Slight skip at 3k rpm

[NEDan]

Can't seem to figure this one out.
I have a totally stock 1980 with 37k that has a slight spiff that happens religiously between 3k & 3200 rpm.
It's not constant but close to it.
A bit Less when warmed up.
It does not matter what speed or gear I'm in.
If I play with the throttle between say 2900 and 3400 rpms I can make it occur.
Seems to be coming from the carbs.
It's not a full fledged back fire but a small annoying spiff. And it sounds just like that...Spiff!
I'm not sure if I should be looking at vacuum, spark or carburetors ?
I just started adding mmo to the gas...?
Any Ideas

 

[joedrum]

hmmmm a lot of oldwings do this its useally a spark and carb combo that gives this id work on getting spark plug wires and ends up to par first ...maybe the resisitors are corroded in the ends ...just start going through stuff

 

[dan filipi]

Very common for the 1100 to do this.

We're thinking it has something to do with the wasted spark system and valve overlap.
Running it won't hurt anything and like Joe say's, go thru the connections and plug ends.
A valve adjustment would be a good idea also.

 

[zman]

That`s a pretty good description..I was thinking about that too but mine only does it when sitting at lights then accelerating away but even then only a few times at maybe 20 stops. It never does it consistently at a cruising speed.

 

[dan filipi]

Oh and be careful with the fuel additives.
Many will turn the carb rubbers to mush. I found out the hard way.
Your safer to run ATF as a cleaner.

 

[NEDan]

ATF it is.
I cleaned the plugs they were all set at .020 I opened them to .030. 3 were nice and brown the right front was a tad bit oily.
No spiff all day today !

 

[NEDan]

Thanks guys for all for the suggestions.
Last night It was back,
but not as bad so I'm pulling the resistors out of the spark plug ends today to check for corrosion and clean. I did notice 3 plug wires went on with good audible clicks and the 4th not so much. I'll look into that too.

 

[1burthabutt]

Freebird told me the other day on our ride that he has been putting in higher octane gas. He said it runs a little smoother. I did notice it did hum a lot better. He has been putting in ATF after I said something too. It has all seemed to help. btw I LOVE THIS BIKE! She sure is a sweet ride. :yes: :yahoo:

 

[C5Performance]

1burthabutt » Mon Jul 29, 2013 9:47 am[/url]":2sqip49h]
Freebird told me the other day on our ride that he has been putting in higher octane gas. He said it runs a little smoother. I did notice it did hum a lot better. He has been putting in ATF after I said something too. It has all seemed to help. btw I LOVE THIS BIKE! She sure is a sweet ride. :yes: :yahoo:

I have a thought/question on this. Higher octane is used to slow the fuel burn which lessens the chance of detonation under load. So unless your motorcycle is "advancing too quickly" i don't see why that would help a bike run better. On a motorcycle with points, the advancer springs can wear out and allow an engine to advance too fast, but the 1100 has a vacuum advance. Anyone care to toss out a few reasons why more octane might help?

*side note...i do know that really cheap low octane fuel has irregular flame fronts compared to higher quality but this depends on how it gets blended and we have no data to show which company has the upper edge. Where are the smart fuel reps to help us out with this one?

:laptop:

 

[slabghost]

Low octane fuel runs better but at most stations the higher grade fuels contain cleaning additives too.

 

[backlander]

I'm not a rep but the octane rating required for your vehicle is determined by the compression ration of your engine. The higher the compression, the higher rating the octane has to be. Gasoline, like diesel fuel, will detonate simply by compression, which causes the knocking sound made by the engine when the wrong rating is used and the fuel ignites before the spark plug fires. This will cause serious damage to the engine. The higher the octane rating, the higher compression ratio it will tolerate before it will detonate by compression.

 

[C5Performance]

backlander » Mon Jul 29, 2013 9:11 pm[/url]":1d4iymcy]
I'm not a rep but the octane rating required for your vehicle is determined by the compression ration of your engine. The higher the compression, the higher rating the octane has to be. Gasoline, like diesel fuel, will detonate simply by compression, which causes the knocking sound made by the engine when the wrong rating is used and the fuel ignites before the spark plug fires. This will cause serious damage to the engine. The higher the octane rating, the higher compression ratio it will tolerate before it will detonate by compression.

I agree to a point, but all the means is your timing isnt set correctly for the octane fuel you use. Higher compression does not mean you have to run higher octane fuel. What it means is you've changed the compression from stock, and now your timing requirements have changed.

Higher compression increases efficiency (same as increased engine load). That's why hauling a load of firewood up a big hill makes the old Chevy knock like its coming apart. You just sped up the burn rate and now your ignition is firing too soon. If you retarded the curve until you got to the top of the hill your truck would no longer knock.

Wow, interesting stuff, huh? :music:

 

[backlander]

Very interesting, but maybe a new thread is in order cause I think we have wondered off this one a little and we could get our wrists whacked. :mrgreen: :smilie_happy: :smilie_happy:

 

[dan filipi]

backlander » Mon Jul 29, 2013 8:35 pm[/url]":3upu56jw]
Very interesting, but maybe a new thread is in order cause I think we have wondered off this one a little and we could get our wrists whacked. :mrgreen: :smilie_happy: :smilie_happy:

Agreed.

A new fuel octane thread would make for some good reading and conversation.

 

[C5Performance]

Well it started out ok, but then slid toward octane, and i had to open my big mouth. The original post was about a running issue and of course, fuel is part of any healthy discussion, right? Luckily we have a cool moderator to keep us on track arty:

 

[backlander]

Don't feel like the lone ranger, I'm one of the worst at getting off track.

 

[dan filipi]

Yeah I do it too. Nasty habit.

 

[NEDan]

NEDan » Sun Jul 28, 2013 5:08 am[/url]":24m5lneq]
Thanks guys for all for the suggestions.
Last night It was back,
but not as bad so I'm pulling the resistors out of the spark plug ends today to check for corrosion and clean. I did notice 3 plug wires went on with good audible clicks and the 4th not so much. I'll look into that too.

Just wanted to follow up and complete the thread.
Lots to clean when I took the plug caps apart, I fixed the loose cap by re-bending the clip wire that clamps the spark plug to the wire. I might just remove the resistors all together but for now I cleaned and dielectric greased everything.
While apart I re-epoxied the igniters I found empty of original epoxy and black goo on the frame below, covered the found coil cracks with a skimming of hi-temp silicone, although not related to the skip it was needed.
I took a 400 mile trip on her running the ATF additive and by the time I got home the skip is all but nil when cold and gone when warmed up. Not sure what exactly fixed it (fuel or electric?) but it's no longer there at least not at all annoying.
What a sweet motor!

 

[joedrum]

cool sounds like a good patch for awhile ... great job

 

[Ansimp]

It nice to know but it s even better when there s no longer an issue :good: :clapping: