Running too lean?

[Cubby's XS1100]

I just replaced a motor in a 78 XS1100 from what I think was a 79. It had a teardrop tank and it had black painted cylinders. The ignition did not have slots in it for adjustment like the 78 did either. It has compression and spark. The carbs are from the 78 and it will start but will not rev higher than 6 grand and will not idle. It is running extremely hot on the outside cylinders. It seems to me it is running real lean and all the plugs are pretty white. Is there a difference between carbs or jets between years of this bike???............Cubby

[DGXSER]

Hey Cubby. IT sounds like perhaps you got a 81 engine. From the factory, they were the only year to get the valve cover and the cylinders painted (Other than the MNS of course). That year also eliminated the mechanical advance from the timing system and built it into the TCI. If yours is lacking the mechanical advance that may have some effect.

As for the carbs, jetting is done by the carb, not the engine or the bike. The older style of carbs which the 78 had started off in 78 with 210 pilot air jets, 45 pilot jets, and 137.5 main jets. In 79 the pilots dropped to 42.5 and the pilot air went to 185. In 80 the entire carb design changed and they dropped the mains to 110-120.

If you look down in the Tech section there is a Carb Identification guide to help you figure out which carbs are on your bike.

Are you running factory exhaust and factory aribox? If not the jetting may need to change. However, if it all ran fine before with the jetting you have and all you changed is engines, it might need some tuning of the mixture screws, and a synch. But the jetting should be fine. If it sat for very long, your carbs may need a good thorough cleaning, these have some small passages that gum up pretty quickly.

[jetmechmarty]

Someone here knows better than me, but I believe black painted jugs make it a 1981 engine. The carburetors from your '78 will work. You have tuning to do. The '81 has different valves and cams than the '78. Your carburetors should still be at least very close if they're in goo working order. It sounds like they aren't.

[Cubby's XS1100]

It does have the vacuum advance pod on the ignition. Should I maybe use the ignition from the 78 motor? I cleaned the carbs twice now and have been pretty thorough. My carbs have a slotted screw over the pilot jet that I thought was weird. It did have the black valve cover as well. From the above post it looks like my older carbs have bigger jets than the newer carbs so why is it so lean??? Oh it does have the stock exhaust and airbox....

[DGXSER]

Ok, it sounds like you have the 81 engine. If it came with the timing setup, then yes you want to swap in the 78 timing set. Both have the Vacuum advance, but the 81 does not have the mechanical advance that lives behind the timing plate on your 78 ignition system.

Did you use the same carbs from your 78 engine, or did you get carbs with the 81 engine? Your 78 carbs should plug right into that engine and run it just fine, minor tuning only. The 78 carbs do have a screw over the pilot jet as they feed the pilot from the main jet, there is a crossover under the main jet in the emulsion tube section.

The newer style carbs do use a leaner main jet 110-120.

[Cubby's XS1100]

Yep, I am running the older 78 carbs, I will swap the ignitions tonight and keep you posted, thanks so much for the help..........Cubby

[DGXSER]

NP, hope the ignition helps it out. You will probably need to adjust eh mix screws and the synch as well.

[crazy steve]

Yep, too much advance. One thing not thought about is these 'electronic advance' ignitions don't really 'advance' the timing at all; what they do is retard the timing at lower speeds, reducing the retard as RPM goes up. If you left the '81 timing components on the motor, the early TCI doesn't retard any and your initial advance is too high.... which would explain the poor idle and overheating.

The other issue you'll have is the '78 advance units are too aggressive for your '80-81 cams. You really need to get a '80 mechanical advance unit and reuse the '81 vacuum can. Using the early parts with the 2H7 TCI will help, but you will still have some tuning issues. As an alternative, if the cams in the '78 motor are good, swap those into the later motor, then you'll have a 'matched set'....

[MAB]

ok all you carb guru'sI need some help.

THE GOOD NEWS IS...Ive added a Supertrap 4-1 and 4 (Mesh) indavidual air cleaners
My 80 XS 11 carbs that came with 115-120 mains And non adj. needles with unknown mismatched pilots Has a good idle now, at 1000 rpm with 47.5 pilots and the idle air screws backed out 2.5 turns

it wont run or make any power after about 1/4 throttle it also misses terrribly & pops thru the exhaust. Ive tryed 145's, 135's and right now am back to the Original 115& 120 factory install. Ive tryed enriching with the choke at speed and thier is only minamal change.

In the 80's when i had two of these both w/ similer bolt ons The choke trick would tell rite now if you needed to in crease jet size of not . Im not getting any info this time . Could it be the simple things that work with the 78-79 carbs dont work with the 80" issue.

I do have a good bright blue spark on #1 but that doesent mean the ign isent breaking down at 4000 rpm. I'm Stumped. Anybody got a direction for me to go to sort this out? God Bless. MAB. If its easier call 858-625-1182, THANKS

[DGXSER]

What do you have your floats set at? The newer carbs float height is 23mm compared to 25.7 on the older carbs. IF you set it for the old spec you will be VERY lean.

Does it start popping and missing as soon as you give it fuel? More fuel makes it even worse? I recently worked on a fellow local XSive's bike with those symptoms turned out to be coils.

[Cubby's XS1100]

Yep, too much advance. One thing not thought about is these 'electronic advance' ignitions don't really 'advance' the timing at all; what they do is retard the timing at lower speeds, reducing the retard as RPM goes up. If you left the '81 timing components on the motor, the early TCI doesn't retard any and your initial advance is too high.... which would explain the poor idle and overheating.

The other issue you'll have is the '78 advance units are too aggressive for your '80-81 cams. You really need to get a '80 mechanical advance unit and reuse the '81 vacuum can. Using the early parts with the 2H7 TCI will help, but you will still have some tuning issues. As an alternative, if the cams in the '78 motor are good, swap those into the later motor, then you'll have a 'matched set'....

Would it be easier for me to get a 1981 TCI box?

[crazy steve]

In terms of the work involved, yes. But being a one-year-only part, they're not so easy to find so you may not have a choice. They're identified by a 4R0 part number....

[Cubby's XS1100]

Well, the cams are in good shape in the 78 motor, I guess I could swap them out as well. Thanks Steve.............Cubby

[crazy steve]

You'll have to do a valve adjustment if you change cams (but haven't you been meaning to do that anyway?....)

[Cubby's XS1100]

However..... I just called the guy I got the motor from and he still has the TCI box on the bike! So now I have 2 ways out of this mess. I have heard the old 78 motors were real screamers compared to the later models, so I still might swap out the ignition and cams just to have a "better" motor. Thanks for all the Help Steve............Cubby