Jetting Help - '78 KZ650 D1

I'm doing a bit of work on my bike this winter which involves adding pod filters and possible shortening the stock mufflers around 6 inches (ends are dented up). So I'm wondering about the jet requirements for these mods.

My bike has (I believe) VM24SS carbs and the main jets are 102.5. So, I'm thinking I'm going to have to at least jump up to 105's?

Will cutting off the last six inches of the mufflers affect the jetting requirements at all? I'm not planning on changing anything inside the muffler, just cutting off the last half foot.

One other thing is that I'm not really sure how it's running now. I bought it before the winter and, since I never had my licence yet, I never really drove it to see how it ran across the full range. Seems pretty good from what I saw though.

I'll be ordering these from Z1 so while I'm at it, should I order the 105's and also the 107.5's just to be sure, so I don't have to order more?

Any help is appreciated.

As you might have read, jetting for pods is a PITA. The high/low pressure has caused jetting problems for a lot of members. Some have no problems. As far as cutting your mufflers (I remember posting a ghost muffler pic for you?) it depends how much factory baffling you might remove. I run stock air box with a K&N, Kerker 4-1 and run 105's. Always seemed too small as I think most everyone else with same set up run bigger. My bike screams up to redline and plugs are a nice color. I've seen guys running up in the 110 range with pods and 4-1. I would think you'll need to up your pilot jets to 17.5's also. The mains are hard to guess but with pods I would order 107.5's and 110's.

HerrDeacon wrote:

Will cutting off the last six inches of the mufflers affect the jetting requirements at all? I'm not planning on changing anything inside the muffler, just cutting off the last half foot.

Yes, look at the picture. On my stock mufflers drilled four 1/4" holes in the rear baffle plate which allowed a more "straight through" flow because part of the exhaust is not forced back into the small holes to exit the final rear pipe.

It got louder and it ran WORSE. Maybe I could have rejetted it, but I bought new headers instead.

Thanks guys for your input. I've read some bad reviews on pods but my bike never had the tubes that connect the carbs to the air box so I went and bought the pods. This was before reading about other's experiences. I'll give them a go and if they give me trouble I'll install and hook up the stock box.

Bluemeanie, I still haven't had an opportunity to cut the mufflers so I'm not really sure how much baffling I need to remove. I think I'll take your suggestion and order the two sizes you mentioned. At least I'll have them to play around with.

Thanks again.

Before ordering the jets just wanted to confirm that I was ordering the correct ones. Here is what I found on z1:

107.5 Large Round Main Jet - www.z1enterprises.com/detail.aspx?ID=54

110 Large Round Main Jet - www.z1enterprises.com/detail.aspx?ID=55

I couldn't find the 17.5 pilot jets on the site, do they carry them?

Thanks

Don't bother with the #107.5 mains... not enough difference from the #110s... get #110s and the #17.5 pilots. Call them and ask for them. They do have them in stock. You will probably also want to reclip the jet needle to the 4th slot although you didn't mention which jet needle you have. Cheers wg

Thanks George, I'll give them a shout. To tell you the truth I'm not sure what jet needle I have, guess I'll need to take a look when I put the mains in.

Thanks again.

To view or reclip the jet needle, you have to pull out the slides and getting to the main or pilot jets won't get you there.

LOL, yeah, I just meant that I'll take a look when I get the jets and make the carb adjustments. I'll do it all the one time. May need some direction though when I'm about to do it, as it's my first time.

Thanks

Not a problem Herr, we'll be here.

Thanks, that's why I love this site. :kiss:

wiredgeorge wrote:

Don't bother with the #107.5 mains... not enough difference from the #110s... get #110s and the #17.5 pilots. Call them and ask for them. They do have them in stock. You will probably also want to reclip the jet needle to the 4th slot although you didn't mention which jet needle you have. Cheers wg

George, I finally got around to taking the jet needles out to see what ones they were and where they were clipped. They are 5CN15's and are clipped in the 4th slot. Is is alright to leave them there for this situation?

Thanks