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Hesitation/Stumble between 3-4K - Delkevic Exhaust with dB Killer....


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Rode hard today with the dB killer "spud"  installed - I put it in a few days ago to tame the noise.   I noticed that there seems to be a noticeable hesitation/stumble around 3-4K, and it seems more common with softer throttle inputs.  I did NOT notice this with the baffle removed.   The logical test would be to remove the spud again and see what happens, but just curious if this is a "thing" that can be solved in another way.   I don't love the idea of going back to "full loud" and I'm not thrilled with spending the money for a Power Commander, which leaves me the option of "stock exhaust" which obviously isn't fabulous either.   Maybe it's in my head?  Maybe it was always there but masked by the outrageous noise?   

 

<Edited to add:  it was crazy hot today with ridiculous humidity - I mean soupy-thick.  Not sure that could play a role, but this is the first time out in 90+ F. heat and extremely high humidity>

 

Thoughts?    Ideas?   Opinions?  Insults?   

 

I'll take anything 🙂

 

Thx!

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I have not heard of that on an 8th gen - tho it's all too common on G6s.  It will be interesting to see what 8G owners have to say. 

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I had a delk muffler for a lil bit and rode it with and without the db killer in place and never noticed a difference in acceleration or idle or rev smoothness.

Mebbe it's just your imagination. 

I dumped delk as soon as I could...

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I just returned from a ride on my 8th Gen with Delkovic exhaust(baffle in) and I didn't notice any hesitation at any point in the rev range. My brother's HOA has a 15mph speed limit, which is just under 3000rpm in 2nd gear. No issues whatsoever.

 

Disclaimer: I have not ridden with the baffle out, so I can't compare.

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There may be calibration/sensor issue. Measure sensors and compare their values with standards given in manual:

 

- IAT & ECT - measure resistance @ room-temp and boiling-point

- TPS output voltage - at closed and WOT

- intake-manifold vacuum at idle with warmed-up engine

- FPR vacuum at idle with warmed-up engine (use vacuum T)

- MAP sensor vacuum at idle with warmed-up engine (use vacuum T)

 

There's something amiss that's causing this stumble. 

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It's a simple process on an 8gen to refit your OEM exhaust then go riding in the same conditions if possible, see if you get the same effects.

 

The only issue I've heard of with an 8gen causing similar effects was caused by a fuel filter blockage from some very bad outback town fuel.

 

Condensation or bad fuel might be a cause, particularly if using Ethanol blended fuel.

I'd be surprised if its related to your exhaust considering the number of 8gens with non OEM pipes out there. I've run two different types of non OEM exhausts on my 8gen with absolutely zero negative effects.

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My 8th gen had similar stumbling issues after I installed an Arrow exhaust.  Luckily, I already had a Power Commander on order and it fixed the issue completely once I had the correct map loaded.  Actually, it's even smoother than the factory tuning with the OEM exhaust now.  

 

Not the least expensive fix, but it worked for me. 

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I have an Arrow on my G8, without a DB killer, and it’s always been as smooth as silk. I guess every bike can be slightly different.

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  • 1 month later...

Just wanted to update this:

 

I went back to "full loud" with the dB Killer removed and the problem persists - I took the "no cost" option of putting the stock exhaust back on last night.  Forgot how quiet it was - disturbingly quiet.  Hopefully ride a little today to see what happens.  

 

I've identified the symptoms a little more accurately - it's between around 3500 and 5000.   I notice it most when coming out of corners where I don't have the RPM's I usually have.  It will stumble and surge to about 5000 to 5500 RPM.  If I'm hard on the throttle it's worse because it goes from stumble/surge/flat to VTEC very quickly, which exacerbates the issue.  It is smooth as silk from 5K to redline, BTW.  If I keep it on the "boil" I don't notice anything.  I've had enough bikes in my life - this is definitely odd.   

 

The stock pipe will be interesting.  I'm riding the bike harder/more aggressively since I removed it, so if it isn't solved, I'm worried to think what the issue might be.  Anyone know a good Honda mechanic in Western PA.  Anyone know a good Dyno shop?  I should know soon enough.   Thx for all the replies to this point!

