A Note To ALL

[Winterhawk]

Most of you know that I've been fighting a problem on the #4 cyl.

IT'S FIXED

The sync tube was slid into the intake boot 1 inch. This increased the velocity of the mixture thus reducing the pressure in the intake. This created more vacuum thus pulling in extra fuel. My bike now pulls from 1,500 rpms thru 8,000 rpm at any throttle opening flawless. It has to be the smoothest XS1100 I've ever ridden because of the hours I spent on the carbs and jetting chasing gremlins.

This should be a sticky because if it happened to me it will happen to a 100 others. I originally pulled the sync cap off, tube slid out with it. I tapped it back down in place and went to far not knowing that it slide into the intake boot approx. 1 inch. This cause it to cut out at about 1/2 throttle opening starting around 4,000 rpm. It also mad the #4 plug dry black, just like a choke opened. All 4 plugs are now white with a light tan coloring on them. Thanks to all of you for your input. I did learn this and another thing on here about calibration of sync gages. My K@L sync gages retail for about $300.00 and I never thought to check calibration using a vacuum pump.

Final thought. A dry black plug and cutting out while semi getting on it could be a sync tube slid into the intake. I'm still amazed. I wish Bob Jones was still around to tell him about this.

[WMarshy]

Im checking mine this evening! THANKS!

[XS1100 Newbie]

I have to pull my carbs off anyway. A good time to check it. I have allmost the same problem.

[Winterhawk]

I have to pull my carbs off anyway. A good time to check it. I have almost the same problem.

Be sure to check the pickup wires. I used a vacuum pump and at idle I opened it and found 2 wires that needed repaired. This I thought was the problem. It was a problem but not the final fix. Thanks to all for the help and suggestions.

[randy]

I don't buy it. A restriction BEFORE the carb would make the mixture richer, but AFTER the carb how????

[dbeardslee]

IIRC didn't you rtv the tube back in place? I'm kind of with Randy on this - that small of a restriction after the carbs - color me skeptical. Could it be that by rtving the tube in place a vacuum leak may have been plugged? May have been as simple as not allowing the cap down far enough on the tube to seal with it seated too far. Still, never hurts to check.

[Winterhawk]

The mixture flowing around the 1/4 inch tube increases speed to catch up with the straight flowing mixture. Increasing the velocity lowers pressure resulting in more suction / vacuum thus drawing in more fuel and or maybe affecting the slide position at speed. This is all I know and it was the item that fixed it. New one on me also.

Somebody on our Planet has had a simmilar problem I'm sure. I didn't use RTV I just squeezed it back into place. It was very tight and I checked for leaks before and after. These were newer intake boots from Merriam.

[b.walker5]

The mixture flowing around the 1/4 inch tube increases speed to catch up with the straight flowing mixture. Increasing the velocity lowers pressure resulting in more suction / vacuum thus drawing in more fuel and or maybe affecting the slide position at speed. This is all I know and it was the item that fixed it. New one on me also.

Somebody on our Planet has had a simmilar problem I'm sure. I didn't use RTV I just squeezed it back into place. It was very tight and I checked for leaks before and after. These were newer intake boots from Merriam.

Being in the HVAC industry and knowing how air movement works I can say that his theory is sound, and has basis in fact. Air is not very elastic and doesnt tolerate changes in direction very well. Any obstruction in the path will change the velocity and pressure, no matter what side of the carb it's on.

[petejw]

glad you got it all sorted out.

[fredintoon]

Most of you know that I've been fighting a problem on the #4 cyl. - - - The sync tube was slid into the intake boot 1 inch. - - -

Hi 'hawk,
I've had my carbs apart many times but I'm vague as to what the real names of the parts are. So WTF is a sync tube?
Anyone want to post a diagram, please?

[DGXSER]

Fred, I believe he is referring to the vacuum tube in the no 4 intake boot used to synch the carbs.

[thewiz]

alrighty then ...

awesome ...

[tadtl1]

venturi theory

Hi,

Winterhawks theory about the increase in air speed ,,,, can hold up,,, if you think about it,,,,,,,,

the entire lift that a fixed wing aircraft enjoys, is due to air flowing faster over the rounded top of the wing,, the air flowing under the wing which is flatter, is moving slower, the above wing vaccuum allows air to rush in under the wing,, lifting the aircraft.

If you will allow this tortured thinking, the air flows around the synch tube at higher speed than the other intakes, this raises vaccuum, compared to the other intakes,, increased vaccuum sucks out more fuel from the jets,,in that intake compared to the other intakes with normal synch tube positions,,,, creating the blackened plug from too much fuel. Wheewwww,,, man I dont know if I can stand too many more brain cells dedicated to this stuff guys. hahaha.