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Discussion Starter #1
I have a 2008 Vstar 1300 cruiser w/5k miles. Has always run great, no problems. Garaged & covered. Ride on weekends.

An issue cropped up recently. It idles fine with no apparent miss but under any load, it has terrible throttle response with no power and sounds like its not running on all cylinders until the engine wakes up and almost throws me off the bike. Once it "wakes up", it has normal strong power if I stay on the throttle but as soon as I get off the throttle, it returns to the muted throttle and power. If I get back on the throttle, the process repeats itself ... no power and sounds crappy then all of a sudden, switch flipped and I'm off to the races again. It's really dangerous actually.

My first thought is it's a fuel system issue. Misfiring injector(s), dirty fuel filter, etc. I added some Seafoam to the fuel no change. Electrical ... misfiring coil? Any thoughts or advice is GREATLY welcomed and appreciated.

Thanks!
 

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I would change plugs. The spark plug has a built in resistance to help deliver a clean spark. When resistance gets high, due to age, fouled, etc, it will fire easily without a load, at idle. The coils deliver more energy the higher the RPM and plug might be "breaking down". It's a cheap place to start. Post back results.
 

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there was a comment in your new member thread about premium gas

these bikes are tuned to run on the fuel octane listed in your owners manual (you can down load them free from yamaha if you dont have one for your bike).

On carbed bikes the jets are sized for the fuel octane called out. On your fuel injected bike the fuel/air ratio is mapped the same way. Unlike a car with a full closed loop O2 sensor feedback long term adjustment, the fuel injection on these bikes does not self adjust when you change octane rating, or change the exhaust, or put a bigger air filter on for more air.

I know it sounds backward but regular octane fuel has more energy per ounce than hi octane. If you put premium in a bike that is set up for regular, it will run lean - with the highest grade premium it will run very lean, stumble, sputter.

It sounds like what your bike is doing is more severe than that, so it might be more than just the premium gas. Checking your plugs like Les suggested is a good start, esp if you dont know the last time they were changed.

Also take a look at your air filter - it should be white like paper, not grey, not tan... If your air filter is dirty it would throw the air/fuel mixture the other way, acting like the engine is choked and it will run rich - but most noticable when the throttle is wide open. Your bike seems to be doing the opposite - idling rough but ok with a lot of throttle twist. So the odds are worn plugs or premium fuel.

If you want to check the fuel, pull the line off the petcock and drain it out into a gas can, put that in your car, and fill the bike with regular octane.
 

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Discussion Starter #4 (Edited)
Thanks Les and KCW .. all good advice.

I drained the premium fuel from the tank. I really think it's a fuel system issue resulting in fuel starvation. It idles perfectly but going full throttle off idle or low rpm cruise and almost no acceleration occurs for like 5 seconds until the rpm suddenly shoots up, as it should when full throttle is applied. My Suzuki 4 stroke boat engine was having similar behavior and it was a bunch of crap in the high pressure fuel filter just before the injector rail.

As you all advised, I'm going to put some fresh regular fuel in the tank and change the plugs and air filter.

I'll report back. Mark
 

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if you think there is an issue with the fuel pump its not hard to check the pressure and flow

youll need a fuel pressure gauge - not sure at what point its easier (cheaper) to have a shop check it out than to buy the equipment you would need to debug the fuel injection system.

you should at least be able to pull the hose off the fuel pump and see if the flow is restricted
 

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Discussion Starter #6
if you think there is an issue with the fuel pump its not hard to check the pressure and flow

youll need a fuel pressure gauge - not sure at what point its easier (cheaper) to have a shop check it out than to buy the equipment you would need to debug the fuel injection system.

you should at least be able to pull the hose off the fuel pump and see if the flow is restricted
Good idea! I'll add new reg fuel, new plugs & new air filter. If no fix, I'll do the simple pump test. If flow/pressure doesn't check out, I'll also consider pulling fuel pump to check strainer and/or reserve fuel tank to check for gunk or debris.
 

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Good idea! I'll add new reg fuel, new plugs & new air filter. If no fix, I'll do the simple pump test. If flow/pressure doesn't check out, I'll also consider pulling fuel pump to check strainer and/or reserve fuel tank to check for gunk or debris.
Can you elaborate on what you found to fix your issues? My bike does the exact same thing
 
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