Any 79 RM250 threads?

Steve125
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Steve125 5/9/2016 1:15pm
5/9/2016 1:15pm
Steve125 wrote:
Anybody running some air in the forks of their 79 or 80 RM? I put much stiffer springs in mine and it still dives pretty badly...
Anybody running some air in the forks of their 79 or 80 RM? I put much stiffer springs in mine and it still dives pretty badly and bottoms easily. Very unbalanced from the rear which has also been stiffened up. I was thinking about running 5-6 psi in the forks. Just like they did back then. Anybody doing similar? Forks currently have 15wt oil and .46 springs. I weigh 225, Vet A rider.
RCN4HIM wrote:
My 79 ran best with 20lbs in each fork leg, people said I was nuts but the forks worked very well even after casing a triple...
My 79 ran best with 20lbs in each fork leg, people said I was nuts but the forks worked very well even after casing a triple it didn't bottom on a modern MX track (I got it next lap, needed to to win race)
Thanks for the info. I think I'll bump it up a bit more then... I tried 7 lbs last weekend, with .46 springs. Still a bit soft for the semi-supercross style track I was on. I was thinking about raising the oil level a bit too to stiffen the bottom of the stroke.
Acl700
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Acl700 2/13/2017 4:36pm
2/13/2017 4:36pm
Can anyone confirm that the 79 and 80 cylinder and muffler are the same? I'm looking to do the mods on both that are recommended for the 79, just want to make sure the are good to do on the '80. Any advice appreciated, thanks.
wolfy0067
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wolfy0067 2/13/2017 5:08pm
2/13/2017 5:08pm
80 cylinder has the exhaust port just about how you want it, blending the port may all that's necessary, the intake is where the power is gained, 79 cylinders were a real pourous casting, a lot of cylinder would crack the fins at the curve in the transfer ports
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Acl700
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Acl700 2/13/2017 5:19pm
2/13/2017 5:19pm
wolfy0067 wrote:
80 cylinder has the exhaust port just about how you want it, blending the port may all that's necessary, the intake is where the power is...
80 cylinder has the exhaust port just about how you want it, blending the port may all that's necessary, the intake is where the power is gained, 79 cylinders were a real pourous casting, a lot of cylinder would crack the fins at the curve in the transfer ports
Thanks. So do I still lower the intake like on the 79? And also cut 10mm out the muffler?

