More carb problems. 1982 Spectre 750

Alright. I have not worked on the bike in about a month or so, and i took my carbs out again. To check them again. Before doing this when the bike would run, cylinder 2 and 3 would randomly backfire into the airbox. I took the carbs out and carb 3 had a very very small pin hole in the diaphram. Im not looking to spend $120 on a new diaphram. So i looked through forums and some people used bicycle tire patches. Well i went to walmart. bought 6 for 2$ and i pactched the hole. All i did was cut a small enough piece off the circle patch they gave me and put it on both sides. The diaphram retained its original flexibility. I checked all the other carbs and found no problems with the diaphrams. SO i put it all back together and hook my aux tank up and i had the battery tender on Turn the key and crank. Bike sputters a few times and fired up. With the choke on the bike was sitting at about 1000 rpms. If i turned the choke off it would die. I let it idle for a minute or two and it started to rev up if i turned the throttle then it would not rev up at all without dying. I turned te choke off and it raised the rpm to maybe 1100 rpm. I have cleaned these carbs out probably 6 or 7 times and i followed pattons advice and made sure i got ALL ports. I just dont know what else could be causing this. I dont know if i mentioned it but cylinder 3 no longer backfires. Just cylinder 2 randomly. Any help would be greatly appreciated.

Also checking temps on the heards with my infared temp gun the 1,3,4 cylinder were around 750 degrees and the 2nd was only 225

Also if it would help i could make a video of it tomorrow.

It does sound like it's only firing on 3 cylinders and not really firing on #2. Use a spray bottle to spray water on the pipes as they exit the engine - or if you're crude like me just spit on em. The water should sizzle right off. if it just evaporates then the cyslinder is not firing and it becomes a case of checking for spark, fuel and compression. Hopefully it's something simple.

JR wrote: ... a case of checking for spark, fuel and compression....

If #2 and #3 spark plug wires are long enough, could swap them to see whether the misfire moves from #2 to #3.

This could help with further diagnosis.

Could also remove the spark plugs;
hold #2 and #3 plug bases against the engine head;
turn ignition switch ON;
spin over the engine;
observe for fat blue sparks while engine is spinning over.

Assurance of fat blue spark is a good place to begin diagnosing lack of combustion within a cylinder.

When finished testing for plug spark, remember to turn the ignition OFF.

Good Fortune!

i will try this tomrrow.

Well, i switched the plug wires. and nothing changed. I took the spark plug out and held it to the head while cranking the motor and it has a bright blue and yellow spark. It is also gapped to approw .30. That number 2 cylinder still randomly misfires and is still about 300 degrees cooler than the other three cylinders. I made an HD video and i will try uploading it later and see how it turned out.

so i guess theres something clogging up the carb still. I rechecked all the diaphrams today just to make sure. So i guess ill take that carb apart and see what i can find. As far as how good of a cleaner it is should i go buy a gallon of carb dip and let it soak for 20 minutes or should i boil it in lemon juice?

If not already done -- and before further addressing the carbs -- would perform a compression test on #2 cylinder AND assure valve clearances are within factory specs in #2 cylinder.

And would also re-test using a brand new NGKB8ES spark plug in #2 cylinder. Because sometimes a plug will fire okay outside the cylinder, and then won't fire when installed.

This should hopefully rule out possible issues with either spark or compression in #2 cylinder.

Good Fortune!

I will test the compression and get a new spark plug tomorrow.

To be absolutely assured that the pilot circuit in the carburetor is clean:
Get a good spray carb cleaner.
Take the little straw and cout one end off at a 45 degree.
Remove all your rubber shit from the carb and all jets/mix screws etc.
Re-insert the mixture screw (if applicable) without its ruber oring, and set it to default position.
Using the spray cleaner and straw, put the straw all the way down inside the pilot jet hole taking note that the open 45 end is facing the direction of the jet passage/tube cut into the casting.
Spray the cleaner like this while looking into the bore of the carb, and you should see a nice even squirt of carb cleaner coming out of all the small pilot holes in the carbs bore.
Repeat this for all the carbs, taking note to assure they all spray the same.
Best to follow with 100psi of compressed air if a clog is found - and the 45'd straw can be used to shoot cleaner backwards into bore holes as well!

This is the only sure fire way to KNOW that the fuel is doing the same thing as the cleaner when your running the bike.

I also have a set super small drill bits that I use as feeler guages to mae sure that knowone has tampered with the air jets on the intake side of the carbs - assuring they are all the exact same size.

Good luck! -and make sure there arent any air leaks.

Have you checked for vacuum leaks? Sprayed some carb cleaner around the intakes while Idling? #2 carb would normally hook to the Vacuum petcock, is the diaphragm there in the petcock leaking vacuum?