Hi, Maybe, like me, it's that old guy thing? I'll drop in some Flowmax if you guys can't help me .
So the GSPD tank supposedly holds 9+ gallons. I've tested the reserve capacity in the garage (about .5 gals right side, and .6 gals left side). My bike starts sputtering with about 3 gals (determined on filling it up) left in the tank. Going to reserve solves this, but it seems like the gas should still be available without going to reserve. This happens under high demand (uphill, 5th gear).
I have tested the flow out of both petcocks, including running it through the crossflow tube. I've pulled the float bowls and let the gas run right out of the open float valves- in all cases at least 400 cc of fuel flows per minute.
THE FUEL CAP IS VENTING OK.
It's easy to solve- switch to reserve, and go find gas. But I'd like better range for the 9 gallons I carry around all the time..
Any ideas?
'83 R80ST
'92 R100GS
'04 R1150RTP
garage full of airhead parts...
Bamboo812 wrote:Check your float adjustment; wide open throttle can lead to fuel starvation if the bowls aren't full enough.
Execuse my lack of knowledge, but why would it not be an issue with a mostly full tank, but would be an issue when the the tank is about 1/3 full? I would think that the amount of fuel in the tank (except for when it's empty) would not have a significant affect on the amount of fuel in the bowls.
Jeff in W.C.
1988 R100 RT
2018 R1200 GS
"I've got my motorcycle jacket, but I'm walking all the time." Joe Strummer/Clash
In a gravity feed fuel system, pressure increases with the height of the fuel level. I would guess that the big tank probably has close to 50% more pressure when the tank is full than when it gets down to the last couple gallons. Since the tank reaches lower than a stock tank, at lower fuel levels it has less pressure than a regular RS/RT tank has on reserve.
This would mean that anything reducing fuel flow - obstructed lines, fuel filters, clogged filters, low float bowl levels, etc. - would have much more impact with the GSPD tank (at lower fill levels) than it would with the other stock tanks.
I get that the pressure is greater with a full tank than a tank 1/3 full. However, I questioned whether or not it would have a significant affect--and I'm assuming adequate and proper fuel flow. Don indicated that he checked the full flow, and it seems adequate based on my limited knowledge. In addition, BMW would have factored in the flow rate of gas at 1/3 tank and made sure the flow was adequate. Now if flow was inadequate, I can see there being a problem with the tank at 1/3 full versus being full.
Tim, I'm not saying you're wrong. You're probably right, but I'm just trying to understand how these things work.
Jeff in W.C.
1988 R100 RT
2018 R1200 GS
"I've got my motorcycle jacket, but I'm walking all the time." Joe Strummer/Clash
Yeah, Jeff, I get your point: that when everything is right, it should work fine. My point was that it would take less obstruction to screw up the flow with that tank than with the others.
We went through this issue on our race bike. It was a R75/5 with considerable engine work and would do 125 + in a long straight away. We got it all buttoned up around 10 pm on a Saturday night for the race on Sunday. That was also a good time for a test ride because our public roads were not busy and those speeds were safer.
For some reason I had stayed late to assist. The rider returned complaining that it started missing at the top end. A quick inspection showed up nothing wrong. Again it came back "missing" at the top end. We really didn't like having to test it above the ton at night. We checked the gas level and it was OK and still well onto the main tank, as opposed to the reserve. We had removed the tank to make sure that the throttle cables weren't shorting out at high rpm. Nope, they were in the clear. We could find nothing wrong, except that it didn't work. This was a new symptom after several races with this set-up.
Out of frustration and the feeling that we had to do something, I suggested that we fill it up for the testing in order to be sure that we didn't run near the reserve level. Walla, the full tank fixed it and it ran all the way up to top end. The level of around 1-2 inches above the reserve inlet just wasn't enough gravity to feed that hungry engine. Oh yes, we had cut down the tube because we didn't need to get to a gas station 30 miles away, we could just pull in anytime for fuel.
Remember, the rider was very light, no fairing, no weight that wasn't needed for the race. Still, it needed that gravity.
In the morning, the rest of the crew showed up and could hardly believe our story.
Long before this incident, we had learned that a stock bike required the flow to be 100 cc in 15 seconds, or trouble could result. That was well enough to assure proper fuel supply. Our many experiences of owner complaints that we fixed with just cleaning out the system to get the flow back to normal is why you often read me getting on my soap box about fuel flow. This race bike hog was so hungry that we wasted at least 3/4 hour finding such a simple solution and it was by accident.
I am telling you once again, many times a year you should be pulling off a fuel line and turning on the petcock. After a few times of running the fuel into a graduated cylinder, you will learn what proper flow looks like and from then on, you can see by just watching the flow to know if it is enough. This is a test that takes less than a minute for both sides to perform. Just do it.
If you aren't in a position to remove everything and clean it properly, you can do a "cheat fix." Just blow compressed air into the clogged up fuel line and blow the crap and dirt up and back into the fuel. It is very temporary, but it will get you down the road. Then you will forget and it will happen again soon, but this time the "cheat fix" may not work and it is midnight in the rain.
Ask the Indians what happens when you don't control immigration.
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