What happens when a fuel pump goes bad?

After having a heavy fuel leak, I pulled the carbs and found a cracked fuel line. Replaced it. Put carbs back on bike, rode well for a week.

Then it began leaking even more than before, I can see fuel shooting out of the fuel rail in more than one place. I don't think I stressed the fuel rail, I know it's fragile plastic. I do understand that the o-rings may have gone bad, but several at once? And with fuel not just dripping, but shooting sideways with the pressure from the fuel pump?

I have removed the carbs again and don't see any obvious damage.

It makes sense at this point to replace all the fuel rail o-rings, but I'd like to know: What regulates the fuel pump? What prevents it from pushing too much fuel with too much pressure? If a fuel pump is going bad, will it push too much fuel? As in, if my fuel pump was on the outs, would it blow fuel past the o-rings and cause it to shoot out of the carbs like this?

Nothing regulates the pump, it only has the ability to push -2psi or so, after it sees that the resistance of the bowls being full it stops pumping. Unless of course you have a leak, then it will keep pumping.

Yep. Fuel pump is pressure sensitive. Once there's pressure, it stalls out.

It shouldn't be the problem, but are you sure you don't have a float stuck. That would cause gas to pour out, but not shoot out, or so I think. Try disconnecting the fuel pump. Perhaps just run gravity feed to get you by or to see if the pump is really malfunctioning.

OK, thanks for the info. I was just wondering how it worked, so I wouldn't chase the wrong parts.

Ya'll don't know how much I DON'T want to break these carbs off the rack. But there's no sense in waiting for anything else made of rubber to fail; I'll just do 'em all.

I did check the float needles and found them in great shape. No indentations in the points at all. Of course I'll polish the seats while I'm in there.

If anybody's been here and has a trick or two I should know, I'd love to hear it.
The o-ring kit for this bike is crazy expensive, I'm hoping the Harbor Freight metric neoprene assortment kit has some to fit.

[image: View Post]coffeebrake, on 17 April 2012 - 09:58 AM, said:

OK, thanks for the info. I was just wondering how it worked, so I wouldn't chase the wrong parts.

Ya'll don't know how much I DON'T want to break these carbs off the rack. But there's no sense in waiting for anything else made of rubber to fail; I'll just do 'em all.

I did check the float needles and found them in great shape. No indentations in the points at all. Of course I'll polish the seats while I'm in there.

If anybody's been here and has a trick or two I should know, I'd love to hear it.
The o-ring kit for this bike is crazy expensive, I'm hoping the Harbor Freight metric neoprene assortment kit has some to fit.

Get ahold of Billy Carr from V4Market.com to get the o-rings that you need.  You can order from him just the o-rings that you need, instead of having to buy an entire kit if it's really not necessary.  I have his business card at home with phone number on it so you can contact him directly and let him know what's going on.  I can scan it for you when I get home if necessary.  I would estimate that you can get just the fuel rail o-rings for $10 - 20ish.  I'm pretty certain he also sells an 'Economy' version of the mega carb rebuild kits that are basically just the rubber parts.  Not certain on the cost, but it may be worth asking about if you call.

Pulling the carbs off the plenum / rack / airbox plate is really not as big of a deal as everyone makes it out to be.  As long as you are very VERY careful with the fuel tees, take pictures as you go, and put everything in a designated spot for each carb body as it comes off, it's simply tedious.  I've had the rack off of mine on 2 separate occasions (once to replace fuel rail o-rings, and another to pull a bent butterfly valve to fix it) and everything is fine.

The Harbor Freight metric o-rings might come in handy.  IIRC I had to stack the new o-rings on top of the old ones to ensure that the tees sealed properly, as they were relatively loose using just the new rings, but I can't remember if the HF o-rings came into play or not.  I'm sure had I soaked the new ones in fuel first, they'd have sealed up, but I wanted instant gratification and to know that I can leave the carbs empty for an extended period of time and they will NOT leak fuel right off the bat.

I believe the pressure is controled by a spring, and it isn't possible for the pump to go beyond 3 psi ever.

[image: View Post]jcarpfishman, on 17 April 2012 - 11:45 AM, said:

Get ahold of Billy Carr from V4Market.com to get the o-rings that you need.  You can order from him just the o-rings that you need, instead of having to buy an entire kit if it's really not necessary.  I have his business card at home with phone number on it so you can contact him directly and let him know what's going on.  I can scan it for you when I get home if necessary.  I would estimate that you can get just the fuel rail o-rings for $10 - 20ish.  I'm pretty certain he also sells an 'Economy' version of the mega carb rebuild kits that are basically just the rubber parts.  Not certain on the cost, but it may be worth asking about if you call.


I'd like that number, please. I bet he knows more what I'm going to need than I do. I already got some bowl gaskets, but might as well do the idle mixture screws too.

[image: View Post]coffeebrake, on 17 April 2012 - 01:31 PM, said:

I'd like that number, please. I bet he knows more what I'm going to need than I do. I already got some bowl gaskets, but might as well do the idle mixture screws too.

Here's what you need!  I'm not sure if the prices are exactly correct, but I they are close (this business card was from a year or so ago).  I've spoken with him on the phone before for carb advice and he's very helpful.

[image: Bill Carr Business Card - Front.jpeg]
[image: Bill Carr Business Card - Back.jpeg]

Also, I found the bookmark that provides a more complete price list of the stuff that he does (although the prices may still be outdated slightly):

http://v4hondabbs.co...p?topic=36751.0

Hope you get everything taken care of and get back on the soon! :smile:

Wow, thanks! I just hope to get the rubber bits I need.

The bike was running great, and I have an ultrasonic cleaner and I've been through these carbs several times before...just never pulled 'em off the rack.

It will be nice to re-assemble with new rubber bits, knowing it should be good for many miles to come. Considering doing a track day on this bike and of course need it at its best for that.

Billy Carr won't answer emails or phone calls. Not even an answering machine. I wonder if he's still in business....

I've got the carbs off the rack and clean, I'm just waiting for o-rings, or at least measurements on the o-rings so I can source some locally.
The old ones were hard and had to be torn off the rails, but I'm not sure at all that any of the ones in my Harbor Freight metric kit will work.

You can get fuel tube O-rings from Jamie Daugherty.


http://www.daughertymotorsports.com/

took a chance and re-assembled with the o-rings I had on hand, and all new fuel lines. So far, so good. No fuel leaks. I hope it stays that way....

Oh, and it wasn't all that hard to break the carbs off the rack and re-assemble. The instructions in the Honda shop manual were pretty clear. I also have a rack of parts carbs that served as a model, that helped a lot.

From what I understand, Billy can be difficult to get hold of at times.  I would assume with the weather getting nice a little early this year, that he is swamped with carb cleaning orders, etc.

Good to know that Jamie has them as well... besides, he's much closer to me anyways!

Told you that splitting them apart wasn't as big of a deal as everyone makes it out to be!  Don't you feel so much more accomplished now for completing a feat that is feared among V4 owners? :tongue:

Yes. Quite frankly I made more mistakes putting the twin carbs from the CX500 back on the rack. Didn't know about the part where they must be tightened down on a flat surface....which the plenum on the V4's does.