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wolfy0067
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wolfy0067 2/14/2017 1:45am
2/14/2017 1:45am
Lower and widen, I have photos in this post of properly modifying an intake. You can use your piston to mark it up I use layout dye
Acl700
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Acl700 2/14/2017 4:14am
2/14/2017 4:14am
wolfy0067 wrote:
Lower and widen, I have photos in this post of properly modifying an intake. You can use your piston to mark it up I use layout...
Lower and widen, I have photos in this post of properly modifying an intake. You can use your piston to mark it up I use layout dye
Thanks for your help, much appreciated. I'm going to go for it, and also cut the muffler. I will let you know how it goes
wolfy0067
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wolfy0067 2/14/2017 6:25am
2/14/2017 6:25am
I recommend you do this in steps, lower the intake 3mm, widen each side 2mm be very conservative. The stock pipe is hard to improve on, I would run I this way if you feel it need changes the cut it. You can take a piece of tape cut it to 10mm wide and wrap it around the pipe, this will assist in making a clean cut, this cut was in the mid section of the expansion chamber, not the muffler.
I like to put my piston in the cyl. Bore with the top edge just opening the port then cover the port about a mm this will make curtain the exhaust and intake aren't open at the same time, then mark the piston with a pencil I layout dye and scribe aren't available. This will then allow you to see how much skirt is over lapping on the piston. Remember, when the engine spins up to 9k the ports are being uncovered extremely fast be conservative with your grinding, you can always go back, some guys will start with cutting the piston skirt, then the mod. Is not permanent , however also not as free flowing as a properly modified intake port. Don't change the transfer ports , if your first time cutting a cylinder, let them go, again most of your gains are in the intake. Of course you then want to look at the carb and bore size to help increase flow.
Acl700
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Acl700 2/14/2017 3:22pm
2/14/2017 3:22pm
wolfy0067 wrote:
I recommend you do this in steps, lower the intake 3mm, widen each side 2mm be very conservative. The stock pipe is hard to improve on...
I recommend you do this in steps, lower the intake 3mm, widen each side 2mm be very conservative. The stock pipe is hard to improve on, I would run I this way if you feel it need changes the cut it. You can take a piece of tape cut it to 10mm wide and wrap it around the pipe, this will assist in making a clean cut, this cut was in the mid section of the expansion chamber, not the muffler.
I like to put my piston in the cyl. Bore with the top edge just opening the port then cover the port about a mm this will make curtain the exhaust and intake aren't open at the same time, then mark the piston with a pencil I layout dye and scribe aren't available. This will then allow you to see how much skirt is over lapping on the piston. Remember, when the engine spins up to 9k the ports are being uncovered extremely fast be conservative with your grinding, you can always go back, some guys will start with cutting the piston skirt, then the mod. Is not permanent , however also not as free flowing as a properly modified intake port. Don't change the transfer ports , if your first time cutting a cylinder, let them go, again most of your gains are in the intake. Of course you then want to look at the carb and bore size to help increase flow.
That is really helpful info, thanks again for sharing such detailed info.
suzuki
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suzuki 7/9/2019 4:12am
7/9/2019 4:12am
Just finished rebuilding my 80 RM250T, Raced it at Farleigh castle at the weekend. I had some issues with the front forks being too soft and the jetting being too rich. I fouled a plug on the line.
Anybody have any set up information that might help?
Thanks in advance
MaxPower
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MaxPower 7/9/2019 5:05am
7/9/2019 5:05am
Did you happen to read any of this thread yet?
Acl700
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Acl700 7/9/2019 2:06pm
7/9/2019 2:06pm
suzuki wrote:
Just finished rebuilding my 80 RM250T, Raced it at Farleigh castle at the weekend. I had some issues with the front forks being too soft and...
Just finished rebuilding my 80 RM250T, Raced it at Farleigh castle at the weekend. I had some issues with the front forks being too soft and the jetting being too rich. I fouled a plug on the line.
Anybody have any set up information that might help?
Thanks in advance
I also rode Farleigh last weekend on my 1980 RM250 and also had issues. The bike doesn’t like hot weather, never has done, and ran like it had a rag in the air box on the Saturday. It ran way better on Sunday as the temp was slightly cooler and managed to win both racesSmile . I’m running 280 main, 50 pilot and 2nd from bottom clip on needle.
As for the forks, I’m running stock forks with 15wt oil and 15psi and find them pretty good.
suzuki
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suzuki 7/10/2019 7:13am
7/10/2019 7:13am
I started off with stock jetting,plug (B9EGV) and forks.Ended the weekend with 440cc of oil, 16psi and a 22mm socket preloading the springs. went from way too soft to too hard I think.Kept 290 main in, put clip on 2nd from top to lean and put in a 50 pilot.along with a B8ES plug she ran alot better.
My bike came from the US with a 37.5 pilot but I haven't tried that yet.
Were you in the over 40 group?
Acl700
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Acl700 7/10/2019 9:53am
7/10/2019 9:53am
suzuki wrote:
I started off with stock jetting,plug (B9EGV) and forks.Ended the weekend with 440cc of oil, 16psi and a 22mm socket preloading the springs. went from way...
I started off with stock jetting,plug (B9EGV) and forks.Ended the weekend with 440cc of oil, 16psi and a 22mm socket preloading the springs. went from way too soft to too hard I think.Kept 290 main in, put clip on 2nd from top to lean and put in a 50 pilot.along with a B8ES plug she ran alot better.
My bike came from the US with a 37.5 pilot but I haven't tried that yet.
Were you in the over 40 group?
Yes, I was in the over 40 class.
I was thinking about going leaner on the main as was not getting any top end and was having to short shift to keep in a very narrow mid range, but didn’t want to risk seizing. They are frustrating bikes when not running right as it’s a big enough challenge already going up against the big bore bikes. I’m now on the lookout for a 400.
notme
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notme 7/11/2019 7:25pm
7/11/2019 7:25pm
Seeing this thread come back makes me wish i still had the bike. Will buy another if one comes along.
suzuki
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suzuki 7/12/2019 12:42am
7/12/2019 12:42am
suzuki wrote:
I started off with stock jetting,plug (B9EGV) and forks.Ended the weekend with 440cc of oil, 16psi and a 22mm socket preloading the springs. went from way...
I started off with stock jetting,plug (B9EGV) and forks.Ended the weekend with 440cc of oil, 16psi and a 22mm socket preloading the springs. went from way too soft to too hard I think.Kept 290 main in, put clip on 2nd from top to lean and put in a 50 pilot.along with a B8ES plug she ran alot better.
My bike came from the US with a 37.5 pilot but I haven't tried that yet.
Were you in the over 40 group?
Acl700 wrote:
Yes, I was in the over 40 class. I was thinking about going leaner on the main as was not getting any top end and was...
Yes, I was in the over 40 class.
I was thinking about going leaner on the main as was not getting any top end and was having to short shift to keep in a very narrow mid range, but didn’t want to risk seizing. They are frustrating bikes when not running right as it’s a big enough challenge already going up against the big bore bikes. I’m now on the lookout for a 400.
mine seemed to be pulling ok but the plug was very black and sooty, what's the fuel tank on yours?
suzuki
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suzuki 7/12/2019 12:54am
7/12/2019 12:54am
Before and after photos of mine





