New Petcokcs But No Flow

[ridingagn]

Greetings once again,
This is an extension of the re-furbish thread I did on the Frankenbike. As you recall, I replaced the vacuum petcocks with standard valves. The octo is gone, so no parts of the original fuel flow exists anymore. The new valves function perfectly, with an in-line filter between each valve and the carbs they service. The right hand valve supplies carbs 1&2, while the left hand valve supplies carbs 3&4. Here's my problem:The fuel does not want to flow freely trom the tank to the carbs. I can watch the fuel empty out of the transparent filters and not re-fill. It's not always the same filter that does it. I have tried elevating the filters, having the lines and filters at different positions relative to the carb bowls, and opening the tank so there is no vacuum problem. The gas just doesn't want to trickle into the filter. Disconnect the lines anywhere along the line and fuel flows like crazy, but once the floats shut off the flow, it doesn't always start back flowing again. This problem is not consistent either.... you can ride for an hour with no problems, then let it idle and the bowls will empty out and it fuel starves. Weird thing is it never does both sides at the same time.
The carbs are the "no vent tube" type, and are in perfect shape, as detailed in the "misfire" thread. Other than this problem, the Frankenbike starts, idles and runs smooth as silk. Anyone have this problem?

Papaloerts

[bikerphil]

Maybe check your gas cap vent? They can get plugged up. Also, if you have the 78-9 carbs, the bowl vents could be blocked.

[ridingagn]

I opened the gas tank, as mentioned in my thread..... no change.
These carbs are the "vent free" type, as mentioned. I did swap out with a different carb bank I have that has vents....... no change.

Papaloerts

[Ken Talbot]

Have you done anything with the carbs and/or airbox? I'm wondering if you may have done something to mess up the float bowl venting.

[Larrym]

Tiny Bubbles....

My diagnosis: FILTEROUS RESTRICTAMUS.

"inability of fuel to flow past filter medium with existing fuel gravity pressure."

Seriously though, a restricted filter usually happens when the filter is dirty. In this case I believe that the filters are new?? If that is true then I would say that your filters (even though they are new) provide so much resistance that the pressure of the gravity fed fuel has a tough time getting through.

This could be because the filters themselves were designed to be used in conjunction with a real fuel pump which pressurizes the fuel enough to get past the filter material. Usually these types of filters are not the "paper element" type but rather a hard block of material the fuel must pass through. The filter material looks/feels metallic.

here's a pic of something similar to what I use:



they are mounted on the bike here:



Big filter area equals more area for the fuel to pass through equals less restriction in the overall line.

Big plus in my mounting position is that the filters are not out of sight/out of mind. I can check them visually for contaminants before each ride. Also it would take a LOT of crud to block off the fuel flow as compared with a tiny filters.


Got a make and model of the filters you're having problems with? Or a picture?

[xs11lover]

I'm not sure why you would want to remove the vacume setup, but I have a set of freeflow petcocks that were on my 79xs11 standard tank when I got it.
If your problem is the petcocks, I'd give you those for shipping cost.

[ridingagn]

Have you done anything with the carbs and/or airbox? I'm wondering if you may have done something to mess up the float bowl venting.

The airbox is gone, running on pods. Carbs have been meticuliously cleaned and adjusted, and the bike runs perfectly. This set of carbs has no vent tubes, being an '80 model. All ports, jets, passages etc are free and clear (I rebuild / clean carbs routinly). The problem persists on every carb bank I install, vented or not.

[DGXSER]

Remind us what year bike youhave and what version of carbs. If you have the newer carbs with the float bowl vent in the inlet bell, adding the pods might have restricted the vents. Some of the pod filters cover a small portion of the inlet bell.

[ridingagn]

My diagnosis: FILTEROUS RESTRICTAMUS.

"inability of fuel to flow past filter medium with existing fuel gravity pressure."

Seriously though, a restricted filter usually happens when the filter is dirty. In this case I believe that the filters are new?? If that is true then I would say that your filters (even though they are new) provide so much resistance that the pressure of the gravity fed fuel has a tough time getting through.

This could be because the filters themselves were designed to be used in conjunction with a real fuel pump which pressurizes the fuel enough to get past the filter material. Usually these types of filters are not the "paper element" type but rather a hard block of material the fuel must pass through. The filter material looks/feels metallic.

here's a pic of something similar to what I use:



they are mounted on the bike here:



Big filter area equals more area for the fuel to pass through equals less restriction in the overall line.

Big plus in my mounting position is that the filters are not out of sight/out of mind. I can check them visually for contaminants before each ride. Also it would take a LOT of crud to block off the fuel flow as compared with a tiny filters.


