Topic: 1978CB750F3 cylinders running at Different temps

[DWS]

1978CB750F3
 Carb's 42A
stock air box
4 into 1
#35 slow jet
#110 main
4900 feet elevation
Timing is at --1&4 F mark now
advance,  not sure what i was seeing timing light.
Number one cylinder running around 190 to 210 Deg
Number 2, 3, 4 are running close to each other, around 530 Deg
write out of the exhaust pipes, where it makes the first turn.
Not sure why?  maybe valve adjustment?
have not adjusted the slow screws either, not sure how?
i have not synced the carbs yet either. (need tool).
Timing jumps a little on 1&4 and 2&3 when looking at it with light.
Changed plugs from Cyl 1 to 4 and it does not follow the plug and or plug wire.
When i rump on the throttle it die's. (pump)
At idle just above 1000rpm it rev up with very small turns with the idle screw and sometimes it will settle back down on its own.
and have to use the choke to control the rpm in till it gets to operating temp.

[flybox1]

If you moved the plugs between 1/4 or 1/2 and the temp did not change as originally found, then your problem is more than likely fuel level in carb 1. Have you verified float height level and whether the jets on the carb are truly, actually, properly clean?

Synch your carbs too. Then re-test for temp variances. 190-210 is barely firing. 500 at the header is almost overheating. If you're running the engine (idling/revving) for prolonged time while sitting in the garage, you're over-heating it. It needs air circulating to cool it.

So you may be low on fuel in 1, too lean 2, 3 and 4. But your info didn't provide enough details to discern this.

+1
get a new set of D8EA plugs, put them in, and let it idle under a fan for 3-4 minutes
pull the plugs and check the deposits.
I bet you are really lean (your #35 pilot jet, [and a little bit your elevation] is/are hinting at this)

[DWS]

thanks guys i will get a big fan and help cool the engine a little and riching the carb out from 1 3/4 to two turns out. Hondaman also said to check compression, so ill do that too and get back.
 thanks for the help

[flybox1]

thanks guys i will get a big fan and help cool the engine a little and riching the carb out from 1 3/4 to two turns out. Hondaman also said to check compression, so ill do that too and get back.
 thanks for the help

'Clear tube test' for fuel level on all carb bowls easily, as your PD carbs drain out the overflow tubes when the drain screw is loosened....Fuel level needs to be verified correct, first, before any fuel screw or jet change shoudl be made.  You cant enrichen the idle circuit if no gas is there to begin with....
How do you know how much to turn it out when you dont have a baseline?  Do the clear tube test, and then the idle circuit plug reading to see where you're starting....

[DWS]

OK Did the clear tube test and all four are over flowing out of the carb itself, don't understand that because i did a vacuum test before putting on bike all four were sealing above 15 pounds.
Floats look good, not new but floating in gas as we type.
needle on all four are new, boots are hard, and clamps will not tighten anymore

[DWS]

 

[CB750F2]

Those carbs vent via a small hole in the body above the float chamber and also via the overflow stand pipe. So during the clear tube test the vent via the stand pipe is blocked and if the hole at the top of the chamber is also blocked flooding occurs. Check the holes at the top of the body. I think that they are all tubed together and the common tube is routed to the air box. Pat

[flybox1]

Clean your tank.
Ensure your in tank filter is good....if not, get an inline filter.
Replace all four float needles, they are rubber tipped and become hard, and not seal.   If gas is flowing into the carb, your float valve is not sealing.  Dirty gas, bad needle, or poorly set float height. 

[DWS]

Tank not on bike, using other device for now, but tank does look like a new tank right now, all float needles are all new, vacuum tested them before putting on bike all was good there, float heights is dead nuts to 14.5 mm and level, it looks like in all four carbs the gas is flowing out of the small tubes closes to the pump riser (for acceleration) right at the bottom inside mouth of the carb's opening intake side.

[flybox1]

Tell me how to vacuum test a float valve....

[DWS]

that would be the float needles,  pressure test, but here is a video, mine did not leak and stayed around 15 pounds or so.
starts at 1:12
url]http://youtu.be/8wg3VJ1STSM[/url]

https://www.youtube.com/watch?v=EGbf9S38bAc

[enwri]

Those carbs vent via a small hole in the body above the float chamber and also via the overflow stand pipe. So during the clear tube test the vent via the stand pipe is blocked and if the hole at the top of the chamber is also blocked flooding occurs. Check the holes at the top of the body. I think that they are all tubed together and the common tube is routed to the air box. Pat

Those tiny little vents are hard to reach when the carbs are on the bike, Get your "Ninja Fingers" on, mine are between 1-2 and 3-4 carbs in the horns facing each other, no tubes on my k7. Small enough that even having a drop of water or fuel blocking them will stop the clear tube test from working, making it flood. Also if they are blocked, any water or fuel forming a drop in the end of the overflow tubes will cause that carb to misbehave until a bit of throttle on, pulls the drop up and breaks the surface tension and lets it breathe at least a bit better until the next drip blocks it again. Cut the overflow tubes at an angle to help the drops break, and position them off to the side away from water flinging off the tyre. Chased what I thought was an ignition problem in the wet (dropping cylinders off and on) until I pulled the overflow tubes off while running in the rain and fixed the misfire instantly. Found those little holes and cleaned them next.

