Hand-turnable idle mixture screws/rear brake light switch

[Schming]

Jat

This discussion is all about air /fuel mixture, but even if those are right, have You checked and adjusted the valve shims?

Trying to breathe with a stuffed nose sucks...well... not

[mr_misfit138]

This discussion is all about air /fuel mixture, but even if those are right, have You checked and adjusted the valve shims?

Trying to breathe with a stuffed nose sucks...well... not

I've got that planned. As soon as I dig into to the engine I'm not coming out until everything's done. I'm replacing piston rings, cylinder, head, and cover gaskets, cam chain tensioner gaskets, oil line copper gaskets, exhaust gaskets, checking valve conditions and clearances, main bearing play, and I might even have a buddy of mine take it in to his machine shop and resurface the head and pull a port and polish job. The engine's 33 years old, and I want spruce it up so it hopefully lasts another 33.

[tarzan]

Is it possible that the butterflies are actually off idle just a hair. That would make the idle screws not work. Did you bench sync the carbs and then sync when on the bike?

[bikerphil]

At first I thought it was just that the Colortune was defective, because I tried it on mine and my brother's bike first, with the same results, but when I tuned up my dad's bike, it worked perfectly, and the blues and oranges were clear as day.

I've had the same issue with my colortune, works fine on one bike and like crap on another. This has to do with the strength of the ignition coils. Weak factory coils with 30 yr old wires (especially the 1.5 ohm ones on 78-80's) can give you crap readings while aftermarket coils which throw a hotter spark will fire the colortune plug much better. My suggestion is to start with the mix screws 2 1/4 turns out from lightly seated and ride it for a bit and check your plug color and adjust from there or drop a c-note and get some dynatek 3 ohm aftermarket coils. JAT, JMHO

[Rasputin]

I have to ask if you have checked the color at other than idle. If you rev the bike up while using a colortune it will change color. Under a no load condition it usually turns orange then when it hits the differing carb circuits it changes again.
I usually try to darken my garage by turning off the lights and have even gone so far as draping a sheet or blanket over the work area so I can see the color better. I am a bit color blind so I need every advantage I can get.
If you can not achieve the yellow to the bunsen blue (or almost white flame) then the jets are wrong.
I do agree with Bikerphil that if your spark is not strong enough the colortune will not work as well as it should. If you want a truly good running bike then there are no shortcuts. You may as well do some fiddling around with changing jetting etc and doing the plug checks.
One last thing I will mention here is that the three tiny holes above the butterflies are not necessarily clean just because air goes through them. Many have made the mistake of seeing carb cleaner come through that point and did not check to see that all three were flowing. I have had to take a dental pick to them while spraying carb cleaner in to get them cleared out.
Just some of the things that are simple that come to mind.

[mr_misfit138]

Is it possible that the butterflies are actually off idle just a hair. That would make the idle screws not work. Did you bench sync the carbs and then sync when on the bike?

Yeah, I bench synced with a twist tie, put the carbs back in, warmed her up, then adjusted the idle down to about 1000-1100 RPM, then synced with the vacuum gauges, then tried the Colortune, but still no good.

I've had the same issue with my colortune, works fine on one bike and like crap on another. This has to do with the strength of the ignition coils. Weak factory coils with 30 yr old wires (especially the 1.5 ohm ones on 78-80's) can give you crap readings while aftermarket coils which throw a hotter spark will fire the colortune plug much better.

Is this the case, even if they're still in good shape, or only if they're worn out? A couple years back, I lost all spark, and I suspected that the ignition coils were to blame, so I checked them according to the manual. The issue ended up being due to worn through wires to the pick up coil, but the ignition coils read 1.5 ohms on the primary, and 15k ohms on the secondary. I was planning on rechecking them when I pulled everything off, but I didn't want to replace them if they're still in tolerance of where they should be.

I have to ask if you have checked the color at other than idle. If you rev the bike up while using a colortune it will change color.

I usually try to darken my garage by turning off the lights and have even gone so far as draping a sheet or blanket over the work area so I can see the color better. I am a bit color blind so I need every advantage I can get.
If you can not achieve the yellow to the bunsen blue (or almost white flame) then the jets are wrong.

