Topic: rebuilt carbs, now running waaaaaayyy rich... and leaking fuel

[stanghater]

hey guys, so i tore apart the carbs and found out they were super clean. got new gaskets and float needles, put those in(do you need to adjust new float needles?) put the carbs back together, and put them back in. also noticed that the plug wires were like waaaayyy shot so i got new ones. now when the bike runs, it is running hardcore rich. any ideas? actually im looking for a quick way to lean it out. Keep in mind that i am fairly young and i would like to know what parts im messing with and why. I have only messed with fuel injected cars and not carbs.... please help, i am itching to ride the damn thing. BTW its a 81 Honda cb650, 6600 miles. thanks

[Bob Wessner]

How did you determine they were super clean? Did you inspect the jets to see if they were clear? The rich condition, is it a low speed, high speed, both? You don't have to adjust the float needles, but you do need to check and possibly adjust the float height.

[stanghater]

they werent dirty or there wasnt any gunk or anything like that. i was awoken this morning to the strong smell of gas. i look in the garage and there is a puddle of gas under the bike. i was leaking out of the air box drain(at the bottom of the bike near the chain) what the hell??

[Bob Wessner]

If the floats are not set correctly, or stuck, the float valves are not closing so fuel will overflow in the bowls and eventually run out the overflow tubes. Does your bike have a manual petcock? If so, always shut it off after you ride/run the engine. This will at least limit the amount of fuel leaking out the the volume of the float bowls. I would definately check the float height and look for sticking or no-seating float valves. The can stick open if there is rust or particles getting down the fuel lines from a rusty fuel tank as well.

[TwoTired]

i was leaking out of the air box drain(at the bottom of the bike near the chain) what the hell??

There is a stand pipe in the carb that should carry away the overflow to the tubes attached beneath them.  You have some blockage in the thoses pipes or tubes.
Also, check your crankcase for gas in the oil.

If you replace your float valve, yes, you have to check.adjust float height.

[stanghater]

ok i know now i need to check the floats and stuff, either way, before i tore apart the carbs, it was running rich. i am looking for a way to lean it out. anyone know, is it those long needle things?

[Robert]

Stanghater, can you illuminate me how you found out that is running super rich?
Do you have the CV carbs? Keihin VB54C?
I have a 80 CB 650. From my experience with the stock setup and the stock pilot screw # of turn outs you're running a tad lean (assuming with 6000 miles the components are worn out next to nothing) .

[stanghater]

Stanghater, can you illuminate me how you found out that is running super rich?
Do you have the CV carbs? Keihin VB54C?
I have a 80 CB 650. From my experience with the stock setup and the stock pilot screw # of turn outs you're running a tad lean (assuming with 6000 miles the components are worn out next to nothing) .

well, when i bought the bike and rode it home, my friend was following me. when i would open it up, it had some flat spots and he said there was black smoke coming out of the pipes. after further inpection, we found out there was no air filter in it. we thought maybe it was running way lean but i bought a air filter and put it in and it made it way worse. it wouldnt even rev over 5500 accelling. then when it would really warm up it would run worse. so we decided to rip apart the carbs and see what they look like. They looked fin but i cleaned them with carb cleaner, got new float bowl gaskets and float needles, but it back together and it started right up. When i went to ride it, it was worse, almost felt like the engine was flooding under full throttle. Brought it back in the garage and reved it, out came black smoke. i think the guy before me adjusted it to run without the filter. where are these pilot screws and how can i adjust them. i really want this to run right without having to pay some mechanic $70 an hour. please help me BTW yes i do have the cv carbs

[eldar]

Well I dont know anything about this bike but normally the first thing to do is to make sure float height is correct and that the idle screws are not too rich. It maybe possible that someone thought they were a hotshot and drilled the low speed jet out for some reason too but that is hard to say.

[Robert]

The problem you described are either carb related or ignition related. (Supposing valve clearance, etc. is good, I'm not sure what has been done already.)
Regarding the carb, since you suspect the PO of having changed things, maybe the jetting/anything else is changed as well as eldar already suggested?

