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Discussion Starter · #1 · (Edited)
I purchased an 04 YFZ from a friend nearly a month ago. The bike has an LRD pro 4 series exhaust on it, I believe (or along those lines), with a K&N, no airbox lid, and supposedly has a port and polish, and has new clutches, not sure on brand. I've been doing the standard maintenance bit as well as riding it here and there, trying to get it squared away before I really get into it.

I've done an oil change, replaced spark plug, header gasket, cleaned air filter, carb and installed new accelerator pump and did the zip tie mod. The primary issue with the bike is that it has been running lean since before I purchased the bike. While cleaning the carb, I noted the jets and clip position on the needle:

168 main, 48 pilot, 50 leak jet, and 5th clip down on the stock needle, I believe NDSR, and the fuel screw was 7/8ths of a turn out. I know he started messing with it as he claimed he noticed a lean pop, though I'm not entirely sure he knew what he was doing. The whole thing has been lean through the whole range for me.

Today I swapped out to a 170 main, kept the rest of the jets the same, moved the clip to the 6th position, and installed a fuel mixture knob, that I set at 2 turns.

Things have improved moderately, though it's apparent it is still running lean, especially once the engine has gotten hot. Elevated idle once hot, will return to normal if I pull it down with the clutch. Once I touch the throttle again, it's back to being elevated. I tinkered with the fuel knob during the process and noticed no changes regardless of the direction I turned it. The header was glowing read, noticeably so through the header wrap when I shut her off.

I let it cool and pulled the plug to check it out, but I'm not the best at reading plugs, so I've uploaded a few pictures to get your opinions.





Also, I noticed the oil before my first oil change (first thing I did before I rode it) was a gray color. My friend always ran 20w-50 Yamalube through it, and I replaced it with the same, with a new filter, and the oil immediately returned to a shade of gray, though a bit more transparent do to not having so much carbon build up. I've also uploaded a picture of the oil on the dipstick, as I'm unsure of whether or not this something to be worried of, or if it's simply new clutches breaking in.



Thanks.
 

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Discussion Starter · #2 · (Edited)
I've changed the jets out again today, I've installed a 50 pilot and a 172 main, needle remains the same, mixture screw at 2 turns. Another marginal improvement, I'll check the spark plug again once it has cooled down enough. I'm thinking I need to do a bigger jump on the main jet , as it might be the top end that is too lean at this point. I don't think I should have to go much higher on the pilot than I already have, right?

Any pointers or discussion would be appreciated. First quad I've owned, first time I've ever messed with a carb on something this big. I've been trying to educate myself to the best of my abilities, but Google doesn't always come up with what I'm looking for.

Also, I'll be doing the timing chain, hopefully this weekend, as well as a valve adjustment. Perhaps a worn chain or valves out of adjustment could be causing some of my problems?

EDIT:

Not much change to the plug. I ran it for a bit, but not extensively. The tip is perhaps a bit darker, but probably not noticeable if I were to take a picture.

EDIT:

Threw in a 180 main, 'cause I had it, three turns out on the mixture, another marginal improvement, but probably not because of the 180. Thinking I shouldn't be above a 175.
 

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What's your elevation? The oil color is most likely from the clutch.
 

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Discussion Starter · #4 · (Edited)
~1000 feet. Figured its probably the clutch. Old clutches blew at the dunes. He cleaned the motor outby flushing it with seafoam and such. Aluminum plates or material from the old clutch? Ill see when I change the oil with valve adjust/timing chain if it clears up more.
 

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Discussion Starter · #5 · (Edited)
Put the jetting back to a 48, 172, clip on fifth position. Replaced timing chain, chain guides looked good, shimmed the valves as they were all out of spec, found out that the head pipe to slip on connection was unclamped under the header wrap. I put an exhaust clamp on that as well as some copper RTV to make sure there would be no leak.

The problems as it stands. Idle sits real low, idle knob doesn't seem to do much, choke creates high idle, high idle position does not much more, there is a misfire around half throttle, hard starting when hot, will not idle while hot even with choke.

I've cleaned the shit out of the carb multiple times, had it all torn down, yet the problems persist, and most of them seem to be carb-related problems. The only thing I have not done is tear the two halves of the carb body apart (4 tamper resistant torx screws in the bowl, along with two smaller hex head screws), partially because like all the other screws, the hex screws are stripping without much effort. I guess that's currently my only option unless someone else chimes in.

EDIT:

I've taken apart the midsection and cleaned it out as well now. It was pretty dirty in there but I cleaned every pinhole, nook, cranny, chamber, chasm of this damn thing, still have the same results. Just checked again for a vacuum leak in the carb boot with no success. I see the views on the thread going up, is everyone as stumped as I am or what?
 
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