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TOPIC: KZ650CSR Bogs from idle

KZ650CSR Bogs from idle 4 years 9 months ago #518269

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Well I finally figured out my ignition problem, now I need to get the carbs adjusted. They have been cleaned (many times), just to get that out of the way.

I have the carbs bench synced, and my pilot needles are 1.5 turns out roughly. It runs without choke, but idles a little high, and my idle adj. screw is all the way out, as in it isnt doing anything. When I am moving on it, it really bogs down at idle, but once it gets past that, it runs fine, at least I think it does. I don't know where to start, since there isnt much adjustment on them.

I do have an exhaust leak at the H-Pipe, would this have anything to do with it? Thanks in advance

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1981 KZ650 H1

KZ650CSR Bogs from idle 4 years 9 months ago #518277

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ShouterVW wrote: Well I finally figured out my ignition problem, now I need to get the carbs adjusted. They have been cleaned (many times), just to get that out of the way.

I have the carbs bench synced, and my pilot needles are 1.5 turns out roughly. It runs without choke, but idles a little high, and my idle adj. screw is all the way out, as in it isnt doing anything. When I am moving on it, it really bogs down at idle, but once it gets past that, it runs fine, at least I think it does. I don't know where to start, since there isnt much adjustment on them.

I do have an exhaust leak at the H-Pipe, would this have anything to do with it? Thanks in advance


When doing the bench sync, the idle adjustment screw should first be set in a position that will allow further lowering of the slides during the later running sync.

Failing to do this is a rather common mistake, perhaps from erroneously thinking that the bench synced position of the slides is the lowest they will ever need to go.

Good Fortune! :)

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KZ650CSR Bogs from idle 4 years 9 months ago #518294

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Wow I overlooked that one. That will solve my high idle problem. What Is the idle speed rpm supposed to be?

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1981 KZ650 H1

- 4 years 9 months ago #518378

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Last Edit: by martin_csr.

KZ650CSR Bogs from idle 4 years 9 months ago #518399

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Will do, this solves my idle issue, but it doesnt solve the boggy performance on the low end. Would the exhaust leak (quite large) cause this?

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1981 KZ650 H1

KZ650CSR Bogs from idle 4 years 9 months ago #518407

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What are you using for air filtration? Ed

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1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

KZ650CSR Bogs from idle 4 years 9 months ago #518408

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I would recommend richening up the mixture a bit. The problem is that each carb will be different in terms of where the mixture screw needs to be. I recently got a colortune plug and was shocked how lean some of my cylinders were. Now I'm from 6 turns out to 2 turns out depending on the cylinder, but no more hesitation or bogging at all off of idle, idles at lower rpms, and throttle response is much smoother. If you can spare a little scratch, get yourself a colortune... its a very handy tool to have around. Adjust your mixture via colortune and re-sync and you will have a night/day difference in how your bike starts, warms up, and runs.

Like others said, you also need to do a bench sync that gives you plenty of room to adjust. Once you get your mixture right, you should really do a vacuum sync. Again, night/day results from bench sync to vacuum sync in my experience. Way smoother idle, faster warm up, throttle response, etc...

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1978 KZ650 B2A
Last Edit: by sft1662.

KZ650CSR Bogs from idle 4 years 9 months ago #518521

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I am using stock air box for filtration.

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1981 KZ650 H1

KZ650CSR Bogs from idle 4 years 9 months ago #518522

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That colortune looks really interesing, I will look into that if I can find the extra money. It seems as though it would make like a lot easier.

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1981 KZ650 H1

KZ650CSR Bogs from idle 4 years 9 months ago #521832

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I have put in a new Accelerator Pump rebuild kit from Z1, and it did not make much difference at all. It still is boggy from a start, it kind of has an erratic idle, where sometimes it idles at 1300, but other times it idles higher.

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1981 KZ650 H1

KZ650CSR Bogs from idle 4 years 9 months ago #522011

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Most stock cable-operated KZ tachs are inaccurate at idle rpm.
Imo it's often better when carb tuning to listen and feel for the best strong idle.

Where turning the pilot air screw doesn't make a noticeable difference, there's typically something wrong inside the carb (usually an imperfect pilot circuit due to an obstructed passage or an issue with the pilot jet itself).

The pilot jet must be perfectly "as new" clean. And when held up toward a light, should be able to clearly see through it, and see a perfectly round orifice. Over zealous cleaning, such as with wire, may damage the jet, so be careful when removing all the crust and crud from an otherwise good jet.

Here's a pretty good method for cleaning the pilot circuit.



Wear eye protection when spraying, because the spray ALWAYS backfires. B)

Also, sometimes overlooked, is that a too high fuel level will cause a too rich mixture, and a too low fuel level will cause a too lean mixture, in an otherwise perfect carb.

Don't be misled by goofing around with measuring float heights while the carbs are partially disassembled and placed upside down on the work bench. An artificially measured float height is not the objective, and by itself, is meaningless. The carb doesn't care about the measured float height figures involved.

What the carb does care about is the fuel level.
Perform and rely on the clear tube test to assure correct fuel level.

Besides an ample supply of fresh clean gasoline and correct fuel level in the float bowls, carb tuning is of course predicated on acceptable compression, valve clearances set to spec, properly timed healthy spark, and a clean unobstructed air filter.

Even perfect carbs can't compensate for deficiencies in the other components.

Good Fortune! :)
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