Topic: I fought my bike and my bike won

[Magilla]

idle mixture screws will affect the idle mixture. I turn mine all the way in and then back out, I believe 1.5 turns each. there are two holes at the intake side of the carbs. one goes to the idle jet and one goes to the idle mixture screws ( it think) both passage ways need to be clean for proper operation. if the idle jet passage is not clear it can cause rich readings due to poor atomization of the fuel according to what I read in my hondaman book.

Do you have a picture that you could post?  My manual is awful.

[Really?]

link with pics provided above

[Roach Carver]

I dont. To clean those, you will have to pull the airbox. If you go that far you might as well pull the carbs. Honestly I find that when I try and cut corners I spend more time then if I had just bit the bullet and done it right in the first place. If it were me I would get those carbs off the bike and do a proper clean up and I think you will be happy you did. Once they are clean you can get by with the little clean up on the bike but it sounds like these carbs ned a thorough cleaning.

[iron_worker]

Some carbs have air bleeds (mine does - 1974 CB750) so if you turn them out you get a leaner mixture. Some carbs control the fuel and turning them out causes a richer mixture. I am not exactly certain what year the change was made.

IW

[Magilla]

The fact that the bike still starts with no choke concerns me.

In regards to the idle air screws, when I turn them out on cylinders 2&3 the bike revs higher and I then need to adjust the idle screw.  When I do the same for cylinders 1&4 it makes no difference in RPMs.

I am certain that ther is no clog in the idle air holes.  I cleaned them yesterday.  I am uncertain if the spring is in the hole. I've got to go pull them and check.  What would happen if the spring was missing?

[Roach Carver]

It will catch fire.


Jk. I dont know.

[Magilla]

Update:  when I went out to the bike today the air box was dripping gas.  Not a good sign. No gas was dripping from the overflow tubes.

 I removed the air box, pulled the bowls and recleaned everything.  I removed the jets and cleaned them.  The small jet is a 40.  There were no readable markings on the larger ones.  I checked each overflow tube to verify it was clear.  They are. I cleaned and recleaned everything.  I also cleaned the air idle screws and ports. I put it all back together and fired it up.  It fired right up with no choke required. 

I took it for a ride with no air box installed.  It ran real strong.  The best it has run so far.  Everything felt good.  Then I pulled the plugs.  BLACK.  Lots of carbon.  Still running rich. 

[phil71]

Well... the overflow tubes should have been leaking, so they may not be clear.. Sounds like you are a little unsure just what to be cleaning. There are a few circuits there that need to be chased , I like to use guitar strings, then air.
Rich condition can be spark related too. What is your voltage when running? Are you certain the points are set properly? Do you have a honda manual ? No one has said it yet, but their 3000 mile tune up check list should get you back to a good place for testing?

[Magilla]

I used gutair string to clean the jets and overflow tubes.  I also used carb cleaner and 60 pounds of air pressure.

I am going to have to check the points again.  They must be off.  Also I changed out the coils and I get the same results with either set of coils.

Would a timing issue allow the bike to start cold with no choke?  That is throwing me off.  I'll keep trying and someday I will get it right.  As you can tell I'm learning as I go.

[750K]

From my experience with carbs you really should pull the whole rack off the bike and not only pull and clean the jets but all the passages in the carb body. Spray carb cleaner or soak it and blow out all the passages as well as the jets etc, then you'll be sure all the circuits are clear as well.

[TwoTired]

If the carbs are overflowing you have a float/float valve issue. 

Did you remove the floats and the float valve?  The float valve has a spring pin on the end where the float "tang" hits it.
Does that work smoothly?  Does the float valve move freely in the seat/holder?
If you have brass floats, do they look crushed /expanded or properly formed??
If you shake a brass float, does it have gas inside it? (eliminate sunk float possibility)

If the float system is not working properly, the carb overflow upsets the mixture delivered to the engine.

If you had gas collecting in the filter box, how do you know it didn't also travel though the intake runner, past the valves, the piston rings and pollute the oil supply?

The engine may not need choke to start if the O.A.T. is high.

