Topic: Help with fuel height please. UPDATE

[cookindaddy]

So the bike is ok when cold (when you are checking the timing) but is not ok when hot?

[Simon]

Bike OK when cold, Not OK when hot.

Timing is the same hot and cold.

I'll try to figure out if there is a different spark between hot and cold engine.

What I know is that my multimeters resistance reading on the stator is different between the cold motor and the hot one. It makes me wonder. Can a bad Alternator affect spark and ignition? I am getting full charge at the battery.

Simon

[Spanner 1]

Simon, check the voltage at the coil primaries.... should not be more than 1volt lower than battery voltage ( with stock coils, like you have ), ignition 'on' but motor not running.......

[scottly]

Is it possible the jets have been drilled?

[Simon]

I was having a voltage drop at the coils. Used to have below 10V at the coils, something like 9.7, with a fully charged battery of 12.9V. Tracing the voltage drop, I found out that the kill switch robbed more than 3 Volts. I cleaned every electrical connector on the bike and used dielectric grease everywhere, I dismantled the kill switch to clean it and I still got a substantial voltage drop.  So I did the «car solenoid» modification to temporarily fix that problem. I plan on getting a new kill switch down the line to replace the present one.

Now, with the mod, when every thing is at off (key and kill switch) I get say 12.9V at the battery.
If I turn the key on with the kill switch at off and with the headlight at off, I get 12.6 volts.
Then, when I turn the kill switch to «run», I get 12.4V at the battery and 12.3V at the coil.

These numbers are kind of approximate since the Voltage goes down when the circuit is powered. The numbers are the highest numbers I get before they go down.

I have yet to test what voltage I get at the coils while the engine is running. I'll check that tomorrow.

The jets have not been drilled. I got them a few years back when I was trying to fix this same problem. They are clearly stamped with their #40 and 75#.

Keep em coming!

Simon

[scottly]

.1 V drop from battery to coil is zip, nada, no concern!!

[Simon]

Yep, Engine off, everything seems to me like like it's a new bike. Engine cold, It is a great ride.

Now i think I have to check all the numbers while it's hot.

The battery gets full charge when it's hot, that I know.

1• I'll check to see if the coil gets full voltage when the engine is hot.

2• I'll compare spark with a new, unused spark plug, between a cold motor and a hot one.

3• I'll compare compression between a cold motor and a hot one.

Any other Ideas guys?

BTW, I might go and see a 1973 CB350G twin (geen tank with white stripe) for sale on friday. Owner says it ran great when he stored it in 1992. Funky windjamer and side luggage but from the pics, bike looks real good. Curious me...

Simon

[scottly]

Uh, does your bike have the funky "press in" main jets with the O-rings?

[BeSeeingYou]

Nothing to add just checking out the twin lens reflex camera in the background in the first picture.

[Spanner 1]

Hmmm.... I think were back to carbs for sure. Overly rich mix would run good until motor heats-up to normal temp.
What Scottly said .... any way the main jet or slow jet is getting 'bypassed' by a bad/ wrong sized 0-ring ( do the carbs have o-rings in the jet seats ??).

[scottly]

Didn't someone post recently about corrosion in the main jet recess that did not allow the O-ring to seal?

[Spanner 1]

Ohhhhhh, 'vary interesting' and a definate possibility..... !

[cookindaddy]

Simon: About the voltage at the coil - are you able to safely leave your multimeter connected, perhaps taped to the handlebars, and take it for a spin until it warms up to keep an eye on that voltage when it is hot and misbehaving?

[david 750f]

Simon, I have been following this thread. I had the same issues, try 1 heat range hotter plugs. Many forum members don't like this recommendation but it worked for me.
Cheers,
David

[Gonzowerke]

I don't know d*ck about the smaller bikes, but I had a similar problem on my 750. It turned out to be my accelerator pump diaphragm. It got progressively worse until the bike would not start and you could smell raw fuel. My hypothesis was that the leak was small at first and then increased until it got to the point where it was flooding. Do the smaller bikes have accelerator pumps?
 
How's this for a theory? Your gas cap vent is clogged and the engine heats the tank, pressurizing it and causing you to run rich. Gas has a rather large coefficient of expansion. I once filled my tank on a hot day, and the gas from the underground tank was cold. I stopped about a 1/4 inch from the top, but after I parked it in front of the station to go inside and pay, a guy comes in to tell me my bike is dumping gas all over the ground. I pop the door and gas was spewing from the vent hole in a little geyser!

On the 750's you set float height by turning the carb upside down, and bend the tab until the float is parallel with the bowl/body seam of the carb, but I don't know if that will work on the smaller bikes.

Hope you get it sorted!

Gonzo

[Simon]

Uh, does your bike have the funky "press in" main jets with the O-rings?

Yes, it does. I too thought it might be the problem so I used a small amount of gray gasket silicone (gas resistant) to seal the jet. I did not want any unmetered gas passing by. It's very clean. I have checked and rechecked the emulsion tubes and the jet for silicone debris using this technique and never saw any. I strongly doubt it could be the problem. There is no corrosion. I would consider the seat good and firmly in place with the spring and all.

Simon: About the voltage at the coil - are you able to safely leave your multimeter connected, perhaps taped to the handlebars, and take it for a spin until it warms up to keep an eye on that voltage when it is hot and misbehaving?

That's my plan today, to check voltage while running. Just wish I was in the country side. Soooo many cars in the city....

Simon, I have been following this thread. I had the same issues, try 1 heat range hotter plugs. Many forum members don't like this recommendation but it worked for me.
Cheers,
David

I found a place selling D7ES not far from here. I was thinking the same thing. Worth the try... I run D8ES, D7ES is a hotter plug, right?

I don't know d*ck about the smaller bikes, but I had a similar problem on my 750. It turned out to be my accelerator pump diaphragm....
 
How's this for a theory? Your gas cap vent is clogged and the engine heats the tank, pressurizing it and causing you to run rich....

There is no accelerator pump on these carbs. I tried with the tank cap open and did no difference...

Guys, thanks a lot for your suggestions, really.

I'll test things and report back.

Simon

[Spanner 1]

One more thing!.... how about your advancer is sticking at full advance when hot ?

[midnightrider]

Simon, did you ever figure the problem out?