Bike idles fine but at cruising speed it is not smooth

I have been running the bike for about a 4 weeks. I went out the other night and about 45 minutes into my ride the bike was not running smooth at cruising speed or when I was accelerating. I got the bike home. Again just sitting at idle it was fine. I pulled all 4 plugs. 1, 2, and 4 looked fine. 3 was black. No oily residue just black carbon buildup. My gas mileage is very low. So does this mean pull the carb rack and start cleaning them all or do I need to look somewhere else first? I also noticed some cracking in the inlet boots near the carbs. Not sure if I have a vacuim issue. Any suggestions would be appreciated.

 

The very first thing you need to do is check valve clearances. Most likely you have a crusty old valve cover gasket and pressure washers (donuts). So you might as well replace it at the same time. If the valves are in in spec. You will NEVER get the bike running correctly and all your work on the carbs is for nothing. Doing the shims is easy I did it for the first time last Friday. I think the valves should be checked at 2K miles and then every 5K after that. I would wager it has never been done on your bike. Here is a link to an amazing how to...

http://xjbikes.com/Forums/viewtopic/t=14827.html

 

It means at the very least you're out of sync; and a vacuum leak won't give you a black plug.

You'll need to clean the carbs, yes; and check and adjust the float levels, then bench sync, and vacuum sync them (with the YICS blocked.)

However, you can't do a vacuum sync unless your valve clearances are in spec first. If the valves on your bike haven't been touched, you're 5500 miles overdue. If they had their all-important 3000 mile initial check, then you're only 500 miles overdue. Do you have any way of knowing they were ever checked?

So in order:

Valves in spec.
Carbs clean clean, slides pass "clunk" test.
Float levels set using fuel and clear tubing.
Bench Sync.
back on bike, Running vac sync, YICS blocked.
Fine-tune mixtures.

Quite often, those cracks on the intake boots look a lot worse than they actually are. They frequently don't go all the way through, and the manifolds are fine. If that's the case, they can be packed with black RTV or painted over with liquid electrical tape (or both.) The only way to be sure is to flex them from the inside when the carbs are off.

AFTER you've pulled the rear brake apart and visually inspected the shoes for signs of delamination: http://xjbikes.com/Forums/viewtopic/t=15874.html

 

Spoke to PO. Valves were checked at 6K miles and ok, but as stated they need checking again. I wondered if I could RTV those boot cracks. Guess I'll get some parts and tools together to check valves. I have found a number of discussions on carb cleaning. Before i clean the carbs, should I get rebuild kits for them? Are there certain wear items inside the carbs I should just replace while i have them apart? This will be a first time attempt at cleaning carburettors for me. It should be interesting.

 

Do your self a favor and get the shim bucket tool it makes life in my opinion a lot easier. Take a good look at the How To I posted above as well, lots of pics and descriptions of what to do, when and how...

 

The motion pro valve tool, a YICS blocker, and a metric only feeler gauge are the way to go.
Spray starting fluid around all the boots while it is idling to see if you have any vacuum leaks.

 

Metric feeler gauges as well will come in handy and a metric micrometer...

 

No performance at Wide Open Throttles when the Engine will Idle like a sewing machine indicates the Carbs are not delivering the Main FUEL JET Supplied volume of Gas in a form that will provide a powerful Mixture.

The Problem can be:
Sticking Diaphragm Pistons
Diaphragm Leak or Tears
Float Heights

Usually, if everything you can SEE is OK
The problem lurks where you can't see nor get too it without disassembling the Carbs.

Fouled Emulsion Tubes

 

PO probably lied. (Wow, that never happened before. PO's have been known to do that, ya know.) If valves were indeed checked for the first time at 6K, they WOULDN'T have been "OK" at that time, a couple would have needed adjusting.

Keep romping around on it without catching up on the maintenance and you're gonna hurt it. It's trying to warn you; as are we.

Listen.

 

Thanks for all your input. Getting together the tools and parts I need for valve clearence test. I have printed out the information on how to perform the clearence checks from the forum. I am going to start searching forum for info on carburettor cleaning. One other question, does carb cleaner leave any residue I should be worried about.

 

Carb Cleaner does not leave a residue.

But, the foreign matter it dissolves needs to be wiped, drained or flushed away.

SPRAY Carb Cleaner is generally safe to use cleaning everything.
DIP Carb Cleaner is harmful to Rubber Parts.