2 ques, shifter box and modern carb

[DewCatTea-Bob]

[quote= double diamond ...
" pic of is an MC piston. These were common replacements in Ducati singles since they cost a lot less than OEM Borgo pistons. "

____ Indeed so,, as I recall they sold bare -(without rings) for near $19.99-retail, which was about 2/3rds of the cost for a stock-piston.
However the main-reason for their sale-popularity, was the promise of increased performance, (especially within a Monza, [due-to the 10.5 vs. 8.0 to 1 cr.] ) !



" The frame tags of the early Monza and Diana had either a “D” or an “M” accompanying the “250”. "

____ I recall now that this is actually correct, and-so I was wrong to have suggested that the foil-tag should state "Diana 250" !



" On one model the letter preceded the 250 and on the other it appeared after the number but I’d have to look at some tags to figure out which. "

____ If this designation difference is to purposely denote Diana or Monza (as I also believe), then it stands to reason that since the official-names of these two 250-models are 'Diana 250' & '250 Monza', that therefore the foil-tags would thusly read 'D250' & '250M' .


Dukaddy-DUKEs,
-Bob

[Timmy250]

Matt, I mis-spoke about no letters, the tag does says 250 M. Seems to be Monza, so how the Ohio title that says "Diana" got that way, don't know.
The story I got from seller seems off. I had the frame powder-coated (black, hope that isn't too upsetting for purists, also painted body parts black and silver. Not original, but I like the look.) The frame was painted blue before going to the powder coater. The body parts were mix and match colors, gold and blue mostly, leading me to believe the story of originally Diana body parts, swapped for miscellaneous Monza parts. The engine number says DM 250 on one case half, 80212 on the other.

Bob, you really don't trust my ability to measure, do you? Ha! Well, I ain't perfect, but I re-checked, and old piston and intake port diameter still as stated, 76 mm, and 25 mm. Adds to the intrigue, eh? Not planning on taking the head off to look at the new piston, but I bought it from guzzino, the pic is from their website, think it does say it's from Italy, I threw the box away. I also won't measure valve diameters soon, but exhaust valve was smaller, by memory anyway, but I might have just assumed that, being the normal situation. Just to clarify, you're saying the early GT heads had equal size ex and in valves?

Another note, adjusted the eccentric and now shifts great, even with my habitual jabbing shift habit. That was a relief.

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" the tag does says 250 M. "

____ I thought maybe I could see an 'M', but it's marking/case-size was considerably much larger than that of the 250-digits,, so I was not quick to declare that the figure I saw was really an actual 'M'.



" Seems to be Monza,
The story I got from seller seems off.
The frame was painted blue
The body parts were mix and match colors, gold and blue mostly, leading me to believe the story of originally Diana body parts, swapped for miscellaneous Monza parts. The engine number says DM 250 on one case half, 80212 on the other. "

____ While of-course the foil-tag does match the motor, it seems that it doesn't also match the frame you ended-up with.



" Bob, you really don't trust my ability to measure, do you?
I re-checked, and old piston and intake port diameter still as stated, 76 mm, and 25 mm. "
____ As for the port-mouth measurement,, extraordinary-findings require extraordinary-checking (in order to be fully accepted), and 250-heads with such small inlet-ports are too rare to hastily accept as what they seem to-be, without question !
__ As for your aftermarket 250 MC-piston,, your measurement of "76mm" hasn't been in question at all ! ... As it's 80-thousandths oversize (above 74mm), pretty-much equals your 76mm-reading !



" Not planning on taking the head off to look at the new piston, but I bought it from guzzino, "

____ Do you-yourself not recall any of it's particular specs, such as exact bore-size or it's rated compression-ratio ?



" I threw the box away. "

____ Seems it would've at-least been still useful for keeping the MC-piston saved within, (even if you had already memorized all data printed on it's labeling).



" Just to clarify, you're saying the early GT heads had equal size ex and in valves? "

____ That's CORRECT, as the early-GT was the ONLY 250-head/model to employ the 33mm-ex.valve for the intake-side AS WELL !



