Problems with 1981 Seca xj750

Hi

I'm fairly new to this forum and I hope I can get some help. After looking for 3 years I found the bike I just had to have - a 1981 Seca 750 with the touring package. I live in California and the bike was in Michigan so I flew to Michigan last week with the intent to ride it home. I had some mechanical problems on the way home and I was forced to modify my trip after 1400 miles (New Mexico) and uhaul the bike home. So now the bike is home but it doesn't run well at all. It will start and idle but has no power. If I let the clutch out in first gear it dies.
Here are some facts about the bike:
I cleaned the carbs and I am getting fuel. I'm getting spark to all 4 plugs. I tested for compression and I have 130 to 135 psi in all cylinders. The coils both have 2.5 ohms on the primary circuit and 25,000 ohms on secondary. My manual indicates the proper amount of ohms should be 11,000 on secondary but I have a 1982 Seca that runs well and the ohms for the secondary on that bike is 22,000.

I'm stymied with this bike. It should run well BBB asked on all the numbers and it did run well when I bought it. What could be the problem?

Thanks in advance
Steve

 

How did you clean the carbs? What did you set your idle mixture screws at? Did you flush the tank? Service the petcock? Check the gas cap to make sure the vent works? Did you do a bench sync? Running sync?

Did you adjust your shim clearances first?

What were the mechanical problems you had?

Dave

 

HI Dave,

Here are the answers to your questions:

How did you clean the carbs?
When I first picked up the bike in Michigan is would get up to about 70 MPH and then it would start to stutter if I applied any more throttle. I know the bike had been sittin gin a garage for about a year and I suspected old gas and varnish in the jets. I ran 2 bottles of Seaform over teh course of the next 1000 miles and it didn't seem to help - in face the performance of hte bike got worse. I decided to clean the carbs on Memorila day in New Mexico. I boght th e toosl I would need and pulled the carb rack off the bike and dis-assemebled all the jets and used 3 cans of carb cleaner in the process. It took me about 4 hours to complete the process. A local car garage owner allowed to use the tailgate of an old pickup as my bench. The inside of the carbs looks a little dirty but I found no blockages in any of hte jets or passageways.

What did you set your idle mixture screws at?
I did not touch the mixture screws. Apparently the bike ran well before storage and I did not think the mixtures screws needed to be adjusted.

Did you flush the tank?
I did not flush the tank. The gas in teh tank was old - probably a year old. I ran that gas through the bike and ran 8 more tanks through the bike. I assume that by now the gas in teh tank is good gas even if it was bad gas to start with.

Service the petcock?
I did not service the petcock. It seems to be working fine.

Check the gas cap to make sure the vent works?
I have tried to run the bike with the gas cap un-locked - so that air can get into the tank. It makes no difference.

Did you do a bench sync? Running sync?
I did not sync the carbs - again, it was running well a year abo and I am assuking the carbs were in sync then.

Did you adjust your shim clearances first?
I did not adjust the shims. I have not checked the valve clearance.

Mechanical problems: After a day of riding, my top speed was about 60 P MPH. Any additional throttle wold cause the bike to stutter and actually lose speed. Going through Oklahoma I ran in a lot of rain. The bike strated bogging down bad - top speed of about 30 MPH. I stopped and determined the 2 outside cylinders were not firing - teh exhaust pipes were cold to the touch. I found a motorcycle shop and then found a crack in the left coil which was liklely the cause of the cold exhaust pipes. They blew water out of the coil and dried it the best they could then sealed it up with JB Weld. The coil started to work - I had spark to all cylinders so I continued on my journey.

The next day I was going through Amarillo, Texas and my top speed had dropped to 45 MPH. However, all cylinders were firing. I bought new plugs but didn't seem to help.

On Memorial Day I was in Tucumcari, New Mexico. I decided to clean th carbs that day (see above desciption). After cleaning the carbs, it made no difference. I decided to try to make it to Albuquerue because there was a bike shop there. It was 175 miles away. After spending an hour riding, I had only gone 30 miles. I decided to return to Tucumcari, however I did not make it back. On the return trip the bike kept losing power. Finally it got to the point that the bike would idle, but did not have enough power to move itself forward at all. It would die when the clutch was engaged. I called a tow truck and that's how I got back to Tucumcari.

