2 ques, shifter box and modern carb

[Timmy250]

Hi, I have a recently acquired '62 250 Monza, narrowcase, 4 speed. Just finishing getting it back together after partial restoration from its complete but rough as-found condition.

Anyway, engine is 4-speed, but someone appears to have installed a later 5-speed shifter control box. Already saw some great ideas to help improve shifting, which isn't working well right now, but before doing a lot of slouthing and clutch/eccentric adjustments, will this 5-speed box work with the 4-speed tranny? Are the detent stops with 5-speed at the correct places for 4 speed drum/forks? When the tranny is in 4th, the shifter box still has another detent stop to go, but the drum and forks stop it from going further... Can't tell if false neutrals are just eccentric adjustment or endemic to wrong shifter.

2nd question: does anyone know of a good modern replacement for the Dellorto 24 ubf that doesn't require a lot of modifications? If so, approximate direction for jetting, etc.? The old carb may be beyond getting it to function properly, too much corrosion.

Thanks, appreciate any thoughts,

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" engine is 4-speed, but someone appears to have installed a later 5-speed shifter control box.
will this 5-speed box work with the 4-speed tranny? "

____ I've before found the reverse of that parts mismatch, and the 4-speed shifter worked find on the 5-speed motor, (5th.gear wasn't accessible, is all). _ So similarly-likewise, as well,, the parts combo which you have, ought-to work for all four gears !



" Are the detent stops with 5-speed at the correct places for 4 speed drum/forks? "

____ Yes, I'm pretty-sure that they indeed are... It's been many decades since I've checked, but I recall comparing the indentation-locations in both 4 & 5 speed selector-wheels, and the first five (including the neutral-spot) locations were set & spaced the same on both, (the 5-speed version simply had a 6th.location further spaced).



" When the tranny is in 4th, the shifter box still has another detent stop to go, but the drum and forks stop it from going further... "

____ Right, as there's no further extended fork-slot in the 4-s.selector-drum to allow that drum to rotate any further past the 4th.gear-position.



" Can't tell if false neutrals are just eccentric adjustment or endemic to wrong shifter. "

____ It's certainly not due-to "wrong shifter",, and-also, the eccentric-adjustment setting is-not a possible factor involved with incomplete gear-engagement ! _ As that adjustment can only affect just the 'resetting' of merely the selector-mechanism itself, (and can't possibly work-through to any of the motor-internals).
__ So since those two suspicions are out of contention, I'm wondering when & how you could possibly manage to find any "false neutrals" ?
Can you elaborate on your related issue ? _ Do you 'press' steady-pressure against the shift-lever (until you have found that the shift has been completed), or rather 'jab' at it (with just mere hopes that the shift-attempt has been successful) ?



" does anyone know of a good modern replacement for the Dellorto 24 ubf that doesn't require a lot of modifications? "

____ Simplest replacement would be an Amal 26 or 27mm carb, possibly from most any 1968-74 Brit.bike.


Hopeful-Cheers,
DCT-Bob

[JimF]

I run a bike with a Mikuni VM26.

I started with this configuration:

140 main
30 pilot
182-02 needle jet
5DP7 needle
2.5 slide
0.5 air jet

If you go this route I could take my carb apart and record where I ended up at.

I have the scrambler' metal can air filter on the carb mouth and that says "DellOrto" so for the sake of appearance it looks OK. It gives me nice engine response from an idle to full throttle.

[Timmy250]

Thanks a bunch, Jim and Bob! Haven't had it out to try shifting technique, jab is what I'm used to, seems to work on other European as well as Japanese, but makes sense that pushing until mesh is positive. Definitely has a problem getting claw back to mid point between pins, bought a new spring, but adjusting eccentric and getting good clutch disengagement are next on list, good news on parts I have being compatible.

