Erratic idling / Cylinder not firing / carburetor spitting back

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Olliefraga

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Alright, what happen was…

I am a US Navy Sailor and last year I went to an unexpected 9 month deployment where I had to leave in a moment’s notice. As you might be thinking already, no I did not have time to “prepare the bike” for the time. Just the usual trickle charger.

I came back, happy and ready to put her back on the road.

Oh boy!

First thing… Gas going all over the place when the fuel pump started to “tick”… Did not start.

Had to have a fire extinguisher nearby. THAT MUCH fuel. Tried 2 more times, same result.

Left her alone for 24 hours for all that fuel to evaporate.

Decided to disconnect the fuel pump. Tried to start again, one of the exhausts (I have 4-4 Cobras) started to vomit gasoline. She started to come back to life, little by little with the help of the choke.

Ran until the carb bowls were emptied.

(My stupidity… I should have drained the bowls… )

Connected the pump again… this time there was no fuel spillage. I figured it was just a stuck float.

Tried to start again, this time she would not stay idling without the choke and one of the cylinders was not firing (cold air coming from the pipe and the engine on that cylinder was just warm)

Came to this awesome forum and read all the signs that led to perform a shotgun cleaning method and so I did… After the cleaning and inspection of the diaphragms, springs and o-rings, I saw some, no much white crud in the fuel mixture screw and spring (the tiny little o-ring at the tip seemed hard but it was too small for a precise analysis.), cleaned all up with a brass brush and cleaned averything with WD-40.

While I was at it and for good measure since I was cleaning the carbs and the previous fuel spill in the cylinder, I exchange the sparkplugs (NGK 4292) and changed the oil (Rotella T4 15W-40).

Now the back starts a bit easier but I’m not out of the woods yet.

As I am testing the bike, the idling goes up and down from 1k to, 3 to 4k rpms, there is some back spit /pressure from the carbs and the cylinder that was dead seems to want to come back to life coming in and out. Throttle is sluggish. After about 10 minutes I can now disengage the choke and and she goes on her own but idle is still erractic.

Hooked up my homemade carb sync tool and the vacuum reader dials are almost at rest with the needle very low. The slide the carb is not is not “shaking” like the others are (yes I removed the airbox) moving.

I feel like I am missing something here (besides talent of course). Any help is greatly appreciated.
 

02GF74

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Firstly good to hear you are back safe after serving your country.

My money is on the pilot jet being blocked, which is common after a prolonged period of no use.

Also check the choke plungers return fully when choke is off.

Mine did similar. The carbs need to come out. I bought mine after it had been standing so the first time the pilot jets were solid with crud and required a sharpened needle clear them.

Second time, after 6 months ( winter and covid restrictions) easier to clear.

Now once or twice a week I'm turning on the ignition to keep the float bowls full.
 

Zeus36

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Alright, what happen was…

I am a US Navy Sailor and last year I went to an unexpected 9 month deployment where I had to leave in a moment’s notice. As you might be thinking already, no I did not have time to “prepare the bike” for the time. Just the usual trickle charger.

I came back, happy and ready to put her back on the road.

Oh boy!

First thing… Gas going all over the place when the fuel pump started to “tick”… Did not start.

Had to have a fire extinguisher nearby. THAT MUCH fuel. Tried 2 more times, same result.

Left her alone for 24 hours for all that fuel to evaporate.

Decided to disconnect the fuel pump. Tried to start again, one of the exhausts (I have 4-4 Cobras) started to vomit gasoline. She started to come back to life, little by little with the help of the choke.

Ran until the carb bowls were emptied.

(My stupidity… I should have drained the bowls… )

Connected the pump again… this time there was no fuel spillage. I figured it was just a stuck float.

Tried to start again, this time she would not stay idling without the choke and one of the cylinders was not firing (cold air coming from the pipe and the engine on that cylinder was just warm)

Came to this awesome forum and read all the signs that led to perform a shotgun cleaning method and so I did… After the cleaning and inspection of the diaphragms, springs and o-rings, I saw some, no much white crud in the fuel mixture screw and spring (the tiny little o-ring at the tip seemed hard but it was too small for a precise analysis.), cleaned all up with a brass brush and cleaned averything with WD-40.

While I was at it and for good measure since I was cleaning the carbs and the previous fuel spill in the cylinder, I exchange the sparkplugs (NGK 4292) and changed the oil (Rotella T4 15W-40).

Now the back starts a bit easier but I’m not out of the woods yet.

As I am testing the bike, the idling goes up and down from 1k to, 3 to 4k rpms, there is some back spit /pressure from the carbs and the cylinder that was dead seems to want to come back to life coming in and out. Throttle is sluggish. After about 10 minutes I can now disengage the choke and and she goes on her own but idle is still erractic.

Hooked up my homemade carb sync tool and the vacuum reader dials are almost at rest with the needle very low. The slide the carb is not is not “shaking” like the others are (yes I removed the airbox) moving.

I feel like I am missing something here (besides talent of course). Any help is greatly appreciated.


