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Discussion Starter · #1 ·
Hello all, new guy here, hoping to get some help with a bothersome issue I cant seem to sort out with my 06 BF750.
first I will start out by saying that wrenching is what I do for a living, however my experience lies mostly in the automotive realm so I am by no means an expert on when it comes to carbureted small engines, much less Kawasaki twins.

back story on the quad, three years ago I traded some work for a 06 BF750 with a grenaded gearbox. Tore it all apart and replaced all the gearbox internals with used parts from eBay, 16 hours, a tech manual, and a gasket set later it was back together. I set the the valve clearance as I put it together and also cleaned the carbs. right out the gate it ran like crap, backfired and bogged out on acceleration etc. I realized if I kept it partially choked until it was fully up to temp it would run pretty good and once the fan had cycled a couple times I could pull the choke off and she would run like a banshee!!

Now, three years later, I have (finally) decided to address the issue which hasn't worsened or improved. I pulled the carbs again and verified the stock jetting: 38 pilots and 152 and 158 mains. plugs are black (could be from having to choke it all the time? I rarely run it long enough to take the choke fully off) I also readjusted the valves to .005" intake .009" exhaust. reassembled and ran it with the following results: starts up with full choke and can be idled without choke after a few seconds. WOT pulls result in bogging and backfiring unless the choke is partially applied, this condition occurs until it is hot then it runs normally with good power with the exception of backfiring on deceleration. I know these things are cold blooded, but of everything I have read on here and elsewhere no one has indicated the need for choke after a few seconds. it seems to me that I need to fatten up the main jets, however there are no mods on this machine and I'm not super experienced with jetting, it just doesn't add up to me, never heard of needing to jet up a bone stock machine I have also read some posts about cutting springs and shimming the needles... safe to say I'm not sure where to start. Thanks for any help!!
 

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Hello all, new guy here, hoping to get some help with a bothersome issue I cant seem to sort out with my 06 BF750.
first I will start out by saying that wrenching is what I do for a living, however my experience lies mostly in the automotive realm so I am by no means an expert on when it comes to carbureted small engines, much less Kawasaki twins.

back story on the quad, three years ago I traded some work for a 06 BF750 with a grenaded gearbox. Tore it all apart and replaced all the gearbox internals with used parts from eBay, 16 hours, a tech manual, and a gasket set later it was back together. I set the the valve clearance as I put it together and also cleaned the carbs. right out the gate it ran like crap, backfired and bogged out on acceleration etc. I realized if I kept it partially choked until it was fully up to temp it would run pretty good and once the fan had cycled a couple times I could pull the choke off and she would run like a banshee!!

Now, three years later, I have (finally) decided to address the issue which hasn't worsened or improved. I pulled the carbs again and verified the stock jetting: 38 pilots and 152 and 158 mains. plugs are black (could be from having to choke it all the time? I rarely run it long enough to take the choke fully off) I also readjusted the valves to .005" intake .009" exhaust. reassembled and ran it with the following results: starts up with full choke and can be idled without choke after a few seconds. WOT pulls result in bogging and backfiring unless the choke is partially applied, this condition occurs until it is hot then it runs normally with good power with the exception of backfiring on deceleration. I know these things are cold blooded, but of everything I have read on here and elsewhere no one has indicated the need for choke after a few seconds. it seems to me that I need to fatten up the main jets, however there are no mods on this machine and I'm not super experienced with jetting, it just doesn't add up to me, never heard of needing to jet up a bone stock machine I have also read some posts about cutting springs and shimming the needles... safe to say I'm not sure where to start. Thanks for any help!!
Welcome. If all the rest of the engine and exhaust is stock then the jetting is where it needs to be for running up to 3900 feet. Your issue sounds like a lean problem and there are several things to look at starting with fuel supply so check that the pump is putting out what it should and at the pressure indicated in the manual as well as the tank vent check valve operation..very common for them to stick shut. Next is float levels. They must be within the range indicated in the manual. Use the clear tube and mark method. Check that both carb boots do not have splits. These usually happen at or under the head side clamps. Check that the air box lid is sealing..that the gasket is intact as it must be on and sealed to run right. Finally check the CV slide diaphragms for splits or that they didn't get in the seal groove correctly and that the slides do move smoothly and freely. Finally I assume you vatted the carbs when cleaning but if not, passages get sealed easily with gas varnish especially the slow circuit so if nothing else blast it out with spray carb cleaner. Set both A/Fs to 2.5 turns out and fine-tune the idle mixture from there. The operable range is from 2.25-2.75 turns out from closed. One more thing. Double check the valve timing on both cylinders. If one is one tooth off it will act a lot like you are describing. Good luck. The problem is in there...somewhere. Just need to find it. Oh and if the battery isn't good..replace it. Low coil power will also make it act that way.
 