" adjusted the eccentric and now shifts great, "

____ The eccentric-adjustment has nothing to do with encountering 'false-neutrals',, but however, it rather can possibly make a big difference in avoiding 'missed-shifts', (which is NOT-always due-to an actual 'false-neutral' encounter !) ! _ As the eccentric-adjustment is merely meant to center the selector-mechanism so that it can be enabled to become reset for the next-following gear-shift action.



" even with my habitual jabbing shift habit. "

____ You really ought-to retrain yourself to avoid letting foot-pressure off-of the shift-lever before fully releasing the clutch-lever, (which is a process that quick&done jab-shifting doesn't take the time to accomplish). _ Cuz otherwise, (jab-shifting, much like playing roulette), you're then just taking the chance (that the moment when you happen to attempt to engage the next pair of spinning gears), that the involved gear-dog/fingers won't happen to collide (rather than engage) ! _ As 'false-neutrals' are ONLY encountered just whenever 'jab-shifting' at the very-moments in time when the dog-fingers happen to land-upon tops of each-other (instead of engaging), and there's then no foot-pressure left-over/ongoing to continue-onward with the rather desired 'engagement' !
THUS the so-called 'false-neutral' type of incomplete shift-attempt !
Whereas on the other-hand,, avoiding the 'jab it' shift-method, allows added time for the expected engagement-window to be fully open,, and-also as well, letting the clutch fully engage before releasing foot-pressure off-from the shift-pedal, will help increase the chance of instantly finding the engagement-window open & ready (for dog-finger engagement) !
__ Think about it... To take your-chances,, or rather, be absolutely-positive at your shift-attempts.


Dukaddy-DUKEs,
-Bob

[double diamond]

Could this be a B type 200 head? Might have had a smaller intake port. Just a thought. Matt

[Timmy250]

Hi Bob, I will train myself as best I can to shift properly, my first training will be to not to shift into 2nd from 3rd when I'm looking for 4th because I instinctively shift up to shift up! Very embarrassing and potentially hard on equipment.

About the new piston, here is the verbatim description, and is all I really know:

"Top quality forged piston kit for Ducati 250cc & 350cc bevel drive singles. These pistons are exact copies of the cast Borgo pistons but made of a much higher quality forgings. Pistons have full width skirts and not the narrow (and noisy) slipper type used on racing pistons. Pistons have the stock compression ratio so you will be able to kick start your bike without breaking your ankle. Kits are supplied with the best ring available, Total Seal made in the good old USA. Please measure you existing piston and order the size you need from the pull down menu."

It is 76.5 mm. And the distance between pin and piston circumferential squish area is greater than the MC-piston that came out, needing shimming of barrel. Seems to work.

I have ordered a 26 mm PKW flat-slide carb that is supposed to be a direct replacement for 26 mm Amal carb used on Brit bikes in the 60's, but better. Will report back on my experience when I get a chance. Here's a pic and description of it.

37f1_1 (2).jpg

This is a direct replacement for Amal 26mm, 600 series concentric carburetor.

The spacing for the flange is 2" on center. This can be jetted to your specifications or it is preset for 500 British twins. This carb will accept your current stock throttle cable and air filter. This PWK 26 mm 26J, has gone through strenuous and extensive testing and development, to bring you an alternative to the poor design of the Amal and the costly price of the Mikuni.

You can convert this carb to a left or right hand application by moving the idle screw to the other side for easy access. The fuel enricher plunger and air mixture screw remains on the left side, similar to MK3 Amals. Comes complete with everything you see in the picture, drain lines, o-ring, and one carb.

[Timmy250]

Could this be a B type 200 head? Might have had a smaller intake port. Just a thought. Matt

I am pretty sure that the intake valve is larger than the exhaust. If the 200 had a 25 mm intake port, but different size valves, then that might be a better guess.

Tim

[DewCatTea-Bob]

Could this be a B type 200 head? Might have had a smaller intake port. Just a thought. Matt

I am pretty sure that the intake valve is larger than the exhaust. If the 200 had a 25 mm intake port, but different size valves, then that might be a better guess.