Are you parking on center stand or side stand?

[ekpent]

You are running the bike with the choke lever on the side of the carbs in the total down position. Just askin  Mine definately likes a little choke to start. Lever up choke on,lever down choke off.

[Magilla]

Choke level all the way down.

[phil71]

not needing to choke tells you nothing.  I have a couple of different 750s in good state of tune, and if it's over 60 degrees, they don't need choke to get going.

[750K]

Correct me if I'm wrong but isn't it a sign of running rich if you pull the airbox off and it runs  better? That would probably be another indicator of why you don't need the choke to start it up, my old 67 Volvo would start with almost no choke due to rich running. Once I set the mixture properly it was back to normal.

[phil71]

<sigh> there are still far too many unknowns here. Put everything to stock spec, then see what's what.

[phil71]

Wait a second.. You do know the main jet and the jet holder are two separate things, right? The behavior you mention sounds like a jet could possibly have worked its way loose of the holder. It would be the only way the idle would get richer , save for drilling or increasing the pilot jet, but you say they're "40" , so let's take it at face value.
76 carbs should still be the ones that don't need tools to remove, right? Drain and yank the bowls and see if the very bottom of each main jet looks the same.

[shinyribs]

RE: Fuel dripping out of the airbox but not the overflow.

It is possible that the overflow nipples are clear,but the hoses they attach to are not. They can get pretty crummy sometimes.

[Magilla]

Wait a second.. You do know the main jet and the jet holder are two separate things, right? The behavior you mention sounds like a jet could possibly have worked its way loose of the holder. It would be the only way the idle would get richer , save for drilling or increasing the pilot jet, but you say they're "40" , so let's take it at face value.
76 carbs should still be the ones that don't need tools to remove, right? Drain and yank the bowls and see if the very bottom of each main jet looks the same.

The main jet has a flat head has a flat head slot in it.  It sits inside a brass holder that requires a 9mm socket to remove.  Do I have this right?  If so all 4 main jets are so tight in the holder I fear I would strip the flat head slot if I forced it.  So I left them together and cleaned them as a unit.

Also last night I re removed all of the float bowls, removed the floats and removed the brass port that the float needle sits in.  I cleaned and inspected them all.  Everything is spotless.  I put it all back together and checked for leaks and as of last night there were no leaks.  I will have to check again today.

I just can't figure out how to make it run leaner.  It starts good, runs good and has lots of power from low RPMs up to high RPMs.  It just runs real rich.

[ekpent]

Since those main jets are not marked with a number or a sylized 'K' logo for stock Kehin or somebody filed of the numbers because they were bored,or junk aftermarked,different brand,who knows, a good idea may be to select a jet size you would deem appropriate and purchase good known new.Stockers ranged in size from #120 in 1970-71 down to 105 in 76. A #110 may be a good starting point. Will have to re read your post again to see what your running as far as exhaust/air filter etc. But thats where you start to lean it up.

[iron_worker]

Do your carb vent lines attach to your airbox? This is the only way I can think of that gas could be getting into your airbox. Unless your bowls are filling so high with gas that it's reaching the level of the carb venturi ... which is bad...and would indicate that your overflows (brass rod attached to the middle of the bowl) is plugged (or the rubber hose that attaches to the nipple on the outside of the bowl is blocked. However if your needle and needle seat are working correctly it should not allow the fuel to enter once the bowl is full.

If your vent lines are attached to your airbox AND you your needle/needle seat are not closing properly then you may be drawing a vacuum on your vent lines and drawing fuels up and into the airbox ... which would cause it to run ....RICH!

Taking the airbox off would definitely lean the mixture so the fact that your bike runs better without it confirms that you are correct and it is in fact rich.

I would suggest to you that you check out your carb vent routing. If it it attached to the airbox ... should it be?

My next test for you would be to remove the float bowls one at a time. Turn on the fuel .... fuel should flow out of the needle/needle seat when the float bowl is down. When you push it up the fuel should stop. Does it? You shouldn't have to push it hard at all... The flow should actually stop completely before the float reaches the base of the carb body.

