Post filter fuel starvation

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sickradsean
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Post filter fuel starvation

#1

Post by sickradsean »

I’ve been sporadically getting a lot of air in my fuel lines post filter lately. It causes the system to run lean, and at times almost like I’m running out of gas. I know the fuel filter doesn’t fill full of gas but I don’t think that there should be this much air, especially after the fuel pump! I’ve already cleaned the gas cap (and then eventually drilled a 1/16” hole in it) to vent better, new fuel lines and filter, new petcock. What am I missing?

Heres a video
https://flic.kr/p/2nQG2Qy
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Re: Post filter fuel starvation

#2

Post by Whiskerfish »

Have seen people spend months chasing air in the fuel lines where their problem was elsewhere. Not saying it is never the problem but I will never own a clear fuel line.
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Re: Post filter fuel starvation

#3

Post by redglbx »

I agree with Whisker and really if it were me the first thing I would do is add some clamps to the hoses, then I’d ride the crap out of it and not worry about it !

Is there a problem with how it’s running ?

How did you determine that it’s running lean ?

On my 76 I have a glass fuel filter that does it all, bubbles in the fuel, full with fuel, bubbling fuel and nearly no fuel in the filter. Used to drive me crazy, but the motor just kept running and I just kept riding!

On the clear lines, I simply don’t run them as they age and get hard they crack & leak, not a fan but I will say the ones on yours appear to be “Tygon” brand which tend to be and stay flexible, still not a fan !
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sickradsean
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Re: Post filter fuel starvation

#4

Post by sickradsean »

Ironically I only switched to the clear lines to be able to see what was going on in them. I was previously chasing down some other issues and in order to rule out fuel starvation put the clear lines in. They are the .25” ones so I have to heat the ends up to slide them over the nipples on the fuel pump (even with clamps the larger size would leak), so I don’t think air is coming in there. I can feel/hear when the engine starts getting too much air. It’ll run rougher and not accelerate as smoothly. Then look down and sure enough, bubbles! I know it’s chasing down small things on a 45yo machine, but when it runs so smooth the rest of the time it really gets on my nerves. Haha
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Re: Post filter fuel starvation

#5

Post by redglbx »

Sick, I can see in you excellent video that the air bubbles are coming from the suction side of the fuel pump, which means it’s pulling air from something on that side. Past one of the nipples/fuel line connections, the fuel filter or the petcock. Or if a spot in one of the fuel lines has a small pin hole, but with the clear lines that should be easy to see where.

Adding clamps to the nipple connections should eliminate that spot, should ! On the fuel filter, I have a glass filter on my 76 that the ends screw on with o’ring seals, if you have something like that then either replace the filter or the o’rings. If it’s a plastic piece with the metal crimp ring it’s either sucking air at the crimp ring or has a crack somewhere in the body. Replace it they’re cheap.

The petcock can suck air at either the nipples, or the valve/handle seal, have you rebuilt your petcock ? If not Randakkhas a pretty nice “kit” for doing this. The only other place(s) that you can suck air at the petcock is the 2 seals on the back between the petcock and the fuel tank, these are special seals in that they are thicker than normal and I think a normal o’ring wouldn’t seal properly, these seals can also be had from Randakk but is also part of the petcock rebuild kit.

So in my opinion you can only be sucking air in from one of the places, so it’s just a matter of going down the line and eliminating sucking air at each spot. Let us know.
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Re: Post filter fuel starvation

#6

Post by sickradsean »

I got my hands on some small clamps for the fuel lines. I hate the way these ones look, any suggestions for something nicer? I tried the band clamps from Honda but they are too big for the 1/4” lines. I also designed a new filter bracket and had my son 3D print it.
ImageImage
Here’s my solution to the clogged fuel cap valve.
Image
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Re: Post filter fuel starvation

#7

Post by Sagebrush »

Do a search on Amazon for 1/4 inch hose clamp types then it will be just a matter of buying the style and quantity you want.
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Re: Post filter fuel starvation

#8

Post by Rednaxs60 »

Look for Oetiker clamps, do a nice job, but have to be replaced each time you remove them.
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Re: Post filter fuel starvation

#9

Post by sickradsean »

Good call on the Amazon! I ordered some nicer T bolt style clamps. Interesting observation: in the morning I don’t have this problem. I store the bike upright in a wheel chock in my garage. In the afternoon after it’s been sitting on the side stand all day is when I get the bubbles. I unfortunately had to eliminate the center stand when I put in a new exhaust last year otherwise I’d use that.
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Re: Post filter fuel starvation

#10

Post by ericheath »

It might be worth a look under the fuel pump cover for something amiss there.
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Re: Post filter fuel starvation

#11

Post by gltriker »

Vacuum pump time. :oldies

I am thinking a commonly available tester for this project is the Mity-Vac manual vacuum pump Kit.