sandman768
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sandman768 7/12/2019 5:25am
7/12/2019 5:25am
Need to make room.... if someone is serious about buying this bike, I can help with meetup/ delivery in northeast. I have a lot of spares, all receipts for everything. If you think it’s too pricey, ad up the Cone pipe & silencer, PVL ignition, Fox shox, and 43mm front end conversion.

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captmoto
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captmoto 7/12/2019 8:31pm
7/12/2019 8:31pm
sandman768 wrote:
Need to make room.... if someone is serious about buying this bike, I can help with meetup/ delivery in northeast. I have a lot of spares...
Need to make room.... if someone is serious about buying this bike, I can help with meetup/ delivery in northeast. I have a lot of spares, all receipts for everything. If you think it’s too pricey, ad up the Cone pipe & silencer, PVL ignition, Fox shox, and 43mm front end conversion.
What did you do to get the brake arm to work. The 79 arm is not a direct swap to the later model hub. Did the 79 backing plate work in the later hub?
Not a big deal if some fab work is needed.
Acl700
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Acl700 7/13/2019 4:18am
7/13/2019 4:18am Edited Date/Time 7/13/2019 4:19am
suzuki wrote:
mine seemed to be pulling ok but the plug was very black and sooty, what's the fuel tank on yours?
My tank is a modified 1981 Cagiva tank, same as Geboers use on theirs.

What pipe are you running on yours?
sandman768
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sandman768 7/13/2019 4:30am
7/13/2019 4:30am
sandman768 wrote:
Need to make room.... if someone is serious about buying this bike, I can help with meetup/ delivery in northeast. I have a lot of spares...
Need to make room.... if someone is serious about buying this bike, I can help with meetup/ delivery in northeast. I have a lot of spares, all receipts for everything. If you think it’s too pricey, ad up the Cone pipe & silencer, PVL ignition, Fox shox, and 43mm front end conversion.
captmoto wrote:
What did you do to get the brake arm to work. The 79 arm is not a direct swap to the later model hub. Did the...
What did you do to get the brake arm to work. The 79 arm is not a direct swap to the later model hub. Did the 79 backing plate work in the later hub?
Not a big deal if some fab work is needed.
Not sure if you are talking front or rear, but the front was complete assembly including the wheel,off an RM 465 and the rear brake arm bolted right to the newer hub, maybe had to bend it a little but do not remember it being a big deal...
Law 131
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Law 131 7/13/2019 4:35pm
7/13/2019 4:35pm
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400.

After years of screwing around with engine mods...we settled on one simple setup.

RM250 with Simmons forks, Fox shocks, Petty front fender. Everything else stock. I'd replace the cylinder, crank bearings, piston, rings, main bearings...every 3 National races.

