Miss at high RPM/power

[Waiex191]

Hey all,
My FJ has been running great. Except when I wind it out at WOT and high RPM, like above 7000, it seems to be missing. I'm not even sure how to troubleshoot this as it's hard to run it like that unless you are on a dyno.  Any ideas are welcome. 

It didn't do this 16 years ago when I parked it. Seems to be since the resurrection. 

[Pat Conlon]

Hello Bryan, yep this happened to me.

It was a definite ignition miss...not a fuel issue.
After a long trouble shoot process, (new plugs, new resistor plug boots, bench test coils, tested pick up coils, cleaned all harness plug connections, etc) I found the problem to be with the handle bar run/stop switch.
The 12v power to the ignition box runs from the fuse box thru this run/stop switch to the ignition box.
My run/stop switch was dirty and causing an intermittent power interruption to the ignition box.
Another possible area to look at is a dodgy connection with the key switch, although mine was fine.

Intermittent electrical problems are a bitch to track down.

How I found the problem was to run temporary power and ground jumpers from the battery to the power leads directly into the ignition box. After a check out ride I found that the high rpm miss went away....after that, it was just a matter of following the circuit with the power jumpers until the culprit was isolated.
First step, I could rule out a bad ground early, so then I just needed follow the + side of the circuit.

Best wishes, stay methodical, log your conclusions, I tend to forget.  Cheers. Pat

[Alf]

I've understand that in a Dyno the bike runs OK, so I think that any electrical fault (i.e. the off/on switch or ignition/coils/plugs) must be discarded at first)
My first suspicion when I got a bike with problems running on high rpm. is a rich carb settings. And higher the altitude above the sea level, the problem gets worse
More details would help

If you give hard throttle in fifth i.e. at 6.000 rpm. the problem gets worse than if it is accelerated more progressively?

[T Legg]

I've just had a similar problem start with my yellow fj1100. At high rpm's wot it will start cutting out and even die completely if I don't back off the throttle. After a couple times I found if I pulled in the clutch and snapped the kill switch on and off it will run normal again for a while. Since it just started this weekend I haven't confirmed it yet by bypassing the switch like Pat did but I'm 99 percent sure it is the kill switch.

[Waiex191]

Thanks all for the replies.  I'll have a look at the switch and document my troubleshooting here.  Due to the weather and the airplane project I am not sure when I'll get a chance.  Any advice on cleaning the switch or would you just bypass to check first?  I never use the switch, I just use the key.

If you give hard throttle in fifth i.e. at 6.000 rpm. the problem gets worse than if it is accelerated more progressively?

That I'm not sure.  I typically shift conservatively from first to second so I don't blow second gear.  Then I go WOT in second to accelerate, and up near the top end of the tach is where it gets rough.  Typically at the speeds I ride at, I'm nowhere near 6000 in fifth gear.  At 55-65 indicated and WOT in fifth it runs and accelerates nicely.

[Alf]

What model do you own?
Have you performed any mod to the carbs?

[Waiex191]

What model do you own?
Have you performed any mod to the carbs?

It's a 1989 US model.  I don't remember the 3 digit number associated with the bike.  It is stock except:
1) FZ1 calipers and MC
2) Holley fuel pump
3) I have a back-to-back diode on the output of the battery to drop the charging voltage by 0.7 volts.

Of those 3 mods, the diode has been there since the early 90's, after I boiled over my first battery due to a 15V charging voltage.  I did the other two when I brought the bike back to life:
http://www.fjowners.com/index.php?topic=19343.0

The carbs were in bad shape.  I ended up getting a set of carb bodies from woodcreekpete.  They are 100% stock, though Pete's carbs were from a '90.  They seemed the same and I used my jets and emulsion tubes.

