Topic: Fuel level headache

[Floshenbarnical]

I'm having a right pain in the neck with my carburetors (CB750F2 PD carbs) at the moment. First of all, I have now helicoiled every bolt hole for the floats. Second of all, carbs 1&2 have been weeping fuel for the past week.

Having done this, and gotten the surfaces mating nice and tight, I noticed that carbs 1&2 were still weeping fuel. I had assumed stripped holes were preventing the surfaces from mating tightly, so having fixed that I analyzed fuel level with clear tube. I had expected fuel level to be a little high, but the fuel level is at almost an inch above the mating surface! And this is with the float level set stock to 14.5mm!

With a fuel level that high, I would expect fuel to be draining through the vent lines! But instead, it seems to be slowly leaking from the tiny gap between the carburetor and the velocity stack that holds the K&N pods in place, and kind of oozing down until it collects on the upper lip of the top half of the gasket mating surface of the main carburetor body, and from there occasionally dripping onto the electric starter compartment cover.

Obviously, this is a bad look.

The carburetors are coming back off tonight and I'll be going through them again. I'm hoping that I can get some diagnostic advice from the community to improve my chances as much as possible.

- Is it likely that the float needles are not seating correctly, causing fuel levels to rise until leaking out of the air intake side? What could cause this? Float needles are like 2 months old.
- If this is the case, why would they not be draining like they should? Debris in drain/ vent passages?
- Is it even possible that an "incorrect" float height could cause the fuel level to be that high? Doesn't seem like there's an inch of tang adjustment to even play with.
- Could it be that this is what is causing my bike to strongly dislike starting when cold, i.e. it's flooded/ way too rich? It refuses to start by kick when it's cold sometimes, so I have had to run it down the street and drop the clutch to get it going. No problems starting when warm - 1/2 kick and it's alive.

Hoping for some assistance developing a plan of attack so I can make the best use of my limited free time.

[denward17]

What kind of float needles do you have, are they old/worn out or new?

There is also a specific way to adjust the float height, if I recall, holding the carb at ~45 degree angle to take the measurement without any pressure on the float, just gravity.

Good Luck, they can be a pain.

EDIT: Look at post #236, pic of bad float needle, the top part does not spring back:

http://forums.sohc4.net/index.php/topic,191326.225.html

[Floshenbarnical]

Float needles ~2 months old, from cb750supply. I'l pull them and check them. Maybe I'll switch them with the needles from 3&4, which arent leaking, to see if thats the problem.

[TwoTired]

I wonder if the floats are installed upside down. 

The flat part aims to the street.

[Floshenbarnical]

I wonder if the floats are installed upside down. 

The flat part aims to the street.

Haha, that would be pretty funny. They're installed correctly. I'll bench test them this evening by rubber-banding the ones I'm not testing. That will let me know 100% if the float needle is seating or not.

[MauiK3]

Fuel maybe going around the threaded seats?

[madmtnmotors]

Start with stock (Honda) float needles. If those are too pricey I have had good results with K&L needles. Other brands of rubber tipped float needles have given me fits in the PD carbs.

[Floshenbarnical]

Ordered OEM Honda needles. Will give those a try, see what happens. If I continue to have problems, I'll try OEM Honda floats. If I continue to have problems after that, I'm going to buy some foam padding and glue it to the wall to lessen the chance of concussion while I bang my head against the wall.

[RAFster122s]

Just buy a good helmet to wear all the time to protect your head from cuts and scrapes. The concussion and brain trauma we cannot help with
..

Some bikes are stubborn and fight you...neglected too long or feels like someone cursed them, or you...

[madmtnmotors]

Ordered OEM Honda needles. Will give those a try, see what happens. If I continue to have problems, I'll try OEM Honda floats. If I continue to have problems after that, I'm going to buy some foam padding and glue it to the wall to lessen the chance of concussion while I bang my head against the wall.

The floats are pretty durable, unless there is actual physical damage to the metal tangs. The aftermarket float needles suffer from several potential maladies, including weak button springs and rubber tips that break down when exposed to ethanol laced fuels. The Honda float needles are more resilient to the ethanol and the button springs are more consistent.

[HondaMan]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

[BenelliSEI]

Last time I had one that just wouldn’t quit drooling it was in fact a split overflow tube (inside the float bowl ).

[rotortiller]

With a fuel level that high, I would expect fuel to be draining through the vent lines!