One last thing I will mention here is that the three tiny holes above the butterflies are not necessarily clean just because air goes through them. Many have made the mistake of seeing carb cleaner come through that point and did not check to see that all three were flowing.

The Colortune does go orange if I rev the engine up, but at idle, I can't even describe it as a color. It's bits of blue and orange at the same time, which almost sounds like it would be close to the perfect setting, except I've seen the "Bunsen blue" before, and this is way different. The colors are super faint and there's a lot of whitishness happening. And I even checked at night with all the lights off just to confirm I was seeing it right.

All the jets should be right, I believe. At one time I was trying to dial her in with pod filters on, and was having the same issue, and when nothing worked, I decided to slap the airbox back on and get her back to stock before I mess around with pods. I've got 110 mains in #1 and #4, 120 mains in #2 and #3, 42.5 pilot jets, and I do not have the rubber plugs in mine, which I believe is correct for '80 and '81's.

It's very possible that I overlooked those 3 small holes, because I definitely didn't dental pick them. I'm going to add that to my list of things to check. This list is getting pretty huge! Haha! I can't wait, though. I'm out of the country until Thanksgiving, but then I've got 4 weeks of vacation time that I need to burn off, and my girlfriend's gotta work, so I'm gonna be spending that whole time in my garage getting my other girlfriend going.

Thanks for all of the good suggestions everybody. If you've got any more, I'm all ears.

[natemoen]

The only way to tell if you need the rubber plug is to look and see if there is a passage between the main jet tower and the pilot jet tower. Passage = plug, no passage = no plug.

[bikerphil]

Just one other thing to mention, have you replaced your pilot jets at some point with different ones? The reason I am asking is that there are 3 different types and although they look pretty much identical, they have different spray patterns designed for different types of Mikuni carbs. Many vendors don't know the difference between the different types and will send the wrong ones causing many owners problems. The correct ones should have 6 holes in the sides, JAT.

[CaptonZap]

It's very possible that I overlooked those 3 small holes, because I definitely didn't dental pick them. I'm going to add that to my list of things to check.

A suggestion if I may.
Anything harder than aluminum should not be used to poke around in the carb bodies. Most picks are tapered, and the holes in question should have straight bores and sharp shoulders, to achieve the correct fuel spray. A pick, carelessly applied, can deform the hole.
A better method, in my opinion, is to take a piece of stranded copper wire, strip off an inch of insulation, cut an inch of wire off, and use one of the strands, gripped with a pair of needle nose pliers, to insert the wire into the hole. The copper is softer than aluminum,, and will not deform the hole. You might have to find the right gauge wire to get the proper size strand, but a trip to Home Despot should get you a sample of each gauge wire to "take to my brothr in law to see if it is the right stuff", with no cost.
Yes, someone with the skills of a dentist can use a pick, so it's your call.
And on my carbs, there are three holes, right next to each other.
Good luck CZ

[crazy steve]

A couple years back, I lost all spark, and I suspected that the ignition coils were to blame, so I checked them according to the manual. The issue ended up being due to worn through wires to the pick up coil, but the ignition coils read 1.5 ohms on the primary, and 15k ohms on the secondary. I was planning on rechecking them when I pulled everything off, but I didn't want to replace them if they're still in tolerance of where they should be..

The factory coils leave a bit to be desired... Remember, this was the dawn of the age when electronic ignitions were coming in and the designers hadn't 'unlearned' everything they knew about point-type ignitions yet. If the coils check within spec and the bike runs good, don't worry about it. But seeing a 'weak' spark with a colortune can be due to stock coils; installing aftermarket coils will help with that (and the bike will run better) but isn't 'required'...

Personally, I'm not convinced that a colortune is that useful a tool. I think you can get the same results with a good vacuum gauge set-up by doing your initial sync to get all the carbs equal, then adjust the idle mixture at each carb by looking for the highest vacuum reading at that carb. You might have to repeat this a couple of times, but it's less work than moving the colortune from cylinder to cylinder.

I know, some love 'em and whatever works for you... Just my .02...