Now the bike sits in my garage. It has 135 PSI comptession, spark and gas. But I can't get it to run. It ran before I bought it and it seems unlikely that the carbs fell ot our sync of the timing got messed up or the valves fell out of adjectment just by sitting for a year.

But I'm open to any ideas - I really want to get this bike running. It's a great bike.

 

It is a good looking bike! Lots of potential there. All that plastic is getting harder and harder to come by, and yours looks pretty clean! You just need to remember that it is 30 + years old, and you must assume that everything the last owner did was wrong. "THe Church of Clean" thread should be your next stop. These carbs are filled with tiny tubes, and spotless is the best way! Also, have you checked the valve clearances? there is a link in my signature... If the valves are out, every other adjustment is futile. Also VERY important to look for a date code on the brake lines, they may be 28 years past life expectancy! Rear brake shoes are prone to delamination, with possible fatal results. Take care of this bike, and you will love it for years!

 

+100

You have a sick bike. The only cure is a thorough going through to attend to all of the maintenance that was likely never done. Making assumptions will leave you stuck on the side of the road ( as you have found)
In addition to the church of clean, I recommend that you visit The Information Overload Hour link
In my signature and read it front to back

 

So you tried to ride it home that far on dirty carbs with old gas in the tank, not knowing what the clearances are.... Or if there even is any-----

Well... Your home now--- start reading and cleaning. All you did was make a few parts look sort of clean.

Got a fuel filter to catch anything from the tank ?

You have a long list of things to attend to before your bike will be ready. BUT... You have a BEAUTIFUL ride sitting there, so take you time and do it RIGHT. You'll be rewarded..... Just have the patience of Job......

 

Holy frig, wonderful looking and probably pretty rare blue edition. Is that a full stainless supertrapp system too? Sounds like something got wet if you were missing on the outer cylinders, that or some dirt in the tank which impacted fuel flow. That being said, take it from the valve clearances onward to make sure all is in spec and all should be OK. Jaysus, nice looking bike...

 

Great looking bike, I admire your nerve in flying out and attempting to ride it back across half the country! Quite the adventure even with the hiccups. If you take your time and follow the maintenance advice on this forum, you'll be one lucky and happy Seca owner. That is a great color.

 

Thanks for all the positive feedback and the suggestions. It will take a while to go though everything that has been suggested so I'll get started and let you know when it's on the road again.

Thanks,
-steve

 

35 year old coils and one's cracked? I'd say that is the majority of your issue. Len sells excellent replacement coils and mounting kits.

 

How about the air filter?

 

Good looking bike, Steve. Does the engine die when you put it in gear or when you put load on it. If its the latter, check for pin holes in the diaphragms and/or sticking slides. It would be a good idea to check the air jets as well. There may be multiple problems here.... A cracked coil will surely cause a loss of power. I agree with others that starting at the basics is a good idea. BTW: nominal compression on these engines is 156 psi. Compression should be checked with a warm engine if possible and with all plugs removed and grounded and the throttle wide open.

 

First off, beautiful bike. PLEASE do the right things, in the right way, so you can get that puppy purring (do puppies purr?) the way that it should.

4 hours is about the time needed to pull the carbs off, give them a quick visual, play around with some spray cans, and re-install. To do a proper rebuild on 30+ year old carbs, plan on about 20 hours if it's your first rodeo, about 12 hours if not. If you don't believe me, ask Dave (the fiddles), he does rebuilds for a meager living and can do them with his eyes closed and two toes tied behind his back......

Recommendation:
- check valve clearances, adjust as needed.
- pull carbs and rebuild completely, throttle shaft seals, fuel pipe O-rings, the whole enchilada....including:
- wet-setting the fuel levels. This is the part everyone hates, do it once and do it right and you won't have to fiddle with this task for another few years or more.
- vacuum synch the carbs as soon as they go back on the bike.
- colortune the mixture screws using, you guessed it!, a Colortune Visible Spark Plug. After you do this procedure, vac-synch the carbs again.
- do all other routine maintenance (plugs, filters, etc. including ALL fluid changes, even the air in the tires and forks since air is, after all, a "fluid", technically speaking)
- inspect the brake system, rebuild and replace as needed.
- inspect the fork system, rebuild and replace as needed.
- added bonus: upgrade to a blade-style fusebox, the original fusebox was a weak point when new, and it didn't get better over time.
- ONLY THEN DO YOU GET TO RIDE AGAIN!

