New Exhaust Carb Tuning Issues

[Conman]

So I'm taking the plunge into carb tuning. They've always been sort of a black magic to me, but its getting frustrating running with the current setup......

Anyways, I had Danny rebuild the carbs last spring and they came back like this:
Jets #90, #170, #155 main
Stg 7 needles on 3rd clip from blunt end
Stg 7 springs
A/F screws @ (3) turns out

I had a Muscle kit and a Mark's 4-2 put on at the same time and now I've got a list of symptoms:
-Backfiring on decel
-Discoloration on the tip of the left pipe only
-Bogs and stumbles when leaving a stop and anywhere below about 2.5k. It idles fine though... best description is that exhaust seems to sync up and come out of both pipes at the same time and get rough when giving it gas at low rpm, but only at low rpm
-feels flat from 2.5-4k
-vboost is there but doesnt have the kick it did before mods

I took it to the local dealer and they said they tuned it, but the symptoms persisted. Now I figure I can drive 4 hrs to PCW or do it myself. I'm looking for recommendations on where to go from here; it seems like its rich to me. The big PITA is the way it runs down low.

I didn't have any symptoms before the new setup by the way.

Thanks,

Connor

 

[Traumahawk]

So back fire on decel......or just rumble...?

 

[Conman]

So back fire on decel......or just rumble...?

Backfire... not consistently but occasionally when going down a hill or after a high speed run

 

[Traumahawk]

Backfire... not consistently but occasionally when going down a hill or after a high speed run

At what rpm? The idle circuits cover 0-4000 rpm, and needles are above that with the mains starting to kick in around 6-7000 rpm. Do you know if the slides are drilled?

 

[Conman]

At what rpm? The idle circuits cover 0-4000 rpm, and needles are above that with the mains starting to kick in around 6-7000 rpm. Do you know if the slides are drilled?

Definitely not below 4k... couldn't say where it happens above that. It's occasional though; if not for the lousy low rpm performance i would leave it as is.

The slides are not drilled so far as i know. I haven't been into the carbs myself though.

 

[Traumahawk]

Definitely not below 4k... couldn't say where it happens above that. It's occasional though; if not for the lousy low rpm performance i would leave it as is.

The slides are not drilled so far as i know. I haven't been into the carbs myself though.

Since Danny rebuilt the carbs, I would guarantee that they are perfect. Now the job is to just tune them.

I will PM you.

 

[sdt354]

Make sure the carbs are fully seated on good rubbers. Take a good look inside the tank for rust & crud.

 

[06VMAXIMUS]

Try putting the stock springs back in. I had the same issue as you, and found the stage 7 springs were allowing the slides to pull too quickly making the bike rich. I was running a smaller main jet too, a stock 152.5. I have 150's in it now, and plan on going down to 147.5 this winter as I am still a whisker rich up top.

 

[Conman]

Make sure the carbs are fully seated on good rubbers. Take a good look inside the tank for rust & crud.

I will check the seating as it was leaking gas pretty badly one day... didn't do it again for months though.

 

[dannymax]

I will check the seating as it was leaking gas pretty badly one day... didn't do it again for months though.

Connor, they were leaking gas around the rubber boots?

 

[Conman]

Connor, they were leaking gas around the rubber boots?

All I could tell is that it was coming from the carbs and not the fuel tank. It was like a gurgling hissing sound that tipped me off to it and then I noticed a little gas on the block. Unfortunately I was late for class and I didn't get a chance to investigate, but when I came back it started fine and didn't do it ever again (this was about sept 1st).

 

[caseyjones955]

Stg 7 springs... have the slides been drilled? If not try the stock springs.

 

[sdt354]

I will check the seating as it was leaking gas pretty badly one day... didn't do it again for months though.

I've hung a float a couple of times and had gas spew out the vents. Trailering over huge road bumps seemed to cause it. A few taps near the needle/seat cured it. Bad rubbers and, not fully seated carb racks shouldn't cause a fuel leak. But they'll make you run lousy.

 

[veebooster]

Check to make sure your stage 7 needles are moving freely within each carb.

Dale

 

[dannymax]

I've hung a float a couple of times and had gas spew out the vents. Trailering over huge road bumps seemed to cause it. A few taps near the needle/seat cured it. Bad rubbers and, not fully seated carb racks shouldn't cause a fuel leak. But they'll make you run lousy.

That's where I was going also Steve-o, the fuel leak sounds like a hung needle which can happen occasionally.

 

[Conman]

That's where I was going also Steve-o, the fuel leak sounds like a hung needle which can happen occasionally.

Is that something that would have been able to take care of itself? Since it hasn't happened again I figured whatever it was had resettled/broken in/freed up in time on its own.

 

[Traumahawk]

Is that something that would have been able to take care of itself? Since it hasn't happened again I figured whatever it was had resettled/broken in/freed up in time on its own.

Sometimes a bit of "junk" will cause the float to stick, and allowing too much fuel to build up, and then the fuel inside the carb will over flow. Then that bit of junk might clear itself......and the problem is fixed. If it does happen again, you can tap on the side of the carb body with the handle of a screwdriver. That "might" knock that junk out, and clear the float.

 

[dannymax]

Is that something that would have been able to take care of itself? Since it hasn't happened again I figured whatever it was had resettled/broken in/freed up in time on its own.

Sometimes a bit of "junk" will cause the float to stick, and allowing too much fuel to build up, and then the fuel inside the carb will over flow. Then that bit of junk might clear itself......and the problem is fixed. If it does happen again, you can tap on the side of the carb body with the handle of a screwdriver. That "might" knock that junk out, and clear the float.

Just as Eric describes it....yes it will often times clear itself up, and sounds like what happened to yours.

I have seen lots of junk in float chambers that couldn't have passed thru the fuel filter....but there they are, sitting on the bottom....how did they get there..........:confused2:

This stuff was collected from some customer carbs.

 

[Bill Seward]

The fuel lines on my 85 were badly deteriorated causing the floats to hang up occasionally. I drained the bowls, and got bits of black rubber out of all 4 carbs. Replacing every rubber hose from the tank to the carbs seemed to solve the problem, as it never happened again. Seeing your bike is an 88, if your hoses are original, this may be the cause of your problem.

 

[tugla]

I agree with the guys with crud from fuel line deteriorating over time, ethonol fuel doesn't help also.
Danny, the extra small clear filter we were adding I think is a must and does help minimize those issues.