Hey Ollie, former Navy Helo Aircrewchief from VXE-6 in the mid 80s here.... Some advice for the next time: There may have been fuel leaking into your cyliners as it was puking out your Cobra pipes. One of the first things you should do with excess fuel after sitting is to pull all four spark plugs and spin the engine to blow out any gasoline in the cylinders. Engine damage from hydrolock or partial hydrolock (engine stall) can be a bent connecting rod, crack in the crankshaft, fractures in the cylinder walls, blown oil seals in the cylinder head...

Hope it's just carb related like 02GF74 says.

Pull the new plugs and tag them, then take a picture of each one. Post the pictures here .

Which cylinder was not firing?

1633045614824.png
 

Fire-medic

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Ten minutes with a phillips or a JIS screwdriver, to drain the float bowls probably would have prevented that. You need to yank the carbs, split 'em into two pairs, and pop-off the float bowls, remove the jet blocks, and their three jets, and clean the carbs. I suggest having new jet block gaskets on-hand, as they often tear when the jet block is removed. Removing the CV caps, don't lose the tiny O-ring at the bottom 6 o'clock position. To get the bike synched properly, and to see it rev, you need the airbox on and secured. While the bike will run w/o it, it won't rev properly.

VMax carb choke out of adjust..jpg VMax carb float area.png VMax carb jet block gaskets.jpg VMax carb pairs left and right.jpg VMax carbs disassembled diaphragm side.jpg
 

DJHess

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Ollie, thanks for your service. I have experienced similar issues with my 2000 VMax. After cleaning the carbs and re-installing them my VMax idled so fast I had the idle adjuster all the way out and it still idled at 1200 RPM. I spent several weekends trying to find out why. I had other problems too. It would crank and run great but often would not crank after a short ride the battery would often not crank the engine. I purchased a new battery and that helped with the rough idle and hot cranking failures. Soon the symptoms returned. I changed the voltage regulator and again it was better for a short time, then the gremlins came back. These odd symptoms have come and gone for the last 2 years and I have not ridden very much because of them. A few months ago it seemed to be fixed and running great again, but then a Non-Ethanol Gas shortages here in GA. forced me to put some E-85 in it. I added some fuel stabilizer hoping to neutralize the E-85 turning to water. Next day it would not idle again during a short ride and I frantically rode home.

During the investigation I discovered a rusty tint in the gas filter and decided to disassemble the fuel system. When I drained the gas tank by removing the drain plug chunks of rust poured out. My tank had an unbelievable amount of rust. I had to remove the tank and clean and seal it with a KBS kit. After that I put in a clear gas filter so I can see what the fuel looks like when ever I want. I removed and cleaned the carbs discovering I had two split intake seals between the carbs and V-Boost. Probably the cause of all the idle issues was the air being sucked in through the split intake seals and maybe some dissolved rust from the tank.

Also when I reassembled the carbs and installed them I noticed you have to really push them down onto the intake or they will suck air there. I can't believe the difference. It hasn't run like this in years. I still need to balance the carbs. I only have a cheap vacuum gauge set which helped but I have more vacuum on carbs 1 & 2 than on 3 & 4. Hope all this rambling helps someone.
 
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I'm a newbie with a recently purchased 85 with 17K miles. I'm having similar problems as Ollie so I am taking the carb out but..... It will not budge. I disconnected everything by the manual and loosened the 8 clamps and it won't budge a hair. So W-40 has made any difference. Any thoughts?
 

Parminio

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loosened the 8 clamps and it won't budge a hair. So W-40 has made any difference. Any thoughts?
To pull the carbs you only need to loosen the top 4.

Once you loosen them, and you need to loosen them A LOT (don't just loosen the screw three or four turns), then you need to break that clamp loose. Push on the screw itself and make sure the clamp turns loosely on the boot. That way you'll be sure that it's actually loose.

You have to remember: you're pulling a lip up past that clamp, so you need a bit of slop in there to allow that. The clamp should rotate freely and have a gap in between it and the rubber boot before you even try to pull the carbs out.

Once you get that done, pull from the corner. Don't try to lift all 4 carbs at once. Grab hold of one carb and pull up and away from that corner.

Example: If you grab the number one carb which is the front left carb as you're sitting on the bike, pull up on it and sort of towards the middle of the carb group.

Once you get one carb broke loose the rest should pop right out.

You put it in the exact reverse way. Pushing all 4 carbs down at once normally doesn't work. You have to get one of them in, then the others will follow.

EDIT TO ADD: You may also have dry rotted boots, which will make it much harder. In that case go ahead and loosen the bottom clamps up just as much as you do the top ones. That way it can break loose from top or bottom. Just stick with it. You'll get them out eventually. Replace the boots if they turn out to be dried up and hard.
 
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desert_max

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If you have a heat gun, I would strongly recommend heating up the rubbers the carbs are seated into until they stink. If they are old and hard they won’t let loose until they’re a little more pliable. Heat helps a lot. A LOT.
 

02GF74

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Undo the clamps, then insert a screwdriver between the rubber boot and carb body and carefully prise the boot from the carb, squirt a bit of wd40 ino the gap.

Once you have done as much as you can on all 4 boots, try to put off the carbs.

If that fails, use a piece of wood to lever up the carbs (is what I had to do) bur be careful where you put the wood to avoid breakages.
 

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