Too much vacuum???/Colortune issues

[mr_misfit138]

Ok, here's my dilemma... I'm working on getting my dad's '81 SH running right after it sat forever. Last year we rebuilt the petcocks, replaced the intake boots, changed oil, and all sorts of stuff, but he ended up taking it in to a shop to have the carbs done. He spent around $700, and when he got it back it would finally run, but it wouldn't idle, and it would have to have the choke on.

Now I'm working on it, and found that the inside of the carbs were surprisingly clean, except #3 which had a gummed up main jet. I pulled everything apart and cleaned all the carbs, then put them back together and it still wouldn't idle. Then I realized that the rubber plugs over the pilot jets aren't supposed to be on there. Whoever worked on the carbs at the shop added them and killed the pilot circuit. I pulled those out and put the carbs back in, and I finally got the bike to idle... kinda. I hooked up my carb synch vacuum gages, got everything syched up, and then went on to the Colortune. This is where it got interesting.

when I pulled the plugs, they were completely black, which I assume was from running with the choke half on everytime it was ridden, but with the Colortune, the colored ring wasn't showing up through most of the pilot screw range, and when it did show up it wasn't really a definite yellow or blue. It was always kinda the same no matter what I did. I checked the tips of the pilot screws, and none of them were broken off. Everything looked really good. I kept adjusting and adjusting each carb with the Colortune, but not seeing any differences, I just went back and set all of the screws at 1 1/4 turns out. This brought the idle up from about 700-800 to the 1000 rpm range.

Then I put all new plugs in the bike, and was going to re-synch, but when I put the gages on the fluid went right up to the very top, and would have gone into the engine if I hadn't killed it first. I adjusted the calibration screws all the way out to lower the fluid level, but even then it shoot straight to the top as soon as I turned the bike back on! I even adjusted the thumb screw to close the butterflies all the way and tried again, and it was the same thing. What could have happened to up the vacuum pressure that much?

Also, what would cause the lack of the colored ring in the Colortune? I just see the spark jumping the gap most of the time, but when I rev the engine I can get the ring to show up.

Any info would be incredibly helpful.

(main jets are all 110's)
(pilot jets are all 42.5's)
(air jets are all 185's... I think. They were hard to read)

[79XS11F]

OH my god. You could have bough a new set of carbs from Yamaha for just over 800.00 They are still listed as available.
In any case I don't know what you mean by a "ring" of color in the color tune? My color tunes show full flashes of color with each combustion cycle Full yellow wit ha hint of blue. I would go through the carbs myself (yourself) and check float heights, jet sizes etc. Make sure your air box is fully clear from snorkel to carb mouths including all vent piping.
Rob

[natemoen]

If you don't see any color other than the spark then that cylinder is not firing.

[skids]

I don't know what would make the pressure so high. Maybe the throttle plates are closed nearly all the way??? Filter completely clogged?

[mr_misfit138]

If you don't see any color other than the spark then that cylinder is not firing.

That would explain the low sputtering idle. I'm gonna have to pull the carbs and clean everything again and see if there's anything in there, but now I'm guessing that it's probably the air box, as I super cleaned them before and set all of the float heights to the stock 23mm setting.

Any ideas on the sudden vacuum increase?

[skids]

Also, the mercury column will rise to the top (and into the engine) if your reservoir allows air into the column. The tubes need to have a continuous column of mercury - no air!

[CaptonZap]

Any ideas on the sudden vacuum increase?

Stuck slides? Leaking diaphrams? CZ

[XS1100 Newbie]

Also, did you bench synch the carbs?

