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Which carbs came on a 750 four cyl
- mountain
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The thing is, it has the original mechanical VM24SS carbs, with the original throttle control and vacuum petcock, etc. I have a set of CV carbs, although I would have to alter the throttle hook up, since it is a sigle cable type.
My question is what carbs generally came on a .738 liter 4-cyl engine? I believe I traced this motor to 1980 E model or LTD perhaps. Anyway, The starting circuit for the VM24SS carbs is built for a 652cc (KZ650) engine and would really supply a fixed starting solution when the "choke" lever is fully egaged. Since this engine is larger by 86cc would this cause a starting issue?
I've hammered away at all the other possibilities. Do you think CV carbs that were originally stock with the 750-four cyl would supply a greater amount of fuel/air in its starting circuit, enough to make the difference.
I'm looking for confirmation here, if you follow my trian of thought.
i157.photobucket.com/albums/t43/benfs/78rightside.jpg
1977 KZ 650 B1, I own two of them. Working on one custom rebuild, one daily rider. Used to have a third. Two 1978 KZ 650 C2 models, sold both. KZ owner since 1987.
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- guitargeek
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1980 KZ750-H1 (slightly altered)
1987 KZ1000-P6 "Ponch"
1979 GS1000 "Dadzuki"
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- guitargeek
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Post edited by: guitargeek, at: 2008/03/06 18:38
1980 KZ750-H1 (slightly altered)
1987 KZ1000-P6 "Ponch"
1979 GS1000 "Dadzuki"
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- Patton
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Will presume the enrichener linkage to all four carbs is being correctly operated by the choke lever, meaning the starter plungers are all being lifted when the choke lever is lifted.
But does seem like a problem may exist in the enrichener circuit (choke circuit) inside the carbs.
Could be clogged starter pipe air bleed holes or maybe clogged starter pipe fuel pickup jet in floatbowl or even clog in passage from fuel pipe to plunger chamber.
The enrichener circuit requires correct amount of both air and fuel in the proper mixture in the plunger chamber (when the starter plunger is raised by pulling up the choke lever) to be drawn into the carb bore, as this design is supposed to provide the proper amount of fuel mixture to crank up a cold engine.
All this is designed to function with the throttle left alone and in the completely closed position.
Just keep hand off the throttle when using the enrichener (choke) to crank up a cold engine, and don't be rotating the throttle (i.e., don't be opening and closing the throttle) while the starter motor (or kick starter) is being operated.
First test would be attempting to crank when cold by using the choke lever in the normal way, and without touching the throttle so that it remains completely closed.
Good luck with the diagnosis and correction!
1973 Z1
KZ900 LTD
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- mountain
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On my other kaw (link picture in my profile), Which starts immediately no matter how cold, all I do is move the choke lever back off slowly as RPM's increase. I sort of nurse the choke off until it holds at idle and let it warm up so it will take off in first.
Carbs on the bike we're talking about were done by WG and they are in great shape. That's (the enriching circuit) not it, spark is strong; compression is good; timing is good. It's just not getting enough fuel in the start.
Just thought I'd see if anyone else has tried the VM24SS carbs on the .738 liter four cyl motor.
I'm going to try my CV's, but I need to identify them to make sure they are the correct carbs for this engine.
1977 KZ 650 B1, I own two of them. Working on one custom rebuild, one daily rider. Used to have a third. Two 1978 KZ 650 C2 models, sold both. KZ owner since 1987.
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- mountain
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I have an extra 4 into 2 exhaust I could swap out and see, although it is nice looking and sounding with the Kerker . Of course then I might have to put smaller main jets in (correct me if I'm wrong).
Patton, I definately have been focused on the carbs for quite a while, but I have come up with nothing there that is out of sorts. Carbs have been the usual culprit in most of my ill running conditions. I have other carbs, both VM's and CV's I can monkey around (I'm real good at monkeying around) with and swap to show same symtoms with different carbs . . . Thanks, Patton.
1977 KZ 650 B1, I own two of them. Working on one custom rebuild, one daily rider. Used to have a third. Two 1978 KZ 650 C2 models, sold both. KZ owner since 1987.
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- steell
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It may be time to rebuild the vacuum petcock.
KD9JUR
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- wiredgeorge
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wiredgeorge Motorcycle Carburetors
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Too many bikes to list!
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- Link14
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See if that helps.
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- mountain
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Steel: Excellent thought, I will try. It is clearly an old petcock, vacuum style, and could be part of the issue. But would not the amount of fuel still in the float bowls be enough for the first blast? Thanks, great idea!
1977 KZ 650 B1, I own two of them. Working on one custom rebuild, one daily rider. Used to have a third. Two 1978 KZ 650 C2 models, sold both. KZ owner since 1987.
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- mountain
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Question: Is there any variables as far as changing the enrichener circuit so it will put more fuel in the fuel to air ratio (when choke lever is on full)? I was thinking that the enriching circuit is sort of a fixed deal, not adjustable. Obviously, the carb is adjustable with jet sizes and needle size and placement, etc. but this occurs after the choke lever is pushed down and the enriching circuit is out of the picture.
I am thinking maybe the 4 into 1 Kerker is leting more air pass through and leaning out the starting circuit.
If I changed the exhaust out to a 4 into 2, might that help? (I like the sound of the Kerker, though)
1977 KZ 650 B1, I own two of them. Working on one custom rebuild, one daily rider. Used to have a third. Two 1978 KZ 650 C2 models, sold both. KZ owner since 1987.
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- steell
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It won't start without starting fluid when it has been left for a few days. I have gone through everything; spark, compression; timing; enriching circuit. After it gets hot, it runs great. It starts fine when hot or warm and usually the next day, although this is hit or miss.
Here's my reasoning:
If it's the enrichener circuit, then it's going to behave the same way when it's cold, whether it's been four hours or four days, it's not going to be "hit or miss".
So instead of being temp dependent, the problem appears to be time dependent, in other words it happens after enough time has passed.
When you shut down the motor there is no more airflow cooling the motor, the heat from the motor heats the fuel bowls causing the gasoline to evaporate rather quickly.
When you try and start the motor with the petcock in the "on" position, no fuel flows until there is enough vacuum to open the petcock. If there is a vacuum leak, or a hole in the diaphragm, then it's going to take more vacuum than is available to open the petcock. So it won't start without starting fluid.
If you start the bike, get it warm, then let it sit for 5-6 hours (or put a fan on it if you are in a hurry), then it restarts just fine, then it can't be enrichener circuit at fault.
Seems logical to me anyway
KD9JUR
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