fuel pressure loss question

[naughtyG]

Hi all,

sorry I haven't been around much - still riding my Max and loving it just not as often as I'd like!

I have a question about the fuel pressure and especially the loss of it: I know that on a normal max, if it's left to sit for a few days, then upon switching the ignition back on there will be quite a few clicks from the fuel pump to rebuild the pressure in the float chambers. Conversely, if the bike's only sat a short while since its last run, then there should be 2-3 clicks at most as the pressure is still there.

Now we come to my bike, which even after just a couple of hours, will have the fuel pump click like it's been sitting for a couple of weeks. The bike starts fine, always, without any choke (I live in a hot country at sea level). It also runs good, the only problem being the fuel consumption being way too high for a 2000 model. I only ever get 200kms to a tank before the fuel light comes on, that's 120 miles, AND I have an expanded 21L tank (that's 6L more than OEM, or a gallon and a half).

Conversely, I know a local guy with a '96 who gets over 200kms on every tank before the fuel light, and he has the OEM 15L tank..

I think my fuel consumption problem is related to too much evaporation that's verified by the constant loss of pressure in the float chambers - hence the crazy fuel pump clicking every time I switch on.

So, which components are actively holding the fuel pressure? I assume the fuel pump diaphragm of course, but which bits in the carbs? :ummm:

Please list them all if you know - I'd love to find this problem and eliminate it!

 

[SpecOps13]

Needle and Seat... Your mileage is terrible, even Skullduggery gets 33 MPG. I do use Non Ethanol and would expect less mileage from E-85.
I take it there are no leaks, don't think you'd miss something like that.

Dave

 

[marsmax85]

top of my head fuel and air filter dirty and loss of pressure could be diaphragm in fuel pump. Also floats bowls levels ?

 

[SpecOps13]

top of my head fuel and air filter dirty and loss of pressure could be diaphragm in fuel pump. Also floats bowls levels ?

Yes, float bowl levels could be off...Absolutely...

 

[jfeagins]

Since the tank sits below the carb level, and the pump is necessary to deliver fuel UP to the carbs, I don't think you are losing much gas out the carbs after shutdown. If your fuel bowl levels were too high, or a needle/seat were leaking during run time, I'd think you'd have idle performance issues to deal with, or worse.

If it were mine, the first place I would check if it were losing pressure between rides would be inside the fuel pump. Easy enough to pull off the bike. Make sure BOTH little rubber diaphrams are firmly in place inside the pump and that both are free of any obstructions, and that they are still soft and pliable rubber, rather than still and/or cracked from age. I'd guess that it's most likely one of them is completely dislodged from it's proper position inside the pump housing. JM2C.

 

[PATMAX]

G, forget the idea of any kind of pressurized fuel anywhere. Unless you had a fuel
injected setup, gas is being allowed into the carbs by the bowl floats and the float needles/seats. Unless you have a pinhole leak in the diaphragm inside the fuel pump itself. I doubt there is any measurable evaporation from the fuel tank itself. As you probably already know, the fuel pump cycles at start up to fill carbs and it's feed lines. When the fuel "sees" the drop in pressure on the carb side of the pump, it kicks in. Unless the reserve switch was deactivated.

 

[Traumahawk]

How is your oil level....has it "grown" any since the last oil change?

 

[[email protected]]

I had a similar issue on my '06. It didn't appear until I swapped the original carbs for a set of unknown vintage. (they were old for sure)

I noticed that the fuel pump would click nearly every time I turned the ignition on....even if the bike was sitting for a short period of time.

I tore those carbs apart and checked things. Never found a problem. Bike ran fine. Gas mileage was normal.

I switched over to yet another set of carbs. These are fairly new, off an '05. Went thru them with new O-rings and gaskets. Put em on the bike and everything is normal again.

Doesn't make sense to me at all but, that's the truth and I'm sticking to it.

 

[naughtyG]

Hmm nothing all that conclusive then eh?

I will tear into the fuel pump and check those diaphragms.

Oil level is fine - no fuel seeping in there.

I'll also check my fuel bowl levels - I kinda need to tear into and clean up the carbs anyway as I haven't done it for a few years now.

Will check both air and fuel filters again too.

The only other thing worth noticing is that the bike sputters sometimes at low revs (idle is always fine) just when coasting around 2-3000rpm. I gotta find out why the fuel mileage is so bad - it makes little sense!

 

[MaxMidnight]

Hmm nothing all that conclusive then eh?

I'll also check my fuel bowl levels - I kinda need to tear into and clean up the carbs anyway as I haven't done it for a few years now.

Will check both air and fuel filters again too.

The only other thing worth noticing is that the bike sputters sometimes at low revs (idle is always fine) just when coasting around 2-3000rpm. I gotta find out why the fuel mileage is so bad - it makes little sense!

You can check float level height externally - no need to pull the carbs.

Are the heat shields that sit atop the cam covers still in place?

 

[huskyman510]

Let me know how you get on

I hardly ride mine but have never had an issue with pump filling bowls and stopping etc until my last ride.
Got home and the next day turned the key pump clicked away and stopped then I normally do the cycle again to make sure bowls are full and it clicked away again for the same time. After doing this 5 times the same thing I tried starting and it appeared normal.
Walked away thinking how does that happen? remember reading the nice thread on tearing fuel pump apart and re-fitting gasket into position, wondering if this is a common issue?

 

[jfeagins]

...? remember reading the nice thread on tearing fuel pump apart and re-fitting gasket(diaphragm) into position, wondering if this is a common issue?

Yes!

 

[naughtyG]

You can check float level height externally - no need to pull the carbs.

Are the heat shields that sit atop the cam covers still in place?

Yea I'll check the floats wet first, but I have a feeling they may be high so will most prolly need to get in there to adjust..

For the heatshield do you mean the big black plastic one atop the rear cylinders? If so yes it is there.