CV tuning - which way is better?

[Guest]

So I've seen two ways to tune CV carbs - by the throttle position, and by engine rpm at WOT.

Which way is better?

[chuck hahn]

There is a CV tuning STICKY at the top of the carb section.

[Ric]

Here's a link to throttle position tuning:

http://www.iwt.com.au/mikunicarb.htm

And here's a link to engine rpm tuning:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,cv,high_rpm_engines.html

[tkent02]

The first one isn't even for CV carbs.

[Ric]

The first one isn't even for CV carbs.

Welp? I'm an idiot.

Thanks for pointing that out, tkent02. I was about to make a bigger mistake than usual. I made some adjustments to richen the BS30s on the 300, and in doing so it runs worse now. Obviously, what I thought was a lean condition in the needle circuit is in fact too rich. What I've done so far is lower the float height after putting in #135 main jets, up from #130(plug chops showed lean beforehand and colder air is coming) when I added pods and pipes. The new jets do run rich as well. Now my idea is to raise the float height to lean out both the main and needle circuits to where they'll play nice with the rest of the plumbing.

I also found out that the fuel line is super hardened, and I had diaphragm cap screws backing out on the left carb. Got those sorted, and I set the float height around 23ish mm. I know that's higher than OEM specs, but I honestly dunno what happened to the extra washers I bought for the needles. So, maybe this'll work???

[posplayr]

The first one isn't even for CV carbs.

See Figure 2 and 3;it is for a slide carb.

[Ric]

I'm tracking, now. Thanks for steering me the right way yall. :-)

So I just got back from checking her out, and while it ain't as bad as before, it definitely still has a considerable stumble at WOT from 5500ish to 7500ish. From 7500ish to redline she cleans up somewhat better.

Here's the left plug after a good chop: 20161029_011841.jpg

[Ric]

And here's the right one: 20161029_011447.jpg

[Ric]

So I had it all together, changed the oil, lubed the chain, even replaced a fuel line that had hardened. And this morning my wife went to start it and gas went everywhere and it wouldn't start. I was about fit to be tied. Pulled the carbs AGAIN, and found more issues:

The hose clamps I'd used were actually squeezing a sort of fold in the fuel line, which made it leak like a sieve. I found an unused length of fuel hose from the past and fixed that problem right quick.

Both the float tabs were bottoming out on the needle seats. I put a "step" bend in them so that now they engage the needles more positively. Going off the above plug chop pics, I set the floats at 22mm.

This one will surely be controversial - the O-rings in both needle seats are hardened, and were allowing gas to leak past them. No wonder it was sending me mixed signals on what it needed! Now, I would normally just swap those O-rings out and be done with. BUT! I had none, nor did I have a way to get any in a pinch. I did though have some oil-resistant tacky glue that I put around the O-rings and set the seats back in the (dry)carbs. They cured while I cleaned pods, reassembled the carbs, yelled at the kids to clean their messes, and put the bike back together. Once I get replacement O-rings I'll fix it right. But till then they close off completely now. I'm happy...ish.

Based on the above finding, I figured I might should raise the needles a bit since the floats are doing what they're designed to do now, and would be controlling fuel flow better. I've had two stainless washers and one fiber washer in there for the longest time, so I pulled a stainless washer since they're thinner and would make the smaller change.

Just got back from another test run, and the sputtering and all is now gone. It used to sputter out after a few seconds of WOT. I just pulled a mile-long incline at WOT in 4th gear, in the rpm range I've had so much trouble with, and it showed no sign of wanting to stumble. The head is MUCH cooler to the touch, too. It still cuts out somewhat when I back off from WOT, but I think I'm headed in the right direction now. :-)

[posplayr]

Just got back from another test run, and the sputtering and all is now gone. It used to sputter out after a few seconds of WOT. I just pulled a mile-long incline at WOT in 4th gear, in the rpm range I've had so much trouble with, and it showed no sign of wanting to stumble. The head is MUCH cooler to the touch, too. It still cuts out somewhat when I back off from WOT, but I think I'm headed in the right direction now. :-)

Now work on the needle.

[tkent02]

They cured while I cleaned pods, reassembled the carbs, yelled at the kids to clean their messes, and put the bike back together.

Should have had the kids fix the carburetors.

[Ric]

Eventually, no doubt. They're still not quite calm and steady-handed enough for me to trust them with tiny parts.

[Ric]

UPDATE: I haven't touched anything on the carbs since last putting them together and back on. It now has zero sputter and zero cutout when backing off the throttle. Yay! Gonna get some O-rings for the needle seats and adjust the float level a tad while I'm in there... left side is a tad rich and right side is a tad lean.