Topic: 3 issues for a new member.

[KC750]

New to this forum.  I am also new to the Honda 750.  I just bought a 750 K4 and it is running fine but I do have 3 issues:

1. There seems to be quite a bit of carbon build up leaking out of the weep hole on the lower right side muffler.  The mufflers have black buildup caked on them (wipes off easily) and it drips for about 3-4 minutes after a 30 min ride.  Is this normal?

2.  After riding for 15 minutes the bike acts as thought it is starving for gas.  I pop the gas cap and it seems to get better.  I have cleaned the air hole in the cap but has no impact on the issue.

3.  On one of the inside over flow carburetor lines it leaks after a ride until all the fuel in the bowl is gone.  Any ideas on why the seal is not working or what is going on inside the bowl? 

Thanks in advance!

KC750

[ekpent]

Hello and welcome.
#1- Is the black build-up from running rich possibly. Spark plugs willhelptell the story.Running rich will create black smoke and leave soot. It is not normal for the pipe to drip from the weep holes unless there is a lot of moisture or condensation in the pipe. What is dripping out,is it oily or watery ?
#2- Does the bike have any fuel filters attached to the gas lines ? Is the fuel line routing good and the petcock clean ?
#3- This could possibly relate to a running issue from #2 question. Have you pulled carb bowl yet to have a look. Check for a cracked brass overflow tube or standpipe that may be allowing to fuel to run out of that bowl till empty if the fuel is running out the overflow line.
  May not be all the correct answers but a start of things to look for.

[KC750]

1. It is more oily than watery.  Plugs seem to be okay but will check again just to be sure.
2.  There are fuel filters attached. Fuel lines routing good?  They are the most direct path to the carbs.  Petcock is clean but I could re-check to be sure.
3.  Carbs have been completely cleaned including all new kits.  This bike had been sitting in garage for about 20 yrs and all the components have been either replaced or cleaned/inspected.  The fuel is running out of the bowl till empty which is the frustrating part.  Something isn't sealing off with this one bowl. 

I'll look a few things over and get back with you.  Thanks for your reply, ekpent.

[PeWe]

2. Tank cap might be rusty and the air vent is blocked. I have got that problem too, stop after 10 minutes ride. I called a friend that came with his car and a trailer. I swapped tank to another new one. Later on when I drained the fuel I noticed the fuel stopped flowing, opened the cap and it started to flow. I have a new cap for that tank.
I could have ridden the bike home if cap was open.

[Phinn]

Something isn't sealing off with this one bowl. 
.

Yes, the something is the float valve.

Gas flows down into the bowl (due to gravity an an open petcock). When it reaches max level, the gas raises the float which also lifts the valve up into the gas inlet hole, plugging it. It's kind of like a toilet tank mechanism.

Early valves were a metal-on metal seal, but later models switched to viton-tipped ones. The all-metal ones need to seat very well. Any irregularity in the valve (especially the tip), or debris caught between the valve tip and its seat, will cause a failure to seal.

Or the float could have lost buoyancy.

Or the hinge pin that holds the float could be corroded or dirty. (The hinge pin just taps out, but you have to be very gentle with the posts that the hinge pin fits into.)

Or the little tab on the float (on which the float valve rests) can develop a divot. The valve has a little spring-loaded plunger, and it can get stuck in the divot, throwing it out of vertical alignment. You can sometimes file the divot out, to make the tab smooth again.

Or the overflow stem can develop a long, vertical crack.

Or the o-ring on the bowl's drain screw could be bad.

[KC750]

Something isn't sealing off with this one bowl. 
.

Yes, the something is the float valve.

Gas flows down into the bowl (due to gravity an an open petcock). When it reaches max level, the gas raises the float which also lifts the valve up into the gas inlet hole, plugging it. It's kind of like a toilet tank mechanism.

Early valves were a metal-on metal seal, but later models switched to viton-tipped ones. The all-metal ones need to seat very well. Any irregularity in the valve (especially the tip), or debris caught between the valve tip and its seat, will cause a failure to seal.

Or the float could have lost buoyancy.

Or the hinge pin that holds the float could be corroded or dirty. (The hinge pin just taps out, but you have to be very gentle with the posts that the hinge pin fits into.)

Or the little tab on the float (on which the float valve rests) can develop a divot. The valve has a little spring-loaded plunger, and it can get stuck in the divot, throwing it out of vertical alignment. You can sometimes file the divot out, to make the tab smooth again.

Or the overflow stem can develop a long, vertical crack.

Or the o-ring on the bowl's drain screw could be bad.

Great explanation for a rookie or newbie as I am!  Do you think this problem is directly related to the oily, moisture condensation dripping from the exhaust weep hole? Or is this a separate issue?  I ask because I can deal with a little fuel leaking out of the bowl and down the overflow line.  If I turn my gas off at the petcock about quarter mile from my home all the fuel is used out of the bowl and very little will be left to leak out.  Thanks again!

[KC750]

2. Tank cap might be rusty and the air vent is blocked. I have got that problem too, stop after 10 minutes ride. I called a friend that came with his car and a trailer. I swapped tank to another new one. Later on when I drained the fuel I noticed the fuel stopped flowing, opened the cap and it started to flow. I have a new cap for that tank.
I could have ridden the bike home if cap was open.

I may start with this issue by buying a new gas cap...when you replaced yours did it solve the problem?  Thanks.

