Popping thru carb.

First carb from left while sitting on bike has been giving me fits. It pops thru carb and misses when letting out on clutch and when cruising at low throttle. I have checked float ( level is at base of float bowl where screws are), cleaned and cleaned carb.. Every hole carb cleaner is sprayed in is clear. Checked diagram.. Plug on that cyl only is soot black. Other three look a little lean. Plugs are new, Complete dyna ignition. (not that matters) Pilot jets are the stock 37 (which are being changed to 40) bike has pods and header.
At full throttle or when easing into throttle slowly it runs ok. Doesn't miss or pop in neutral while revving.. Any ideas

76KZ900 wrote: First carb from left while sitting on bike has been giving me fits. It pops thru carb and misses when letting out on clutch and when cruising at low throttle. I have checked float ( level is at base of float bowl where screws are), cleaned and cleaned carb.. Every hole carb cleaner is sprayed in is clear. Checked diagram.. Plug on that cyl only is soot black. Other three look a little lean. Plugs are new, Complete dyna ignition. (not that matters) Pilot jets are the stock 37 (which are being changed to 40) bike has pods and header.
At full throttle or when easing into throttle slowly it runs ok. Doesn't miss or pop in neutral while revving.. Any ideas

Insufficient intake valve clearance could result in the reported symptoms.

If not already done, would assure that valve clearance of the intake valve is within specs.

Insufficient compression -- for whatever reason -- often results in a sooty plug (due to incomplete combustion), which insufficient compression may be due failure of a valve to completely seal. Would check clearance.of both intake and exhaust valves.

Backfire through the carb may result from failure (for whatever reason) of the intake valve to completely seal when it's closed.

A leakdown test could help diagnose failure of a valve to completely seal. Then it becomes a matter of determining why the valve isn't fully sealing when it's supposedly closed, such as insufficient clearance, burnt valve, cracked valve, bent valve, damaged seat, need for grinding, etc.

A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).


Good Fortune!

It appears you have the air injection system. Try capping off the two ports that control it. You have pods already causing a lean condition. Intake boots leaking just a small amount can cause this.
Steve

I tried to include all pertinent info but left two three things out. All pollution stuff has been removed. Including caped the reed valve ports. Also recently did compression test all cyl above 130. Sorry for lack of info on first post as it was pretty late when I posted. Intake boots are brand new and compression on the cyl I'm having trouble with is 160 psi.

76KZ900 wrote: First carb from left while sitting on bike has been giving me fits. It pops thru carb and misses when letting out on clutch and when cruising at low throttle. I have checked float

Using clear tube? Mine pops when the fuel level is too low.

Yes clear tube. If anything I'd say it was a little high. It's pretty close to bottom of base where screws hold float bowl on. I believe 4mm down was where it was supposed to be. I took carbs off again and noticed that slide was stuck up (open) way more than rest. I pushed it up and it came back down to same spot. Took carbs apart again checked diagram reassembled it (the slide) was where it was supposed to be but I'm guessing it won't stay. So maybe new slide is in order ?

76KZ900 wrote: . . . compression on the cyl I'm having trouble with is 160 psi.

With a too tight valve, the cylinder will lose compression as the engine reaches normal operating temperature.

That's one reason why a compression test alone isn't enough, and why it's also important to assure correct valve clearances.

Good Fortune!

I have a leak down tester but haven't done it yet. After seeing slide stuck up I'm pretty convinced problem is in carb. I warmed engine before taking compression test

You might have a burr or crud still in the slide bore or on the slide itself.
Steve

swest wrote: You might have a burr or crud still in the slide bore or on the slide itself.
Steve

My thought as well.. I work midnights so it will likely have to wait until my next days off. I tried taking it for a ride with no pods on it.. What a mistake lol thought maybe I could check slide to see if it was moving and closing. Bike ran pretty bad with no filters on. Bike ran great when I got it with the exception of the way over rich condition. PO had 148 mains but never touched the pilot jets. I've ordered a set of 40 pilots and changed the mains to 135. I believe this is also the carb that the emulsion tube falls out after jet is removed. Ill probably order a new slide/diagram then carb body from ebay if I don't get it figured out.. Just sucks when you create problems lol

I just got some new diaphragms for my keihin cv34s from a company called JBM industries. Super good quality and easy peesy install... The website is a bit jumbled but has tons of carb/diaphragm info and shipping is the same rate for 1 diaphragm or 100...

Do the thumb test first.
Steve