Vintage Dirt Bike Q & A

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PostPosted: Sat May 30, 2015 8:01 am 
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Joined: Fri May 29, 2015 7:34 pm
Posts: 34
Hello folks,
this is my second round of Elsinore ownership since I was privileged enough to own a CR125 when I was 14. :)
The problem with the MT is no spark!
I've found and put right th PO's bodges but still can't get any spark. All components are showing continuity with the DMM; stator coils;
main switch; ignition coil; rectifier and points and condenser.
The black wire on the ignition stator coil wasn't connected to anything so I soldered it to the black and white lead at the points. Logic tells me that this is where it should go but can someone confirm for me please?
I don't understand why the black with white lead at the points should be showing 3 ohms to ground when the points are open.
Please help! :)


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PostPosted: Sat May 30, 2015 11:57 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
The black wire was most likely a coil ground; if so, you'll want to reconnect that to a ground point on the stator, preferably the point it was originally connected to. The black/white wire is the 'hot' end of the stator source (ignition) coil, you will definitely not want to ground that, or connect it to any other stator wire.

When the points are closed, you should read nearly 0 ohms across the points contacts. When the points are open, you're reading across the ignition source coil, not an open circuit. Most stator coils are quite low resistance, so .3 ohms may or may not be correct. Continuity readings are not appropriate with resistances this low, nearly everything will read continuous with everything else.

Here's a link to an MT250 shop manual, the wiring diagrams are near the end:

http://honda-elsinore.alp-sys.com/manua ... 5mt250.pdf

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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PostPosted: Sat May 30, 2015 6:04 pm 
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Joined: Fri May 29, 2015 7:34 pm
Posts: 34
Thanks for the reply Ray. :)
If there is nothing connected to the points but the black with white wire, how could it be reading through a stator coil? On this bike, that wire runs straight to the ign coil and doesn't connect to anything else. That is if I disconnect the black stator coil wire from the points where I guessed it should connect.


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PostPosted: Sat May 30, 2015 7:27 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
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Location: Connecticut, USA
In a properly-wired MT250 ignition, one points contact is connected to one end of the source coil, the other contact is connected to the other end.

The stationary points contact is screwed directly to the stator (grounded). The ground side of the source coil should also connect there (black wire).

The spring-loaded points contact is insulated from ground, and is connected to the hot side of the source coil and the ignition coil input via the black/white wire.

When the points are closed, the source coil is jumpered across and does nothing.

When the points open and the source coil is active, the flywheel magnets induce a current through it, creating a large voltage across it which appears at the ignition coil input. That coil (actually an autotransformer) steps the source-coil voltage up many times to fire the plug with thousands of volts.

Many vintage points ignitions use metal (stator, cases, frame, etc.) instead of separate ground wires. If a wire appears to be missing, check for a ground path through metal instead.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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PostPosted: Sat May 30, 2015 7:47 pm 
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Joined: Fri May 29, 2015 7:34 pm
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Beautiful explanation! I'll give it a go.


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PostPosted: Sun May 31, 2015 10:53 am 
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Joined: Fri May 29, 2015 7:34 pm
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"In a properly-wired MT250 ignition, one points contact is connected to one end of the source coil"
The end of the source coil would be the black wire.
"The spring-loaded points contact is insulated from ground, and is connected to the hot side of the source coil and the ignition coil input via the black/white wire."
This is telling me that both the black and the black with white wires are connected to the insulated points contact. Is that right?


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PostPosted: Mon Jun 01, 2015 7:58 pm 
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Joined: Fri May 29, 2015 7:34 pm
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Can someone please post a picture of the connections at the points? I'll be eternally grateful for just a nice clear pic. of this area.
Thank you.