Remove the fuel pump output line at the inlet fuel barb fitting on the plenum. That now open end of the wet circuit is where the vacuum pump is to be attached.

Taking into account liquid gasoline will damage the internals of a vacuum pump, an in-line, liquid catch vessel must immediately precede the vacuum pump, itself.
Also, Limit the amount of time the vacuum pump internals are exposed to gasoline fumes. Yes. Quite a lot of work to prepare this vacuum pump testing, isn't it..

Turn the fuel petcock lever, Off. The vacuum test should indicate where the suspected ingestion of unwanted air is occurring at any void in the tested circuit. Including the fuel pump (diaphragm assembly?). But, keep in mind its internal inlet and outlet check valves' dynamic performance is not part of this static test.
(I am not familiar with the actual pump disassembly and visual inspection of its 2 internal fluid check valves' physical appearance and condition. )

For that purpose, a dynamic ( engine running) fuel pump outlet pressure tester with a low pressure gauge is required. The Shop Manual pump outlet pressure test specification is approximately 2 1/2 psi.
The fuel pump's liquid output volume is also listed in service literature.

All of the vacuum testing might answer what may be happening in the transparent hoses' plumbed, visible section of the fuel delivery system.

Although you've said the fuel petcock assembly is 'new', there's 2 sealing rings between the petcock and its fuel tank mounting pad.

viewtopic.php?p=453019#p453019
see this :oldies fuel pump testing information link. Perform this quick and easy testing, first
Last edited by gltriker on Sun Oct 09, 2022 11:53 pm, edited 2 times in total.
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RE: a thorough fuel tank cleaning
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Re: Post filter fuel starvation

#12

Post by LuckyEddie »

FWIW... I have replaced my fuel pump on both my GL's. The pump offered by Honda has a superceded part number. It is my belief that the diaphragm has been upgraded to withstand modern fuel degredation. Again, that is my opinion...
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Re: Post filter fuel starvation

#13

Post by gltriker »

LuckyEddie wrote: Sun Oct 09, 2022 7:56 pm FWIW... I have replaced my fuel pump on both my GL's. The pump offered by Honda has a superceded part number. It is my belief that the diaphragm has been upgraded to withstand modern fuel degredation. Again, that is my opinion...
Agreed tumb2 possibly a 45 years old fuel pump ? just do it sickradsean ;)
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New users please visit our "Shop Talk" for common tips and help: <---jdvorchak
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^^^^^^^click up here^^^^^ :oldies

RE: a thorough fuel tank cleaning
"And your carbs will thank you. They no longer live down stream from a sewage plant." -gregforesi tumb2
"Can't see the paint when your looking thru the handlebars..........." -Oldewing ;)
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Re: Post filter fuel starvation

#14

Post by redglbx »

If you watch Sickradseans video in his first post you will see that all the air bubbles are coming from the suction side before the fuel pump (definitely doesn’t rule outa bad fuel pump though) so it has to be sucking the air in at one of the fuel line connections, the fuel filter or one of the seals in the petcock.
Red 1976 oe owner
1976 LTD restored
1980 CBX , in the que, to fix the ignorant heavy handed owner
1981 CBX
1977 CB750 K7
2014 FJR OE owner, sold
1980 GL1100
1984 GL1200 naked
1969 CL350, in the que
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sickradsean
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Re: Post filter fuel starvation

#15

Post by sickradsean »

I replaced the fuel pump a few years back and the petcock this past spring. I’ll take both apart for a visual inspection but Red has is right, it’s somewhere in the line. After this much hunting I’m starting to suspect the fuel filters. Maybe they don’t seal at the crimp point where they are put together?
1977 GL1000 "Goldie"
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