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I do know of a 6gen situation of rough running under 5000rpm. Even though the spark plugs looked good, replacing them cured the problem.

6 and 8gen plugs are identical except for the center electrode being projected in the 6gen IMR9B-9H, 8gen is IMR9D-9H.

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OK - so I swapped in the factory exhaust, and it made no difference so this has evolved from a swap in/swap out bolt-on experience to a full-blown trouble shooting exercise.   I will try to set the table accordingly.

 

Here's what we know:

 

-  The bike stutters and surges at low RPM's.  Careful testing today shows that I get the stutters/surges at essentially anything under 5000 RPM.  

- The bike pulls strong and clean from 5k to Redline

-  At the moment the bike is bone stock 

- The bike (2014) was stock when I got it.  It had 1100 miles on it and the OEM tires (yes - I replaced those in short order)

- Fluids were changed prior to my purchase but likely nothing else 

- The bike was subject to what appears to be a light tip over on the left side by previous owner- everything is straight and you have to know where to look for the marks

- I have done nothing but swap the exhaust and change the oil.   

- All visible/tangible electronics work fine

 

Here's what we don't know:

 

- Where the bike sat and for how long.   I don't know if it languished on a dealer floor or got snapped up early and lived in a garage.

- The previous owners riding habits/style (other than infrequent...)

- Previous modifications that may have been removed.   It was stock when I got it save for a link lowering kit that was removed.

 

So - where do I start from here?   I think I should check the airbox, and maybe SeaFoam it.  Beyond that, I have no idea what to do beyond that or what order I should do it in.  I've never had a bike with an issue like this but I would prefer to at least try the routine stuff myself before if subject it to the services department's abilities.   

 

Thx in advance!!!!

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vacuum leak or sensor-calibration issue

 

It affects low-rpms worse because leak-volume is higher percentage of total intake. At higher RPMs with much more flow, vacuum-leak contributes less overall and engine runs normally.

 

Effective troubleshooting (quick & inexpensive) requires measuring and coming up with numbers. Then comparing those numbers to standards in manual to figure out what's wrong. Then fixing/adjusting just that one area/component that's out-of-spec. No random guessing needed because you've got red-flag waving you in face. No desperate shotgunning random piles of parts at bike hoping and wishing. You have to positively identify problem first before you can fix it.

 

For example, bike runs fine, then sputters and dies with no warning, no dash warning lights, nothing, kaput. Rather than automatically replacing fuel-pump, fuel-filter, fuel-lines, fuel-rail, fuel-injectors, FPR, spark-plugs, coils, ECU, TPS, ECT, IAT, MAP, KGB, CIA, etc., you just pull out multimeter and measure battery voltage and that number tells you tonnes of info!

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Thx Danno!

 

The problem is that it also requires tools and skill - something I lack at the moment 🙂   I had a multimeter at one point - not sure where it is at the moment.  Also would need to know where to measure - is that covered in the service  manual?

 

Are there any obvious things to check first that require only visual inspection?  🙂

 

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Nothing much you can do visually. There have been cases of vacuum-lines being disconnected from MAP sensor or airbox. Perhaps somthing got jarred in 1st exhaust swap?

 

Yes, sensor-tests outlined in manual.

Typically measuring resistance/voltage of TPS @ closed and WOT.

MAP-output at atm and at idle

ECT/IAT at room-temp and boiling.

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So I have a buddy coming over Saturday - he's a mechanic and understands such things.  Also has the tools I don't.  I found the sensor reading "flow chart" in the service manual so I at least know where to start some of the process.   I need to get myself a good meter.   

 

Stupid question:  is there a preferred method of siphoning out the gas from the tank other than the time honored "plastic tube hope I don't swallow gasoline in the process" trick?

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For anyone that cares, the latest:

 

Friend came over and tore it down past the air box.  We did some basic sensor measuring on the meter per the manual, but everything seemed within spec.  The air filter looked fine ( I have a new one on order - it is the original), and everything was fairly tight/clean - nothing seemed amiss.  We did the "flapper mod", made sure all connections were clean and tight,  and I had run a tank full of Seam Foam through it  over the last week.   We did tweak the idle as it was a little low.  

