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Discussion Starter #1
Yesterday, when I went for a ride on my ZN700, it started bogging when I twisted the throttle and seemed to do it worse in the higher gears. Then, the engine would only rev up high and stay there. I wasn't far from home and managed to make it back by braking to keep the engine rpm down and the traffic lights cooperated. I haven't had a chance to look at it yet but I'm suspecting a bad vacuum leak, possibly a bad carb diaphragm? Those carbs are not fun to remove and re-install due to the throttle cables connections. I did see some carb diaphragms for sale on fleabay. Anyhow, time to remove the tank and take a look.....
 

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Discussion Starter #2
Trying to move this discussion back to where it belongs and not in the thread about speed testing the ZN700. Hoyt, you had a good tip about the carb holders. The clamps were a bit loose. I tightened the clamps a couple of turns. I inspected the diaphragms in carbs #1 and #4 and they were okay. I may have to remove the carbs to get to the other 2. I clamped off the engine vent vacuum line, plugged the petcock vacuum line, hooked up my new test tank and the bike is too lean to start. So, about the only thing left is the carb diaphragm in one of the two last carbs. I'll have a lot to learn about replacing those diaphragms. May be a bit difficult.
 

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JBM Industries sells replacement diaphragms & there's a how-to for replacing them. I had seen a good 440 how-to on EB, but can't seem to find it. There may be some youtube videos.
 

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Discussion Starter #5
Have you ruled out a plugged or dirty pilot circuit in your carbs?
Don't see how that could be the problem since it was revving up at zero throttle and the throttle cables work fine. After managing to get it home and letting it sit, it won't start now. But with the test tank hooked up, it will sputter a little with full choke. With less than full choke or no choke, it won't fire at all. So, I'm fairly sure it has to be a blown diaphragm. I'll get around to checking the last two this week maybe.
 

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Discussion Starter #6
JBM Industries sells replacement diaphragms & there's a how-to for replacing them. I had seen a good 440 how-to on EB, but can't seem to find it. There may be some youtube videos.
Thanks for the tip on JBM Industries! They sell the diaphragms individually if that is what you want. Last night I found several utube videos on how to change the diaphragms. Seems there are different styles that require different methods. Doesn't look too bad though. I should be able to change them out easy enough.
 

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If you need an adhesive for the diaphragm rubbers, I believe you can use Gorilla Glue or Elmers Pro Bond >> the ones with cyanoacrylates &/or isocyanates. Here's a topic about repairing diaphragms, so if the stuff works for repairs, it should also be suitable for installing new ones.
KawasakiMotorcycle.org >> Carburetor diaphragm repair that works by lovethosetwins
JBM mentions using super glue which may be the same type of adhesive.

Also, there's an excellent CV carb repair tutorial with good pics floating around the internet. I think it's for a Suzuki w Mikuni carburetors, but it should be pretty much applicable to any CV carburetors. I can get the link if needed.
 

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Discussion Starter #8
Surprise! I removed the regulator/rectifier today and was able to inspect the diaphragms on the center two carbs and they are okay. Sooo, I suppose I'll remove the carb holder clamps and check those allen bolts for tightness. If that isn't it, I suppose I'll remove the battery and look harder for a vacuum leak somewhere else. The plot thickens!
 

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So when you say it bogs when twisting the throttle, at what point does it bog? Can you be travelling at 60 MPH and then crank it and then it bogs? Or is this at lower speeds and lesser throttle?
 

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Discussion Starter #10
It was bogging at higher rpm. It started and ran fine at lower rpm. Then the engine woudn't idle down. It was revving fairly high and the throttle is working fine. Seems to me like it had to be a bad vacuum leak. It's getting interesting because it isn't the carb diaphragms, or the engine vent vacuum line, or the vacuum line to the petcock. I did tighten up the clamps on the carb ends of the carb holders a couple of turns each but the clamps are in the way of checking the allen head bolts holding the other ends of the carb holders. So, that is next.
 

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Do you have an inline fuel filter? With bikes our age, dirt and rust in the tank is likely and if some of that found its way into the carbs you might have a partially blocked main jet.
 

