'82 650 Turbo Engine on '81 XJ750 Seca?

I will start this off with the statement that I really am new to motorcycles in general and working on them is just something that I haven't done.

That said, I do have a working understanding of how engines work, just enough to know how little I really do know.

Last weekend I bought my first bike, what was sold to me as an '81 XJ750 Seca. After looking through this site for a few days I think that I have learned the following:

*The serial number/short VIN on my frame does not match the engine. (Frame starts with 5G2 engine starts with 16G.)

*The engine code (and black side cover) lead me to believe that the engine is from an '82 650 turbo

The bike starts and runs, although it is pretty hard to start cold, seems to idle high - around 1200 RPMs, and runs pretty rough. The P.O. said that the gas is fresh, but I don't have any way to prove that.

What should my first steps be? My thoughts were to pull the plugs and air filter tonight, and replace them if needed, plus change the oil.

The rest of what I have read on here says that the carbs on these things need to be clean clean clean. I doubt the PO did much maintenance on this thing, so this probably needs to be addressed, but I also don't want to cause myself tons of suffering if I take them apart and mess something up. My thought on this was to buy the appropriate Haynes manual and go from there. Would a mix in gas carb cleaning agent do me any good at all?

Which book should I buy? Is my diagnosis of the engine correct, is it really a 650 turbo?

And the one and only picture I have so far of my newest treasure

 

Everything sure looks like a 750. I wouldn't make any diagnosis based on the black side cover either. Those things get interchanged every now and then. Go to the XJ4ever page and look for TECH TOPIC: Model ID's and VIN's. Use the engine numbers to look it up and verify. I suppose its possible. I know The 750 and 650 (non-turbo) engines are swappable (with a few mods).

I'm willing to be its NOT a turbo. They're not too common in general. And its even less common to see them get mixed and matched with the other xj bikes (apart from the oil cooler). But maybe someone else can verify based off the number.

If I were you, I would go ahead pull your carbs. Read through Rick Massey's "The Whole 9 Yards". Learn to clean them, and clean them right the first time. After you clean your carbs, then get new plugs, change the oil, make sure your battery is charged (or get a new one), dump out your gas and put in some fresh stuff (93 or higher).

As for the manual, I would go ahead and buy the XJ 650/750 Haynes.

And idling at 1200 RPM's is pretty ok. 1100 is ideal. But that's not bad.
Also these bikes are notoriously hard to start cold. Check into cleaning the Enrichment (Choke) circuit when you do your carbs. There's a tricky jet in there to clean. But there's a pretty good article on here about it.

And lastly, never trust the P.O.

 

Nice looking XJ!

According to the engine VIN, yes, the ENGINE CASE is from a 82-83 Turbo 650. However, what any PO did to replace the componets is anybody's guess.

Your New(old) bike tune up list should be as follows:

a. Pull the rear break and look for delamination.
2. Bleed the front breaks. Also consider changing the lines, especially if they are the originals.
c. Change oil, oil filter, air filter, plugs. Cheap insurance and you'll probably end up needing to do them soon anyways.
d. Charge battery and have it tested.
e. Test petcock. It should only flow fuel freely in "PRI", not "ON" or "RES".
f. If it doesn't have an inline fuel filter, install one.
g. YES, by all means, clean those carbs!
h. The best thing to do for manuals is get a Clymer or Haynes, AND an original shop manual
i. Use the gas for the lawn mower and put fresh in the tank. That way you KNOW.
j. If it still has the original fuse box, replace it with a blade style fuse panel.

k., l., and m. Read "the whole nine yards" post by Rick Massey, Read "clunk test" by Rickomatic, and ask questions here. Believe me, you'll have questions, and the guys on here are the best source of info you can find.

and when you get everything done...

n. ride one of the most reliable bikes ever made!

With 32k on the odo you shouldn't have too many problems, seems the more miles they have, the more they got used, so the better they were taken care of. (usually lol)

Oh, almost forgot, also check the valve shim clearances and re-shim if needed.

 

Thanks both of you for the advice, I will grab books and go through the steps you gave me, I really appreciate it.

