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Discussion Starter · #1 ·
Hi Guys/Gals...
My issue... My ATV started smoking (fuel) a few days ago and has the Keihin twin carb setup. When I first start it up, there's no smoke for about the first 3-4 minutes, then it starts smoking. The longer I let it run (up to 5-6 minutes) at idle, the more it starts smoking. Upon further inspection, while at idle, if I disconnected the front cylinder plug wire, it would still idle with no audible change in RPMs. When I reconnected the plug wire and then disconnected the rear cylinder plug wire, the ATV immediately dies. It will even start and run on the rear cylinder alone but will not even start on the front cylinder alone.

My troubleshooting thus far:
1. I changed swapped existing coils to see if it followed the coil, it did not.
2. I swapped existing spark plugs NGK-CR7E to see if it followed the plug, it did not. Plugs look clean, not fouled.
3. I rebuilt the carb with a complete rebuild kit, each Pilot Air Screw is turned out at 2 turns. It did not change anything. The carb has been rebuilt before so I do not have the OEM jets or anything but I did replace them with the same OEM numbered jets that my service manual specs reflect even though I am aware that precision quality is not likely as good as the OEM
4. Checked cylinder compression, 50 on the front, 60 on the rear.

Could this be a weak spark on the front cylinder? Remember... I swapped coils and it didn't make a difference.
I am baffled at the moment...
Is there an expert in the house?
 

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Well..to me it's clear that the front cylinder is dead..but not dead as in no compression, dead in that it isn't being fired. That only happens because of only a few situations. One-system or coil power is low because of a bad battery or charging system. Two-CDI had a problem internally. Three-Bad coil or plug but you swapped both and no change. Four-failing pulse coil but one is still firing so check it anyway. Five-poor connection between the coil and CDI.
 

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Discussion Starter · #3 · (Edited)
Well..to me it's clear that the front cylinder is dead..but not dead as in no compression, dead in that it isn't being fired. That only happens because of only a few situations. One-system or coil power is low because of a bad battery or charging system. Two-CDI had a problem internally. Three-Bad coil or plug but you swapped both and no change. Four-failing pulse coil but one is still firing so check it anyway. Five-poor connection between the coil and CDI.
Thank you for that reply. Forgive my ignorance, where is the CDI typically located on these things?
The battery is brand new. I am not familiar with the term "pulse coil" or how to test it. I can and will check the connection between the CDI and coil once I locate the CDI.
 

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Discussion Starter · #4 · (Edited)
Well..to me it's clear that the front cylinder is dead..but not dead as in no compression, dead in that it isn't being fired. That only happens because of only a few situations. One-system or coil power is low because of a bad battery or charging system. Two-CDI had a problem internally. Three-Bad coil or plug but you swapped both and no change. Four-failing pulse coil but one is still firing so check it anyway. Five-poor connection between the coil and CDI.
Ahh, it's that box under the seat..... I searched for it online $200. OUCH!!!!!!
I see what and where the pulse coil is, damn........
I'm thinking the best option for me is to have the CDI tested. I was told by Kawasaki they test more than just the CDI when they run a diag on it and that would be 79+tax.
Is there any way I can test it myself? Some kind of process of elimination?
 

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Ahh, it's that box under the seat..... I searched for it online $200. OUCH!!!!!!
I see what and where the pulse coil is, damn........
I'm thinking the best option for me is to have the CDI tested. I was told by Kawasaki they test more than just the CDI when they run a diag on it and that would be 79+tax.
Is there any way I can test it myself? Some kind of process of elimination?
Not the CDI, but with the manual you can test other things. I would just get a Dynatek CDI for it anyway.
 

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Discussion Starter · #6 ·
Not the CDI, but with the manual you can test other things. I would just get a Dynatek CDI for it anyway.
Thanks for your recommendation. I think I'll need to get it diaged to pinpoint the issue. :-(
If anyone else thinks they have a good idea of what it might be, please let me know. My ears are open and listening. The fact of the matter is, I'm disabled and poor as poor can be so even try9ing to find $79 is a real tough go for me. I use my ATV strictly to get around my farm, move cows, repair fences, and such. So it's a farm tool, not a mudding ride like most of you get to enjoy.
 

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Discussion Starter · #7 ·
Thanks for your recommendation. I think I'll need to get it diaged to pinpoint the issue. :-(
If anyone else thinks they have a good idea of what it might be, please let me know. My ears are open and listening. The fact of the matter is, I'm disabled and poor as poor can be so even try9ing to find $79 is a real tough go for me. I use my ATV strictly to get around my farm, move cows, repair fences, and such. So it's a farm tool, not a mudding ride like most of you get to enjoy.
Well, I took it to the Kawaski shop this morning. We'll see what they find/say. I did not tell them anything of my troubleshooting concerning what I've ruled out as any potential root cause. This is one way of discovering the honesty and integrity of the shop as a whole and more specifically the person working on the issue. I should hear something back in 24-48 hours and will update again then.
 