If the fuel does not stop you either have a faulty needle/seat or the tang on your float is way out of adjustment and not contacting the needle at the correct angle.

*Note* to get my main jets out of the jet holder I had to use vice grips on the jet and a wrench on the holder.... not ideal but it worked. You should note that it's probably not really necessary to remove the main jets. If you pull the holder out you will see the emulsion tube. That is where it will require cleaning, if any. The larger ports don't clog up as easily as the pilot jets.

IW

[Magilla]

One other thing to share.

Fuel bowl:  at the first removal of each bowl, bowl 1 had crap floating in it.  The other 3 bowls has a small amount of residue in the bottom of each one.  Almost not noticeable.  Each bowl has been pulled at least two more times after running the bike. All bowls are clean each time they are removed.  Also the float needles were in good shape as we're the tiny filters on top of the float port assemblies.

The first time I removed the main and slow jets:  all four were very clean with no sludge or residue on them.  One the main jet there are two large diameter holes that were all fine.  There are two small diameter holes that had a slight buildup on them.  The inlet ports were residue free.
The slow jets looked great.  No residue of any kind.
All jets were cleaned with carb cleaner and gutair wire.

The idle jet screws were dirty but not blocked.  They were cleaned as we're the springs and ports.

Not sure if this info helps but I am trying to provide as much detail as possible.

[Magilla]

Do your carb vent lines attach to your airbox? This is the only way I can think of that gas could be getting into your airbox. Unless your bowls are filling so high with gas that it's reaching the level of the carb venturi ... which is bad...and would indicate that your overflows (brass rod attached to the middle of the bowl) is plugged (or the rubber hose that attaches to the nipple on the outside of the bowl is blocked. However if your needle and needle seat are working correctly it should not allow the fuel to enter once the bowl is full.

If your vent lines are attached to your airbox AND you your needle/needle seat are not closing properly then you may be drawing a vacuum on your vent lines and drawing fuels up and into the airbox ... which would cause it to run ....RICH!

Taking the airbox off would definitely lean the mixture so the fact that your bike runs better without it confirms that you are correct and it is in fact rich.

I would suggest to you that you check out your carb vent routing. If it it attached to the airbox ... should it be?

My next test for you would be to remove the float bowls one at a time. Turn on the fuel .... fuel should flow out of the needle/needle seat when the float bowl is down. When you push it up the fuel should stop. Does it? You shouldn't have to push it hard at all... The flow should actually stop completely before the float reaches the base of the carb body.

If the fuel does not stop you either have a faulty needle/seat or the tang on your float is way out of adjustment and not contacting the needle at the correct angle.

*Note* to get my main jets out of the jet holder I had to use vice grips on the jet and a wrench on the holder.... not ideal but it worked. You should note that it's probably not really necessary to remove the main jets. If you pull the holder out you will see the emulsion tube. That is where it will require cleaning, if any. The larger ports don't clog up as easily as the pilot jets.

IW

The vent tubes do not connect to the air box.  They drain in front of the rear tire.  I did the float test with the bowls off and each one seems to be in working order as of last night.  Also the flow stops prior to the body of the float touching the body of the carb.  It works by lifting the needle into the slot and closing the fuel in port.

[ekpent]

I will dump a little more gas on the fire.
  The only bikes that I have noticed those little filter screens on top of the float needle holders in the past were off 75-76 F model engines.I had a 76 K model and do not remember having them but hopefully some other 76 K guys can report on that.
  Just for fun post the serial number off the engine sometime so we can verify its year and model.
  A quick check of the petcock bowl,if its a 76 should screw off,and the filter screen can give quick clues if the tank is passing debri.
  I have had gas go into the airbox before when the overflow brass tube or line is plugged,has to go somewhere.Those tubes and hoses need to be clear for the whole circiut to work correctly.  Are you turning the petcock off when you are done with it. They are not vacumm operated but  mechanical.

[Magilla]

I left the petcock on the night the air box had gas in it.  Also I pulled the petcock and changed tanks.  The tank that it on it is completly debris free.  I will post some pictures of the carbs and plugs,