81 gs 750 no fire

[shopguy]

have gs 750 with no fire,put new igniter still no fire.when i was checking coils one coil has 12 volt onboth wires(orange&black/yellow)the other checked 12 volt orange,white checked to ground,sitting on bike left coil is hot right is cold butno spark at all.any help would be great

[tom203]

"No fire" means no sign of spark at plugs?
Welcome, head to this link

http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17

Your bike has an ignitor, not a CDI; check all connections

[shopguy]

alright but can you explain why one coil has 12 volts on both sides and the other is 12volt and ground,which one is bad or are they

[tom203]

The orange/white wire going to both coils is the 12 volt positive-this comes from kill switch. The other connection on coil runs to ignitor (one solid white to one coil, yellow/black to other coil (??)). At right time when triggered, the ignitor grounds out one coil, then the other- this is same thing that contact points do, open and close. If you have ignition on ,but bike not running the ignitor might not be grounding out one coil (the ignitor will be waiting for trigger signal), so you'll measure 12 volts on both of that coil tabs as there's no connection to ground.
Head to that link; unplug your coil connections and check primary resistance- should be 3 to 5 ohms if you got stock coils- which seldom go bad. Ignitors and/or connections are more likley culprits in non firing episodes

[shopguy]

ill check ohms at coil,what is procedure fo testing signal or pulse generator

[tom203]

ill check ohms at coil,what is procedure fo testing signal or pulse generator

Head to that link- step 11 gets to the signal generator test. So you have yet to see this thing fire a plug? or was it ok, but something happenned?

[shopguy]

bike was no fire when the guy gave it to me,ive already been thru carb,tested igniter last night it was good tried to test puls/signal generator with ohm meter but kept getting different readings ,using digital meter started at 746 stopped reading at 221,the only other thing is how the fuel lines hook to petcock looks like it uses vacuum line from carb to a diaphram on petcock not familiar with this setup.

[tom203]

Here's a link with pic of all hoses- Basscliff's site has 99% of info you need

http://members.dslextreme.com/users/storagecliff/images/hose_locations.html

When you test signal generators for ohms, make sure they are disconnected from ignitor.

[shopguy]

ok so i rechecked signal/pulse generator with other tester it said 324 ohms this is within range of 250-360 still no spark at plugs,coils tested at 4.3-5 ohms,what else could cause no spark,noticed it had oil sending unit is this just for warning or iit like generator that can shut it down under low pressure.

[tom203]

No the oil pressure sender won't effect ignition system.
Your signal generator seems good- doublecheck all connections from signal coils to ignitor and from there to ignition coils.

A few posts up, you said ".....tested igniter last night it was good "- how did you reach this conclusion?

Remember that when you test spark plugs for spark, both plugs on that coil have to be grounded to head - the current shoots down one plug lead and back up the other.

[tom203]

Also try Mr. Matchless's simple test; remove signal generator cover; remove #4 spark plug, reinstall plug wire and hold spark plug against head as to ground it. With ignition "on" (and kill switch on "run") , flick a small screwdriver tip across the face of the signal coil for #1 and #4 - this duplicates what that little metal tab on rotor does as it spins by signal coil telling the ignitor to fire 1 and 4 plugs. See any spark on #4?

[shopguy]

found post that told testing procedure it went like this.uhhook blue &green lead from pulse /signal generator at igniter,on leads that go to igniter take 1.5 battery hook ground lead to blue side,with ignition on and kill switch on, plugs removed from motor grounded to engine briefly touch 12volt to green wire you get spark at plugs 1&4,when you take 12 volt off green wire 2&3 fire

[tom203]

Well, I'm impressed that you did the test- ignitor seems fine (when triggered by battery); now you need to determine why it doesn't get the urge when the signal coils do their thing. I believe the ignitor sends a small current to the signal coils which gets "disturbed" when metal tab on rotor flies by coil face -ignitor senses this and fires.

[shopguy]

im going to try the other test you suggested that way the system is all wired back together as it shoud be,see if we get spark then

[shopguy]

ok i tried mr. M signal test it did not work,an electrician friend of mine used his ohm meter on pulse generator his read 324 ohms,tested coil thru ht wires,1/4leads,2/3 leads with ignition off one coil triggered reading on ohm meter the other did nothing