Problems with 1981 Seca xj750

Anything new, that bike is way too nice to be sitting in the garage not running.

I couldn't quite make sense of the video, as it seemed like each time I could count a different number of pulse sequences between the two lights. I even tried stepping through frame by frame by stopping the video and using the left and right arrow keys, however even that was a bit odd as the timing lights did not fire at the same frame count every time?? Must be the video format, and not like old school where you could actually step through each frame of a video.

 

I had high hopes of getting the bike running yesterday when the new pickup coil arrived that I bought on ebay. The new pickup coil tested good with 657 and 670 ohms for each of the pulser coils. However when it was installed... it made no difference. With the addition of this new pickup coil, now every component in the ignition system has come from a working bike. I have a good carburetor from a working bike. The compression is about 150 on each cylinder. The timing is correct. I hooked up a car battery to the bike as to eliminate any battery issues and it still won't run. I suppose the next step is to trace and test all the wires and connectors in the wire harness.

I kinda feel like I'm wasting everyone's time on this forum. I do appreciate all the help I've received and I've learned a lot... but the bike does not run. If I hold the choke just right I can get it to start and run (poorly) for about 30 seconds. Any added throttle or choke movement kills the engine.

I've got a really nice looking garage decoration that is getting more expensive each passing day...

 

That sounds like a vacuum leak...... Have you replaced the carb holders? Are there any signs of cracking around the carb holders?

 

I agree that it sounda like a vacuum leak. The mechanic that looked at the bike 3 weeks ago also thought vacuum leak and convinced me to buy new OEM carb boots at the cost of $412.00. So I have brand new carb boots. Also remember that I can spray starter fluid directly into to intake ports and it only kinda runs. So I still think it's somehow spark related.

I'm gonna re-read the entire thread today and see if I missed any suggestion, but I think I have done everything that anybody has suggested.

This bike ran when I bought it a month ago. It's gonna run again... but it's sure taking a long time...

 

I don't think I would worry about wasting anyone's time. I think most of the members would enjoy the challenge.

So some other thoughts:

PO's are notorious for doing things that will make you scratch your head and wonder why. So, lots of talk of valve timing and you have verified. However, is there a possibility that the pointer or timing plate have been moved or modified and "T" does not really represent TDC? Therefore, when checking valve / ignition timing an incorrect reference is being used. Hard to imagine this since it ran when you picked it up or that it could be moved that far.

Are you completely assembled again with carb to air box boots installed? I have read several opinions on this, so some members say it doesn't matter and the bike will start and run without the carb to air box boots. Some say it is imperative that the boots and air filter are installed.

Did you ever get the voltage reading on the TCI? The most informative one would be probing at the TCI engine harness connector. Positive probe to R/W wire, negative probe to Black wire on the 4 pin connector. Make this measurement when trying to start it and the starter is spinning.

Carbs have been swapped, but have you done a sanity check on fuel level on the bike. With the bike on the center stand and checking at the middle of the carb body it should be quite close to the 3mm spec. even though the carbs are not level front to back.

 

Bill & Rooster53 - thanks for not giving up on me... Here are the answers to your questions:
Timing plate and pointer - I did a static check to verify the pointer lines up with actual TDC... Both valves shut and piston as high as it goes. I'm sure the pointer is correct. In fact there is a picture of the timing plate in post #50 of this thread.
Carb and airbox- the carb is hooked up to the engine side boots only. The airbox- side boots are currently off the bike allowing for max air flow and the occasional squirt of starter fluid.
Voltage to TCI- I jammed the DMM leads into the backside of the connector of the 4 pin connected with the TCI still hooked up. I did 2 tests with the red lead on the R/W wire and black on black. I have 13.8 volts on a fully charged battery before turning the key. Then I connect to the TCI as described above. At first there are a few millivolts on the DMM. When I turn on the key the DMM instantly shows 12.8 volts and slowly decreases to 12.24 and seems to be stable there. The first test I cranked the starter and the engine caught for a second - enough to turn on the headlight but not keep the engine going. The DMM shows 8.1 volts while the starter is cranking away. The second test the headlight did not come on. The DMM showed 8.8 volts while the starter cranked. I actually did a third test just now and got the engine to run for 5 seconds. The DMM showed 11.2 volts while the engine was running.
Fuel level- I checked the fuel level of the float bowls while the carbs were mounted on the bike by using a clear tube connected to the drain hole and unscrewing the drain screw on 3 of the bowls. The screw is stripped on the forth bowl. All three that I was able to check looked good.

