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ZR rider
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2,064 Posts
Discussion Starter #1
I got a tough one for you guys... my zr was running like crap for a while. It would bog before 3500 rpms and I had to feather it every once in a while to get it going faster. Once it got above that, it would scream. I cleaned the carbs and that solved the problem. Now last night I came across something I've never even heard about. I was taking her up the road on a bank to get to a field and she was running perfect. When I got into the field it suddenly bogged. I couldn't get any more than 4-4500 rpms out of it no matter how much gas I used. My friend rode it around and told me that if he eased into it coming out of a corner, it would run a little better (6k rpms) but then it would drop right back down. I brought it back to the house and rode around the yard a few times and I was bewildered. It would run great every once in a while, typically when I went downhill, and then it would bog out again and again. I figured water in the gas somewhere, poor spark, dirty carbs again, something along those lines. I pulled it into the garage again and tested the spark. Perfect spark. Cleaned the carbs again. Nothing wrong there. Pulled the lines and looked at the gas. Looked clean and I had just replaced it so that was probably not it. Took it around the yard again and it would get right up to 9k rpms and ran fine. Parked it to talk to my friend and figured there was nothing wrong. But then when I went to start it again, there was almost no compression. I could sit on my sled and pull it over one handed. Based on a finger compression test it was fine, but when I pulled it over it was like I didn't even have my plugs in. It started, ran like crap, and wouldn't go over 4k rpms again. I parked it for the night and tried it again today. At first it felt like it was running on one cylinder and the engine sounded like crap. I figured it was a piston. But then I started it again and it ran fine, YET AGAIN! After 2 or 3 minutes it went back to crap.

I've looked at the fuel filter and it's not clogged at all, I can blow through it and everything. I'm thinking maybe one of my clutch weights is sticking?


Any ideas?
 

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Sconnie
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1,745 Posts
Something intermittent like that I would hazard a guess at spark. But what confuses me is the loss of compression!
 

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My guess would be maybe clutch not coming down to a lower gear but it might be motor related. Take out your clutch and see if everythings all right in there... The only reason i would lean more to clutch is because it would run up to higher rpm every once and a while, but then again it should be idling fine if it's not motor related. so it's a little confusing. maybe spark? anyway good luck!
 

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My guess would be maybe clutch not coming down to a lower gear but it might be motor related. Take out your clutch and see if everythings all right in there... The only reason i would lean more to clutch is because it would run up to higher rpm every once and a while, but then again it should be idling fine if it's not motor related. so it's a little confusing. maybe spark? anyway good luck!
I was thinking clutch too. My old Exciter 570 had similar symptoms that were resolved with a good clutch cleaning. Hopefully it's somthing that simple.
Compression has me stumped too, thats not an intermittant problem.
BTW have you checked to see how hot it's running when it starts running like crap?
 

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compression issue would lead me to believe either something with the pistons or the gaskets... i would put it on a real compression tester and check it both when you have it running correctly and like junk. sounds like you have a blown seal or something
 

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I had an almost identical problem after doing a complete engine rebuild 2 years ago. (minus the compression stuff). It was completely random, ran great at times then wouldn't go over 4,000 rpm at other times. I ended up finding that when i put my carbs back on I didn't put my vent tube in the right place. If i remember right I had it going off to the side instead of straight down. I know mine was sucking gas and oil like it was going out of style too. Nice easy thing to check.
 

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Do a compression test @WOT! Then replace all the fuel lines including the pick up in the tank. There isn't any condition that alows compression to come and go that is good!
 

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ZR rider
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Discussion Starter #8
I haven't had access to the internet until now and haven't tried much since I posted. I'm thinking I may have worn my piston ring out on the side opposite of the PTO. I had it running (had to pour gas into the cylinder because the damn choke lever broke off when it was frozen) and I stopped it to give everything a quick look. I felt the spark plugs while I was checking the spark again and noticed that the PTO side was fairly warm while the other side was burning hot to the touch. Then I took a look at the threading to that cylinder and noticed that there was a decent amount of oil on that side. So I'm thinking that's probably the culprit, right? Could it be a scored cylinder? Worn ring?

In either case I'm going to have to pull the engine apart myself because I'm practically broke. I'm a little worried because I've never had to before but I'll have a friend come up and supervise so I don't screw myself even worse.

If it is a ring, do I have to replace the whole piston?
 

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No, you can do just rings.. While you have it all torn apart tho, prly a good idea to do pistons to.
 

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ZR rider
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2,064 Posts
Discussion Starter #10
Is it true that the ring and piston brands have to match? I'm thinking about replacing both pistons with wiseco but I don't really have the cash. I can either lose a month of riding while I save up or I can go the cheap way and just get one ring within the next few days.
 

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ZR rider
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Discussion Starter #15
That wouldn't explain the loss of compression and the oil problem on the right side.
 

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That cylinder typically runs cooler than the other.
Loss of compression can be a number of things, a hole in the piston, broken rings, chunks off the top o the piston, gouges in the cylinder wall.........................

You can't know for sure until you open it up.
 

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ZR rider
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Discussion Starter #17
I was just about to pull it into the garage about an hour ago to pull off the head when my friend came up unannounced and diagnosed the problem for me :D. According to him, I have too much oil coming from my injector. At idle it runs fine but as soon as I get on the gas it has a major bog and will sometimes come out of it by feathering now. It has a very odd behavior and I was almost certain it was a ring but according to this guy (who knows a lot more about it than I do) it's oil. So I'm going to work on that as soon as I get a chance and pull off the head if need be later. It sucks trying to find the time for it all.
 
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