Sounds like a lot of work. It is. You're making up for 30+ years of previous owner's neglect, ineptitude, and incompetence. Once it's done you can ride it at redline all day long and impress your friends to your heart's contentment.

 

That's a SWEET bike. Take the advice and it will run great for a long time.

 

That is a fine looking seca 750. Do all the catch up maintenance as recommended, I did, and it will be very reliable. Good luck with it.

 

I wanted to give an update on my bike. I took the advice that was given and checked the valve clearance. They were all with in spec:
Cylinder #1: intake=.006/ exhaust=.007
Cylinder #2: intake=.005/ exhaust=.008
Cyliuder #3: intake=.006/ exhuast=.007
Cylinder#4: intake=.006/ exhaust=.007

I chedked the compression on each cylinder this morning:
The caburetor was off the bike when I did this test so there was no chance of having the throttle partially closed
Cylinder #1: 150
Cylinder #2: 145
Cylinder #3: 145
Cylinder #4: 150

I have new plugs. The plug gap is set at .028 Each plug fires with a blue spark.

The coils both test to be in spec - I have 2.8 ohms across the primaries and 11K ohms on the secondary (coils only - the plug caps are removed.) Each plug cap has from 5K ohms to 8K ohms so total resitance from plug cap to plug cap is 22K ohms on one coli and 26K ohms on the other.

The carburetor is clean based on the Church of Clean. Just to validate that the carubetor is not the problem, I have another Seca - 1982 xj750 that is in working order. I removed its carburetor and installed the carburetor from my new bike on it. The old bike ran fine with this new carburetor so I have eliminated the carb as a problem.

I previously took the TCI unit from my old 1982 Seca and installed it on my new 1981 Seca - it made no difference.

I hired a mobile mechanic last week who went through all the things I have listed above. He suggested I had a vacuum leak in the carb boots that connect the carbs to the head. I argued that the symptoms did not support that theory. The boots pulsated when the bike was idleing but when we sprayed starting fluid on the boots there was no change in idle speed (I would have expected some change if there was a leak.) Still, he convinced me to spend $412.00 on new OEM boots and gaskets. He came back today and installed the boots and it made no difference. To his credit, he worked on the bike with me for a total of 4 hours and did not charge me a dime.

We used new gas to try to start the bike. After minutes or cranking, the bike will occasionally start to idle, but it idles poorly. Any throttle movement causes the engine to die.

I'm planning on buying a leak down tester today mainly because I have run out of ideas. But I've got decent compression so I don't know what I will learn by running a leak down test.

Any ideas what I could check next? The only thing I can think of is to pull the head and visually inspect the rings, valves and cylinder. The mechanic suggested there could be excess carbon build up on the piston or that the cylinder walls could be glazed - But I'm not sure why either of these conditions would cause the symptoms described above.

Thanks,
Steve Gold

1981 Seca XJ750
1982 Seca XJ750
1982 Virago XV750
1982 Virago XV750 Cafe Racer
1990 Virago XV1100

 

Does the engine run with a bit of choke applied to it?

 

You said you cleaned the carburetor---

Which one? You still have three more to do. You also have the bowls to do, and you must make sure the tubes are clear, and the jets are in the right spots.

Did you bench sync them? Running sync? Valve shim clearances checked?

Just how did you clean everything?

 

Chacal - the engine does NOT run with a bit of choke.

Hogfiddles - I cleaned all four carburetors. I took all the jets out and cleaned each one according to what I read in the Church of Clean. I verified the emulsion tubes were clean and blew compressed air through all passages. I did a visual bench sync. I was not able to do a running sync because I cannot get the bike to run. Also - I installed this same carburetor onto a different bike (my 1982 Seca) and that bike started right up and ran like a chanp. So I am confident the carburetor is not the problem. I also checked the valve shim clearances - I mentioned that in my previous post and the clearances are in that post.

