Yamaha Star Bolt Motorcycle Forum

Yamaha Star Bolt Categories => Technical Discussion => Topic started by: zhamid on August 20, 2020, 03:50:58 pm

Title: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on August 20, 2020, 03:50:58 pm
I can make the rpm go up if I am gentle with the throttle. But hard throttle (or full throttle, even if I increase it to full gently) makes the engine hesitate. Somethings it bobs (as if I am in a very high gear) and other times it feels like someone did a kill switch. 

Assuming the fuel manager is fine, what else could be wrong? 

- I ordered new spark plugs to eliminate that possibility, waiting for them to arrive.
- I cleaned the air filter with the K&N cleaner and K&N oil (I have the K&N filter).

What else should I check?

The bike has a Cobra slip-on exhaust, a Cobra intake (that uses the K&N filter) and a Cobra fi2000r fuel manager.  I'll take out the fuel manager this weekend to eliminate that as a possibility, but until thn I want to see what else to test because I don't thinnk it's the fuel manager. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on August 20, 2020, 04:00:16 pm
It's probably the cobra fuel processor.  may need to adjust the pots, or just remove it.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: legion95928 on August 22, 2020, 05:51:06 pm
It's probably the cobra fuel processor.  may need to adjust the pots, or just remove it.

--- Agreed!!!
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on August 23, 2020, 02:40:22 pm
It's probably the cobra fuel processor.  may need to adjust the pots, or just remove it.

--- Agreed!!!

Tried, didn't help!


What I've tried:
1. The fuel controller has manual pot settings (3 different pots). I've tried every permutation.
2. I took out the filter and completely cleaned it. 
3. I've taken out the fuel controller completely, it just made it run leaner (and therefore pop more), but otherwise the same symptoms. 
I haven't tried changing the spark plugs yet, but ordered them and am waiting for them to arrive.   I don't think it's the O2 sensor because it idles perfectly and is perfect if I mainain <= 3,000 rpm.   
It might be the throttle position sensor, but I doubt it.  There's no symptom below 3,000 rpm and beyond that point it feels more like it's too rich or too lean.   
Any other ideas? What else can I try?
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on August 25, 2020, 03:01:13 pm
With the Cobra Fuel Controller, are you supposed to run an O2 sensor?  Most FCs say to remove it. 

Pull the sparks and see what condition they are in.

It also almost sounds like it could be a badly slipping clutch. How many miles?
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on August 26, 2020, 12:38:14 pm
Fuel pump might be taking a sh!t on you.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on August 27, 2020, 06:34:15 pm

It also almost sounds like it could be a badly slipping clutch. How many miles?

I am not mechanically inclined. How would a slipping clutch cause this, considering it happens on neutral too.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DrM on August 27, 2020, 08:34:18 pm
I would very curious to learn what happens when you put your new sparkplugs in. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on August 28, 2020, 12:24:26 pm

It also almost sounds like it could be a badly slipping clutch. How many miles?

I am not mechanically inclined. How would a slipping clutch cause this, considering it happens on neutral too.

Ha! Sorry, didn't see that it happened in neutral too.  Otherwise, if RPMs go up and bike speed doesn't, that's a pretty good indicator of a bad clutch. 

Did you pull spark plugs yet?  See this article: https://motorizedbicyclebuilder.com/how-to-read-your-spark-plug/ (Not an endorsement, didn't even read it; but the chart at the bottom is what you need).  So even before you get the new sparks, you may be able to tell a lot by pulling BOTH plugs and comparing them to the chart in the linked article.  This bike's plugs are EASY to pull out.

I didn't see the mileage in the posts.  That could help us help you. (for example, if it's over 15k miles, I think it should have had the valves adjusted? did it?) 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on August 28, 2020, 11:07:55 pm

It also almost sounds like it could be a badly slipping clutch. How many miles?

I am not mechanically inclined. How would a slipping clutch cause this, considering it happens on neutral too.

Ha! Sorry, didn't see that it happened in neutral too.  Otherwise, if RPMs go up and bike speed doesn't, that's a pretty good indicator of a bad clutch. 

Did you pull spark plugs yet?  See this article: https://motorizedbicyclebuilder.com/how-to-read-your-spark-plug/ (Not an endorsement, didn't even read it; but the chart at the bottom is what you need).  So even before you get the new sparks, you may be able to tell a lot by pulling BOTH plugs and comparing them to the chart in the linked article.  This bike's plugs are EASY to pull out.

I didn't see the mileage in the posts.  That could help us help you. (for example, if it's over 15k miles, I think it should have had the valves adjusted? did it?)

Thanks, that's the project for this weekend :).

It only has 6,000 kms. But it's 5 years old and I am the 3rd owner, so who knows.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on September 02, 2020, 03:52:45 pm
I would very curious to learn what happens when you put your new sparkplugs in.
Didn't help :(. Same problem.

