[JasonO]

--I recently got ahold of a 83' GPZ750. The engine turned over fine so me and my dad took apart the carbs and cleaned them thuroughly first. After that, and some minor airflow/gas flow problems, we got it cranked and running. . .
--the only problem is, you have to choke it all the way out to crank it and it revs high, then as you put the choke in it revs lower and lower until it shuts down. This happens even when its been running for an hour or so give or take, so its plenty warm.
--When you go to gas it while its idling, which is about 2k rpm < not sure what it should be at > it bogs down before it revs and sometimes shuts down, etc. . . Its like the air is cutting off when i gas it or its not getting enough gas / too much gas is flowing, i'm not sure, this is my first bike.
--anyone have any input on this engine or anything i should check/replace. . . we haven't looked into the block really itself yet. . . and we're trying to get it used to running again and lubed up, in hopes it'll start running smoother. . . any ideas would be appreciated.

---Also, anyone with any gpz750 parts/body pieces that are in decent shape, let me know, i may be needing it.

Thanks anyone,
- Jason

 

[ZX-2R]

RUNNING

Although it sounds like carbs, out of adjustment, go get the proper spark plugs for the bike and make sure that they are gapped correctly. make sure tha you are running the air filter and airbox in place or you will be running to lean. If you have the stock factory pipes on (I've only known of one case here on this) they have a double wall exhaust pipe...and if someone hit water while they were hot it is Possible to collapse the inside pipe like an inverted blister on your hand...) after you have put the plugs in then try it again...if it wants to stall then try removing the muffler and trying it again (bees and stuff can build nests in them...REALLY). make sure that you have good gas not old gas...if this doesn't fix it then remove the plugs get a compression gauge and check all the cylinders (Reme=mber to ouse wide open throttle when cranking the motor over for the correct compression reading). If this is good then I think that it has to be carb adjustment...

 

[ZX-2R]

ELSE

Just wondered if yo have tried cleaning hte fuel petcock, or even tried running it in REServe...most of hte bikes have a very fine mesh screen that can get plugged up and fouled with crud over a period of setting time...

 

[JasonO]

its running off a makeshift gas tank atm made out of a plastic jug. . . the actual tank was, lets say. . . worthy of replacement. another is on the way. . . its hooked up through a fuel filter at the moment, getting plenty of gas and such. . . i can get it running and it will idle at about 2k rpm. . . then when i barely push the choke in it will rev, then fall lower than before, and usually shut off, its like its not getting enough air to idle without choke, yet its getting too much air to actually throttle rev it with chokebecause i can crank it with a little throttle and it won't bog down after it gets warm but it won't idle. hope that made since, little late here, thanks though, i'll check all of that you mentioned above, i'm pretty sure the plugs are fine, and i'm getting spark, haven't checked compression yet though.

 

[GPZBob]

Have you tried raising the idle with the adjustment knob to get a idle with the choke off and the engine warm? Also, when you cleaned the carbs what all did you remove and soak?

 

[JasonO]

I've played with the idle knob, aye, but that just makes it want to die unless i turn it to far in, in which case it revs high in the rpm's. When we took the carbs apart, we took out everything that would freely come out, cleaned it all out, soaked most of it in carb cleaner to free up any junk, and cleaned out those little bitty holes that are in that pin that comes up < not sure of technical terms > I didn't see anything else that could really be removed without a chissle and a hammer, it could still be stopped up and just need to be ran a lot, i'm not sure, thanks.

 

[ZX-2R]

Still sounds like carbs to me...

just have to wait till one of the carb guru's jump in, or post CARB HELP??? and see what bites you get...it's okay to start another posting...

 

[woundwort]

Hmmmm. Sounds like air problems in carbs still

Exactly what did your dad use to clean the carbs? a good cleaning to me is half hour dip in carb and parts cleaner that comes in 1 gallon can. Then, followed by compressed air Or spray out with off the shelf canned carb cleaner. The dip does wonders though...... REMOVE ALL RUBBER PARTS for this though. Don't mess with the linkage between the carbs. If you already have, take the bike to a shop to get them syncronized

Check your mount boots from the carbs to the engine. Not loose, no thru cracks. It's an 83. I bet these have some cracks. I'd not replace unless you find thru cracks. At around $25 a pop you want to KNOW it's bad

When running smooth your bike should idle about 800 to 1k rpm

If you get this mostly smooth take it in and get the carbs synced

Try and find a jetting kit. Sometimes these wear funky or get damaged by previous owners that say the bike ran fine for them 2 to 5 years ago...... Hey, they are trying to sell a bike fast and mostly cheap.

