Do I need to rejet for "drag pipes" or low restriction mufflers?

Hopefully I won't get too flamed for this...

My bike already has some sort of aftermarket pipes on it with no crossover, and some sort of aftermarket "bullet" mufflers, that don't fit very well and leak.

Just out of curiosity, I took off the mufflers tonight and started it up and holy bejesus does it sound awesome!

I had already been planning to do either some sort of drag pipes on it or at least straight-through "home brew" mufflers (got it in the works already) since drag pipes might be a little much on a daily basis.

Anyway- will I need to rejet the carbs if I go this route?

Without knowing how the bike runs or what the current intake system looks like or the current jetting, I would say no one in the universe could make a guess at this one. Best advice with no other info is to change the pipes and see how it runs.

Before you tear into a running bike, I would advise that main jets are not available for the old 750 twins. If you open up the pipes you will need bigger mains and nobody I know of sells them for the old twins.

It still has a stock air filter at the moment...I suppose there's a chance I might swap to a K&N in the future, but I'm not changing it for now. Also I assume it still has the stock jets.

I read somewhere just the other day that twins usually don't need rejetting for pipes, but I can't completely remember where I read that and who knows how accurate it is.

And, are you saying these jets wouldn't work?
www.crc2onlinecatalog.com/misc_carb_parts.htm#Main%20Jets

They look just like the main jets that came in the carb rebuild kits I just bought.

Hunt, You have BS38 carburetors and the main jets are located in your float bowl and not in the carb body. The main jets have no Mikuni nomenclature that I know of as they are unique to the BS38. The pilot jets shown on the website link are not correct for your bike. They are VM22/210 type and you need VM30/96 type pilot jets. There are no oversize replacement main jets for your bike. The small main jets from your bike are also not a great candidate for drill due to their very small size.

Ah.

Well damn, that sucks.

ghunt81 wrote:

I read somewhere just the other day that twins usually don't need rejetting for pipes, but I can't completely remember where I read that and who knows how accurate it is.

When I had the Kerker clone on mine, I had to go up one on the main jet. With MAC pipes, the stock main is OK but's that's because MAC pipes don't flow any better than stock pipes.

wiredgeorge wrote:

Hunt, You have BS38 carburetors and the main jets are located in your float bowl and not in the carb body. The main jets have no Mikuni nomenclature that I know of as they are unique to the BS38. The pilot jets shown on the website link are not correct for your bike. They are VM22/210 type and you need VM30/96 type pilot jets. There are no oversize replacement main jets for your bike. The small main jets from your bike are also not a great candidate for drill due to their very small size.

I believe I bought BS30/96 pilot jets for my BS38's back when I bought jets. I got them here:

www.psep.biz/store/mikuni_pilot_jet.htm

bountyhunter, thanks for that link.

Now the stock jets are 45's, right? Is it the norm to go up one size, or two sizes?

Also the formatting on that page seems to be screwed up, but why do they have the sizes listed like they do...i.e. it has the 45's, and then 55's directly below them...then the next line down has the 47.5's, and 60's? :huh:

Why not just call Z1Enterprises and find the jets you need there? They spend quite a bit of money supporting this site. I doubt psep.biz is a site sponsor. I doubt you will get as good a price either. But hey, what do I know???

Z1enterprises doesn't even list jets for my bike.

But hey, what do I know?

wiredgeorge wrote:

Why not just call Z1Enterprises and find the jets you need there? They spend quite a bit of money supporting this site. I doubt psep.biz is a site sponsor. I doubt you will get as good a price either. But hey, what do I know???

I only put up the link because back when I bought jets, Z1 didn't have them. PSEP was also the only site I could find at the time that sold ANY jets in pairs as opposed to sets of four which cost twice as much. They also had the FULL range from 30 to 60, which I found nowhere else at the time. They also had the lowest prices.

I plug Z1 every chance I get. The only reason I posted that link was because that's where I bought the pilot jets.

FYI:

I searched the Z1 site using their search engine looking for "BS30/96" and found nothing.

I searched for "pilot jets" and found nothing.

I searched for "jets" and found five pages of main jets, not a single pilot jet.

Maybe they sell them, I don't know. I could not find them.