1978 gs750 turbo questions

[rspector]

I just bought a 1979 gs750 that has a turbo on it !! the bike is in great shape and starts very easily. 500 bucks, I figured ya can't go wrong. I have two questions, 1)At a low rpm would the boost gauge be showing a vacuum or pressure? 2) I got abunch of the guys old tools, and one of them is a tuning fork with a suzuki emblem on it, any idea what the hell thats for?


Took it out for the first ride this morning, seems real doggy at low rpms? when you tach the thing up it goes pretty good, but seems very close to red line before the turbo starts doing anything, any one ever seen or had experience with a bike like this? any answers would be greatly appreciated.
Thanks
Rob

[tcraft128]

First CONGRATS on the find...how about some pics.

The boost gauge will show vacuum while the turbo is spooling, on a car with a good turbo match, this is about 3000 to 3500 rpm to reach full boost. Bikes I have noticed are a little bit less predictable due to the rate that the engine spins up, much faster than a car! This can make the turbo lag seem longer, but in all reality, it is not...it is an inertia thing...the airpump read engine, is not moving the correct volume of air long enough to spool the turbo with any consistancy. The Doggyness (newword) is because of said LAG. (turbo lag) where the engine is actually breathing through the turbo, instead of being feed by the turbo. Lag can be caused by many things including improperly sized exhaust, oversized exhaust housing or on the bad side, failing journel bearings. Just make sure that you take it slow, make sure your carbs are good, check your plugs, clean your airfilter and change your oil...and remember that things melt very fast in boost ie pistons.

HOW MUCH BOOST ARE YOU RUNNING? IS THE GAUGE INCREASING ALL THE WAY TO REDLINE? WHAT TYPE OF CONTROLLER IS ON THE BIKE....POST UP SOME PICS OF THE REAR OF THE TURBO AND THE COMPRESSOR HOUSING SO WE CAN SEE WHAT TURBO IT IS.

[rspector]

it says jay ray or ray jay on the turbo housing, the gauge has a broken needle on it and even with the bike off does not register at 0 so I don't know how trust worthy it is, but untill the bike hits 8 grand its really doggy. The waste gate is hooked up to a box on the frame with a what looks liek to me an upside valve from a head , so I would imagine when the turbo pressure gets too high it opens the valve in the waste gate. Should that have an adjustment on it? there is a big allen bolt on the bottom. I'll take some pics later today.

[rspector]

http://www.satanicmechanic.de/turbo.shtml this is a link to basically what the turbo kit looks like minus the waste gate

[lecroy]

I doubt he has any controller on it. It is old school.

If I were you I would just send the bike my way. It's going to be more trouble than it's worth. If you want to keep it, read on.....

No matter what the turbo is doing, if the throttle is closed off you will see a vacuum.



IMHO, Rule #1 when playing with turbos, learn what your doing before you make any changes. So, don't start mucking with the wastegate until you know how to read a plug correctly.

Rule #2, more important that Rule #1 and coming from a very reliable source, don't use the internet as a source of information on turbo charging a bike. Your not doing anything new here, so it's best to ask. I say this after being humbled this summer with 2 blown engines.



The first thing you need to do is figure out what you have. There is normally a stamped plate on the RaJay near the compressor's outlet that shows the model. It may not be marked by RaJay. It could be Roto-Master, ArKay, etc.
We are looking for something like 303ff blah blah blah. There are several combinations that the turbo could be but my guess is that it is a B or F compressor and an F turbine. There is also an EF combination that was used a lot on the high HP funny bikes but I doubt this is what you have. If there is no plate, look at your turbo and tell me if it looks like the one on the left or the right.



What does the wastegate look like? Is there any ID that would tell you who made it or the model number? If it looks like the one in the following picture it was built by Mr. Turbo. If this is the case, look near the set screw on the bottom and see if it has an "R" stamped in it.



The lag could be almost anything. The turbo runs from exhaust heat. Higher exhaust temps, faster blade speed. Once we know what turbo you have, the next thing is to have it checked out. There are two basic bearing housing that were used, 303 Single Fed and Dual Fed. There are also two different heat shields that were used, stamped and cast. The stamped ones (and even the cast ones) can warp under heavy loads. Once they warp they can cause a massive amount of lag like you are seeing.

"Took it out for the first ride this morning, seems real doggy at low rpms? "
Well, yea. Depending on how the motor is setup, it may very well make less power than a stock engine with no boost.

