Carb Synch and Enrichener Circuit

[BA80]

Mine starts up just like Greg's does. It will cold start instantly without the choke. Mine was running extremely well with the mixture screws guesstimated and a very good bench sync. I used a Morgan Carbtune to fine tune the mixtures and sync in the idle. The bike seems to run perfectly at all throttle settings. I should add that the valves were recently adjusted and the cam chain replaced. Cold or hot weather, low or high altitude, the bike performs very well. My only gripe is that I'm looking for fuel at 80 miles. I get 25 to 30 mpg.

Honestly Ian, I have never fussed much with the earlier carbs, and the later ones do not have adjustable needles. So, no, I have not messed with the needles.

You might just be heavy handed Marty. I get 35 ish most of the time. On longer rides it goes up to about 40mpg or so.

Between 30 and 35 is what I usually get. The slower I ride the better the mileage. Got about 42 once following Bob Falter through Iowa running about 60 - 65mph, that's the best I ever got. We generally run anywhere from 70 to 90mph on the highway going somewhere. Coming back from The Lost Rally in Wisconsin last summer by myself on the SF I would catch myself up over 100 a lot. I was stopping every 80 miles for gas then.

I moved the needles up and down before just to see what difference it made and it never seemed to run right unless they were on the center slot. With this 79 engine there has always been a spot between 5 and 6 K that is a kind of transition between power bands. It seems kinda like a stumble but it isn't. My SF had the same thing so I think it has to do with the cams.

It'll take off strong and pull hard until it hits that spot and then there is that little glitch. You better be hanging on when it does that because it's like it gains 30hp right then and it will (and has) pull the grips right out of your hand. I even tried a different set of carbs and it still does the same thing.

[BA80]

Hi Schming.
Just curious how many"Redline in 5th gear" episodes you have survived ? on public roads?
Phil

I personally have never been able to redline in 5th. The engine just runs out of poop at 6.5 - 7K. Even laying on the tank with a naked bike there is too much wind resistance. The XS isn't aerodynamic at all.

125 - 130mph is about the best I've done with the right conditions.

[James England]

After extensive labor on the old beast, I finally got to the synch and did a pretty fair job of lining them up and getting a smooth idle. I find now that I often don't need the choke (enricher) to get started on warm days.

Does that mean I have it dialed in, or is it too rich to start with and constantly doing the enricher's job? My plugs look fine.

You shouldn't need the choke on warm days, IMO

[Schming]

No, it's no rumor, definitely true. However, each person comes to a point where they say their tune is "good enough". And, I can guarantee that "good enough" for some does not allow a full-on throttle from 5th gear without bogging, including my bike. It's an ideal tune that mandates that each circuit has been tuned perfectly. Main jets, pilots, float, needle clip setting, air idle, etc.

What it comes down to for me regarding tuning is cracking throttle wide open in the beginning without stumble. That, and MPG's. If you're happy with those two things, and you have no bogging near the top, you should be good to go.

Another thing I believe someone said for another way to do a plug chop when I did mine, was to ride in 5th for a few miles, going no faster than 25 mph.

You've hit the proverbial "Nail on the Head" with your second sentence, first paragraph. Most just want to get on and ride instead of wrenching.

My quandary is "Wrench or Ride or Wrench"

I love to see what performance can be squeezed out of any stock engine, bike or other.

When I rode dirt, the abrupt cracking of the throttle was my way of "testing" those engines which have a totally different rotating mass than the XS 1100, but yes another good way to "test the tune".

The XS 1100 engine and drivetrain with its "Freight Train" demeanor may be more oomph than the average rider has ever been exposed to misleading them towards the real potential of these machines, so "good enough" is good'nuf.

[jetmechmarty]

I had a mid range stumble a few months ago. The problem turned out to be with the mechanical advance. I took it all apart, cleaned it, lubed it, and reassembled it. No more stumble.

[Schming]

Hi Schming.
Just curious how many"Redline in 5th gear" episodes you have survived ? on public roads?
Phil

Never made it to redline in 5th gear. Just stated that a bike in optimum tune should be able too.

Would you agree, if you can do that, your bikes in good tune ?

[BA80]

Never made it to redline in 5th gear. Just stated that a bike in optimum tune should be able too.

Would you agree, if you can do that, your bikes in good tune ?

