Solved lack of power problem - wasn't the carbs

[gaines]

I'm having trouble accelerating above 45MPH with my 1979 XS1100 Special. It goes from a smooth purr to a chugging the more gas I give it. It seems even worse when going up hills if I don't have momentum.

The other problem I'm having is every time I break my engine stalls if I don't throttle it up. When my bike is sitting it idles just fine and I have the idle set at 12-15k rpms. I even tried bumping it up closer to around 18k rpms, but it still stalls when I come to a stop.

I just rebuilt the carbs. I checked the float levels (all at 25mm) and pre-synched the butterfly valves. After connecting the carbs I adjusted the idle to ~12k rpms. I then synchronized the carbs at 25k rpms and was able to get all four carbs to within a couple psi of each other. Everything seemed to run well while sitting on the center stand in neutral.

I'm willing to admit the possability that I did a poor job synching the carbs. I'm using a DIY manometer and have very little experience doing this, but I understand the basic principle. I started off making sure the 1 and 2 carbs were synched. They already were both at just under 30 psi at 25kr pms. I then made slight adjustments to bring the 3 and 4 carbs to the same psi, which were around 40 psi. I then adjusted the center screw to bring both sides (2 and 3) to just over 35 psi.

I should mention that before my most recent rebuild I was able to accelerate to 80mph without problems, although it did run a little rough. This definitely seems to be a problem I've caused during the past few days.

Any help would be appreciated.

- Gaines
615-414-9739

[mro]

re-synk the carbs
set idle around 1000/1100 if will run at that rpm
do 4 to 3 first
once those two are equal
then 1 & 2 to same as 3

go back and check that 4 still same as 3
then check 1 and 2 agin
try to keep idle around 1000/1100 while doing the synk
______
after synk, adjust pilot screws
______
check synk agin
______

I use a single vac gauge and have had good results even tho this is not exactly how some others are doing it.

Multi-gauge or mercury tool are very cool but can achive same result with a single gauge, just takes a little longer.


mro
would also check fuel hose routing for kinks.

[gaines]

Thanks for the reply. I guess I just need to keep at it.

What do you mean by "adjust pilot screws"?

[underdog57]

Idle mixture screws .......

Bob

[gaines]

Originally posted by underdog57
Idle mixture screws .......

Bob

I mean, what does that involve? I read a post on the forum that talked about setting them at 1 1/2 turns out, but nothing other than that.

[underdog57]

You sync , then set your idle around 900 rpm .

turn in the idle mix screw till the engine slows , turn out the screw (richen) till the rpm goes up . you want it on the lean side of when the rpm's pick up ...
when you get too rich it slows the engine too ...

thats the gen idea , someone might have a hint also .
do each carb seperatly ....

Bob

[gaines]

Solved lack of power problem - wasn't the carbs

Back in this now merged thread I talked about how I was experiencing inability to idle and a severe lack of power (primarily in the top end).

The first thing we found wrong was that my coil wasn't providing enough juice at low RPMs to fire all cylinders. This was causing the engine to die when trying to idle. I ordered a new one from MikesXS and it did the job.

We had all the cylinders firing, but it still wasn't running well. I have a small hole in my exhaust and the carb boots are starting to crack so we were thinking maybe there was a lack of back pressure and/or vacuum causing the problem. The plan was to try to seal the carb boots and get a small patch welded over the hole in the exhaust, but I wouldn't be able to get to it until the weekend.

So yesterday my friend and I were leaving my house and I gunned it coming out of my driveway. To my surprise, after a hiccup or two it started driving well. I later found out from my friend that a cloud of black smoke had come out of my pipe. It turned out that I had a clogged baffle and the blockage had worked it's way out. Now it's running great!

My only complaint at this point is that it dies if I pull in the clutch and make a sudden stop. It idles well sitting still so it's odd that slowing down (with the cluch disengaged) would cause problems. Any ideas?

[TopCatGr58]

Hey Gaines,

Merged your threads! Now that you've gotten rid of your exhaust restriction, you'll need to go back and redo your synch and pilot jet settings. You're probably a bit too lean now, and slightly richening it up, along with a slight tweek/increase in the main idle screw, it should then behave and not die on decel when closing the throttle plates and clutch in!?
T.C.

[gaines]

Originally posted by TopCatGr58
Now that you've gotten rid of your exhaust restriction, you'll need to go back and redo your synch and pilot jet settings. You're probably a bit too lean now, and slightly richening it up, along with a slight tweek/increase in the main idle screw, it should then behave and not die on decel when closing the throttle plates and clutch in!?
T.C.

Right now it's idling at around 10-12k while sitting still. I thought that was the ideal idle range. What should I turn it up to?

I did go ahead and purchase some larger pilot jets when I ordered the coil just in case I neeeded to re-jet, but am guessing I'll just need to use trial and error.

[mro]

79' idle 950 to 1050...
At idle, pull plug wires one at a time. Idle should drop as that cylinder fails to fire. Should you find one where RPM stays same..that one needs some attention.

Would check that clutch is adjusted right and is disengaging fully too.


mro