Classic ZN700 A-1 Suggestions for solid performance? - Kawasaki Motorcycle Forums
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post #1 of 17 (permalink) Old 02-24-2016, 05:58 PM Thread Starter
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Classic ZN700 A-1 Suggestions for solid performance?

Hello everyone!

Just picked up my first Kawasaki yesterday! It's a 1984 ZN700A-1 LTD. Now she runs alright, but that's about it! Some pretty cruddy performance in low RPMs and I have a hard time keeping an idle under 2500 without giving at least a little throttle. Did the usual, cleaned carbs, new sparkers, fuel/air adjustment screw turned 1.5 from close, new air filter, put in an inline fuel filter, nice battery, everything is A-OK. Only thing is a slight air leak from the airbox boots (would that really cause it to run THAT bad though?).

I have some new float bowl gaskets on the way and I'm considering getting new airbox boots, but I'd rather save 50 bucks.

Really making this post to get some advice on this 30 year old bike! Trying to get her running to my daily driver level. Almost at that point!

If anyone has any advice on this bike or has experience with the ZN750, just let me know what you'd found out about this baby! I'll post some pictures and update pictures documenting ole' Sandy's restoration. My other experience with motorcycle was restoring a Rebel 450 from the graveyard. Gave that bike to a buddy that wanted to get started and found this deal. Lets get this girl going!
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post #2 of 17 (permalink) Old 02-24-2016, 09:25 PM
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It is rated 74hp. So, it should haul butt pretty good. Mine does. How many miles are on it? Have you checked the compression? When I bought mine it only had 1k miles on it in 2009. It had 178 to 180 psig compression when checked cold.

Mine ran terrible on 3 cylinders when I bought it. It was part of an estate and the nephew cleaned the carbs and couldn't get it running right so he put it on craigslist. It was running ragged on 3 cylinders when I bought it. I put a full bottle of Valvoline Complete Fuel System Cleaner in a tank of fuel and ran it through. After that it ran smooth but still on 3 cylinders. I took the carbs apart to clean them and that is when I found out the nephew had tried to clean them. I replaced the carb holders because of exterior cracks but they didn't go through. the #2 cylinder had a dead spark plug. I had checked the spark to the plug but not the plug before. After that it ran great!

this is the manual you need.
Kawasaki 82 84 KZ750 Shaft Factory Service Shop Repair Manual 99924 1035 03 | eBay

the manuals that were printed in 84 or later have a supplement that covers the ZN700. There may be one cheaper than the one I posted the link to.

1985 Kawasaki ZN700 Shaft, 4cyl
1989 Yamaha Venture Royale
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post #3 of 17 (permalink) Old 02-24-2016, 10:10 PM Thread Starter
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I actually have one of those KZ750 manuals on my computer than I reference to, but information directly on the ZN is kinda spotty. I heard these bikes run like hogs once you get em straight and take care of them. Right now I'm getting spark, no knock, and all of the headers are hot after running, so that's always good!

I still just find it hard to believe that I'd actually have that bad of an idle issue from having a leaky airbox boot. I guess it is possible with a vacuum operated petcock.
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post #4 of 17 (permalink) Old 02-25-2016, 08:56 AM
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The carbs are very sensitive to changes in the air inlet. Pods don't work well on these engines either.

1985 Kawasaki ZN700 Shaft, 4cyl
1989 Yamaha Venture Royale
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post #5 of 17 (permalink) Old 02-25-2016, 09:08 AM
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Your bike has cv carburetors, so the vacuum leak could be problematic. The petcock would be a separate issue if it's defective. CV carbs need a stable air intake environment --- if one is getting more air, then that cylinder will be out of sync with the others.

I wouldn't overlook the petcock. You can check it by priming the carbs, disconnect the fuel line & add a section of clear tubing routed to a fuel container, then start the bike to see if fuel flows. be sure to check ON, RES & PRI. ON & RES should only flow fuel when the engine is running. PRI should flow with engine off or engine running.

Another way to isolate the petcock would be to remove the vac line to it, cap the ports, then set it to pri & ride the bike.

1981 KZ650-CSR. Competition, Sports & Road.
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post #6 of 17 (permalink) Old 02-25-2016, 09:57 AM Thread Starter
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Quote:
Originally Posted by martin-csr View Post
Your bike has cv carburetors, so the vacuum leak could be problematic. The petcock would be a separate issue if it's defective. CV carbs need a stable air intake environment --- if one is getting more air, then that cylinder will be out of sync with the others.