And definately replace the plugs. keep an eye on them also. look for fouling, tons o black soot , or lean , white ash deposits. lean is REAL bad for your motor as it is running really HOT . light browish to tan is normal

 

[GPZBob]

The reason I asked about what you took out is that the pilot jet on those carbs is under an aluminum plug. It controls the fuel circuit under 6k rpm's. It's probably still clogged. Get a manual and learn the name of the parts in your carbs and I'll help you get them right. Or keep at it yourself (hell, even a blind hog finds an acorn every once in a while)

 

[GPZBob]

At around $25 a pop you want to KNOW it's bad

Carb boots for an '83 GPZ are under $12 each at the dealer. Best repair under $50 I've done this summer.

 

[GPZBob]

The pin doesn't move and it's the main jet. That's why you can't get a reasonable idle. By the time you move it off it's seat you have enough gas to run 4-6k rpm.

 

[JasonO]

OK Bob, i believe those pilot jets are the problem, the previous owner plugged them with silicon and we just today got a good carb diagram and noticed that we hadn't specifically cleaned those out, thats the next step i suppose.

woundwort, we used carb cleaner, greased lightning, parts cleaner, and some nice air support to clean them out the best we could, so we thought. we didn't play with anything between the carbs or anything, and the mounts are good, i think they were replaced previously

Thanks guys, much help.

 

[GPZBob]

Let us know how it turns out

 

[JasonO]

Pilot jets out and cleaned, just the pin and the spring, is there anything else i should worry about in that area? Also, is there a specific distance or amount that they should be screwed in. They weren't tight when we took them out. . . off to see if i can find any info on it.

 

[GPZBob]

Jason, the pilot jet you removed is actually the idle mixture screw. Part 32 on Kaw's diagram. The screw you need cleaned is part 37 and is under an aluminum plug in the bottom of the carb. I hope you counted the number of turns the #32 screws were off their seats or you'll have to retune them. We can go over that later. Just tighten them to snug and then loosen them 1 1/2 turns until then.

 

[JasonO]

Ahh, thanks, i see now. Well it did do some good cleaning those, but looks like we'll be taking it out again. I've got some time tonight, so i'll try to go out there and learn something. Thanks again

Also, i can't seem to find the exact diagram for an 83 GPZ750. On the kawa site it doesn't even list one on the 83' 750's list. Am i missing something really obvious or what, any idea or links would be awesome. Thanks

-Jason

 

[GPZBob]

The carburetors didn't really change from 82 to 85 (mikuni bs-34) so all you'll find is a diagram for the 82 carbs. Kawa only updates the tech info as needed. There is a manual in adobe acrobat here http://kz.mbsween.com/ if you have broadband. It's 45mb but you can browse it online if you can't download it.

 

[JasonO]

Okay, thanks.

 

[JasonO]

Ok, yeah, that jet is right by the main pilot jet in the carb, correct? We pulled it and cleaned it, was grimy as hell. But, it didn't have the cap or o-ring that the parts diagram shows. . . i'm sure someone has worked on this bike before, did they screw up and just not replace these caps? all four are missing. . . are they essential?

 

[GPZBob]

Jason, I really can't say. My '84 didn't ever have those caps as far as I know (it was in boxes when I got it though). I bought some '82 carbs off ebay and it had the caps. I asked a 30-year Kaw mechanic about the caps and he said "yea, it'll run like crap without them". I will say that my low end response is much better with them. I would see how it runs now that the jets are clean. It should definately idle now. I know what a PITA it is to remove/replace the carbs so if it concerns you not having them you may be able to order some from the dealer for later. I'll know tomorrow evening whether my buddy's GPz '83 has them but his bike's a junker we're reviving so it's not definate info. I've got one other guy in town that may know so I'll try to call him tomorrow as well.