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Discussion Starter #1
I'm totally stumped on this one. Started running on 1 cylinder. Pulled plugs while it was running to see which one wasn't firing, and the rear isn't. Front is firing strong. Checked spark with an inline spark tester. Sparks appears same on both coils. Compression is 50PSI front and 40psi rear, which seems low to me, but I know these have decompressions. Went through both carbs while I had them out and both were spotless. Checked valves on rear cylinder and they were good. Leakdown test on rear cylinder: Put in 75PSI and leakage gauge read 73PSI and the breaker bar I was holding to stop the engine from turning was brutally hard to stop from coming out of my hand (I guess that's good.....little leakage!) Checked voltage at idle and was reading 13.7 volts at idle, so I don't think the coils are starving for power. Used a scope to look in spark plug hole and rear cylinder is mint. No scratches and can still see cross hatches. Unplugged and plugged all connections to CDI box and gave the harness a quick check for any open wires and didn't see anything bad there. Rear cylinder comes in and out when it wants to, at random times.

Now, the revving thing. Not sure if running on one cylinder makes it act like bad timing, but it only revs up to maybe 4500 RPM, and just hovers there and won't go higher.

I'm stumped. Any help, any pointers, anything would be appreciated. If anyone needs more detail, video, pictures or whatever, let me know. Thanks!!
 

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Check the CPS, Try a different plug in the rear, Check the valve timing, If anyone has ever ben in and R&Red the roter (flywheel), it may not have been torqued correctly and the key may be partly sheared. Have to pull the cover for that.
 

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Discussion Starter #3
Check the CPS, Try a different plug in the rear, Check the valve timing, If anyone has ever ben in and R&Red the roter (flywheel), it may not have been torqued correctly and the key may be partly sheared. Have to pull the cover for that.
Alrighty. I'll get new plugs for it and if that doesn't change anything, I'll pull the flywheel cover off and take a look. Hoping I don't have to pull valve covers. Waiting for rtv to dry is annoying. I'm an impatient guy. What's the CPS?
 

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Crank Position Sensor. Also called a pickup coil. You can check it easily with a multimeter. There's a Youtube video showing how to do it.
 

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Discussion Starter #5
Alright, so I found the issue with it running on one cylinder. The spring in the vacuum diaphragm collapsed and caused the needle in the slide to go up in to the slide, so it was getting so much fuel, it couldn't ignite it all. Fixed that issue and bam! 2 cylinders. So that's one issue solved, i guess. Now, I am in the process of rebuilding this engine because for the past month, it has progressively started to burn a lot of oil just under normal use on flat ground. Checked ring end gap and it's getting near the end of the service limit and there is piston slap going on judging by the marks on the piston and cylinder and it is sloppy in the cylinder. Oil level is a tad below full, so it isn't overfilled. I took the valves out to put new valve guide seals in because these ones were hard. I noticed the intake valves on both cylinders had quite a lip on the end of them, so I was going to get the valve seats cut, but service manual says 45, 32 and 60 degrees. I've never cut valves, but know someone from work who can. Why are there 3 different angles? I'm confused. Thanks for the help everyone!!
 

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The machine shop will know what to do as far as the seat cutting. But have them call VFJ and get his directions for the 2mm cut. Will save your valves from sinking into the heads. Best thing I've ever done to my machine.
 

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Discussion Starter #7
The machine shop will know what to do as far as the seat cutting. But have them call VFJ and get his directions for the 2mm cut. Will save your valves from sinking into the heads. Best thing I've ever done to my machine.
I sent VFJ an email this morning and he said he doesn't tell anyone his setups anymore and to have it done correctly by him. Well, depending on the prices. If it is ridiculous, i'll probably just go to the local machine shop and have them do it instead.
 

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The seats are just cut 2mm wide with standard angles for that width. My machine shop knew exactly what needed to be done as soon as I said 2mm.
It's not that expensive.
 