We found that that gave us a crisp reliable bike that would run fast.
sandman768
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sandman768 7/13/2019 6:10pm
7/13/2019 6:10pm
Law 131 wrote:
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400. After years of screwing around with engine...
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400.

After years of screwing around with engine mods...we settled on one simple setup.

RM250 with Simmons forks, Fox shocks, Petty front fender. Everything else stock. I'd replace the cylinder, crank bearings, piston, rings, main bearings...every 3 National races.

We found that that gave us a crisp reliable bike that would run fast.
You must have had some serious support! How did the transmission & clutches hold up?
notme
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notme 7/13/2019 6:24pm
7/13/2019 6:24pm
If you could afford all that for a season, i hope you took care of the mounting bolts!
Law 131
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Law 131 7/14/2019 10:15am
7/14/2019 10:15am
Law 131 wrote:
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400. After years of screwing around with engine...
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400.

After years of screwing around with engine mods...we settled on one simple setup.

RM250 with Simmons forks, Fox shocks, Petty front fender. Everything else stock. I'd replace the cylinder, crank bearings, piston, rings, main bearings...every 3 National races.

We found that that gave us a crisp reliable bike that would run fast.
sandman768 wrote:
You must have had some serious support! How did the transmission & clutches hold up?
Yup. I had a great support. Dad!

After 6 National or regional pro races, we would retire the bike to a practice ride.
Law 131
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Law 131 7/14/2019 10:16am
7/14/2019 10:16am
notme wrote:
If you could afford all that for a season, i hope you took care of the mounting bolts!
Don't remember the mounting bolts being an issue. I did check torque every moto.
Law 131
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Law 131 7/14/2019 10:19am
7/14/2019 10:19am
Law 131 wrote:
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400. After years of screwing around with engine...
I ran the RM250 in the AMA PRO Class in 79. Most of my races were on the 400.

After years of screwing around with engine mods...we settled on one simple setup.

RM250 with Simmons forks, Fox shocks, Petty front fender. Everything else stock. I'd replace the cylinder, crank bearings, piston, rings, main bearings...every 3 National races.

We found that that gave us a crisp reliable bike that would run fast.
sandman768 wrote:
You must have had some serious support! How did the transmission & clutches hold up?
Law 131 wrote:
Yup. I had a great support. Dad!

After 6 National or regional pro races, we would retire the bike to a practice ride.
12 hours of run time and then retire it.
captmoto
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captmoto 7/15/2019 9:26pm
7/15/2019 9:26pm
sandman768 wrote:
Not sure if you are talking front or rear, but the front was complete assembly including the wheel,off an RM 465 and the rear brake arm...
Not sure if you are talking front or rear, but the front was complete assembly including the wheel,off an RM 465 and the rear brake arm bolted right to the newer hub, maybe had to bend it a little but do not remember it being a big deal...
Rear brake. The 79 arm is a lot wider spacing than the bushing of the 83-84 backing plate.
sandman768
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sandman768 7/16/2019 5:35am
7/16/2019 5:35am
sandman768 wrote:
Not sure if you are talking front or rear, but the front was complete assembly including the wheel,off an RM 465 and the rear brake arm...
Not sure if you are talking front or rear, but the front was complete assembly including the wheel,off an RM 465 and the rear brake arm bolted right to the newer hub, maybe had to bend it a little but do not remember it being a big deal...
captmoto wrote:
Rear brake. The 79 arm is a lot wider spacing than the bushing of the 83-84 backing plate.
I have an82 or 83 rear wheel assy, it’s not an 84 for sure. I do remember having to use an additional thick washer as a spacer from brake plate to swingarm...but it was easy. I will take a photo of the setup ....
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suzuki
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suzuki 7/22/2019 3:41am
7/22/2019 3:41am
suzuki wrote:
mine seemed to be pulling ok but the plug was very black and sooty, what's the fuel tank on yours?
Acl700 wrote:
My tank is a modified 1981 Cagiva tank, same as Geboers use on theirs.

What pipe are you running on yours?
It's a Jan Geboers pipe and silencer. I think they are made by SPES in Belgium. I didn't ride the bike with the stock pipe so I can't say how good it is. It sounds nice though

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