Topic: jetting challenges with bored 400f carburetors

[Redline it]

i don't know anything about boring carburetors, nor what they're purpose fits, if they're for oversized cylinder boring kits, or even if they'd run on standard motors cb400f 1976. i don't know what the processes are for the boring operations, spec limits etc. but i have a set that is fairly in good shape other than 16 holes that were the results of someone's bore job.

it looks like they are or were intentional as the 4 holes were in each carb. i can't see a bore operation being done all 4 at one time. and whoever bored them couldn't of overlooked (missed)  the holes before mounting the next carb, or they would have stopped.

i might get a chance to get these holes patched, and if that works will jetting be a nightmare from stock jetting at 3000 ft, stock motor, kerker 4into1 or stock 4into1 exhaust? the bore measurment at the intake side is 22mm. the marks from the bore work doesn't show up until going through the venturi or slide area. the cuts daylight out of the 22mm by what looks like a slight ridge on top feathers out. looking in the aircleaner side the cut left an eggheaded shape of casting material taken off the top of the circle. i didn't measure the cut at the venturi, i'm using an old thread caliper, a plastic general/national made in switzerland .010 and 1/64th dial, mm on top slide, 5 inches slide on the bottom, it's the grey one with a yellow and white dial.

is that how they normally are cut? leaving the holes also? larger holes in front and 2 smaller holes in the rear of the carburetors.  what are the current changes in jetting for bored carbs such as these, like what am i gonna need to get them started. thanks. in your opinion are these even worth attempting to seal. the carbs gotta expand and contract due to so many thermal variables involved. i gotta hunch they'll do the unthinkable and be fixed, they had some jb weld on them, applied excellent but only old and shrinking slightly, they were difficult to get off.

[HondaMan]

I think I'd recommend some other carbs...the 400F had some of the most carefully-tuned carbs of the whole SOHC4 group. That's why they look like they do.

[scottly]

How about a picture showing the "bore" job? Also, why did you start another thread about these ruined carbs???

[Redline it]

I think I'd recommend some other carbs...the 400F had some of the most carefully-tuned carbs of the whole SOHC4 group. That's why they look like they do.

i'm actually pretty fond of the stock carbs, even as touchy as they are. i'm running out of them. i'm digging in the junk pile now. know where to get any? they don't have to be pretty. i would've bought some new ones that were selling for 1800.00 out the door. but he didn't have any left.

[jakec]

I think I paid $200 ish for a set that needed rebuilding last winter. I have a set that could be sold, but then the parts bike wouldn't have carbs anymore..

[Redline it]

How about a picture showing the "bore" job? Also, why did you start another thread about these ruined carbs???

it was to fish out some info if there was any hope by someone who's got experience in the boring or tuning with them before i decided to go against all odds and try it. i know the stuff has to flex quite a bit being a carburetor, and it's right on the throttle valve or close enough that a long shot at best could patch or fill those holes. but like normal no answers came and i sent 2 to let the guy try it. oh my question was more centered around why do people bore these, more area to pull more fuel? but what happens if say a set of carbs on a stock bike gets bored and no modified cylinders or valve work is done then they return to that motor, i'd image larger jets? where would be good starting middle of road size to shoot for?

[Redline it]

There are 4 FULL RACKS sitting in a crate at Western Hills Honda.  We should be there tomorrow after 11 am eastern.  I can ultrasonic and blueprint them for you if you want, just let me know.  I'm building a personal 350F and a 400F as well, and at every corner I've found "it's just easier to stay stock".  If you can buy stock components, it's darn-near guaranteed to run.  If this were the last set on earth they might be worth saving, but they're not, so save the time and headache...make a display piece out of these.

where's western hills? and yes i'm interested in buying one of those racks. ultrasonic yes, blueprint i don't know about that kind of work or what's involved for how much, or if it's an advantage to have. if you're still there or let me know some figures when you can. thank you.

