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Motorcycle Repair/1983 Yamaha Seca Turbo Elecrtical Problem


mike wrote at 2006-07-14 16:13:00

Randy's answer has alot of assumptions that direct it down the wrong path. These bikes are ridden to this very day. I have put over 100,000 miles on Yamaha Seca Turbos. It is a very streetable motorcycle and reliable. As for your problem, it is hard to diagnose without being there, but I have two suggestions. If you can eliminate the idea that the one of the carbs is flooding, then I would try to get another CDI box. This is the big black box on the right side of motorcycle near the battery. I have had one of me Seca do this same thing to me. Riding along, and just shut down except for idle, when you gave it gas, it acted like a rev limiter was set to 2k RPM. Also check all the connectors to make sure there is no corrosion causing problems. I would also suggest finding a parts bike to pull some of these parts from. Check google for TMIOA, plenty of turbo bikes running all over the world.  

skiber wrote at 2006-09-02 19:07:41
hi in the fuse box the main 20 amp fuse holder was weak. so i had the same problem i change it out with inline fuse holder runs great.

Greg wrote at 2006-09-13 16:44:41
I own a 650 seca turbo. I ahd the same problem. I tried coils and chasing shorts. With all of the connectors on these bikes most often it is a bad connection somewhere. The CDI units on these bikes ned a very clean signal or it will misfire. IF you have got all the connections good then I found that changing out the CDI unit always fixed the problem. Good luck finding one if you do not have a spare though. You can check your coils for resistance on spec. The same CDI unit will cut out the signal if the resistance across teh coils is not balanced.  A low battery affects the spark timing as well. these bikes are very sensitive to voltage level and voltage drops.

Once you get everything working properly though they are an absolute pleasure to ride.

Good Luck  

Eric Eller wrote at 2007-06-08 21:35:47
If the tachometer is falling to 0 I would say the wire between the tach and the ignition module is not seeing signal. If the wire itself was to ground, It should kill the bike. Does it cool off for say 5 minutes and run again? If so my money is on a hall effect or pick-up coil or whatever takes the place of the points. That or the module (CDI box) is bad. I rode one of these bikes for years and never had any trouble save for the final drive breaking once, my fault.  

supertankerm60a3 wrote at 2007-09-19 01:41:42
Let me start by saying I am an M1 Abrams tank mechanic and avid rider.  (and after writing this THEN noticing the date, hope it will help someone else.

Your problem is in the ignition system somewhere.  The big indicator of this is the tach dropping to zero, it is not getting any signal from the ignition system at that point. It is not likley that the seconary wires are shorting or arcing as this would not cause the tach to drop.  It is much more likley to be and open cicuit than a short ciruit.  Shorts burn wires and or blow fuses (but are easier to find).  Do just what you did to the carbs and turbo.  Take every ignition system electrical connection apart, look for corrosion then clean them with contact cleaner, then use a pick to CAREFULLY tweek the socket sides of the conectors such that they grip the pin sides better.  Also check the trigger itself, that it is not loose mis-aligned or the gap is too wide.  When you put the plugs back together, tie them very securely such that vibrations will not effect the connections.

To all who read, hope this helps.

dale wrote at 2007-10-18 22:24:32
This bike has pressurized carbs not injection, thats why they run so well

bruce boulay wrote at 2008-01-21 12:08:09
your problemm is in the ignition control box on the left side of your bike under the left side cover I had the same problem with mine replae it and go riding with no worrys.

James wrote at 2008-04-24 18:03:40

I believe your problem could possibly be in one of your ignition coils. Usually there are good or bad but it's possible that when one of the coils gets hot it shuts down usually to a crack in the case of the coil or internally with a short caused by expansion and ground the coil out. Check all the ingnition coils resistance and compare to the shop manuals specs. Also another problem could lie in the pulser coil that supplies voltage to the igntion coils. Check the wiring from the pulse coils to the ignition coil for possible shorts or bare wires. If every thing checks out good with the ignition coils and the pulser coils and associated wiring the problem coul lie in the main ignition switch. Good luck

Fourcammer wrote at 2008-06-30 03:01:48

I have an 82 Seca Turbo that I bought new, and ride regularly.  A very good motorcycle. I have been a bike tech for over 40 years, and I'm pretty good with electrical.

Symptomatically, it appears you're losing a pair of cylinders, either 1-4 or 2-3 since each pair are on a twin-lead ignition coil.  Since you lose the tach at the same time, either the coil is going away, or the electronic switching is winking out.  A very common cause of dropped ignition is a sporadic pulse from the trigger or "pick-up" coil, either because it is going away, or because it has a connection problem. The XS1100 Yamahas were notorious for severing the pulse coil wires because they had a moving mounting plate operated by a vacuum advance cannister.  The constant flexing of the wires eventually severed them, and then you had random drop out of one of the coils, which took out its two cylinders.

