'74 Suzuki GT380 "The Nostril Assaulter" *New seat*

Primo_Toy

New Member
Well, I'm both new to the site, and the world of bikes. Just a few weekends ago I fell in love with a bike and did a midnight run down the highway to go get it. (I'm in the military and couldn't get time off during the day to go from Edmonton to Calgary and back).

The bike in question was a 1974 Suzuki GT380. The fact that it was a 2 Stroke Triple was cool, but what really grabs me about the bike is the "Ram Air System" shroud on top of the engine. To me it looks like some old kitchen appliance missing its power cord (has about the same amount of power too). The bike was mostly stock and original with the exception of new tires, brakes, chain, sprockets, a random set of bars, and a poorly recovered seat. The red paint was very faded and there were signs that the bike had tipped over at least twice. I drove with the windows down in my truck following the owner to a 24h self storage lot to use the loading ramp. I swear I can still smell that bike in my truck.

Here is a few pics of the bike both on its way home and in my work bay.

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Like everything I own, I can't leave it alone or stock for longer than 5 minutes. I have always liked old cafe/bobber styled bikes, and now was my opportunity. I started by washing the bike followed by leaning against my work bench drinking beer continuously closing one eye imagining the finished product. Sadly I had to work in only a few hours so I decided to call it quits and get some rack so that I could still function after work.

Work on the bike began immediately after I punched out. I was still wearing my fatigues as I began removing things faster than I could decide what to keep. Within a few minutes the fenders were gone and I was left with the predicament of how to mount a tail light. I decided that since brakes only slow you down, the light could wait. I made a quick run to Canadian tire for some Autosol aluminum polish. I tried correcting the heavy tarnish on the engine side cover, but soon became bored with the slow process, and wanted more visual bang for the buck.

Here is what a few minutes of polishing did

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I decided that a colour change was in order. Something other than what I would describe the current colour to be "Sun Dried Salmon" would do. Once again I jumped into my truck and sped down to Canadian Tire. I picked up some scuff pads, a razor, masking tape, pinstriping vinyl, and some paint and primer. I also grabbed myself a late night snack at Tim Hortons as well as some tea to fuel the evening task of prep and paint.

I started by using a razor blade to remove the faded gold pinstripe that defined the side of the tank. That was time consuming and made my fingers sore, not to mention wasn't really doing as well as I had hoped. I stuffed a donut into my mouth and walked next door to grab something to make my life easier. I ended up with an electric belt sander from the woodwork shop in the bay next to mine. It wasn't a precise tool, but then again, the already dented tank couldn't get much worse. Within a few minutes, and a few close calls of accidentally putting the damn thing down while it was still spinning, I had a gas tank down to a fairly uniform layer of 1973 green. (From what I understand is the lazy buggers resprayed tanks that weren't used the previous model year). I masked around the tank and removed the side covers to get the same treatment. Primer went on and dried quickly since the shop is heated to something I can only describe as something just short of "Kill".

Tank in primer (yes I was too lazy to remove it, but with the center stand it put it at a nice working hight)

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The duplicolor self etching primer dried very quickly so I began applying the chrome silver in multiple coats until I got the look I wanted.

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Since the bike was still stock minus fenders, I decided to add a bit of "café" and began cutting the 1 1/2" masking tape into squares. I lauded them down over the 3" high feature running the top of the tank as well as the side covers.

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I hit that with some semi gloss black and some mystery brand automotive clear. (I should ad that this paint was all on clearance since caps, labels and sprayers were missing)

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With the smell of paint fumes affecting my ability to see straight, I decided to call it a night and went to bed. The next day I returned to the bike with a new powerball wand and a $14 el-cheapo drill. I made quick work of the oxidized engine. I also jerryrigged a Honda Ruckus tail light to the underside of the seat using some zip ties and a pair of jewelry box lid props.

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I flipped the bars to simulate poor-man's clubman bars. I also bought a retro Bell helmet, some goggles and dug through my things to find a set of cool old leather gloves.

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It didn't take more than a few days but, now I had a bike that was mine. I was very excited to take it for a spin, and tooled around the base after work for a few days.

(more to come)...
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

That sexy little minx is off to a great start! Nice work on the paint! Looking forward to what comes next... How 'bout some real clubman's?
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

I like the finish you got out of a couple of spray cans. Nice write-up also. My friend had one of those when I was a kid and it actually went fairly well. Have fun with it.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

In my infinite wisdom, I decided to remove the airbox to give the bike some better throttle response as well as the sound that only open side draft carbs make under load. It was intoxicating, the sound of the bike echoing off different things as I motored past. I put a tank of fuel through it in just one night. I decided to hit the highway to go show a friend what had kept me up for the last few nights.

