No power at2500 RPM

[jeffe]

My 78E just started to have a very bad stumble, actually almost no power at 2500 rpms and up. I looked at the plugs all look ok. Cleaned out the vent hole for the gas cap, checked vacuum lines to the petcocks, put petcocks to prime and reserve, no difference. All header pipes seem to be running hot. No matter the load or throttle setting the bike runs perfectly fine up to aprox 2500rpm. It won't die just stutters very badly and will not pick up any more rpms. I tried slowly increasing rpms with the bike in nuetral and it would rev up to aprox 2500 then start to stutter. It doesn't seem to be missing on any one cylinder or completely shutting off. I was able to nurse it home at about 25 to 30 mph. It would occasionally "kick" in and run ok. At rpm's below 2500 the bike has low end power as it always does.

Any ideas? Thanks, Jeff

[jeffe]

Forgot to mention that it idles perfectly fine and starts up with no problem

[mro]

On the carb side, just about 3000 is where you leave the idle circut, so could be a fuel problem (main jet?)

Another item is the pick-up wires
Take a look at this
http://www.xs11.com/tips/repair/repair8.shtml



mro

[jeffe]

After rereading my first post I see that something got let out. I was up to speed on the freeway, around 65 when it first cut out on me. he bike has an almost new set of pick up coils on it. A question about the main jet, unless by some fluke all 4 mains went south , would it still run ok on the other ones?

[Ken Talbot]

Main jets do not tend to all of a sudden go bad. Pick-up coil wires do. Even if you've got brand new NOS coils and wires recently installed, all it would take is for one of the wire loops to have been a big big, or too close to the rotating plate for it to wear through the insulation and short out. I've repaired broken sections, and I've also had to work on spots where the wire was still okay but the insulation had got rubbed through.

[TopCatGr58]

Hey Jeffe,

We really need more info on what you've done to the bike in the past, any previous repairs, mods, etc.!

Like MRO said, it idles, but can't do much over idle! That could mean that it's not getting fuel, or enough of it!?

Okay, it's a 78E. You said Prime or Reserve made no difference, di did you mean no difference on how it ran?? Are the petcocks flowing fuel? You said you checked the vacuum lines to them, but did you take them off and verify they flow fuel?

Next, you said that it has an almost new set of pickup coils! Did you replace the entire PU coil AND wires assembly with NEW, or used? Have you checked to see if the timing plate will rotate properly and freely? If the timing can't advance, it won't be able to run/rev very high!

Have you checked your vacuum slides for free movement, not sticking?

When you were running on the highway at 65, did it act like it had NO POWER AT ALL, no response to throttle input? Did it just slow down to the under 2500 rpm range and that's it!?!?
T.C.

[jeffe]

Entire history since I got the bike.Got bike 2 years ago
First year... Bike had sat with fuel in the tank for 5 years. Had carbs cleaned and rebuilt and new carb boots installed. Tank was relined. After carb rebuild one float was bad and installed new one. Pickup coil wires were in bad shape and installed new set from BikeBandit. Bike ran fine for about 3K miles and quit running with no warning. Was the end of the season so I didn't spend any time looking at it. Drained carbs and added Stabil to tank and primed carbs so they had the gas with stabil in them.
2nd year...which was this spring. Installed new battery Found the reason the bike quit running was that one wire had come lose in the pickup coil wire bundle. It was where one of the "bendy" wires was connected to the harness that leads out from inside the timing cover. Fixed wire and bike ran fine. Have put around 5k on it this year so far. Last week end throttle cable broke and had to be towed home. Installed new cable and have ridden about 100 miles since then. The only other thing that I did was install a new H4 headlight instead of the sealed beam unit. What happened last night was while I was cruising at a steady 65 on the freeway the bike lost power. I pulled in the clutch and it went right bike to a normal idle. I was right at an exit ramp and got off there. The bike would idle normally and rev up to aprox 2500rpm. It would do this either while If moving or if I was at a stop in nuetral. While I was in nuetral and slowly increased throttle it would rev to aproximately 2500rpm and then start to surge. It would surge up to about 3500 and then drop to around 2000. It acts like this most of the time but it would very occasionally run completely normally. When it is acting up it would " backfire". It did not seem like it was coughing back thru the carbs but instead like it was just igniting fuel in the exhaust system. Other than the headlight that I mentioned and the Vetter fairing and hard luggage the bike is stock. No aftermarket exhaust or airfilters. By the way the backfire only occured a few times. 5 to 10 times in the 10 mile ride home. I hope this answers all the questions you had. A couple more things. The bike starts up as always. First notch on the "choke" and just a second of cranking. Also When I checked the head pipes using some water to see if they were hot they all warmed up equaly. Sorry things keep popping in my head. Thanks, again

[jeffe]

Sorry, I have not had a chance to check put the timing plate and the wiring for the coils. Too busy of a day today. Is there any chance that this could be the TCI box? I have a working spare.

[jeffe]

Sorry one more answer. It does not make any difference on whether it is on prime, reserve or run. I pulled off one fuel line and put it prime and fuel ran out of the petcock.

[TopCatGr58]

Hey Jeffe,

First, thanks for the detailed info!
Well, hate to say it, but looks like you need to visit your PU coils again. Even though you put new ones on, they were probably NOS!!! Meaning they were probably 20+ years old stock!

At low rpms, the PU coil wires don't flex much, but once you start trying to rev it, the cent. adv. starts to kick in and rotates the timing plate, flexing the wires, and probably inducing a short, cutting power to the cylinders, until the rpms drop back down! SO....that's what I'd look at first. Doubt the TCI, you're getting fire to all 4 cylinders. Good Luck, hope it's a simple fix!
T.C.

[jeffe]

This was where I was thinking to. Have to admit I would much rather work on electric thatn carbs. Never ever have I had any luck with a carb. Sturting with a lawn mower up to a Holley 750spreadbore. All I've ever done is get myself aggravated and made it harder for who ever was fixing it.

[jeffe]

Finally got a chance to look at the bike today. It was the pick up coil wires. It had started to come apart on a different wire than it did last fall. It was where the "bendy" wires connect to the bundled harness that runs to the rest of the bike. I used some shrink wrap stuff to reconnect it. The bike runs fine.

This set was installed 2 years ago and have 6 to 7k miles on them. They were supposedly new ones from Bike Bandit. My question is has anyone else had a problem with these and if so is there a better source. This was the second time one of these wires have come apart at the same place.

[Ken Talbot]

Originally posted by jeffe
It was the pick up coil wires...... I used some shrink wrap stuff to reconnect it.

Are you saying you did not actually solder the broken strands together?

[jeffe]

Did solder it.

[DiverRay]

Take a look at the "clamp" they used to hold the pickup coil wires in place. The wire SHOULD BE ABLE TO SLIDE THROUGH THE CLAMP, or you will break wires. Yamaha had the wires clamped too tightly from the factory, and IMHO, that is the main cause of the problems.
I leave the wires a little loose in Daily Ride, and put a LOT of miles per year on it with NO problems.
Ray