Anybody still remember how to tune a carb?

[R3Tex]

Not Rocket related but here goes...this is on a 2004 Yamaha Vstar 1100 Custom with 1500 miles on it that I am trying to get back together. Long story but it just happened to be sitting in my shop when we were slinging paint so it got disassembled and shot with a custom marble paint job and I'm trying to get it back together and out the door. There have been multiple wrench turners involved from the inception and the carbs have indicators that they have been fooled with before...like there is no brass plug over the pilot mixture screws. In my experience Mikuni carbs all have the PMS sealed under a brass plug after being set at the factory. Anyway here is where I'm at now. The bike has dual Mikuni constant velocity carbs on it and a set of free flowing curb burner type exhaust pipes installed and all of the intake plumbing taken off in favor of individual K&N pods on each carb. I have installed a jet kit to compensate (152.5 mains with the needles raised by one 0.020" washer and #20 pilots). The pilot mixture screws have been backed out 3 1/2 turns per the instructions that came with the kit. The problem is that the bike will not start...at all...won't even sound like it is trying to fire.

I initially had fatter jets in it but the first test ride showed me it was running way too rich so I rode it back into the shop, put it back on the lift and dropped down to the jets that are in it now and the b!tch won't start. I have checked for fire...fine on both cylinders. It seems to me that there is a problem in the idle circuit. The bike seems to flood immediately when the key is turned on. So here's what I'm thinking...either the floats need to be adjusted or there is a pilot air jet plugged.

Thoughts? Anyone? Beller? @TO rocket you jack around with old carbureted bikes....a little help?


I'm about ready to set fire to the POS and tell the girl that is supposed to ride it to Leaky in a week that she will have to become ballast on a Rocket

 

[HansO]

3 1/2 turns sounds like a lot for the idle mixture Morris, have you checked the diaprams are not leaking other than that what is the needle and seats like they are not sticking are they

 

[R3Tex]

Don't appear to be

 

[HansO]

Wish I was there to help I used to love playing with carbies but the CV ones can be a pain
Try turn fuel off, use some "start you Bastid" spray or Ether Starter spray and see if she will start kick over then turn fuel on see if it floods alternatively if you think there is blockage get some carbie cleaner pull carbies of and spray every orafice

 

[Rocket3Pilot]

If it's flooding as soon as you turn the ignition on then I'd say it's got an electric fuel pump and one or both float valves are sticking in the open position or the valve seats themselves are damaged. They could have rubber tips that are dry rotted or hardened or brass that is worn and won't seat. It's been my experience that most of the older carburetor bikes that have been sitting a long time have the same issue.

 

[BenchracerBob]

3 1/2 turns sounds like a lot for the idle mixture Morris, have you checked the diaprams are not leaking other than that what is the needle and seats like they are not sticking are they

That's what I thought then I thought it means three half turnes I.e. 1 and a half.

 

[HansO]

Sounds more like it

 

[Speedy]

Check the chokes to see that they seat closed. Otherwise, needle and seat issues.

Bike will run much better with #25 or even #30 pilots and less idle screw turn out.

Does this thing have the fuel shut off system for rpm limiting; as in a little electric solenoid valve at the bottom of the float bowl? When on almost no fuel gets into the main jet well. Just remove the o'ring around its body. This bypasses it and eliminates the valve's function entirely.

Good luck.

 

[3Katz]

I haven't messed around with them for quite a while and it won't be the cause of your start problem but I always found that CV style carbs did not seem to run as well with individual pods. It seems they prefer to draw from a plenum/airbox or a bit of still air. I swapped to pods when using flatslides and that was never an issue.

 

[rocketjohn]

CV carbs do indeed need or at least work better with an airbox. You can fit pods to some but it requires considerable retuning, including jets needles and exhaust system. It's a big experiment for which there are no hard fast answers. You dig in and change things til it works. Or resolve to work within the range of possibilities that you get retaining the airboxes and there's enough latitude there to satisfy all but drag racers. I have Suzuki Intruder 1400 a notoriously difficult engine to sync and maintain in sync. But runs sweet when it's right.