At wits end with ignition - need help!

[STEVENM63]

your AAU is the magneto type. notice the short cam lift duration compared to the longer lift of a battery ignition unit.

image.jpg

Thanks. So it appears that you and Bob have helped me determine that my rotor/flywheel assembly is not set up correctly. The plot thickens... I will have to obtain a flywheel tool and get it set up right. Now I should also be able to get a good look at the mag coils as well.

Steve

[DewCatTea-Bob]

[quote= STEVENM63 ...
" I did a brief test with a 12 volt battery
The bike was able to be started and seemed to rev okay "

____ If that confirms that the particular ignition-matter (which you had experience when running the ign.system off-from the mag.power) has ceased to continue (with the battery-powered ign.setup), then that results tends to confirm that your AAU's advance-range advances the ign.timing to a point when the mag.rotor no-longer happens to be timed to be producing a sufficiently peaked power-pulse.
__ Next to confirm this possibility, you could retry using the stock ign.circuit-setup and lock-up the AAU.cam-advance mechanism to confirm that the timing-concerns are all that's really wrong.



" I didn't do this very long because I noticed things were getting hot. "

____ So does that include noticing whether the ign.coil got hot to the touch, as well ?



" I also retested the coil and got consistent readings of 3.9-4 ohms. "

____ That resistance-level is good enough for being battery-powered, but it's likely too high for being matched close enough to the ign.power-coil



" I retarded the timing a few degrees from where I had set it (originally 21* based on the table specs in the manual).
I just retarded the points plate a few degrees based on feel (maybe, 8-10*).
The bike started and rev'd fine (although starting was a little harder, but still manageable). I took the bike for a quick spin and noticed that the bike ran fine until maybe mid-throttle and I would get what felt like a misfire. "

____ You didn't confirm positively for-sure whether or not you retained & continued with the temporary battery-powered ign.setup.
But if you had gone-back to the stock ign.circuit-setup (which is wired-up to the ign.coil quite differently !), then your having retarded the points-plate setting would've tended to accomplish about the same effect-result as having tried-out locking-up the AAU (as I've suggested trying-out [to confirm that the rotor-timing is off]).



" Did some more testing and investigation and experimentation with advancing and retarding the ignition timing and I was able to duplicate my previous tests. "

____ I'm left to assume that you actually mean 'test-results' (rather than merely duplicate "tests"),, and-so I gather you must've found that advancing the ign.timing back to spec (with the stock-type ign.system all correctly restored), expectedly recreated the very-same issue-symptoms once-again, as you had before. _ Correct ?



" I removed the left cover.
I did notice the position of the flywheel index mark was at 0* with the engine at TDC "
According to the manual,
a 0* rotor/flywheel position would indicate
a 250 with a 28* AAU. The 28* AAU would require a 5-8* static setting instead of the 21* static setting that I set. "

____ Apparently some wording-illiterate (but not-bad with numbers) mechanic had set both the mag.rotor & ignition timing-settings as if the engine was a battery-powered model, (so it seems !)



" So do I have the 18* or 28* AAU? "

____ You do indeed have the correct/18-degree type of AAU.cam that's stock for pre-1968 Scr.engines
!

" My timing settings were based on the 250 Scrambler, which I thought we established was what I had. "

____ When so much time elapses-by, it's not always easy to recall what specific model a faceless member-name may still remain in reference-to. _ And also, whether a '250-Scrambler' is a pre-66 n-c or '66~67 n-c/w-c or post-67 w-c model, can certainly make a significant or even critical difference !
__ Your AAU & 3-wire mag.stator do indicate a pre-68 Scr.model, but your ign.coil does-not.



" If this is correct, then the flywheel/rotor position should be 32-36*, correct? "

____ I think that may indeed be the correct recommended mag.rotor position-setting (for most n-c.Scrambler-engines), however whether your flywheel-rotor is actually original (or a stock model-type), can possibly be quite questionable (since it's apparently been messed-with since leaving the factory).



" Now I should also be able to get a good look at the mag coils as well. "

____ Might be nice to see a picture of it's wire-lead rework-job then too.
__ And,, if you could do better work, perhaps consider modifying it for any other possible power-circuit setup-schemes you may wish to rather employ in the future (without having-to get-at the stator-connections again).


Hopeful-Cheers,
Bob

[STEVENM63]

Pulled the mag rotor off and here is what I found.

IMG_4919.jpg

Obviously the wires have been changed but what can be determined about my coil from this? Do I need to change anything before I put everything back together?