 

Be careful; you've got a "hybrid" of some flavor there. Of interest would be the carbs; if they're Hitachis, then those would be correct for a naturally-aspirated 650/750. If it has Mikunis on it, those would be the Turbo's carbs, and you would be better off to locate a "rack" of Hitachis.

Even though it has an engine block from a Turbo motor, it's NOT a turbo at this point, you'd be able to see it in the exhaust system. (By definition, a turbocharger is driven by the exhaust gasses.)

I wonder if it's a 650 or a 750? Look on the front of the cylinder block, up by where it meets the head, and see what displacement is cast into it. It won't say "650" or "750" it will be 653cc or 749cc IIRC. The Japanese often represent "cc"s as "CM3" so that will probably follow the number. Then you'll know a little bit more, like if it's a 650 Turbo bottom end with 750 "jugs" or a 650 motor that's been "de-turboed." If it's YICS-equipped (YICS cast into valve cover) then the head and cylinders have been swapped, but for what?

You'ge going to want the Haynes for sure; but you might be well off to track down a factory book as well; the Haynes is kind of "cloudy" on some things, and you're already dealing with a "bitsa." (Bitsa this, bitsa that.)

 

Are there any pics? If any were already posted let me explain that work filters them out so I can't see them but I'll check back tonight and let you know what you have as long as there are some pics. PM me a email address and I'll send you some pics along with the turbo service manual.

jeff

 

The pic he posted looks like a pretty stock 750 Seca with a 4-1 on it; no Turbocharger in sight.

Somebody used a Turbo engine block, but how much is different from the base up will take some investigating. It ain't a Turbo no more, though.

 

I ordered the Haynes on Amazon this morning, I will look into getting a factory book too, I remember the Haynes manuals always being a bit weak in some areas when I have used them on my cars, and I am sure this won't be an exception.

I will take a closer look to see what I can find out by looking at the castings. From memory I believe the valve covers are marked YICS. I will take some better pictures too.

I did find yesterday that the engine was only firing on two cylinders, but I ran some SeaFoam through it in new gas and after a few of backfires it started running on all four, which leads me to believe that the carb really needs a good cleaning, I just want to wait on a manual to do that, I don't want to start tearing things apart until I am ready, that never ends well.

 

Engine says 653, time to change up my sig I guess.

See below for more detailed pictures. Is there a way to tell which carb I have without pulling it off?

Fuzzy, but you can make out the 653:


Engine Left Side:


Engine Right Side:


Bike Left Side:

 

So to recap,
1. You have a 1981-1983 XJ750 we would need to know the VIN# to determine exactly what year, but if your title said 1981 then it in all likelyhood is an '81. Which would be an XJ750H.

2. Somewhere along the line someone installed an XJ650LJ motor, which is from a 1982 650 turbo, according to your engine VIN#.

3. I'm guessing, and it's ONLY a guess, that the motor assembly is the complete assembly from the Turbo, as the turbo did have the YICS motor. The non-turbo seca used a non-YICS motor.

4. I've never seen the Mikuni carbs, so I have no idea how to tell the difference, but someone on here will know. But you do need to figure that out, just because they used the turbo motor doesn't mean they transplanted the carbs also.

5. You ABSOLUTELY need to check valve shim clearances. Since you aren't dealing with the original mill, you can not go by the mileage where the motor is concerned. It could have 400 miles, it could have 40,000 miles, there is just no way to know.

 

If it has the 650 turbo motor. Its gonna feel week on the bottom due to less compression. But other then that if it runs good no problems run it

 

Look closely at the carbs. Mikunis say "Mikuni" on the RH side of the carb, up on the "flared" part directly below the hats.

Hitachis generally have a "flat" on the rear portion of the hats; if they're completely round, they're Mikunis. If Mikunis, they probably are Turbo carbs, indicating possibly a more complete engine "transplant."

If they're the Turbo carbs, you're gonna find out when you take them apart; they have "o-ring" sealed floats and other intracacies because they're meant to be "pressurized."

Concern: If those ARE Turbo-intended Mikunis, you need to check things like jet sizes and needle markings, etc., the Turbo carbs were set up completely differently from the normally-aspirated, Hitachi-carbed XJ750 Seca.

I would suggest that if they are Mikunis, you find a set of Hitachis off a (normally-aspirated) XJ750R and rebuild those, for a long-term solution.