I know it's tempting to say "well - this new guy didn't clean the carbs right - he doesn't know what he's doing." But I have followed all the advice I've gotten from this forum and I appreciate it. I have 4 other bikes - all Yamahas. One Seca and three Viragos. I've been into the carbs and engines on the other bikes and I keep them on the road, running well. I have a basic understand of engines. My carburetor works on bike #2. I have 150 pounds of compression on each cylinder. The valves are adjusted according to spec. I have a blue spark - new plugs. Coils have the correct resistance.

Compression - Fuel - Spark - I've got them all. What am I overlooking?

 

Ok, then in light of that, let me go back and read through everything again see what I may be missing

 

Timing perhaps. Is it possible the cam tensioner has failed and the chain has jumped a tooth.... Ignition timing is another possibility..

 

Ok... So theoretically everything seems in order because it works fine on the other bike.

So, lets look at some things that didnt get swapped around ( unless I missed it)

Fill your tank, Pull the fuel line off of the petcock ( put a fuel-catch underneath first). Now turn it to PRI and see how the gas runs out.... It should gush out.

Try swapping tanks

Swap your spark plugs

Swap your pick-ups under the left engine cover

Check all your ground wires

Swap your batteries

Do only one thing at a time, and swap back before going to the next thing, so you don't "contaminate" the cause

Before doing all that...

Pull the seat and air filter ---- can you get the bike to run with either starter fluid carefully sprayed into the carb throats first ?

Or, if you pull the plugs and squirt some "extra" gas right into the cyls first?

I'm trying to narrow down whether its not getting enough electric signal, or if its just not getting enough gas yet.

Let me know these things, and if answers still seem normal, then we start all over again.

Hang in there........

 

You have spark, but do you have spark on the correct cylinders at the correct time? Check your plug wire locations.

 

He said he had 1/4 so at least the pairs are correct, and I don't think he would have been able to ride that far with them switched ----- so I didn't go there----

 

Ya. I though about that after, but then thought that they might have gotten switched while he was checking things.

 

Thanks again for all your support and suggestions:

bstig60 - Love your bike!!!
k-moe - The wires are hooked up to the correct cylinders and the camshafts are timed correctly to the crankshft.

I'm focusing on the electical - especially the TCI. I read today about a TCI test - pull a spark plug and ground it (still attached to the plug wire) and turn on the key. After 2 second there will be a spark across the plug. I tested that on both bikes (the 82 that works and the 81 that I'm having troubles with). The TCI on the 82 passed the test (spark after 2 seconds). The TCI on the 81 did not pass the test (no spark after 2 seconds). So I swapped the TCI from bike to bike and re-ran the test. With the TCIs swapped, neither bike passed the test (no spark on either bike). Then I put the TCIs back on the correct bikes and the 82 bike passed the test (spark). The 81 did not pass (no spark).

So it seems to me that the TCI on the 81 might be bad since it did not pass the spark test on the 82. However the known good TCI from the 82 did not work on the 81, so there must be something else wrong with the 81...

 

I've never heard of that spark test before ----

 

Thanks, Steve. Not familiar with that spark test either. I don't have my book with me to verify this, but I believe there is a black ground wire on the TCI. It should be a ground wire. If so, you might want to try cutting it where you can splice it back together if need be and running a wire from the TCI side to the negative ground post on the battery. Also, If you haven't already done so, use a good brand of contact cleaner and clean the connectors on the TCI and the wiring plug that attaches to the TCI. Also check the RW wire to make sure you have a good power supply. Did you put a new battery in the bike before you started the trip home? If not, swap the battery with the 82.

 

RICH, LEAN, or possibly even ritually UNCLEAN or OBSCENE: THE CARB REBUILDING FAQ:

Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

- When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result.

 

That's true. I have seen it on other Yamaha models. It would appear then that the TCI is not putting a pulse out to the coils. But why would the test not work when the TCI's were swapped?

 

That is the $ 64,000 question............

 

Someone said it before - air filter?

 

Oh.... I didn't realize that was a way to test though....

