Help! I bought...a Yamaha

[The1970's]

I dont really need any help but I just thought I'd share this pretty unique project I just bought:

It's a 1982 Yamaha XJ650 Seca Turbo
20181104_162911.jpg

I picked it up from a guy going through a divorse, he planned on keeping it forever but because of the circumstances it has been parked for a little over a year. At some point he found a rebuilt turbo and never fully finished putting it back together. It's missing the whole fuel system betwee tank and carburetor. Got some parts ordered and hoping to have it running soon.

Fortunately the previous owner was constantly on ebay finding good deals on spare parts so I also have 5 crates of hard to find parts that go along with it.

[scratch]

14 year old me from 1982 thinks that is gawdy-awsome!
IME the XJ bikes have always been easy to bring back to life... never had a turbo to play with though.
I dig it!

[steve murdoch]

Congrats on the new project.
I remember reading about turbo seal problems but seeing as you already have a rebuilt one hopefully that won't be an issue.
A quick search turns up lots of info. http://home.netcom.com/~rvtucker/Seca.html#problems

[LAB3]

The guy who owned the local Yamaha dealership back in those days sold his about two years ago. He had parts on it that came diectly from the Yamaha race team and needless to say it sold for a pretty penny. Saw it out on the road once and will never forget hearing the turbo spool up, definitely a one of a kind.

[gsrick]

Almost got dumped off the back of one back in '82.

I heard once the Renaught turbo was practically a direct replacement. Don't hold me to that though.

[fbody_mike]

https://www.tapatalk.com/groups/tmioa22687/yamaha-seca-650-turbo-f10/

Welcome to the turbo club! I have owned a several Seca Turbos over the years. They are a fun bike especially when you get the boost up to 16 or so PSI. My current one is an 82 that I converted to 83.
There is still a few of us over on the TMIOA forum (see link above) that are eager to offer our advice on troubleshooting and projects.

[nvr2old]

Yeah, turbo bikes are a "blast". I've had my Honda CX500T for 20 years. Once you learn the new technique (adjusting for lag) of riding them, they really are fun. Surprisingly fast for 35 year old machines.

[storm 64]

There's a low mile Seca Turbo at Cochise Motorsports in Sierra Vista Arizona that is pretty sweet!🌞

[The1970's]

It's awesome to see so many are interested in the project also. I'm sure I will make use of all of the resources suggested. The plan for now is to get it running on the factory low boost and sort out all of the issues/leaks. Then turn it up to 15 psi or so and see how quick it really is. I've put together a fully aftermarket fuel system that should let me run a little more boost that the power up kit allows for...hehe

[GS1150Pilot]

They weren't amazing performers stock. I'm sure increased boost will help. I modded the snot out of my GPz750 Turbo and scared myself in ways that only turbo bike owners can understand.

[rphillips]

How much boost will the stock pistons withstand? If I've read correctly, in "82" these bikes were set, from the factory, with 8lb. boost, in "83" Yammy turned them up 33%, to 12lb, I know there is a limit, too much boost & you will burn a piston, very very quickly. 16lb. will be double the orig. boost pressure, be careful. My experience, in 1981 a buddy of mine took his Kawasaki KZ1300 to Mr.Turbo & had them install a turbo kit. He decided to stay with the stock pistons. When he picked it up, from Mr Turbo, they advised him to never go above 8lb. boost & the stock pistons would be fine, more boost & the pistons may not withstand the extra heat. After about a week, he couldn't stand it, he dialed it up to 12lb., after the 1st, wide open, run it was missing bad. Upon tare down found a piston, with the side burned out of it. Just say'in be careful.

[red1100]

Checked today and didn’t see them but on Seattle area Craigslist a guy had two complete no title parts turbosecas that he was about ready to give away. Thinking a couple hundred each.Might be a stretch to get to Florida but you’d have parts forever.

[The1970's]

How much boost will the stock pistons withstand? If I've read correctly, in "82" these bikes were set, from the factory, with 8lb. boost, in "83" Yammy turned them up 33%, to 12lb, I know there is a limit, too much boost & you will burn a piston, very very quickly. 16lb. will be double the orig. boost pressure, be careful. My experience, in 1981 a buddy of mine took his Kawasaki KZ1300 to Mr.Turbo & had them install a turbo kit. He decided to stay with the stock pistons. When he picked it up, from Mr Turbo, they advised him to never go above 8lb. boost & the stock pistons would be fine, more boost & the pistons may not withstand the extra heat. After about a week, he couldn't stand it, he dialed it up to 12lb., after the 1st, wide open, run it was missing bad. Upon tare down found a piston, with the side burned out of it. Just say'in be careful.

I've heard from a few different sources that Yamaha did their destructive testing at just over 21 PSI. The stock turbo should be plenty large enough to do some damage. I think the issue with higher boost on the XJ is a matter of cooling, or lack thereof. Being an aircooled turbo bike I can see how managing heat is an issue. You are correct, the stock boost was somewhere near 7PSI and the 83' "power-up kit" brought it to somewhere just over 12. My bike has the power up kit installed, but I am going to revert it back to the stock boost until I get everything sorted.

All that being said, many owners disconnect the wastegate all together and rely on the poppet valve in the intake that opens at 15PSI. The specs of the stock fuel pump list a maximum pressure of 14.2 PSI of fuel pressure so I imagine this was put into place to avoid running lean at any higher boost levels.

[fbody_mike]

The stock fuel pump is capable of pressure far greater than 14 psi, I've bench tested the pressure regulator and have found that it will easily go past 30 psi.
Your right to be cautious with the boost levels, the extra complexity of the turbo brings more gremlins that have to be worked out and going for high boost right off will make it harder. I suggest a cheap manual boost controller that bleeds air off the wastegate. Fully close it and you will have the factory 7psi. Start opening it and you will find that you can't go above 14 psi until you modify the poppet valve in the surge tank.
Yes, cooling is a limiting factor, I run 2 psi boost less in the summer, 16 psi is only for when it's not 100 degrees outside. Water injection is still a project that I keep thinking about.