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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 25 Nov 2020 20:27 #838950

  • Bruce Springsteen
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First post here. I recently bought my first motorcycle - a 1977 kz650c. I'm linking a video below, has anyone experienced this before? Any theories on the issue or advice would be GREATLY appreciated.

^^^ VIDEO^^^

THE PROBLEMS
-bogs out when throttling quickly or sometimes even lightly or just idling
-super rich
-occasional leak out of float bowl overflow valve
-only runs with choke on
-clearly sounds awful

WHAT I'VE TRIED
- cleaned carbs (but did not remove the needle or anything from under the top cover)
-replaced pilot jets and main jets with same size (102.,5) also replaced float needle valve and not sure of specific name but what is between that and the float itself
-adjusting air mix screws and/or idle screw
- changed spark plugs and checked that all have spark
-replaced old warped air box boots and springs and checked for vacuum leaks


LONG WINDED STORY OF THE HISTORY OF THE BIKE SINCE I'VE HAD IT (probably optional to read-video says it all)
I bought the bike almost 2 months ago. I have learned a lot since then but at the time knew essentially nothing about motorcycles. My friend looked it over for me and test rode it. The bike started right up via its stock ignition. We live in the city so the test drive was just a light, 25mph cruise around a couple blocks. All checked out in his opinion, he accepted my offer and my friend rode it home. Once we got into some open space he was able to really open it up, and by the first stop light after that, it wouldn't idle anymore - just bogging out. I should have probably taken it back right then and there. My friend tells me we just need to clean the carbs and its easy and he'll help. Being so excited about watching him open it up just now and picturing myself doing the same, we pressed on, requiring the choke to get back without bogging out. A few days later we took the carbs off and they're filthy. Can't see through some of the jets, totally clogged. Cleaned them out good but never fully disassembled them or replaced anything. Took hours to get them back on with the old stiff airbox boots, a heat gun helped. It never had springs on the boots so I used hose clamps and duct tape (i know...) to hold them on because i warped them with the heat gun. The bike actually ran well when all was said and done. It DID run rich but, between a leak from the seal of my float bowls and me realizing it was dumb of me to not clean the tank and eliminate the inline fuel filter because it was dirty, and me ordering new airbox boots and springs, I never fine tuned the carbs because I figured I was soon going to have to take them back off anyway. Weeks passed, I learned how to ride and rode every single day for hours. I fell in love with this bike. The electric start stopped working at some point in there but that's for a different thread - I learned to kick start it and pressed on. Eventually, after a few weeks, there was a sharp decline in performance, to the point where it sounded awful and I couldnt get it over 30mph and by the final ride I had on it, it needed the choke to not bog out again. At this point I knew a thing or two about the bike and knew that my rusty tank and filterless fuel line meant the carbs were filthy and it was finally time to take them off that second time, so I did. Even filthier this time around. When I took the first float bowl cover off a pile of dusty rust fell out. Remember I mentioned it had a leak from my float bowl seal? It did, but every once in a while it would piss some out the overflow on the bottom too. From what I read I figured the gasket may need to be doubled (it did) and also I could have some rust underneath or on the tip of my needle causing it to not seat properly (I did). May be worth mentioning that it didn't seem to have these leaky float bowl issues till after I took the carbs off the first time. I cleaned them up and this time replaced the pilot jets, main jets with the same size that was already in there 102.5, float needle valve, and whatever is on top of that. I did not remove the needle or anything under the top cover of the carbs, just cleaned them the best I could as they were - I figured I didnt do that the first time and it ran good, so I dont need to now. I did not remove the choke plunger things either. I knew that the carbs would be dirty but I ultimately attributed the horrible sound of it and the not being able to get over 30mph to a vacuum leak because of my warped boots and duct tape job. When I took the duct tape off 2 of the boots were totally off of the carbs so I figured that was it. I buttoned everything back up nicely with the new boots and springs this time, reset the air mixture screws to 2 1/2 turns out, rebuilt the petcock, tried twice and failed to clean the tank but said screw it and slapped a fuel filter on and started kicking. Unfortunately, it still took like 20-30 kicks to start it and it still runs the same. This takes us to present day

THANK YOU SO MUCH FOR ANY HELP

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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 26 Nov 2020 09:39 #838986

