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PostPosted: Mon Jul 27, 2015 11:39 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
A completely-gutted MT125 pipe should be an absolute low-mid beast, with much-improved top end as well. If your MT pipe is louder than it was but has only a weak mid-top powerband, you may have removed the spark arrestor section (rear of the pipe, ahead of the tailpipe) but not the center baffle (middle of the pipe, above the center frame mount ahead of the toolbox). Sorry, I should have gone into more detail but I didn't think you would actually do it ;) as it's a fair amount of work, but the payoff is big as well. If there are two round welds on the back of the MT pipe about 11.5" - 12" ahead of the body/tailpipe weld seam, the center baffle is still in place (and killing power everywhere). It's also important the clean-out plate below the '361' stamped on the pipe side is installed & sealed; I welded a plate over the hole. The MT pipe tucks in great, especially with the heat shield removed and a few small tweaks to the mounts. If you decide to go with the snail pipe that should be OK, but the modified MT pipe will have more power over a wider range if it's working right.

The CR125M ignition installation is two parts: replace the MR stator/cable/flywheel with the CR ones (pretty easy), then replace the MR coil with the CR CDI box and coil (not as easy). Below is a composite photo of how I did it:
http://i399.photobucket.com/albums/pp74 ... 1754-1.jpg

Here's another thread that has CR-ignition info - if you search "cr125m ignition" you should find more:
viewtopic.php?f=21&t=3771&hilit=cr125m+ignition&sid=ad03385ea218af4377af4eb6b9236a3e#p13002

I don't think I'd try the XL ignition swap, even if it has CDI and lighting. A four-stroke motor needs more ignition advance with increasing rpm, while 2-strokes need the reverse.

Ray

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'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: Mon Jul 27, 2015 1:37 pm 
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Joined: Wed Jul 27, 2011 12:31 pm
Posts: 38
Ha, it was a fair amount of work :shock: but what I did was removed the center baffle, but not the rear spark arrestor portion. I actually cut a section out of the back of the pipe almost the length of the bellow to "explore" while gutting it. then welded it back on after removing the baffle. Keep in mind however, the compression is very poor on this bike. I can turn the rotor by hand with little resistance. So I would suspect any performance changes would be seriously hampered by that condition. The main reason I put the snail back on was that the last time it had any power was with that pipe. And I realized I had serious issues after returning everything on the bike to the state it was when I first got it running and performance never returned.

For now I am working on getting the parts bike shipped from New Mexico, and I'll start looking for the cr125 parts as you posted about. I'll get them trickling in soon. Perhaps by Barber vintage fest in October I can have a running bike again. With whatever is left of the spare bike I may start on one of these mt gearboxed mongrels I've been reading about :)


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PostPosted: Mon Jul 27, 2015 2:20 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
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Location: Connecticut, USA
OK, so the baffle on the left below has been removed, and the one on the right remains?

http://i399.photobucket.com/albums/pp74 ... 0small.jpg

The MT125 spark arrestor section on the right above has a small 'turbine core' insert inside it, which is very restrictive when new and gets worse with time - it's a good idea to get rid of it, and use an aftermarket spark arrestor if needed.

The MR175 motor is very sensitive to compression - it makes noticeably more power when the compression is increased from stock (@ 140 psi, give or take), and gets weaker pretty quick when the compression drops below that. I think mine was around 175 psi the last time I checked. If you can turn your crank easily by hand, yours is probably below 60 psi - I'm surprised the bike starts. I don't think I'd run it again until you do a top-end service; I waited too long on mine, and it ate the top ring.

Ray

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'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: Mon Jul 27, 2015 9:59 pm 
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Joined: Wed Jul 27, 2011 12:31 pm
Posts: 38
Yep, that's exactly what i did. Didn't know about the turbine core bit. I'll consider going back in after it now. And yes about not running the bike until it gets serviced. It sucks to not have my favorite to ride, but the xr200 tractor still gets me down the trail for now. Just feels like twice the weight and half the rocket ship. Oh well..


