Suzuki Rm125c 1978 ?

Joko
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Joko
Edited Date/Time 6/9/2017 3:18pm
I have an opportunity to buy one for $450, engine is good, will need suspension work.
Is Race Tech a good Susp source for this bike?
Are the old Fox airshox worth finding?
Who does good porting work for mid-top?
Pipe recommendation? Thanks!
I had bought the '78 RM125 as my first bike in High school, time to revisit the past!
Thanks, Joe
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xnationalwrench 3/17/2014 6:40pm
3/17/2014 6:40pm
Race Tech does good work, Fox Air shocks are good but takes a nitrogen tank to set up properly. We used Works Performance with good results. We used a stock pipe that was modified (shortened the head pipe 6mm)
edgo897
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edgo897 3/17/2014 7:23pm
3/17/2014 7:23pm
I got a new one in '78 too. The motor was pretty good for the era. I'll second the Works shocks. Buy a new pair, bolt them on and forget about it. Are you going to race it or just ride it?
Joko
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Joko 3/17/2014 7:30pm
3/17/2014 7:30pm
I plan to race it, some ACR events or nearby CT.
MaxPower
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MaxPower 3/18/2014 5:17am
3/18/2014 5:17am
Build it trick with porting and high dollar suspension because you want to not because you think you really need to. ACR does not run all that many events throughout the season and the class you are racing in isnt all that large. There are other Ahrma events to get your fill of racing old bikes. You will spend a lot of money to be racing four or five guys in your class. Now if you want a bad ass 78 rm 125 that's a different story. I would love to Have 78 RM.
Make that thing ready for the beginning of June to raise unit Dilla.

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Lonestar_399 3/18/2014 11:29am
3/18/2014 11:29am
The motor is pretty good to begin with. Just have someone clean up the ports initially. The 78 model already had a little extra port work done over the 1977 model for top end gains. The pipe mod mentioned above should be sufficient instead of dropping $300 plus dollars on a pipe that won't be much better, if at all. Spend your money on suspension.

The 1978 model RM125 races in the Grand Prix class for AHRMA. This is the group for most 1978-80 model bikes. You have a competitive and good handling bike for the class so don't think your at a disadvantage with an earlier model. The 1978 RM125 I think had one of the best overall motors in this bunch. You will want a little more travel on both ends. The 1978 model I have is fitted with 1980 model forks. Basically you just press out the old stem from your 78 model into some 1980 model clamps. On the rear you can then easily go with some 15 1/4" rear shocks (stock is 14 7/8"?) . I would not go any longer with the stock swingarm or you will be changing the handling characteristics.

Suzuki has an amazing amount of parts still available. Vintage-Suzuki (google them) is a good resource for plastics and other things you may need for the bike.
vet323
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vet323 3/18/2014 12:05pm
3/18/2014 12:05pm
xnationalwrench wrote:
Race Tech does good work, Fox Air shocks are good but takes a nitrogen tank to set up properly. We used Works Performance with good results...
Race Tech does good work, Fox Air shocks are good but takes a nitrogen tank to set up properly. We used Works Performance with good results. We used a stock pipe that was modified (shortened the head pipe 6mm)
I've got a '78 too-what kind of detail can you give us about the pipe mod? (I followed some crank advice you gave me last year for a different bike with great results-thanks!)
xnationalwrench 3/18/2014 1:03pm
3/18/2014 1:03pm
vet323 wrote:
I've got a '78 too-what kind of detail can you give us about the pipe mod? (I followed some crank advice you gave me last year...
I've got a '78 too-what kind of detail can you give us about the pipe mod? (I followed some crank advice you gave me last year for a different bike with great results-thanks!)
It is a simple modification, simply remove 6mm from the front of the head pipe (a hack saw will work), remembering you should move the tabs back for the pipe springs and you will have to adjust the pipe mount also.
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PN27416 3/18/2014 3:14pm
3/18/2014 3:14pm
MaxPower wrote:
Build it trick with porting and high dollar suspension because you want to not because you think you really need to. ACR does not run all...
Build it trick with porting and high dollar suspension because you want to not because you think you really need to. ACR does not run all that many events throughout the season and the class you are racing in isnt all that large. There are other Ahrma events to get your fill of racing old bikes. You will spend a lot of money to be racing four or five guys in your class. Now if you want a bad ass 78 rm 125 that's a different story. I would love to Have 78 RM.
Make that thing ready for the beginning of June to raise unit Dilla.
Right on to this first sentence!
Correct me if I'm wrong but AHRMA is non existent north of PA except for mx rewind at dilla and maybe 1 in the catskills?
ACR will be in CT and NH.
Lonestar_399 3/18/2014 5:16pm
3/18/2014 5:16pm
There is another mod to the pipe but I cannot find my notes on it. Maybe someone here can remember....anyway, it involved cutting about 10mm out of the fat part (belly) of the pipe. I'll update this post if I can find it. Occasionally I'll see a 77 or 78 RM125 with this trick done also...btw, not to be combined with cutting 6mm off the header of the pipe!

