450 Scrambler /jupiter project

[john jupiter]

Ok, huge spark out of the plug in there now with .8mm gap but ill get some new ones anyway.. Is the consensus plug choice NGK b6hs or b7hs?
The engine luggs so much in first gear that i thought i was in 3rd.. Came back and measured 5.75 engine rotations per tires rotation

[DewCatTea-Bob]

" huge spark out of the plug in there now with .8mm gap "

____ Have you been using & maintaining that same gap-size all along ?
Has the rest of your ign.system been kept all stock ? _ Cuz I don't think it was intended to run with exactly a .032" gap.
Have you ever tried any other gap-sizes, as small as .024" ?


" Is the consensus plug choice NGK b6hs or b7hs? "

____ For racing & constant hard-riding, use the B7HS,, and for constant easy-going & lower-RPM running, the B6HS is less likely to get fouled-up.
Have you tried a BP_HS ?


" The engine luggs so much in first gear that i thought i was in 3rd.. Came back and measured 5.75 engine rotations per tires rotation "

____ Have you enough experience with Duc.Singles to realize what their shift-pattern is ? _ Cuz the high ratio you've stated has got to be 5th-gear !
I figure that to get your 5.75 crank-rotations per wheel-rotation, you must then have either 34/12t or 36/13t sprockets and have to be engaged-into 5th-gear, during your rotation-test, (as stock 35/12t gearing would produce very-nearly 6 complete turns of the crankshaft, per rear-wheel turn,, and of course lower-gearing would produce still more crank-turns!).
__ Please let us know what seems to be the circumstances with your gearing & rotation-test.


Hopeful-Cheers,
-Bob

[Bevel bob]

As DCT-Bob says, sounds like you are in a high gear, you do know these bikes are one up 4 down??.

[john jupiter]

____ Have you been using & maintaining that same gap-size all along ?
Has the rest of your ign.system been kept all stock ? _ Cuz I don't think it was intended to run with exactly a .032" gap.
Have you ever tried any other gap-sizes, as small as .024" ?

The rest of the ignition system in all stock. I have not tried any other gaps. How might a smaller gap help me?

" Is the consensus plug choice NGK b6hs or b7hs? "

____ For racing & constant hard-riding, use the B7HS,, and for constant easy-going & lower-RPM running, the B6HS is less likely to get fouled-up.
Have you tried a BP_HS ?

I have not tried a BP plug but i picked one up today when i purchased a few B6HS plugs today at the marine supply. Whats is your opinion on the BP plug?

" The engine luggs so much in first gear that i thought i was in 3rd.. Came back and measured 5.75 engine rotations per tires rotation "

____ Have you enough experience with Duc.Singles to realize what their shift-pattern is ? _ Cuz the high ratio you've stated has got to be 5th-gear !
I figure that to get your 5.75 crank-rotations per wheel-rotation, you must then have either 34/12t or 36/13t sprockets and have to be engaged-into 5th-gear, during your rotation-test, (as stock 35/12t gearing would produce very-nearly 6 complete turns of the crankshaft, per rear-wheel turn,, and of course lower-gearing would produce still more crank-turns!).
__ Please let us know what seems to be the circumstances with your gearing & rotation-test.

Errrr of course i knew it was an inverted shift pattern!...... Hahah. It went through the gears nicley this morning once i stopped trying to start off in 5th...

New plug, sunny day about 65 in CT. Took it about a mile this morning. Idle still wandering a bit. Seems to prefer to start without the choke this evening even though engine is cold.. After i took e choke off, it started and ranvery slow for about 30 seconds and stalls, same stall if try to open throttle a bit.. No luck starting with choke.

Noticed my superpractic throttle to be very soft as far as snapback compared to my brothers tommaselli daytona.. Wondering if that could be part of my idleing problem(cable might be getting hung up jsut a bit) also wondering about this carb. im no expert but it sure is tempermental starting.
Ive also been trying not to redo the original crusty wiring but i may just do that to eliminate one possibility.

[Bevel bob]

A 32 thou plug gap puts the ignition under more strain than a 24 but may not be a problem, difficult behavour at tickover can be from too much ignition advance,which is why I suggested reducing the points gap as an experiment to see.

[DewCatTea-Bob]

By: john jupiter...
" How might a smaller gap help me? "

____ Well, it should be that a larger gap should be superior for igniting a charge but,
while a more modern ign.system that's meant to run with it's plug gaped at .060", might still perform well enough with a .080" gap,, I'd still doubt that it's designer would agree that ya can simply go-ahead & set the plug-gap as large as ya wish.
__ And the stock-Ducati ign.systems certainly weren't 'state-of-the-art' back at the time when they were installed on our old DUKEs, so their plug-gap settings were accordingly relatively small. _ And so understandably, it ought be expected that stretching-out their plug-gaps could lead to inconsistent sparking.
So reducing the gap-size to that recommended by Ducati, ought to be maintained, at least until all your bugs have been worked-out,
(although at the possible expense of easier firing-up).
Smaller plug-gaps help prevent juice-bleeding through insulator-deposits built-up on used spark-plugs.
If you increase the gap-size, then you should replace the metal-conductor wire-type spark-cable with 'resistor' type cable,, but then, that mod ought be in combo with a fresh/modern ign.coil.


" Whats is your opinion on the BP plug? "

____ I believe them to be superior, (providing that there's enough space for their extended nose), as they have an advantage of staying clean without getting too hot.
__ If you only got one of those type, then save it for after you've got all your bugs worked-out, as it won't stay as clean as regular/B6HS plugs will.


