A new life for a '75 GT550 2stroke triple - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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Other Motorcycles Forum for you to discuss anything about any other motorcycles. Good place for former (and soon to be) V-Strom owners to keep on the site even though they are without a strom.

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  #1  
Old 05-06-2009, 09:00 AM
Jeff Kushner's Avatar
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Default A new life for a '75 GT550 2stroke triple

I bought this yellow POS last fall to add to my collection.
I made command decision to only buy two strokes from now on since those are the one I really like. I have a few four strokers but I don't plan on actually buying any additional ones. Last month I was able to trade my V65 for a beautifully well-kept RD350 so maybe that will become next winters project although I'll ride it stock this summer.

I started working on this one with a master plan to give it some additional power although with it's high weight, it will never be a rocket. I repainted everything myself and even learned how to pinstripe. I put the pinstripes under a couple of coats of clear to protect them. On the performance side I decided to use as many of the tricks from my roadracing day as practical. This meant mapping the cylinders then raising the exhaust ports 2mm, beveling the transfers, matching all the ports to the liners, lowering the intakes 1.2mm and milling out the intake spiqots 3.5 total mm and moving and reshaping the intake bridge. I had a very old and very good machinist take 20 thou off the heads and split them into three seperate pieces in lieu of the one-piece stock head. I had Jon Easton in TX build me a set of expansion chambers to match the work I was doing on the cylinders and I also retarded the timing 6 degrees to compensate for the change in porting and higher compression. I can always advance it once it's running but i wanted to play safe to start with.I installed 30mm carbs from an H2 kawasaki and had to marry several cables together to combine my seperate oil pump and throttles to work in concert.

It seems that no one really had any experience modding this engine so being able to learn from others was pretty much out of the question. I ran my new numbers on a "two stroke engine building program" and accordaing to it, I should net nearly 74 hp which would be a 24hp increase over stock. I went to work while praying that the engine would start and still have some power below 5000rpm<LOL>. I finished up this past Saturday and after wheeling it outside my basement shop, I fired it for the first time. It spun for about 10 seconds before firing and came to life. My GF who doesn't know a lot about engines exclaimed "that things sounds like it just wants to take off!"

I've ordered new pilots and mains and yesterday raised the needles one notch. It still needs to be dialed in but it runs great. A short run in the driveway told me that it has plenty of low end power so that fear is soothed. I can't wait to give it a full road test.....from the sound of it, this engine should run really nicely.

jeff
Attached Images
File Type: jpg GT550 before.jpg (83.6 KB, 134 views)
File Type: jpg Completed GT550_320x240.jpg (14.3 KB, 83 views)
File Type: jpg GT550 front rightside.jpg (97.1 KB, 88 views)
File Type: jpg Completed GT550.jpg (94.1 KB, 78 views)
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My VStrom 1000 K7
Stock bikes: a purple '74 RD350 in great shape, '70 H1, '72 H1, 1975 GT550, ,original 1975 H2 750 triple (purple of course), 1976 CB400F Supersport. '73 CB350-given away Modified bikes: Fully ported 1974 H2 750(my go-fast), a scary fast '82 Yam 650Turbo running 18PSI, a '75 GT550 built up & ported. To-Restore list: '72 H1, 2-'75 H1's, '82 920 Yamaha Latest acquired: 1974 GT750 can't wait to replicate our old racebike of the 70's!

Last edited by Jeff Kushner; 05-06-2009 at 09:04 AM.
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  #2  
Old 05-06-2009, 11:43 AM
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Very cool.

I think my next one may be a 2smoke.
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Old 05-06-2009, 05:32 PM
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Beautiful work. It takes me back to the 70s (R-reg) GT380 I had when I lived in the UK for a while. After a fair bit of work to get it running reliably it grenaded on the M1 one day. I'd put precisely 500 miles on it before the center cylinder seized, the con rod separated and smashed through the front of the cases. I sold the whole thing for 75 pounds to a fourteen year old who was going to rebuild it with his dad, intended to be rideable when he was old enough to drive.
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  #4  
Old 05-07-2009, 07:59 AM
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Thanks guys. Yes, the GT380 is on my "to get" list. I've always thought that the '74 in red was one of the best looking bikes ever built! I was able to trade my V65 for a very nice '74 RD350 a few weeks ago so that will get plenty of riding time as soon as the baffles I bought arrived.

Back in the day, a 350honda(1st bike) was the only 4 stroke I ever owned....everything was a two stroke. There is nothing like a modified two stroke coming on the pipe!!

jeff
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My VStrom 1000 K7
Stock bikes: a purple '74 RD350 in great shape, '70 H1, '72 H1, 1975 GT550, ,original 1975 H2 750 triple (purple of course), 1976 CB400F Supersport. '73 CB350-given away Modified bikes: Fully ported 1974 H2 750(my go-fast), a scary fast '82 Yam 650Turbo running 18PSI, a '75 GT550 built up & ported. To-Restore list: '72 H1, 2-'75 H1's, '82 920 Yamaha Latest acquired: 1974 GT750 can't wait to replicate our old racebike of the 70's!
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  #5  
Old 05-11-2009, 10:37 PM
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Default Take it easy

