Popping On #4 Carb

[MrOzz]

I cannot figure this out.

I synced the carbs, Timing is good.

Yesterday I took my ride out for a test ride all was good.

Today took my ride out and now I am getting a popping on #4 carb. Checked the sync, noticed that the sync is good until the popping. I the loose all vacuum in #4 carb.

I put up a video. The popping is almost rhythmic.

http://www.youtube.com/watch?v=UX0oL6YLL40

Any ideas?

Thanks again all,

Ozz

[crazy steve]

Have you checked your valve adjustment? A too-tight intake can cause this...

[heatmanal]

try turning your pilot screws out 1/4 turn at a time.I had this problem on my xj,running to lean.

[bikerphil]

Ozz, check the vac caps and stems on carb boots. The stems come loose and the caps could leak causing a vac leak. Engine side gasket leak maybe? Popping is a lean condition, plugged fuel filter? How does it ride that way?

[MrOzz]

Have you checked your valve adjustment? A too-tight intake can cause this...

I did the valve adjustment last fall. I will double check it once it has cooled overnight. Is this something that can happen all of a sudden? Fine one day, then not the next?

try turning your pilot screws out 1/4 turn at a time.I had this problem on my xj,running to lean.

I just did adjust them with a colotune this week before I adjusted the timing. All seemed good then.

Ozz, check the vac caps and stems on carb boots. The stems come loose and the caps could leak causing a vac leak. Engine side gasket leak maybe? Popping is a lean condition, plugged fuel filter? How does it ride that way?

I was thinking the same phil. I did the propane test. I did not get any change in the rpms. Carb boots look good. I did replace the vacuum caps thinking they might be the cause. I will have to double check on the gasket. Fuel filters and carbs were just cleaned a week ago, fuel does look to be flowing through my fuel lines, Clear fuel lines, no octy.

As the ride goes, all was fine yesterday. Today loss of acceleration in low to mid throttle. Then fine until the popping, now no matter what #4 keeps popping and the bike runs like crap from low to wide open throttle.

When I put my carb synchronizer on carbs 1,2,3,4 were even at 23cmHg, until the pop on #4. #4 would drop to 8cmHg, but thats the lowest # on the scale of my carbtune.

At one point I removed the vacuum cap on the #4 carb boot and thought I saw a little flame. I could not get it to happen again.

Thanks guys for your help with this.

[Winterhawk]

Check and see if your carb sync tube didn't get pushed down into the intake manifold. This happened to me and I fought this problem for over a year. Runs great now and all I did when removing the carbs for the 20th time was look into the carb boot and see and feel the tube sticking down into the intake manifold.

[MrOzz]

OK I am 1 step closer. After double checking everything again. Setting up my color tune everything was running fine. After a little bit #4 starts to pop again.

I noticed that I had very little fuel in the fuel line. Removed the filter. Same issue. If I disconnect the fuel line from the carbs fuel flows with no problems.

Where in the carbs do you think this problem lays? I am thinking in the float needle seat?

[bikerphil]

I would guess in the pilot circuit. Maybe a loose air jet at the back of the carb? Could try a dose of Seafoam first.

[MrOzz]

I would guess in the pilot circuit. Maybe a loose air jet at the back of the carb? Could try a dose of Seafoam first.

I will check that air jet. I have pulled the carbs and giving them a cleaning, again. I this will be the 5th time in a week the carbs will be cleaned out.

[TopCatGr58]

Hey Ozz,

From what you described, that sounds like the culprit, a sticking non-dropping float so the valve isn't opening to allow enough fuel flow to keep the bowl filled. You could do an experiment, run it till it starts popping, then quickly shut off the fuel, and the bike, and then remove the float bowl and ses if there's much fuel in there? If there isn't much, then it's a supply issue, and could be a sticking float or a sticking needle valve?

T.C.

[Toolmaker Tim]

Did you check your bowl vent? if that isn't working it might lean out hte carb because the bowl can't keep up with demand. Just a thought.

[MrOzz]

Hey Ozz,

From what you described, that sounds like the culprit, a sticking non-dropping float so the valve isn't opening to allow enough fuel flow to keep the bowl filled. You could do an experiment, run it till it starts popping, then quickly shut off the fuel, and the bike, and then remove the float bowl and ses if there's much fuel in there? If there isn't much, then it's a supply issue, and could be a sticking float or a sticking needle valve?

T.C.

Sounds like a good idea. I will compare the fuel in the bowls.

Did you check your bowl vent? if that isn't working it might lean out the carb because the bowl can't keep up with demand. Just a thought.

I was thinking that also. I cleaned everything so far the carbs were nice and clean.

I am having a brain fart. When you measure the float level that is with the gasket removed?

[bikerphil]

When you measure the float level that is with the gasket removed?

That is correct.

[DGXSER]

Yep, Gasket removed for float level. You may also check the fuel T itself for any debris or the screen on the float valve.

I would also think this could be the bowl vent. I am sure you already have, but make sure you spray cleaner through that vent passage.

[MrOzz]

That is correct.

Yep, Gasket removed for float level. You may also check the fuel T itself for any debris or the screen on the float valve.

I would also think this could be the bowl vent. I am sure you already have, but make sure you spray cleaner through that vent passage.

Thanks guys. Glad I have WiFi. Keep my laptop next to me while working. Makes life a little easier.

So far, the screens were clean. The vent passage clean also.