Topic: whats the trick?

[famoussas1]

hmm..actually i cleaned the carbs over winter, but maybe i missed something...i guess i know what i gotta do. take em off again and recheck my work.

[BobbyR]

hmm..actually i cleaned the carbs over winter, but maybe i missed something...i guess i know what i gotta do. take em off again and recheck my work.

I have learned the hard way that cleaning carbs is more than just spraying chemicals. You really need to take a strand of copper wire from an old lampcord and loosen stuff up and then spray out the debris. I found white deposits on my slow jets which Hondaman attributes to the MBTE that was used in gas for a number of years. I know this sucks, but it is a process of elimination exercise. The good news is that it runs.

[famoussas1]

thanks, well i am gonna make sure the petcock isnt clogged (shouldnt be, its brand new but who knows, make sure my in tank filter is clear as well), then take the carbs off again, grr, and really give them a good once over. i was scared the first time, partly becuz ive never taken any carb apart, but now i gotta go thru them better. po said he cleaned them, but the bowls were pretty tarnished when i did them, maybe a hint that it went deeper than i cleaned them. thanks for everyones help..gotta get her running before the first warmer days arrive!!

[flybox1]

doesnt sound like your petcock.
check and re-check float levels.  they might be set too high, starving the system.
clean jets/emulsifier tubes.
clean float valves
check airscrew settings.

trick...
when you reinstall your carbs and turn on the fuel, do it slowly, allowing the carbs to fill up gradually, while tapping on the bowls with something.  this will get your floats unstuck (if they settle) and your fuel level to where it should be before start up.
if the floats are stuck, and you crank it on, you might have a puddle....

fuel should rise to ~4mm below bowl gasket level.  screw a clear tube into the bowl drain screwhole, and hold it up next to the bowl, turn on your fuel and see where it stops.

[jhawes]

Here's the opposite problem. I just put a brand new petcock on my '72 cb500 and even when the petcock is shut the carbs continue to dump fuel out of the overflow tubes.  Any ideas?

[Noel]

These bikes pee gas. It's axiomatic. The only sure-fire solution I have found is to bring every fuel-handling surface to perfection:

1) Ensure that no particulate gets from your tank to the petcock. This means a pristine inner surface (chemical etching, ie. Phosphoprep, etc.) and keeping it that way, which may mean a tank liner, depending upon your situation.

2) Ensure that your petcock works correctly. Z1 claims that a rebuild works about 50% of the time. NOS petcocks are around $50 on Ebay.

3) Replace all fuel lines, including any carb-to-carb lines.

4) Replace EVERY SINGLE GASKET AND O-RING in the fuel system. This includes the doubled O-rings that seal the brass T fittings that connect each pair of carbs to the main fuel line on the 500. When these leak it may appear to you that the fuel is draining from the overflow tubes rather than running down the outside of them. I once had a leak from the #4 carb T fitting that ran down the outside of the tube, but on the surface facing away from me. It looked for all the world like it was draining from inside the tube. I nearly went insane before finding the problem.

5) Ensure that your floats actually float IN GAS, not water, and that they are set to the correct height FOR YOUR BIKE.

6) Carefully polish the float pins and any surfaces which they contact. IMO sticking floats are a key cause for leaky bikes.

In my experience the above operations will solve the gas leak, with one caveat: it's not unusual for carbs that have been dry on the bench to leak when the gas is first turned on. This, again, is usually caused by a sticking float and can often be cured by a good whack on the float bowl with a screwdriver handle.

HTH!

[famoussas1]

not petcock (brand new) and not vapor lock from tank cap. gas flows perfectly from tank and line. got the carbs apart now, taking my time trying to see if i can find any gunk plugging up any passage ways. no luck yet.

[BobbyR]

not petcock (brand new) and not vapor lock from tank cap. gas flows perfectly from tank and line. got the carbs apart now, taking my time trying to see if i can find any gunk plugging up any passage ways. no luck yet.

Just rod out every passage and flush it out.

[famoussas1]

OK!! so i took apart carbs, blasted, soaked, did the whole 9 yards on the carbs, put em back on and wham, first tap of the starter she popped like brand new. let her idle for a few min. then shut her off, but now guys help me out (again im a rookie here), the 2 and 3 pipes were cold....1 and 4 (the outter pipes) were hot...but 2 and 3 cold.  new plugs. havent checked if they were sparking yet...too excited i got the fuel prob. fixed.  so am i looking at a new coil? what can i test/check to make sure its the coil?

by the way, you guys all rock. this is my first bike, and i feel helpless but a little confidence and you're guys advice and i feel like im heading in the right direction learning bout these awesome bikes.

[TwoTired]

2 and 3 cylinders share a common coil and spark delivery system.

However, it is possible that a vacuum sync is required, or even idle fuel passageways still aren't fully clear.

[754]

Because it is 2&3 it is now an ignition problem.

 Do yourself a huge favour and try to actually listen to the advice given, and it will go a lot quicker.. (trying to put this nicely, you did a lot of extra inneeeded work, on last problem)

[bender01]

Check the 2-3 plug boots and unscrew them to see if they will spark bare to the head. Maybe the plug wires just need  a small snip to pass the spark through the plug boot? Its odd that its both so nothing to lose with trimming.

[754]

I wpold clean the 2/3 pointset before cutting anything.. the 2/3 leads are pretty short anyway.

[famoussas1]

pulled the 2 and 3 plugs, still brand new not a trace of firing or anything burnt on them.  pulled them and placed them to the engine, tapped the starter, no spark.  

[bender01]

 I meant take the wires without the plugs or boots and see if that will spark to the engine. Sorry.

[famoussas1]

oh i thought u meant trimming back the wire, i didnt do that however i will try the wire without the boot or plug. thanks for clarifying.

[Bodi]

Take a carb drain screw out and check the flow rate there... you can make a trough out of foil and direct the gas into a jar to pour back in the tank. It should trickle out, if it just drips you have a definite problem. The flow will never be as strong as an open tube on the petcock. The float valve, even fully open, offers a small orifice. The ID of the carb fuel fittings is smaller than the tube. The fuel system must deliver as much fuel as four carbs can need, so flow from one carb has to be less than 1/4 of the open petcock flow even at the end of reserve. This is easy to check, just time filling any jar to some marked level.
I don't know the maximum fuel consumption of the engine. Assuming it's a 750: I estimate about 240ml/min maximum, 60ml/min per carb. (Volumetric efficiency is best at the torque peak, 7K rpm. Overestimating this efficiency at 100%, you have 2625 litres of air ingested per minute - 3500 intake cycles x 0.75l. This is about 3.16kg of air, using a 14:1 ratio you use ~.225 kg of gas. Gas weighs about .920 kg/l., so 244ml. Because volumetric efficiency will never be 100% it is probably less than 200ml in reality)
That's not a lot of fuel, really. If you can't flow 60ml of fuel in a minute through a carb, something's wrong for sure.
I have seen bubbles in many fuel and fluid lines. The fluid flows past the bubble pretty freely as the bubble "floats" up into the fluid flow. There's no restriction. If fluid could not flow past the bubble, the bubble would simply be pushed through the hose... and be gone. With enough flow the bubbles do move on until the next time air gets in there.
Bubbles are not a problem.

[bender01]

oh i thought u meant trimming back the wire, i didnt do that however i will try the wire without the boot or plug. thanks for clarifying.

Well, that is what I meant but try it without trimming first.