Sigh..... ANOTHER "this doesnt make sense" Carb Issue.... :(

[Grouper]

Hey guys, I hope someone can help me with my carb delema!

I just put a freshly honed cylinder and new rings on my '71 ct70. my compression was down to around 90psi. The bike has less than 1000K on it. The piston has seized from lack of use. I also cleaned the carb and fuel tank(plastic) before i started it up.

Heres my issue. It idles ok, but when you hit the gas hard, it will just die. if i run with my choke, and mash the gas,(so to speak) it revs up as high as i dare for a fresh motor not yet broke in. So I say to my self: Hey! it needs more fuel!! I better check the float level.
So I get the clear hose attached to the float drain, run it up beside the carb, and backoff the drain screw. The gas keeps climing to JUST PAST THE IDLE MIXTURE SCREW! AHH! so my float level is WAAAY to high, But my motor will rev up when i starve it of air and richen the mixture with the choke on. I dont know what to think except possibly my float needle is leaking. Im stumped.
....I did consider it weird that I didnt have a little oring or seal for the float needle to rest on. It just sits on the brass insert to seal. Or did I loose a tiny oring?

...Please help!

 

[69ST]

Okay, first some clarification, FWIW...

Pistons don't size from lack of use. The cylinder walls become rusted, from a combination of atmospheric moisture, old combustion byproducts (which turn acidic when mixed with water) making contact over a prolonged period of time. This is 100% preventable. A light spray of fogging oil, a few crank rotations by hand, and turning the crank until compression is felt means both valves are closed and the combustion chamber is sealed. I'll guarantee that your engine sat with one valve open...for years...and that's what allowed your upper end arthritis, a.k.a. rust. I wouldn't be surprised if one valve face & seat had some rust, too.

First thing to check is the condition of both intake gaskets and the large rubber O-ring between the carb & heat insulator. If you're getting "false air" (vacuum leak) the engine is never going to run right. Next thing to check is the main jet holder/emulsion tube. Those tiny holes all need to be squeaky clean, or the main circuit will run erratically lean. Last, check your breaker point gap. If it's too small, the engine will rev fine with no load...then fall flat on its face, once in gear.

If gasoline is draining out of the overflow tube, then the float level is too high.

 

[Grouper]

Right, thanks for the info. Sorry, I forgot to say I just meticulously set the points gap. And cleaned the carb after a 5 day soak in carb cleaner! There is no fuel leaking from the drain.... Please re read my post regarding the clear hose attached to my drain.
Thanks for your help!

 

[b52bombardier1]

If you are absolutely certain that you have set the float height properly and that your float does not have a hole in it, consider the following.

Take a look at the hollow brass standpipe sticking up from the interior floor of the float bowl. See if it has a long split in the hollow brass that would allow gas to overflow. You can check this by pressurizing the brass float bowl outlet with the red Brake Kleen straw and liquid and holding your thumb over the tiny hole at the top of the standpipe.

They freeze up and leak after being exposed to water and a cold winter. But the tube can be repaired with some hobby brass tubing.

Rick

 

[Grouper]

If you are absolutely certain that you have set the float height properly and that your float does not have a hole in it, consider the following.

Take a look at the hollow brass standpipe sticking up from the interior floor of the float bowl. See if it has a long split in the hollow brass that would allow gas to overflow. You can check this by pressurizing the brass float bowl outlet with the red Brake Kleen straw and liquid and holding your thumb over the tiny hole at the top of the standpipe.

They freeze up and leak after being exposed to water and a cold winter. But the tube can be repaired with some hobby brass tubing.

Rick

Sorry guys, I must have miss lead you. My carb isn't leaking fuel...... My drain tube isnt leaking fuel......

 

[darrel gunderson]

The air horn inside the frame off the back of the air box has to have the sleeve inside of it to restrict the airflow also. If its missing the bike wont run properly. This is if all is stock. HTH

 

[Grouper]

with much regret I pulled the carb of AGAIN late last night and cleaned All the jets and then cleaned them, then cleaned them again, and spent about 20 minutes being insainly precise with the float level adjustment. Threw it back togeather, Problum solved!!!
I still have a bit of a hesitation from the idle circuit to the mid throttle, which is bugging me, but my initial problum is solved!

 

[69ST]

Try richening the idle mixture setting, that should help. Dropping the jet needle clip will fatten the main circuit with less throttle opening, just where you want it. Try lowering it one groove a time and re-testing.

Did you pull the emulsion tube and clean out those tiny little holes?

 

[Grouper]

Yup, Carb is as clean as new!
I took it for a spin yesterday and played with the throttle needle every couple k, and by far the best running setting was with the needle at the very lowest point. So! I suppose I should raise my float level a couple mm and re adjust the throttle needle. Do you guys agree? I suppose with such a low float level (im assumming) my idle jet could also be running leaner than it should..... Im proposing to raise the float hight, re ride the bike and set up the needle height, then tweek the idle screw.
Does this sound right to all of you?
O yea, Is there any "proper" way or procedure for setting the idle mixture screw just right?
Thanks Guys!
Alan

 

[69ST]

You might need to replace the main jet with the next larger size. I've been running into more and more of this each year since 2008, as pump gas gets progressively more diluted with ethanol, panther piss, etc.