[STEVENM63]

Well, I guess I can change the subject of this thread from "At wits end with ignition..." to "Wow, is this thing fast". The holiday weekend gave me some much needed project time which included work on my NC 250. My mag/rotor puller tool arrived Friday so I was able to get everything apart and reassembled (mag/rotor now at 32*). Adjusted timing again and gave it a start. Took about 5 kicks and it fired up. Throttle response seemed a lot better on the work stand.

I let it run for a bit on the stand to warm up. Idle still needs some work though (will run at low speed but needs a little bit of throttle manipulation), so I will likely need to do a bit of carb work and adjustment, but that would be for another day because I wanted to ride. Took it off the stand and restarted for a quick run around the neighborhood. Great power through the whole rev range with none of the hesitation I had before. Upon my return I removed the plug and it now appeared normal, without the fouling I had before.

So, for now, we can probably close the thread on this one, unless there is something that you guys think may assist with making startup a bit easier (although, it seems to fire consistently after a few priming kicks). I will be getting into the carb again, so maybe starting will improve.

Thanks
Steve

[STEVENM63]

So we have established that the person who originally built this bike configured it with a Scrambler motor, but with Monza timing. The bike also has a UBF24 carb, instead of an SS1 which I believe originally came with the 250 Scrambler.

Curious, could part of the reason for my idle issue be due to having the incorrect carb?

[bodge]

no expert just generalising but any carb wrongly setup could give you idle issues. tho usually a smaller carb will help the low end and hold it back at the top end.
ub24 was used on 250 monza 250 g.t and even 350 monza so the idle circuit should probably be capable of allowing yours to idle tho i cant find any jetting specs,do you know what cam you have installed ?one of the hotter ones would probably give you a rough idle

[amartina75]

glad to hear you have it running and found the main caus of your problem.
it's possible you have a Monza head or even more maybe the whole engine and they only swapped out the charging system so they didn't have to rewire the bike. easiest thing to check first is the intake port size get a really good measurement where the carb flange bolts up.

any carb you have is probably better then the one you are using now. some people will say put a mikuni on it I would say get a VHB27AD and use it that's what I have on my 250 and it works great.

[DewCatTea-Bob]

Pulled the mag rotor off and here is what I found.

IMG_4919.jpg

Obviously the wires have been changed but what can be determined about my coil from this? Do I need to change anything before I put everything back together?

[quote= STEVENM63 ...
" Pulled the mag rotor off and here is what I found. "

____ Sorry I didn't get-to responding to this thread before you went-ahead & reinstalled your mag.rotor.
__ Because my modem's connection to the internet has once-again began providing only sporadic live-connection, it's thus less likely to keep the internet available whenever I happen to be inclined to be on-line ! _ So therefore I don't get-around to responding to all the posts I care to address, in a more timely manor.



" what can be determined about my coil from this? "

____ Since the power-coils appear as-if they might've been overheated & somewhat burnt, their ohm-readings ought be scrutinized for making-sure they're still remaining as stock.



" Obviously the wires have been changed
Do I need to change anything before I put everything back together? "

____ Since the stock wire-leads (which are known to go bad) have already been replaced, I wouldn't have strongly recommended changing the (apearently well attached) wires again,, however I would've suggested replacing the present non-stock wire-leads with stock-colored wire-leads.
But more importantly than that mere wiring-concern, I would've recommended also reconnecting the ground lead-ends (that are originally connected to the stator-core) to additional wire-leads so that the grounded opposite-ends of the power-coils could then rather be grounded externally of the motor-case. _ Not because an external ground-connection point could provide any improved circuit function,, but rather just because you could've then had complete access to all the poles of both power-coils, so as to be conveniently-able to choose any power-system scheme which you might ever prefer to employ. _ Otherwise you're pretty-much left stuck with being only able to use just the stock '28-watt' type electrical-system, (although there still remains some limited options to tweak-around with).
____ Now finally to the main point of interest to be concerned with before reinstalling any mag.rotor...
__ It's known that the factory-stamped 'timing-mark' located on the front-face of the flywheel-rotor isn't always placed in the very-same optimum location (in exact relation to the specific arrangement of the four-magnet/pole-fields supposedly properly aligned over-on the opposite-side [in relation to the stamped line-mark]).
So it would've been of worthy interest to check-on the specific alignment-arrangement relationship between the timing-mark's stamped-location on the rotor-face and the actual location of the magnet-array setting.
So since this issue of concern could always possibly be in actual play to a significant degree, one ought check-into it (before going-ahead & blindly putting all trust into merely only that which the workshop-manuals just list).
__ Here follows a link to a pertinent thread closely-related to this issue (concerning the mag.rotor timing-mark/magnetic-field alignment topic)... viewtopic.php?f=3&t=23&p=9582#p9540
__ However if a decent ign.spark is still produced even during slow kick-over crankshaft-revs,, then the optimum mag.rotor-timing has probably been achieved, and (if accurately set according-to the manuals), indicates that the factory-mark indeed was actually located as factory-intended.


