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TOPIC: Running poorly

Running poorly 22 May 2020 13:17 #826347

  • wco56
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Hello everyone. I have been on the forum for some time now, and find great info here. I recently bought back a 1976 KZ900 that I purchased new in 1976, sold in 84 and found and bought it back last year. Engine is stock bore 20,000 miles), head has been done (primarily for valve guide seals but valves were lapped in by my machine shop. He also set the valves to spec. Bike has K&N pods and Delkevic 4 into 1 header. I rebuilt the carbs and have 20 pilots, 120 main jets, needles set in middle slot. I have read everything I can find on jetting. My issue is that for the first four miles or so it runs very poorly, spitting and sputtering. As it warms up it runs better but it still runs a flat thru mid and high range. As it is building revs and speed it actually runs better when I let off on some throttle. Timing is spot on, points are properly set and I have checked tank cap vent. Compression is good. Runs the same with cap open or closed, and slightly better with choke on until warm. Coils are good and getting 12v after the Wiredgeorge mod (10.5v Before the mod). It starts and idles fine and runs good on the pilot circuit, but anything more and it runs poorly when cold. So, I am thinking that I need to start with a larger main jet and work my way back to raising the needles when I get that main jet right. I am concerned I may be missing something, and I recall a couple of people saying it should run good with stock jets and my pod and header setup. Any thoughts would be appreciated, and thanks in advance.

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Running poorly 22 May 2020 19:42 #826362

  • hardrockminer
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A couple of questions for you. First, are the carbs original VM26SS with fuel/air screws on the side? Are the needles and needle jets original or did you replace them when you rebuilt the carbs? What is the setting on the fuel/air screws? What are the float level settings? And lastly, were the carbs synchronized?

Edited to add that I have a set of 1976 carbs on my 1980 KZ1000 and they are in my view the best carbs of the Z1/KZ series. Certainly the easiest to set up.

One last thing...have you checked your plugs to see how the bike is running a low rpm's?
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.

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Last edit: by hardrockminer.

Running poorly 23 May 2020 02:07 #826373

  • wco56
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Carbs are the original VM26SS that came with the bike new. Air screws are in the 1 1/2 to 1 3/4 range, depending on which one it is. The needles and needle jets were replaced when the carbs were rebuilt. I set the floats to spec with the clear tube method and carbs were bench synchronized. I did have some trouble getting number one to sync up but got that straightened out. The plugs read a little dark but not sooty. I still have the parts I pulled out of the carbs in case I need to switch things out. I can tell you that the carbs are clean and the passages are open. I have checked (and rechecked) for air leaks as well. I agree that from everything I have read these should be the easiest of the Z1 bunch to set up, so this is a bit of a humbling experience. I’m no race tuner but I have rebuilt a number of different bikes, so I am not flying completely blind here. Thanks hardrockminer.

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Running poorly 23 May 2020 02:46 #826374

  • zed1015
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Before you go any further read the attached thread to the end.
www.kzrider.com/forum/23-for-sale/611992...-round-slide-mikunis
With pods , stacks or open carbs etc you need air corrector jets to cure the off idle flat spot and hesitancy, they also improve running throughout the range.
The pods you use must be good quality free flowing K&N etc as cheap chinese items can actually be more restrictive than the airbox and really screw up the jetting and restrict air intake.
Delkevic exhaust needs no main jetting mods but the pods do.
Set all carb settings to stock..
Leave needle in middle position and use stock size pilot.
Fit air corrector jets.
Your mains are already too big at 120 and you only need 2 sizes up from stock to around 115 max depending on original main.
Backing of the throttle to improve running indicates too rich on the main and running on choke indicate the lean mix caused by the pods which the air jets will fix.

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Last edit: by zed1015.

Running poorly 23 May 2020 03:28 #826375

  • wco56
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Thanks ZED1015. I will send a PM.

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Running poorly 23 May 2020 05:29 #826376

  • hardrockminer
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zed1015 has given you great advice.

For comparison, I have 17.5 pilots with screws 1-1/4 out, 108 mains and the needle in the second from top position. It ran OK with the needle in the middle position but the plugs looked a bit lean when running at 100 kph..

The bike is a 1980 KZ1000 but the air intake is off a Z1 (with a K&N filter) and the exhaust is a 4/1.
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.
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Running poorly 23 May 2020 07:29 #826389

  • wco56
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Thanks hardrockminer. I did connect with zed1015 and ordered his corrector jets. I will be ready to put them in as soon as they get here. I appreciate that there are folks who would take the time to help out and offer the benefit of their experience.
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