[mr_misfit138]

I didn't bench synch the carbs, but the the gauge worked perfectly the first time, and it still works fine for synching the carbs on half choke and full choke. They read almost exactly the same all the way across. Now, I went and adjusted all the main butterfly thumbscrew so that #3 is open right at the thickness of a bread twist tie, and the rest are close, but I kept them where they were set when I synched them on the vacuum gauges. I've read that that will cause the bike to idle pretty high, which sounds way better than not at all. I also check out everything in the carbs again, and all of the floats are at the stock height of 23mm and the entire pilot circuit is spic and span. I did find that 3 and 4 did not have the small washers and O-rings on the idle mixture screws, so I replaced them with some off of a parts bike. I then set all of the idle mixture screws at 1 1/4 turns out, which I read was the stock setting. The carbs should not be the problem now, but I'm hoping I'll at least get a somewhat normal response from them when I put them back on tomorrow. I also checked the air box, and everything is stock and in good condition there, so I'm not sure what else it could be, and there were no intake leaks. If anyone has any other ideas that I should look at before I put the carbs back in let me know.

[cywelchjr]

I didn't bench synch the carbs, but the the gauge worked perfectly the first time, and it still works fine for synching the carbs on half choke and full choke. They read almost exactly the same all the way across. Now, I went and adjusted all the main butterfly thumbscrew so that #3 is open right at the thickness of a bread twist tie, and the rest are close, but I kept them where they were set when I synched them on the vacuum gauges. I've read that that will cause the bike to idle pretty high, which sounds way better than not at all. I also check out everything in the carbs again, and all of the floats are at the stock height of 23mm and the entire pilot circuit is spic and span. I did find that 3 and 4 did not have the small washers and O-rings on the idle mixture screws, so I replaced them with some off of a parts bike. I then set all of the idle mixture screws at 1 1/4 turns out, which I read was the stock setting. The carbs should not be the problem now, but I'm hoping I'll at least get a somewhat normal response from them when I put them back on tomorrow. I also checked the air box, and everything is stock and in good condition there, so I'm not sure what else it could be, and there were no intake leaks. If anyone has any other ideas that I should look at before I put the carbs back in let me know.

If you didn't have the o-rings and washers there is NO WAY you could get a good idle on them. And if you put old used o-rings in, it's also unlikely as unlike the early carbs for some reason the late carbs suck air through the idle mixture screws, making it impossible to adjust the idle mixture unless those o-rings are in almost perfect condition so they seal around the base of the screw where it screws into the carb. That could also cause your other problems as well, as having those missing (or just old and flat) is basically an intake leak.

[natemoen]

Also go back and put all the butterflies at the same spot instead of all of them closed and #3 slightly open.

[DGXSER]

First off, check the jets that are installed. For an SH, the mains should be 110s across the board, the pilot jets should be 42.5 and they need to have 6 holes in the sides of the jets. The idle air jets should be 180s I believe.

If all of those are correct, then make triple check sure your entire pilot jet circuit is very clean. Also note, that 1-1/4 turns out is not written in stone, I for one always start at 2 turns out.

As to the o-rings on the idle air (mixture) screws, you can go to Harbor Freight and for about $5 pick up a nice set of nitrile o-rings in assorted sizes. They have the right size for those mixture screws, so replace the used ones with new ones.

As for the throttle plate settings, since you changed those mix screw o-rings, the setting will almost surely change. So it will hurt nothing for you to set them all evenly across using the bread tie. Yes, use the main idle screw to set #3 with the bread tie, then change the rest using the synch screws.

[mr_misfit138]

The idle air jets should be 180s I believe.

The idle air juets are 185's. How big of a difference is this in comparison to 180's? I tried to check a few places, but I couldn't find what these were supposed to be. I'm assuming that since the entire bike is stock, and my dad's the original owner, that these would be right, but he did take it to a shop, and I'm not sure what they did, besides plug up the pilot circuit with the rubber plugs.

[DGXSER]

I was on the fence as to 180 or 185s. Been about a year or so since I rejetted 80-81s. The 185 could be correct. The pilot jets are what I would look at close for size and the number of holes. The shop might have decided to change them out for you, and put the wrong ones in. Happens more than you would like to think it would.

[ruffrider]

Floats?

Does your carbs have brass floats? If so, you might want to check them for leaks by putting them in almost boiling water and see if any bubbles come out. I had 3 bad out of four. The floats wouldn't ever shut off the gas and was always running way too rich. I replaced mine with plastic floats from MikesXS and problem solved.