Project The Second Fizzer

Well thanks to all for the help guys. I can confirm she revs all the way through with no hollow sound anymore so the main issue is definitely solved. I'm now back to a rich problem as she's backfiring quite a bit and boggy in the mid range, but I think I know what settings will make her fully happy. I was half expecting that when I put the carbies back to the stock setting anyway - easy solved.

I do vaguely recall reading about the keyster error from somewhere else but I hadn't clicked on it. Everything I was referencing suggested I had the jets right, lesson learned for me to go back to the Japanese documentation rather than rely on what is in front of me (even though the odds might slightly have been skewed out of my favour ).

 

Well I had a last play today, needles up a notch and back to 2.5 turns on the pilots. A bit better but still backfiring. The exup doesn't seem to be moving freely (like it has got a bit of friction) so I need to give that some attention.

The other thing I noticed is when the bike is cold it runs fine all the way through to the top end, but once it starts to get warm it is starting to chug a bit through the mid to high rev range around the 14k RPM mark. No hollow sound so a different issue, I'm sure.

Sometimes I think it never fizzin' ends...

 

I will back it down from 2.5 to 2 turns and see what it does, it's ok if I go too lean for the moment I just want to stop it backfiring. I'll then try to "adjust" it on the fly, but I have never had any luck trying to do the tuning "by ear" because I've never been able to pick any RPM changes. I might have to get one of those heat/temperature guns and do it the same way others have done it with header temperatures.

The problem with the exup is one of the bolts that holds the cable bracket in place is stripped out, meaning there is uneven pressure applied to the plate that holds the valve in. it's creating some friction when the motor tries to pull the valve back and forth and gases are leaking out the side a little. I have only one other spare header set that is any good - the one that came with the mexican fizzer the bolts are rusted in the holes so that's annoying. I had to cut one of the heads off and the other is broken internally so unless they're both drilled and tapped I couldn't use them again.

So I'll do the swap out on the header and adjust the mixture screws this afternoon.

 

@2 turns out...

 

Yeh one of the bolts is missing.

 

So I decided to pull it off the stand and see what magic would be worked @ 2 turns out after I had one of the club members swap the headers over at our last toolbox night on saturday evening.

Magic! I couldn't go fast enough up my street to go over 16K as I was already going at least 80... but she was revving cleanly and I was smiling all the way until I had to slam on the brakes to avoid our lovely speed humps...

She is dripping coolant in a couple of places though, most apparent when the engine is warm so probably these old hoses aren't sealing properly and I think an O-ring on the bore cooling pipe needs attention. But these would be the only things left I'd say apart from a polish and all the fairings back on!

 

Well, backwards or forwards? The fizzers are a mystery. Today, we finally had nice day where it wasn't bloody hot or raining and I thought "let's see what she's got". Doesn't rev over 10-12k again. Oh yay, I've always loved playing with my fizzer carbies.

 

Ok so I had a bit more time to think today, yes my brain hurts now because I think I was really missing the mark. Goes to show that if you overthink things you can hold up progress (I tend to do that a lot!)

I was really convinced it wasn't the carburetors, mainly because they came off a good running bike prior and were drained and stored properly. I couldn't see how a problem of this magnitude could be attributed to small changes in pilot or needle settings. This is what stumped me because the bike was obviously leaning out at high RPM, so all signs pointed to a fuel issue, and the inconsistency in the problem occurring (eg I thought I had already fixed it before) added to my confusion.

So I decided to sit back and consider what I changed. Yes the engine is rebuilt with new rings, no it's not ticky, the clearances are fine, no the carburetor is fine... and then it hit me. The damn fuel filter. I actually broke the previous one, which was a small aftermarket plastic thing. The one recommended to me by Yamaha as a direct replacement from OEM was this beast:



You can see it's running at 1/4 full. So why is that relevant? Simple - it sucks a load of air in! (yes a bit of fuel but a lot more air than it should). When the bike was revved it didn't fill up much more than that level, the damned thing was clearly too big and it was causing an airlock at higher RPM. Man was I keen to finish work, went straight to the bike shop and bought this for $6.95:



This one runs at about 3/4 full and goes to about 95% full when revving at high RPM. Time for a quick test ride and... feels good. Finally. I am still slightly skeptical because I've been here before but apart from a lean tweak around 17k (most likely due to running 2 turns out and a needle up so it's a little lean) she revs cleanly. Hopefully it stays this way now. I'll look at it again on saturday, make some minor carby adjustments and take her for another test ride.

 

Ok so a bit more playing today. Put the needles back to stock setting. Still seeming to lean out at 17k ish on the test run. So turned the pilots to 2.5 turns out, took forever to get it to idle after that but I found the happy place. It's now boggy down low, with a hesitation (but will pull through) the 15-17k range. Above that it's hard to tell because I don't sit at 18k rpm and I'm probably upsetting the neighborhood screaming around at 16k+. Whoops.

I think I'm close, but I need to get rid of the low end boggy. I did that on the original fizzer by putting the needle setting up a notch, so I might do that again and see if I'm closer. Wish I could do this tuning "by ear" or whatever the saying is, I turn the pilots and never notice any changes so maybe I just don't have "it". And without a temp gun well, trial and error is about all I've got.

Or maybe I should just put the keyster kit emulsion tubes and needles in and start from stock...?