Back again, I'm having torubles with a 90 1200 sportster, can't get ti to start. I believe I have weak spark. I checked the coil as per maunual and it seems to be ok. Checked the ignition module and I believe it is bad, however I'm not sure. I pulled the 3 prong plug as per manual and checked the volts on the red and black terminals, the book says you should have 4.5 to 5.5 volts, however I have about .4, with ignition off. I checked across prongs with ignition on and have 12+volts. Decieded to do next check in manual and removed one spark plug and ground in to the frame, jumped the green and black wires to check for spark, I have spark however it looks weak to me. Bike ran last week, however it is fouling plugs really bad. I thought the carb was not jetted properly and have been trying to eliminate the fouling issue by changing the jets. Just got the bike about a month ago, needed some work, carb needed to be rebuilt, got master kit for an S&S super e, had a .66 main jet and a.28 intermediate jet in it, wiring harness needs to be replaced, original owner cut and respliced wires way too many times, harness is on order. Bike was backfiring and seemed lean, went to .68 main jet, now fouling plugs. I am confused now that it will not start, has or is my problem all along with the ignition module, next to the battery or the timing plate causing weak spark and just getting progressively worse. I'm confused, not used to bikes that have all this electrical stuff on them. Irons, Shovels, kick only is my comfort zone. When trying to check out the issues, I find battery dies quickly from using starter, could this all just be a bad ground somewhere. Any help would be great.

 

Just a quick suggestion, have you checked the gap on your plugs?

 

Backfiring is typically timing or an air leak in the intake or the vacuum lines.

I always cringe when I hear someone tearing a carb apart that isn't sure of what they are doing. If it's a factory carb then you should have gotten a rebuild kit for the factory carb. Jet sizes you changed to seem like the wrong sizes to me.

You have to have a full charge on the battery, even while cranking, in order for the electronic ignition system to fire correctly with a hot spark. Also don't run the battery down it will not fire spark, and don't hold the starter on for long periods. A starter will heat up in no time. The heating issue can also drag it down. Low battery can cause the starter to overheat and you don't want to add a starter to your parts list or repair time.

'90, that should be an EVO motor correct?

So you were able to trigger the coil and did see what you thought was a weak spark.

If it were me I'd put the carb back together with a stock rebuild and put back in the factory jets designed to work effectively with your setup.

Bad Ignition Modules and cam sensors were more of the weak link in your system. There's only a few steps. If you know you have a good supply voltage to the module and you're getting below 1 volt on the cam sensor connection (3 pin plug) then the sensor is not getting it's correct voltage to even operate. That voltage is supposed to come from the ignition module. The module reads that voltage to actuate the coil to spark the plug.

Two things come to mind ... Make certain you have a perfect connection to the battery. Corrosion on connection causes resistance and can cause a no start situation even with the motor turning over. A low battery often turns the starter slowly, too slow to get it to start.

AND consider fresh plugs and new plug wires could be all it takes.

Good luck with the wiring harness!

 

Yes they are set @ about 38, currently have Autolite 4164 in it, they were all the parts store had. NGK, Champion, Autolite, all fouled out no matter what. That is what led be to believe the carb was jetted wrong in the first place now I'm thinking the problem was weak spark form the beginning and it is just getting worse.

 

JohnnyC, Thanks for your feedback, howvever this is not a stock carb, it is an S&S super E, very basic carb to rebuild. I have a .66 main jet & a .28 intermediate jet in it which is what the previous owner had originally. I will check the voltage, to my understanding to check the voltage on the module I should disconnect the 3 prong plug, red lead on volt meter to red plug wire and black to black. According to the book I should 4.5 to 5.5 volt with key off. I know I don't have that could this be my issue? And yes it is an Evo.

 

Found out I was experiencing a weak spark condition due to some bad connections in the wiring harness. Also found that the Air Fuel Mixture Seat was F**kd. When I bought the bike the Mixture screw's tip was broken off, bought a rebuild kit and found that when the screw was turned in completely seated it would still idle, and rather well at that. The carb should have stalled out. Found that the screw was over turned and reshaped the seat too big. Makes sense why it was running too rich and was fouling plugs. So I had to break down and buy a new S&S Super E. Installed a .295 intermediate jet and .70 main jet, runs great. Tahnks to all for your help