The pilot screw is located at the engine side of the float chamber (see arrow in pic)





The upper pic is from the "Honda Technical Manual on Motorcycle Carburetion" which is mentioned and linked to in the carb faq, a good read btw.
For setup you screw in clockwise until a slight resistance is felt. STOP!! Then you simply screw it out again to a certain number of turns given by the manufacturer.
The workshop manual tells about a hundred times (so they are really serious about it) to be careful when screwing the pilot in, as its seat can easily be damaged. 

There might be some kind of security cap over the pilot, now if that's the case I would forget about the pilot since its setting is stock anyway, which is what you (at least initially) want.

If the carb identifies itself on its side as a VB 54C or D, the pilot setting is 1.75 turns out. Mainjet #98
If the carb identifies itself on its side as a VB 54E or B, the pilot setting is 2.625 turns out. Mainjet #95

Now, hmm, the thing is I don't really think it won't help a bit. I'm smelling a problem with the ignition (gets worse when warm, doesnt rev over 5K) but then again this is maybe because I know the cb 650 ignition inside out and have only limited knowledge with carbs....do you have a timing light?

[stanghater]

yes i have a timing light but how do you go about timing it? i am gonna try that pilot thing either tonight or tomorrow, thanks a lot for the help but keep it coming

[eldar]

Well an inductive (?) timing light is best since it does not draw power from the spark and you can hook it to a battery besides the one on the bike. There will be a third large plastic clamp. This will go on your plug lead as close the the plug as you can with out melting the insulation on the clamp or wire. Now with bike running and timing cover off, since I dont know if you have points, aim the light at the marks. At idle, the light should flash just as the f mark lines up. It will look like it is frozen in time. as you advance the throttle, the light should advance as well and at a certain rpm, hit it max advance and there will be marks for this that should line up. If this all looks good, then timing should be accurate. It would be time to test your plug caps and this I cant help with as for the readings you should get. With my 78 750, I use NON-resistor plugs cause the plug caps are the resistor.

[stanghater]

for some reason the timing thing makes no sense to me... dont you have to have a distributor? also the plugs that are in it are ngk dr8ea.... thats all i could find at napa

[Robert]

There's no distributor. The CB 650 has two independent ignition circuit, one for cylinder 1 and 4 (cylinder 1 is the left one in driving direction) and one for cylinder 2 and 3. Each circuit has three components.

Each circuit has its own impulse generator (AKA pulser) located below the right round cover that says "HONDA", a spark unit (located below the seat, it reads mps 200) and an ignition coil (below the fuel tank).
A faulty component of the ignition system will most likely manifest itself in a way that either cyl. 1 and 4  OR 2 and 3 are not firing. With one exception: a faulty ignition coil. Since the ign.coil  has two terminals, it is possible that only one cylinder is affected. And another exception: faulty plug wires/caps or a connection problem between the ign. coil and the spark plug.

I would suggest you use the timing light not to adjust the timing for a start, but to determine if all cylinders getting constant fire.
I expect one or two cylinders to have problems.

So hook up that timing light and connect it to all cylinders in turn, one at a time.
See this thread: http://www.sohc4.us/forums/index.php?topic=1746.0 for details.
Each cylinder should provide a constant flashing light with the timing light at all operating conditions (when the machine is cold/warm at various rpm).
A failure would be displayed by short interceptions of the strobe. Use the advancer located below the mentioned cover (where the pulsers are) as a help. If the advancer in the strobe light appears to be not moving (constand rpm) or only slowly moving (de/accelerating rpm) the ignition is fine for that cylinder. If the advancer  "jumps" more or less from time to time, there's a problem.
If the strobe light is off for one cylinder, the cylinder doesn't fire at all...or the timing light is broken

As a side notice. The test will take about 30 minutes, since the machine (aircooled only) isn't moved you want to put up a fan in front to provide some kind of air to prevent the engine from overheating. If that's not possible split the 30 minutes in 2 x 15 minutes with some time between.

