Can exh packing effect jetting requirements?

[caseyjones955]

Can exh packing effect jetting requirements? 4k stumble.

99 Vmax with 4-1 Kerker, stage 1 jet kit and drop in K&N. I have been doing some reading but a couple questions remain.

I'm seeing a stumble/miss from around 4000 to 5500 rpm, feels like starvation. I'm guessing when Vboost starts to open it resolves the starvation as it begins pulling from both carbs on each bank. It's more pronounced in higher gears, gentle acceleration masks the issue. I have to wonder how much top end power I might be leaving on the table along with the ridability issue.

The Kerker is loud, really loud. If the bike were jetted for a normal Kerker baffle but had the competition baffle (or just has the packing blown out) would the difference in back pressure be enough to lay on different jetting requirements?

I have read that electrical problems can cause symptoms like this. I duplicated the misfire yesterday and played with the choke and it didn't seem to make much difference. I'm at about 3500' and can double that on a day ride. The stage 1 kit was installed with the 170 mains. Not really sure where to go from here, it would seem there is plenty of main jet installed already. What other factors or adjustments might I try before tearing into it?

Thanks.

 

[Traumahawk]

Re: Can exh packing effect jetting requirements? 4k stumble.

Do you know what clip the needles are on? The reason why I'm asking is that the needles start kicking in around 4000 rpm. ....and is this when you suddenly whack open the throttle....or is this all of the time...and at part throttle up to 5500?

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[Traumahawk]

Re: Can exh packing effect jetting requirements? 4k stumble.

And usually for an exhaust that flows better....you jet leaner not richer. The quicker flowing exhaust will pull more fuel into the carbs. When you say 170's....do you mean DJ 170's?

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[caseyjones955]

Yes to the DJ170. It's a Dynajet kit. The directions in the kit say to put the needle clip on the 3rd rung but the kit was installed when I got the bike. The work was done at a known decent shop before I bought the bike.

The stumble/misfire only happens between about 4k-5500 and really only when I roll the throttle on a bit. Cruising or gentle acceleration and it's barely noticeable. I can lug it from about 3k just fine and when it hits 4k its like starving for fuel. It's like a very select small hole in the fuel delivery. It idles and runs very well other than this.

Could it be anything to do with a couple Oz Sea Foam I put in the first tank of gas, or the fact that I'm running premium (only way to get fuel w/o ethanol tainting)?

Thanks for helping out! much appreciated.

EDIT. I just got off the phone with the powersports outfit that serviced it since 08 when they jetted and piped it, I'll have all service Hx since then but still no word on which baffle they sold him with the exhaust. I'm sure it needs a repack since 08 was the last time it was touched.

 

[blaxmax]

Yes to the DJ170. It's a Dynajet kit. The directions in the kit say to put the needle clip on the 3rd rung but the kit was installed when I got the bike. The work was done at a known decent shop before I bought the bike.

The stumble/misfire only happens between about 4k-5500 and really only when I roll the throttle on a bit. Cruising or gentle acceleration and it's barely noticeable. I can lug it from about 3k just fine and when it hits 4k its like starving for fuel. It's like a very select small hole in the fuel delivery. It idles and runs very well other than this.

Could it be anything to do with a couple Oz Sea Foam I put in the first tank of gas, or the fact that I'm running premium (only way to get fuel w/o ethanol tainting)?

Thanks for helping out! much appreciated.

EDIT. I just got off the phone with the powersports outfit that serviced it since 08 when they jetted and piped it, I'll have all service Hx since then but still no word on which baffle they sold him with the exhaust. I'm sure it needs a repack since 08 was the last time it was touched.

Repacking will make a difference -- also have you checked for cracks in your vboost manifolds? Try a shot of wd-40.

 

[caseyjones955]

I will do both of those things. It's really quite loud for me to assume there is any packing left at all.

Thanks for the fast comeback. I'll post the results in the coming days.

 

[blaxmax]

I will do both of those things. It's really quite loud for me to assume there is any packing left at all.

Thanks for the fast comeback. I'll post the results in the coming days.