[flybox1]

that would be the float needles,  pressure test, but here is a video, mine did not leak and stayed around 15 pounds or so.
starts at 1:12
url]http://youtu.be/8wg3VJ1STSM[/url]

https://www.youtube.com/watch?v=EGbf9S38bAc

good video.  take into consideration debris in the gas flowing down the fuel line and blocking the float valve from closing, causing leaks.  you dont want this ruining your good work.  the only cure for this is a clean tank, and known good filter (in tank or in-line)

once you get the bike back on, crack open the bowl drain screws, and then turn on fuel.  allow the gas to drain out the overflow tubes and into a container.  one at a time, close the bowl drain screws.  gas should immediately stop flowing out the overflow tubes. this is also a good method for dislodging debris holding a float valve open.

[DWS]

thanks for the guys!
ok, my gas is clean and and using clear tubing to see if any debris is there but i still have a in filter just in case there is, what is weird is that all four carbs are leaking out of the same little tube that is in the throat of the carb, if i squeeze the gas line going to the main inlet of carbs you can see the pumping/squeezing action from the tubes in the front intake of the carbs throat.

[flybox1]

with the carbs on the bike, give us a picture of a clear tube test on the #1 carb. and point to the tube the gas is coming out of in your ^ description....

[DWS]

took air box off and found all four carbs over flowing over / thought the main jet and out the intake of the carbs all four. I have carbs off bike, took apart and really did not find anything really wrong, floats are at 14.5 and level on all and put back together and no leaks, don't get it.
But still my accelerator pump not working, all holes are clean. it looks like the accelerator pump rod it not getting depressed, weak spring maybe?
i'll get you a pict tomorrow.
Thanks
Modify message

[enwri]

The holes in the throat opening are the air inlets for the emulsion tube air supply, and the mixture screw air supply.
If they get filled with fuel while flooding, fuel will sit in the passage until it is removed either by running the engine or manually blowing it out. The exposed area of fuel to the air in the small passages is too small for it to evaporate quickly and surface tension will prevent it from just flowing out when stopped. Drain the bowls and blow the passages out after each flooding event. Only takes a drop of fuel to effectively block a vent or small passage, without any real pressure differences in the carb to dislodge it. (static testing , opposed to running ).

[enwri]

pulling them apart may have removed the residual fuel in the passages.
 fat Orings can squeeze over the acc. pump outlet in the bowl blocking the pump passage into the carb,

[DWS]

thank you for that Enwri.
Thats what i thought too, so i looked for that on the oil ring, tried defer-rent sizes already,  if i remember it is 4mm*1mm now,  needs to be closer to 4mm* 1.3 or 1.5.      1.9 was to big.

[enwri]

I've got a box full of hundreds of o rings I can't use on this bike.
Got the spring on the right side of the pump diaphragm? (pushing it back up) Spring on the pump lever on the throttle shaft? I'm just guessing now, you or someone here will sort it.

I've been using one of those laser guided temp. sensors to find weak cylinders at idle, four into one makes it hard to tell otherwise, best thing ever.

[DWS]

spring on top not the pump, if i could i would attach some picts,  but it wont let me

[DWS]

I have small little leaks out of three leaking of the float bowl drain tubes. can barely see from two of them, unless you curl the tube up,    Is that why it keeps over flowing up the main jet then out the emulation tube to front side of the throat of carb? (bottom Picture)
and my pump is not working i think cause the little spring on top of the pump arm is weak.
Sweet pictures finally work, nice.
Need Help finding float bowl drain screws would be appreciated.
Thanks Duane

[flybox1]

if your fuel is the same across the board, as shown in your picture above with the zip-tie indicating fuel level in your yellow fuel line, your floats are set too low.
floats too low will RAISE the fuel level in the bowls and you'll get fuel draining out where it should not, as youve described.
The level in shown in the clear tube test needs to be betwen 3-4mm below the bowl gasket seam. 

its probably your method for measuring their heigths that is incorrect.
IIWM, id INCREASE all float heights by 2mm.

[DWS]

Just touching the shock on the needing, then measure

[DWS]

So you saying that they should be 3-4mm below the bowl gasket seam on each carb bowl, even if the measurements are different on each of the floats? makes sense since each bowl is going to react different over time. i guess a float can act different when there 30 years old and some areas on floats have been eat away.