OEM Carb Mods While You Are Saving For FCR Flatslides.

[Howie]

That is not what I had in mind -- that adds an obstruction to the air intake.

I'm saying to shape the intake bell mouth sids in such a way as to have a vortex shape -- not add vanes to the center.

You probably don't believe in these either
http://www.jcwhitney.com/airaid-econoaid-throttle-body-spacers/p3089913.jcwx?filterid=j5

[koko64]

I was just wanting to refine and finish the part to bring it up a bit in an attempt to follow the established practices of people smarter than me. Well, the easier ones anyway.

There are mods I just don't have the theoretical knowledge or equipment to attempt. It no longer surprises me that so many theories when put into practice, often don't work as expected. I have access to two dynos, one is very free access, but someone's gotta pay for it and I don't want to anymore.    

[ducatiz]

You probably don't believe in these either
http://www.jcwhitney.com/airaid-econoaid-throttle-body-spacers/p3089913.jcwx?filterid=j5

"Jc" means "just crap"

[Howie]

OK, how about this?
http://www.kjmagnetics.com/proddetail.asp?prod=FuelMag1&gclid=CJ2Xhvzci8YCFcMSHwod1kAAsA

[koko64]

Also good for lumbago.

[Howie]

 

[koko64]

Just an update.

Things were quiet, so out of interest, I thought I would try out my finished "ported" OEM carbs and road test them. I have no idea if they make more peak power as I have not taken the bike to a dyno, but they definitely give more response. The small throttle transitions are more responsive as is roll on response. Nowhere as good as FCRs, but better than the dyno tuned jetted stock carbs that I was running as a comparison.The carbs could be better tuned as my synch tool is at a mate's place at present, so response should improve even more with the carbs synched.

I tested different slide springs and needles, OEM, Factory Pro and Dynojet. I did not encounter any slide flutter even with the DJ springs (maybe a smidge, maybe). Normally the slides quiver at larger throttle openings with soft springs (iirc from a while ago). Mind you my test was looking down the carbs on a revving, stationary bike, and not at "speed" on a dyno. I'm guessing the carbs flow more air due to less turbulence with air being better guided down the throat of the carb. Any thoughts on that?

I got good response with the DJ springs and ended up using them with DJ needles. The richer DJ needles on the richest notch gave the best response as the bike wanted more fuel than with the stock carbs. The lean spitting/missing was eliminated only on the richest notch.The plug colours were milk chocolate brown. I suspect 1/4 and 1/2 throttle are good, but that it may be too rich at 3/4, or vice versa, but we'll see. Maybe the FP needles might work on a high setting there. I may go back a notch for economy at cruise after more testing, not sure.

[koko64]

I wont understand all the ramifications of the carb mods until I do more road testing, plug chops and dyno test with an EGA. 
There was a better connection between the throttle and the back wheel. Quite noticable. I will try adding an airbox mod when I can get a fresh airbox lid to molest.

[scaudill]

When you say taper bore, does that mean tapered from inlet toward engine?  I have heard of doing an oval bore, that is actual boring the same size as carb bore but moved up so as not to disturb holes on floor of bore.
Sterling

[koko64]

Expert tuners/builders like Doug Lofgren have used taper bore modifications as you describe. I mentioned such modifications among the more expensive options requiring specialized equipment in skilled hands. I can understand not wanting to bugger anything up!

I think the Mikuni CV38s have a good taper in the bellmouth but the transition to the carb throat is poor imho. It starts well then ends poorly. Im just porting the transition area by hand to finish things. As I've said you can see how they are built down to a price. In the past, going from CV carbs to FCRs was a no brainer, but FCRs are becoming very expensive down here with the falling Aussie dollar, new import taxes and increased shipping costs, so I've had a rethink on that. Just playing with jetting and slide springs, while giving some improvement was still very frustrating, but this has been a step in the right direction. Its all about acheiving that linear response.

I have been encouraged by some recent testing of hand finished carbs akin to "porting". There is evidence so far of increased midrange air flow and increased air velocity at lower revs/throttle positions. There is improved throttle response and a more direct feel. More testing is needed with airbox and jetting mods however to determine and adjust fuel requirements. At least test riding is fun!

The idea of this thread is to show what so many very capable hands on members here can do themselves. It's pretty much the Ducati story of polishing up these pearls.

Mikuni have "Pro" series flatslide carbs which are hand finished. Mikuni claim flow improvements applying the principles of hand porting to these carbs and you pay a premium accordingly.

I have seen oval and "badge" or "heart" shaped inlet bellmouths in the Dellorto catalogue. The smaller diameter lower section promotes air velocity over the slow fuel circuits and the large top section gives the air volume for top end power. Some of Dellorto's premium flatslide carbs have this feature. Pretty cool looking carbs.

[scaudill]

Here is some interesting tuning information from Factory Pro.
http://www.factorypro.com/tech/carbtun.html
There are two sections, up to 7000 rpm and  7000 rpm and above.

Cold weather will be here soon.  I have a big list of projects for my M750.  These carb mods will be another.
Sterling

[koko64]

I got that one, it's a good guide.

[koko64]

Here is some interesting tuning information from Factory Pro.
http://www.factorypro.com/tech/carbtun.html
There are two sections, up to 7000 rpm and  7000 rpm and above.

Cold weather will be here soon.  I have a big list of projects for my M750.  These carb mods will be another.
Sterling

Feel free to ask for help tuning the carbs if you modify them. Im testing jetting at present. If Im not around, there are other more knowledgable people who can help. Cheers.

[koko64]

Just a tuning update for anyone considering this. Some things that stand out so far:
1. Idle mixtures may or may not be affected depending on what type of airbox mods you are considering.
2. The mid range requires more fuel. With no or only simple airbox mods hopefully not more than one or two notches on the needle.
3. Running a stock airbox or open but otherwise stock airbox will be easier to tune.
4. The extended or expanded open airboxes I have been testing appear to make greater demands on the tuner to change jetting in a sometimes counter intuitive way. This is a subject for a seperate thread.
5. Consider normal jetting for stock or open airboxes with an extra notch richer on the needle to start with.
Edit:
6. Further testing has indicated that the fuel may be atomized more efficiently at low rpm as I have needed smaller pilot jets and/or idle mixture settings. This may mean you have to play with the needles to compensate for the area that overlaps the two circuits in the lower mid range. Just thought I'd add this as you will need to be prepared to play with the jetting if you do these mods.

CCW has 37.5 pilot jets if you find the bike will run with the idle mixture screws closed like I did. I even tried 35s but would need even more lower midrange fuel again.

If you try these mods, let me know and we can discuss jetting options.
Cheers.

[koko64]

I have sold my Monster, so my testing has ceased until I  work on another carbed bike with this mod.
First time in my life that I dont own a carbed vehicle.