1982 750 Spectre - Kawasaki Motorcycle Forums
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post #1 of 12 (permalink) Old 10-16-2017, 10:10 PM Thread Starter
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1982 750 Spectre

Hello, I'm new to the forum. Lots of great stuff on here! I have a 1982 Kawasaki Spectre 750n1. It has 32000 miles on it. Here is my problem. The bike will ONLY start/fire up when the petcock is on the PRI setting. The petcock only has RES/ON/PRI settings. Also, i have to have it full choke. It then starts, and runs, but then starts to rev really high RPM's like 5000 to 6000. I back the choke off to about 1/2 choke, and it idles to around 2000 RPM's. I then turn the petcock to the ON position. Bike still runs for a couple of minutes on 1/2 choke, but then dies. If i try to turn the choke off, it dies instantly. It seems like the only way it will stay running, is the petcock on PRI, and full to 1/2 choke. I drop it in gear, and start to let out the clutch and it just dies. Try to give it throttle, and it dies. Won't start again unless petcock is on PRI, and full choke. I recently cleaned the carbs, and they weren't really very dirty. Made sure they are seated good and the air filters are seated good. Seems almost like a petcock issue to me, how it only runs when on PRI, turn to ON, and it will eventually die, no matter what. I've tried adjusting the idle screw, in/out, does not seem to make any difference.

Any ideas?

Thanks,

Jay
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post #2 of 12 (permalink) Old 10-17-2017, 06:51 PM
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Petcock is vacuum operated (from carbs) when in ON and RES position. When in PRI petcock is in manual, thus first thing is checking if the vacuum line is connected, and if so, does it have vacuum when engine run?.....if all this is true, and does not flow, then the petcock may be bad.
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post #3 of 12 (permalink) Old 10-18-2017, 10:38 AM
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Did the motorcycle have the stock airbox beforehand & was it running before installing the individual pod filters?
Were the carburetors rejetted/tuned? this can be difficult with cv carburetors & I think the hi-revving is a common symptom.
If the motorcycle has an aftermarket 4-into-1 exhaust, instead of the stock muffler system, that would be another consideration for tuning the carburetors. I would install the stock airbox with stock type air filter.





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post #4 of 12 (permalink) Old 10-23-2017, 12:11 PM Thread Starter
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There is only one line coming from back of petcock, down to the carbs throttle (?). It looks like there is a screw in the vacuum hole on the back of the petcock. It also has the air filter pods, not the original air box. Does this make any sense? Do I need to install the vacuum line?

Thanks,

Jay
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post #5 of 12 (permalink) Old 10-23-2017, 12:16 PM Thread Starter
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Quote:
Originally Posted by martin-csr View Post
Did the motorcycle have the stock airbox beforehand & was it running before installing the individual pod filters?
Were the carburetors rejetted/tuned? this can be difficult with cv carburetors & I think the hi-revving is a common symptom.
If the motorcycle has an aftermarket 4-into-1 exhaust, instead of the stock muffler system, that would be another consideration for tuning the carburetors. I would install the stock airbox with stock type air filter.





....
It has had the pod filters since I've owned it, and it ran "ok" up until about 2 weeks ago. It only has one line coming from back of petcock down to the throttle. It looks like there is a screw in the other line of the petcock, which I'm assuming would be the vacuum line. It has the original exhaust, 2 into 1, on each side. I took the carbs off, and cleaned them, and noticed they were not very dirty at all, nothing was clogged, not much if any sediment in the bowls. I made sure they are "locked" back into the engine body, and the air filters are seated good. Should or can I connect the vacuum line back up to the petcock? Good or bad to do this? Thanks for all the help.

Jay

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1982 Kawasaki Spectre 750n1
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post #6 of 12 (permalink) Old 10-23-2017, 12:21 PM Thread Starter
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Also, it will only start and stay running on "PRI" setting with it fully choked. After it warms up a bit, I can move petcock to "ON", and it continues to run, but rev's very high. I can back the choke off about 1/2 way and it will bring the RPM's down to about 2000, and continue to run for about 2 or 3 minutes, then it just dies. Won't start again, unless on "PRI" and full choke. Seems like its running out of gas, as it will only stay running on "PRI".

Jay Stanley
1982 Kawasaki Spectre 750n1
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post #7 of 12 (permalink) Old 10-23-2017, 02:47 PM
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There is really no much on a vacuum operatated petcock. It is only a diaphragm held close by spring against vacuum. Vacuum opens it if not in PRI, when is always open. Normally the vacuum line simply plugs in on a nipple on the back of the petcok, and the vacuum line comes from one or two carburators nipples on the engine side, top of the carbs discharge. The other carburators nipples should be capped if not used. In the States, the other carburators feed vacuum to a Kawasaki emmision system (kleen). In reality the vacuum system is very simple, accesible, and easy to follow and check for any leaks. If no leak is ovious, very likely the petcok needs rebuilding or replacement.


Also, the engine does not run directly from the gas tank, but the carburetor bowls, so if starved, the engine will continue running until the level in bowls gets too low to suck the fumes.

The air intake pods are more trouble than what they are worth, but first thing is first, verify the petcock.

Last edited by Hugojose; 10-23-2017 at 02:56 PM.
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post #8 of 12 (permalink) Old 10-23-2017, 02:59 PM
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If you leave in PRI, can you operate it normally? Even riding it? As long as engine is running, you can leave in PRI.
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post #9 of 12 (permalink) Old 10-23-2017, 08:15 PM Thread Starter
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Originally Posted by Hugojose View Post
If you leave in PRI, can you operate it normally? Even riding it? As long as engine is running, you can leave in PRI.
It will stay running in PRI, but also only with full choke. Then it rev's really high, like 5000 or 6000 RPM's, until you back the choke off to about 1/2. Then it will idle around 2000 RPM's for a few minutes, and then die. Anytime I put it in gear, and let out the clutch to start riding it dies. The only way to get it started again is to leave on PRI, with full choke.
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post #10 of 12 (permalink) Old 10-23-2017, 08:45 PM
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Rebuild the petcock and see if it is any better. I bought a kit from partzilla.com when I rebuilt mine.

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