Old Brown

Spent all afternoon out in the barn working on Old Brown. Had a few temp connections to make in the headlight bucket For some reason I have not worked out yet, I could not get a good connection from the fuse box on the main power wire to the headlight bucket After crimping on new connectors etc. I said to heck with it and made a jumper from the fuse box to the headlight bucket to power the kill switch.


A shot of carb cleaner in the carbs made it pop and turn over so confirming spark. Next I fill the carb bowels with fuel and grab a can of carb cleaner to spray a shot in each side to primp the pump so to speak. I go to set down the can and notice something missing.
dont.JPG

So off come the carbs to retrieve the spray straw. Crap.
Put everything back together and crank it.


It will start and run for about 4 seconds on the left jug and then die. Wait 20 sec and will do the same thing.


Any Ideas
 
Well now that the temperature has dropped below the mid 90s I went back out to the barn and experimented a bit. It will run on its own for about 3 seconds then quit and continue cranking the starter in about 10 seconds it will fire again for 3 seconds but only if the choke is on. I find it odd that it needs the choke at this high of a temperature. If I cover either throat it sucks gas up from the bowel. I have swapped plug leads side to side with no change.
 
One thing I used to do long ago, while diagnosing difficult-to-start engines, was to do frequent plug pulls and inspections, looking for dry and/or fuel fouling.

Also, temporarily closing the plug gaps down to 0.010"-0.015" would allow firing thru any fuel fouling...
 
As you well know it was too damm hot do do much in the barn today to get much done. I did go out and crank it and it would start and run for about 3 seconds and re fire after cranking for 5 or six seconds. I'm not real clear on how the fuel gets to the pilots. It seems like the pilot sucks all the fuel from under it and it takes a few seconds for fuel to flow from the bowl to under the pilot. You saw how bad the bowls were. I will pull them off and try probing with a guitar string.

Looks like you had a little rain today. hope it cooled things off a little.
 
I got three drops. Oddly that came from the tail end of the hurricane. Talking about spark, I need to check if the tci box is working properly. That could explain the odd behavior.
 
I went out looking for a pair BP7ES plugs here locally. Found them at the 4th place I went to. Came to find out at someplace online that are discontinued and replaced by resistor equivalents. Humm.

Pulled the carbs again. Soaked the bowls , checked that the pilot jets were clear and went to town on the passage ways with air. Reinstalled them and noticed I had not reinstalled the hose that I had been using between the petcock barbs. Fixed that, filled the bowls with fuel and hit the starter. Damn if if didn’t fire and settle into a good idle with the choke on. Let it run until it burned all the fuel, refilled the bowls, turned off the choke and it cranked up and idled.

Now it starts just fine cold or hot. What a relief. I’ve been working on this project for 3 years and this is such a milestone. Those carbs were real nasty. Looked like asphalt in the bottom of the bowels.. I was afraid that I was going to have to find another set of carbs.

Now I need to get the tank and fenders painted, the seat mounts worked out, Install the new tires and work out the rear master cylinder mounting and a few wiring details.

Onward and upward
 
I was keeping this under my hat so to speak until I got the bike to run and see if it even worked.. The late model engine that I bought was equipped with a tci pick up. No TCI box.

There on my parts bike, a xj700 was a hitachi TCI box that used magnetic sensing coil to trigger it and a matching dual output coil. I wire the pickup wire to the retarded pickup, is that P.C. ?

So finally I get the bike to fire up. At idle the timing light shows the timing mark lined up with the F mark. Great. Rev the engine and the timing retard 5 degrees. WTF

Hook up to the advanced pickup . Hard to start, idles very high. Timing way advanced. So here we are.

I know it’s a great secret about how the IC in the TCI works. I figured up till now that the advance worked by monitoring the frequency of the pulses from the pickup. So it should work , right ?

Anyone have thoughts about this?
 