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Discussion Starter #12
Thanks for the suggestions. Yes, I have an in-line gas filter. But carb clogging wouldn't explain the runaway idle.
 

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Discussion Starter #13
Well, I found out why it was bogging I think. The OE foam air filter had come apart and was clogging at least one carb. The air filter design on these bikes is a really bad design with the air going from inside to outside with no mesh to hold the filter media. I'm trying to order a Hiflo filter from DennisKirk but their site seems to be down at the moment. It looks like a paper filter with a mesh on the outside holding the filter element from going into the carbs. Looks like a design correction Kawasaki should have taken care of long ago. K&N also makes a filter but it costs a lot, about 5 times as much.
 

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Discussion Starter #14
I'm a little worried about that HiFlo air filter that I ordered fitting because I checked their web site and it does not list the ZN700 as one of the bikes that it will fit. However, the ebay vendor I ordered from, and DennisKirk that I attempted to order from, both claim it will fit the ZN700. So, I will find out when it arrives. I see that Emgo makes a corrugated paper filter for it also.
 

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The ZN700 has the same basic airbox assy as most if not all KZ650/750-4 models and it has the same air filter holder & cap, so they all use the same air filters. The air filter is supposed to be replaced regularly before it can fail, especially paper air filters. The foam type should be cleaned/serviced regularly & probably replaced periodically before failure occurs.
Note: in the diagrams at Partzilla, some models use a paper air filter, while others use a foam filter with a cage-like filter element holder. The diagrams for the ZN700 show the foam type w filter holder cage. I believe the foam type are intended to be treated w an air filter oil.
 

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Discussion Starter #16
The ZN700 has the same basic airbox assy as most if not all KZ650/750-4 models and it has the same air filter holder & cap, so they all use the same air filters. The air filter is supposed to be replaced regularly before it can fail, especially paper air filters. The foam type should be cleaned/serviced regularly & probably replaced periodically before failure occurs.
Note: in the diagrams at Partzilla, some models use a paper air filter, while others use a foam filter with a cage-like filter element holder. The diagrams for the ZN700 show the foam type w filter holder cage. I believe the foam type are intended to be treated w an air filter oil.
Yeah, the paper filters are probably not ideal since oil does get blown up into the air box at high rpm and I do love to wind it out. This is one instance where the K&N filter may be the best choice. The Hi Flo filter does have a mesh around the outside to prevent the filter media from being sucked into the carbs. The stock foam filter media fits around the outside of the holder cage so it can't hold the media from being sucked into the carbs and when it gets old, that is what happens. Confession time. When I bought the bike 10 yrs ago, most of the foam filter had been sucked into the engine. The bike had 1k miles on it. I replaced it with the stock foam element after oiling it and 10 yrs and 4.5k miles later I didn't replace it and it came apart and got sucked into the carbs. So, shame on me for not replacing it sooner. I will check the paper element often to see how it holds up and may buy a K&N next time.
 

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Well it sure sounds like you found the problem. When I got my bike, the carbs were off and the air filter was missing so I ordered an Emgo pleated paper one. It looks pretty good. $11 and free shipping.
 

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Discussion Starter #18
The Emgo will probably work just fine. The reason I went with the "Hiflo" brand was because the cage that holds the filter media is on the outside, not the inside. Cost me $15.62.

The Hiflo filter HFA2601 did fit perfectly even though the manufacturer does not list the ZN700 as a bike that it will fit. The holder that was used with the foam filter media is no longer used with this cartridge.

I attempted to get all of the foam element out of the carbs but when I started the engine, I think there was a little left because the engine didn't run right at first. but it appears that the foam disintegrated and blew through the engine because it is running strong again. Yaay!
 

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The nice thing about foam is it cannot really hurt your engine. It could have plugged up your carbs but your engine should eat that foam without any problems. Glad to hear your troubles are over and it was an easy fix! A friend of mine with a single cylinder bike forgot a rag inside his carb and put the airbox back on. It took a while but we finally figured it out. Luckily the rag had not gotten sucked into the engine. It was a two stroke but I hate to imagine what might have happened to that rag if it got sucked in.
 
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