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78 SRX vs 76/77

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78 SRX vs 76/77

Postby GP396 » March 23rd, 2006, 1:55 am

I realize that the 78 was "de-tuned" from the 76/77 versions. Just wondering what was actually done and why.

My vintage wrenching buddy picked up a 78 in boxes for $250. We put it back together last weekend to see if anything was missing and near as we can tell only thing not included was the spindle boots.

The sled fired up and seemed to run fine but is now being torn back down for the complete rebuild.

So were just wondering where it lacks compared to the 76/77. Did they further de-tune on later models as well?

Thanks for any info.
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78 SRX vs 76/77

Postby Snojet Steve » March 23rd, 2006, 7:52 am

1977 frame is all aluminum up front instead of steel on the later models. It uses a unique suspension that has alot of aluminum parts on it. The arms are aluminum and 2 links protrude up through the back of the tunnel and attach to the top/sides. The engine is said to make 100 hp+ in stock form and used different pipes, pistons, porting and 44mm carbs compared to other SRX's. The 77's also have one of a kind aluminum skis and racing handlebars.

1978 used a fairly standard suspension like the Exciters and Enticer 340 with aluminum rails but steel arms. The engine is de-tuned down to about 80 hp with smaller carbs, different pipes and milder porting. This was all done to beef the SRX into being a better trail sled and "safe" for public use. Try tuning carbs and clutches on a 100+ hp 440. You have to constantly re-jet for temperature and conditions or BOOM!

I'm helping a guy rebuild a 1980 SRX this summer when I strip my GPX down for a frame up. It has butterfly Keihin carbs like the Exciters and an all steel suspension. Someone said the 1980 is the most powerful production SRX of the old bunch. So maybe an expert could better clear that up too.
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78 SRX vs 76/77

Postby SRX 440A » March 23rd, 2006, 11:42 am

the 1980 was the least powerful year. thats he reason they only used those crappy butterfly carbs on the srx 2 years [80-81] they went back to the vm mikunis in 83 on the v-max.
the 77 is the strongest,76 next then 78-79. also the 76-77's both had 40mm carbs not 44's. 77's also had the shortest intake run compared to all other years. the intake port on the 77 is bridged because it is so wide.
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78 SRX vs 76/77

Postby sled_king » March 23rd, 2006, 5:25 pm

the 77 was all aluminum chassis and rear suspension, along with aluminum gears and skis. the intake and exhaust ports were HUDGE on the 77 8F2 cylinders, the heads were also high compresion. wrist pins were 18mm in diamater. carbs were 40mm mikuni powerjet.

the 78 had much smaller ports, steel bulkhead, skis and gears, smaller 36mm powerjet carbs and a rubber track. wrist pins were 20mm in diameter
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78 SRX vs 76/77

Postby kawicat » March 24th, 2006, 3:10 pm

77 fastest, least trail ridable
76
78
80 slowest, most trail ridable

76 340 was nothing to sneeze at either.
[[green]RIDE HARD, PLAY HARD, STAY HARD, DIE HARD![/green]
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78 SRX vs 76/77

Postby duncn70 » March 27th, 2006, 10:36 am

Are the heads from the 78 SRX a lot better than the heads from a 79 SRX? I'm thinking about buying a pair of them that are milled down for higher compression. What do you guys think? Thanks, Mike.
[b]Sleds I own:[/b]

[ul][*]1977 Yamaha GS 340 (mint for sale)[*]1973 Ski doo TNT Silver Bullet 340[*]1976 Rupp Nitro 440 L/C[*]1979 Yamaha SRX 440
[/ul]


[COLOR=#ff3300]IF IT DOESN'T GO [b]BAAAAAAAAAAAAAAAAAAAAAAP[/b] IT'S JUST A TRAIL SLED!!![/COLOR]

[COLOR=#0000ff]Check out the T-Jets.[/COLOR]
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78 SRX vs 76/77

Postby AHood » March 27th, 2006, 12:37 pm

[quote=duncn70]Are the heads from the 78 SRX a lot better than the heads from a 79 SRX? I'm thinking about buying a pair of them that are milled down for higher compression. What do you guys think? Thanks, Mike.[/quote]

the SRX heads are******all years suck. the 76 and 77 will just give you higher compression. offset domes and plugs are obsolete. if you really want some power from that srx you should get some billet head inserts with a toroid shaped dome and proper squish band. where can you get these you ask? well they would have to be custom made. the stock chambers get milled out and an insert is made that will fit inside the stock head shell O rings seal the insert to the new head.
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78 SRX vs 76/77

Postby kawicat » March 27th, 2006, 4:44 pm

You could also have the original head tig welded and then remachined which I think is the most common way to fix them.
[[green]RIDE HARD, PLAY HARD, STAY HARD, DIE HARD![/green]
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78 SRX vs 76/77

Postby AHood » March 27th, 2006, 7:04 pm

[quote=kawicat]You could also have the original head tig welded and then remachined which I think is the most common way to fix them.[/quote]

you still cant relocate the plug by welding. a central plug location is key because then you can easily chuck the head in a lathe with a spark plug mandrel and cut the squish and chamber to any configuration you wish plus surface the sealing surface easily. plus welded aluminum doesnt machine well with out re heat treating which is costly.
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78 SRX vs 76/77

Postby ZR800XC » March 28th, 2006, 1:44 pm

You can just cut 'bout .077" off it and cut the squish back about .015" and slap some race fuel in it! :p No need for a doughnut shaped dome, I got COMPRESSION BABY.

LOL!


Or you can just buy a MERC head and bolt on it, instant HP...C'mon, some of you Yammi guys have tried that to try and keep up!


[img]http://my.core.com/~twister76/twister1.jpg">[/img]

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