1982 Seca 550 & 1981 Seca 750 carb questions

As stated in the title, I have both a Seca 550 & 750. I just bought the 750, have had the 550 for 6 years. When I first bought the 550 it hadn't been run in several years so I went thru it. Cleaned the carbs, oil change, cleaned fuel tank, new plugs, etc. The bike ran perfectly after that. I also run nonoxygentated fuel with Seafoam. This spring the bike wasn't running well on low end so I thought the pilot jets might be plugged. Infact, they were. I took the carbs apart, cleaned the carbs and the jets. Put the bike back together and it fired right up but has a miss on low end. If I crack the choke a tad bit, it fires on all 4 at low end. So I thought I'd take the carbs back out and check the pilots again. They appeared clean & open but I cleaned them again. Put it back together, it does the same thing. Misses with no choke but runs clean with just a tad choke.
Fast forward, I just bought a clean. low mileage, one owner Seca 750. It also sat for a few years. Took the carbs apart yesterday. Cleaned them out, brand new jets. Bike fired right up but has the same slight nagging miss on low end. Again, if I crack the choke just a tad, it runs clean.

What could I be missing here? The floats were adjusted and the float needles all appear in good condition, etc. Any help would be appreciated!!!

Thanks in advance....

 

Did you check the valves?

 

Needle valves? Yes.

 

No engine valves need clearance checked and shims may need changed to get everything in tolerance

 

To me, that doesn't make sense because the Seca 550(8,000 original miles) ran perfectly without a miss last fall as well as the 5 seasons prior. It would idle down and run on all 4 and very smoothly. Now this spring it's not running smoothly at low speed unless the choke is just cracked ever so slightly. If I do that, it will run on all 4 smoothly. I still think it's in the fuel system somewhere.

 

cracking choke open a little adds more fuel, are you running lean in one cylinder possible vacuum leak?
how did you set the mixture screws?

check your ignition coils, ohm out the spark plug caps and the wires , your caps could be failing or plug wires may be corroded at the cap and need to be trimmed back

also test your battery charging

it is likely time to check your valve clearances

 

Tight valves can effect carburation throwing it off, you should check them, then pull carbs and do a full tear down ie new shaft seals and gaskets , check needle and seat. You can find info in the Church of clean , I did mine WAS running great till I tore one of my airbox boots( ordered brand new ones from xj4ever Thanks Len)
this has caused no amount of problems in my case I had K&N filter switched back to stock filter and jets hope this helps with some of my problems with eratic problems with stuttering and popping ( my synch has been off that did not help) . From the sounds of your problem sounds like your jets are plugged up our gas is junk anymore.

 

I don't see anything about balancing/syncing the carbs after you put them back on the bike

 

^^ WHAT they said
Valve clearance checks should be done every 5,000 miles.
Carbs get gunked up when sitting for so long.
Any bike that sits needs to be thoroughly gone over to get it back in proper and safe running order.

 

Cleaning the pilot jets is only covering 1/3 of your pilot circuit. There is an air jet (more than likely just fine) and the mixture screw (more than likely in need of attention). You could try just opening the mixture screws an 1/8 turn and see wht that gets you for the easy way out, or you could pull them, blast some carb clean in the holes, and then re-set them and tune from there.

 

It's your carbs, take them to the house of clean, that mean adjusting screws everything if you have the time and do not need them running right this minute. Or you can keep adding seafoam to your tank and hope that it eventually cleans out all the tiny orifices, which it probably won't and then you will have to take the carbs through the full house of clean anyway. You may even want to order carb kits from Chacal to help you on your way, seals have a way of deteriorating over time, not looking like they are then suddenly disintegrating on you causing you to need new ones, at the least opportune moments. Like 12:30 am on a dark country road 5 klicks from the nearest house you can find to get a phone because there is no reception on your cell... Believe them, they know what they are talking about.