Yeah those use a different spec pick up
HCP12427H
OEM Pick-up COILS AND HARNESS
Resistance of each coil: 120 ohms +/- 10% = 98 - 132 ohms

Applications:
XJ700 all models
Through all these years and thousands of attempts, no one has ever found the holy grail, a TCI from a different bike that will "work" LOL
 
Been biding my time today. A rare cold front is a couple of hours away. High tomorrow of 90. Frigid for this time of year so hope to try a few things out in the barn.

The timing light seems steady so the box seems to be triggering ok.

The fact the timing retards with higher revs seems strange. My only thought is perhaps the polarity is reversed. Will try reversing the pickup leads. I assume the pickups are isolated from ground.

The higher resistance of the 650 pickup coils 700 ohms vs 100. perhaps 200-300 ohms 1/2 watt resistor in parallel to the pickup coil. (thanks gggGary)

The advance almost has to be frequency controlled. Voltage rise with the speed of the magnet passing the coil would be sketchy.

Worst case an e advancer cobbled in maybe.
 
Started this morning by wiring a 3 pin pig tail for the pickup so I could probe around the connection. Reading the thread about using the Mazda TCI box I came to the conclusion that polarity of the 650 pick up coils was reversed. Turns out I was getting a double spark with it hooked up with the black wire as the negative. With it reversed I get strong spark about 4 degrees retarded from the F mark Close enoungh if I slot the pickup mounts. Found the page about early 1980s Virago 535 I looked at when I took this route several years ago. The one thing I noticed was the trigger magnet was a curved bar on the top of the stator. I’m thinking that the small round 650 magnet is not producing the duration of current that the TCI needs to advance. I’m going to try putting an electrolytic cap from the pickup coil winding to ground and a 200 ohm ½ watt resistor in parallel with the pickup to extend the pulse.

What I have learned about the Hitachi TCI

1980 -~1985
700 ohm pickups
~2.5 ohm coils
5k ohm plug caps with non resistor plugs

1985-1986
120 ohm pickups
~2.5 ohm coils
10k ohm plug caps with resistor plugs

I don’t know how the hell they got enough wire into the 650’s pickups to create 700 ohms of resistance.

I plan on opening up the xj to look at the magnet and coils to see if anything jumps out at me.
 
Put a voltmeter on the pickup coils today. .02 volts on the active coil and .03 volts on the open one. Seems low to me.
 
None of my digital meters distinguish between ac and dc. That's why I questioned the readings. I'd love to own another scope. Mine is a 2" rack scope that has not been powered up in 30 years.
After marking the timing marks so they are more visible, the timing is falling right on the F mark. I have to assume that the TCI is correctly sensing the signal from the pickup coil. From what I read last night the advance is based on the frequency of the signal, not the voltage, so if the signal is present why isn't the advance happening ?

Bottom line, I'm getting a good solid spark. The bad news is I'm still having carb problems. The more I run it the better it's running so I have not panicked yet. I did apply power to the charging system today and it is charging the battery so that is good news.

I guess time to move on to getting the tank and fenders painted.
 
Been biding my time today. A rare cold front is a couple of hours away. High tomorrow of 90. Frigid for this time of year so hope to try a few things out in the barn.

The timing light seems steady so the box seems to be triggering ok.

The fact the timing retards with higher revs seems strange. My only thought is perhaps the polarity is reversed. Will try reversing the pickup leads. I assume the pickups are isolated from ground.

The higher resistance of the 650 pickup coils 700 ohms vs 100. perhaps 200-300 ohms 1/2 watt resistor in parallel to the pickup coil. (thanks gggGary)

The advance almost has to be frequency controlled. Voltage rise with the speed of the magnet passing the coil would be sketchy.

Worst case an e advancer cobbled in maybe.
My understanding is the XS650 TCU computes an advance by picking a point after the first pick up pulse to fire based on time between pulses/ speed of the previous revolution. until 3000 RPM when it just fires on the second pulse. (something like that)
My guess is the later TCI uses a completely different system based on just one pulse. (really all you need) solid state design was advancing :sneaky: VERY rapidly in those years.
 
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