High RPM miss

[Johnny Boy]

Thanks Dave. I will try to feel for a week valve spring by hand with the valve covers off. I understand what you are suggesting. I'm 99% sure the ignition spark is good. New coils, new wires, resister removed from plug cap and hot w/relay to the coils. I've been in the carbs. Correct float heights, correct and clean jet sizes. New Mac exhaust.

I'll report back after I try this in a couple of days. Thanks again all for your help.

 

[Johnny Boy]

OK, popped off the valve covers. First re-checked the valve clearances, all good. I then pushed the rocker arms at all the valves. With a thick piece of hard rubber in the palm of my hand I could move them all. I couldn't tell if one was weaker than the others. They all felt the same. It did take a healthy push to move them.

I should also mention that the miss also happens when I put a heavy load on the engine. Like when I'm in a high gear at low (3K) RPM. Or climbing a steep hill before I downshift. It's not a pre-ignition pinging, it's the same as the high RPM miss.

Because the bike starts, idles and runs so well (except for the dang miss!) and the carbs don't leak I didn't do a full rebuild. I just checked the jet sizes and made sure they weren't plugged, confirmed the upper slides moved freely and checked the float height. I understand the air cut-off valves can't be reached unless the carbs are separated from the pleneum, which I didn't do.

Could that cause the high RPM/heavy load miss? Could this be a carb problem?

Sheesh....

And in the back of my mind I'm wondering if the non-stock Mac (loud) exhaust has something to do with it.

 

[dan filipi]

Have you tried fresh spark plugs?

Seems obvious I know, but I’ve chased problems similar that new plugs fixed.

 

[slabghost]

Are you running ATF or seafoam in the fuel? Are all the plugs gapped the same? Are all the resistor caps the same resistance?

 

[Johnny Boy]

I run a few ozs of ATF in every tank. I just today burned a whole tank with 5 ozs of Seafoam. I run nothing but pure gas, no ethanol. The plugs are new, just checked the gap today. I removed the resistors from the plug caps. Replaced them with a piece of solid copper wire. Same size as the resistor. The plug wires are new copper. The coils are new. Straight hot from the battery to the coils, with a relay. The battery is 6 months old.

I gotta have the best spark on Earth.

I ordered a 12mm adapter for my compression tester today. I'll check that when it comes in.

Either one of you guys or me is going to solve this mystery sooner or later. Keep the suggestions and ideas coming. I really do appreciate the help.

 

[joedrum]

Hmmmmmmm this is a rare problem ...oldwings mostly miss and fart art around at mid rpm

 

[Johnny Boy]

Hello fellas, got an update on the high speed miss.

I was thinking as a last resort I would either bring the carbs over to Pistol Pete (less than an hour drive from me) or get the Randaac (sp?) rebuild kit. That was as of summer of this year. In the mean time every tank got Seafoam or Berrymans B-12 or ATF.
i rode almost daily and put on over 3000 miles in 4 months.

In that time/miles I went through 2 cans of Seafoam and 2 cans of Berrymans. Mixed in was the ATF. EVERY fill-up got something.

The miss is gone. Problem gone.

For anyone who runs into a similar problem in the future, give the various gas treatments ample time to work.

Thanks gang for all the help and suggestions. This is a great forum.

 

[Ansimp]

Johnny Boy » Thu Dec 13, 2018 3:03 pm[/url]":15u4cnsu]
Hello fellas, got an update on the high speed miss.

I was thinking as a last resort I would either bring the carbs over to Pistol Pete (less than an hour drive from me) or get the Randaac (sp?) rebuild kit. That was as of summer of this year. In the mean time every tank got Seafoam or Berrymans B-12 or ATF.
i rode almost daily and put on over 3000 miles in 4 months.

In that time/miles I went through 2 cans of Seafoam and 2 cans of Berrymans. Mixed in was the ATF. EVERY fill-up got something.

The miss is gone. Problem gone.

For anyone who runs into a similar problem in the future, give the various gas treatments ample time to work.

Thanks gang for all the help and suggestions. This is a great forum.

:good: :salute:

 

[Johnny Boy]

The saga continues......sheesh!
The miss returned. I then put on a set of good stock exhaust. I bought the bike with a really nice looking, but way too loud, Mac exhaust. Still got a miss.

Decided to bite the bullet and took the carbs to Pistol Pete. Together we went through them, checked everything then put them on his test engine set-up. Started, idled and reved perfect. He declared them good. Took them home and put them on the bike.

Still had the miss.

Don't know why I didn't think of this before but I touched each exhaust pipe close to the head. Three of them were hot enough to burn my fingers, but #2 was just warm! So I pulled the (1 year old, eBay aftermarket) coils and ohm tested them. Both showed 2.7 ohms on the primary side and 13.5 K ohms on the other side. Those readings were taken with the coils off the bike and the plug leads removed. I think those are good numbers. If anybody knows different let me know.

But today I read on Randakks site that at least some resistance is needed. He wasn't just talking about radio noise, but just to run right. Either in the plug wires or the plug caps or the plugs. While chasing this problem over the last year I got rid of all that resistance. Stranded copper wires, non-resistance plugs and I replaced the 5K ohm resisters in the caps with a piece of thick copper wire the same size as the removed resisters.