I wouldn't overlook the petcock. You can check it by priming the carbs, disconnect the fuel line & add a section of clear tubing routed to a fuel container, then start the bike to see if fuel flows. be sure to check ON, RES & PRI. ON & RES should only flow fuel when the engine is running. PRI should flow with engine off or engine running.

Another way to isolate the petcock would be to remove the vac line to it, cap the ports, then set it to pri & ride the bike.
Thanks man I appreciate it!

I'm going to order those airbox boots and I'll post back here or make another post on what it does for performance. I'm curious to see how much it will make a difference!

My petcock is fine after a good rebuild. The diaphragm was torn, but now it works as it should. Nothing on ON or RES without vacuum and free flow on PRI. Watching the fuel flow right through the fuel filter
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post #7 of 17 (permalink) Old 02-26-2016, 08:10 AM
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If the new airbox ducts don't help, idling problems are typically caused by plugged pilot circuits. I think your carbs should have polyester caps over the pilot jets, so you'd need to remove the caps to access those jets & clean the orifices. The caps have o-rings that would probably need replacing if it hasn't been done already.

just for future reference. polyester caps. 11012-1128

Battery & Ignition. the bike needs a good & fully charged battery to run right. I use a Ctek US 0.8 smart charger & VC97 digital multimeter. The spark plug wires may need replacing. or at the least redo the connections. unscrew the ribbed compression boots at the coils & untwist the wires. if there's a lot of the white crusty oxidation, nip off the ends a tad.

The ignition coils are old & may or may not need replacing.
Your bike should have a timing rotor that requires no service, but it wouldn't hurt to remove the right side engine cover just to have a look. in case there's some corrosion or something.
.....

1981 KZ650-CSR. Competition, Sports & Road.
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post #8 of 17 (permalink) Old 02-26-2016, 09:21 AM Thread Starter
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One of my jet plugs is a little cracked on the top, but that shouldn't hinder its perfomance as the crack is just the little lip on the top. When I pull apart my carbs, clean them and add in my new float bowl gaskets I will check those O-rings to see their health. Last I checked they looked fine.

I will also check the things you mentioned as well. I ordered some new spark plugs, so i might as well get new wires as well. I see that stock it uses 8mm spark plug wires, will 7mm wires hinder the performance at all? That's all that is available at my local shop.

ALSO, the fuel/air mixture screw should be somewhere between 2 and 4 turns out right? The guy had it at 3 turns, but I moved it to 2 before I decommissioned the bike for a week due to buying all these parts. Wasn't sure what a good stock setting was for these carbs and my engine. I guess I could just tweak it around and see what runs best..

84' ZN700A-1 LTD
89' 351 F150
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post #9 of 17 (permalink) Old 02-27-2016, 01:51 AM
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Quote:
Originally Posted by KiwiCruiser View Post

I will also check the things you mentioned as well. I ordered some new spark plugs, so i might as well get new wires as well. I see that stock it uses 8mm spark plug wires, will 7mm wires hinder the performance at all? That's all that is available at my local shop.
.
7mm wires should be fine but if you want to maximize performance get copper core wires with non-suppression caps. Some Kawi coils had the wires hardwired in and so in order to install new ones you would need a connector like this. https://www.z1enterprises.com/product/TU38-1024
Speaking of coils, the original coils on these bikes were very lack-luster when they were new and they don't get better with age. If you have the budget at all, you will not regret upgrading to high performance coils like these. https://www.z1enterprises.com/product/DYDC1-1
I was skeptical until I finally tried them. Now I think that they are one of the best upgrades I ever made. (along with cartridge emulators for my forks, but that's another story)
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post #10 of 17 (permalink) Old 02-27-2016, 08:36 PM
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ALSO, the fuel/air mixture screw should be somewhere between 2 and 4 turns out right? The guy had it at 3 turns, but I moved it to 2 before I decommissioned the bike for a week due to buying all these parts. Wasn't sure what a good stock setting was for these carbs and my engine. I guess I could just tweak it around and see what runs best..
My ZN700 carbs idle mixture screws were set at 1 1/2 turns off the bottom when I got it. It runs great there and gets good gas mileage, so I left them at that setting. I haven't diddled with them.

1985 Kawasaki ZN700 Shaft, 4cyl
1989 Yamaha Venture Royale
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