650 Mod's 78 Fighter Build

congrats devin.
had a blast following along.
now get out and enjoy the fruits of your labor.

leon

Thanks Leon! Unfortunately, she's not 100% there quite yet. I still need to tune up the carbs, and then get the dyna ignition on. At some point, I'll be fabbing up an exhaust that gives me more than 3" ground clearance so I don't jam it into the pavement so much. But for now, she's ridable and a blast at that!
Also, the snow isn't quite all off the ground here yet, and the roads are still pretty sandy. I figure it will be another 2-3 weeks before I have the bike on the road steadily.

Devin

Alright guys, so I'm having a head scratcher moment here with the bike. So since I got that petcock issue sorted out where it was pulling fuel through the diaphragm and causing cylinder 2 to run rich, I went up a size on the pilots to a #17.5 and tuned the pilot series with my Colortune unit (absolutely love the tool). I got every cyllinder dialed right in (nice blue flame, caramel to tan color electrode on visual inspection) EXCEPT for #2 (running the petcock vacuum line). The bike's engine specs are as follows: bored to 720 forWiseco big bore kit, Dynajet stage 3 jet kit, pods on all carbs, 4-1 pipe off 2002 Z750 with Yosh can, no valve work (cams, etc), soon to go on Dyna ignition. The cylinder isn't wet fouling like it was with the leaky diaphragm, rather dry fouling like there's excess oil on that cylinder. No matter how far out I turn the pilot screw (at 3 turns now, pretty well the max before it falls out), she still burns orange (rich) on that cylinder. When I rebuilt the engine around 2000 km ago, I had the valves professionally re-faced to seat into the head properly. The valve seals were replaced at that time as well. The coils were also replaced, and there's even spark and good blue spark on both cylinders 2-3 from that coil.

Last year I took the carbs out and did a full clean on them multiple times- soaked in cleaner, passages cleaned with a wire/blew air through passages while plugging other ones to increase pressure in that passage.

With that in mind, I'm kind of stumped as to what the issue could be. I'm not overly worried about it as it really doesn't affect performance that much. The bike fires up super quick even when it's "cold" (10 celsius, 50 fahrenheit). I would, however, like to get this issue sorted out if possible so that I have a nice burn across all 4 cylinders.

Does anyone have any ideas as to what could be going on here? I'm thinking some of these ideas could be what's causing it:
- oil control ring is worn/seated funny from when that cylinder had the leaky valve with too much fuel
- leaky valve seal
- slightly blocked air passage on that pilot

Any and all input is appreciated! Thanks guys!

Devin

Hi Devin,

This is really tricky.
I had one cylinder running cooler than the other three and could not seem to sort it out. Changed the intake cam and the issue swaped to a different cylinder. I finally found a set up where the difference was acceptable and I let it be.
Guess things will change when the engie i fully broke in.

With all the mods you (we) done it´s extremly hard to determine how they correlate together.

Is the Engine run in after rebore ? Have you checked compression, vale clearense...?
Have you measured the temperature on the exhaust pipes to compare the four ?

I would run it as is and revisit the issue after the summer. I honestly dont think the engines were perfect even when they left the factory.

Sorry I can help

Hey Arnold,

Hmm, that's a weird one with the cams. I've never heard of that. When I had the head rebuilt, evert hinges was shimmed up properly and clearances were checked. That being said, I haven't checked since the break in and the 2000 km. I should check though., good point

The engine was put through a complete proper break in at the time. Jetting was adjusted properly and vacuum synch/pilots were checked. Compression is within spec. As for pipe heat, all should be fairly close due to using the color tune to tune the pilots to a good burn, except for the one that is running rich right now. I know that one will burn a little cooler.

I might just do that and recheck occasionally to see what happens. Thanks for the input!

I forgot to mention that the clear tube test has been done to make sure the float bowls are all within spec as well.

Were the valve stem seals replaced at the time your head work was done? What kind of seals?
I've read here on the forum of other guys having bad luck with the machinist "knicking" the new valve stem seals and causing them to fail prematurely. Also others mentioned that using "NOS" rubber anything is a waste as the rubber is too old to be useful anymore.
Just thinking out loud here. These would explain your rich cylinder/fouled plug with equal compression readings...

Wrench- Yeah, the seals were all done up at that time. I'm not 100% sure on what brand the seals were, but they could be Athena (the rest of my seals were this brand).

That being said, I didn't think about the seal in that sense. That very well could be what's going on here. I have to replace some seals soon (should have done it this winter), so the head will be off anyways. I could always toss fresh seals in at that point and see what happens. Any suggestions on the brand to use for replacements?

Thanks!

Devin

Viton seals. Not a brand, type of material. I got mine on eBay when I got my valves ans springs. Someone here sells them too.
Steve

Perfect! Thanks Steve. I remember you mentioning that before now. What's the difference in material? Is the viton just more pliable under all temp ranges?

It's a little bit of a read but this sure seems to reflect some of the issues you are seeing:
[ speaks to Viton seals applications ]

Hope this helps shed some light...

I just bought Viton seals for the KZombie's head rebuild going on as we type...

Wrench- That sure does sound like what's going on here,,, I had the head re-assembled by my local Kawi shop where they put the valves back in and then checked valve clearances. Maybe when the valve was going into the seal it scraped it lightly and is slowly letting more oil into the engine?

This definitely sounds that way with what I'm experiencing. Thanks Steve and Wrench- you guys are wicked

I guess I know what I'm for sure doing this winter...

Devin