Need some carb help

[Haarstad]

So i have synced my carbs after i put in the proper jets, which ended up being 142.5 mains. i tried all of the jets from stock to 147.5 and the 142.5's were the best running. My pilots are My bike is a 1979 XS1100 Special and i took it out for a spin and it's a little slow when starting out, i really have to feather the clutch when starting or it kind of cuts out. So i took it out on the inter state because it seemed to have been running fine at 55-60 mph and while going 75 mph it would cut out pretty regularly, it was really odd, it would run fine but every 15 seconds or so, it would kind of cut out. My pilot jets are 45 by the way but i need some help so i can figure out what to do next. Any help is appreciated.

[fredintoon]

So i have synced my carbs after i put in the proper jets, which ended up being 142.5 mains. i tried all of the jets from stock to 147.5 and the 142.5's were the best running. My pilots are My bike is a 1979 XS1100 Special and i took it out for a spin and it's a little slow when starting out, i really have to feather the clutch when starting or it kind of cuts out. So i took it out on the inter state because it seemed to have been running fine at 55-60 mph and while going 75 mph it would cut out pretty regularly, it was really odd, it would run fine but every 15 seconds or so, it would kind of cut out. My pilot jets are 45 by the way but i need some help so i can figure out what to do next. Any help is appreciated.

Hi Eric,
unless you are running pods and a 4 into 1 exhaust those mains are way bigger than the recommended size.
But mains are only critical at WOT and I see no way they'd cause the intermittent cutting out you describe.
I'd say clean the carbs. Again. And again. Especially the smaller jets and passages that control at partial throttle openings.
And check the ignition trigger wires too. Many a carb problem is a mis-diagnosed ignition problem.
And vice-versa.
One time I fought my ignition for a week to no avail but a half-hour spent cleaning the #4 carb set all to rights.

[skids]

You did try running the bike on the PRIME setting didn't you?

[Haarstad]

I have pods and 4-1 kerker exhaust and i have tried multiple sizes of jets and this is the one that it runs best on. I have not tried running it on prime though. Why would running it on prime change anything?

Also, i have new plug wires and green mike's xs coils from last year because we were having problems last year with that and those are still working good. I will try running it on prime and see if that changes anything.

All of the jets are new and clear and i have thoroughly cleaned these carbs multiple times while changing out the jets every time. when opening the carbs from the top, there is a long needle type thing with notches on it and there is a c-clip on it, what is that for and what happens if i were to move the c-clip up and down?

[James England]

Is your fuel cap breather hole unblocked? Do you ever hear any hissing from the fuel filler cap?

[Haarstad]

nope, the breather hole is not plugged and when i open the gas tank, it isn't pressurized. The cutting out only happens when i start moving and i need to feather the clutch and it happens at higher speeds like on the interstate, it is bad on the interstate though.

[skids]

Why would running it on prime change anything?

Because the vacuum operated fuel supply may be malfunctioning and prime bipasses this. If for some reason it isn't working right, it may be starving the carbs of fuel. I have two standards that do this on the left side at highway speed. The octpus is the same type of system, just configured differently.

[Haarstad]

I'm gonna try this tomorrow. I'm interested though, if that was the problem, how would you fix it?

[jetmechmarty]

I'm gonna try this tomorrow. I'm interested though, if that was the problem, how would you fix it?

Repair the valve, or bypass it. Make sure the vacuum line to the valve is not leaking. (if the diaphragm ruptured, there would be fuel in the vacuum line)

[skids]

Depending on the affects from the exhast system you can get some "anti-scavenging in the exhaust gases. This can cause low vacuum at particular rpms and also be a reason for shutdown of the automatic petcocks. Just sayin...

[jimbyjimb]

I recently had a cutting out/erratic idle issue and the members here helped me trace it to the resistor on the ignition circuit that I didn't remove when I swapped coils. I have Mike's black coils, not the green. If you didn't remove the resistor and the green coils are 3 ohm that could be your problem.

Make sure the green coils don't need it, but it's located on the left side just under the tank. Removal is two screws and simply removing the resistor from the circuit, JIC you didn't remove it.