 

those voltages just don't sound right. i just went out and checked mine.
13.09 before anything was done, it was run 3 days ago
12.28 key on
10.2 crank before start, it's hard to keep it from starting
12.2 barely running at 500 rpm
14.5 running at 1300
this is with a 12 a/h agm battery about 3 years old

 

Too low, bad battery or bad connections somewhere..............


How do I know if my battery is good?:

Is it your battery, or your charging system, or something in-between?

The best way to know for sure is to use a multimeter (voltmeter) attached directly to your battery positive and negative terminals, and observe the following:

1) with the engine and all electrical accessories off, the battery should read a minimum of 12.8 volts DC. If not, the battery is either not fully charged, or it is bad (it is incapable of holding a full charge). Charge the battery fully and check again; if the reading is less than 12.8 volts, the battery is bad and should be replaced.

NOTE: most manuals describe checking the specific gravity of each battery cell electrolyte (fluid) as the preferred method of checking the condition of the battery. This reading should be between 1.2650 - 1.280 per cell. If a fully charged battery cannot reach these levels in all cells, then that cell is bad and the battery should be replaced.

2) If the first test above passes, leave the multimeter hooked up to the battery terminals, and press the starter button. While the starter is engaged (but before the bike starts), the battery voltage should be 9.5 volts or greater. If not, then this signals either a bad battery, very dirty or weak electrical connections, or it could be a incredibly problematic starter motor (not likely; it's probably the battery!).


By the way, the TCI needs a minimum of about 10VDC to operate………and while the starter will spin the engine over like mad with low voltage, the TCI falls on its face at less than 10 volts…which can lead to all sorts of confusion when a battery low-voltage condition occurs!.


Voltage at coil positive input terminal (the red wire with the white tracer stripe) with the engine running: 12+ VDC. This measurement should be taken at the back of the connector shell (stick the volt meter probe in thru the back of the connector) and the battery negative terminal. Compare this reading with the measured battery voltage (voltmeter connected between the battery negative and the battery positive terminals). Any significant difference or lack of voltage indicates corroded or broken connections in-between the fusebox and the ignition coils, and reduced voltage at the coil input will result in reduced coil output (at the spark plugs). Although reduced voltage input (and thus less coil output voltage) may not significantly affect engine performance once the engine is warmed up, it can and will result in "hard start" situations when the engine is cold and/or when the choke system is engaged (since richer fuel mixtures require a much stronger spark to create ignition of the fuel mixture).

 

At 9 volts there isn't enough power to operate the TCI.

 

I think thete might be some confusion. In the post I just did that I replied to Rooster53's question about TCI voltage I had the DMM probes hooked up to the TCI wires. However if I connect the DMM probes to the battery when I'm cranking the starter the voltage never drops below 11 volts. So I think my battery is OK. In fact I used this same battery to start and run the Widow. Besides that I hooked up a brand new lithium ion battery to my bike and that didn't make a difference. Also yesterday I hooked my car battery to the motorcycle and not even that made a difference.

So I don't think it is the battery. I'm willing to buy a new one but nothing indicates that a new battery would solve the problem.

Here's a question... While the starter is cranking the battery shows 11 volts but the TCI falls to 8.6-ish... Shouldn't they be the same? How can I lose 2-1/2 volts before I get to the TCI?

 

Corrosion somewhere in the wire path between the battery and the TCI.

 

We are back to a grounding problem perhaps. Try pulling your Kill Switch apart and clean it up. Also pull off the connector on the Ignition Switch and clean the contacts there. Another option would be to cut the power wire that goes to the TCI and splice a wire in direct from the battery. Although I would be careful with this. Another option would be to splice into the R/W wire where it comes from the Ignition switch and run that direct to the TCI.

 

At some point it becomes more efficient to inspect and clean the entire wiring harness, and all of the ground cables. I think you are at that point.

 

he was at that point 4 pages ago but nobody specifically told him to

 

OK. I've got a wiring diagram and I want to see why the R/W wire on the tci shows 8.6 volts when cranking the engine. I think I need to test voltage in the wires and connectors. This is my plan. Start by turning the key on but do not crank the starter. Place the black DMM probe on the positive battery terminal and place the red probe on the positive side of the kill switch ( for example) and check for a voltage drop. The number on the DMM at this point should be small but whatever it is, it means that up to that point the circuit I am measuring has consumed that many volts. If the number turns out to be 2.4 that means that 2.4 volts have been used up from the battery to that point.
Is that how I should approach this circuit testing business? Will I get good results if the key in on but the engine is not running?

