Bought a nice 1980 Yz 250 yesterday

450exc115
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450exc115 5/10/2015 12:57pm
5/10/2015 12:57pm
450exc115 wrote:
Rob, what do you weigh? I've been looking to up my spring rate for my 79 yz400 and don't feel like going trial and error. Looks...
Rob, what do you weigh? I've been looking to up my spring rate for my 79 yz400 and don't feel like going trial and error. Looks like you also added some padding to the stock seat too. I have a Honda early 80s aluminum rear brake arm that looks like it will be a direct swap for the aluminum one. Nice bikes guys.
sandman768 wrote:
I have a 79 400 also, all rebuilt, plan on racing at Unadilla rewind this june, Carb was replaced with a brand new one, what do...
I have a 79 400 also, all rebuilt, plan on racing at Unadilla rewind this june, Carb was replaced with a brand new one, what do you run for jetting? my bike starts & runs fine for about 2-3 laps then the idle seems to increase slightly, replaced every seal, intake boot, ect, donot think its an air leak, maybe lean pilot?
I run stock jetting. I raced a 1 hour harescramble yesterday and it did what you described. I will move the needle clip down one first before going up on the pilot. If it doesn't change the idle then I'll up the pilot.
sandman768
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sandman768 5/10/2015 3:27pm
5/10/2015 3:27pm
450exc115 wrote:
Rob, what do you weigh? I've been looking to up my spring rate for my 79 yz400 and don't feel like going trial and error. Looks...
Rob, what do you weigh? I've been looking to up my spring rate for my 79 yz400 and don't feel like going trial and error. Looks like you also added some padding to the stock seat too. I have a Honda early 80s aluminum rear brake arm that looks like it will be a direct swap for the aluminum one. Nice bikes guys.
sandman768 wrote:
I have a 79 400 also, all rebuilt, plan on racing at Unadilla rewind this june, Carb was replaced with a brand new one, what do...
I have a 79 400 also, all rebuilt, plan on racing at Unadilla rewind this june, Carb was replaced with a brand new one, what do you run for jetting? my bike starts & runs fine for about 2-3 laps then the idle seems to increase slightly, replaced every seal, intake boot, ect, donot think its an air leak, maybe lean pilot?
450exc115 wrote:
I run stock jetting. I raced a 1 hour harescramble yesterday and it did what you described. I will move the needle clip down one first...
I run stock jetting. I raced a 1 hour harescramble yesterday and it did what you described. I will move the needle clip down one first before going up on the pilot. If it doesn't change the idle then I'll up the pilot.
i have 1.0 total on this bike after complete rebuild of everything, Breaking bike in with yamalube, but will run amsoil now. 32:1 91 non ethanol with 50% sunoco leaded 110 race gas. First few laps feel good, then idles up, almost like slide is hangin up, plug looked mocha tan, but donot want to blow this thing up! maybe Zi should richen up also. I bought this bike fram a nice guy in Ct.
450exc115
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450exc115 5/10/2015 7:13pm
5/10/2015 7:13pm Edited Date/Time 5/10/2015 7:17pm
I'm just running pumped 93 with 10% ethanol and honda pro 2 stroke at 40:1. I have about 2 hours on the motor after a bottom end rebuild and a refreshed topend. Runs well but this weekend was the first time I pushed her hard with a lot of wide open straights in 80 degree plus heat. Can't complain as I won my class and the overall for the event (racing against a bunch of late 80s bikes too. Smile ). Still got some work to do to the forks to make it even better. How do you seal the expansion chamber to the cylinder on your bike. I've tried silicone orings and rtv and have blown both out in short order. There is no seal listed on the parts diagram but the pipe is very loose at the connection so it's loud and messy.
sandman768
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sandman768 5/11/2015 4:18am
5/11/2015 4:18am




this is my 79, I have 81 465 forks, with stiffer springs & emulators, forks are great! rear shock rebuilt by Kps.


good dampening but needs stiffer spring, bottoms when I pick up the speeds.

The Shop

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rob.boucher.547 5/11/2015 7:32am
5/11/2015 7:32am Edited Date/Time 5/11/2015 8:53am
For the exhaust problem
Machine up some 3000 series aluminum exhaust rings
dia of exhaust spigot
anywhere from .04-.100 thick
and place in pipe
1 it will take up any gaps
2 its soft it will form to pipe, spigot to seal
3 use new ss springs(short)
and or extra spring's

This will work for the stock set -up
Most DG pipes do not have a flat bottom (spigot)
so you might have to make something different(tapered)
ring?
Shawbridge Husky 5/11/2015 8:04am
5/11/2015 8:04am Edited Date/Time 5/11/2015 8:06am
Good info thanks Rob ! Your help here is always appreciated !
My '79 YZ250F is coming along, got a nice tank and near new oem seat !