  • Mikaw
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Just a quick comment as Im out the door to turkey day. It sounds like its not running on all four. If you have an inferred temp gun check the exhaust temp at the head tubes where they make the first bend. If you dont have a temp gun use drops of water and watch how fast they evaporate. last but be careful it to quickly touch each tube, be careful they can get extremely hot. Good luck
1976 KZ 900 A4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 26 Nov 2020 15:09 #839007

  • Rick H.
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Wow does your story take me back to a different time and a different bike. Forgive me for saying this, but your situation reminds me of "ME" in my Dad's garage with a 1966 Triumph 650 twin carb in about 1971ish. It was my very first bike and I fell in love with it. Didn't know Jack about bikes, especially English bikes, but that was the best bike in the world as far as I was concerned. I can't tell you how much I laughed and smiled reading your novel. Well done!

Okay, I am sure many others will chime in on this, after they have finished their turkey, but I will make a few obvious suggestions. First off ditch the duct tape. Put it far away and leave it be. If you don't have a factory service manual get one ASAP. You need to read it cover to cover before you do anything more. You already know some of the things you desperately need such as carb holders etc., but remember this......you can't take short cuts and expect things to work right. If you got "dusty rust" out of a carb bowl you REALLY need to clean the entire fuel system including a good rebuild of the carbs. Obtain new OEM carb holders if possible.

As Mikaw has already stated your bike doesn't seem to be running on all its cylinders. This could be a carb problem, or an ignition problem or both. It is really difficult to tell you exactly what is wrong with your bike, but educated guesses can be made. I would start with going thru the fuel system first cuz you know it's in need of work. There's no guessing on that one. It sounds like nothing short of a complete carb overhaul is in order along with cleaning the rest of the system. Install new fuel filters right away. I would then check your engine settings including valve clearances. Proper valve adjustment is critical to a good running engine. If you have a point ignition make sure to check that out too. Replace points and condensers, set gap and static timing. Check the ignition advancer for sure if you have one. On my KZ-1000 the advancer is behind the point plate and means having to remove the point plate to get at it. It must be done though if you have one and I assume you do. Advancers cause all sorts of grief at times. Look at your spark plugs, are they wet or dry? Don't worry about electrode color just yet. Make sure your battery is in good to great condition. You don't know, nor does anyone else, if the carbs are adjusted properly including synchronization and cable adjustment. This is all part of the steps you must go through to eliminate potential problems and work towards a good running motorcycle.

I don't have a 650 so I don't know exactly what you have to work with, but the basics are always the same. If your engine has fuel, air, spark and compression it will run. The hard part is fine tuning all the components to work together. Think of it as a flow chart. You check and correct one item and move onto the next. Once you work thorough the flow chart you will have a much better understanding of your bike and what makes it go varoom-varoom. Good luck.

Rick H.
Rick H.

1977 Kawasaki KZ-1000A1

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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 27 Nov 2020 09:57 #839059

  • 650ed
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Why are you trying to run it with the choke on? Ed

1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)
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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 27 Nov 2020 10:32 #839061

  • kevski
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Sounds as if it's only running on two, wonder if two plug leads are on the wrong plugs.

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77 650c just won't run right -bogs out/unresponsive throttle (VIDEO) 27 Nov 2020 10:44 #839063

  • Mikaw
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650ed wrote: Why are you trying to run it with the choke on? Ed


Ed thanks for posting the picture. I was thinking the OP was refering to the inlet boots when he mentioned the springs.

Bruce, the boots you replaced will not cause vacuum leaks, the are actually allowing air into the engine. But they could be causing your LEAN condition by bypassing the restriction of the air filter. You mentioned the bike will not run with out the "choke" on. That is a misleading term as it relates to these bikes. "Choke" brings to mind reducing air, when in reality the system is an enricher circuits. When the bike is cold they need additional fuel to run, and as such when lifting the choke lever it is actually inducing additional fuel. So with your bike needing the choke to run it indicating that it is lean. Now why is it lean. Like Rick H mentioned we can only make educated guesses without knowing the baseline of your bike is good. You will really do yourself a big favor by doings as Rick says. Get a Factory Manual. Read it and start with all of the maintenance adjustments. Without knowing the basics are set correctly you could be chasing your tail finding something wrong thats caused by a completely different reason.
1976 KZ 900 A4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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Last edit: by Mikaw. Reason: spelling
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