Jet size

[Andy S.]

I've recently aquired a very clean 79' that's pretty much stock except for a Kerker six into two. The problem is that the bike came from an altitude of about 5000 ft. The seller suggested that I changed the jetting from 95's which he said it currently had to 105's for my altitude of about 250 ft. I went ahead and bought the 105's only to tear it down and find it already had 105's! Can anybody suggest what size to try next? I was thinking 110's but am afraid it may not be enough and I don't want to do it twice. 112's is what I was thinking might work. If there is anybody out there near Fresno CA maybe you could give me some pointers. Thanks!!

[Terry]

Andy, I have a fairly early Z model myself originally sold in WA state. I'm pretty sure the carbs are stock. I'm in San Jose but I've had her over 10,000' with the only problem being that she was a bit sluggish. Still fast, just not very quick to speed. Runs the same way with the stock pipes or with a DG/Kerker 6into1. Did yours ever run bad in Fresno?



BTW, a great ride nearby is over Tioga Pass in Yosemite and then back over Sonora Pass just north of YNP. Both climb to over 9,000' and have a great variety of road challenges and sights to see.

[Andy S]

Yeah, The bike runs terrible here near Fresno. When I picked the bike up at altitude it ran and sounded awesome! The seller said I would have re-jet. I got the bike home and started it and it started falling all over itself. The chrome Kerker went from a nice gold to terrible blue within a few minutes. Any help would be appreciated! Thanks!

[ELee]

Andy,

You are in a bit of guess work now that the carbs are taken apart.

The pipes changing may not be a good indicator i.e. could have been cleaned up before you bought it.

You do know it's not running the same so that's a start.

How it's running bad is the thing to figure out i.e. many steps to consider before you decide on jet size to replace.

Does it run better cold off the choke and get worse as the bike warms?

Does it run in the lower revs and goes bad in upper or vise versa?

All this means something!

If I were to guess I'd say go with the 110, I've concluded after studying dyno runs that a 4-5 number jet change is equal to about .8 on the AF reading. Remember to look check what kind of jets are in there i.e. Honda or Dyno-Jet, they are different shape inside same orifice of course.

Put it all back together and go "Dyno" it makes sense of guessing, after first checking float level, ignition timing; then you will be in the club of change, change, change in the interest of the perfect tune!!!!

Later,

Ed Lee

Oakland

[Passx]

Andy, if all you have is the Kerker and other than the jetting change is stock I would agree with Ed although that I would bet that something else is not right, My 80 w/79 cams , 6-2-1 Alphabet header, a replacement K+N, Dynojet stage1 ran 98 mains and showed about perfect on the dyno. Now maybe I'm missing something on the 79 carbs but I think a very careful visual inspection and check for vaccum leaks is in order. Ed has covered everything else very well and you might think about running it and then as you are running along try putting the choke on a little at a time and see what happens. By the way, the jet size of say 105 is in fact 1.05mm's and you can multiply that by .03937 and it will give you the english size in thousands of an inch. Good Luck



Steve P. #5220