Jim, just checking, but the 24mm carb fits intake diameter smoothly, does 26mm amal leave a smaller diameter intake ridge where they mate without issue? Or did you grind to mate the crab to head? Thanks again,

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" Haven't had it out to try shifting technique, jab is what I'm used to, seems to work on other European as well as Japanese, but makes sense that pushing until mesh is positive. "

____ Indeed, that certainly DOES make "sense" ! ...
The rather common (and untrained) toe-jabbing shifting-technique is an inferior shifting-method for most-ALL motorcycle-transmissions ! _ So seeings-how your overly quick toe-movement releases the shift-lever BEFORE fully releasing the clutch-lever ALL the way back-out,, THAT rather non-methodical manor of shifting is NO-DOUBT the certain cause of your missed-shifts (into false-neutrals) ! ...
__ Here follows a couple of links to related posts on this matter... viewtopic.php?f=3&t=26&hilit=toe+jabber&start=10#p257
viewtopic.php?f=3&t=1057&p=7156&hilit=toe+jabber#p7156



" Definitely has a problem getting claw back to mid point between pins, bought a new spring, but adjusting eccentric "

____ Such as that can certainly be quite common on long used motors.
__ Here follows a link to a related thread-posting, in which you ought find another link to still another related post, (also from back in mid-2012)... viewtopic.php?f=3&t=626&p=7894#p4035



" the 24mm carb fits intake diameter smoothly, "

____ Are you really sure of that size of inlet-port diameter ? _ If so, then perhaps you have a GT-cyl.head.
If you have a stock Monza-cyl.head, then it ought-to have a 26.5mm intake-port.
__ The smallish 24mm carb.size was most likely due-to holding-down production-costs. _
And that size of carb on a 250-engine, only made good-sense just for the GT-model.



" does 26mm amal leave a smaller diameter intake ridge where they mate without issue? "

____ Yes, the inlet-track mating diameters (with 26/27mm-carbs) are a better dia.size match (than with the stock 24mm carb). _ Which is why I recommended a 26 or 27mm sized carb.


Hopeful-Cheers,
DCT-Bob

[Timmy250]

Thanks again Bob. I'll have to measure the intake port diameter, but pretty sure the carb and intake are matched at 24 mm, appeared so when casually fitting together, maybe I just assumed. I didn't realize the GT head was different, so, Monza = 26 mm and GT = 24? Could be GT head, the bike is definitely a hybrid, it's titled as a '62 Diana, I was told someone took all the Diana parts off and replaced with Monza parts. Monza body parts fitted now.

A couple of the engine covers have "175" cast inside, maybe crash damage replacements? A surprising find was the piston was stock 350 size, 76 mm. I fitted the next size up, my machinist says there is adequate material remaining. Had to shim the barrel to get squish correct (roughly 30 thousandths, by my eye, anyway - ha, well, sorta joking, but close enough) the piston I removed must have been way off, much too large squish, the crown to pin distance was much smaller than the replacement piston I fitted.

BTW, the motor number is DM250 80212, which seems to be pretty early, '62 accurate? Foil stamp on frame matches that engine number which would seem to belie the Diana story, if the foil is original?

Great resource here in forum, managed to get pretty far on the bike without terribly screwing up, but could have asked questions sooner to clear up a few mysteries. Thanks again,

Tim

[DewCatTea-Bob]

[quote= Timmy250 ...
" pretty sure the carb and intake are matched at 24 mm,
I didn't realize the GT head was different, "

____ The later GT-cyl.heads (and all internals) are exactly the same as a Monza-head, but the early GT-heads have a smaller inlet valve-seat (with a 33mm in.valve & a real GT-camshaft).
I-myself have never measured the in.port of an early GT-head, but I've been told that it's barely only 1-inch (about 25mm) in diameter.



" so, Monza = 26 mm and GT = 24? "

____ I'm not sure about the exact diameter of the early-GT's, however I do KNOW that the 250-Monza & later GT in.ports are 26.5mm (+/- .15mm) !



" Could be GT head, "

____ I'd tend to doubt that it's an early GT-head, (due-to their rarity),, and there's no way to tell-apart a later GT-head from any Monza-head.



