some puffs of black smoke from exhaust.

I just started fixing my 86 xv700 and after cleaning the carbs and installing them the bike finally fired right up. It ran prior to this but real bad. I found the idle speed screws to be way high and it idled at about 2500rpm. I adjusted them but now it seems to have some black smoke coming from the exhaust.I think that means too much fuel so my question is --if the idle screws are not synced to eachother could that cause too much fuel and blow black smoke during idle. If I crank on it I get a puff of smoke and then it clears up.

 

Maybe.

WHICH idle screws? The mixtures or the idle stops?

Synchronizing involves the idle stop screws and the use of a manometer (vacuum gauge) of some sort, either store bought or homemade.

On a twin, you can sometimes get away with pulling one plug and setting the running cylinder to a set RPM. Reconnect the wires, clear the motor out; pull the other plug wire and set to same RPM. But nothing beats a vacuum sync for accuracy, and I don't know if you can do that on your XV without damaging its TCI or whatever ignition it uses.

The mixture screws (on each carb) should be set to a baseline based on where they were to begin with, and then adjusted either by using a ColorTune or by ear and doing plug chops.

IN ORDER, no shortcuts and don't skip a step, nearly the same as your XJ:

Check/adjust valves. Out of spec valves will drive you crazy trying to tune carbs. Check your manual, I think this is easier than on the XJs.

-Bench sync (carbs off bike.) In your case I believe it would be "bench match." Again, check your manual.

-check and adjust float levels using the clear tube method and gas (carbs off bike) check your manual for the specified level for that bike.

-remount carbs.

-running vacuum sync. Again, check your manual for the specific procedure.

-THEN you can begin mixture tweaking. (Manual again...)

If you missed any of these procedures you are not going to get the bike running right, ever. Close maybe, but you will be at it a while. Do it right and you'll be all set, and it won't take forever. Just like an XJ.

 

Thanks,
The mixture screws are actually gas mixture I think and not air mixture. They are covered with some sort of copper insert so I have not touched them yet. I did check the plugs and they were pretty black but that is not a true plug chop it was at idle. The screws that I did adjust are the idle screws for each carb. 1 screw is a big thumb screw with a heavy spring on it and the other carb is a small set screw with a lock nut. It is sort of strange that there is such a big difference between the carbs. My first guess is that my carbs were so far off from eac other that 1 cyclinder was getting way too much gas at idle and thats why I got black smoke. I like the idea of removing 1 wire and setting the idle 1 at a time. I am not sure if the bike will run on 1 cyclinder but it`s worth a shot. Anything that I should know prior to doing this?

 

The Pilot AIR Screws are hidden beneath the so-called: "Idiot Plugs".
They don't want Idiots messing with them.

But, Members in this Forum aren't Idiots ( Except for 1 )*

You are going to have to Drill-out those Plugs in order to to Performance Fine Tuning.
You carefully Drill a Tiny Hole in the Center of the Plug.
Carefully!
Very Carefully!!!
You have to Drill just deep enough to get a Self Tapping Screw started.
Then, pull it out.

Just remember, ...
Just below those Plugs is the HEAD of a Precision Screw made of BRASS.
You DO NOT want to hit the Screw by drilling through the Plug.

Here's a Visual Aid.

 

That spring/linkage/one big screw/one small screw thing is what I was talking about.

Most likely, the big knurled spring loaded screw is the "master" adjuster; the one on the other carb is adjusted to the first one and then the locknut is set. You need to mechanically synchronize them, the equivalent of a bench sync on a rack of XJ carbs. Do that first before tweaking mixtures.

If you've never touched the mixture screws your carbs aren't truly clean, BTW.

So, what about the valves then?

 

You could hop in the car and take a ride down RT-3 and be at my Garage in less than a half-hour.

I could grab a set of Parts Carbs and give you a 15-Minute tutorial on how the Carbs work and what each and every Screw and Adjustment does.

Until you ACTUALLY Know what you are doing, ...
You are just messing thing up.

Bring along the Carbs off your Bike, 4 Cans of Carb Cleaner plus Workbench, Toolbox and Private Instructor fees ... and, YOU WILL Clean your Carbs and I will tell you what to do every step of the way.

 

private instructor fees?

 

golden instructor brain beverage! lol

 

private instructor fees... aka: a case of beer.

 

I run an Alcohol Free World Headquarters.

 

If thats the case Rick I will bring a pepsi for you and Sam Adams for me. LOL