Yamaha Starbike Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 · (Edited)
I've been working on my grandfather's 2012 vstar 950 tourer with around 50k miles. I'm losing power around half throttle in 5th gear. Yesterday morning it hit about 82-83 for 10ish miles and then started bogging down, wouldn't go over 75. got back on after work and for around 30 miles it wouldn't go over 70 and lost speed with any more than 1/3 throttle in 5th. I've been hunting this problem down for about a month when I first started working on the bike it wasn't stored well tank was full of rust dead battery bad oil the usual suspects.

work done so far
- cleaned and resurfaced the fuel tank
-changed the fuel pump strainer
-oil/airfilter/plugs new
-cleaned out the fuel lines without taking off throttlebody/intake

There's only a few things left that i can think of to do like pull the injectors and see if there is any debris blocking them when there's more fuel pressure and cleaning/replacing the fuel pressure regulator. originally I was thinking maybe dying fuel pump/bad throttle position sensor but it would be acting weird in all gears not just top gear if that was it wouldn't it?

Any help is appreciated.
 

·
Registered
2014 V Star 1300 Tourer
Joined
·
114 Posts
I think you’re on the right track, fuel demand is usually higher in the upper gears. If the bike was mine, I would tee in to the fuel line before the pressure regulator (with a handlebar mounted pressure gauge) to check the status of the pump while riding in the upper gears. If the specified pressure checks out ok on the pump, I would hook up after the pressure regulator to check the operation of that component. I do not have the pressure specifications on the pump but I will see if I can find it and edit this post. (Edit: If you ever get around to checking fuel pump pressure it should be around 56.9 psi) you can go to manualslib.com to find free downloads of service manuals, good luck in your trouble shooting. Product Font Parallel Pattern Circle
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #4 ·
I would tee in to the fuel line before the pressure regulator (with a handlebar mounted pressure gauge) to check the status of the pump while riding in the upper gears.
Running some seafoam through it now but if that doesnt work out ill try that out before i start digging around in the reg/injectors thanks!

Not familiar with your specific bike, so forgive me if this isn't applicable, but I see no mention of replacing the fuel filter? Assuming it has one.......
you can put an inline filter on for this year but they didnt come with one just the fuel strainer on the pump. I've considered putting in an inline filter but for some reason yamaha went with a weird slide over locking bracket with buttons for the fuel line rather than normal hoseclamps so im trying to avoid cutting into that line for now. I really don't know why yamaha went with FI instead of carb for the 950 but its starting to feel more like a headache than a benefit lol.
 

·
Registered
99 Roadie
Joined
·
962 Posts
The fuel pump will get varnished up just like the inside of the fuel tank causing reduced fuel flow and low fuel pressure under load.
Only way to tell is to look at fuel pressure with an inline guage and see if if falls down under heavy load.
Injectors and filters can become restricted as well but that is far less common than a weak pump from sitting in stale fuel.

Trying to fault trace injection without a pressure guage is not easy. If you can post a pic of the fuel line connector l can identify it.
As I remember they are Ford type, but I'm not positive.
You shouldn't cut that type of fuel line to look at fuel pressure, they can't be properly spliced and it will become a fire hazard

Any advanced automotive tech should have a guage set that will service that system.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #6 ·
Trying to fault trace injection without a pressure guage is not easy. If you can post a pic of the fuel line connector l can identify it.
As I remember they are Ford type, but I'm not positive.
You shouldn't cut that type of fuel line to look at fuel pressure, they can't be properly spliced and it will become a fire hazard
not shown in the diagram but thats the line with fittings orange to fuel pump black to back rail


Ruler Office ruler Font Auto part Cable
Font Parallel Diagram Engineering Drawing
 

·
Registered
99 Roadie
Joined
·
962 Posts
My kit has fittings that service that style, they don't look identical but they will fit that system.

If you know a good automotive tech, see if they have the guage setup to look at running fuel pressure.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #11 ·
solved cleaned out injectors got a little better, dropped in new fuel pump and the problem is either gone entirely or not noticeable now. Hopefully he'll store it better next time. thanks for the help all. If anyone runs into this going forward the fuel pump assembly is pretty easy to work on and pump/strainer will run you around 80 dollars +/-. A lot better than the whole assembly at around 500. Just be careful with the cables on the pump and you should be fine assuming that you have done the work up to that point working on the pump is the easy part.
 
1 - 11 of 11 Posts
Top