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Air Screw Behavior
- bemoore
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Edit to add:
I've installed WG's coil power mod. The points have less than 2500 miles on them, and they were adjusted with a dwell meter. I get a little bit of black smoke when blipping the throttle at idle. Float levels were set with the "wet" method.
77 KZ650C1 w/Kerker 4-1
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- bemoore
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77 KZ650C1 w/Kerker 4-1
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- KZQ
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I've found that that means there is a jet or a passage that's plugged and preventing the air screw adjustment from being effective.
KZCSI
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1968 BSA 441 Shooting Star, 1970 BSA 650 Lightning, 1974 W3, 1976 KZ900, 1979 KZ750 Twin, 1979 KZ750 Twin Trike, 1981 KZ1300, 1982 KZ1100 Spectre, 2000 Valkyrie, 2009 Yamaha Roadliner S. 1983 GL 1100
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1985 ZN1300
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- KZ_Rage
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Are those VM26 carbs? If it wasn't rich before and is now after you adjusted only the air screws and the sync on the slides, I'd have to go with you put something out of spec when you sync'd them.
Maybe if you detailed what you did in the sync process and any other tweaks at that time it would help pinpoint the problem. I'm a firm believer in the last thing touched law of causes for problems but that get complicated when you do several things at once which is a fault of mine for sure! :silly:
1979 KZ1000E1 SOLD!
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- bemoore
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The plugs were dry and sooty before sync'ing the carbs.Are all of your plugs equally sooty? Are the insulators black and dry or black and wet?
KZ_Rage wrote:
Not sure which carbs I have. They're the stock units for a 77 650C1. The rich/lean condition hasn't changed as a result of the sync. I adjusted the air mixture screws trying to lean it out as much as I could and still retain good throttle pickup off idle. I wound up adjusting the screws out 1/4 turn, and I may have to go back to the original setting, as it sometimes stumbles of idle now. So it appears that the only effect of the carb sync is a much smoother idle now. I'm hoping for better fuel mileage, too.Are those VM26 carbs? If it wasn't rich before and is now after you adjusted only the air screws and the sync on the slides, I'd have to go with you put something out of spec when you sync'd them.
KZ_Rage wrote:
For my sync tool, I used a cheap 20ft clear plastic tube with water in it as a differential manometer. I decided to use carb 3 as the reference since it appeared to be the hardest to get to. So I removed the caps from carbs 1, 2 and 4. I cranked the engine and let it warm up. I shut it off and I hooked the sync tool to the vacuum ports on 3 & 4. I cranked it and sync'ed 3 & 4 by adjusting carb 4. I repeated this for carbs 1 & 3, and 2 & 3. Then I tried to set the air mixture screws for max idle speed, but they didn't seem to have any effect. So I put the bike back together and hoped that I could set them by test riding and adjusting for best throttle response, hoping that I'd be able to lean out the mixture due to having the carbs in sync. I started off at 1-3/4 turns out on all the screws, and finished at 2 turns out, and it may be too lean now as I'm getting a stumble off idle when the bike gets up to temp.Maybe if you detailed what you did in the sync process and any other tweaks at that time it would help pinpoint the problem. I'm a firm believer in the last thing touched law of causes for problems but that get complicated when you do several things at once which is a fault of mine for sure! :silly:
77 KZ650C1 w/Kerker 4-1
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- Qdude
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I've read that it is important to sync the manometer too. This is done by running all four lines off of one vacume source through a one to four splitter. Apparently there can be differences in the readings from tube to tube. If there are differences in the levels, then this can be noted, marked or amended prior to testing on the carbs.
If this was the case here, then it is possible that you synced your carbs to be equal, but if there were differences in the readings from line to line, there will be inequalities transferred to the carbs.
As far as the air-screws, I experience the same thing with my bike as well.
I recently ran a can of sea-foam gas treatment through the system, and it has greatly affected the performance of the bike. I will try the screws again to see if any deposits have been dislodged that might cause the air screws to act correctly again.
Sea foam did help my bike to run more smoothly.
77 KZ 650 C1.
77 KZ 650 C1.
Crashed-Repaired, Pods, Kerker pipe, re-wired core bundle, lamp upgraded, homemade rectifier, solid state regulator , Dyna-s ignition, repainted, slightly modified, year-round commuter
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- bemoore
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Thanks.
77 KZ650C1 w/Kerker 4-1
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- roystaylor
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