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5-6000rpm hesitation/bogging


Clintonjl

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Hi all,

i have recently replace the headers on my 1999 vfr as the original suffered heavily with header rott (kept the original silencer and installed delkevic headers). Ever since I replaced the exhaust it bogs at around 5-6000rpm under hard acceleration. Didn’t notice this before 🤦‍♂️ . It accelerates fine up to then and fine after.  

Was just wondering what could be the cause of this?

Any help would be much appreciated. 

Many thanks

Clinton 

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It may be just coincidence with you changing the headers, but it could well be a dirty fuel filter causing your issue and seeing your bike is 21 years of age, good chance the fuel filter could be clogging up. Also what's the state of your air filter?

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Among  other things, the non OEM headers may have different flow characteristics, but the ECU wouldn't know that. You may need to do some tuning to recalibrate for your new setup.  Also as Grum pointed out,  if your fuel system is clogged or not flowing as it should,  the ECU cannot know about that  either.  In addition to a fuel filter,  one typically overlooked maintenance item is to bench clean the injectors.  Forget adding cleaner to the tank - for one it will never have the solvent capacity to truly dissolve 20+ years of accumulation.  Also, it won't help with dislodging any non soluble particles the way reverse flushing can.  There are many shops that clean injectors,  it runs about $25 ea - a Google search will turn them up readily.   So step 1 is to get the fuel / air intake system in good nick (as pointed out, the air filter is clean and also the fuel pressure regulator checks ok?) then 2 if it's not resolved satisfactorily, get a tune to suit.  On a 99 a PC-V with a pre made map would likely be fine.   Best of luck with it. 

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I don’t think the problem is your headers. 

I replaced item with the same on my 2001, and found that I lost some top end but gained bottom and middle (they’re not a very free flowing headers, pretty crap design really)

I did have a PCIII installed, but when I sold the bike I removed it and took it for a ride to make sure everything was fine, no hesitation at all, but it was an 01. 

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Ok, I have just serviced the bike new oil/filter and air filter so that shouldn’t be the issue. I’ll check out/replace the fuel filter and get injectors cleaned, if not we’re off the tuning shop. 

Many thanks for your reply’s 🤙

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What's the status of your airbox?  Did you (or a prior owner) do a "de-snorkel and flapper valve" modification?

 

If your bike is missing its snorkel and its airbox flapper has been disabled I can easily imaging you might get a flat spot in the RPM range you described.

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Hi,

 

Ive recently made the same change - Black Widow exhaust, ever since putting them on has this stuttering under hard acceleration just how you describe. 

Not sure if its related but ive also got an issue with it cutting out at a particular speed 70-80, Fi Codes point towards injectors. SO its either a TPS or injectors need a clean for me. 

Might be not related to your issue, but seeing as we have similar symptoms thought id share. Let us know if you find a solution. 

 

Cheers

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If the fuel filter was restricted then the higher the rpm the greater the hesitation...

 

Look to remapping which means a new 3-D map of injector on-time, throttle angle, and

engine rpm to be worked out on a dyno, then stored in memory in engine’s ECU because if

you change the exhaust system odds are you have to install a new fuel system map to go with it...

A Dyno tune will cure your deep torque flat spot just before engine torque begins its climb toward peak torque...

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I hear you BLS. Still think it's a good idea for Clintonjl to at least carry out the Fuel Flow Inspection as specified in the service manual, without the need to remove the Fuel Pump assembly, running this test he can at least establish correct or not fuel flow. Especially given that the Fuel Pump and filter are most likely as old as the bike, 21 years!

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12 hours ago, Grum said:

I hear you BLS. Still think it's a good idea for Clintonjl to at least carry out the Fuel Flow Inspection as specified in the service manual, without the need to remove the Fuel Pump assembly, running this test he can at least establish correct or not fuel flow. Especially given that the Fuel Pump and filter are most likely as old as the bike, 21 years!

 

It's always good to know what is the condition of the pump and filter BUT if go by the logical steps in the Honda manual checking the fuel flow is troubleshooting for poor performance at high speed...

Its worth remembering that Motorcycle troubleshooting is a form of problem solving... It is a logical search for the source of a problem so that it can be solved...

 

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