Running out of ideas!

[geobiker]

I have owned a 1979 F model for a little over two years. When I bought it it ran poorly. The bike is in very nice shape and only had 19,000 miles on it when purchased. The bike is stock except that I have done the fuse box mod, it has Mac 4-2 exhaust system, and a K&N air filter in a stock air box.

I took it to a local mechanic and he was upfront and honest when he commented "I typically don't like to work on bikes older than me" He cleaned the carbs and adjusted the valve timing and got it to run better, but again admitted that he did not think he could do any better . . . at least he was honest with me. I have worked off and on with it for two years and am running out of ideas,

I have done a lot of research on this forum and have tried to pin down the problem.

The bike consistently runs rich on cylinders 2 and 3. The plugs on 1 and 4 look just about perfect - a light tan). It does not matter the rpm setting at which I run the bike. Yesterday I ran it about 6 miles at between 6,000 and 7,000 rpms (in second gear so I did not kill myself), and hit the kill switch and coasted to a stop. The plugs are still heavily carboned on 2 and 3.

I'd like to think that I could rule out the carburators. The mechanic cleaned them once. I pulled all the jets and ultrasonically cleaned them all back this spring and rebuilt them with a George Fix kit (all new jets). I cleaned them again yesterday with a can of carb cleaner and compressed air, paying special attention to the pilot circuit and the enricher (choke) circuit. I have replaced the floats and set them accurately. Too make sure that the fuel is at the same level in the bowls, I drilled-out some 8 mm Zerk fittings and put them in the bottom of the float bowls. I ran some vinyl tubing and leveled the bike. I ran the bike a few minutes and the levels in all four bowls were identical . . . 1-2 mm below the gasket surface.

Now from an electrical stand-point:

I have replaced the ignition coils with NOS ignition coils.

New NGK spark plug caps.

The generator/voltage regulator is charging the battery within spec according to the Yamaha Service Manual

A previous owner did the pick-up coil fix. I tugged on the wire while checking the resistance and it did not vary and was within spec.

The vacuum advance is rotating to 36 degrees when a vacuum of 150 mm is applied.

Tip-over switch resistances are within spec.

Ballast resistor resistance is within spec.

Checked, cleaned, and coated all electrical connections with dielectric grease.

About the only thing left, that I can think of is the TCI box. I am thinking of replacing that, but before I spend the money, I would like to know of any other possible issues that I may not have addressed.

Also I checked the Snorkel . . . it is clear. I also replaced all the vacuum hose on the bike just to be sure that I did not have a vacuum leak somewhere.

I am sorry for this being so long, but I wanted to cover everything that I have done on the bike, so maybe someone could give me afresh perspective!

[petejw]

hi geobiker,
other than the plugs looking rich how does
the bike perform?

the only thing i noted was that you stated the fuel
level was 1-2mm under the gasket surface,
the float levels all have to be exact, if the bikes
acceleration is flat, then the floats are to lean, if the bike
bogs down under acceleration its to rich.


regarding the tci, if you have spark on all 4 cylinders,
then your tci is fine.

[Incubus]

When you cleaned the carbs did you pull out the emulsion tubes (that's the thing the main jet screws into) and make sure all the little holes along the side were clear? Plugged emulsion tube holes can negatively impact the fuel mixture - make it run too rich. If the plugs are black then they are firing. I would rule out spark. I really suspect your problem is in the carbs.

Patrick

[cywelchjr]

I'd have to ask what size are your jets? Are they the same all the way across? I would agree that it's unlikely that there is a TCI problem if all 4 are getting spark. For a test, you could switch the coils so that they are running the opposite set of cylinders, just remember to also switch the primary leads at the connectors as well. If it IS ignition, that should move it to the other set, which I think unlikely, but that would rule that out at least. The other possibility as I understand it, is that the emulsion tubes are different on the center two carbs, maybe they got swapped, or maybe they are wrong?

[Incubus]

The emulsion tubes are different for 2 and 3 than for 1 and 4, but I couldn't remember which had more holes.

[WMarshy]

cywelchjr, you probably know better than but I have to ask, for the 78-79 carbs are you sure the #2 and #3 emulsion tubes are different than #1 and #4? That sounds accurate to me but I was under the impression (from top of my head) that it was for the 80 and 81 carbs that had two different emulsion tubes...

geobiker, like cywelchjr and petejw asked already, what size jets are you running and how is the performance? From the mods you listed you should have 137.5 mains and 43.5 pilot jets (stock!). What setting is your needles on? All four should be on the middle setting, with your setup no reason to have them at any other place.

[geobiker]

Guys, thanks for the replies.

The only thing that made me think that it is an ignition based problem is that 2 and 3 fire from the same ignition coil, and both plugs look identically black. 1 and 4 are clean. (It really is a night and day difference). With the TCI is it all or nothing? The owners manual says that sooty plugs can result from poor ignition.

Pilot and main jets are the stock sizes that came in the rebuild kit and match those specified for that model year.