So, back in go the resisters in the plug caps, then I'll reinstall the coils and keep my fingers crossed.

Anybody know if my coil resistance numbers (2.7 and 13.5K) are OK?
Is it common knowledge that some resistance, to run right, is needed?

 

[pidjones]

The 13.5 sounds pretty close. I get 25.4k from cap-to-cap (which includes both ~5k cap resistors). Is your timing and point gap spot-on? Condensers in good shape?

 

[Johnny Boy]

CDI ignition. No points or condenser. 1980.

 

[ekvh]

Did you look into the exhaust headers at the head. Some will develop an inward bulge between the two walls. It’s not visible from the exterior. Not sure how this would affect heat, but at some rpm it would reduce flow and create too much back pressure on one cylinder. Google it or search here, there are pics out there. I have seen one in person. You need ample light to see down in the header as it’s towards the bend where it bulges usually. Theory is a bit of moisture gets trapped between the walls and when super heated creates enough steam pressure to bulge them inwards. The 1200 headers have a relief hole drilled near the top to prevent it.

 

[Johnny Boy]

I looked over the exhaust before I installed it. It's good.

Well, just got in from the garage. Had full continuity from the wires through the caps. I replaced the cap resisters with a piece of thick copper wire and ran it with resister plugs. Still had the miss.

I then put the resisters back in the caps, put in non-resisters plugs and blasted up and down the highway. Still had the miss.
Ran it without the air filter, still had the miss. Changed the fuel filter, still had the miss.

Popped open the fuel pump. The large round rubber piece was not tore up. Pulled off the out hose, gas shooting out just fine.

Then I did a compression test.
#1 155lbs
#2 150lbs
#3 125lbs
#4 150lbs

Just checked the valve clearances a couple days ago so I know #3 isn't out. I guess what I have to do now is pull the right head and hope it's a valve and not the piston or the rings, right?

That darn miss really felt electrical. I didn't know that low compression in one cylinder could make it miss like that....assuming that's the cause. Anyway if anyone's got anything to ad I'm all ears.

 

[dan filipi]

I believe you said in an earlier post that #2 had the cooler exhaust, but now the lower compression on #3 would suggest #3 to be the problem?

How do your plugs look? Can you post a clear and well lit picture of them, lined up 1 to 4?

 

[desertrefugee]

I would not be so quick to indict low compression as a reason for a miss. If you had all four holes running with 125 psi compression, you would probably be happy as a clam albeit with somewhat reduced horsepower.

I would keep poking at it. Maybe try swapping coils for starters. I'm not sure you mentioned this, but it might not hurt to even try some new spark plugs. To me it really smacks of a flaky ignition component.

 

[Johnny Boy]

Desertrefugee, that's what it has felt like since day 1, electrical. And Dan, the cooler pipe on #2 and the low compression on #3 was unexpected. I don't think flipping the coils will do anything. I just had them out, separated and the resistance was very close on both of them. And they're less than a year old. Can a coil's primary and secondary readings look good on the bench and preform not so good on the road under load?

I have a couple sets of new plugs that I have been switching out. 1 set non-resistance and a set of resistance. They are new NGK and look good. But other than a few blasts up and down the highway to test after whatever fix I've been trying, there are no real miles on them for a good reading. It's running that bad now.

The other component in the ignition system, those 2 spark thingys that the back melts out, look good. Not leaking or melting. As I mentioned earlier I ran a hot with a relay to the coils. New coils with good ohm readings. Wires and caps reading good. Couple sets of new plugs and a good charged battery. Although everything looks good still feels electrical.

I think next I'll pull the belt covers and see if the cams are lined up right. If they are good maybe I'll try a home brew leakdown test. I think I can push air into the combustion chamber through my compression tester hose with a air compressor. Then listen for air leaking from the carbs or the pipes.

I'll try to get pics this time. Thanks all for listening and suggestions.

 

[D-50Dave]

Even though you may not think swapping the coils will do anything, if others who've been down this road before suggest it...

 

[Johnny Boy]

Understood Dave. Have a Dodge Neon coil on the way. will report back. By the way, I have a box of assorted coils, from this bike and others. Almost all of them show a primary resistance between 2.5 and 6 ohms. Yet I read that the primary resistance for our bikes should be .2 or .3 ohms. I don't have a factory manual just an old Haynes and it doesn't say. Anybody know for sure?

 

[desertrefugee]

I don’t recall the impedance specs on the GL coils, but can tell you that that’s only part of the equation. The secondary windings of the coil can behave much differently under load then during a static resistance/impedance check. The dielectric or insulation that separates the windings Is susceptible to thermal break down usually caused by bad wires or plugs. That break down or loss of insulation sometimes only shows up during operation. Your spark can jump between windings intermittently. Depending on which windings are involved, the result can be misfires or completely dropped output.

Then again it could be the flux capacitor. Just throwing out ideas.

 

[Johnny Boy]

LOL. I'll look in my box of grid squares for that flux capacitor. Anyway I got the Neon coil, just waiting on the pigtail. It'll be a couple of days. I'll post back when I got something. Again, thanks guys.