Trouble running uphill

Adam R · February 07, 2004, 07:14:37 PM

I've noticed that my bike is having trouble running up hills. After a little while on a steep mountian incline, the bike will start to wheez as if it were running out of gas. The bike sometimes even stalls out and I have to wait a few moments before it will start again. I would think that the issue would be fuel related, but it might be oil restricting air intake. I haven't pulled the tank in order to check and see if its oil coming out of the valve cover breather, but that seemed to be the problem last time I had this occur.

Has the happened to anyone? Any ideas?

Adam

Jared · February 07, 2004, 08:53:56 PM

How much of an incline and did you have a full tank of gas?....Perhaps the fuel level isn't high enough to reach the petcock....?

Rich500 · February 07, 2004, 09:35:24 PM

To me it sounds liek a fuel delivery problem! Perhaps Im crazy though.

JLKasper · February 07, 2004, 10:58:26 PM

The problem is most likely in the fuel delivery, but not because of the angle on an incline causing the fuel starvation. The GS's lower petcock is vacuum actuated; a vacuum line tapped off a carburetor causes the fuel diephragm to open. When riding up a hill, more of a strain is placed on the engine and the vacuum decreases. The petcock diaphragm slowly constricts and fuel flow decreases, causing that wheezy feeling. However, the diaphragm only operates when the petcock is switched to the "on" position. When switched to reserve or prime, the fuel is diverted through a different route, bypassing the diaphragm and providing fuel directly to the carbs. Gravity-- it's the LAW!

The solution is to switch the petcock from on to the other settings anytime the bike feels like it's running out of gas on a hill. The other changes to avoid this scenario is to downshift early, in order avoid lugging the engine to maintain revs. If it ever warms up here in the snowy midwest, I intend to experiment with placing a large metal inline fuel filter in the vacuum line as a reservoir, so the vacuum builds in straight and level, but has vacuum to spare when needed.

mjm · February 08, 2004, 11:46:32 AM

Quote from: JLKasper... I intend to experiment with placing a large metal inline fuel filter in the vacuum line as a reservoir, so the vacuum builds in straight and level, but has vacuum to spare when needed.

You will have to install a one way valve - possibly a pvc valve - otherwise the vacum in your accumulator will go down about as fast as it does in the carb. A restriction in the line would work except the float bowls might not hold enough gas to get the accumulator charged and to open the valve before they ran dry

Adam R · February 08, 2004, 12:37:54 PM

I have the vacuum plugged up on my bike and run a Pingel petcock directly to the carbs. I'm not sure that it's fuel delivery here, it only happens when going uphill. Even when I ride at 10K rpm, if its flat, I don't have any starvation problems like I did with the stock petcock.

500rider · February 08, 2004, 12:44:24 PM

The accumulator (with one way valve) may keep the petcock open after the bike shuts off therefore allowing gas to possibly overflow the float bowls and spilling gas ... interesting concept though.

There are a few posts about this phenomena of bikes choking on hills. I don't know if there is one single cause for it. I've never experienced it because we have no big hills around here.

Rob

JLKasper · February 08, 2004, 12:48:45 PM

Quote from: mjmYou will have to install a one way valve - possibly a pvc valve - otherwise the vacum in your accumulator will go down about as fast as it does in the carb. A restriction in the line would work except the float bowls might not hold enough gas to get the accumulator charged and to open the valve before they ran dry

Good points... Perhaps a simpler solution would be to connect another vacuum line from the connector on the second carb, then tee them together to the diaphragm?

JLKasper · February 08, 2004, 01:08:30 PM

Quote from: Adam RI have the vacuum plugged up on my bike and run a Pingel petcock directly to the carbs. I'm not sure that it's fuel delivery here, it only happens when going uphill. Even when I ride at 10K rpm, if its flat, I don't have any starvation problems like I did with the stock petcock.

Man, I like that avatar!

I've seen some threads on this issue. The stock petcock diaphragm is apparently weak enough (on some bikes) to not allow enough fuel flow at sustained high speeds. The key in your example is you mentioned it's a flat stretch. The engine is producing enough vacuum to keep the valve open, but the flow rate is insufficient. But this phenomenon can also occur at lower revs, especially if pulling up a long incline. In this case, the vacuum is apperently insufficient to keep the diaphragm open, and the carbs run dry. Same problem, different causes. I like the idea of a vacuum petcock, since it should prevent overfilling the carbs when not running.

Adam R · February 08, 2004, 03:23:22 PM

Its not fuel related, I just had a look at the bike and I'm getting oil coming out of the valve cover breather hose that coats the pod filters with oil and starves the motor for air.

Why would this happen? I have the proper amount of engine oil, so I don't think its excess oil being forced out. And why does this only happen when climing up hills?

JLKasper · February 08, 2004, 07:16:52 PM

This is not a good sign. How many miles do you have on the odometer? Is the breather filtered in any way, or is that hose just laying there open?

Adam R · February 09, 2004, 01:15:37 AM

25K miles and I have a Uni individual oil filter connected to the stock breather hose.

JLKasper · February 09, 2004, 06:36:51 AM

You might have piston blowby issues. Have you run a compression and leakdown check on it?

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Trouble running uphill