You also want to check the wastegate, lines, etc. All the RaJays can build 40 pounds of pressure. More than enough to melt most engines. Get you camera out and lets start there.....

[lecroy]

Oops, did not see you last posts. In those pictures you linked to, that appears to be a Mr. Turbo wastegate. It looks like a B compressor.

[BSinCO13]

Turos can be tricky things. From those pictures it would seem to have an intergrated wasegate but I see no actuator. As far as the turbo take off the air filter and check for play. You should have minimal in and out and you want no side to side play. If you do encounter side to side play check the condition of the fins. Although one of the first things I would do is buy a new boost gauge, any performance parts house should have one (eevn autozone). Good luck and happy boostin'.8)

[rspector]

ok, leroy thanks for the indepth reply, the waste gate is on the frame in the front, it is a rectangular unit , with a hole in one side of it and an upside down valve(like out of the head)looking thing. I will take plenty of pics tonight and post them. The guy who owned this bike before me used to drag it up at the new england speed way, won a bunch of trophies with it to, I have not changed any settings since I got the bike. I will also try to find a working boost gauge. Thanks again

[lecroy]

If it was a little drag bike he may have made some other mods to it. I would start with a compression test. It would at least give you an idea of what your looking at. It could very well have lower compression than stock, even if it has a larger bore. This is why I said that it could make less power than a stock engine with no boost. Of course the best thing would be to just pull it all down and start fresh. A good winter project.

Bearing wear is a big deal with thte turbo, but you don't inspect it with your fingers. Besides, he's showing a draw system so the carb or pipe need to be pulled to get into it. If you want to do it right, I scanned the manuals for the RaJay a long time ago and made them free for downloading. Them some dink head decided to make a profit from them and sells it on eBay now for $13 a copy or something.

Just go to my site http://dickey.no-ip.org/rajay.html. It may take a while to download now with my DSL.

If you don't have access to tool shop with the guages to check it, the best thing would be to ship it to Mr. Turbo.

Not sure on your wastegate. Normally with these old setups there was only one line from the manifold to the wastegate. That's your whole controller. You build as much boost as you can as fast as your can.

If he was racing it, he may have not been using pump gasoline. Another good way to melt the engine. If your not wanting to take the time to check anything, I would get some real fuel for it, at least to starve off any major melt down. VP C16 is common but a few of us are now running the Torco MACH116NOS and MACH118NOS without any problems other than the red dye gets into everything.

[rspector]

He road the thing on the street as well as on the track. Tonight i'm going to test the boost with a guage i'm borrowing from work. Imho it does not seem to be giving it much boost at all, the bike falls on its face if you wack the throttle so I don't know if its a carb problem or a turbo problem, what do you think it would cost to get the turbo rebuilt asuming thats where the problem lies? Also there is no chance you live in NewHampshire and would like to come out and look at the old girl is therE?

[chiphead]

Hey rspector, I think I saw this thing on craigs list and actually emailed and got a response back from Heather. Then I came to my senses.
Good luck with that thing!
Where you at in NH?

[rspector]

i'm in keene, yup it was on craigs, the thing was in such good shape when i got there I had to buy it

[Kaptain Ketchup]

Rob?

Congrats on the turbo bike. Hows the bandit running? It's Mark. I came to pick up that 83 1100 engine/frame with my girlfriend in my van last year some time.

I have a proposal for ya.... Still interested in an FJ1200??

I think I have ya on my msn list still...

[Commodus]

Heh - see, I told you this was the place to ask!

[lecroy]

He road the thing on the street as well as on the track. Tonight i'm going to test the boost with a guage i'm borrowing from work. Imho it does not seem to be giving it much boost at all, the bike falls on its face if you wack the throttle so I don't know if its a carb problem or a turbo problem, what do you think it would cost to get the turbo rebuilt asuming thats where the problem lies? Also there is no chance you live in NewHampshire and would like to come out and look at the old girl is therE?

I would contact Terry at Mr. Turbo and have them give you a quote. The last two bearing kits I bought from Turbonetics were under $200/ea. I think the last heat shield I bought was under $100. If you decide to send it out, use a reliable source. Some of the parts are no longer available for these.

Again, the bike falling on it's face could be a lot of things. With him riding on the street he may have the "box" that you spoke of cobbled up to run lower pressures when he wasn't running down the track. Normally there was only a single line from the manifold to the wastegate to control the pressure.

Send some info on the carb as well.


I'm not close enough to stop by for a beer.