[ekpent]

 Drive it around with the cap unlatched and see if it acts up. If its not too full you won't have a problem. That will test that theory. Some people report problems when using inline fuel filters other don't. I try to avoid them and like a nice clean tank.
  One thing for clarification. Does the 'bad' carb your talking about completely empty the bowl when its parked. Have you unsnapped it and seen it empty like your implying or does it just leak out the overflow hose when parked with the petcock on and your assuming its draining till empty. If draining till empty then it could be the standpipe is cracked,if just leaking in general then look at the float valve.  If your carb is chronically overflowing,even while driving you may be putting raw fuel into your cylinder and out the exhaust pipe hence the weep. Not good for cylinder lubrication and can contaminate your oil. Does the weepy pipe correlate to the problem carb ? An easy test when the bike is good and warm is to put a wet rag on the header pipes and compare the sizzle. See if the weepy pipe is running cooler.

[Phinn]

I would not tolerate a chronically leaking bowl. Gas is a hazard. You're likely spraying gas from that bowl everywhere you go. It is not only wasteful and polluting, but the fuel level in that bowl will be low, causing the carbs to be imbalanced.

Now that I think about it, the fact the bowl drains to empty after each drive tells me that either the overflow pipe is cracked (or damaged somehow), or the drain screw isn't closing. Either way, I'd bet that bowl loses gas constantly, but you only notice it when stopped.

[KC750]

It sounds as though your issues #1 and #3 are related to the same carb possibly. I would also suspect the tank cap is obstructed.

You did not mention whether you have made any air box/induction changes.
You stated fully cleaned carbs with "new kits". What "kits" did you buy and which components from them did you use?

No air box changes carbs - replaced jets, needle and float seats.   

[KC750]

Thanks for the replies.  Much appreciated and very helpful.  I will investigate the issues and respond accordingly.  Hopefully with a more defined question.

[KC750]

Okay.  This is where I stand with my issues.  I removed the carb bowls on 3 and 4.  Realized #3 was full to close to the rim with fuel. It appears the float was in a bind so I pulled the pin and it was slightly bent.  I adjusted the tab slightly, straightened the pin and no fuel leak.  I hope this fixed the fuel overflow problem. 
Gas cap not venting_- I removed the rubber seal and blew out (air compressor) the entire gas cap mechanism, replaced the seal. Took it for a ride and no issues as well.  So far so good with those two.  Time will tell.
However, I am still running rich in cylinder 4 (spark plug full of black dry soot, wipes off easily).  I have opened the air/fuel mixture screw 1.5 turns with no luck.  I don’t think this is the problem. 
Any suggestions are appreciated. 

[Paintedseat]

Have you done a sync? The fuel leaking from the bowl is most likely a bad O ring on the drain screw. Changing float height will not help if fuel is passing through the over flow tubes. You said you removed the bowl on 4 but did not say if the float needed adjustment.

[754]

Did the leak stop ? It sounded like a cracked drain tube in the bowl..
 There is a thread on fixing them on this page.

[KC750]

Have you done a sync? The fuel leaking from the bowl is most likely a bad O ring on the drain screw. Changing float height will not help if fuel is passing through the over flow tubes. You said you removed the bowl on 4 but did not say if the float needed adjustment.

Sync done.  O ring replaced when I completely rebuilt and cleaned the carbs.  I actually removed the bowl on 3 and 4.  3 was the problem and is the one i adjusted the height on, straightened the pin on and took it for two thirty minute rides and so far so good.  Fingers crossed.

[KC750]

Did the leak stop ? It sounded like a cracked drain tube in the bowl..
 There is a thread on fixing them on this page.

So far so good after 2 rides.  I checked the drain tube out when I pulled it.  Seemed okay.

[KC750]

However, I am still running rich in cylinder 4 (spark plug full of black dry soot, wipes off easily).  I have opened the air/fuel mixture screw 1.5 turns with no luck.  I don’t think this is the problem. 
Any suggestions are appreciated.

Dry sooty plugs are indication of a weak spark. Replace that plug, check the plug cap for its resistance, and if necessary replace the cap. You can also trim the end of the HT lead 1/4” and install a new cap to help.

I did a spark test...not sure how to determine if it’s a weak spark or not.  It did seem a little weak to be honest.  The wires and caps could be original.  I have not replaced them and the bike was sitting in a garage for about 18 years untouched. What do you mean by “trim the end of the HT lead?”

[jgger]

Ht lead =spark plug wire. That is a free fix, so do it and while the cap is off of the wire check the resistance with an ohm meter. The caps just unscrew/screw on to the wire. Hold the wire and twist the cap off, ezy .pezy

[Yamahawk]

Cut off a 1/4" of the lead while the cap is removed, and then screw the cap back onto the wire.
Charlie

[Paintedseat]

I would order some new ones. Replace them.

[dave500]

the leads don't come out of the coils they are fixed.

[KC750]

Ht lead =spark plug wire. That is a free fix, so do it and while the cap is off of the wire check the resistance with an ohm meter. The caps just unscrew/screw on to the wire. Hold the wire and twist the cap off, ezy .pezy

Okay.  Thanks.  Makes sense and give it a try.  What should the reading be on the OHM meter?  Just make sure it’s good?

[evinrude7]

on a k4 i think it should be 5.

[Paintedseat]

Looks like the PO install some cb900 coils. It's my first cb750 and I had no idea the coils I had were not stock.