Fuel cap lid, Vapor Lock, and VOES
#1
09-12-2018, 09:43 PM
Fuel cap lid, Vapor Lock, and VOES
Ok guys, so here’s my issue of the week.
those who have followed my threads know I’m kinda new to working on motorcycles. But I have it running pretty damn good now. Issue is that intermittently I will get sputtering and lack of power at WOT. At first I thought maybe I had a dirty petcock filter, but that wasn’t an issue.
So after looking at the tank, I have a gravity fed petcock and a Vacuum fuel cap (tank is not vented). This didn’t make sense, but apparently the petcock was swapped at some point by the previous owner. I was thinking Vapor Lock was what was going on, and after some research, it made sense. I waited until I noticed that first sputter, pulled off, and fuel cap was under a lot of pressure. I went ahead and filled my tank, left the fuel door unlocked, then went WOT for about 15-20 miles and it started again. I lifted the door, opened the cap almost fully, ran a bit better, then had it totally unscrewed (not off, just fully vented) and it was probably the best it had performed since I got the bike.
so obviously I’ll need a vented gas cap, but will I need to adjust the settings of the VOES? And if so, what would I need to do to it?
probably dumb but it makes sense to me (change the vacuum to the carb, then the vacuum coming out doesn’t work right?
Short version:
Bike runs like **** randomly after getting hot, it is vapor locking, and the fuel cap is non vented. If I change to a vented style do I need alter the VOES?
those who have followed my threads know I’m kinda new to working on motorcycles. But I have it running pretty damn good now. Issue is that intermittently I will get sputtering and lack of power at WOT. At first I thought maybe I had a dirty petcock filter, but that wasn’t an issue.
So after looking at the tank, I have a gravity fed petcock and a Vacuum fuel cap (tank is not vented). This didn’t make sense, but apparently the petcock was swapped at some point by the previous owner. I was thinking Vapor Lock was what was going on, and after some research, it made sense. I waited until I noticed that first sputter, pulled off, and fuel cap was under a lot of pressure. I went ahead and filled my tank, left the fuel door unlocked, then went WOT for about 15-20 miles and it started again. I lifted the door, opened the cap almost fully, ran a bit better, then had it totally unscrewed (not off, just fully vented) and it was probably the best it had performed since I got the bike.
so obviously I’ll need a vented gas cap, but will I need to adjust the settings of the VOES? And if so, what would I need to do to it?
probably dumb but it makes sense to me (change the vacuum to the carb, then the vacuum coming out doesn’t work right?
Short version:
Bike runs like **** randomly after getting hot, it is vapor locking, and the fuel cap is non vented. If I change to a vented style do I need alter the VOES?
#2
09-13-2018, 03:37 AM
Seasoned HDF Member
Short answer to your short version: No.
The VOES is triggered by engine vacuum and is not effected by negative pressure in the tank.
The condition traditionally referred to as vapor lock it's different from the condition you're describing. Yours is a case of simple fuel starvation caused by negative pressure building up in the tank when air is unable to enter to replace the volume of fuel as its used. Eventually fuel flow slows/stops, the carb bowl runs low, and that's all she wrote. It's not directly a result of the engine being hot. It's just that by the time enough negative pressure builds up, and by the time you've used up all or most of the fuel in the carb bowl, the engine will be hot.
The VOES is triggered by engine vacuum and is not effected by negative pressure in the tank.
The condition traditionally referred to as vapor lock it's different from the condition you're describing. Yours is a case of simple fuel starvation caused by negative pressure building up in the tank when air is unable to enter to replace the volume of fuel as its used. Eventually fuel flow slows/stops, the carb bowl runs low, and that's all she wrote. It's not directly a result of the engine being hot. It's just that by the time enough negative pressure builds up, and by the time you've used up all or most of the fuel in the carb bowl, the engine will be hot.
#3
09-13-2018, 04:00 AM
I agree with Omaha, forget about the VOES, it has nothing to do with your situation.
What bike and year do you ride? Stock fuel system? Did the bike originally come with a vented cap? Is there a vent in the tank somewhere and that is blocked or obstructed somehow? I know my dyna has a vent in the tank and it is semi-hidden. It's a small metal nipple/bung coming off the filler neck with tubing running under the tank dash to frame, then along frame to rear of bike.
Once you post your year and model (or put it in your signature) someone will come along and tell you about the venting system and/or if you need a vented cap. It might be as simple as you needing a new gas cap. YD
What bike and year do you ride? Stock fuel system? Did the bike originally come with a vented cap? Is there a vent in the tank somewhere and that is blocked or obstructed somehow? I know my dyna has a vent in the tank and it is semi-hidden. It's a small metal nipple/bung coming off the filler neck with tubing running under the tank dash to frame, then along frame to rear of bike.
Once you post your year and model (or put it in your signature) someone will come along and tell you about the venting system and/or if you need a vented cap. It might be as simple as you needing a new gas cap. YD
#4
09-13-2018, 04:22 AM
Banned
The following users liked this post:
Rsbenden (02-03-2020)
#5
09-13-2018, 05:10 PM
#6
09-13-2018, 05:21 PM
Join Date: Jan 2011
Location: Haslet Texas
Posts: 20,999
Likes: 0
Received 4,317 Likes
on
1,946 Posts
#7
09-13-2018, 05:22 PM
Seasoned HDF Member
Trending Topics
#9
09-13-2018, 06:42 PM
Join Date: Jan 2011
Location: Haslet Texas
Posts: 20,999
Likes: 0
Received 4,317 Likes
on
1,946 Posts
#10
09-13-2018, 09:05 PM
Seasoned HDF Member
The following users liked this post:
Mattbastard (09-18-2018)