Had a cousin used to hot-rod Kawi 750 triple 2-strokes way back when. Usually managed to seize at least one piston every couple of weeks, regularly blowing crankcase seals, and every year or two would twist the crank. I kinda think you'll have a tough time getting someone who knows how to rebuild that crank, although your machinist friend might be up for it. If you haven't, might want to look into Wiseco pistons, which probably have much better metallurgy than the OEM slugs. If the ignition is up for it, would probably go to premix as well (or set the oil injection pumps to full on all the time), to head off lube failures and all that entails. One tip from him I remember: Muriatic acid works fairly well to remove the smears of aluminum from the bores when you seize a piston. Yeah, the ring-dingers are fun, and thrilling when the power takes a sharp jump, and the multi's sound sweet with expansion chambers. But they can be VERY touchy when hot-rodded. Be darn sure you approach peak power mixture from the rich side, not the lean side. Good luck.
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  #6  
Old 05-12-2009, 07:11 AM
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[quote=Jimding;404099]quote]

Thanks, Surprisingly, there are still a bunch of places that still work on these classics. I do all my own work except crank rebuilds but I was pretty amazed to see how many good machinists are still working on them. A rebuild for a twin goes for around 75-100 bucks with a triple going for between 100 and 150 bucks. I used to roadrace a GT750 engine stuffed into a Bimota frame back in the late 70's. We started with a H2 but like your cousin, suffered way too many failures. I did learn how to weld a crank on the H2 though to keep the pressed on flywheels in place<LOL>. Our H2 was just too tempermental to roadrace although there was a H2R that was watercooled but we didn't have the money to actually BUY a bike.

I spent a lot of time back then learning and building. I had a guy kinda take me under his wing and he taught me quite a bit of how and why a two stroke can be so powerful and how to move the powerband around. A lot of folks knew the guy and he wrote a few books. He passed away in '00 or '01 and from what I heard, a lot of folks went to Gordan J's funeral. Yeah, I was lucky enough to learn from one of the best.

I always liked keeping the oil pump on anything other then a race engine. The main issue is getting oil to the main journals with premix and no matter how rich you run it, it just doesn't get in there like the oil injection. On a race engine, you're going to tear it down each week but for the street, you really don't plan on taking it apart all the time, hence the oil pump remains.

I just got all the jets I ordered lastnight and I installed the mains and pilots that took me nice and rich....so I can finish dialing it in.

It's get a nice bark to it and I've never heard a gt550 rev like this one does. I din't get them in till late last night though so there was no time to start plug chops.
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My VStrom 1000 K7
Stock bikes: a purple '74 RD350 in great shape, '70 H1, '72 H1, 1975 GT550, ,original 1975 H2 750 triple (purple of course), 1976 CB400F Supersport. '73 CB350-given away Modified bikes: Fully ported 1974 H2 750(my go-fast), a scary fast '82 Yam 650Turbo running 18PSI, a '75 GT550 built up & ported. To-Restore list: '72 H1, 2-'75 H1's, '82 920 Yamaha Latest acquired: 1974 GT750 can't wait to replicate our old racebike of the 70's!

Last edited by Jeff Kushner; 05-12-2009 at 07:14 AM.
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  #7  
Old 05-14-2009, 03:09 PM
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Nice Jeff! I am soo jealous of your kind of talent and skill! Oil changes and chain maintainance are about the extent of my mechanical prowess. Being born in 63, those bikes are what I grew up wishing for and luckily riding a few. From a rookies point of view, it might have been easier to put the clear coat on top of the pinstripes...musta been a bitch to put the pins UNDER the clear j/k.
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  #8  
Old 05-14-2009, 03:20 PM
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Looks good!

My first road bike ever was the GT750. I was able to borrow it from a friend who only asked I put insurance on it for the season. My mom wasn't happy but she only said I couldn't "have" a motorcycle, nothing was mentioned about borrowing one. I had a lot of fun that summer...
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  #9  
Old 05-15-2009, 02:58 PM
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Thanks Mtn S, it only takes being very poor at a young age to force one into learning by necessity to work on ones own machines<LOL>! I was surprised after coming back to bikes after a 22 year layoff to raise my family that so many guys don't have the slightest clue how to work on thier machines. It didn't used to be that way, everyone knew how to work on them to some extent. I credit you though for at least admitting it.

Fire, we used to roadrace a GT750 back in the day. We were able to steal (did i really admit that after all these years) a bimota frame and we stuffed it full of GT engine with a dunstall tranny, raised exh ports and lowered intakes, a few mods to the tranfers, exp chambers and just like that 190mph on the straights. Was a whirlwind of the next two and a half years and I'm just thankful that my racing partner and I made it through with our lives. We used to have a third rider and he weighed a whole 95 lbs soaking wet but he trashed the bike almost everytime he got on it so we sent him home. That GT engine was really bulletproof. With the changes I had made to it, we had no trouble beating the non factory guys on Kaw 1000's. They were powerful but heavy and with the GT, we had heat continuity(more consistant power) and no valve trains.

There's another member here who restored one to stock condition within the past year and he did a fantastic job. I don't remember who it was but I remember his work and it was very, very good, much better then mine.


jeff
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Present only:
My VStrom 1000 K7
Stock bikes: a purple '74 RD350 in great shape, '70 H1, '72 H1, 1975 GT550, ,original 1975 H2 750 triple (purple of course), 1976 CB400F Supersport. '73 CB350-given away Modified bikes: Fully ported 1974 H2 750(my go-fast), a scary fast '82 Yam 650Turbo running 18PSI, a '75 GT550 built up & ported. To-Restore list: '72 H1, 2-'75 H1's, '82 920 Yamaha Latest acquired: 1974 GT750 can't wait to replicate our old racebike of the 70's!
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  #10  
Old 05-18-2009, 05:32 AM
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Nice work. I wouldn't mind adding a 2 stroke to my collection as well. I like the triples, either suzuki or kawasaki but I'd happily settle for an rd350 LC.
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