Hi guys, I need help...
I purchased a zilla and I changed the head gasket and put it back together... I didn't run it before doing this exept when I bought it and it seemed to run well. Something important to mention is that the air filter wasn't oiled when I tried it that day, so now, I assume the mixture will be quite rich. Today I went for a run and ... it needs some serious jetting.

First, I let the motor heat a couple minutes on idle w/ choke. Then, when I gave a LITTLE throttle, the motor reved way to much, and way too long. I thought about the air filter, so I turned the air screw out but it was worse. Finally I did the opposite ... screwed it all the way in, one turn out, and it was better. That surprised me because I thought I was supposed to lean the mix !

Then, I shifted the gears and checked the rest of the throttle... UGLY. At about 1/4 - 1/2 the sound was like ammmm a 300ex hitting the rev limiter and making a sort of bubbling sound. I wasnt even able to go threw that range so, I have no idea about the w.o.t.
To me, thats means its rich. BUT with the air screw thing I also thought it was too rich... It wasn't because I richened and it was better. I don't want to lean a too lean mixture or something like that...

I read jetting guides and techniques from multiple authors but I didn't get the most important part: how a motor is supposed to react with a rich/lean mixture ??? They say it bogs when rich and doesnt respond well when lean... To me, its the same thing.

I have 22.5 slow, 360 main, air screw 1 turn out, no lid, fmf pipe, .080 over, using yamalube @ 32:1, and 94 octane.
My conclusion, the mix was too lean on idle (ok now), and is too rich on mid (I have to put the clip higher on needle)

Is that right ? any comments/suggestions for jets or anything ? Thanks !!

 

Sounds to me that your bike is loading up. I had the same problem when i bought my 89. The main was way to big and the bike kept loading up. Try switching your main to a 350 or a few sizes down and i betcha it will start getting better. Also a good way to tell if your loading up is to rev it out in gear and hold to see if it starts clearing up. But i would try going to a smaller main. Let me know how it turns out. And besides, jets are cheap its not like its an expensive gamble.

 

Loading up ! Loading up ! What does that mean ??
Sorry, english isn't my natal language... lol

 

Read this, its from Duncans website, good jetting info

http://www.duncanracing.com/techfaq/...-jetting.phtml

Futhermore, I would suggest ditching the stock carb in favor of a 39mm PWK as the stock carb is a bitch to tune, there is nothing wrong with the power that the stock carb can make, but the PWKs are way less finiky when it comes to jetting.


On a side note, I busted off the Zilla today, first time in 6 months she has been cranked. I drained the old fuel, changed the SP, kicked her a couple of times and BOOM!. We finally got some nice weather here and It was nice to ride around the block, even for a short time.

 

I read that already.
The thing is, there is some therms that I dont understand like... Loads up, bogs, surge, cut-out, doesnt responds, ... things like that. (I'm french)

 

If your reving high by just turning the throttle alittle means that you are running lean. By turning the air screw in you are mixing less air with the fuel so it is running richer. Sounds like you need to get bigger jets.

 

What he said. Lean jetting will cause the engine to rev (like turning off the gas while it's running or a leaking base gasket). That sound (of a 300ex hitting the rev limiter) was the engine pinging aka predetonating. Adjusting the air screw will not be a big enough change if it's pinging that much. Try bumping up the pilot (slow) jet by one or two sizes. I would run it rich during break in just to be safe. Better to foul a few $3 plugs from being overly rich than to melt down your new piston, especially since you're on the last bore size before you need to resleeve. Once you get it close at 1/4 to 1/2 throttle then you can start working on getting the right main jet in there.

Keep in mind that (in stock form) Zillas are very prone to predetonation, which is why the have a reputation for being hand grenades. Being .080 over, running pump gas, cold weather and increased compression will only make this worse.

 

That's for idle only... from 1/3 to full throttle its another story.

How do you call this:
The sound of the motor isnt clean, like when running cold, kind of hard to rev but doesnt do the brrrrrroooooooooooooa sound, it more like bubbling... NOT the braaaaaaaaaaaaarp "steady" sound. If I put this in words it would be: bra braaabraarb ba ba brraab (that when I'm ACCELERATING from 1/2 to full throttle) Do you know what I mean ?

anyway... this weekend I'll check this more deeply, with plugs, choke, test runs and everything. Just wanted some advices to begin somewhere.


The blue one in your pics ? Niiice zilla you got !! Can't wait to try mine ..

 

hey sam250 are you sure ?
I dont think it sounds like pinging.... and that is usually caused under load ? ... well it did the same thing when I was spinning on ice or on packed wet dirt. Please read the other post above for more description

It really wasn't the sharp metal knocking noise... more like the opposite of sharp... a fat lazy sound

 

I couldn't make heads or tails of your description of the sound but just keep in mind that you may be lean on one fuel circuit and rich on another. If it's smoking, your plug is wet or dark and the throttle response is poor - it's rich. Little or no smoke, white or gray plug and faster revving - it's lean.

The word ping is confusing because I don't think it sounds like a metallic or high pitched sound. Kinda like a knocking that is out of phase or rhythm with the normal sound of the engine. And it can ping even if it's not under load. Mine used to do it only when deccelerating because my pilot was a bit lean. You can be at 1/4 throttle at 2000 or 8000 rpm and the pilot circuit still needs to provide enough lubrication for both conditions.