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Discussion Starter · #8 ·
Update 16:45 Monday - Well, I heard back from the KAW shop not expecting to hear what I was told. They have confirmed the CDI is good and the culprit is actually the "Fuel Tap Assembly". Mine is vacuum operated and it was explained to me that the Tap is not shutting off as designed b/c of a bad diaphragm which is letting excess fuel into the cylinder where it then gets pushed into the exhaust which is burning off as it goes through the exhaust. He said it needed a rebuild kit or a new Fuel Tap, whichever I decided to go with. Does that make sense to y'all?
 

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Update 16:45 Monday - Well, I heard back from the KAW shop not expecting to hear what I was told. They have confirmed the CDI is good and the culprit is actually the "Fuel Tap Assembly". Mine is vacuum operated and it was explained to me that the Tap is not shutting off as designed b/c of a bad diaphragm which is letting excess fuel into the cylinder where it then gets pushed into the exhaust which is burning off as it goes through the exhaust. He said it needed a rebuild kit or a new Fuel Tap, whichever I decided to go with. Does that make sense to y'all?
No. The float valve in the carb would stop it from over-fueling and if it didn't, the bowl has an overflow stem that wouldn't allow it to get high enough to pour into the cylinder. Pulse fuel pumps either pump or they don't. They do not over pressure.
 

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Discussion Starter · #10 ·
No. The float valve in the carb would stop it from over-fueling and if it didn't, the bowl has an overflow stem that wouldn't allow it to get high enough to pour into the cylinder. Pulse fuel pumps either pump or they don't. They do not over pressure.
Well shit... I was told that when he bypassed the Fuel Tap Assembly it ran fine and normally on both cylinders. I took it in there with the specific description that it will not run on the front cylinder by itself but it will on the rear cylinder by itself (and rather smooth I might add). I guess I'll find out soon enough... and if it doesn't resolve the issue, it's on them b/c they were very very confident of the root cause. I will hopefully know if it's resolved or not sometime this Fri and will post my findings.
 

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Well shit... I was told that when he bypassed the Fuel Tap Assembly it ran fine and normally on both cylinders. I took it in there with the specific description that it will not run on the front cylinder by itself but it will on the rear cylinder by itself (and rather smooth I might add). I guess I'll find out soon enough... and if it doesn't resolve the issue, it's on them b/c they were very very confident of the root cause. I will hopefully know if it's resolved or not sometime this Fri and will post my findings.
I guess if the diaphram has a split in the right place it can leak fuel to the vacuum side and get pulled all the way to the intake port of the cylinder and dump in...it's happened before...So let them fix it and see.
 

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My 05 750 does the same thing with the firing of cylinders.
 

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No troubleshooting - I thought that was normal with the cylinders since a lot of brute owners have seen the same scenario.
 

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No troubleshooting - I thought that was normal with the cylinders since a lot of brute owners have seen the same scenario.
If it's not the normal stuff like compression, fuel supply, coil voltage or valve timing, it might be carb sync...especially if at idle one stops firing and is sluggish to come back up the first little bit. A closed butterfly will stop the air and fuel completely killing that cylinder and what's in the pilot or slow fuel circuit will drain back to the bowl. Just a thought.
 

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Actually my 750 wont start up and idle with front plug wire off, and rear connected. but will with front plug wire connected and rear wire off. But runs normal with both plug wires connected
 

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Hint. It’s why the cam profiles with lift rate and close rate are different too.

This is a normal thing for a brute. My 750 will not start with front plug wire disconnected and rear plug wire connected.
I have a post on Facebook on this subject on Brute Force Monsters
 

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Discussion Starter · #18 · (Edited)
Hint. It’s why the cam profiles with lift rate and close rate are different too.

This is a normal thing for a brute. My 750 will not start with front plug wire disconnected and rear plug wire connected.
I have a post on Facebook on this subject on Brute Force Monsters
The question is, will it run on the front cylinder alone and vice versa? Mine would start and run on the rear cyl alone but it will not on the front cyl even though the front cyl plug is firing. This just doesn't sound like normal operations to me. If it is, can someone please explain to me, a 30+ year auto mechanic how/why this is normal? This is the reason I took it in and they have assured me this has been fixed (but I am very reluctant to believe them). I am going to test it before I leave their shop. I do not have Facisit Book so I cannot view your blog on that
 

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Discussion Starter · #19 · (Edited)
I guess if the diaphragm has a split in the right place it can leak fuel to the vacuum side and get pulled all the way to the intake port of the cylinder and dump in...it's happened before...So let them fix it and see.
Well folks, I got'r back today. It was in fact the diaphragm in the Fuel Tap Assembly. Attached is a pic of the old one. It runs like a bat outta hell now once I adjusted the carbs and the replaced plugs after the diaphragm was replaced. Also
The mech said the diaphragm was letting fuel bypass and getting sucked straight into the cyl by the vacuum line.

note: My original issue was that the ATV would NOT run on the front cyl by itself but would on the rear. Now that has reversed for some odd reason. It WILL now run on the front cyl by itself but not the rear cyl.
Any ideas about that?

Also, thank you to those that took some time to try and help me figure out what was going on. I appreciate it. Live and learn
 

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I was told it is due to the carbs being out of sync. I re synced my carbs, but still have the same scenario. Oh well, I can live with it.
 
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