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PostPosted: Mon Nov 02, 2015 8:52 am 
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Joined: Wed Jul 27, 2011 12:31 pm
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So, Back during the Barber vintage festival, I had a friend from NM deliver a craigslist score - a '75 mr175 with "fresh top end." I wasnt expecting much for the $160 it cost. But hey, a mostly complete bike. Turns out the head and cyl base gaskets arent there, but lots of red rtv and yamabond was. great. It also had a mikuni carbduct taped to the manifold, and an mt250 pipe. The cylinder measures 2.602 (66.09mm) but I don't recall the piston measurements at the moment (I am at work.) I also pulled the ignition off and checked over everything. It looks good except the usual snip/tape job that everyone loves to use to "fix" things. I've got the motor out of my original elsinore too so will put it on the bench and open the lid also. I see re-mx offers bearing and seal kits for this bike. Are they any good? I'm looking for a head gasket and a cyl base gasket as well. Found them on ebay, just wanna make sure I get them as cheap as I can because I've noticed if i buy something, it shows up cheaper the next day, ha.

Also, A friend picked up an mr250 for me in West Virginia last weekend. So I'll be getting that one home soon. It still has the correct head and tail light :)


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PostPosted: Tue Nov 03, 2015 4:27 am 
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Joined: Sun Nov 30, 2008 12:10 pm
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Location: Connecticut, USA
Quote:
I see re-mx offers bearing and seal kits for this bike. Are they any good?

I'd use OEM Honda seals if at all possible, especially on the crankshaft.

Ray

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'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 Nov 03, 2015 1:38 pm 
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Joined: Wed Jul 27, 2011 12:31 pm
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I have managed to source a few oem seals, and a oem head gasket too, but western hills honda wants $50 for it :shock: And the seals aren't much less. Oh well, pay to play I suppose. I've found a couple on ebay too. At least at the end of all this I will have a 100% complete bike.


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PostPosted: Tue Nov 03, 2015 2:40 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
This item might be of interest:

http://www.ebay.com/itm/like/2014364606 ... ps&lpid=82

All the 9120x-360-xxx and 91206-286-xxx oil seals in the diagrams below are currently available on eBay, some for less than $10:

http://www.westernhillshondayamaha.com/ ... 175-JPN-A/

http://www.westernhillshondayamaha.com/ ... E13373206A

Ray

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'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: Wed Nov 04, 2015 10:10 am 
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Posts: 38
Ha, Ray I don't know how you find that stuff so fast! I put an offer in on the gasket set. Thanks! Hopefully I'll have all this stuff bought before Christmas and do some assembly during the downtime. I'd shoot for sooner but my side business of machining small hammers and pens has taken every minute I can find lately.


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PostPosted: Wed Nov 04, 2015 10:50 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
I've had good luck with parts-number searches, on both eBay and Google. It seems like the sellers with part-number listings have better inventories and sometimes cross-linking to other sites for parts they don't have in stock, although their prices can be higher (not always, though).

Ray

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'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: Wed Nov 04, 2015 11:41 am 
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Joined: Wed Jul 27, 2011 12:31 pm
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Good to know. I didnt especially mind the Western Hills Price, it was the shipping that killed it. $15 to ship a gasket was just a bit high. I did win the gasket set on ebay tho for $42 and change shipped. Much better deal!

Sometime in the next couple months I've got to go to Alabama for an MT250 from a friend too. I think that is gonna be my back door in to getting a road registered elsinore 8)


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PostPosted: Wed Nov 04, 2015 5:36 pm 
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Joined: Sun Nov 30, 2008 12:10 pm
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Location: Connecticut, USA
The Western Hills links were just for P/N info and diagrams - for actual buying I'd go with eBay, or even your local Honda dealer if the parts are still available (no shipping, very fast sometimes, and usually easy returns if needed).

Ray

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'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: Wed Nov 18, 2015 12:32 pm 
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Joined: Wed Jul 27, 2011 12:31 pm
Posts: 38
Attachment:
IMG_20151117_8906.jpg
IMG_20151117_8906.jpg [ 85.1 KiB | Viewed 5188 times ]


It happened again last weekend... A 76 mr250 I picked up from an eBay purchase in Maryland. Motor was full of swamp water, but oddly enough it was also clean inside :shock: bearings are all tight and the seals are good. Odometer says 1300 miles. Bore and piston are nice and clean, within spec. Carb is packed in mud and the boot is gone tho. I'm sure that's how the water got in the motor.

I'm guessing the story goes that the previous owner submerged it in water and it wouldn't start, so it got forgotten and sold. Oh well, it's got one of the unobtainium lights and a tail light too!


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