I neglected in my last post to mention how the bike runs. It idles pretty smoothly. I have synced the carbs numerous times. I have the pilot screws out 1.25 turns. The bike has the notorious 2,500 to 3000 rpm stumble that many other have mentioned on this site. Above the 3,200 rpm the bike runs like crazy. It was slow in accelerating above 6500 rpm and that is the range of the needle height so I actually did raise the needle one clip position. Now if I hit WOT at 2000 rpm the bike hesitates a little through that 2500 -3000 rpm range and then takes off like a shot, right up to 7500 rpms (I did not want to red-line a 30 year old bike, but the way it was pulling, I think I would have got there) . So in my opinion, raising the needles one clip position improved the performance, in that range. The plugs had about the same amount of carbon on them with the needles in the lower position.

When I cleaned the carbs in April, I did them one at a time so as not to mix parts. As a result, the emulsion tubes went back into the same carbs that I pulled them from. Other them pulling them, I did not look at them too closely. If in fact the inner and outer cylinders have different numbers of holes in the emulsion tubes, maybe it is possible that a previous owner or mechanic swapped them incorrectly. If in fact they have different numbers of holes, would I be correct to assume that you would want the ones with the fewer holes in the interior cylinders?

I know that I can switch the secondary leads on the coils and switch the plug leads. Would this help eliminate the igntion system as a potential source of problems? Are there any dangers in damaging the electrical components by doing this.

We all know that you need a proper mixture of air and fuel as well as a properly timed spark to make an engine run. I think that I can rule out air as a problem (Good filter and clean snorkel). If I can definitely rule out the ignition as an issue then all that is left is the carbs . . . sooner or later it has to work out!!

Thanks again for the ideas. The bike is an impressive machine running at about 90%, I can't wait to get it perfect!

Patrick . . . how did the oil spill clean-up in the garage?!

[dbeardslee]

The emulsion tubes are different for 2 and 3 than for 1 and 4, but I couldn't remember which had more holes.

On a '79F the emulsion tubes are all the same. The SF has different tubes on the outside than on the inside. Just looking at the pairing of 2 and 3, I'd take a look at the secondary resistance readings on the ignition coil. Poor spark can get your plugs sooty too, and all too often thirty year old ignition wires are the culpret. JAT

[79XS11F]

Switch your coils and see if the issue follows the coil. If it does, NOS or not, that coil is likely delivering a weak spark. Just switch the power supply at the front of them and the plug leads so the effect is the same as physically moving the coils.
Rob

[Incubus]

"Patrick . . . how did the oil spill clean-up in the garage?!"

It rained. The indoor wall has a permanent tattoo.

Patrick

[Larrym]

Cyberspace help VS Garage Space....

geobiker,

Carbs or electrical??? Which One is giving you grief??? That's the problem. Finding out which one. Me? I'd say to rule out your carbs as the culprit (or NOT!!) one technique is to swap out the whole bank with a known good set. Just for troubleshooting/isolation purposes. If the known good performers don't solve the problem then look elsewhere: ignition or mechanical. It really is that simple.

Other owners in your immediate area?? They May/may not have a set of known good carbs sitting on the shelf. Take a look here:

http://www.xs11.com/forum/showthread...t=Pennsylvania

Send some PM's out and/or offer an XS/XJ owner a place to go and a reason to go there.

It's all 'bout what's best for the bike. NETWORK in the REAL world...

Just sayin'.......

[geobiker]

Let me synthesize what has been said and feel free to add any other comments.

As I understand it, to test the coils, all I have to do is swap the secondary leads on the coils (orange from the coil to gray on the harness; and gray on the coil to orange on the harness). Then swap the primary wires. If 1 & 4 become sooty and 2 & 3 become clean, then I know it is a problem is with the coil. If, however, 2 & 3 remain sooty after the coil swap, then carburation is the likely problem and I should look at the emulsion tubes for starters.

Patrick . . . I hope you took your wife out to dinner to make-up!

[geobiker]

Larrym thanks for the link . . . I may go that route before long!

[natemoen]

Sometimes troubleshooting is more about figuring out what is not wrong than figuring out what is wrong. Rule out the electrical first, its an easy wire swap.

[dbeardslee]

As I understand it, to test the coils, all I have to do is swap the secondary leads on the coils (orange from the coil to gray on the harness; and gray on the coil to orange on the harness). Then swap the primary wires. If 1 & 4 become sooty and 2 & 3 become clean, then I know it is a problem is with the coil. If, however, 2 & 3 remain sooty after the coil swap, then carburation is the likely problem and I should look at the emulsion tubes for starters.

Orange and grey are the primary wires, and the high tension wires are the secondary - as far as testing is concerned. I find it easiest to check them with a digital multimeter. Take the plug caps off, and stick one probe in each high tension wire for a given coil. Set the dmm to the 20k ohm range and take a reading. Spec is 15k ohms, plus or minus 10%. You should probably check the plug caps too - if they're stock they should be 5k ohms, plus or minus 10%. You might also check the primary resistance at the TCI by pulling the big connector and testing the orange with the red/wht, and the grey with the red/wht. Should get a reading of 3.3 ohms, or thereabouts.