Got a make and model of the filters you're having problems with? Or a picture?

Thanks Larry....... I am runnig the exact same filter you have in your picture. They are brand new, and I too have them in plain sight, and yes..... the arrow on the filter is pointing in the direction of fuel flow. I know it should not be significant, but the outlet pipes on the valves are a size smaller than the carb inlets. We are using a smaller size line fron the valve to the filter and a larger size line from the filter to the carb. Unfortunately these valves from "Mikes" don't come with the larger lines. I am inclined to try to get the lines all the same size from tank to carb to see if that fixes it (if I can find a larger outlet for the valve)
Martin

[ridingagn]

I'm not sure why you would want to remove the vacume setup, but I have a set of freeflow petcocks that were on my 79xs11 standard tank when I got it.
If your problem is the petcocks, I'd give you those for shipping cost.

The vacuum setup was removed because they leaked badly, re-build was out of the question and the consensus on this forum seems to be to toss the octo and get rid of the vacuum valves. The oct was tossed long ago, and the free-flow valves solved the mis-fire and runnig starved problem that I documented in the "misfire" thread a few months ago.
Martin

[ridingagn]

Remind us what year bike youhave and what version of carbs. If you have the newer carbs with the float bowl vent in the inlet bell, adding the pods might have restricted the vents. Some of the pod filters cover a small portion of the inlet bell.

The Frankenbike is Caseys (oldest son), and is an '80 standard. The carbs are the ones without the vent pipes.
The pods are the oval shaped red XS pods. New mounting boots (comes with).
I removed the pods to see if it made a difference (per your point about the vents), but the problem persists. As far as I can tell, the boots are smooth with no flange that restricts the vent holes.
Martin

[Larrym]

Mo' Flow

Thanks Larry....... I am runnig the exact same filter you have in your picture. They are brand new, and I too have them in plain sight, and yes..... the arrow on the filter is pointing in the direction of fuel flow. I know it should not be significant, but the outlet pipes on the valves are a size smaller than the carb inlets. We are using a smaller size line fron the valve to the filter and a larger size line from the filter to the carb. Unfortunately these valves from "Mikes" don't come with the larger lines. I am inclined to try to get the lines all the same size from tank to carb to see if that fixes it (if I can find a larger outlet for the valve)
Martin

Right! Looks like we both chose the same solution to the same sorta problem. Here's a fuzzy pic of the petcock(s) I chose:



Since we're both using the same filters/manual petcocks then the problem isn't likely to be the hardware. We do have different carbs with different venting but for the moment I'll go along with the notion that isn't the problem.

What I found was that after installing the filters and then opening up the petcocks the fuel flowed briskly down/into the filters and then up into the carbs. (The clear fuel lines made this easy to see...) I noticed an air bubble in each filter due to the shape and the fact that each was lying sideways with no way for the trapped air to escape.

At this point I tipped the filters so that the bubble would escape into the inlet orifice and then the outlet orifice. Since then no more air has entered into the filter. You may not have the clear fuel lines but if your filters are clear/translucent then it would be an easy step to take.

My reason for eliminating the air bubble was to eliminate the possibility of the dreaded "VAPOR Lock" where an air bubble expands due to heat and then limits/stops the fuel flow. Sorta made sense to me that if there were a bubble in the filter that the filter medium might act as enough resistance to cause the bubble to expand out and away from it. Then the only way for fuel to get through was for it to trickle past the material side to side with only the pressure from the weight of the fuel in that little chamber. A little too wimpy IMHO.

I'm sure that if you eliminate any air bubbles in the fuel filters then the full gravity pressure will be there to force the fuel through the filter. Hopefully that will be enough to permit the best flow possible. So far that's been enough in my situation.

HTH

[bikerphil]

Ridingagn, sorry I misread your post earlier. My experiences with in line filters is that the air pocket never seemed to make a difference for me. Although, I run my filters on the top, right after the petcock, then directly down to the fuel T's. I still have an air pocket (bubble) in the cone shaped filters I'm running and the bike runs fine.

[tarzan]

JAT
You know, the bowl gaskets have a jog on one side to miss a hole .If you install the gasket the wrong way the gasket can cover that hole.I don't know if it will cause you're problem, but it's worth a look.

[ridingagn]

JAT
You know, the bowl gaskets have a jog on one side to miss a hole .If you install the gasket the wrong way the gasket can cover that hole.I don't know if it will cause you're problem, but it's worth a look.

Good point Tarzan, thanks...
I put on other banks of carbs that have the vent pipes, and still have the problem. I will, however, check that out next time I have the bank off.

Martin