Personally, I would get it back to stock and running before I started modifying anything.

You can PM me if you need any guidance for parts locating.
Joko
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Joko 3/18/2014 6:19pm
3/18/2014 6:19pm
Thanks ls399! I would imagine that the engine responds well to a head squish adjustment & C12 gas? Need a bit more
power, I'm at 170, a few lbs over my HS days race weight.
Mugen racer
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Mugen racer 3/19/2014 5:00pm
3/19/2014 5:00pm
I remember machining the one side of the reed block and installing another set of Boyesen reeds. Anyone else do this mod?
RF145
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RF145 3/19/2014 6:11pm
3/19/2014 6:11pm
MaxPower wrote:
Build it trick with porting and high dollar suspension because you want to not because you think you really need to. ACR does not run all...
Build it trick with porting and high dollar suspension because you want to not because you think you really need to. ACR does not run all that many events throughout the season and the class you are racing in isnt all that large. There are other Ahrma events to get your fill of racing old bikes. You will spend a lot of money to be racing four or five guys in your class. Now if you want a bad ass 78 rm 125 that's a different story. I would love to Have 78 RM.
Make that thing ready for the beginning of June to raise unit Dilla.
PN27416 wrote:
Right on to this first sentence! Correct me if I'm wrong but AHRMA is non existent north of PA except for mx rewind at dilla and...
Right on to this first sentence!
Correct me if I'm wrong but AHRMA is non existent north of PA except for mx rewind at dilla and maybe 1 in the catskills?
ACR will be in CT and NH.
PN27416, you do not need correcting, you are correct about the ACR/AHRMA situation. With nine race days, ACR has what is a balanced schedule for the older VMX racer with other responsibilities in their life. With an average turnout of close to 200 entries per event, and the ability to run the 1978 RM 125 in multiple classes, that should be enough racing for one season. And do not forget that ACR will also be at Broome-Tioga for 2 days of racing and on that Friday, a Donnie Hansen VMX school. A typical AHRMA NE event has less than 100 entries per day and I am not sure how that equates to more racers in any particular class, as their classes are for the most part consisting of only two or three entries.
Lonestar_399 3/19/2014 6:36pm
3/19/2014 6:36pm
Mugen racer wrote:
I remember machining the one side of the reed block and installing another set of Boyesen reeds. Anyone else do this mod?
I have not heard of doing this reed block mod to the 77/78 models but you could machine a RM250 reed block down and open up the intake to match. That was a mod I've read about in the past. BTW, the intake and reed cage typically don't match well so you should have someone match them for you. I have an old R&D or DG 6 petal intake on my 1977 model I'm building. It has reeds on each side and was supposedly one of the best upgrades for the motor. When I get mine up and running I'll let you all know my thoughts on it.
minifig-phil 3/20/2014 4:21am
3/20/2014 4:21am
Mugen racer wrote:
I remember machining the one side of the reed block and installing another set of Boyesen reeds. Anyone else do this mod?
Lonestar_399 wrote:
I have not heard of doing this reed block mod to the 77/78 models but you could machine a RM250 reed block down and open up...
I have not heard of doing this reed block mod to the 77/78 models but you could machine a RM250 reed block down and open up the intake to match. That was a mod I've read about in the past. BTW, the intake and reed cage typically don't match well so you should have someone match them for you. I have an old R&D or DG 6 petal intake on my 1977 model I'm building. It has reeds on each side and was supposedly one of the best upgrades for the motor. When I get mine up and running I'll let you all know my thoughts on it.
Can you post some pics of the reed block?
Lonestar_399 3/20/2014 10:24am
3/20/2014 10:24am
Well, I would but it's in the motor currently. I do have one for the 1979/80 model somewhere in my garage. I'll see if I can find it over the weekend and get some pictures out. There was a guy re-popping these (CNC) about a year ago on that auction site so I would suggest to watch as they do pop up every blue moon on there.
project racer 3/20/2014 12:35pm
3/20/2014 12:35pm
Mugen racer wrote:
I remember machining the one side of the reed block and installing another set of Boyesen reeds. Anyone else do this mod?
The late E.C. Birt offered this mod for all RM's when they came out in the fall '75.
RiV
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RiV 3/22/2014 12:23pm
3/22/2014 12:23pm
Mugen racer wrote:
I remember machining the one side of the reed block and installing another set of Boyesen reeds. Anyone else do this mod?
project racer wrote:
The late E.C. Birt offered this mod for all RM's when they came out in the fall '75.
Yes, as I recall though that's only partially true. If I remember correctly the
Rm 125A you can or Rm250/370/400 but I'm pretty sure you have to replace
the reed block on the RM125B/C with the earlier style. I have modified them
myself or used yes E.C Birt ones as well as his billet 3-pedal he made too also
similar professionally modded ones, they do work well IMO & are not hard to
replicate. You will need to run a reed stopper for sure on the modified block or
it will break the short reed if it is a single stage pedal say .020" fiberglass.