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Discussion Starter #10
So, got a call from the local machine shop, and he said his valve cutting stuff can't do the job because it will cut in to the aluminum on the heads. At this point, I can send it to VFJ I guess. The shop I brought it to is the only one around here that does smaller engine stuff within a few hundred mile radius. Big bummer.
 

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Discussion Starter #11
So, VFJ no longer does engine building or any engine work like that. I called him and he says he doesn't. I can't find a good machine shop around here. Who knows where or who I can have these heads done at??
 

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Discussion Starter #12
Who's still here? Got it all rebuilt and put together. Found a shop and got the seats done. Now....running on one cylinder again and it's the rear. I've checked cam timing, carbs and the slides, fuel, spark plugs, coils, connections to electrical stuff, compression, valve clearance. Nothing is changing. I'm at the end of the road with things to try. Any ideas?
 

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So it was running on the front cylinder before and now it's running on the rear? Swap your plugs and fire it up. See if it runs on the front. Wouldn't be the first time a bad plug has caused havoc, even a new one. If nothing changes, swap your coils and do the same thing. Same for your plug wires. Just because they look OK doesn't mean they are. Some parts will test Ok and still not work properly, so this is an easy way (although it is time consuming) to field test your components. Try that and see if it helps.
 

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Discussion Starter #14
So it was running on the front cylinder before and now it's running on the rear? Swap your plugs and fire it up. See if it runs on the front. Wouldn't be the first time a bad plug has caused havoc, even a new one. If nothing changes, swap your coils and do the same thing. Same for your plug wires. Just because they look OK doesn't mean they are. Some parts will test Ok and still not work properly, so this is an easy way (although it is time consuming) to field test your components. Try that and see if it helps.
I read what I wrote and worded it wrong. Front cylinder is running perfect and the rear cylinder is giving me the issues. I have put an inline adjustable spark tester and opened it until it stopped sparking on both coils, and both coils stopped at the same gap.Tried different plugs/ swapped plugs, and no change. What I don't understand, is it will run flawlessly for about 10 seconds when cold, then after that the rear cylinder begins to act up.
 

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Ok, new information. From what you had written before, I assumed it wouldn't run at all on one cylinder. If it runs OK for a few seconds, I would lean towards 3 different issues. The first I would look at is the exhaust. If it's plugged at all on the rear cylinder, it would do exactly what you are experiencing, as it will run great at startup, and then run like crap due to an obstruction in the exhaust as backpressure builds. Second is fuel. Pull your carbs and rebuild them, don't just check them. Rip them apart, clean everything and put them back together. There are numerous small ports in those carbs that need to be clean or it won't run right. Last is air. This is the last thing I would check as it is running great on one cylinder. Can't hurt to check it though.
 

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Discussion Starter #16
Alright. I done fingered it out. For some reason, it is starving for fuel on the rear cylinder. I stuck 2 fingers over the carburetor opening and it smoothed out, so it is definitely fuel related. I'll probably get a rebuild kit and rebuild these carburetors. I do know now they need bigger pilot jets.
 

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Don't know if the 650's have the same carbs as the 750's, but I got my jets at Rockymountainatv. If they are the same carbs, the pilots are Keihin N424-74C series. The mains are Keihin 99101-393 series. BUY KEIHIN JETS!!!! I bought a Moose rebuild kit that came with everything you need, and then ordered the keihin jets as I had to rejet my Brute. Pilots are the same front and rear, but the main in the rear is slightly larger so make sure you order the appropriate jets. We all know you wanna put some bigger jets in there anyways!! I used all the gaskets and new bolts in the rebuild kit, but used all Keihin jets and diaphragm needles. Might as well shim the needles while you have it apart. I used the floats needle and seat that came with the kit, as well as the AFR screws. Go here and have a look. 2005 KAWASAKI BRUTE FORCE 650 4X4 Parts & Accessories
 
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