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 Post subject: MR175 - need info
PostPosted: Mon May 23, 2016 8:28 pm 
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Joined: Mon May 23, 2016 6:43 pm
Posts: 4
Hello

I just picked up a MR175 without paperwork from a friend near Fancy Gap VA. He bought the bike from a fellow who intended to restore it, but wanted to buy a house, so he needed it to go away. I intend to chase that lead a bit further but I doubt I'll learn much more about the bike.

The numbers on the frame/engine do not match. The last two digits vary by 40-50. I'm not sure what is normal, so any information would be appreciated.

The wiring harness is clean, but there is no headlamp, ignition key switch, or indicators. The stator side cover has allen-head screws, leading me to believe that someone has been in there before. The head has two spark plugs. The coil has a single output.

The tank is missing. A very small metal yamaha tank sits on the backbone. The seat looks ok. It still says Honda. There is rust and grime but not nearly as much as you'd find on a neglected bike of this age. It was well-kept for a time, but appears to have been mis-treated in recent years.

The bike runs but not well. It doesn't idle and needs constant blipping to keep running. First gear seems really really really low. It seems like its meant for pulling stumps? It is willing to go faster than I am, but letting off the throttle makes it run poorly. The carb has only two external adjustments and I don't know what each one does.

Does anyone know what coil is needed? Are fork seals still available? This bike is not a restoration candidate: it has a missing frame gusset and a cracked tube where the rear brake should mount. It looks like someone came down from out of the sky with their right foot on the brake pedal instead of the foot-peg. I'm going to attempt welding it back together and putting a new gusset in, but I have no intention of beating the bike once this has been done.

If anyone has any insight into this old bike, I'd be most appreciative.

-Ash


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 Post subject: Re: MR175 - need info
PostPosted: Tue May 24, 2016 9:33 am 
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Joined: Mon May 23, 2016 6:43 pm
Posts: 4
based on the vin, i've learned its a 1975 mr175.


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 Post subject: Re: MR175 - need info
PostPosted: Tue May 24, 2016 9:47 am 
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Joined: Mon May 23, 2016 6:43 pm
Posts: 4
According to one line-drawing I found online, there should not be a second spark-plug in the head. On ebay there are several heads for sale with descriptions like "MR175 AHRMA Engine Head Dual Plug"

So now I'm confused. Should I remove the second spark plug and hunt for a bolt that will fit the opening?


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 Post subject: Re: MR175 - need info
PostPosted: Tue May 24, 2016 10:15 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1010
Location: Connecticut, USA
With an MR in that condition, the first thing I'd do is read the shop manual cover to cover, especially the carburetor section:

MR175 shop manual here

All the problems you've mentioned - and many you haven't - have been covered at this site, some in great detail. Since the search engine no longer accepts 'mr175' as a valid input, I'd try searching my username (which will bring up a lot of threads) and then going through those for MR175-related topics. If you intend to get this bike running well again, it will be the best hour or two you ever spent. :)

The frame and engine numbers on 70's Honda 2-strokes almost never match when new. 1st gear is very low on the '75 and '76 MR175's.

I've had my frame welded 3 times, once at the brake-pedal pivot. If the threaded piece for the pivot bolt is still there it should be no big deal, but if it's missing maybe you could weld in an M10x1.0mm (fine thread) nut instead.

The bike came with one spark plug and a 90061-358-000 head sealing bolt installed in the other hole. This bolt is available on eBay etc., but honestly I'd concentrate on the carb first, there's surely plenty to be done there.

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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 Post subject: Re: MR175 - need info
PostPosted: Tue May 24, 2016 2:34 pm 
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Joined: Tue May 24, 2016 3:52 am
Posts: 2
At least from what I know about the dual plug is pretty much that its a backup. Since back then and I guess still now, they were prone to burning them out(may not be correct wording). My MT250 has a head with 2 plugs but only one coil. I tend to look at the parts manual for the part numbers to find out if there is another model with the same part. I do not know if the 77 is the same as the model you have but here is a link to some manuals if you don't already have them.

http://honda-elsinore.alp-sys.com/manuals/

As far as needing to throttle it a little so it stays on, did you check the float? Is it at proper angle?

Also my Frame and Engine have different numbers too. I think as long as the Frame stamp and plaque are the same.


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 Post subject: Re: MR175 - need info
PostPosted: Wed May 25, 2016 6:24 pm 
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Joined: Mon May 23, 2016 6:43 pm
Posts: 4
Thanks for the pointers.

I think the bike might be a lucky find. Compression came up to 120psi. I adjusted the float thinking that would solve the fueling problem but found the main jet was mis-threaded into the jet needle. It was about 2mm from being seated. I snapped it off while trying to "clean the threads" [read: force it home. hey i like cheap fixes].

That explains why the mix and idle screws did nothing*. I've ordered a carb kit. Hopefully the jets will be good-enough for tinkers-sake. I'm going to have to put tires, a new throttle tube, brakes, and a rear brake pedal on it. I'd like to find a headlamp and maybe a small mirror. The guy I bought it from is an ace at getting titles for vintage bikes and it would be nice to have it road-legal, allowing me to putt-around in search of places to ride.

I am new to two-strokes. It seems the exhaust was gutted. I doubt this is ideal, and it certainly isn't making my neighbors happy. Is there anything I can do [cheaply] to solve the horrendous noise problem?


* i was pretty sure it was getting too much fuel so i cut the fuel flow back to a trickle. for a brief moment, when the bowl wasn't swimming in fuel, the exhaust cleaned up, the idle got smooth, and the air mix actually affected the way the bike ran.


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 Post subject: Re: MR175 - need info
PostPosted: Thu May 26, 2016 6:13 pm 
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Joined: Tue Jan 27, 2004 8:51 pm
Posts: 136
Location: Gilbert, AZ
Pictures please. It will help us figure things out faster.
As for the exhaust, the only packing is the silencer/baffle area. That is the part about 6-8 inches long at the rear of the pipe. Is there a removable part on there [baffle] or is it open?

My MT250's baffle was plugged up which made it run poorly. If yours is removed that will make it much louder without much performance gain considering the additional noise.

Good find on the main jet. Use every part possible especially the "O" rings including the ones on the seat and the large one on the float bowl.

Rick


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