R1150 Fuel System Diagnostic Tool

[Roger 04 RT]

It seems every week someone on one Board or another has a suspected fuel system problem. After my system failed last summer I realized that there was a very simple diagnostic point that can check the pump, strainer, filter and in-tank hoses. To test the integrity of the system takes only a couple minutes, after you have the right side plastic off.

The in-tank pump has a capacity at standard pressure of about 120 liters per hour, which is 2 liters per minute. At idle the bike uses very little fuel. Therefore in a good fuel system there is about 2 liters per minute returning from the fuel distributor to the fuel tank.

To make the test you need two feet of hose with a female QD installed on one end and a collection tank. Open the return line QD (upper QD pair on an 1150 RT), plug in the hose and measure the fuel at idle for one minute. If you get a couple liters your system is most likely in good health. The only thing you don't know is the accuracy of your FPR but they don't fail often.

If your bike won't start the test is to connect the hose and make sure you have at least some flow for two seconds at key on. That says the pump has pressurized the system enough to open the FPR.

I keep a hose with a QD for just that purpose. The kit below has a collection tank and fuel pressure gauge with QDs but the best part is the two foot hose with one QD that couples to the line going from the distributor back to the tank. If I'm pushing fuel out that line, the rest of the system is good.

The return hose is light enough that you can add it to your tool kit for longer trips.

RB

PS: What often goes wrong are fine cracks in the in-tank hoses that can leak for years before they suddenly rupture. The return test may give some warning to avoid this event: Fuel System Failure and Highway Breakdown.

 

[Roger 04 RT]

The photo at the start of the thread shows a pressure gauge but that tool isn't usually needed since fuel pressure regulators are very reliable.

Some information on the system
--Fuel Pump: 110 liters per hour, which is just under 2 liters per minute.

--Injectors: 310 cc per minute, which means that both injectors, fully on deliver 0.62 liters per minute, only 1/3 of the pump's capacity.

--The R1150 produces 94 HP. Most engines consume less than 0.5 lbs. of fuel per HP per hour at WOT. Fuel weighs 6 lbs. per gallon. 94HP times 0.5 lbs./HP divided by 6 lbs./gal = 7.8 gallons per hour, which translates to 0.5 liters per minute. In other words, the engine needs about 1/4 of the fuel pump's capacity to produce full power.

The reason I went through that engine math was to show that the in-tank hoses can leak quite a bit of fuel or the filter can be quite restricted and you won't detect it by the engine's performance.

Even pulling the tank to inspect the hoses won't necessarily allow you to find cracks and leaks visually. It is easily possible to replace the filter (or externalize it) and miss the leaking hoses or a weak pump.

Bottom Line
Consider making up a hose with QD and measuring the fuel returning to the tank as an alternative to filter replacement or externalization. And if you do replace the filter or externalize it, make the return-flow test to know for sure that your system is up to snuff.

 

[Smug]

Thanks for posting. You've obviously thought it well through.

 

[(RIP) Bin Ridin]

Yep, thanks for that, it makes sense!