Never tried it on the 125's but on the B/C 250's it worked really well to grind
modest sized "Boyeson" ports below the base gasket surface from the wall
in the reed cavity into the transfer area. Worked well with either 3 or 4 pedal
setups. Hope this helps.....

Sorry to hear about E.C., met him once at Ponca City....a great guy, besides
being a 2-stroke guru!
Lonestar_399 3/23/2014 5:02pm
3/23/2014 5:02pm
Here are some photo's of the 1979 DG 4 petal reed cage. It forced me to clean up my garage some to find it!







1

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minifig-phil 3/24/2014 10:04am
3/24/2014 10:04am
Lonestar_399 wrote:
Here are some photo's of the 1979 DG 4 petal reed cage. It forced me to clean up my garage some to find it! [img]https://p.vitalmx.com/photos/forums/2014/03/23/49205/s1200_rm125_79_dg4petalreed.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2014/03/23/49206/s1200_rm125_79_dg4petalreed_2.jpg[/img]...
Here are some photo's of the 1979 DG 4 petal reed cage. It forced me to clean up my garage some to find it!







Thank-you!
That looks awesome!
I'd like to make something for my '76 RM125 that's better than stock.
RiV
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RiV 3/25/2014 7:26am
3/25/2014 7:26am
Those look like great examples, just be wary of any using self tappers.
Pretty sure it was a company R&R that had them & were known to fall out,
results were not good.
WRH
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WRH 5/5/2014 10:40pm
5/5/2014 10:40pm
Lowering the intake 3 to 4 millimeters would liven up your RM, lowering it up to 10 millimeters is about max however. I wound up with a Myerscough pipe from R&D racing back in those days and sent it to Jemco in Houston for them to measure and build a patterns for. John still builds that pipe on request. It was the absolute best exhaust available at the time for the 78 RM125. We tested them all.
minifig-phil 8/27/2014 10:11am
8/27/2014 10:11am
Will a good pipe from the '77/'78 RM125 work well on a '76 (different bore and stroke)?
What are "Boyeson" ports
domoguchi
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domoguchi 8/31/2014 4:42pm
8/31/2014 4:42pm
WRH wrote:
Lowering the intake 3 to 4 millimeters would liven up your RM, lowering it up to 10 millimeters is about max however. I wound up with...
Lowering the intake 3 to 4 millimeters would liven up your RM, lowering it up to 10 millimeters is about max however. I wound up with a Myerscough pipe from R&D racing back in those days and sent it to Jemco in Houston for them to measure and build a patterns for. John still builds that pipe on request. It was the absolute best exhaust available at the time for the 78 RM125. We tested them all.
Would that pipe fit on a 77 RM 125 ? Never heard of Meyerscougj.....
Mugen racer
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Mugen racer 9/1/2014 12:19pm
9/1/2014 12:19pm
Boyesen ports are located in the intake tract. They communicate directly to the transfer ports. Sometimes they are called injector ports. Most of the factories licensed Eyvinds patent for these ports. Eyvind built me several of these cylinders for my 1975 CR125. Pulled alot of holeshots with them.
WRH
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WRH 9/2/2014 6:40pm
9/2/2014 6:40pm
WRH wrote:
Lowering the intake 3 to 4 millimeters would liven up your RM, lowering it up to 10 millimeters is about max however. I wound up with...
Lowering the intake 3 to 4 millimeters would liven up your RM, lowering it up to 10 millimeters is about max however. I wound up with a Myerscough pipe from R&D racing back in those days and sent it to Jemco in Houston for them to measure and build a patterns for. John still builds that pipe on request. It was the absolute best exhaust available at the time for the 78 RM125. We tested them all.
domoguchi wrote:
Would that pipe fit on a 77 RM 125 ? Never heard of Meyerscougj.....
You could call Jon at Jemco and ask him to build that pipe to fit the 77/78 model and see what he says. Tell him Billy Holt says Hi!
ky_savage
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ky_savage 9/6/2014 6:45am
9/6/2014 6:45am
I have this one. Not sure what it is.


minifig-phil 9/7/2014 6:44am
9/7/2014 6:44am
ky_savage wrote:
I have this one. Not sure what it is. [img]https://p.vitalmx.com/photos/forums/2014/09/06/64435/s1200_image.jpg[/img]
I have this one. Not sure what it is.


Is it for sale?
ky_savage
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ky_savage 9/7/2014 7:08am
9/7/2014 7:08am
ky_savage wrote:
I have this one. Not sure what it is. [img]https://p.vitalmx.com/photos/forums/2014/09/06/64435/s1200_image.jpg[/img]
I have this one. Not sure what it is.


minifig-phil wrote:
Is it for sale?
Not for sale. I'm trying to figure out what reeds I need for it to get my '78 RM125 up and running. It has nothing stamped on it and no markings. The reeds that were in it are frayed.
xnationalwrench 9/7/2014 10:20am
9/7/2014 10:20am
If you can't find any reeds you might try a go-kart shop and see if they can match up the old reeds.

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