About 10 minutes of solid 110kph down the highway and the bike was starting to feel sluggish. I knew my tank was full and that my carbs were clean (I dismantled them and checked float hight and cleanliness when I removed the airbox). I rapped on the throttle and the bike did nothing other than make noise. I carefully watche the speedo and tach to make sure that the clutch wasn't slipping when all of a sudden a loud "POP" came from underneath me. The bike imidiatly began to slow down and sounded rough. I looked down half expecting to see a sparkplug lead flapping in the wind. Instead something caught my eye behind me. Like a World War 2 bomber going down in flames, I had a smoke cloud billowing out of my #3 pipe and a steady spray of oil coming from the carb. Before I could react, a second "POP" was made. I clutched in expecting my motor to grind to a halt and lock my rear tire. I took a look behind me as I was pulling over and the smoke cloud was almost comical.

I safely made it to the shoulder of the 3 lane highway, and stepped off the bike. Within seconds a familiar truck pulled up to me. It was the buddy I was going to see. He somehow knew it was me. Aparantly I am the only person he knows who is crazy enough to ride in -10 with an open face helmet and set of pilots goggles. We had a good laugh as we loaded the bike into his truck and carried off to his place.

Within minutes of being in his garage I realized what happened. I leaned the motor out with the lack of a restrictive air box. Piston #1 and #3 had holes burned clean through.

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I got on the horn, and orders some pistons, rings, bigger jets, and some gaskets from the local Suzuki dealership. As soon as I was done on the phone I began pinstriping the tank. I used the cheap stuff from off the shelf at Canadian Tire that I still had in my jacket pocket. I also used it to create Foùx knee dents. While I was at that noticed that the long winded name on the side of the tires had the name of my all time favorite jet hidden among all the numbers. I used a whitewall repair paint pen to make it stand out as well as the brand name on the tire.

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Re: '74 Suzuki GT380 "The Nostril Assaulter"

Thanks for the kind words. Yes, Clubman bars are on order.

As far as paint is concerned, I have painted 2 cars with rattle cans and had people call me a liar when they saw the finish. It's all about the prep, temperature of the paint (a bucket of hot water helps) and a bit of wet sanding and wax.


Some of my parts came in today...

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I'm still waiting on piston rings and a couple more gaskets as they were back ordered...


I have been calling around and there is a shop here in Edmonton that builds custom expansion chamber exhausts. I will be going there for some new pipes as well as some dyno tuning to make sure I have a proper jet size in there. Melted pistons suck.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

Until those parts come in, this is about as fast as I can go...

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I will post again once I have something worth posting about...
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

Pretty good for rattle cans. SR71 - agree. Amazing piece of engineering. Detonation and melted pistons can't say I didn't see that one coming. If the pipes are coming from Walms or Triplenut they will be fine, others I can't speak for.

You need to at least flush the crankcase out. Most of the piston went out the exhaust, but as it blows through the crown, the rest of the debris heads south into the crank and tends to fill the mains and big end bearings. Smart money would be on a crank rebuild with new seals. Bill Bune in nearby Anoka MN is the man to go to for cranks.

It's worthwhile fitting an electronic ignition too.

While I'm thinking about it, low bars are a pain in the neck (and wrist) at the best of times and with stock pegs they can be torture. I'd recommend either drag bars or superbike bars or fit rearsets.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

I have plans on washing out the engine, I have mye eye on a second motor, and may fully build it and do a bit of port timing. The motor I had melt down is already out and on the bench.

I would love to swap to electronic ignition. I was thinking of using a MSD setup I have for an inline 6 and just bridging the setup to run for 3 cylinders. Is there an easier, more swap ready setup?
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

MSD is actually an incredible ignition. A bit large and heavy but lots of spark energy. If you have one with two channels or more, it can be made to work. The usual trick is to fire two cylinders together (wasted spark) with one channel and the other one on its own channel. Newtronics used to offer one for that bike and Powerdynamo in Europe have a complete alternator/magneto type system and I'm sure they list the 380.

Light clean up of the ports isn't a bad idea. Try to not go mad on those. Too much exhaust port raises power and kills bottom end. Too much intake timing adds next to nothing at the top and kills bottom end. A little extra compression and getting squish right helps all through the range but too much raises combustion temps too far and melts things too.

