Topic: Carb woes, AKA Check your fuel level.

[Sticky Gerbil]

Fair enough. However, the bike ran fantastically until yesterday. So that tells me that the setup worked alright until yesterday.

Anyway, I pulled the bowls and all the jets and needles. Soaked them in carb cleaner, and ran carb cleaner and compressed air through all the passages I could find with the carbs still on the bike. Went back together and bike wouldn't start without starting fluid. Looks like no fuel through the filter. Did I destroy some rubber part or something? What pumps the fuel down to the carbs?

[madmtnmotors]

Have you checked to see if the stock filter screen is still in the tank? If so, is it clean and clear? Have you done a compression check?

[Sticky Gerbil]

How would I check for the screen? Gonna compression test this afternoon- I gotta pickup adapters.

[madmtnmotors]

The stock screen is inside the tank where the petcock would attach to the tank. You indicated that there is no petcock, how does the fuel line connect to the tank? The filter screen fits up inside the bung where the petcock should be. Sometimes you can look through the fuel cap and see the filter from the inside, although this would be hard to access it's condition. Use a flashlight if you need to... no lighters! Or remove the fuel line from the tank and see if the plastic filter tube is still inside the bung.

[Sticky Gerbil]

My tank has just a steel elbow. I guess look up there? Without a boroscope it would impossible to see in through the filler cap.

[Sticky Gerbil]

would spraying carb cleaner and following it with compressed air have messed anything up if all I removed wasjets, needles, and seats with the carbs on the bike?

[andrewk]

Shouldn't have affected anything with the cleaning.

What kind of tank you using?  Is this steel elbow the only one on the tank?  or are there two?  If you're hooked into the crossover tube of a honda twin tank, you might have some flow issues to deal with too.  Might explain the purple passion pipes.

I would start with cleaning all the carbs, and making sure you have a clean and free flowing source of fuel that you can shut off.  Inline petcocks can be had but I would make sure that elbow you're using now is located properly and has adequate flow.

Knowing how long (mileage) it "ran fantastically" before this event would help with the tuning suggestions too.

[Stev-o]

If I were you, I would trade those cb750 carbs to someone for 650 carbs.  At least then you'll be in the ballpark.

+1.  I have some 650 carbs if you want to trade.

[Sticky Gerbil]

Damnit. It ran about 500 miles before being a douche. I think I'll take the tank off and examine it more closely.

[madmtnmotors]

My tank has just a steel elbow.

Then you may have a different tank as well. The tank you have may not even accommodate the in tank filter that would have been used on the original tank.

[goldarrow]

Now I feel like we need picture of your tank or bike

[Sticky Gerbil]

I'll take a couple when I get hone I am going to Oak Ridge to do a forest inventory.

[harisuluv]

If I were you, I would trade those cb750 carbs to someone for 650 carbs.  At least then you'll be in the ballpark.

+1.  I have some 650 carbs if you want to trade.

There you go, what a guy.  Highly recommend you explore this option.

[lucky]

and the paper filter restricted the air flow too and acting as a choke

.
Do you have any data that confirms your statement? No, you don't and your remark is nonsense. Why would a motorcycle manufacturer want the paper air filter to work as a choke?

When I say "choke" I mean less air and more gas.
If you take the air box and air filter off of the motorcycle it will run leaner.
The idle will slightly increase and the throttle response may not be as good.
Also it may pop on decel after revving it up.
When you put the air filter back on you will notice an improvement in the idle (going down ) and the better throttle response and no more popping on decel.

If you measure the inlet of each carb and figure the sQ. inches if intake, THEN measure the inlet of the air box, you will notice that the opening of the air box is LESS than the area of the 4 carbs intake openings.

So it is just like putting you hand partially over the carb opening, which chokes or richens the mixture by giving them less air and more gas.

[lucky]

Yeah, like I said I just wanted the carb type. Not same old tired ass lecture on air filters. That's why I ignored that statement.

If you look on the carb stay plate on the top right side you will see some numbers.
Also the difference between the 71-75 models can be diffrentiated by the location of the throttle return spring ,float bowl drain screws head size, and several other features.
The 1978 float bowl drain screws did not have a shoulder on the drain screw. The earlier ones did.

Also some float bowls are held on with screws.
 Some just have a simple clip holding on the float bowl.
You would need to show us a clear photo of the carb set first.

[lucky]

Fair enough. However, the bike ran fantastically until yesterday. So that tells me that the setup worked alright until yesterday.

Anyway, I pulled the bowls and all the jets and needles. Soaked them in carb cleaner, and ran carb cleaner and compressed air through all the passages I could find with the carbs still on the bike. Went back together and bike wouldn't start without starting fluid. Looks like no fuel through the filter. Did I destroy some rubber part or something? What pumps the fuel down to the carbs?

Just spraying the idle jet with carb cleaner will not do the job. It gets sticky residue in the jet from sitting, and many times requires a #10 guitar string ,carb cleaner, and compressed air to get it clean. Paper clip WILL NOT work and can damage the brass jet.
the only way to tell if it really is clean is to take it out of the carb and hold it up to the light to see if it is plugged up. It is a very common problem with modern gas mixed with ethanol.

[Sticky Gerbil]

Which is why I took it out and soaked it. See previous posts.

[Sticky Gerbil]

So the # 1 and 2 carbs had splits in the gasket, causing a fuel leak which apparently I was too stupid to notice. When I resealed the carbs and cleaned them, I just assumed the tank was full still. I am dumb. I am stupid. I am an idiot. With no gas leak, the bike runs fine.

[Sticky Gerbil]

Did I mention that I was stupid?

[seanbarney41]

no...but you did say you were a car mechanic

[calj737]

Hey Gerbil - what brand of cars do you work on so I can buy something else? Just messing with you.... It's always the simple things that cause the most embarrassment.

Glad you got it worked out. And didn't have to do away with your pods

[madmtnmotors]

If you go back to your first post, you can change the title (therefore changing the title of the thread) to:

"Carb woes... carbs work better with gas in the tank!

[Stev-o]

Did I mention that I was stupid?

Yes, twice.   Wanna buy some 650 carbs?!

[Sticky Gerbil]

No, not yet. The bike runs pretty well normally (although I guess 500 miles of ownership isn't the best indicator). It is still leaking a bit from the overflow tubes- I tested it overnight. I think it might have cracks in them. Anyway, I'm gonna pull the bowls again and either solder or heat shrink those, and check float heights while I'm in there. Also, #4 wire boot came off while I was cleaning the plugs; I put it back, but it didn't wanna screw on there real well. It looks like the coils just have screw on wires so I'll pick up some new wires (copper) tonight. Otherwise, the bike runs like a motherlover.

[madmtnmotors]

That's better!

Don't know about the 650's, or even what type of coils use "screw on wires", but the 750's only used screw on spark plug boots. The wires on the 750's are molded into the coils (i.e. nearly impossible to replace). When the boot won't "grab" when trying to thread it back on you can often trim back the end of the wire about a 1/4" or so to give you a clean end for the boot to grab into.