ignition problem

why does it run at all? 1983 750 maxim,starts great,runs great up to about 5k,then lays down and tach goes crazy. runs up with no problem when in garage.checked ignition coils,ok.(just for ha ha switched them over,same deal)checked plugs,wires,cleaned connectors.checked both p/up coils resistance,there is none.when I check for continuity between the grey right side coil and tach signal wire I get a reading to ground .

 

Don't have my schematics handy, I'll take a look tonight.

 

OK, according the the schmatics in the venerable Haynes manual (all praise to the Haynes man, he doth lead the unknowing to enlightenment, oooohhmmmm), the Grey wire on the coil is connected directly to the Grey/Yellow wire that feeds to the TCI and the Tachometer. I am a little confused as you mention measuring between two points and reading to ground. If you mean that you measured from the Grey wire to a chassis ground and read a short, you have found your problem and need to chase the short down. Given it is one wire, that shouldn't take too long. If I misunderstood your description, you are reading a good connection from the ignition coil to the tach line. Reading between the two ends of a wire should be a measure in continuity. I hope this is simply a misunderstanding of electrical terms.
You also need to read at the coil connectors:
From Red/White to Grey and Red/White to Orange should be 650 ohms plus or minus 20 percent.
That will check out the pickup coils. They can and do drop (as they age)when under load or heat up. Ensure you are seeing 12VDC at the coil Red/White wire. That wire is feeding power from the sidestand relay and if the relay isn't feeling happy, no bike running.
Check out your options and let me know what you find.

 

i guess we had a misunderstanding. here are my readings. 12v at coil red/wh wire. 3.2ohms at coil primarys,23-25 at secondarys w/plug caps on.680 for both p/up coils,I was on the wrong scale,DUUUH. coils,p/up coils,reluctor plate,etc.all look newer.I have original owners manual.I downloaded haynes.Bike starts w/tap of button,plugs tan,and as I said previous,runs great up to 5k,then lays down and tach goes crazy. Blue Max posted way back same symptons for bad TCI.Sooo,am thinking bad right side circuit to coil. PS,fuse holder has been upgraded,bike has not been monkeyed with cutoff switches all work as they should.

 

Had a fellow with a 900 Down Under which did a similar thing, nothing over an idle (and sometimes not even that). I couldn't save it.
It is possible it is the TCI but I'd see if you couldn't borrow a buddy's unit for a quick check first. Otherwise, I do offer a TCI refresh service but I can't repair the daughter boards (the aluminum oxide one) or replace the chip (unobtainium). Once they die, it's over.
I have got to get a collection of TCI's together and rent them out for testing (there will be a HEFTY deposit on them).

 

Robert,thanks much for your response. Have no access to a loaner. really do not want to buy used off e-bay.So,if no one here has a known good one,I will send mine to you for possible repair.

 

problem solved! kickstand safety switch was not breaking circuit in up position. Why it only affected running above 4500 I have no clue but have seen electronics do some strange things.I hope this can help another member. Robert,thanks for your advice and I will keep your address just in case.