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PostPosted: Sun Jun 07, 2015 5:36 pm 
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Joined: Fri May 29, 2015 7:34 pm
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What I did:
place points lead on correct side of insulator;
heat shrink the black with white lead where the wire holder had rubbed it raw;
attach black source coil lead to points terminal and voila, she's a one kick starter. :D


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PostPosted: Sun Jun 07, 2015 6:56 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
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Location: Connecticut, USA
Excellent! These things can be hard to wake up once they go to sleep, it's great to see another one back up and running.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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PostPosted: Tue Jun 16, 2015 9:59 pm 
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Joined: Fri May 29, 2015 7:34 pm
Posts: 34
Since I got the old girl running, I've:
changed fork seals and replaced fork oil;
stripped, cleaned and painted tree, brackets and headlight bucket;
cut and removed swing arm (pivot bolt was completely fused in the collar :( );
installed Uni filter element;
cleaned and refurbished gauges and control cables and
stripped the fuel tank.
Tomorrow I'll machine a banjo bolt for the oil injector and this weekend...
prep and paint the tank metallic aluminum, orange and urethane clear.
Big grin!


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PostPosted: Mon Jun 29, 2015 3:58 pm 
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Joined: Fri May 29, 2015 7:34 pm
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She's all ready to go except for the swingarm which should arrive tomorrow.
Maiden voyage on Canada Day. :D :D :D


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PostPosted: Wed Jul 01, 2015 12:19 pm 
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First ride. Some kinda fun! :D


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PostPosted: Tue Dec 22, 2015 8:21 am 
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Joined: Fri May 29, 2015 7:34 pm
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I've been busy since I last posted:
the MT started up readily for a short while and then became hard to start and no longer had that sweet 2 stroke aroma. :(
I took the engine out and have tracked down everything it needs so I'm finally able to start reassembly. The piston and bore were worn out of tolerance of course but I found a new Wiseco .5mm over from Universal Cycle Service in Alberta for a very reasonable price.
Soon!


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PostPosted: Sun Sep 11, 2016 10:43 am 
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Joined: Wed Aug 27, 2014 6:14 pm
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Hello. I was wondering if anyone know how Killer Canary got the dimensions of the banjo bolt for the oil injection system. I am currently trying to finally ride my MT 250 after 2 years of not being able to. Luckily for me I now have a job as a tool makers apprentice and my boss also happens to be a motorcycle mechanic, I got Lucky!!

Any way I misplaced my oil injection line when we were reassembling the motor, so I order the only one I can find from ebay. When I got it and we tried to out it on we resized that we were missing one of the banjo bolts, the one that fixed the line to the oil pump. we quickly machined one by copying dimensions of the banjo bold that goes into the intake manifold. is that rite?

It was running fine on premix when there was no oil in the reservoir, the other day I was testing the oil injection system with a light premix and the oil injection hooked up. Quickly the line filled up and oil was running through, but I believe too much oil. I though this was because of the pre mix plus the injection, but now that I put in straight fuel it is still happening and fouling my plugs. The injection system is delivering too much fuel.

Does anyone know if this is the banjo bolts being exactly the same? Or can I simply adjust the fuel pump to deliver less oil? Please help all I want todo is ride this fall!!!!! Thank youuuU! :D :D :D


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PostPosted: Sun Sep 11, 2016 12:57 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
The two banjo bolts are different, and honestly I don't think I'd swap them around if it were my bike.

The banjo bolt at the oil pump output is Honda p/n 15542-358-000. It looks like an M6x20 shoulder bolt, with the center drilled out & another hole at a right angle in the shoulder section. 7 or 8 of these are available NOS on eBay right now.

The banjo bolt at the intake manifold is Honda p/n 15543-358-000. I believe this is nearly identical to the one above, except it has a short rounded 'nose' section after the threads that pokes into the air stream inside the manifold. This one's harder to find, at least right now.

I think these pumps put out too much oil when new, and just got worse with age & internal wear. Vintage injector oils were also lower-tech and may have been designed to burn rather than stick around, thus allowing more oil to be used without fouling. You can turn the pump cable adjuster down all the way without worry; it will put out the same oil at idle/low throttle and less at mid/high throttle, still too much though. :( Be sure to run the bike at full throttle for at least three 20-second bursts, to clear out at least some of the massive crankcase oil buildup the bike almost certainly has (and if it doesn't, the full-throttle runs aren't going to hurt anything).

We put an NGK BP7ES plug in my friend's MT250 recently, it definitely worked better w/less misfiring than the stock B8ES. A BP7EVX would be even better.

Ray

_________________
'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric


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