Automatic Fuel Valve

[Loose Chain]

Hi, I'm new here. I am just wondering how people feel about the automatic fuel valve on their bikes? Do many of you disconnect it? They are a pain when you are trying to get fuel to the carbs when they are empty. You either have to prime the carbs or crank like hell to get the vacuum to open the valve. I notice that after the bike sits for a few days the fuel seems to have evaporated and I have to crank it lots to get it to run. If I start it every day, it flashes right up. What do y'all think?

 

[brettp]

Removing it was the first thing I did. I had a VTX1300 and made it gravity fed. I have always been in the habit of turning petcocks to OFF, so removing those are a no brainer for me. If it fails when you're on a ride, you have to bypass it to get home. If it fails before a ride and you don't want to wait for a new part, you have to bypass it to ride.
Does this mean your petcock won't ever fail? No. But you can do some pretty simple maintenance on a petcock every 10 years and you will likely never have a failure.

 

[Loose Chain]

That is what I had in mind, was to eliminate it. I was just checking to see if I was thinking the same way as others. Thanks!

 

[mrtwowheel]

That subject is a controversial one. I do not use the vacuum monster, it is removed and the vacuum port is plugged with fuel hose and a cut off stainless bolt. With or without the monster these bikes are notorious for fuel flow problems, especially when a large fuel filter is used. There's only a small distance between the petcock and the carb inlet, this causes a gravity problem for fuel flow and also an air lock problem in fuel filters.

I'm in the process of a new mod for my bikes. I'm going to use an electric fuel pump, probably attached to the bolts on the starter motor cover. This will allow me to use a fuel filter in the vertical vs horizontal position, goodbye airlocks. Should be an easier transition from main to reserve too. The fuel pump will be powered by the ignition so that when the ignition has power the fuel pump will also have power. Honda has done this on other bikes. I'm looking forward to 100% fuel flow at all times, and any fuel filter that I choose to use.

 

[brettp]

I've had air lock problems before with inline filters. That's a good point! I have a 1/4 filter that prevents air locks for that reason. Been on there for 4 months without issue, thankfully. My vtx1300 had a fuel pump (the first year of production had one then they got rid of it 2004+. I eliminated it because I didn't want it to fail and leave me stranded. Could I make it gravity fed if it failed? Sure. Did I want to spend time trying to diagnose why it wouldn't start up and risk draining my battery away from home? Nope. But in all fairness you should be able to hear the fuel pump is not running and easily diagnose that.
In any case, the filter is a good point.

 

[Bo82CB]

I don’t know what fuel filter airlock you guys talking about!? Yes it is short route from tank outlet to carb inlet to accommodate fuel filter of any substantial size….I used longer hose routed towards carb 3, bend there and on return plenty room to accommodate fuel filter with nice little downhill to the carb inlet. It’s been like this since I finished project last winter and never had fuel filter air lock and I drain my carbs regularly!
Another question is how do you get airlock when gravity pressure created by the volume of the fuel in the tank is forcing fuel into carbs!? Unless you guys riding your bike until tank is VERY LOW on fuel!

 

[brettp]

I think the airlock is caused by an ability of the filter to let air on the outlet side to travel backwards into the tank side. Or something like that. The filter truly makes a difference. The level of fuel in the tank is immaterial.

 

[mrtwowheel]

Unless you guys riding your bike until tank is VERY LOW on fuel!

Exactly, I expect to use the main and reserve the way that they were designed to be used on a motorcycle that has no fuel gauge. Riding down the road, engine stumbles, reach down turn the petcock to reserve, engine recoups and no one but me knows that I just ran out of gas. This can't be done with finesse on a bike with a hose routing like that and a fuel filter that was already half full of air. The process turns into.........park on the side of the road, remove the fuel cap, blow into the tank until the fuel flows down again. And no, this is not a result of bad venting.

 

[brettp]

Exactly, I expect to use the main and reserve the way that they were designed to be used on a motorcycle that has no fuel gauge. Riding down the road, engine stumbles, reach down turn the petcock to reserve, engine recoups and no one but me knows that I just ran out of gas. This can't be done with finesse on a bike with a hose routing like that and a fuel filter that was already half full of air. The process turns into.........park on the side of the road, remove the fuel cap, blow into the tank until the fuel flows down again. And no, this is not a result of bad venting.