 

After buttoning it back up, it;'s like a different engine.  Well, not quite that extreme, but it pulls strong and smooth from 2500 to redline.  The VTEC transition is almost imperceptible.  Off-idle/low RPM performance is significantly improved.   I can't get it to surge/buck/hesitate/stumble.   I could reproduce it at will previously.  It sounds a little better on the intake, but that was to be expected.

 

The only problem?  I don't feel like I "did" anything.   Other than the flapper mod to the air box and the Sea Foam, plus some random tightening/re-plugging sensors that didn't actually seem to need it, not much changed.  My brain tells me that none of it should have made a huge difference, but the bike is running much better/smother that it was.  

 

Since I can't leave well enough alone, I put the Delkevic back on this evening and will report my findings after I ride tomorrow.   Thx for all the help/advice so far!

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Thanks for the update.

I could make a bit of a guess and say that, perhaps disabling the Variable Air Intake (flapper now fully open) may be what has solved it.

 

The flapper is normally Closed during low to medium RPM's, add to that a possible diry airfilter with poor flow then you would certainly expect some performance issues. Your original Airfilter is 7 years old, how many miles? Possibly well overdue for replacement, good you have a new one on order.

 

At high RPM's the flapper is fully Open and this is the zone where you are not having issues.

 

Or perhaps the addition of Seafoam has gotten rid of some fuel moisture contamination? 

Good luck keep us posted of any further findings.

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So success... I think....

 

Rode it today with the Delkevic exhaust (with the dB Killer installed) and its still running really well.  Idle still a little high but only by 100-200 RPM so I'll deal with that at some point.  It rode as well as it did the other day, but obviously sounded much better.   

 

I did notice that there was less popping/crackling with the exhaust off-throttle - it was pretty obnoxious before.    I was very careful to torque everything down to spec this time (hey... its a science experiment...) and I do wonder if maybe I was sloppy on the last couple installs.  Not saying it contributed to the symptoms overall, but and interesting observation none-the-less.    

 

The only other variable is that the weather is a little cooler/drier that it was a couple of weeks back.  Saturday was cool, and today was low 70's.  2-3 weeks ago it was mid-high 80's.    Alas, I can't test for that for 9 months at this point 🙂  

 

 

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Awesome work! :)

 

There was probably something off with flapper sync & adjustments and disassembly/reassembly with disabling probably fixed your problem! So nice when bike runs as it should.

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On 10/12/2021 at 1:06 PM, thestumper said:

Just wanted to update this:

 

I went back to "full loud" with the dB Killer removed and the problem persists - I took the "no cost" option of putting the stock exhaust back on last night.  Forgot how quiet it was - disturbingly quiet.  Hopefully ride a little today to see what happens.  

 

I've identified the symptoms a little more accurately - it's between around 3500 and 5000.   I notice it most when coming out of corners where I don't have the RPM's I usually have.  It will stumble and surge to about 5000 to 5500 RPM.  If I'm hard on the throttle it's worse because it goes from stumble/surge/flat to VTEC very quickly, which exacerbates the issue.  It is smooth as silk from 5K to redline, BTW.  If I keep it on the "boil" I don't notice anything.  I've had enough bikes in my life - this is definitely odd.   

 

The stock pipe will be interesting.  I'm riding the bike harder/more aggressively since I removed it, so if it isn't solved, I'm worried to think what the issue might be.  Anyone know a good Honda mechanic in Western PA.  Anyone know a good Dyno shop?  I should know soon enough.   Thx for all the replies to this point!

At those rpm what’s your speed and gear?  

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It was across all gears at low RPMs.   Speed...  that's hard to say.   Lower speeds typically indicate lower RPMs for me, but I could get it rolling out from 0-25, coming out of tight corners at 35-40 or at highway speeds between 45-80.  Anything beyond that the RPMs are high anyway.  Speed didn't seem to matter much - it was all down to RPMs.  It's about perfect now - no issues.   I took it out for a good thrash on Wednesday (probably our last 70+ degree day😪) and it was a joy to ride.  Everything is smooth from 1500 to redline.   

 

So I guess I'm keeping it, much to the chagrin of the Ducati dealer 😆

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