 

When you test the voltage at the coils, use a brake light bulb, not a digital meter

 

While I was looking for clues I found a reference on this site (XJBikes.com) that linked to here:
http://www.jetav8r.com/Vision/IgnitionFAQ.html#a12p0

The above link is a TCI FAQ for the Yamaha Vision motorcycle, but I learned a lot about TCIs on here, and that's where they mentioned the "TCI Power-on test".

Last night I conducted a leak-down test - I have between 15% and 18% leakage on all 4 cylinders - from what I have been reading, those are good numbers. So I'm double sure the engine is fine (compression for all cylinders was between 145 and 150). I know the carbs are fine (since they run on my other bike.) So it MUST be something electrical.

I have another symptom that I neglected to mention, but it might provide more insight now that I am convinced it's an electrical problem. A few hundred miles before the bike refused to run I started having these problems: The headlight and dashboard stopped working. All the fuses were good and the headlight bulb looked fine. I spent an hour removing the front fairing and checking all the wires and everything looked fine. And the headlight started working again. But the dash was acting really weird - when I turn the key on and started the bike, all the insturments seemed to work. But as I shifted gears, the whole dash would lose power and regain power and cycle through the diagnostics as if it were starting up. That would happen each time I shifted. Keep in mind that the bike was running crappy at this point and I could not go faster than 50 MPH. Also the tach would read about half what the engine was actually doing (I know that each 1000 RPM equates to about 13 MPH - so at 50 MPH the tach was reading about 2200 RPM where as I would expect to see about 4000 at 50 MPH. The day before it was showing the correct RPM for the bike speed.

The current state of the bike is that it takes over a minute to stat - if it starts at all, and it idles very rough and any throttle will stall the engine. Battery is good and strong. So after everything I've learned so far, I suspect the TCI might be bad and/or I have a loose or corroded connectin somewhere that is eating up a lot of current and that's causing the spark or other electronics to be weak.

If I get deperate enough, where can I but a good TCI?

Thanks for all your help and suggestions thus far. I'm learning a lot...

-steve

 

Jeez... you left THAT out?! Start looking very carefully for the intermitant electrical break that you have. Does it have the original fusebox? The fuses can look fine but the fuse clips likely are not fine at all. At this point I seriously doubt that the TCI is bad, and there really won't be a way to test that until the rest of the electrical system is working as it should be.

 

Beginning to sound like a bad ground somewhere...........

 

It could also be grounding. If I recall, there is a ground multiple that runs throughout the wiring harness and provides ground to all systems. I have seen the connections inside the wiring harness fail before. That is one reason I suggested providing the TCI with its own ground directly to the Negative battery post.

 

You all have been a wealth of information.

Is there a write-up on how to exhaustively test the wire harness and electtical connections?

bstig60 - I re-read your previous suggestions just now. I have some (stupid??) questions:
1) Is there a way to test the black ground wire that is connected to the TCI? Can I hook up my digital multimeter to the wire blade that connects to the TCI and also to the negative battery post and meaure something to validate the wire is good? I know you suggested cutting the wire and hooking the TCI side directly to the negative post - I'm just trying to understand if there are other methods to test.
2) When you said "check the RW wire to make sure you have a good power supply" - I assume I would use a multimeter and connect the probes to teh RW (red/white) wire and the other to ground and that I would check for 12 volts and that would be a good value?

 

Positive lead on the black wire on the TCI connector, neg lead on the battery negative post. If there is a poor ground there will be a voltage drop. I would expect this to be less than a couple hundred millivolts. There are two eyelet terminals on the Seca main harness that are secured via the coil mounting hardware - these two eyelets account for all the grounds and attach them to the frame. Engine to frame mounting provides the connection to battery return.

That is correct. Current path is from the battery, through a single plug connector, main fuse, ignition switch, ignition fuse, kill switch, and then to the coils and TCI. Any of those points can cause a voltage drop with poor connections. Typical voltage 12.20V battery, and approximately 11.5V at the TCI R/W wire.

I'm not a TCI expert, but I can tell you on my 82 Seca that only the 2 and 3 cylinders spark after two seconds. You can verify this by placing a meter on the gray wire on the TCI. At power up it will read 1.5V for 2 seconds, and then switch to 12V, which collapses the field in the coil producing a spark. For some reason, the orange wire at the TCI always seems to power up at 11.5 volts, so the 1 and 4 coil is not going to fire.

