TOPIC:

I have an 1981 CSR 1000 - it currently has the stock exhaust and the stock jetted CV carbs as far as I know, plus the stock airbox and stock type filter. I have a new Mac 4-1 header that came with the bike that I am thinking of installing - if I leave the baffle in and stay with the stock airbox, will I need to rejet or can I get by without changing the carbs? The bike currently runs great and I hate to mess with it, but would like the improved sound of the header. Thanks.

I doubt that you would need to re-jet just for a header change, but install it and check the plugs to find out for sure.

I would rejet...4-1 header will grratly increase scavening thru head...i.e..it will pull alot more air thru...so more fuel will be needed..

P.S. sorry for shitty typing...beer 7...lol

brianrae33 wrote:

I would rejet...4-1 header will grratly increase scavening thru head...i.e..it will pull alot more air thru...so more fuel will be needed..

Can't pull more air out than the stock airbox allows in

very true...i sometimes assume everyone switches to pods...lol...i know the driveability is somewhat compromised but i love the punch a jet kit can give with a decent header..

An aftermarket set of pipes MAY flow better than a stock set or MAY NOT... best to put the pipes on... the pilot system won't make a big deal with just a pipe change but run the bike up to redline and see how it pulls... may need some bigger main jets, really hard to guess because not all aftermarket pipes are the same. I am guessing that with a MAC 4 into 1, you will be just fine but may have a flat spot if you yank the baffles. If you get a flat spot somewhere in the mid-range, first, raise the jet needle by reclipping down one slot and if that doesn't work, put the baffle back in or repack and get rid of the "improved sound" or live with the flat spot.

I am looking at a V & H 4 into 1 to put on mine..I am not sure I am ready for really loud but it would be fun to be able to have some more growl as i love that sound. It sounds like I may be able to get by with just putting on the pipe? I'd like the ability to switch back to the stock set up without too much fuss. Also the one I'm looking at is supposed to be off a 78' Kz650 so it should fit, right? I did hear some stuff about bad fits on pipes..was it V & H?

When I put a 4 into 1 on my 80 1000 i left the jetting alone. I had a little bit of a miss around 8000 rpm.