" the bike is definitely a hybrid, it's titled as a '62 Diana, "

____ Do you actually mean 'Diana 250' ?
Diana-heads are also exactly the same as all Monza-heads.



" I was told someone took all the Diana parts off and replaced with Monza parts. "

____ As far as the 250-motor goes,, that would-not make much sense, since the Diana-engine is no different than a Monza-engine.
However, in the case of a 'Diana Mark-III',, it was a fairly common practice to acquire the hot Mark-III engine-parts and replace them with (milder) Monza or Motocross engine-parts.



" A couple of the engine covers have "175" cast inside, maybe crash damage replacements? "

____ No, not likely ! ... The original narrow-case motor was a '175',, and any such interchangeable parts which have remained unchanged and-so still found on newer/updated motors, ought understandably still also remain so cast-marked, as well.



" A surprising find was the piston was stock 350 size, 76 mm. "

____ That's something that's often done by Duke-collectors who have to juggle-around their various spare engine-parts, in order to save on replacement-costs. _ Some others install 350-pistons thinking that engine-performance will be increased,, not realizing that the resulting extra 16cc.capacity will be pretty-much canceled-out (power wise), due-to lowered compression.



" the piston I removed must have been way off, much too large squish, the crown to pin distance was much smaller than the replacement piston I fitted.

____ You may've removed a rather flat-top Sebring-piston.
Do you know what piston-model your replacement piston was ?



" the motor number is DM250 80212, which seems to be pretty early, '62 accurate? "

____ I'm not sure (for motors that far back), could possibly be a 1961, I suppose.



" Foil stamp on frame matches that engine number which would seem to belie the Diana story, if the foil is original? "

____ The foil-tag should state 'Diana 250' in the model-name line-box.
Can you post a picture showing your 250-frame's foil ?



" could have asked questions sooner to clear up a few mysteries. "

____ Wish you had, as that's what we mainly exist for !


Duke-Cheers,
-Bob

[Timmy250]

guzzino_2263_56937357.jpg

[img]C:\Users\me\Desktop\guzzino_2263_56937357.jpg[img]

Bob, intake port indeed = 25 mm exactly, would have photo of caliper reading, but too awkward with only two hands , funny that the carb/intake port gasket that came in the gasket kit I bought listed for 250 NC Monza measures just under 25 mm, same diameter as plastic isolation block, would really obstruct if my intake port were 26.5mm instead of the 25mm it is. I guess there's another mystery, I ordered a new plastic isolation block, listed to fit Monza, it's also at 25 mm - the one on the bike was 27mm, seemed a mismatch to port and carb/gasket, so ordered for Monza. The parts suppliers must be selling stuff listed as fitting Monza, but really fitting old, rare GT heads. The gasket and block I purchased would really fit poorly if my intake were the more common Monza at 26.5mm.

foil doesn't specify the model name, no words, only numbers, hard to read in pic, but no words, just 250.

I think the piston that came out is not oem, neither is my replacement, thanks,

Tim

[double diamond]

Tim, The original piston you provided a pic of is an MC piston. These were common replacements in Ducati singles since they cost a lot less than OEM Borgo pistons. The MC piston crown did not match the squish band of the Ducati head well. The frame tags of the early Monza and Diana had either a “D” or an “M” accompanying the “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. Obviously on your tag the letter would be after the number but I do think I can barely make out a letter. If it’s a D, it left the factory as a Diana, if M it was a Monza. But as Bob mentioned, they were mechanically the same, the difference being in body parts and paint color. What color is the frame underneath the frame tag? The early Monza frames were gold, the Diana was blue. 80212 is a pretty early number. I expect the number is stamped on the left case half and the DM250 is on the right which would be consistent with a 1961 or ’62.