Nice ride Sandman !

I have a complete '83 CR250 front end for mine. Am planning on using IT200
triple clamps. You think a Honda front end would be oddball or trick ?
They were well rated forks that year, will drop in Emulator. I do have the IT200
43mm forks still in good shape, a little shorter and 10 3/4" travel only.
450exc115
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450exc115 5/11/2015 9:41am
5/11/2015 9:41am
I run stock 38mm forks with emulators and 1" more preload. I have 43mm forks and clamps for it but want to buy springs and emulators before I swap it over. I may shorten the springs this week in the 38s to up the rate but I haven't done the math yet to see what that will get me. I need close to a .5 kg/mm for my size.

Strawbridge I have a 81 Honda CR250 with the 41mm forks which are the cousins to the 43mm forks on the 83. Great forks with emulators and honda ran them in some form up to 1989.

Rob I will go that route if the yamaha gasket rope I ordered over the weekend doesn't do the trick. Up till 78 Yamaha used a rope seal for the gasket. It's still available and I have some on the way. Springs are new and the flange bottoms out on the motor face and not on the spigot face. Sad As a engineer by trade and having worked in a small machine shop I really enjoy your approach to solving problems and the skill level in fabrication you poses.
project racer 5/11/2015 5:24pm
5/11/2015 5:24pm
Not sure if it's still around, but used to use a product called Chamber Seal on those rattling YZ pipes / cylinder spigots.

It was a rubberized, elastic type of tape, that with a few wraps around the cylinder spigot, shove the pipe on, it was quiet and sealed very well. No rattles. Only problem was once you removed the pipe, it needed to have the tape replaced with a new wrap.

It was about nine bucks a pack. Would do about 3-4 sealings if used sparingly.
sandman768
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sandman768 5/12/2015 5:01am
5/12/2015 5:01am
450exc115 wrote:
I'm just running pumped 93 with 10% ethanol and honda pro 2 stroke at 40:1. I have about 2 hours on the motor after a bottom...
I'm just running pumped 93 with 10% ethanol and honda pro 2 stroke at 40:1. I have about 2 hours on the motor after a bottom end rebuild and a refreshed topend. Runs well but this weekend was the first time I pushed her hard with a lot of wide open straights in 80 degree plus heat. Can't complain as I won my class and the overall for the event (racing against a bunch of late 80s bikes too. Smile ). Still got some work to do to the forks to make it even better. How do you seal the expansion chamber to the cylinder on your bike. I've tried silicone orings and rtv and have blown both out in short order. There is no seal listed on the parts diagram but the pipe is very loose at the connection so it's loud and messy.
my bike came with new DG pipe & silencer when I bought it, the fit is actually vey good, minimal vibration & spooge come from the pipe cylinder joint, but I only have 1 hr on the bike. I"m sure I put an oring or rtv when installing the pipe. The Netra race you speak of is at Catra, I am a member of that club. I have not ridden there in 2 yrs, focusing more on Riding MX tracks lately. Catra can be very rugged with big rocks & mud bogs, good for enduros & h/ scrambles, but not good for my vintage queens! In years past the club used to layout a brutal course, but I think sign up started dropping, so, I have heard this yrs course is not as brutal. as a general rule, I would not ride there without full skid plate, rear disc guard, bark busters & pipe guard! the mud should not be too bad this year, it has been a very dry spring...bring bug spray! good luck!
450exc115
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450exc115 5/12/2015 5:39am
5/12/2015 5:39am
Thanks for the tip. I've been racing there since the early 2000s and they have really made the courses a lot more fun. Plus us vintage guys get mostly the pee wee track to keep us coming back. Smile