You have to explain this to me! Does blowing into the tank really help?!

 

[mrtwowheel]

Yep, this has been done by many on various engines. Nice to make a dam with a rag or your fingers. It's faster than waiting for gas to flow.


P.S. Don't inhale gas fumes, that will make you stupid.

 

[brettp]

How do you do it? I'm having a hard time picturing this...

 

[mrtwowheel]

How do you do it? I'm having a hard time picturing this...

Really don't know how better to explain it. It doesn't take much pressure to disrupt the air that is causing the block between the carbs and tank. It doesn't even have to be a leak free closure between you and the tank. Just causing a little pressure in the tank does it. Otherwise, you can tip the bike from side to side or wait forever with maybe no results.

 

[Loose Chain]

(It doesn't take much pressure to disrupt the air that is causing the block between the carbs and tank. )
If the carbs are properly vented, what is stopping the flow? It's all down hill.

 

[mrtwowheel]

Believe me, I didn't invent this problem, it is inherent to this bike and well documented by many on the Honda DOHC Custom forum. Have never heard of a great fix for this either. What's hard to understand? A gob of air under a space of fuel with no pressure to move the air. Even if vented there is nothing to move the air, no pressure/not enough gravity.

 

[Loose Chain]

Sorry, but I'm not buying what you are selling. The only reason I started this thread was to see how many people take the "Automatic Fuel Valve" off. I had already made my mind up. I was more curious to see if anyone modified the valve so it flowed all the time so they could leave the valve in place so the bike "Appeared" stock.

 

[mrtwowheel]

Sorry, but I'm not buying what you are selling. The only reason I started this thread was to see how many people take the "Automatic Fuel Valve" off. I had already made my mind up. I was more curious to see if anyone modified the valve so it flowed all the time so they could leave the valve in place so the bike "Appeared" stock.

Do you have a 750C? Do you use a fuel filter? Do you run your tank to reserve level? Does your bike transition QUICKLY when switching to reserve? I am not saying to not trash the automatic fuel valve. I have seen these bikes pumping fuel out the exhaust when the afv fails while the engine still runs, it's a scary sight. Hell yeah get rid of it.

 

[mrtwowheel]

By the way, be sure to block off the vacuum port at the #2 carb or you will be burning off valves and holing a piston.

 

[Loose Chain]

Yes I do have a CB750c. Do I have a fuel filter? Yes. Do I run it down to reserve level? Yes. Does my bike transition QUICKLY when switching to reserve? Yes. What you are saying about trapped air in the line (or whatever you said) is wrong on many levels. In all my years of riding, I have never experienced what you are talking about. I have 41 years of experience in civil aviation where a large number of small aircraft run on basically the same setup, gravity. Do you have any experience working on carburetors that work upside down?

 

[SenseAmidMadness]

Sorry, but I'm not buying what you are selling. The only reason I started this thread was to see how many people take the "Automatic Fuel Valve" off. I had already made my mind up. I was more curious to see if anyone modified the valve so it flowed all the time so they could leave the valve in place so the bike "Appeared" stock.

Nah, no reason to do that when that fuel valve is a somewhat ugly octopus and the tops of the carbs look so much more round and pretty. If anyone even bothers to look in there.
Maybe on a museum bike but those are definitely a slim minority of UJM's in general.

Remove the sucker, cap the vacuum port, and run the fuel line straight to the carbs.

 

[brettp]

By the way, be sure to block off the vacuum port at the #2 carb or you will be burning off valves and holing a piston.

Great reminder for that vacuum port. You will know something is wrong if you don't block it because the bike idles differently.
I have to search that forum for air in the fuel line and blowing into the tank. I have had air locked fuel lines beforebut that is because of the filter I used. Switched to a filter that prevents that, and didn't happen again.
For what it's worth, you can move the air trapped in the line by opening carb drain bolt. Blowing in the tank seems pretty silly, I gotta look into that.