Matt

[DewCatTea-Bob]

[quote= Timmy250 ...
" intake port indeed = 25 mm exactly, "

____ Quite interesting, as I-myself have never measured any 250-head which had an inlet-port mouth-hole of less than 26.4mm,, nor had I ever before even heard-of more than one other 250-head* which was claimed to have an in.port-mouth of merely just-about an "inch", (* off-from an early-GT).



" would have photo of caliper reading, but too awkward with only two hands "

____ Were you sure to take your most competently-done measurement-reading with the caliper-prongs placed into the port-hole's mouth-opening at whatever position-angle yielded the greatest reading-figure ?
__ It's now (so far) seeming that you may indeed have a real GT-head,, but for that to be the actual case, then your 250-head ought-to have both of it's valves with the same 33mm head-size. _ Have you yet checked-into that as well ?



" funny that the carb/intake port gasket that came in the gasket kit I bought listed for 250 NC Monza measures just under 25 mm, same diameter as plastic isolation block, "

____ The stock factory-setup only included just a black-rubber isolation-gasket between the carb.manifold-flange & cyl.head-port, (but your stated-wording seems to refer-to two separate gasket-pieces for that location ?).
__ Anyhow, those gasket pieces really ought-to actually have a hole-dia.size somewhere in-between 24 & 25mm, as they were intended to specifically match just the stock 24mm-carb's port-flange, (and not particularly the cyl.head-flange's inlet-port itself).



" would really obstruct if my intake port were 26.5mm instead of the 25mm "

____ Well, that would of-course be true, IF you were to replace the stock 24mm-carb with any carb.size that's any larger.
__ Concerning the stock rubber manifold-gasket,, I've many times found upon removal of an over-tightened carb (against the head), that the rubber had become overly compressed and-thus squeezed-out & into the port-way. _ Which after having been left that-way for so long, it's resulted hole-shape left it with only an oval-diameter of just 23.5x22mm (if not even worse !).



" I guess there's another mystery, I ordered a new plastic isolation block, listed to fit Monza, it's also at 25 mm - the one on the bike was 27mm, seemed a mismatch to port and carb/gasket, "

____ The 27mm rubber-gasket which you originally found installed, was actually meant for a 27mm intake-manifold (for a 250Scr/Motocross),, however THAT rubber-gasket can fit against a stock Monza-head quite well enough, cuz after being adequately compressed (between the carb.manifold-flange & in.port-flange), it then becomes a good dia.match for the Monza-head's 26.5mm port-mouth !



" The parts suppliers must be selling stuff listed as fitting Monza, but really fitting old, rare GT heads. "

____ It really wouldn't matter whichever of those cyl.head-models the 25mm-gaskets are intended for, as both of those (stock) Duke-models employ the very-same 24mm-carb !
__ (If I-Myself had been in charge at Ducati back in those-days, then the Monza -[named-after a famous road-racetrack], would've instead gotten a 27mm-carb !)



" The gasket and block I purchased would really fit poorly if my intake were the more common Monza at 26.5mm. "

____ Again,, those inlet-port pieces with 25mm-diameters, would only interfere with the inlet-tract's air-flow, providing that your chosen carb is actually larger than the stock-carb.size, (as of-course the airflow's tract-pathway can't be further restricted by them, any more-so than that which the 24mm-carb itself already does).



" foil doesn't specify the model name,
hard to read in pic, "

____ Yes, your foil-tag picture is indeed difficult to see very well.
So I've posted another pic.version of it which has been adjusted in attempt to improve on it's view of your tag's stamped data,, but even-so, there's still certainly no sign of a complete model-name !



" I think the piston that came out is not oem, "

____ Indeed-so, as it's actually a 10.5:1 'MC Supply' forged-piston, and probably their 8th.oversize -(74mm + .080") 250-piston,, (not a "350" piston as you had suspected).



" neither is my replacement, "

____ Your replacement appears to be a w-c.350-piston.
Can you tell us anymore about it, (such as what markings it has stamped into it's crown-top) ?


Duke-Cheers,
DCT-Bob