Your bike runs the tach off of the coil attached to the gray wire in the harness. Both coils are fed hot juice on a red/white wire, but one connects to orange, and the other to gray on the switching (negative) side.  The wiring schematic shows the tach pulse is taken from the gray wire, but doesn't tell me whether it's 1-4 coil or the 2-3 coil, and I'm not disposed to remove my fuel tank for a peak.  My guess would be 1-4, but it really doesn't matter at this point in the diagnosis.

So, check your pick-up coil connections (pick-up coils are under the left side crank end cover), and do a resistance check through the coils.  They should be almost exactly the same at about 120 ohms.

Also check your coils for visible cracks, the coil connections, spark plug caps and wires, and the plug-in connections at the ignition module (right side of bike, under the body fairing).  Look for corrosion and poor connections.  Sometimes the flat terminals in those multi-plug connectors aren't snapped in good, and they push out the back of the connector when plugged together, and that results in a poor connection that can become a random open.

What you have is probably not a "short" (that usually blows fuses), but a sporadic "open" or disconnected circuit. Historically, the XJ series engines have been very reliable electronically, so I think you have either a bad connection (either at the coil, at the pick-up coil connectors, or at the ignition module), or a failing pick-up coil, that may be nothing more than a compromised wire.  The only kind of "short" that would drop out a coil, but not take out a fuse would be a bare spot on the pick-up wire that's interrupting the signal to the ignition module when it grounds out.  That is usually the result of crash damage.

If you don't find any compromised connections, and the pick-up coils test good, then try a coil off of just about any other XJ model. There are lots of them around.

One other place that can sometimes cause problems is the fuse holder clips.  They get weak, and don't get a good grip on the fuse, which can cause low voltage on a particular circuit.  If it's a higher amp circuit, like the headlight, it will usually lose the connection.  But a low amp circuit like the ignition coils and module can simply drop below adequate voltage and misfire.  So, make sure they are tidy and tight.  I often replace the fuse panel with a generic automotive one with screw connectors for the wires, and good husky fuse clips.

That's the best I can do right now without more information.


Stan wrote at 2010-03-29 03:47:50
It's may not be an electrical problem. It may be vacuum. Check all vacuum hoses and replace the check valve.

I take offense to your comment that Turbos are conversation pieces. I have owned a 1982 Seca Turbo since 2002. I bought it used with 7,800 miles on it and cleaned the carbs and adjusted the valves. It still to this day runs like a champ. And the bodywork is pristine. If I could I would post you a pic of my turbo just to make you eat crow.

Also, it's electrical system is not an antique. Wires are wires, voltage regulators are voltage regulators, and ECU's are still solid state units. Today's bikes still employ the coils IN the spark plug wires, so I don't know what's obsolete about the Seca Turbo's electrical system. Elighten me where I am wrong in this observation.

If he inspects the vacuum hoses and they are good, then I would suspect the ECU or the plug wires (coils), or even the fuse block.

Earthbound4now wrote at 2011-02-20 22:27:28
I don't think 'conversation piece' describes most Seca Turbos correctly!  I toured the United States on one in 1982 & 83.  Probably the most reliable bike I have ridden.  Replace the CDI unit.  To close with a slight aside - my wife and I are buying two more Turbos next week and looking for more.  These bikes are worth owning and maintaining!!  Just this biker geek's opinion of course!

Turbo82-3 wrote at 2011-03-10 05:12:17
Randy... you're absolutely NO help whatsoever. I don't know why you bothered to post. CONVERSATION PIECE??!! I have two that run... and run WELL. Not only that but they look pristine. THAT'S the hard thing to pull off given that body parts are limited to what you can find on Ebay or swap meets. Decal sets have been reproduced for the bike, but the paint code is nonexistent.

If it's an electrical short he can still find wiring harnesses for this bike. If he's as handy as he says he is, then rewiring is not a real issue. Any Yamaha mechanic could do it for you but that's at a cost.  

Turbo82-3 wrote at 2011-03-10 05:24:42
Oh, and btw, if it is an electrical issue, start at the battery! Nothing worse than tearing a bike apart or taking it to a dealer that takes 5 hours to diagnose and then comes out to tell you you have bad battery cables! Let's see... 4 hours at $80/hr = DUH... So start there. Also, on the Turbo there is a fuel sending unit. It's just a couple wires with a sensor. You can find that on Ebay. Possibly you can even get it OEM if you know what Yamaha parts dealer to call.

It can also be mechanical in nature. The biggest downfall of that bike was the fuel check valve. It can clog easily. That's a hard but not impossible part to find. And nothing for a mechanic to replace.

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Randy Neiman


I can answer questions regarding Japenese streetbikes from the 80s to current models. Driveability, suspension, electrical, cosmetics and winterizing. Customizing and performance questons including carburation, engine internal and exhaust modification are welcome. No specs questions please.


25 years building racing and customizing cafe racers and sport bikes.


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