Duke-Cheers,
-Bob

[DewCatTea-Bob]

[quote= STEVENM63 ...
" The holiday weekend gave me some much needed project time which included work on my NC 250.
so I was able to get everything
reassembled "

____ I had expected that you would've spent that time rather doing something more special, so I didn't expect you to get so much accomplished so soon.
If you had warned of that possibility in your Friday-post, I then would've made sure to post my response-post to it ASAP.



" (mag/rotor now at 32*). "

____ If the mag.rotor is actually the correct model-version intended for your particular engine-model, then you possibly now have the mag.rotor-timing set as factory-intended.



" Throttle response seemed a lot better "

____ Whenever the throttle is opened-up, the optimum air-mix is then momentarily disturbed & leaned-out towards an air/fuel-mix that's not as easily ignited (by weak ign.sparks). _ And-so when you adjusted the rotor-timing so that the ign.power-coil then happens to provide a stronger pulse of power-juice during the times when the contact-points open,, the resulted stronger ign.spark has thusly become better able to ignite those less volatile fuel-mixtures, thus explaining any such notably improved throttle-response.



" I removed the plug and it now appeared normal, without the fouling I had before. "

____ The improved fuel-ignition causes better burning that's thusly hotter, which in-turn makes the spark-plug run hotter enough to then keep itself clean of fouling-deposits.



" unless there is something that you guys think may assist with making startup a bit easier "

____ Are you still using the wrong ign.coil ?
__ The ign.power-coil certainly can't transfer-out all the developed power it's capable of providing, if the ign.coil's resistance-level is-not impedance-matched with that of the connected power-coil !
So unless you employ a suitably 'matched' ign.coil, you really can't expect to take full-advantage of all the capability your ign.system is able to muster-up !



" The bike also has a UBF24 carb, instead of an SS1 which I believe originally came with the 250 Scrambler. "

____ Your carb.model was rather employed on 250Monza-engines, while all n-c.Motocross/Scrambler-models came stock with a 27mm SSI.carb.



" could part of the reason for my idle issue be due to having the incorrect carb? "

____ No,, if in stock-condition, that Monza-type carb.model actually improves the engine's running-behavior (compared to any SSI.carb) ! _ I know this for-sure,, cuz it used to be a regular practice of mine to swap such Monza-carbs with the stock SSI.carbs on Scrambler-engines, for the purpose of improving Scr.engine performance-behavior, (and that change always provided a noteworthy improvement) !


Duke-Cheers,
-Bob

[DewCatTea-Bob]

So we have established that the person who originally built this bike configured it with a Scrambler motor, but with Monza timing.

[quote= amartina75 ...
" it's possible you have a Monza head or even more maybe the whole engine and they only swapped out the charging system "

____ Considering the Monza-type carb.model, that's a fair suspicion.
So-then perhaps it's actually the case that a previous-owner had figured that the motor must actually be a Monza-version, and-so had dealt with it as such.
__ To tell if the bottom-end is indeed a Scrambler-version, look at the drive-chain intake-hood of the motor-case and see whether it's slightly-elevated boss includes a 6mm-hole though it or not. _ As only Scrambler-motors utilize that particularly located hole (for attaching the Scr.motor's internal chain-guard).



" some people will say put a mikuni on it I would say get a VHB27AD and use it that's what I have on my 250 and it works great. "

____ I agree ! ...
__ The 'square-slide' carb is much-more better behaving over the 24mm-Del.carb (than the lesser-amount that presently-employed carb is over a SSI-carb) ! _ As the side-located float-bowl carbs won't allow good engine-idling at both vertical and side-stand resting-levels !
__ And besides,, most-all Mikuni-carbs are just plain ugly, and-thus look much out-of-place mounted against the rather pleasing-appearance of the Italian-designed cyl.heads !


Dukaddy-DUKEs,
-Bob