 

That is mostly correct, but the number you will see on the meter will be the actual voltage present between the two points, not the voltage drop. You have to figure the drop from a refrence voltage that you will measure at the battery terminals (or prior to any component, and than again after that component) and subtract the voltage being measured at any other point from that. For example: battery terminal voltage reads 12.8 volts; measuring between the positive battery terminal and the switched side of the kill switch yields 12.1 volt; 12.8 - 12.1 = 0.9 volt drop between the kill switch and the battery (which includes the individual voltage drops of all of the componenets in between).

 

no that's not the right way, not yet. first, take every electrical plug there is apart, clean it put dielectric grease in it. why trace the problem with one wire, when they all need attention.
unplug them, shoot some brake cleaner in both sides, plug/unplug several times, more brake cleaner, shake out excess, dielectric grease, plug/unplug again, another little shot of grease, move on.

 

Polock's advice is good as usual, and k-moe also suggested this earlier - two members with a lot of experience and knowledge. Even if it doesn't solve the problem, it is not too hard to do or very time consuming and should be done as periodic maintenance. He didn't mention the ignition switch itself, so maybe that could be addressed afterwards if needed.

http://www.xj4ever.com/clean and lube the ignition switch.pdf

And, since I was writing as Polock posted here is this if needed:

Your logic is correct when using the positive terminal as the reference. So, theoretically when you check the voltage at the kill switch in a perfect world you would measure zero. However, all switches and connectors have a bit of voltage drop and the cumulative total can cause problems. The advantage of doing it with the positive as a reference is you don't have to worry about the battery voltage changing slightly as you go through your measurements adding to the confusion.

To check just the ignition circuit the best way would be to place one probe on the input side of the ignition fuse, and the other probe on the R/W wire at the TCI. This will measure the voltage drop of the fuse, the wiring and connectors, and the kill switch. Once again though, you need some current to highlight a defective circuit as in actual operation. For this test you could engage the starter and note the voltage. This is the maximum drain on the ignition circuit as everything is powered, most notably at this point the starter solenoid, which if stock draws an extra 3 amps through the ignition circuit.

To check the input of the ignition circuit use the same logic. One lead on the battery positive terminal and one lead on the ignition fuse input. This will check the battery connections, wiring, connectors, main fuse, and ignition switch. It's also easy to get some current usage by engaging the brake light and then noting the measurement. It could also be done by engaging the starter, which will increase the current through the main circuit a bit more.

 

Update - I unplugged every connector - even the ones in the headlight housing and I inspected each for corrosion and then cleaned each with electric cleaner and plugged and unplugged each several times. I did not use dielectric grease yet because my understanding is that dielectric grease prevents corrosion but does not help connections so after I get the bike running I will go back and put the grease on.

I jumpered the R/W wire on the TCI directly to the positive battery post. It did not help.

I did voltage drop test from the positive battery post to the R/W connection on the TCI. There was a .47 volt drop on my new bike. On the Widow I measured .87 volt drop on the same circuit. The Widow runs but the new bike doesn't even though the numbers are better on the new bike.

I had exhausted all the possible tests so I decided to call in another mechanic. This new guy was sure he could fix it. He used to race in Brazil and has been wrenching on bikes for 46 years. He came to my house and immediately pulled the carb and cleaned it out good. When that didn't work he checked the timing then pulled the valve cover and checked the valve clearances. I showed him that the Widow runs great so he swapped the coils then the TCI. So he seemed to know what he was doing. After 3 hours of testing, swapping, and a lot of head scratching he said he did know what else to test. I asked him how much I owed him and he said there was no charge. So two professional mechanics have worked on the bike for a total of 7 hours and it still doesn't start.

As the mechanic was working on the bike today I was able to just observe and I noticed something. On the rare occasions that the engine starts and the throttle is turned, the noise from the carbs sounds more like air is being pushed out rather than sucked in. If I place my hand near the carb - not blocking air intake but about an inch away from the carb - and crank the starter until the engine starts and then roll the throttle I get a little gas on my hand. I would not have expected that. Keep in mind that I can pump 100 psi into the Cylinder ( at TDC through the sparkplug hole) and the valves both hold the pressure. A little pressure leaks past the rings - I can hear it coming from the oil filler cap.

So does it seem reasonable that I have 150 psi compression but there might still be a leak in the intake valves when the engine tries to run? Is it time to pull the head? Can I pull the head with the engine still in the bike? Can I inspect the valves without pulling the head?

 

no,no,yes,no
i want to see a picture of your cam timing marks.
did you ever try to start it with the intake boots on? it's possible that had that gas that blew back on your hand been sucked back into the carb it would have run. in other words it's dieing lean because it has no air cleaner on it. any pod guys shed some light on that?

he's just a pup