The engine doesn't have enough HP even if it is in tune to overcome the forces of resistance over about 115 in most cases. Even a perfectly tuned factory test 11 would only go about 125. Red line in 5th would be approximately 150 - 160. Possibly the reason for the 160MPH speedometers on the early bikes.

http://www.motorcyclespecs.co.za/model/yamaha/yamaha_xs1100%2078.htm

[MaximPhil]

Never made it to redline in 5th gear. Just stated that a bike in optimum tune should be able too.

Would you agree, if you can do that, your bikes in good tune ?

Hi Schming,
I have used this test myself in 5th from about 1500RPM the key is roll on gently not snap the throttle. It gives a good indication of " rideability" that difficult to define characteristic of a well designed and operating bike. Peak HP for mine came at 7200RPM Max torue was at an even lower number according to the Dyno print out.
Phil

[Schming]

Hi Schming,
I have used this test myself in 5th from about 1500RPM the key is roll on gently not snap the throttle. It gives a good indication of " rideability" that difficult to define characteristic of a well designed and operating bike. Peak HP for mine came at 7200RPM Max torue was at an even lower number according to the Dyno print out.
Phil

Yes...agreed...a gentle roll on of the throttle lets me know how well I wrenched, under load, and if the carbs need more tweaking.

When I do the "test" on my XJ 750 at 6500 rpm or so I'm satisfied with the results from the Carbtune and Colortune.
It'll pull past there, with the redline at 9k or so, but I'm 20 years past those days.

[Schming]

The engine doesn't have enough HP even if it is in tune to overcome the forces of resistance over about 115 in most cases. Even a perfectly tuned factory test 11 would only go about 125. Red line in 5th would be approximately 150 - 160. Possibly the reason for the 160MPH speedometers on the early bikes.

http://www.motorcyclespecs.co.za/mod...s1100%2078.htm

Huh. . .physics. . .what are ya gonna do ?

Greg, you spoke of the "glitch" in your other post and I have experienced this also, not sure at what rpm, but would it be the TCI adjusting the timing curve maybe ?

Oh yah, sorry LoHo for getting so far off track, but the climate your in locale probably doesn't warrant much enriching so sounds like your bike pretty is close to where you want it.

Here in Western PA, in the middle of Summer, I have to use the "choke" on cold start ups for just a minute or so then not necessary for the rest of that day.

[MPittma100]

Enricher

I have an 80G that is somewhat cold natured. I start it on full enricher, then first stage enricher, then enricher off. It will idle fine then. But, until she warms up completely, there will be a stumble (without enricher) off idle into about 2500 RPM. Let it warm up all the way and there is no stumble.

None of the others that I have are "cold natured" like this one. Have not tried any adjustments. The carbs have been off and cleaned and they all synced in with the carbtune.

Mike

[BA80]

Greg, you spoke of the "glitch" in your other post and I have experienced this also, not sure at what rpm, but would it be the TCI adjusting the timing curve maybe ?

78 - 80 all the timing was done mechanically or with vacuum. It wasn't until 81 that the TCI had anything to do with it. My SG has a 79 engine and my 79 SF, they both do it. When I had the 80 engine in the SG it never did it even though I was running these 79 carbs on it then too. I think it's something characteristic of the 78 - 79 engine. Either in the cam grind or the centrifugal advance curve, or a combination of both.

Personally I think it's cool

[BA80]

I have an 80G that is somewhat cold natured. I start it on full enricher, then first stage enricher, then enricher off. It will idle fine then. But, until she warms up completely, there will be a stumble (without enricher) off idle into about 2500 RPM. Let it warm up all the way and there is no stumble.

None of the others that I have are "cold natured" like this one. Have not tried any adjustments. The carbs have been off and cleaned and they all synced in with the carbtune.

Mike

RockinD's SG is like that too. It's really cold blooded. Not sure why, I've had those carbs apart several times. It warms up quickly and runs great.

He get's HORRABLE mileage though.

[Schming]

78 - 80 all the timing was done mechanically or with vacuum. It wasn't until 81 that the TCI had anything to do with it. My SG has a 79 engine and my 79 SF, they both do it. When I had the 80 engine in the SG it never did it even though I was running these 79 carbs on it then too. I think it's something characteristic of the 78 - 79 engine. Either in the cam grind or the centrifugal advance curve, or a combination of both.

Personally I think it's cool

Almost feels like the powerband on a dirt bike when it kicks in.
Suprised the S#!t out of me when I first got my '80G, with the flatter stock seat I found myself sliding to the rear, once recomposed the grin is priceless.

[jetmechmarty]

I had mine turning 8000 in forth gear while climbing Pine Mountain. I rolled off the throttle and crested the hill at less than 60 mph. A state trooper was waiting at the top. Lucky day.