So would I. Maybe check the overflow tube etc for blockage while servicing the float valve.

[Floshenbarnical]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

Upon inspection I have the tiniest amount of powdery grit at the bottom of the float bowls. This is annoying because I spent a week - *a week* - servicing the rust inside my tank via electrolysis and acid and agitation. I’m not sure what else I can do other than send it to a professional.

But I have OEM needles coming, and an in-line fuel filter that allegedly does not restrict fuel flow like the one I had.

[willbird]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

Upon inspection I have the tiniest amount of powdery grit at the bottom of the float bowls. This is annoying because I spent a week - *a week* - servicing the rust inside my tank via electrolysis and acid and agitation. I’m not sure what else I can do other than send it to a professional.

But I have OEM needles coming, and an in-line fuel filter that allegedly does not restrict fuel flow like the one I had.

If you pull the fuel lines off, or have them detached from carbs flip it over to reserve and run some fuel into a container, the reserve fuel circuit sucks right out of the bottom of the tank. In the "good old days" of non ethly fuel lots of gas tanks had at least a little water in them, flipping to reserve could put you roadside with the float needles held open with "stuff" LOL. Maybe before your time but the onset of cold weather had us adding drygas to our gas tanks. Sohio advertised that they included "ice guard" in their fuel, "you go or Sohio pays your tow". That was probably Isopropyl alcohol.

Bill

[Floshenbarnical]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

Upon inspection I have the tiniest amount of powdery grit at the bottom of the float bowls. This is annoying because I spent a week - *a week* - servicing the rust inside my tank via electrolysis and acid and agitation. I’m not sure what else I can do other than send it to a professional.

But I have OEM needles coming, and an in-line fuel filter that allegedly does not restrict fuel flow like the one I had.

If you pull the fuel lines off, or have them detached from carbs flip it over to reserve and run some fuel into a container, the reserve fuel circuit sucks right out of the bottom of the tank. In the "good old days" of non ethly fuel lots of gas tanks had at least a little water in them, flipping to reserve could put you roadside with the float needles held open with "stuff" LOL. Maybe before your time but the onset of cold weather had us adding drygas to our gas tanks. Sohio advertised that they included "ice guard" in their fuel, "you go or Sohio pays your tow". That was probably Isopropyl alcohol.

Bill

Right, I think that’s part of the problem. How does the reserve circuit/ “on” setting actually work? On the petcock face that meets the gas, it looks like they sit right next to each other. Should the “on” circuit have a tube that rises up vertically? Mine came with a tube but it didn’t fit …

[willbird]

OK so I have my OEM apart on my desk and looked it over quite a bit.

"ON" the fuel goes down the brass standpipe and then a port in front face of the fuel lever routes it down into the sediment bowl.

When you select "Reserve" the fuel goes from the cavity where the bolts go through, again across the port in the fuel lever, and into the sediment bowl.

So reserve is literally the bottom of the barrel.

https://images.app.goo.gl/h9r9SKGLQCXAyRaz7

Bill

[RAFster122s]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

Upon inspection I have the tiniest amount of powdery grit at the bottom of the float bowls. This is annoying because I spent a week - *a week* - servicing the rust inside my tank via electrolysis and acid and agitation. I’m not sure what else I can do other than send it to a professional.

But I have OEM needles coming, and an in-line fuel filter that allegedly does not restrict fuel flow like the one I had.

If you pull the fuel lines off, or have them detached from carbs flip it over to reserve and run some fuel into a container, the reserve fuel circuit sucks right out of the bottom of the tank. In the "good old days" of non ethly fuel lots of gas tanks had at least a little water in them, flipping to reserve could put you roadside with the float needles held open with "stuff" LOL. Maybe before your time but the onset of cold weather had us adding drygas to our gas tanks. Sohio advertised that they included "ice guard" in their fuel, "you go or Sohio pays your tow". That was probably Isopropyl alcohol.

Bill

SOhio/BP was the worst gas to try to run in winter when I lived in Ohio. Problematic and low fuel economy when you tried to run it.
I avoided it like the plague. I used Shell mostly and it with occasional use of Techron FI cleaner kept an 82 vehicle mechanical FI system trouble free for over 15 years I owned it, bought used in ‘86

[willbird]

Most of the time, it is tiny grit in the fuel, coming from things like old fuel lines, fuel tank grit, stuff like that which holds open the tiny float valves and overflows things.