Tim

____ I'm somewhat surprised that d.d./Matt would suggest such, as I'd expect (with his extensive knowledge), that he'd already know that the 'square' head-bolt pattern of 200-models is-not compatible with the rectangular-pattern of 250-models.
Perhaps however, I may-not be properly understanding as to what he exactly means by "B type" 200-head...
__ I assumed he's referring to the later-type of 200-motor, which is significantly updated with respect to the earlier 175-based 200-motor type. _ However, the cylinder-heads of both those types of 200-engines, have no significant differences (which I'm aware of).
And-also, I've never heard-of ANY 200-model (even made by Mototrans), which employed cyl.heads based-upon the 250-head design (which could also fit on a 250-motor).
If there's indeed any such animal, however,, then I'd be very hungry to eat-up all I can of it !

[DewCatTea-Bob]

[quote= Timmy250 ...
" I will train myself as best I can to shift properly, my first training will be to not to shift into 2nd from 3rd when I'm looking for 4th because I instinctively shift up to shift up! "

____ UP for up-shifting may seem logical (in a nonfunctional way),, however due-to the fact that it's functionally-easier for a foot to apply pressure by pressing-down (more-so than by lifting-up), then it makes GOOD-sense for rather-important UP-shifts to get done more reliably (than relatively UNimportant down-shifts) !
__ So Ducati had it RIGHT, (and the Jap.bikes got it wrong) !



" About the new piston, here is the verbatim description, and is all I really know:
"Top quality forged piston kit for Ducati 250cc & 350cc bevel drive singles. These pistons are exact copies of the cast Borgo pistons
Pistons have the stock compression ratio
Please measure you existing piston and order the size you need from the pull down menu."
It is 76.5 mm. "

____ The "stock compression ratio" varies -(8:1 ; 8.5:1 ; 9.2:1 ; 9.5:1 ; 9.8:1) depending on the engine-model...
I'm led to guess that since you have chosen a piston-diameter that's greater than the max.bore-size -(75.0mm) made by Borgo for 250s,, then thusly, you probably have a w-c.350-piston (which was meant to have a 9.5:1-cr.). _ However, installed within a 250-engine, the resulting comp.ratio ought end-up only being just-merely 7.4:1, (and certainly no higher than 7.9:1 !),, which will considerably reduce engine-power (especially compared-to the rather high-comp.ratio MC.piston you replaced) !
__ So anyhow, what was your reason for replacing the MC.piston, in the first-place ?



" And the distance between pin and piston circumferential squish area is greater than the MC-piston that came out, needing shimming of barrel. "

____ Raising-up of the cyl.jug/barrel, will have reduced your comp.ratio even more-so, (so you'll be lucky if your engine even has as much as 7.2:1-cr.) !
__ Assuming that you were already aware of this lowered compression situation,, did you go-on ahead with it because of a bad-leg (for kick-starting), or is your project-Duke rather intended for a kick-shy woman-rider ?



" Seems to work. "

____ Well, it should make kick-starting considerably easier, (especially for dealing-with & working against the more-intense compression difficulty produced by a mild Monza-cam, [in relation to other, wilder cam.models] ) !



" I have ordered a 26 mm PKW flat-slide carb that is supposed to be a direct replacement for 26 mm Amal carb used on Brit bikes in the 60's, but better. "

____ I've seen those rather more-modern carbs listed on eBay,, but can't say for sure whether they're actually "better", however I'd tend to expect so.
I'm suspecting that you've chosen a better replacement-route than choosing to go-with either an Amal or an old Mikuni.



" Will report back on my experience when I get a chance. "

____ I'm sure I'm not the only one who's looking-forward to that ! ... As I suspect that after you've given a good/thumbs-UP report, that then many others with Monza-models will also choose to go that same carb.replacement-route.



" Here's a pic and description of it. "

____ I've re-posted your posted-pic so we can now have a better look-see at that carb.model.
__ If it lives up to it's claimed sales-hype, then it really ought-to be a good carb.option for all 250-Monza models.




" This is a direct replacement for Amal 26mm, 600 series concentric carburetor.
The spacing for the flange is 2" on center. "

____ It's nice that there's finally another carb.choice (other than the stock-carb or an old Amal) that can be a straight bolt-on affair (without having to screw-around with manifold-adapters [like with MIKUNIs] ) !
__ Also, it's more modern cold-starting method ought provide for superior results, compared with the others' air-choke setups.