I think there are three GT380 projects on this board at the moment. That must be some sort of record.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

teazer said:
MSD is actually an incredible ignition. A bit large and heavy but lots of spark energy. If you have one with two channels or more, it can be made to work. The usual trick is to fire two cylinders together (wasted spark) with one channel and the other one on its own channel. Newtronics used to offer one for that bike and Powerdynamo in Europe have a complete alternator/magneto type system and I'm sure they list the 380.

Light clean up of the ports isn't a bad idea. Try to not go mad on those. Too much exhaust port raises power and kills bottom end. Too much intake timing adds next to nothing at the top and kills bottom end. A little extra compression and getting squish right helps all through the range but too much raises combustion temps too far and melts things too.

I think there are three GT380 projects on this board at the moment. That must be some sort of record.

There might be a fourth one too. I am in the middle of a deal for a trade (trading an old S&W collectors revolver) for a 71 gt380. Crossing fingers.

As for this build. Love the paint with the rattlecans! Looks real good and I am looking forward to seeing what more you do with this bike. Unless you blow it up more. ;D
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

When I read that you removed the airbox, I thought, "Oh! No! He is going to burn up that engine!"

Running regular gas will do that, too.

Forget your plan to "wash out the engine." Split the cases and change the bearings and seals. You can probably find bearings from an industrial bearing source rather than paying OEM prices and waiting for them to come in. Try to get new seals, too, if you can. When those pistons blew through, a shitload of molten aluminum debris blew into your bottom end. It makes a horrible mess. Split the cases, do it right.

Listen to the wisdom with regard to porting. VERY easy to port too much. Don't touch the transfer ports except for a little clean up. Matching the transfer ports to the cases has a bit of benefit. As far as the intake port goes, don't do anything except maybe trim half a millimeter from the piston skirt. THAT is reversible by replacing the piston. But seriously, as was already explained, it will hurt powerband more than it will add top end.

Don't raise the exhaust port any more than a millimeter. More that that, and you will have a very poor powerband. Don't even consider raising the exhaust port unless you increase the compression. Two strokes lose compression when you raise the exhaust port, so you have to compensate. The squish area of the heads should follow the contour of the piston crowns as much as possible. In stock form, they do not. Be careful not to raise the compression too much. Detonation will hole your pistons again. Don't raise the compression unless you raise the exhaust ports. You are looking for a cranking speed compression of 150 psi. Any higher, and the engine will not hold up. I built an engine to 185 psi compression, and the engine couldn't make it through one race. <G>
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

BTW: all that smoke is due to the fiberglass wrapped around the baffles. Pull out the baffles and remove the fiberglass. Don't leave the baffles out, as it will sound like shit and won't run better. The fiberglass gets impregnated with oil, and creates smoke, especially when you run hard and really heat them up.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

Some really good info in that post. Thanks for the tips on porting.

My baffles no longer have the fiberglass wrap. It was the first thing I removed. I had intentions of leaving the baffles out but the bike would idle at 7000rpm. I put them back in very quickly. Like I said, I'm going to run a set of custom expansion chambers to build power, I'm not concerned with porting, but I may whip out the dremel and clean up some casting imperfections in the runners.

As far as splitting the case, I shouldn't need to. The engine let go so quickly and was so hot that it sprayed a "dry graphite" like compound out the tail pipe. The crank chamber is remarkably clean still. There is actually no sign of the failed engine from beneath the pistons (at least what I can see). The bearings are almost new in this engine, one of the previous owners changed them and the case end gaskets it seems.


I will deffinatly investigate, but I won't spend money where it isn't needed. Most of the 2 stroke dirtbike guys that I know say washing out the engine with a Varsol like cleaner is plenty good enough. Besides, the melted aluminum is softer than any steel bearing surface. If it ends up being worse than I orriginally thought, I will deffinatly pull it apart and give it a full going through.

As I mentioned before, I am keeping my eye on another GT380 to steal the motor from since the bike is a pile of F***. If I am going to put money in an engine I want to put it all in the same engine.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

150 isn't a bad rule of thumb for an air cooled bike. Race sleds often run up to 220psi but they use 116 octane race gas. My street bike is 165psi and the exhaust was raised 4mm or more and it runs fine on premium street gas.

Te only way to know what the motor needs in terms of porting is to work through the numbers. Most old bikes were pretty conservative and can use a lot more port time and area but there often is not enough metal to do it. Clean up with a dremmel is a good idea.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

With the new rings and pistons I will deffinaltly check compression.

You said cranking pressure of 150psi. How many kicks should that be? GT380s were the only ones to not receive an electric starter.