The 350F is the worst!

Upon inspection I have the tiniest amount of powdery grit at the bottom of the float bowls. This is annoying because I spent a week - *a week* - servicing the rust inside my tank via electrolysis and acid and agitation. I’m not sure what else I can do other than send it to a professional.

But I have OEM needles coming, and an in-line fuel filter that allegedly does not restrict fuel flow like the one I had.

If you pull the fuel lines off, or have them detached from carbs flip it over to reserve and run some fuel into a container, the reserve fuel circuit sucks right out of the bottom of the tank. In the "good old days" of non ethly fuel lots of gas tanks had at least a little water in them, flipping to reserve could put you roadside with the float needles held open with "stuff" LOL. Maybe before your time but the onset of cold weather had us adding drygas to our gas tanks. Sohio advertised that they included "ice guard" in their fuel, "you go or Sohio pays your tow". That was probably Isopropyl alcohol.

Bill

SOhio/BP was the worst gas to try to run in winter when I lived in Ohio. Problematic and low fuel economy when you tried to run it.
I avoided it like the plague. I used Shell mostly and it with occasional use of Techron FI cleaner kept an 82 vehicle mechanical FI system trouble free for over 15 years I owned it, bought used in ‘86

This was middle to late 1970's. Gas stations on 4 corners in my small town. Sohio always a few $.01 more than the other three so the place was empty, quicker in and out. Plus the owner had been my cub scoutmaster :-). They sold Atlas tires too which we kind of liked.

[Don R]

 I've been known to turn on the fuel while the needle valve is out to give the passages a flush. Usually into an oil bottle cut to fit.
 I also have a bike or two with an inline filter, even though I've campaigned about them plugging. I posted a video of it once. The F0/1 round top carbs came with a tiny screen attached to the top of float valve. I haven't tried them in a k but some K's came with the same carb.

[BenelliSEI]

Mine came with a tube but it didn’t fit …

The tube has to be there or you are always sucking from the bottom. I try and never turn the reserve on, for this reason……

[seanbarney41]

Just about anytime I look into my float bowls. there is some kind of material in the bottom.  if you ride your bike, it's gonna happen...not necessarily a problem.  These bikes run fine, are perfectly dependable, and get ridden thousands of miles a season, generally with no attention paid to the fuel sysem.

[Floshenbarnical]

Thanks for the wisdom folks. Anyone got a line on a petcock that will fit my F2? Mine fits but is chinesium that wasn’t made for the bike. OEM one seems to be out of stock everywhere. The thread on my fuel tank is larger than what most “good” petcocks fit. It’s M20x1.5. Vintagecb750 sold me mine but it doesn’t have a brass tube, just a plastic one that doesn’t fit. Failing that, a way to reduce an M20 thread to an M16. The “good” petcock I have is M16.

If you could have a line on an M20 petcock with a brass tube where the fuel line spigot exits horizontally that would be even better. The angle getting the fuel line into the F2 carbs runs the risk of kinking with a vertical spigot. I don’t have anything against kinks per se, just prefer not to have them in a fuel line situation.

[RAFster122s]

Don't think I would be sending my carbs or tanks to anyone. Just might need to drop the float bowls every 3 months to clean any debris from them.
Don't panic and throw in the towel, it is premature...
Just relax and in a soothing voice tell your old girl you are gonna fix this too and she's gonna be fine. If you can she will be as good as new...

Often we cloud our minds and judgement when we give into defeat without giving it a good go. Something else comes up you address it and plod on towards the end goal.
It is not personal...just a mechanical puzzle to solve and 9nto the next. I'm glad these old bikes are analog and no computers, that would just make things that more complex...

Lots of smart mechanical types here with vast experience to draw upon. Just getting a bit of the right brains working for you can be the challenge occasionally. I think you have a bunch that are attentive and working to help you solve the stuff that is happening.

Best to start with the simple stuff and establish a good solid baseline foundation...then you have a solid base to build upon.

Take courage, it is not as bad as you can imagine.

David

[BenelliSEI]

If your purchase from Vintagecb750 doesn’t fit or go together, contact them for a replacement. That petcock should have come with the inner “straw” and a screened in cover that fits over the straw. They stand behind their stuff if it was shipped incorrectly or incomplete. An occasional photo would help.