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Discussion Starter · #3 ·
Looks like I have some homework to do! Of the things you mentioned I can say for certain the airbox lid is on and sealed, and the battery is new. The air screw is still capped so I haven't messed with it at all. I did not vat the carbs, what solution have you found works for soaking them?
Sounds like I need to check the air boots better, as well as fuel delivery and floats.
Lastly, is there a good way to confirm the timing without removing the valve covers? I know I was careful when timing it on reassembly but you never know. I appreciate your insight and knowledge!
 

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Looks like I have some homework to do! Of the things you mentioned I can say for certain the airbox lid is on and sealed, and the battery is new. The air screw is still capped so I haven't messed with it at all. I did not vat the carbs, what solution have you found works for soaking them?
Sounds like I need to check the air boots better, as well as fuel delivery and floats.
Lastly, is there a good way to confirm the timing without removing the valve covers? I know I was careful when timing it on reassembly but you never know. I appreciate your insight and knowledge!
Without pulling the A/F's there is no way to flush or force stuff out of those tracks other then with the pressure of the spray can...and carb spray is the only stuff other then the chem-vat/dip and ultrasonic vat that can break the stuff loose. On the timing you will have to be able to see the marks on the cam sprocket but just set the TR and or TF through the view port on TDC of the compression stroke to view those marks against the deck.
 

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Hmmm... Ok, I will check everything out and soak the carbs and check back in.
I think after already cleaning them I would look at that last..and again, soaking them in anything other then a chem-dip vat or ultrasonic vat is useless. Blast carb cleaner through the pilot jet and back through the idle ports if you must but look at the rest first.
 

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Discussion Starter · #7 ·
I hear ya, I just figured I need to pull the carbs to check the boots so I might as well tare them down and soak them while I check all the other stuff. Gonna grab a gallon can of gunk brand carb soak. Also I don't see how I'm gonna check the timing without taking the valve covers off which will be easier with the carbs out of the way I think? Left side plastic is still off anyway.
 

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Discussion Starter · #10 ·
Ok, I checked compression, 40ish on both cylinders, cranking, WOT, not awesome but ok. Pulled fuel line off the carb side of the fuel filter and there seems to be plenty of fuel available when cranking, couldn't seem to find a spec on that in the manual, but each pulse was a solid stream that I would expect to see from a diaphragm pump. Yanked The carbs like a idiot not realizing your supposed to check the fuel level first then adjust the float level as needed. Typical guy, didn't read the instructions before hand. Oh well, learning as I go. Anyway, I checked the lower boots, found some minor dry cracking on the front boot, didn't seem to be all the way through though. Gutted the carbs, checked small and large diaphragms carefully, no tares. I currently have carbs and internals soaking.
I was a little bit confused with the pilot screw situation though, as I mentioned they are capped, so I started drilling a small hole in the center of one to allow removal and stopped because I was expecting a thin freeze plug type but it seemed to be aluminum not steel and quite thick, Not sure what the best way to remove them is. also I thought it odd that the manual does not mention the plugs at all. So far no major breakthroughs, when I reassemble I will verify float height is correct before remounting the carbs.
 

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Discussion Starter · #11 ·
Ok here's an update. Got the carbs reassembled after soaking for several days. Mounted them on the quad and fired it up and ran well, after a brief time warming up it seemed to be running better than ever and there was no need to choke it to rev it up. However, it seems that I have developed a whole new problem. I can not achieve full throttle. Engine accelerates smooth to about half throttle and then stops climbing as I continue opening the throttle. Partial choke does not improve anything ln fact it makes it worse. I can't figure out what I have screwed up, all the hoses and lines are hooked up. Almost seems like the vacuum slides are not opening all the way, but I'm not even sure how those operate. Any ideas? Never had an issue winding out before just needed a little help with the choke. I also went for a little ride and it seems to function normally just won't accelerate past a certain rpm.
 

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Check a couple of things. 1-that the cables are not twisted and that the carbs are synchronized. Ensure both butterflys are opening completely. 2-ensure that the diaphragms on both CV slides are without splits/damage, that they were in their seal track and...that both the bleed-off orifices are installed. If not it will bleed-off vacuum faster then it can develop stopping full operation. 3- while there the needle retainer has several legs that the spring rests on, ensure that no leg is covering the hole on the bottom of the slide that goes straight down. That..is where it get's it's vacuum from to draw up the slide. Covered by a leg...and it can't work either.
 
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