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post #1 of 24 (permalink) Old 04-28-2015, 11:01 AM Thread Starter
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Stuttering at full throttle / higher revs - help!

OK, just got back from a race weekend. I won my division on Saturday (bike ran great) , and then ended up in third on Sunday because of a recurring, but inconsistent, mechanical difficulty . I could definitely use help diagnosing this, as I don't have the time or money to get a full engine rebuild...

Here's what happens - at 13k or 13.5 rpms, under full acceleration, the engine starts to "stutter" and won't go to redline (and beyond). The first time this happened, I had just put on pair valve block-offs, new spark plugs (Brisk AR12-zs), a PC quickshifter and PC ignition module. None of this should cause stuttering - but I quickly removed the ignition module and quickshifter with no change. Then I put in different fuel (switching from VP100 to pump gas) and the problem disappeared.

I had assumed that the problem was with the upper injector bank, since they only switch on at 13.5k rpms. My assumption was that I had accidentally got gunk/dirt in the fuel line to the upper injectors when I tore my bike down for the pair valve replacement, and that the new fuel had dissolved it - or something.

So, two race weekends later (all on pump gas with the bike running well) and I switch back to VP100 between Saturday and Sunday. Problem recurs, and now it is happening at lower RPMs (can't tell how low because I'm hanging off the bike driving out of curves when it happens).

The bike isn't burning oil; makes great power when it's not stuttering; nothing else seems to be wrong. (My PCV map was done on pump gas, by the way.)

Question - would the fuel really cause this problem? (VP claims the 100 is a direct replacement for pump gas.) Is there something I'm missing?

Thanks in advance for any help - I really want to get back on the podium!

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2012 CBR250R (track)
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post #2 of 24 (permalink) Old 04-29-2015, 01:11 PM Thread Starter
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Bump - any help?

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post #3 of 24 (permalink) Old 04-29-2015, 01:24 PM
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I don't have any personal experience with these situations, but from a few years of forum posts, my first guess would be the fuel filter. Also, I'm pretty sure your upper injectors kick in well before 13.5k RPM. More like 8 or 9k I believe.

Has this problem ever happened on pump gas? If not, I think you have your answer already. Get a second map made for VP100 fuel or just run pump gas.

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post #4 of 24 (permalink) Old 05-19-2015, 02:02 PM Thread Starter
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Bump again - it's not the fuel - same thing happened this weekend at Hallett with 93 pump gas. Any help would be appreciated (before I start taking it to mechanics and spending money).

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post #5 of 24 (permalink) Old 05-19-2015, 03:56 PM
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My guess is it is the fuel.

is VP100 race gas? with about 100 octane? (higher octane resists detonation)

your ecu will try to compensate for the changes in octane, but if you don't have a specific map for the higher octane, this could explain the stuttering. But since your ecu did some learning on the VP100, switching back to 93 could cause issues again.

just my two cents based off your explanation, and assuming VP100 is race fuel. (always map for race fuel)

get your bike mapped for the two different gasolines

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post #6 of 24 (permalink) Old 05-19-2015, 06:13 PM Thread Starter
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Quote:
Originally Posted by v-tec crx View Post
My guess is it is the fuel.

get your bike mapped for the two different gasolines
The map I'm using was made on 93 octane pump fuel. I don't have the autotune hooked up, so my ECU isn't learning and going back to pump fuel should have solved the problem if it was fuel.

Thanks for the help, though - but any other thoughts?

If not, I'll take it to a dyno and get it re-mapped. That should at least determine whether its ECU related or mechanical.

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post #7 of 24 (permalink) Old 05-19-2015, 06:25 PM
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The upper injectors can come on after 5500RPM and when the throttle is at certain openings.

Are you absolutely sure those spark plugs are a complete match for the NGKs in temperature range? If they are actually colder or warmer you could have problems.

Re-check the PAIR valve block off to see if any air is escaping. Did you use any gasket material or did you just bolt them in?
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post #8 of 24 (permalink) Old 05-19-2015, 06:38 PM
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Also, what year is your bike?
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post #9 of 24 (permalink) Old 05-19-2015, 10:10 PM Thread Starter
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Thanks! I checked the pair valves after doing them, and no air was escaping, but I should check again at high rpms. I left the OEM gaskets in per instructions because the minimal weight savings wasn't worth the hassle of sealant for me.

I may try putting the old spark plugs back - but it's hard for me test since it is a track only bike and riding on the street at high rpms scares me even in first (no mirrors, no brake lights or headlight, slick tires that are cold...). But that's a great suggestion that I hadn't thought about.

It's a 2012.
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post #10 of 24 (permalink) Old 05-19-2015, 11:49 PM
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The PAIR is probably okay then. The plugs I wonder about and are possible, though not probable.

Do you not have a Z-Bomb or similar to patch the power drop? 2009-? year bikes have that fueling dip after just about 13.5k rpms to remain EURO3/5 compliant. I *think* it's only in 6th gear at that RPM but I am not certain, and don't really know if it can account for the symptoms you're experiencing. Just wanted to bring it up as a potential factor.
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post #11 of 24 (permalink) Old 05-20-2015, 11:53 AM Thread Starter
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I have the ignition timing module for the PCV - I think that does the same as the Z-Bomb. However, the stuttering happens in all gears.

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post #12 of 24 (permalink) Old 05-20-2015, 12:06 PM
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Pull the PCV, see if that helps it rev all the way; might be the PC. Bike won't run perfect, but see if it will pull to redline.

Mike
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post #13 of 24 (permalink) Old 05-20-2015, 04:57 PM Thread Starter
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It looks like Fightingchance wins the prize. (OK, there's not really a prize.)