" This can be jetted to your specifications or it is preset for 500 British twins. "

____ Whether pre-jetted for such as that, or, a 250-single or 750-tripple Brit.bike,, the same jetting ought-to be quite close enough for most-any 250-Duke, (without NEED for mussing-around with it).



" This carb will accept your current stock throttle cable and air filter. "

____ That statement is no-doubt aimed at Brit.bikes which came-stock with Amal-carbs, only.


Hopeful-Cheers,
-Bob

[Timmy250]

Bob, man, you're questions are harsh! Are you a trial lawyer? Ha, just joking, I appreciate it.

I didn't realize that the larger 350 piston would reduce c.r. I might be glad it did, as it is now, kicking it over equires a big old full body leap and shove. Judging just by the kick start effort now, the c.r. is just as high as it was with the old piston in it. If my plan was to make it so my 115 lb girlfriend could start it, I don't think it would have worked, she would struggle mightily to kick it over. I would say couldn't do it with a very bad leg either . I won't be racing this bike, and power seems good to me, tons of low-down grunt. Sounds great accelerating. I'm happy with it, except the poor idle and part throttle cruising, spitting and erractic, which I am hoping new carb will fix. Nice at full throttle though.

Speaking of the old piston, it was badly scuffed, with some bright shiny spots. If it wasn't completely seized at some point, it was close, both cylinder and piston showed some metal to metal contact time. So, I needed a new piston with a re-bore size one bigger than the 76 mm in it. Since the 76 mm made me assume it already had a 350 piston in it (in my searching, I never saw a listing anywhere for a +2mm 250 piston) the 350 looked like the ticket, glad it wasn't a major glitch. Low c.r. doesn't seem major, and maybe makes it more practical. I'll use that rationalization, anyway.

I have heard that jetting for a single cylinder is in general richer than a multiple, even with similar displacement per cylinder. Do you have different experience from that?

Thanks again, when the carb comes, I'll see how it goes.

Oh, by the way, after hearing all the kick starter fork spring issues, I went ahead and fashioned a piece of 1/8" steel bar stock to extend from the bolt point to the fork tines, so about 3/8" of the flex is taken out of the spring from its original point at the bolt head. We'll see if that works.

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" man, you're questions are harsh! "

____ Well, they gotta be asked someway.



" I didn't realize that the larger 350 piston would reduce c.r. "

____ A larger/increased piston dia.size itself, doesn't have any effect on the comp.ratio,, unless the squish-band clearance is reduced to near-zero, (and it's with THAT unlikely situation that I came-up with the [rather optimistic] "7.9:1" c.r.).
The reason that a 350-piston's resulting compression-ratio is lower than a 250-piston's c.r., is because the dome-top of the 350-piston's crown is-not as tall as that of any 250-piston.
And also,, the reason that a 350-piston's rated comp.ratio is reduced within a 250 -(actually 266cc in your-case), is simply because there's then only 78% as much cylinder-volume to be compressed (into the same chamber-volume at TDC) !



" as it is now, kicking it over equires a big old full body leap and shove. "

____ That's little-doubt probably because you (most often) merely work just your own self against the compression, (with only random assistance from the flywheel)...
It seems you need to pre-work the kick-lever (between each start attempt), so as to bring the piston towards TDC and bleed-off the comp.pressure (until you feel the piston reach TDC),, and, (after having reset the kick-lever's angle of engagement to your best advantage), THEN kick-through, and thusly allow the flywheel a sure-chance to FULLY assist with getting you through the next comp.TDC/power-stroke. _ That way, YOU-yourself then don't need to put so much effort into your kick-start attempts.



" Judging just by the kick start effort now, the c.r. is just as high as it was with the old piston in it. "

____ Then perhaps the previous (worn) ring-gap wasn't so up to spec as you now-currently most likely have it refreshed to.
Cuz after-all, there HAS to be some difference,, as you've taken your comp.ratio from one extreme, to the other !



