- Posts: 558
- Thank you received: 80
Richer Jetting on the Inboard Carbs?
- VTEC
- Topic Author
- Offline
- User
I've read about the theory of jetting richer at the inboard cylinders to aid in cooling, since they get so much hotter. Also read that some Suzuki straight-fours went richer on the inboard mains from the factory.
Any incite on the theory?
Thanks.
KZ1000-K2
ZRX1100
XR400R
Please Log in or Create an account to join the conversation.
- SWest
- Offline
- Sustaining Member
- 10 22 2014
- Posts: 23012
- Thank you received: 2756
Non stock applications might call for this but I doubt it.
Steve
Please Log in or Create an account to join the conversation.
- missionkz
- Offline
- Sustaining Member
It did make a difference in that one.... but they were notorious for killing the middle piston in 5000-7500 miles.
Never had very much of a difference in plug readings on my 4 cyl Kaw engines if it was running right, and if I did see a difference, seems like a small pilot jet or idle screw setting would clear it up well enough. I don't think I would pull a needle up or down for this tweak and unless a track bike. Different main jets seems way over the top.
If you see that much difference on a street bike, I think you have other problems besides minor carb jetting.
Like cheap chrome, bad valve guide seals, valve lash, valve/seat wear,,, stuff like that.
Bruce
1977 KZ1000A1
2016 Triumph T120 Bonneville
Far North East Metro Denver Colorado
Please Log in or Create an account to join the conversation.
- SWest
- Offline
- Sustaining Member
- 10 22 2014
- Posts: 23012
- Thank you received: 2756
Steve
Please Log in or Create an account to join the conversation.
- VTEC
- Topic Author
- Offline
- User
- Posts: 558
- Thank you received: 80
Think I'm gonna try 1/4 to 1/2 turn more out on the screws (viewed the plugs after idle), and maybe up one on the main. Seeing these beasts are at their hottest at high RPM, and it's bored making it even hotter.
I scanned the engine hot with an infrared thermometer, and the inboards are significantly hotter. Just common sense with two sides up against another combustion chamber, and way less cooling fin area.
Ultimate tuning on these things would be an O2 sensor in each pipe.
Funny thing is I also read that some bike's factory jetting (Suzuki again) was leaner on the inboard mains. Maybe due to air box design?
KZ1000-K2
ZRX1100
XR400R
Please Log in or Create an account to join the conversation.
- SWest
- Offline
- Sustaining Member
- 10 22 2014
- Posts: 23012
- Thank you received: 2756
Steve
Please Log in or Create an account to join the conversation.
- VTEC
- Topic Author
- Offline
- User
- Posts: 558
- Thank you received: 80
Running it on a dynojet dyno never really picked up the lean spot just off idle. So I used the state inspection emissions analyzer at work, and rode the clutch while coming just off idle. Using the CO reading I finally achieved 13/1 air/fuel. The trick was maintaining the correct idle mixture at the same time. On the FCRs that means you should be able to cause a lean misfire with the screw all the way in, then find the best spot between 1 and 2 turns out. I lost count of how many times I pulled and disassemble the carbs, swapping PFJs and tweaking the the PAJs to get it right. But now it's runs great.
KZ1000-K2
ZRX1100
XR400R
Please Log in or Create an account to join the conversation.
- bountyhunter
- Offline
- User
- Posts: 7246
- Thank you received: 337
1979 KZ-750 Twin
Please Log in or Create an account to join the conversation.
- SWest
- Offline
- Sustaining Member
- 10 22 2014
- Posts: 23012
- Thank you received: 2756
Steve
Please Log in or Create an account to join the conversation.
- Tyrell Corp
- Offline
- User
- "You were made as well as we could make you"
- Posts: 1650
- Thank you received: 261
In reality Suzuki made a legendary motor largely copied from the kawasaki z1 heritage, a lot of internal parts and the design is very similar. Kawi went with the uniform carb jetting, Suzuki with the different inner/outer jetting, plus a greater variance in carb balance .
It is a good question, just not sure of the answer. Maybe the jap big four were undecided on this issue too?
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
Please Log in or Create an account to join the conversation.
- SWest
- Offline
- Sustaining Member
- 10 22 2014
- Posts: 23012
- Thank you received: 2756
Steve
Please Log in or Create an account to join the conversation.
- VTEC
- Topic Author
- Offline
- User
- Posts: 558
- Thank you received: 80
swest wrote: The Z1/KZ series was over engineered with a full roller bearing lower end, Babbitt cam bearings which made them superior to the other bikes of the day. If there was a oiling problem, the bearings in the head could be replaced. Not on the others. I have been able to do a complete overhaul of the engine three times in the 40 years I owned my bike. If I had a Honda CB or one of the others, it would have been in the scrap heap long, long ago. :whistle: I have never had issues with the two center cylinders overheating and I live in the desert. I may install a oil cooler though, maybe not.
Steve
Hey Steve,
If you're thinking oil cooler, check out www.kipkawa.co.uk/parts.php?link=1981%20Z1000J
This is a real, quality, bolt-on oil cooler kit for a J engine. Not sure about earlier KZs.
I originally bought a kit from Earls, but nothing fit. But my hat is off to Earls, because they bought me the kit from kipkawa to make it work. You don't see that kinda stuff in the U.S. very often.
KZ1000-K2
ZRX1100
XR400R
Please Log in or Create an account to join the conversation.