running really rough

[WDB_xs1100s]

ok guys i have another problem with my bike. i can start it up, let it warm up and will rev fine from 3grand up. i took it down the road and on take off it feels like its running off of 2 cylinders but after 3-4 grand it will pick up really quick. i have cleaned the carbs and the tank. what could possibly be doing this?

[planedick]

Possibly

Needs a good synchronizing (sp). Probably THE most important part of tuning your bike.

[vileneeds]

I have a similar issue. Having trouble finding someone who will do it.

[planedick]

I do it

Unfortunately you're too far from Southern Cantaffordya.....

[WMarshy]

I have a similar issue. Having trouble finding someone who will do it.

You can make.your own sync tool with some clear hose and some trans fluid... someone made write up on it somewhere...

[Ken Talbot]

it feels like its running off of 2 cylinders but after 3-4 grand it will pick up really quick.

Start it up, let it run for a few minutes, then check the relative temperatures of the headers with the old "spit on a fingertip" test. You may in fact be running on two cylinders until the revs pick up. A big part of your solution will be found by discovering which header(s) is(are) cooler than the others.

[BA80]

ok guys i have another problem with my bike. i can start it up, let it warm up and will rev fine from 3grand up. i took it down the road and on take off it feels like its running off of 2 cylinders but after 3-4 grand it will pick up really quick. i have cleaned the carbs and the tank. what could possibly be doing this?

It sounds from what your saying that you are running on 2 cyls all the time. These engines have the power that two cyls feel normal at higher RPMs until you actually feel all 4 working once.

Check you spark plugs, are there 2 that are wet and don't seem to be firing?

[CatatonicBug]

If you have a bike, you should have a sync tool of some kind. Simple as that. Either make one or buy one. The carbs should be sync'd EVERY time you clean them, and some will say every time you do anything to the bike. It's amazing what a difference it makes!

The main jets kick in right around 3K, so if you determine that the engine picks up on all 4 after that point, your pilot jets are likely still clogged. That's not hard to do, with all the tiny holes in them. However, as Ken mentioned, there could be any number of things happening, and determining the actual symptoms is important.

[crazy steve]

If you have a bike, you should have a sync tool of some kind. Simple as that.

I don't need one for my Sportster....

[natemoen]

I don't need one for my Sportster....

Yeah thats true, single carbs do not need to be synced...

[CatatonicBug]

I don't need one for my Sportster....

Yeah, but that's not a bike. It's a hardley.

[WDB_xs1100s]

Ok so I took the carbs off once again cand cleaned all jets. #4 cylinder jet had fallen out, but the bike still ran. The bike will spit and sputter around 2grand then pick up at 3. I put fuel filters on the carbs so it would stop the dirt and junk. I pit the carbs back on the bike and now the cylinders 1 and 2 are colder than 3 and 4 could my idle mixture screws be out of adjustment? Could anyone point me in the direction of how to make a sync tool?

[DiverRay]

You DO need to sync the carbs EVERY TIME you remove them! so yes, you will have to build or buy a sync tool. The mercury carb stix no longer use mercury, but they still work well, as you just need all 4 the same.
If you do a search on idle screw adjustment, you should find the well written directions on how to properly set them. The bike WILL run a LOT better once everything is correct!

[3Phase]

WDB, do you have fuel in the tank?

Check the simple stuff before you dive back into the carburetors!

Make sure the left fuel tap is working. Turn the fuel tap to Prime and see if the 1 & 2 carburetor pair gets better.

Do you still have the octopus (automatic fuel control valve) on your '79 Special carburetors? It has nine hoses attached to it, you can't miss it.

If you do have the octy, make sure all nine hoses are connected correctly and that the line from the octy to the lowest black tee between the 1 & 2 carburetors is supplying fuel.

The upper tee between the carburetors is the float bowl vent and there should be a hose connecting it to the air box. Make sure it's not plugged by dirt or nesting insects.

If no one has messed with the stock seat there should be a diagram/sticker on the bottom of the seat pan showing how to connect the lines to the octy.


In general, problems with pairs of cylinders can be narrowed down to fuel or spark by taking note of which cylinders are not working:

Carburetor pair 1 & 2 are fed by the left fuel tap/octy line.
Carburetor pair 3 & 4 are fed by the right fuel tap/octy line.

Spark plug pair 1 & 4 are connected to the left ignition coil.
Spark plug pair 2 & 3 are connected to the right ignition coil.

[WDB_xs1100s]

update

ok sorry i havent gotten back in a while. i recently found out that cylinder #2 wasnt getting warm..she had fire to her and fuel. after the bike warmed up i could still grab the header pipe and not get burned. i have 140 jets in her now with the 4-1 header.does anyone know the factory air fuel mixture adustments. i'm really concerned, dont wanna hurt the motor. when i try to take off really hard the bike spits and sputters until it hits that sweet spot. this bike is really stumping me