I did some 0-60 testing with the 40mm carb today. I caught the 2 runs on video then went back and timed them with a stop watch. Both runs were below 7 sec with a best of 6.56 !

Not too bad..

In fact there was a guy who did 0-60s with both his bike at 250 and later at 351 and put the vid on YT. I timed it today with the stop watch and it looked to be 7.5 seconds for his 351. Though his test did seem to be uphill slightly.

I may buy a SJ4000 camera or the like, in an effort to get better video quality. Even though my camera is very cheap, the video-ing of the runs did seem to produce consistent results.

I see my 40s float bowl gasket is leaking a tad, so I'll pull the 40 off and put the 36 back on to go ahead and see how that does 0-60

 

I've switched to early morning testing. No traffic and cooler temps to boot.


Testing first the 36mm that was on it already, I ran the bike through my new test area's highway starting and end points that begin with me rolling at 30 kmh, the 36mm carb did 97 kmh.

I tested the 40mm with these dual inserts in its throat about half an hour later, and it was right behind at 96 kmh.. Kind of what I'd seen previously when the 40 (with no inserts) was .2 sec or so slower than the 36 from 0-60.




Hooking up the a/f meter and going for a ride I see the 40 is lean-around 14-15:1 at WOT with the 142.5 main jet

I went up 2 sizes to 147.5; the a/f ratio was better but still lean

(I was worrying I'd have to use a bigger needle jet or raise the needle if those hombres were blocking the main jet WOT flow I needed)

But, forging ahead - I next jumped to 152.5; better again and very close but in need of one more increase...So I went to a 155mj

WOT jetting is now very good at low 12s and the occasional hi 11 registering. I see that's the same a/f numbers I posted here earlier with a 150 main jet.. evidently I'd gone down to 142.5 since then, because I did look at the main when I took it out today and it was 142.5.



Anyway ... if the 40mm was just 1 kmh behind the 36 even when the its main jet was so lean as to register 14s & 15s, then I am really looking forward to my next morning sprint to see what kind of speed it'll generate now that the WOT jetting is where it should be


I'd really be up a creek without this a/f meter. There was just no obvious sense of being down on power with the smaller main jet. If I'd noticed it somehow, I may have blamed it on the bigger carb or the inserts...



When I set off on this adventure with the 40mm, I'd already assumed there were ways of perking its flow up should it prove to be a little too large of a carb. I already have it set up for a single divider in the throat (which I photoshop'd out), so after testing the 40 with its 155mj, I'll switch to the single center divider and see how it runs.


Since that photo was taken I've bent over the ends of the insert tabs that run through the carb spigot's top and bottom, to have the inserts be sort of self locking and self centering, and also to have them stay perpendicular to the slide and parallel to the direction of flow.

 

Tried it this morning-it's running much stronger through the gears with the revised main jet

But only a gain of 1 kmh, as I sailed through the traps at 97 kmh; matching the 36's performance.

Doing calculations at GearingCommander.com, I see I am at 8200 in 5th@97 kmh. The engine doesn't seem to want to rev any higher-it just drones on at that rpm over the last of the stretch. I may be kind of rpm-limited regarding hoping to pick up much more speed in 5th gear.

I don't feel it's time to shift into 6th though, but I wonder how the speed would change if I did.

Maybe Bernie's timing mod will have it revving higher/easier at it did for him ...Yehey - more mods!


Next I'll try the 40 with a single vertical insert, and also without any mods to it at all. But it's pulling very well right now

 

Very interesting,, It seems the 40 is a viable option. I would have thought low to middle RPM ranges would not carburate correctly due to low vacuum.
Perhaps your testing method could be tweaked a bit - high RPM high MPH is a little dangerous..?


Eager, as always, to read your next observation(s)..

 

Not at all, it's carburating as well as the 36mm carb.

My end speed is only 70+ mph after correcting my speedo's built in error and the 18/21 tire combo vs the original 17" wheel set. The roads are empty at 5:30am , so speed is not a problem! A huge improvement in safety etc-and - there's time to make changes and try again before rush hour begins.

I reduced the 45 AP nozzle to 35 while adding the 40mm yesterday, and it seemed to eliminate the bog that turned up while hitting WOT in 2nd gear from 30 kmh (18 mph). Which wasn't a low rev hit by any means, but I didn't notice a bog this morning.

These Mikuni carbs evidently don't use a leak jet to by pass as much of the gas going to the AP as you feel is necessary to fine tune the AP shot.

I thought about shortening the distance I test over to measure speed as it's still accelerating well, but it would complicated the accuracy. Instead I am really leaning on trying Bernie's timing mod next before I try anything else in case it yields more rpm as he said it did, thinking future mod results may be dependent on timing that makes good power at higher rpm.

This section of road I use has a slight uphill grade.

 

Well the stock flywheel with the added 3mm piece of steel at the front of its' nose is on. The bike started normal, and seems to be idling at a higher rpm (which would happen if your static timing was advanced)

I took it for a short spin..it runs strong..seems like maybe more power as you open it up through the low to mid range.. but for now I didn't notice any tendency for it to rev higher easily as Bernie described-but I only hit it a few times.

I'll see what kind kmh it'll generate tomorrow morning over my test stretch of highway.

 

Fantastic Richard. If this ignition advance shows an increase, you may want to start a thread on the results. Something like "Effects of advancing the ignition on performance" - " Ignition Advance performance measurment" or some such...

 

I think I'll just try one good shot down the road tomorrow then pull it back off. I don't want to leave that JB'd piece of metal on there any longer than necessary. If it feels better in any way, I'll grind away what I've added and have a good welder build that area up.

Previously he said he couldn't weld that little piece on because the heat required for adequate penetration was melting the tiny tab of metal..

When he's done I'll have a machine shop turn off any excess height in a lathe, and I can trim it for length and width.



- I'll probably do it no matter how it feels tomorrow. Labor's cheap here and it's my spare flywheel. It didn't feel any slower today that's for sure.

In the end, it may get me to speed quicker, but my trap speed may still be rpm limited if it doesn't want to go past 8500.

Guess I could always put the 34 CVK back on at some point and see how it does since Bernie loved that little 32mm carb

 

This morning's sprint saw 98 kmh - a gain of just 1 km with the timing advanced. It may have gained some low end though at the same time.

When I have the alternator cover off again I'll see if it's possible to cut the bracket that holds the pick up coil, shift it 3mm, then weld it back together. Less effort than welding up my flywheel. I'll order another bracket rather than cut this one up.

I had the bike lugging in a few gears as I rode around warming it up, and didn't notice any signs the advanced timing was causing any preignition or detonation problems

 

Oops...as I go to replace the flywheel I see my little 3mm wide piece of steel I'd JB'd on there is GONE. Just as one member here had predicted might happen !

After a few seconds of terror I spot it up against the alternator case's inner wall.

Whew.

Well I don't know when it came off. It might have come off yesterday before this morning's test, or sometime today. So for now maybe this timing test's results may have to be considered inconclusive.