I called to schedule an appt at the dyno. When I was describing the situation, he asked what type of spark plugs. When I told him "Brisk", he immediately said that is the problem. He's got a tub of Brisk plugs that he keeps just to show people how much of a negative affect the wrong plugs can have. He said Brisk plugs cause this same high rev problem in most or all supersports.

So the lesson is, don't use Brisk plugs. Worth the try to get a extra HP or two, but a failed experiment.

If the OEM plugs don't fix it my next track day, I'll be back...
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post #14 of 24 (permalink) Old 05-20-2015, 05:18 PM
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I also balked at the price of four spark plugs; but, at those pressures and temps, it is required to have a control you can depend on so your other factors can be accounted for. If a plug is a third of the price (and promises impossible things like HP gain), they've got to be cutting corners somewhere. I haven't done my plugs yet, but when the time comes, I'll clench and get NGKs.
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post #15 of 24 (permalink) Old 05-20-2015, 10:20 PM Thread Starter
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Unfortunately the Brisks were about 2x the price of NGKs.

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post #16 of 24 (permalink) Old 05-21-2015, 11:27 AM
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Quote:
Originally Posted by kfox View Post
The map I'm using was made on 93 octane pump fuel. I don't have the autotune hooked up, so my ECU isn't learning and going back to pump fuel should have solved the problem if it was fuel.

Thanks for the help, though - but any other thoughts?

If not, I'll take it to a dyno and get it re-mapped. That should at least determine whether its ECU related or mechanical.

FYI: the stock ECU is capable of learning and making minor adjustments to the fuel trim and ignition maps based of readings from the bikes various sensors. Ie/ if you are stuck and are forced to use 87 octane fuel, your ECU will read this and adjust timing slightly to prevent pre-detonation. Your bike won't run great on 87, but it will get you home and keep the engine operating "safely".

You never mentioned what this other fuel was that you were using. Was it race fuel?



As for the plugs; never use anything other than what is stated in the owner's manual.



Edit: Since you are racing this bike. I suggest getting the bike mapped for what ever fuel you are using: 91 octane, 93 octane, race fuel, etc... Switch the map every time you switch fuels

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Last edited by v-tec crx; 05-21-2015 at 11:35 AM.
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post #17 of 24 (permalink) Old 05-22-2015, 03:11 PM Thread Starter
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Quote:
Originally Posted by v-tec crx View Post
You never mentioned what this other fuel was that you were using. Was it race fuel?


Edit: Since you are racing this bike. I suggest getting the bike mapped for what ever fuel you are using: 91 octane, 93 octane, race fuel, etc... Switch the map every time you switch fuels
VP100 race fuel.

Yep - a separate map for each fuel is ultimately the way to go. Some day...

Thanks.

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post #18 of 24 (permalink) Old 06-04-2015, 08:18 PM Thread Starter
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I sent an inquiry to DynoJet on this, and below is their response. They responded almost immediately, and I think this information is very useful - hence the post. Now I have three things to try on my next track day.

"This is not a known issue so I’m not quite sure what could be causing it. Being intermittent makes it even worse.

We are building a turbo 07 CBR600RR and we chased an issue that sounded like it was ignition related for a month. It turned out to be our plenum design but while searching the problem I talked to some of our contacts that used to tune for Erion racing. They both said they guaranteed me it was either the crank pickup sensor or harness for the coil sticks. They were both wrong in our case but they said these were common on these models. Something to consider?"

P.S. A turbo 07 CBR? Sweet!

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post #19 of 24 (permalink) Old 06-22-2015, 01:49 PM Thread Starter
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Closing this out, as the problem is solved. I'm not positive what caused it, as I changed as much as I could reasonably do before this weekend's races at NOLA Motorsportpark. But it ran perfectly this weekend, right up until I got t-boned going into turn 13.

It was probably the spark plugs, but I also changed out the harness for the coil sticks and the fuel lines to the upper injectors.

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post #20 of 24 (permalink) Old 06-22-2015, 01:51 PM
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Well great that the problem is fixed - sorry about the racing incident.
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post #21 of 24 (permalink) Old 06-23-2015, 02:17 PM Thread Starter
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Quote:
Originally Posted by FightingChance View Post
Well great that the problem is fixed - sorry about the racing incident.


Thanks. (I would hit the "Thanks" button, but apparently now that the site has upgraded I don't have permission to thank people. )


Now does anyone know a place near Austin or San Antonio that I can get a piece of aluminum welded to my frame to repair the rearset bracket that broke when I got t-boned?

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post #22 of 24 (permalink) Old 06-23-2015, 02:35 PM
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Curious, what brand rearset were you using when the crash happened?
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post #23 of 24 (permalink) Old 06-24-2015, 01:01 PM Thread Starter
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Quote:
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Curious, what brand rearset were you using when the crash happened?


Vortex rearsets. The rearsets held up very well, just road rash on the pegs and a little bent in (which I should be able to unbend). But maybe they held up too well, because the bracket on the frame that the rearset screws into broke off.


So now I'm in the position of either getting a new frame or finding someone to weld a piece of aluminum to the frame where the bracket was (and then sinking the bolt into the new aluminum).


Anyone know a place near Austin or San Antonio that can weld a piece of aluminum to the frame to replace the broken bracket?

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post #24 of 24 (permalink) Old 06-24-2015, 01:24 PM
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... yeah, this is not the first time I have seen the Vortex bracket snap off the mounts from the frame instead of giving out itself. The good news is, I've seen this repaired a couple times so it should be no problem for a good welder.
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