe he leaves the big ends as is in most cases. Is this not true BW?

[Bullet Whisperer]

Hi Wilf / Simon. Yes, the bottom end of my 350 is untouched, as far as I know. I bought the bike cheap, as it had virtually no compression with a burnt exhaust valve, but was still running [just]. I rebuilt the top end only, replacing the valve, porting the head, shortening the barrel, fitting a Meteor Minor Sports piston and the big Monobloc. It already had the short, loud silencer fitted. I also put a 17t gearbox sprocket on, which it JUST copes with, in my opinion. Compression ratio is nudging 10:1. Cheers, Paul.

[simon]

Squish band mod?

[Bullet Whisperer]

No squish band mod on this one at present.

[simon]

So apart from the shortened barrel it sounds like a very similar set up to mine although mine is only running the 8:1 piston it does have .5mm head gasket and a recent 12 thousand off the head. I guess it's at 8.5:1 or some such. The 1 1/8 carb does let them breath nicely that's for sure.