hello all. yamaha newb and NO START troubles...

hey guys. i am new to the yamaha world and will post an intro in a few but need some help getting this thing running.

i picked up a 81 750 seca for my wife and got the story that it ran when parked 8 months ago so it probably just needed a fuel system cleaning.

i cleaned out the carbs, new fuel filter still no start. it backfires and sometimes sounds like it wants to start when i let go of the start button.

when i checked for spark, it seemed to have a strong spark once, then nothing then again when i let go. online reading sounded like the ignition so i ordered one and just plugged it in. it now has a strong spark the whole time i crank it. i just changed the plugs anyway since they were wet with fuel from cranking and still the same backfiring and almost start when i let go of the button.

i have read about replacing the fuses, but i have constant spark so i dont think that is my issue.

just out of ideas, all of the things i read to try like sidestand and center stand and battery/ fuse connections doesnt seem like the problem, because again i am getting good spark and fuel. from my harley experience it almost seems like the timing is off but the cam chain tensioner is automatic and the ignition electronic.

any ideas? thanks in advance

 

If your plugs are wet that indicates too much fuel. Have you checked the float levels using the clear tube method. proper fuel level is critical.
Did you by chance mix the plug wires while changing the pugs? One coil goes to cylinder 1 and 4 the other goes to 2 and 3.
When you cleaned the carbs did you;
remove all jets and blow passages clean?
remove idle mixture screws , emulsion tubes and blow clean?
benc sync the carbs?
Wet set float levels?
Most improntant have the valve clearences been checked and adjusted?

 

i took the carbs off in one piece and cleaned out some crud from the bowls and removed the jets and sprayed them out, cleaned the float valve and all passages. ya know what, i missed the idle mixture screws.
i also have not yet checked valves as i didnt think they would be far enough off that it wouldnt run

i just changed out the fuse block since i had one laying around and the one for the headlight was getting hot and was a good idea anyway. no change

i wish i noticed before now, but the rear tire is obviousley melted around the middle from someone doing a nice burnout. this scares me as now anything could have broken rather then the reported "ran when it was parked"

i stated before that i was getting a strong spark in all four cyl when i first hit the start button and again when i let go but nothing while cranking. i replaced the cdi box and check the #1 cyl and have a good strong spark the whole time. but i just checked all four and 2 &3 are still no spark while cranking but strong at start and stop. 4 is constant strong. i know that 2&3 share a coil. sound like i need a coil or maybe a lose wire or i got another bad cdi?

and yes i believe i have the coil wires in the right order. they are numbered 1-4. 1 being on the left and 1&4 come off of the coil on the left and 2&3 off of the coil on the right.

 

Having the ignition fire when you LET OFF the button is a sure sign of a weak battery.

Why this happens is that the starter is drawing all available current, leaving nothing left to fire the ignition.

If this happens with a fully charged and TESTED good (at the auto parts) battery, then it indicates a need to service the starter, solenoid, or a wiring issue.

The reason the valves need to be in spec is because you won't be able to (post-cleaning) adjust the carbs properly if they aren't. You DO need to acccurately wet-set the float levels and get a good bench sync though, or it won't run well enough to vacuum sync.

 

but only on cyl #2&3 ?

even though it appears to be a new battery and cranks hard for a long time, i tried hooking jumper cables to my harley battery with no change.

 

I would do a compression test. You know you have spark, you might have good fuel mix (if your pilot/idle circuits aren't clogged) you could still get fuel from the enrichment circuit but the pilot needs to flow at idle for combustion-ie plugs wet but still no fire. So start with the compression test, if that is good and battery is solid 12.4V or more at rest, then your carbs become suspicious.

EDIT: I just reread your last post. You need to do a primary and secondary resistance test on that suspect coil. That will tell you if its the coil or your TCI, but I'd bet on the coil. Make sure you test secondary from plug wire to plug wire with caps removed.

 

Hi I had a similar problem when I was restoring my XJ650 Seca. It took me a long time to track it down but it was a faulty engine cut off relay. Everything seemed to be working ok but as soon as a load came on the ignition circuit this relay cut the power to the coils. I replaced the relay and all has been ok since. This was on a 1980 XJ650 Seca so your machine may be different. On my bike this relay was a square relay with 4 square tabs sticking out for the plug to plug onto and is located under the tank just behind the self cancelling indicator relay. Haynes manual says that in an emergency you can put a loop in the plug connecting the two red and white wires so the relay is bypassed allowing the machine to be used until you can get a replacement relay. Page 247 of the haynes repair manual. I tried this and it worked until I replaced the bad relay with a good one.

 

If it's only firing on #2 and #3 when it does fire, then it points to a coil or pickup (or associated wiring) issue.

The coils on the XJ fire 2/3 together, and 1/4 together, every stroke; it's a "wasted spark" system. One coil is 2/3 one coil is 1/4 and each has its own ignition pickup.

Don't go by how "hard" it cranks. Fully charge the battery, take it to the auto parts, and have it load tested.

 

Thanks for the help guys. I got it running. I used a post on this site called "how to: ignition troubleshooting" which said i had a bad pickup. When i went to inspect it i found that the previous owner put the side trans cover on and sandwiched the wires in it cutting one wire and the other two were barely connected. Cut, soldered and running nice.

On a side note, i did test the coils and was about to order some. The manual says primary should be around 2.6 and secondary 11k. My primary tested 2.6 in both but one coil tested at 22k and the other at 34k ohms. Weird, right since it is now running?

 

Did you remove the plug caps before testing? The caps have a built in resistor.

 

Well, the manual shows testing with the caps, but i thought i noticed a change in ohms when wiggling one so i thought a wire was broken and ended up pilling it off. They were all crusty (The screw in the cap and the wire end) so i cleaned them up and trimmed a 1/4" from the wire. But for fun i did test with one cap off and got the same read

 

The resistors inside the caps screw in and sometimes work loose. Look in where the spark plug goes, you'll see screwdriver slots on each side of the hole. Gently ensure the resistor core isn't loose.