Could it simply be a blown fuse?
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on September 02, 2020, 05:25:06 pm
What did the old plugs look like? 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: lunkhead on September 03, 2020, 02:24:33 am
Test your clutch switch. Another forum member recently said his Bolt didn't run right when he removed it. It's wired to the ECU so it'll rev differently whenever the lever is pulled in. If the nub broke off or the switch is faulty, it'll act as if the clutch is always pulled in and run poorly under load.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on September 03, 2020, 10:13:20 am
Test your clutch switch. Another forum member recently said his Bolt didn't run right when he removed it. It's wired to the ECU so it'll rev differently whenever the lever is pulled in. If the nub broke off or the switch is faulty, it'll act as if the clutch is always pulled in and run poorly under load.

Thanks, I'll check it out. Question: would that cause a problem in neutral?

It happens in neutral too.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on September 03, 2020, 10:33:45 am
fuel pump
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on September 03, 2020, 06:21:54 pm
Hey, DMV in the house.  We need to do a socially distanced ride.  What are you guys up to this weekend?

Also, I'm betting on FP at this point too.  Would love to know if those plugs showed lean. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: lunkhead on September 04, 2020, 01:10:38 am
Test your clutch switch. Another forum member recently said his Bolt didn't run right when he removed it. It's wired to the ECU so it'll rev differently whenever the lever is pulled in. If the nub broke off or the switch is faulty, it'll act as if the clutch is always pulled in and run poorly under load.

Thanks, I'll check it out. Question: would that cause a problem in neutral?

It happens in neutral too.

It's not the switch but it would be the cheapest fix if it was. May be the pressure regulator. They don't have the relatively high failure rate like the fuel pump but it sounds like how a bad regulator act. Could be either one but failed pumps usually quit altogether.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on September 04, 2020, 11:33:50 am
Mid-Atlantic Region in the the house.  I moved full-time to the beach in delaware.  if you're ever out this way let me know. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on September 04, 2020, 11:36:20 am
Also, Yamaha fuel pumps are notoriously bad.  We know that.  I would lean more towards that.  You are right that they do normally just crap out completely, but we JUST had a customer who's wife put sugar in his gas tank when she found out he was sticking his wiener in a different bun.  That debris totally effed up the fuel pump. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Crilly Wizard on September 04, 2020, 01:23:48 pm
lol, I like her style. Hit him where it hurts. Unless she was a munter. And the other bun was sweet. In which case, bummer.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: DelawarePete on September 04, 2020, 03:27:39 pm
lol, I like her style. Hit him where it hurts. Unless she was a munter. And the other bun was sweet. In which case, bummer.

I won't lie.  I had to google Munter.  I want to thank you and ImMrEd for expanding my insult arsenal.  I love international forums!

MUNTER: An ugly person. I'm never going to date her; she's a right munter. (New Zealand, Australia, slang) A person often impaired by alcohol or recreational drugs. He's a real munter; he was really munted at the party.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: lunkhead on September 05, 2020, 01:04:33 am
We've diagnosed many dead fuel pumps by tapping on them to get them to work temporarily. One customer didn't want to pay for a new one and actally drove off and it lasted for quite a while longer before it completely crapped out.
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: taoster on September 05, 2020, 04:25:38 pm
 so there arenít any symptoms of a failing fuel pump until one day your bike will just randomly dies on you?
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on September 06, 2020, 05:42:02 pm
Thanks guys.  Can one of you pls do a video of what the priming sounds like when you turn the key on? 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on September 07, 2020, 01:45:08 pm
This is from a Raider, but at 6:42 when he's pumping the fuel out of the sub tank you can hear the pump running, it's a similar sound and should last about 5 seconds or so after you turn the bike on.

https://www.youtube.com/watch?v=jKaqwBeV1Vw&t=275s

Edit:
Here's exactly what you need.  At 1:30: https://www.youtube.com/watch?v=3XTrPIWHlx0
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: legion95928 on September 08, 2020, 07:12:16 pm
Does our Bolt(s) have fuel filter(s)... In the tank or inline or...? 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: zhamid on September 08, 2020, 10:02:24 pm
Thank you for all your help. It'd have taken me forever without you all.

After eliminating all possibilities, I took it to Yamaha and the mechanic there, who regularly works on Bolt, took seconds to find the issue :-). A fuel line was twisted!  Doh!

He untwisted it and the bike runs like a Champ. 
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Pir8 on September 09, 2020, 09:03:54 am
Well that's awesome!  Glad you're back up and running!
Title: Re: Bike poops out on hard throttle (or full throttle)
Post by: Sdaniels on September 10, 2020, 06:20:21 pm
Does our Bolt(s) have fuel filter(s)... In the tank or inline or...?

There is a filter...underneath the tank, towards the seat.