So far I am really glad I signed up here. Lots of great info in such a short amount of time. I appreciate all of the advice amd tips.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

Primo_Toy said:
Besides, the melted aluminum is softer than any steel bearing surface.

Ever hear of aluminum oxide? It's a hell of an abrasive. In fact, they make sandpaper out of it. Also, if one of those sphere's of melted aluminum lodges in a bearing, it could cause the bearings to slide instead of roll. The result would be a blown bottom end in NO time.

It won't cost but a few bucks for bearings. They are like $10 each. You have the engine out of the frame already. You should split your cases.

That's my story, and I'm stickin' to it. :)
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

teazer said:
150 isn't a bad rule of thumb for an air cooled bike.

For an air cooled two-stroke bike. I'll go 190 psi on something like a Harley. My '93 Wide Glide was running 195 psi. It was a bit problematic at that compression. Pushing the limits IMO.
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

Primo_Toy said:
You said cranking pressure of 150psi. How many kicks should that be?

I'm not saying that is what your compression should be with a stock engine, just saying that you should not raise the compression much more than that. I don't know what the stock compression would be, but I'd guess 135-145. That will drop quickly if you raise the exhaust port.

Adding expansion chambers would be cool. That adds a lot of performance. If you get chambers, maybe the chamber maker has porting specs that the pipes are optimized for.

3 or 4 compression strokes should be enough for the reading to peak. As per standard practice, make sure the throttle and carb are open. (Can be done with no carbs on the engine.)
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

AlphaDogChoppers said:
When I read that you removed the airbox, I thought, "Oh! No! He is going to burn up that engine!"

+1

Could see that coming a mile off! I was reading the rest of the thread saying 'Nooooooooooooooooooooooooooooooooooooooooooooooooooo!'
In a parallel universe I'm sure it is a punishable crime to put a vintage engine through that kind of abuse.
It maybe better to get a GT550 or GT750 if you are that desperate for more fire and brimstone!
Pipes, pods, and electronic ignition should liven things up, but still leave you with a rideable and reliable toy.
Engines have feelings too ;)
 
Re: '74 Suzuki GT380 "The Nostril Assaulter"

AlphaDogChoppers said:
I'm not saying that is what your compression should be with a stock engine, just saying that you should not raise the compression much more than that. I don't know what the stock compression would be, but I'd guess 135-145. That will drop quickly if you raise the exhaust port.

Adding expansion chambers would be cool. That adds a lot of performance. If you get chambers, maybe the chamber maker has porting specs that the pipes are optimized for.

3 or 4 compression strokes should be enough for the reading to peak. As per standard practice, make sure the throttle and carb are open. (Can be done with no carbs on the engine.)

Again, great info. I'm really glad there are guys willing to share knowledge like this.

I will at the very least split the case and do a careful inspection. I want to delete some of the wires coming from the gear position switch anyways since the did digital gear position gauge between the speedo and tach has kicked the bucket. I will probably just modify the existing tach so I can use it on its own and add a mini digital speedometer to cut down on the clutter.


I have to dig through my stuff, I have a tube of Rolls-Royce Hylomar gasket maker sitting around since my last transmission re build... That's should be adequate for re sealing the case halves.

As far as porting, my exhaust builder has (back in the day) done several GT380s and currently owns a GT750 water buffalo. He recommended just a mild port match if anything, and said I can't hurt anything by smoothing out some poor casting flaws. I'm not building a psyco race bike, just something that is peppy and fun to ride. I should gain close to 10hp with his pipes on stock internals as long as we dyno tune the carbs for propper jetting.

Before I dyno the bike, I think I will take the advice of trying to switch over to a electronic ignition. Points are cheap, and the majority of my cars run on them meaning I am comfortable dressing and adjusting them regularly. However making the bike as reliable as possible is always a goal. Before it melted, the engine would fire up in 2-3 kicks cold with choke, and 1 half kick warm. Apparently that is a good indicator of a healthy engine as far as compression goes.



If anyone else knows of a popular/cheap/simple electronic ignition swap, please let me know. Maybe I can shop around this weekend.



In other news, I have acquired some dense insulation foam, and hope to laminate it together and carve out a mold base for a fiberglass seat/rear fairing. Pictures to come of that soon. I'm sure my '73 Corolla Coupe project hates me for neglecting it. But with the amount of work it needs it wont be ready for summer, whereas the bike will. If anyone is interested, that project may pop up in a few of my posts here and there.

Thisis getting a full body restoration as well as a roll cage:

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It is also getting this, a JDM 2000cc 210hp twin variable cam engine and 6 speed transmission:

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