I like the header tape but it looks like they are out of business.
450exc115
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450exc115 5/25/2015 5:39am
5/25/2015 5:39am
What a great time at the Catra race! Finish 2nd and the YZ did well. Both ends are too soft for my size and the motor ran hot with one step up pilot (90). I'm going to try a 430 main next and I have a 95 pilot too. Bumped up the spring rates for the vintage event in Massachusetts this memorial day weekend and it was better but a little stiff on the roots and rocks. Good stuff.
sandman768
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sandman768 5/25/2015 3:38pm
5/25/2015 3:38pm
450exc115 wrote:
What a great time at the Catra race! Finish 2nd and the YZ did well. Both ends are too soft for my size and the motor...
What a great time at the Catra race! Finish 2nd and the YZ did well. Both ends are too soft for my size and the motor ran hot with one step up pilot (90). I'm going to try a 430 main next and I have a 95 pilot too. Bumped up the spring rates for the vintage event in Massachusetts this memorial day weekend and it was better but a little stiff on the roots and rocks. Good stuff.
i rode mine some more at our local mx track last thursday. starting to get a feel for how this bike needs to be ridden... short shift, ez on the clutch, nice smooth arcs thru the turns. bike now has 1.0 since complete rebuild, did not have idle issues this time. last time I rode it I was concerned about tranny shifting being kind of hard, but seems to be getting better the more it is ridden. I like the bike, starts ez, nice & slim, sounds tight.
MaxPower
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MaxPower 5/25/2015 5:52pm
5/25/2015 5:52pm
Shawbridge Husky wrote:
Good info thanks Rob ! Your help here is always appreciated ! My '79 YZ250F is coming along, got a nice tank and near new oem...
Good info thanks Rob ! Your help here is always appreciated !
My '79 YZ250F is coming along, got a nice tank and near new oem seat !

Nice ride Sandman !

I have a complete '83 CR250 front end for mine. Am planning on using IT200
triple clamps. You think a Honda front end would be oddball or trick ?
They were well rated forks that year, will drop in Emulator. I do have the IT200
43mm forks still in good shape, a little shorter and 10 3/4" travel only.
The Honda forks would be trick. Especially if you got a Honda hub since in my opinion Honda had the best drum brakes in both single and dual leading shoes
If the emulator works good then that's it. But you can still tweak those forks to run cartridges
Shawbridge Husky 5/26/2015 6:48am
5/26/2015 6:48am
Cool thanks Max will do ! Yes complete front end take off wheel, hub, dual leading shoe brakes, triples. The triples are a no go because of steering stop issues, so the IT200 clamps it is. Thanks for the tip ! Lot of knowledge on this forum.
Hugh
WIESEL
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WIESEL 5/26/2015 9:26am
5/26/2015 9:26am
Where are you guys getting the nice white side panels? My 400 needs them in a bad way, love that look.
vanillaice782 5/26/2015 3:57pm
5/26/2015 3:57pm
We put the new piston in and were able to hone the cylinder to repair it. We drilled two holes in the piston to help cool the exhaust port bridge. Its almost ready for round two. Just waiting on an intake gasket at this point.

450exc115
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450exc115 5/27/2015 5:58pm
5/27/2015 5:58pm
Are those high enough to cool the whole bridge? The ones in my CR are a lot higher up.

Pit Row

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vanillaice782 5/27/2015 11:42pm
5/27/2015 11:42pm
450exc115 wrote:
Are those high enough to cool the whole bridge? The ones in my CR are a lot higher up.
I will double check with my dad. Him and a buddy actually did it.
sandman768
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sandman768 5/28/2015 4:28am
5/28/2015 4:28am
WIESEL wrote:
Where are you guys getting the nice white side panels? My 400 needs them in a bad way, love that look.
DC plastics sells the white/ opake plastics, take your time when drilling mount holes & use rubber grommets at mount points, if not the plastic is brittle & will evenually crack.
dynohut
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dynohut 5/31/2015 8:06pm
5/31/2015 8:06pm

One of the best MX bikes ever made! My set up came right from LOP in the day. .015 off of the head,boyesen reeds, one tooth up on the front and two up on the rear for gearing, and cut the head pipe and add a 15 mm piece of HP by the frame downtube. No one will beat you to the first corner...no one. Enjoy. This was my local money machine a long time ago that missed qualifying at nationals in the day by a sniff
dynohut
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dynohut 5/31/2015 8:15pm
5/31/2015 8:15pm

The mighty 1980 YZ250G at the first Lakewood Colorado Natl' track a pic of my first 1-1 250 pro overall. Big fella enjoy your YZ250G thats all I know
rob.boucher.547 6/2/2015 3:26pm
6/2/2015 3:26pm
My 1980 Yamaha YZ250G
Does not have a vertical exhaust bridge!

Its a numbers matching low hour original engine
It is the fastest air cooled 250 mx bike , I have ever owned
The 78-80 CR250's , not even close!
The 81 RM250, close but no cigar.
dynohut
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dynohut 6/6/2015 6:19pm
6/6/2015 6:19pm
Oh BTW my YZ250G had leftover factory Yamaha fork and shock internals from Arlo Englund's PDQ top ten Nat'l bike! Thanks again Bruce and Vickery Yamaha after all these years. The LOP set up reference mentioned above was a fluke! Kippy Peirce's mechanic was in the room next to me with his bike at a nat'l, looked at mine and said DUDE do this and I did. Pretty good set up dudes, also advance the timing .5mm. Thats all I know about the YZ250G

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