" If my plan was to make it so my 115 lb girlfriend could start it, I don't think it would have worked, she would struggle mightily to kick it over. "

____ With the application of the right kick-starting technique, (as I've gone-over above),, she too, ought-to experience success as well.



" I'm happy with it, except the poor idle and part throttle cruising, spitting and erractic,
Nice at full throttle though. "

____ Seems likely that your fuel-mix adj.screw isn't set at it's optimum-setting.



" I needed a new piston with a re-bore size one bigger than the 76 mm in it. Since the 76 mm made me assume it already had a 350 piston in it (in my searching, I never saw a listing anywhere for a +2mm 250 piston) "

____ You ought-to have posted your concerned issues here, before-hand.
__ The only 250-pistons greater than 75.25mm (that I know-of), were made by 'MC Supply', and that supplier would've had .090" & .100" 250-oversizes for addressing cyl.bore concerns such as yours.
(I still have an example of the .090" oversize, which is near 76.3mm.)



" glad it wasn't a major glitch. "

____ Actually, even if it were-so, (in that a larger-sized & workable piston wasn't available),, you rather could've gotten a new cyl.liner/sleeve and fit a piston other than the new 350-piston you've chosen-to.



" Low c.r. doesn't seem major, "

____ Your resulted comp.ratio may be only 7.5%-down from stock.
__ Do you know how much clearance-space your squish-band ended-up with ?



" I have heard that jetting for a single cylinder is in general richer than a multiple, even with similar displacement per cylinder. "

____ In the case of some Brit.twins where a SINGLE carb feeds BOTH cylinders,, then yes, it stands to reason that the carb doesn't need to be jetted as richly (since the fuel has already been pulled-up & pre-suspended by the previous action of the other cylinder). _ However, that added effect on mixture is-not greatly significant, (and is almost akin to the same effect as altered camshaft-timing has), and is less important than the effects which varying exhaust-systems cause on the carb.mix.
So the relatively small difference is-not much to be concerned with, unless you've already been concerned with fine-adjustment such as 'tuning' the carb.mix to be optimally-set for your particular ex.system.



" Do you have different experience from that? "

____ My-own experience has been that if a carb has been jetted to properly feed a 4-stroke single-cylinder, it will remain close-enough for feeding any other of the same, (regardless of being just a sole-cylinder, or part of a bank of cylinders [with independent carbs] ).
In other-words,, a carb meant to feed one cylinder of a 750-triple, will require NO jetting-change for feeding a single 250-cylinder,, (unless of-course the triple has balance-tubing interconnecting it's intake-ports).



" after hearing all the kick starter fork spring issues, I went ahead and fashioned a piece of 1/8" steel bar stock to extend from the bolt point to the fork tines, so about 3/8" of the flex is taken out of the spring from its original point at the bolt head. "

____ Did you get the notion for that modification/fix from one of my old posts, or did you also come-up with that idea independently ?
__ For myself, I had noted that the leaf-springs were always getting bent right-near the washer under their mounting-bolt,, so I reasoned that a rather stiff metal-strip included under the washer and atop the springs, would prevent the springs from getting so easily bent again. _ But instead of using such a thick piece of steel-bar, I recall rather using a piece of a bracket removed from an old ign.points-cover,, which worked rather well for backing-up the springs, cuz IT wouldn't remain permanently bent (after another wild kick-back).
__ Along-with your thick piece of backing-plate,, I hope you thought to replace the rather short original-bolt, with a suitably longer one. _ Cuz if your rather tough backing-plate ever gets clobbered really hard, then the bolt-post will have-to absorb more of the shock, (and it's hard-saying exactly WHAT may give-out, [since the springs will no-longer absorb as much of the shock] ).



" We'll see if that works. "

____ It would be nice to see a picture of exactly what you've come-up with,, but whatever,
since you have a 250-Monza engine (with an AAU), I'm pretty-sure you won't experience any kick-backs strong enough to bend your leaf-springs out of working shape.
__ It's rather those who have Motocross & Mark-III 250-motors, who most need to-be concerned about wild-ass kick-backs that can really launch the ks.gear out against their engagement-springs !


Hopeful-Cheers,
-Bob