Either the orange or gray wire needs to be low when checking the above voltages, otherwise the current is so small poor connections are not going to be obvious. When the orange or gray wire is low for that two seconds, the TCI is sinking approximately 2.5 amps. That is the point to Polocks suggestion to use a brake light bulb, sometimes you need the extra current to show the fault. He suggested it on the coils, you could also disconnect the TCI and attach the bulb from the engine harness R/W to the black wire to simulate approximate current demand on the ignition circuit. While the bulb is connected voltages could be verified.

 

One other note on the spark after two seconds is make sure the other plugs are installed and the plug wires connected. The wasted spark system requires the corresponding plug that you are testing to be connected to ground and electrically connected.

If 2 and 3 circuit failed the 2 second spark, I would try the 1 and 4 for good measure, or vice versa. There might be a good reason that the design of the electronics within the TCI results in an either or. Theory on that is electrically it makes no sense to fire on power up after two seconds (other than to scare the crap out of you if you have overflowing carbs and all the Yammie engineers are still laughing their A$$ off). The reality is it actually produces a bit of a fire hazard.

 

Your electronics acting up the way they did indicates a grounding problem. Yes to #2; you should see the same voltage as going across your battery posts or close to it. no to #1. You can have continuity with a meter, (its rare that a meter has a Ohms x 1 scale anymore), and still not have a good connection. Best to for the TCI to have a ground of its own. This has fixed a lot of TCI problems in the past.

 

Swing test the coils and wires with your running '81 Seca. I had similar symptoms from bad coils on my '81 Seca. They also ohmed out good but didn't perform under load. Can you High Pot the coils?

 

What does High Pot mean?

 

It is a testing method that applies 100% or more of the normal working voltage to the windings in order to test the insulation on the windings. It is normally used during manufacturing, and I have not heard of it being used as a diagnostic tool otherwise. I humbly suggest that the coils are not the cause of the problem. The poor ground needs to be addressed regardless, and prior to investigating any other possibilities.

 

I thought I had read every post from the OP twice. Somehow I missed the flaky electronics issue on page 2.

I withdraw my adamant coil issue suggestion until further testing is completed.

BTW, if you have the ability, and I realize most won't, High Potential testing can show weakened insulation in a coil winding that may be problematic when the coil heats up under load.

 

OK. So I reinspected my fuse box and they all "looked" good but when I hooked the voltage test up on each side of the fuse it was apparent I had a problem. The fuse labelled "signal" had a hole in the end and that was causing my dashboard problems. I replaced the fuse box with inline fuses last night and my dash lights all work as they should.

However the main problem still persists. Now I can't get the engine to run at all.

So here's what I did this morning. I took the carb off both bikes - my 82 Seca that works and my 81 that does not. I sprayed 1 squirt of starter fluid in each intake port on both bikes. Then I hit the start switch. The 82 started up immediately and revved to 4000 rpm and then died because the fuel was gone. The 81 sputtered and didn't really start - in fact it backfired through the number one intake port - a nice yellow flame...

Now here comes the part you won't believe. I hooked up a timing strobe light to the 81 with the induction lead on the number one Cylinder. It seems the light is strobing at about 15 degrees AFTER tdc. How is that possible? I have already verified that the cams are timed correctly to the crank. As a sanity check I hooked the strobe up to the 82 and hit the starter. The strobe showed on tdc for Cylinder number one. Keep in mind the the bikes are not running during this test. I'm just cranking the starter - the strobe light has a built in tach which told me the engines were cranking at about 525 rpm.

Someone suggested that I swap the pickup coils on the 2 bikes. I have not done that yet. It looks complicated but I suppose I need to do it unless someone has another idea?

 

Pull the left side crank cover (4 JIS machene screws, has the YICS emblem on it) and take a picture. I want to see what the pickup plate looks like and see if someone monkeyed with it, or if there are just loose screws. I think we're right back to not getting spark at the right time being the problem, and I hope that the solution will be apparent once that cover is off.

 

I already had the cover off to do the timing test. In fact I have set the reluctor to the same orientation that the strobe lights up when I did the timing test. All the screws feel tight. Here's the picture.