Running lean after carb rebuild

Installed new rebuilt carbs. Took them down to the bodies. Replaced shaft seals, air/fuel adjustment screw o-rings, fuel distribution pipe o-rings, float valves, and float bowl gaskets. Also replaced Carb 1 and 2 diaphragms. Rubber/fabric damaged beyond repair. Bench synched. Wet set float levels. Synchronized carbs and color tuned. Took bike out and ran like a cheetah with it's tail on fire. Held idle well. Pulled the plugs and they were white. While bike was hot did a propane check on input boots, shaft seals, etc. Nothing changed the rpm. Went back with color tune plug and richened up to where a saw orange on all 4 cylinders. Resyched and took bike back out for ride. Still ran well. Pulled plugs and all four are still white. I am pretty sure float levels are set correct. Could this be alignment issues with butterfly valves seeping air through? If that was the case wouldn't the idle be messed up? Any suggestions on what to check next would be appreciated.

 

You need to put 100 miles or more on it before you get a reliable plug color.

 

I have about 50 miles on it now since I installed the carbs and tuned them. I'll put some more miles on it and see if the color changes. I am worried I might be damaging the valves or pistons if it is really is lean.

 

Are you hearing popping on deceleration?

Have you changed gas recently?

Idle would probably rise a lot when it got warmed up if the butterflies weren't aligned correctly. when you take the rack apart you have to make sure the butterfly valves *tink* when they close and will not bind whatsoever (take it from me). Ahh carbs... gotta love a good challenge.

 

Hopefully Fitz or one of the other veterans can chip in on this. I thought I read that you shouldn't change one or two of the diaphragms. That they all should be changed at the same time due to a "balance" between all the carbs. Could this be a reason for the bike to run leaner than it should?

Don't know if this is helpful or not...

 

If the Colortune shows that your mixture is good, and you have no vacuum leaks, then your mixture is good. What fuel are you using? Paper-bag brown is getting harder to use as a refrence for mixture since fuel blends are changing all the time. If you were dangerously lean there would be flecks of aluminum on on the ceramic and the electrodes. Post up a pic of your plugs.

Bruce: you can change just one diaphragm. Any differences will be adjusted during the running throttle synch. I have never seen, nor heard of putting a "matched set" of diaphrams in a rack of carbs. Matching the diaphram piston springs I've heard of though, and done.

 

I put a new tank of gas in. Running non-ethanol 91 octane fuel. You know come to think of it its not a real loud popping sound at deceleration but more of a bubbling sound. I don't have the experience to tell if it could be lean do to fuel float levels or improper fuel/air mixture screw settings. I am seeing a change in color of the colortune plug when I adjust the mixture screws on all 4 carbs. A question I have, am I supposed to have the YICS tool installed when using the colortune plug? I have not had it installed. I will take some plug pictures and get them posted.

 

I hope you are reading the bottom of the "meniscus" when setting the floats.
The YICS blockoff tool should be installed for ColorTune and running sync.
But - lots of folks leave it out.

Did you get your Pilot circuit completely - Zestfully clean ?? including the little transfer ports and passages ??

 

Ok, now I remember, it was a post where a guy said he stretched out the springs thinking it would improve the return response and Fitz told him that he now needed 4 new springs as they were balanced...thanks K=Moe

 

Here is some sparkplug photos.

Sparkplug #1

Sparkplug #2

Sparkplug #3

Sparkplug #4

I cleaned the heck out of the carbs. Carb dip, carb cleaner, compressed air, ultrasonic cleaner. Cleaned all the jets, nozzles. You name it I cleaned it. I am pretty sure I set the fuel levels correctly. They were a bit of a pain but I took my time. The jet #s are correct based what I have in my Yamaha manual and what I have seen listed here. Is this analogy correct, If my fuel float levels are low, I can still get that nice bunson burner blue when I colortune at idle but when I am running at highway speeds I am starving for fuel. You can correct by enriching the mixture (going into the orange color range) this will give me more fuel at normal highway speeds but burn very rich at idle. Not a good situation for startup or the piston rings.

 

Number 3 looks pretty good, certainly not too lean. 1, 2, and 4 show a dark fire ring but it appears that you used a flash or there's too much light and we can't see the ceramics very well. Personally, I would not try to compensate for low fuel settings buy enriching the pilots. My plugs have a slightly dark fire ring and a touch of gray on the ceramic tips and the plugs have about 125 miles on them.

 

Carb DIP? As in submerged?

Were they fully disassembled, as in butterflies and throttle shafts removed?

 

I completely broke down the carbs. Everything removed before putting them in the dip. Replaced all seals when I did the rebuild. One item I did want to add was when I reinstalled the carbs and fired the bike up the idle was high so I adjusted it and let the bike warm up before synchronizing it. I started out at 2-1/2 turns out on mixture screws. I synched the carbs and started the color tune process. I remember the #2 and #4 Carb plugs had black soot when I pulled them to install the color tune plug. The other two were a light brown to white. Brand new plugs installed. Adjusted to get that blue and richened it up a little. I did not record how many turns out or in on each carbs mixture screw. So is this looking like I messed up on the fuel float levels? I can't see putting the color tune plug back in and increasing the richness more. Unless you think I will see different results with the YICS block off tool installed.

 

I completely broke down the carbs. Everything removed before putting them in the dip. Replaced all seals when I did the rebuild. One item I did want to add was when I reinstalled the carbs and fired the bike up the idle was high so I adjusted it and let the bike warm up before synchronizing it. I started out at 2-1/2 turns out on mixture screws. I synched the carbs and started the color tune process. I remember the #2 and #4 Carb plugs had black soot when I pulled them to install the color tune plug. The other two were a light brown to white. Brand new plugs installed. Adjusted to get that blue and richened it up a little. I did not record how many turns out or in on each carbs mixture screw. So is this looking like I messed up on the fuel float levels? I can't see putting the color tune plug back in and increasing the richness more. Unless you think I will see different results with the YICS block off tool installed.

 

Since reinstalling the carbs I have about 120 miles on the bike.

 

Float levels are uber-important.

The YICS block-off tool isolates the cylinders from each other; without it you are "reading" not only the cylinder you're attending to, but also whatever is coming back from the intake tracts of the other three.

You are absolutely correct in that adjusting mixtures is pointless if you have an out-of-spec float.

 

Well, it looks like the carbs come back off and I go through the fuel float levels. I take it that I reset the mixtures screws back to 2-1/2 turns and start the synch and color tune process from there? Do I have to bench synch again?

 

I wouldn't touch anything besides the floats. If you raise the levels you should notice an improvement in the plugs from the get go. You're not touching the sync screws and you mentioned ildeand was okay right?

The big thing is to get some miles on it after changing one thing, only. Baby steps. Keep us posted...

 

He didn't keep us posted.