Low RPM Troubles

[danteinien]

Hello, I have a 1980 XS1100, turned Cafe', I Have Indy Filters and Stright through exhaust, 4 into 2, 2", running just past where the rear Foot Pegs were.
The carbs had 110 Mains across the board when I got the bike, and considering the Indy filters and Straight pipes, I went to 120 across the board. Now, after about 3500-4000 rpm, it runs like a bat out of hell, but off of Idle, if you give it full throttle, it pops and stumbles, like its getting too much fuel.
I thought that might be the case so I had some 115 Mains laying around so I put them in, It seems to still do it, just not as bad. So
I'm assuming that its running rich, but why only in the Low rpm's?

I know I need to read the plugs, but Im just lookin for some quick ideas as Im just sittin at work

[jwoell]

Two things to consider...is your exhaust truely straight through with no baffles or anything? With no back pressure it's going to be very difficult to get your bike to run right at low RPMs.

Also, you've been changing the main jets to fix a low RPM problem. The main jets on these motorcycles don't have a whole lot of effect until you get to higher RPMs. The pilot jets are the ones that would have the biggest effect at the engine speeds you mentioned, although at 4000 RPM the mains definately have some effect.

[danteinien]

Yes, they are truly straight pipes, I have been considering the Washer method, but I wasn't sure if it would make a difference.

The Pilot jets I haven't touched, and It ran fine before it was straight piped...
So it appears that is most likely the issue then? No backpressure?

Thanks a bunch

[TopCatGr58]

Hey Dan,

Your setup does call for MORE fuel due to the increased air flow. I remember reading some tips from PROM IIRC, about when it's too lean and you crack the throttle wide open, it's getting way too much air, the vacuum level drops and it's not able to draw enough fuel thru the pilot circuit to feed it properly.

Have you removed the brass caps over the pilot screws on the top of the carbs next to the engine? IF not, then before you go with trying more JETS, try adjusting the pilot screws OUT a 1/2 turn or so each and retest it's response.

Once you get to 3500+ you are getting mostly into the mains by then, and the 120's you had sounded right, especially if it could run to redline in most gears without feeling like it's falling on it's face!
T.C.

[danteinien]

Ok, that makes sense. I'll go and adjust the Pilot screws, although there aren't any brass caps on top of them. I'll try that and try that with the 120's and see what happens, Thanks man

Any ideas on the Exhaust affecting it also?

[petejw]

u could also try raising the needle by
a notch, this could also help,
115 mains should be ok,
and as TC said adjust the pilots,
its usually caused by the effect of the carbies leaning out
between off idle and quarter throttle.
good luck with it.

[danteinien]

Ok, I adjusted the Pilots screws out about 1/2 and then 3/4 out from the suggested 1 1/4. It didn't seem to make any difference in the problem I'm having, Although, it does seem to idle a little better now..

Should I turn them out even more and try it?
Maybe larger pilot jets?

And I haven't adjusted the needles yet, going to that today

Thanks a ton guys

Oh, and I'm not getting very good mileage either, I haven't figured it out yet, but, it's not very good

[TopCatGr58]

Hey Dan,

It's recommended to try 1 adjustment at a time! "They" say that if you have to go over 3 turns out, then you probably need to go up 1 size in the pilot jets. However, you can also slightly richen things up overall by raising the float level 1 mm(right side up), or lower it(upside down).

The poor mileage could be due to having to run it in the upper rpm range getting into the mains too much, vs. being able to give it smaller amounts of throttle input with good working pilots!?!?
T.C.

[danteinien]

Perhaps I need to do this?

Clicky

[Axel]

Colortune

I have 2 full turns that I playwith to tune so they are more than 2 turns out ,maybe 3 + . I use a colortune cuz I can get my head around that. See this post i just wrote :

http://www.xs11.com/forum/showthread...&threadid=1756

[danteinien]

Update:

Okay, so I took off the carbs, did the bread tie sync and added some 45 pilots, so now I'm at 45's and 115's. The stumble got a little better, but did not go away.

I added a 3/4 in washer with a 5/8 hole to my 2" straight pipes, that seemed the corrcet the problem, never would have thought it, but she is running like a champ now!!

I'm no engineer,and it 'baffles' me that there needs to be 'backpressure' or, a better word, scavenging effect for this motor to run correctly, time to go to wyotech I guess.

[petejw]

great 2 hear u found a solution to ur problem. :-)

[danteinien]

Update on this one...

I redid my exhaust into a 4-1, no baffles. Runs even better now.

Pods, Velocity stacks, 4-1 straight piped and 45 pilots and 115 mains, runs like new! No stumbling or hesitation anymore.

I also added MikesXS coils and new plugs/8mm wires.