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Bike loses fuel riding up steep hill?

  • Thread starter Thread starter rockhammer
  • Start date Start date
Steve said:
Before you install the new petcock try that same hill with the lever in PRIme.

It's possible that you have the throttle wide open, especially if you are in a higher gear, which would leave no vacuum to keep the petcock open.

If it works in PRIme, and you are trying to go up that hill in fourth or fifth gear, try it in ON and in third gear to see if it makes a difference.

.
Click to expand...

Yano Steve, something is wrong with your theory. I have pinned the throttle all the way up hundreds of long grades, several thousand feet vertical at a time, never had this happen. Usually it's in whatever gear puts it in the 7,500 - 9,500 RPM range, but sometimes less, maybe as low as 5,000. On the bigger bikes maybe even lower. I think even with the throttle wide open there's enough vacuum to keep the petcock open.
 
rockhammer said:
Tomorrow I have the hill to climb. I will do what you suggested. I was going to change the petcock either way though because I read it is one of those things that is suggested. I will also check fuel levels this weekend. The bike rids amazing after the maintenance work recomended. Just that darn hill is still giving me problems. In regards to the throttle I do not have it totally open but I am going pretty fast 75 the hill is very long it is not a short hill it takes about five minutes to get to the top. Before the maintenance I would have the throttle fully open and I could not get the bike past 70mph and it would die half way up. After the bike easily passes 70 with out a fully open throttle but it still dies.

I will update this post for those curious as to what this issue might be. I appreciate all the suggestions.
Click to expand...

I think your problem is that fuel flow is marginal and insufficient at or near full power. Back of the envelope calculation you will need 400cc per minute delivery to the bowls. I don't think the hill has anything to do with it apart from needing high flow rates - you could probably get it to to die on the flat at full power. Many older bikes have marginal delivery systems even with clean taps that shows up as soon as you try to increase power output. Bet your petcock filter is blocked partially or something like that, the inline filter after the petcock if fitted perhaps.
I would run to a jug on PRI and see what I'm getting.
If this theory is correct you should be able to maintain lower speeds up the same hill - it would eliminate the angle of the bowl also.
 
Last edited:
Any chance that the tank itself has a quantity of water/rust/debris, just enough to foul the petcock as the tank angle on the hill forces some of that stuff (if it has any in it) back to the petcock pick-up?
 
tkent02 said:
Yano Steve, something is wrong with your theory.
Click to expand...
You could be right, Tom, that's why it's just a theory.
icon_shrug.gif


Although, if there is a bit of a vacuum leak, possibly due to a cracked hose or a hole in the diaphragm,
the vacuum signal to the petcock would be compromised, letting the petcock shut off the fuel.

Some day, I might attach a vacuum gauge to see what actual numbers are while riding in various conditions.

.
 
I'm going for the gummed up petcock filter -as in Brendan W 's theory- real long uphill is taxing fuel flow even in "pr" spot.
 
tkent02 said:
Yeah that sounds likely. I have seen that a time or two.
Click to expand...

I installed new petcock earlier today. I will ride that darn hill in about an hour and find out if this improved. But the old one did not look to bad. it was the original though.
 
Ok well I scooted up that hill today full throttle and had zero problems. So it was the old petcock. I did take it apart looked ok, but maybe diaphram was bad. Not sure. Just glad she works up hill now.

Thanks for all you input riders.
 
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