Please post results.

[eldar]

those dr plug are resistor plugs. Napa is not the best place for plugs I have found. get the correct set for your bike before even doing anything else.

[Bob Wessner]

I was so anxious last fall to try and start mine for the first time in MANY years, when I went to the Honda dealer for plugs, they claimed they only had resistor plugs. I took them. It did start and it did run. After all my fiddling since then, I thought it best to treat her to some new plugs. This time the dealer had non-resistor plugs. I does run better with them, it didn't erase 35 years by any means, but you could detect a diff.

[eldar]

that stronger spark can make all the difference in combustion.

[stanghater]

i know i can order the right ones from NGK so i think i will. also, i think the floats are stuck, or at least thats what everyone else thinks. i am gonna rip them apart tonight

[TwoTired]

I was so anxious last fall to try and start mine for the first time in MANY years, when I went to the Honda dealer for plugs, they claimed they only had resistor plugs. I took them. It did start and it did run. After all my fiddling since then, I thought it best to treat her to some new plugs. This time the dealer had non-resistor plugs. I does run better with them, it didn't erase 35 years by any means, but you could detect a diff.

Maybe this will help.
When the points close, a magnetic field is created in the primary of the coil.  When the points open, this field rapidly colapses.  As the secondary windings are also in this magnetic field, the collapsing field induces a voltage in the secondary, or output of the coil.  The voltage builds and rises until there is sufficient energy to ionize the gasses between the electrodes of the spark plug forming a lower resistance path for the electricity to jump.  The voltage builds no higher as this discharges the energy stored in coil.  The voltage required to achieve the spark is effected by the spark gap, the surface conductivity of the electrodes, and the composition of the atmosphere between the electrodes.   As combustion byproducts are deposited on the electrodes and the electrodes erode, the required spark voltage increases.  Thus, as the spark plugs age from use, the coil is required operate closer and closer to it's peak capability.   At some point in the life of the spark plugs the requirements for generating a spark will reach the threshold of the coil's peak capability.  The result is misfires which become more chronic as operation progresses.

When the plug does spark, the rapid energy transfer along the ignition wire builds an energy field around those wires and is dissipated into the surrounding atmosphere.  While this energy is insignificant in proportion to that needed to spark the plugs, sensitive electronic receivers such as is found in radio and televisions can detect this energy and pass it into their systems as noise.  If, however, a resistance is placed in the ignition wire current path, the initial rise of the spark voltage is delayed.  This effectively lowers the initial impulse frequency of the sparking current through the wire to a point below where nearby electronic receivers are tuned to accept signals.  About 5K-10K ohms is enough to achieve this.  More resistance will lower the rise time slope even more.  However, any resistance does lower the voltage as it passes through it at a rate comensurate with the added resitance.  The spark still occurs at a voltage determined by the spark plugs, but the coil voltage will have to rise a bit further to compensate for the resistive loss.

The result of adding resistance is shortening the effective life of the spark plugs.  And, of concern, is that the voltage provided to the coils during a low battery start and/or when the starter motor is drawing the voltage down may not allow the coils to store enough energy, thereby lowering its peak output below that require to spark the plugs.

And, don’t forget the connectors in an old bike may have oxidized and this, too, can lower the voltage to and from the coils.

Cheers,

[stanghater]

well here is an update on the situation. we found out one of the floats was stuck open so we fixed it and measured them. they are in spec. we also checked the main jets, they said 120 on them and that is the size my manual says they should be. we also adjusted the pilot screws to factory specifications(2 were at different positions that the other 2) so we put it back together and it started right up. i had to adjust the fast idle because it was idling was low. so i got it idling right and took off for the first ride. keep in mind i replaced the spark plug wires. when reving the bike up now, instead of having choppy flat spots, it has a smooth long flat spot. any ideas? please