poor idle until it warms up, sometimes no power until i down shift

[Korr]

Hi guys

So this morning when i turned her on to warm up she was being difficult. It took maybe about 20 seconds full choke before it fired up and idled. The idle was horrible! It was very low and unsteady. It jumped from 1-1.5k to about 3k rpms once it warmed up. It did not gradually increase like usual. So i thought that it was just being lazy because i have not taken it out for a ride for a month. Once i got out onto the street, i shift to 2nd and give it some decent throttle. It sped up just fine, but then it stops accelerating and becomes unresponsive to more throttle. To get it back to normal i have to downshift. This is the second time that it has happended during a ride. The first time was on the freeway about a month ago while i was heading home. It happened 3 times that day, twice on the highway, once in town. At the time i thought it was all due to the fact that my rpm's were too low for the gear that i was in...bogging. On a side note, my turn signal lights are now working without needing the rpms to be above 2.5k I will try to get a video of the horrible idle up in a few days. Any help is appreciated guys, thanks again for taking the time out to read this

[DGXSER]

Perhaps the pickup coil wires? Most likely an electrical issue since the bike was running fine before. A month of sitting should not have gummed up the carbs.

You could also test out the coils.

[Korr]

Ok i will try to move the wires around and see if they do anything while it's running.

[Rasputin]

I found I had similar problems. It did keep getting worse. In my case it was the pick up coil wires. Dont be scared to give em a pretty good pull and for the engine to in fact die. A good wire will take a lot of pull. Mine was really low and almost outside of the cover, where the wire comes into the left side. It runs so much better with it fixed and it was an almost intermittant problem before.

[Korr]

here's a picture finally

Sorry it took me so long to put up a picture. Just got a new phone and couldn't figure out how to upload pictures.

So in the picture i used my awesome skills to draw a circle and arrow to show the area where it is killing the engine when i put some decent pressure on it. I tried to pull the wires, but cannot figure out how to get a good grip on them. There's barely any room to work with in there. The problem wire is the ugly light bluish one. I will always kill the engine if i push it where it goes into the black rubber. I have no idea how i will be able to fix it in there. Thanks for listening guys

SORRY the arrow is pointing to the wrong wire. It's supposed to be the one on the left hand side.

[Ken Talbot]

Yup, that's a broken pick-up coil wire. The good news is you have found where it is broken. The bad news is there may be other breaks too. The other bad news is that spot might be a bit tough to fix. You're going to want to remove the whole pick-up coil assembly so you can see if there is still enough good wire to splice some new wires onto. When you get it all out, and if you find the rest of the wire is all okay, you might get away with just fixing it at the broken spot.

[oldyam80sg]

Also on E-bay there are complete units for sale every once in a while.

[thewiz]

I think that the Diver ..

has the best way I've seen here for fixing PU coil wires, IMHO. I have always soldered in little patches made from old PU coil wires at the break point or points ... but ... he says it's better to get some leads for a multi meter at Radio Shack. They are the right kind of strand and flexibility. Then solder 'em in right up close to the coil and run 'em back a foot and attach them to the harness there. I think it's OK to even leave the broken wires in place, if you don't mind the clutter. Less likely that they will fail the same way again. Made sense to me anyway ..

[Korr]

Once i fix it, should i pull the wires out a little bit to give it some slack? They look really tight in there.

[thewiz]

Wouldn't hurt ...

should i pull the wires out a little bit to give it some slack?

Although the originals lasted between 25 and 30 yrs ... that's not bad, right?

[tarzan]

When I fixed mine I gave it just enough slack to move freely without rubbing on
any fixed(non moving) parts.

[clyderider]

weak to no real idle

I have the same problem with "clyde" and you think it's the pickup coils???? yeiiiieee I did the pickup coil fix soldering those wires together with a battery operated solderer is a %#@!$@!#$ now I gotta recheck and maybe do them again yieeeeeeeeeeeeeeeeeeeeiiiiiiiiiiiiiiieeeeeeeeeeeee e.no fun...welll maybe in nov.dear hunting ya know!

[TopCatGr58]

Hey Cycle,

IF you did your repair properly, and used good flexible test meter lead wire, then it may still be okay!?

Aside from the PU coils, several folks have reported that after they replaced their high tension coils their idling problems went away. These 25+ y/o stock coils, wires, plug caps, all age and can contribute to loss of spark energy, and a weak spark can cause all sorts of running problems. YMMV!?

A thorough inspection, metering of your ignition coils might reveal unknown problems. Take the plug caps off the plug wires, inspect for corrosion, the cap resistance(~5kohm), then the coil high tension secondary resistances without the plug caps(should be ~15Kohm +/- 10%, as well as the primary wire/coil resistances(1.5 ohms). Also check your ballast resistor for proper resistance, and connection corrosion. Check the power at the coils red/white wires, when running should be about 9 volts, will be 12 during starting but lower when running since it's routed thru the ballast resistor.
T.C.

[DiverRay]

Korr,
One of the biggest problems the '78 had was that Yamaha crimped the wires too tight in the holders! I had to do a pickup coil wire fix in 1979 on my first bike! When you replace the wires, or coils, leave the clamp open just a little so the wire will slide back and forth as needed. That will help the fix last a LONG time. And yes, the front one shows up because it gets pulled at idle, but then works as your RPM's increase.

[Korr]

Man that main crimp on the lower right side that's holding all the wires together is hard to fiddle with I can't get a good grip on it with anything to open it up so that i can pull in more wire. I was over at Radio Shack yesterday and couldn't find the ones that stretch. They had about 4 leads for sale, but they were just regular wires. Anybody got a link or part number? Atleast i got the soldering gun