[Alf]

In my experience, typical high rpm troubles are given by:

- Faulty fuel petcock or fuel pump/inappropriate fuel filter

- Poor spark. If everything is right, have you measured the coils voltage?. For experience I can tell that usually is around 9v when it must be 12v. Do the problem appear when the bike is hot?. Usually simply a bad connection wire/spark plug. I understand that not in your case, because on the dyno your bike works

- Rich carb settings, hence my question about your mods. Or emulsion tubes being oval. Here the problem is the transition from low to high rpm: you open hard the throttle and the bike don't respond, being better a progressive throttle

- Maybe lean settings in your bike? When transplanting your main jets, did you check that all of them were completely free ob obstructions? I've seen on a lot of years parked bikes that the jet inner passages are even blocked simply by its own rust, and no cleaning method is capable of unblocked the thing

I hope this helps

[Waiex191]

Alf,
Thank you for your reply.  Here is some discussion on your suggestions:

- Faulty fuel petcock or fuel pump/inappropriate fuel filter

The fuel petcock has not been rebuilt.  But since I filled and drained the tank a few times, it seems to flow out fine.  The '89 does not have a vacuum petcock, just on/off for removing and replacing the tank.  The fuel pump is not stock, it is a Holley 12-426.  It is rated at 25 gallons per hour.  The fuel filter is stock, and is new.  I replaced the old filter and lines when I brought the bike back to life.

- Poor spark. If everything is right, have you measured the coils voltage?. For experience I can tell that usually is around 9v when it must be 12v. Do the problem appear when the bike is hot?. Usually simply a bad connection wire/spark plug. I understand that not in your case, because on the dyno your bike works

I think there is a misunderstanding, probably from how I wrote my first post.  I have never had it on a dyno.  I was thinking a dyno would be an easier way to troubleshoot because you can run high power/high RPM with the bike standing still.  I have not measured the coil voltage.  I'll look at the schematic to see where to attach a sense lead, or if you can point me to it that would be helpful.

- Rich carb settings, hence my question about your mods. Or emulsion tubes being oval. Here the problem is the transition from low to high rpm: you open hard the throttle and the bike don't respond, being better a progressive throttle

I made a tool on the lathe to remove the emulsion tubes, so they came out nicely and were undamaged.  Plus I did get them very clean.  When I open hard the throttle, the bike responds very well.  As the RPM increases somewhere up above 7000, that is when the miss occurs.

- Maybe lean settings in your bike? When transplanting your main jets, did you check that all of them were completely free ob obstructions? I've seen on a lot of years parked bikes that the jet inner passages are even blocked simply by its own rust, and no cleaning method is capable of unblocked the thing

I did go through the carbs and jets very thoroughly.  It took me two tries to get the pilot jets clear.  Initially I had bad low speed operation and used an IR thermometer to see that two of the cylinders were not firing at idle and low speed.  I have cleaned a few carbs before, so I have some experience.  Typically I hold the jets up towards a light and verify that I can see through all the passages.  And, the bike runs great, except when that miss happens.

[Alf]

- Poor spark. If everything is right, have you measured the coils voltage?. For experience I can tell that usually is around 9v when it must be 12v. Do the problem appear when the bike is hot?. Usually simply a bad connection wire/spark plug. I understand that not in your case, because on the dyno your bike works

So my bet with all your info is here. Additionally, cut 1 cm from your wires where those connect with the spark plug caps.

Or the kill switch, check it too. I think simply disassembly an a good clean with wd40 is enough

Let me this afternoon to go to my garage and I take pics from the OE Yamaha FJ workshop manual how to measure the coils. It is very informative & easy to perform

Sorry not to have understand your post in first time about the dyno, English is not my first language

[Old Rider]

I would have checked that fuel level is not set to low with a clear plastic tube.I know you did a good job setting the float level after reading last post on page 8 here: http://www.fjowners.com/index.php?topic=19343.105  but you mention that you think it was odd you had to adjust that much. mayby something has happened when replacing the bowls or something.

[Waiex191]

I would have checked that fuel level is not set to low with a clear plastic tube.

Thank you, that is also a good idea.  I used a clear plastic tube on my GN400, and rode it around like that for a couple of weeks.

[Waiex191]

Sorry not to have understand your post in first time about the dyno, English is not my first language

¡de nada!  Your English is much better than my Spanish.

[Alf]

Here it is!
The additional page is where your 3CV coil specs are. The procedure values are for 1100s

[Waiex191]

Some follow up - I had the bike out yesterday and it would not miss at all.  Ran great!  I like self healing problems.

So here is a dumb question.  I am nowhere near the rider I used to be, especially after a 16 year break from riding.  Is there a rev limiter to hit?  Is it possible that due to a lost feel of the bike I was on it?