[Redline it]

Western Hills Honda-Yamaha is Cincinnati's oldest Honda dealer, their number is 513-662-7759 and they've got a fairly active Facebook presence.  I would most likely be the one preparing these carbs for you in the restoration department.  In addition to whatever the price of a rack of carbs is, I think an investment of 1.5 hrs shop time to ultrasonic, choose/replace jets/spec for your setup [drilled emulsion tubes?, etc.], and some new gaskets would be money well spent.  Basically ensures a bolt-on, fire-up, fine-tune procedure.  I'd also recommend new intake rubbers, 4into1 has these and W.H.H. is a dealer for them...you might be able to bundle and save.  I've seen entire intake tracts, fenders, exhausts, etc. around the back rooms of the place.  Call and let us know what you need, we'll get you a price and shipping info.  Shop hours say 10, but try around 11, you want to talk to Herschel, the owner and expert.

gee wiz rob,
that's quite an offer you got goin on. all those awesome shop services offered and did i read this right-4into1 jets? man i thought i was lucky, until i heard your shop is a 4into1 dealer! wow, i know those guys up in the warehouse is San  Francisco certainly need help in basic instructions for the most basic china grade parts they supply, it's only a couple hour ride for me. i've bought some things from them and was scheduled to buy a lot more, but one of line operators, i forgot his name, company owner i don't know, but he pretty much opted out of any future transactions me, hurt my feelings to say the least. i think what it was, is that i was buying parts off of the "non riding trailed showbike tier" you know those shiny lookalikes parts that look good from a distance for up to a full year of reliable expected shelf life? (totally my bad as i didn't specify the parts were going on a bike that's used for transportation for the last 38 yrs   hey, oh i almost forgot i was going to call that shop where the carbs are and got sidetracked, those carbs, are they like from rentals? so i was thinking along the lines of maybe a photo and a price,  as a starting point with nothing extra, if that runs into favorable thing, then from there i'd see what i can do for any extra service work, like maybe a jet question. specifically whether those carbs have already been fortified with 4into1jets, like those emulsion tubes does 4into1 sell factory blanks to drill out to fit the needles, i know you were talking about the importance of stock parts. i can feel the crispness of custom emulsion tubes right here at the desk, something maybe in the future,   thanks, i still can't believe you guys are so lucky to be 4into1 dealership. high five on that one.

[Rick4004]

What has happened to your carbs is that whoever bored them got greedy and bored thru the bodies. This was common in the old days for all out racebikes. The thin areas were built up with JB weld before boring.

I've bored probably 30+ sets of 400F carbs. I do them in a 2 stage operation, one on a CNC mill to raise and widen the venturi area into an oval shape, then on a CNC lathe to open up the throat and taper the throat back to the venturi.

Jetting wise it isn't any trickier to jet the bored carbs vs the stock ones. If you need jetting help you can contact me directly, rdenoon@mymts.net

There is also some additional jetting info here:
http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

The factory pro write up is for CV carbs but the proceedure is the same for the 400F carbs.

http://www.denoonsp.com/jetting.htm

If you ride a 400F with bored carbs, a good pipe, and open filters,  a stock one feels like it's got rags stuffed in the airbox.

Rick Denoon

[Redline it]

What has happened to your carbs is that whoever bored them got greedy and bored thru the bodies. This was common in the old days for all out racebikes. The thin areas were built up with JB weld before boring.

I've bored probably 30+ sets of 400F carbs. I do them in a 2 stage operation, one on a CNC mill to raise and widen the venturi area into an oval shape, then on a CNC lathe to open up the throat and taper the throat back to the venturi.

Jetting wise it isn't any trickier to jet the bored carbs vs the stock ones. If you need jetting help you can contact me directly, rdenoon@mymts.net

There is also some additional jetting info here:
http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

The factory pro write up is for CV carbs but the proceedure is the same for the 400F carbs.

http://www.denoonsp.com/jetting.htm

If you ride a 400F with bored carbs, a good pipe, and open filters,  a stock one feels like it's got rags stuffed in the airbox.

Rick Denoon

thanks rick, so the jb weld stays on after the bore work? and they'd run it. i wish i would of got this earlier, right at the time of the post i sent out 2 to get an experiment on the laser welding, the larger holes were about the size of a pea, pretty big, the test fell through on stringing the beads to fill, then he tried a patch then, (it looked like a clean grade of pure aluminum a little thick i thought, yet the short weld on it, looked like it would've worked   i sent the slides with the 2 carbs for at least a sample to replace with a back stop to keep the slag from building up. i was looking at 65 per carb if it would've worked. the extra patch work would've blew way past that. so.  guess i'm still looking for a stock set of carbs, with good jet and float towers and fairly flat bowl joints. slim chance.