Hoping to be pointed in the right direction. Running on 3

[Guest]

So just went through a complete carb rebuild including all new jets, cv boots, and a 4 week dip in berrymans. All the boots on both sides of the carbs are brand new as well as spark plugs. i got the bike back together and got her started up and it is only firing on cylinders 1-3. i confirmed this by an infrared temp sensor and by pulling the plug boot on #4 which did not affect the idle of the bike at all. I did though feel a nice pulse of electricity through the boot and into my hand when i pulled the #4 boot while the bike was running. i don't know if this is normal or even safe for the bike but it is what it is. i get this same shock thing when i pull any of the other plugs but the bike immediately starts to die. i unscrewed the boot from the 4th wire and cut the wire back about an inch to nice fresh unmolested wire. i also unscrewed the components from inside the boot and cleaned the parts up with steel wool. i put it all back together and no change. all idle mixture screws are screwed out 2 turns and the carbs were bench synced before installing them on the bike. Any suggestions for a next troubleshooting step?

[chuck hahn]

The butterfly isnt open enough. loosen the adjuster jam nut and turn the slotted screw..the one on the very far right on the linkage on the back. Left ( counter clock wise ) should open the butterfly. Start the bike with some fans blowing on the engine and turn the screw and youll most likely hear the cylinder fire off.

Even though you benched them you can still not have them open sufficently..even though they looked even when off the bike. Ive done this myself on CV carbs.

[shibby_cbs]

wow you were exactly right. I was really hoping I wasn't going to have pull the carbs again and thank the lord I didn't. it was really satisfying hearing that cylinder fire up. thanks a million. now its time to vaccume sync.

[chuck hahn]

like i said...been there and done that myself.

[shibby_cbs]

so it seems now that it is running on #4 but barely. I can't get it to pull enough vacuum to be able to sync it. the fluid level on the sync tool is staying right where it was before I started the bike. the fluid is shaking but not rising. I pulled the line and put my finger on the fitting and confirmed that it was pulling a vaccum but a weak one. the adjustment screw is noticeably further in than the others so I can tell the butterfly is much further open than the others yet somehow its barely running. the valves shouldn't be an issue as these were clearanced about 4 years ago but I haven't put more than a few hundred miles on the bike since then. when I touch the number 4 plug boot I feel a bit of a shock. is that normal? could I be getting a weak spark? not enough fuel? where should I start?

[wymple]

I can lay hands on my spark plug boots without issue as long as I don't ground myself to the bike. If that's any help.

[dorkburger]

My bike has the resistor type spark plug caps and a few years ago a cap went bad- the cap read open with the meter, and wasnt sparking.

[Steve]

I can't get it to pull enough vacuum to be able to sync it.

Stop for a moment and think about the physics of the whole process.

What causes the vacuum?



The vacuum is caused by the cylinder trying to suck air past a CLOSED throttle.

Now read the answer to your question that YOU wrote.

... the adjustment screw is noticeably further in than the others so I can tell the butterfly is much further open than the others yet somehow its barely running. ...

It is kind of hard to generate vacuum when the butterfly is noticeably farther open.

Why is it barely running?

Probably because the other three aren't even open, and the bike is trying to run on ONE cylinder.

where should I start?

Start by adjusting #4 back where it was. Remember, if vacuum is low, the butterfly is too far OPEN. As you start closing down #4, the engine is going to try to die, so turn up the master idle speed control to open up the other three carbs.

.

[shibby_cbs]

So according to what you are saying in theory the futher shut the butterfly valve the higher the vaccume? With the butterfly completely closed on #4 the bike runs and idles just fine. when i get ready to tune i set the idle to about 2k. i start to open #4 with the adjustment screw and i can hear it start to kick in but i see no change in the vaccume level. it bounces like the rest of them so i know its pulling some but just barely. I will mess with it again tonight of course keeping in mind what you said. And for good measure i have checked the fitting that goes into the boot and comfirmed that it is not clogged. i also switched the tuner lines between 3 & 4 to see if there was an issue with the tuner but thats not the case.

[wymple]

Check the diaphragm on that carb.

[shibby_cbs]

Check the diaphragm on that carb.

good call. all of the diaphrams are new but maybe i accidently got it flipped around and the hole on the slide is on the wrong side. ill double check that when i get home.