" Errrr of course i knew it was an inverted shit pattern!...... "

____ To my long-experienced opinion, the Ducati shift-pattern is as perfect as can possibly be !
As pressing-downward to shift to successive gears is easier for the more important success of up-shifting, than for the much less demanding need for down-shifting !
__ Also I wish to point-out that real MotorCycles had always had the foot shift-lever located on the Right-side, and sissified motor-bikes began the feeble notion of shifting on the left-side.
So I'm of the opinion that if it shifts on the left, then it must be a mere 'bike' ! _ And of course a Duke is thus a true 'Motorcycle' !


" Took it about a mile this morning. "

____ That's not long enough to get the oil heated up to operating-temp.


" Idle still wandering a bit. Seems to prefer to start without the choke this evening even though engine is cold.. After i took e choke off, it started and ranvery slow for about 30 seconds and stalls, same stall if try to open throttle a bit.. No luck starting with choke.
also wondering about this carb. im no expert but it sure is tempermental starting. "

____ Are you experienced enough with carbs to realize that your 450 doesn't really have an actual 'choke' ?
Thus your starting-lever should be pulled-open, (rather than let shut, like with a choke), for getting a cold motor started ! _ And once warmed-up a bit, then release the lever back to full-off position, (just the opposite of a true choke set-up!).
__ So it will help to know exactly what you've BEEN doing !


" Noticed my superpractic throttle to be very soft as far as snapback compared to my brothers tommaselli daytona.. "

____ It should have a damper-screw, do you have it set too tight for your preference ?


Hopeful-Cheers,
-Bob

[john jupiter]

A 32 thou plug gap puts the ignition under more strain than a 24 but may not be a problem, difficult behavour at tickover can be from too much ignition advance,which is why I suggested reducing the points gap as an experiment to see.

Bevel Bob, i am Going to try this as well. Problem is.. Sometimes she likes to start... And sometimes she doesnt... One stall at the wrong time and experiment over, which was the case when i tried this on sunday.

[JimF]

As for the Super-Practic snap back, you could also look to the spring inside the carb to be weak though I have never found this to be a problem. Perhaps your throttle cable is binding?

As for the wander, this could be related to a worn carb slide.

It might be a good exercise to open the carb top up. In a couple of seconds you could check to see that the throttle cable slides smoothly in the sheath when it is detached from the slide.

Another couple of seconds you could also check the spring is OK.

In another couple of seconds you could pull the slide up and down in the carb body and check for excessive slop.

You can also check the cut of your slide (for future reference) if you haven't already and also note what notch the slide is set at along the needle. You can also check what needle you have.

I also like setting the carb stop when there is no tension on the cable.

[john jupiter]

As for the wander, this could be related to a worn carb slide.

How much "slop" is ok? Its def not a precision fit.
I checked the usual sources for a new slide but it doesnt seem avalible.
If i needed to buy a new carb, any reccomendations on what to go for? I Dont mind going older for style or or bigger for performance

It might be a good exercise to open the carb top up. In a couple of seconds you could check to see that the throttle cable slides smoothly in the sheath when it is detached from the slide.

Another couple of seconds you could also check the spring is OK.

In another couple of seconds you could pull the slide up and down in the carb body and check for excessive slop.

You can also check the cut of your slide (for future reference) if you haven't already and also note what notch the slide is set at along the needle. You can also check what needle you have.

I also like setting the carb stop when there is no tension on the cable.[/quote]


I'll go through it one more time and report back. I noticed there are two differnt wieght springs listed as replacments.. I have a V7 needle set on the middle groove.
Im not sure what you mean by "check the cut of the slide". What am i looking for?

[DewCatTea-Bob]

" How much "slop" is ok?
I checked the usual sources for a new slide but it doesnt seem avalible. "

____ Unless the carb & slide have over 10k-miles of use, it's doubtful the slide is worn-out, (which means your current slop is normal),, I doubt it's already worn-away more than .003", and nothing under .010" should make any real difference.
So you shouldn't need a new one.


" If i needed to buy a new carb, any reccomendations on what to go for? "

____ The stock 29mm-carb is certainly on the small side for a 450-single ! _ So 450-DUKEs ought to have at least a 30mm-carb, (like the 1973-350s came with).
__ You ought to check-out most posts placed by MotoMike, as he also has a 450 but with a 32mm-carb. _ Find one of his posts about a '32mm-Amal', and try asking any questions, from there.


" I noticed there are two differnt wieght springs listed as replacments.. "

____ Unless your return-spring is busted, it ought still be up to doing it's job, (as I believe you're using a new throttle-cable).


" Im not sure what you mean by "check the cut of the slide". What am i looking for? "

____ That's common biker-talk for the 'Slide-Number', which rates the value of the 'cut-away' variance of the slide's inlet side... Larger inlet-side*slide-openings (referred to as the 'cut-away'), cause leaner conditions,
(* compared to the lack of any cut-away on the slide's opposite side).
__ If there were no 'cut-away' at all, then both front & rear sides of the slide would look the same, (and the mix would then be extra very rich from off idle, up-to over half-throttle).
It is possible to put the slide in backwards, which would then cause quite rich & very poor running ! _ (Not to mention possibly also curtailing proper return-spring operation.)
So it's fairly good to know all about slide 'cut-away' !


Dukaddy-DUKEs,
-Bob