Is Carb Rejet on a Delkevic 4 into 1 - on a 1977 KZ650B?

baldy110 wrote: You don't have the time rejet the stock carbs? What were you going to do with the FCR's, those take a LOT of tuning.

No FCR. CRs my bad. These are them on my CB900F

Spoke to Delkevic today (surprised they are open on Xmas eve, They said 90% of ppl who buy their full exhausts DONT need a rejet. They said customers always call them back saying they slapped them right on and didnt have to rejet.

The only way you'll really know how much of a fueling impact they have VS stock is if you get the air fuel measurements across the RPM range.
Otherwise you can do several (dozen) plug chops at various throttle/RPM levels to hopefully get an idea.

I wonder if Delkevic have done baseline pulls on a dyno or have some test exhaust systems with lambda/wideband sensor bungs welded in that they can use to add confidence to that claim.

Move0ver wrote: The only way you'll really know how much of a fueling impact they have VS stock is if you get the air fuel measurements across the RPM range.
Otherwise you can do several (dozen) plug chops at various throttle/RPM levels to hopefully get an idea.

I wonder if Delkevic have done baseline pulls on a dyno or have some test exhaust systems with lambda/wideband sensor bungs welded in that they can use to add confidence to that claim.

They developed it using a stock bike for each model and tested it after. Thats why 90% of their customers dont have to rejet. I checked around on web as well and a LOT of ppl say they didnt have to rejet

Can't be 100% sure for your particular bike - but I fitted a set to my '78 Z1-R and didn't touch any jets. No welding or difficulty with fitting, apart from the fit being so snug around the frame and engine that there's not a lot of "slack" to manoeuvre the headers into the collector. It's a really nice bit of engineering which allows full access to sump and oil filter whilst retaining centre stand (on my bike anyway!) Also sounds great - even with quietest baffle configuration ie both baffles fitted.

Like others said, you don't always have to rejet just for an exhaust change. I ran a Kerker 4-into-1 with stock jetting for years. The only side effect was that I had to run the choke a bit longer on colder days. But being a tad leaner than stock made it scream on hot days. Later on, I rejetted for colder weather, but that did reduce the zing factor on hot days.