You can burn a valve without the packing.

 

[Traumahawk]

On my bike.....with a kerker 4-1 with 2 inch competition muffler, I got my best dyno numbers with 150 MK's and stage 1 needles on the first clip. The Vmax likes to run a little bit lean, and your way too rich.

Below is a pic that compares MK jets to DJ's.

 

[caseyjones955]

On my bike.....with a kerker 4-1 with 2 inch competition muffler, I got my best dyno numbers with 150 MK's and stage 1 needles on the first clip. The Vmax likes to run a little bit lean, and your way too rich.

Below is a pic that compares MK jets to DJ's.

That is a really handy chart, thanks!
What altitude are you at?

I have the smaller jets that came in the kit, luckily the PO saved all that stuff. I'll repack first, it sounds delicious but I should take a few db from it. I returned 34mpg yesterday at 4000+ feet with 3 Harley kills and several WOT passes. From what I've read thats about normal. I'll have a look at the plugs as well. Even if it runs well I would like the jetting to be appropriate for optimum power and efficiency.

How long does muffler packing last? The 2 Bros on my Sprint lasted about 40k mi before getting louder and it was nowhere near as loud as this Max. The max barely has 15k on it.

 

[Traumahawk]

Well on a Vmax.....the higher the altitude the leaner you go. I'm at 1100 feet. I remember Rusty going to Utah, and went to 145's and was surprised at how well it ran.

I would still try the 150's.....see how you like it....and possibly go to 147's after that.

 

[caseyjones955]

I have the stock jets, DJ160 and DJ165, it's wearing the DJ170s. Again, I live at 3500' and often go higher.

When you say 150 do you mean MK? I see the DJ160 crosses to the MK150. I might try the DJ160 as it is the smallest jet I have. If the 160 turns out to be a touch lean can I compensate by shimming the needles to avoid taking the top of the bike apart again? I'm trying to get the best educated guess on jet size because it looks like a real pain in the as to actually swap the jets out. Although I'm a DIY guy I have not ruled out having it done because I don't have a carb sync tool for bikes.

I see them hiding in the float bowl in the chart, it looks like I have to remove the carbs, install the jets, reinstall the carbs and have them synched again, If there is an easier way to do these main jets I'm a listenin' :ummm:

Thanks again.

 

[Traumahawk]

Re: Can exh packing effect jetting requirements? 4k stumble.

Can you pm me with your phone #? It's hard to go into detail typing on the phone.

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[caseyjones955]

Thank you! You rock! It was exactly the starting point I was looking for. I will post all once I see how it works out.

The only thing I need to do now is get a synchronization gauge set. I'm checking ebay now and pondering something adequate and cost effective (cheap). It looks like one or two trips to have it done covers the cost of the gauges.

 

[DMAN999]

I have the Carbtune and Love it.
I bought it back on 2002 or so and I synch my carbs once a year so it has paid for it self many times over.
http://www.carbtune.com/

 

[blaxmax]

+1 on the carbtune---no way on a motion pro.

 

[caseyjones955]

I was checking ebay on the motion pro but believe it or not I was put off by the fact that the seller thought I would buy it faster if it was embraced by a large breasted woman in a cleavage shirt. When I see gimmicky salesmanship I run the other way. Besides it looks sort of cheesy.

I'll go back now and order my Carbtune off Ebay unless there is a better source within the USA here. They are $117 shipped on ebay. Thanks!

 

[Traumahawk]

Re: Can exh packing effect jetting requirements? 4k stumble.

The motion pro is kinda cheesy. I've had one.....I have a Morgan carbtune now.

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[blaxmax]

Morgan carbtune never fails- motion pro i sent back after a week-Too many air bubbles that do not want to come out no matter what you try.

 

[caseyjones955]

I just ordered the Carbtune pro 4, should see it by the 10th. I plan on keeping this bike indefinitely so I'm sure it will pay for itself in short order. Thanks for chiming in with your positive experience with this one.

I guess when it gets here I'll be leaning things out a bit.

 

[DMAN999]

I'll go back now and order my Carbtune off Ebay unless there is a better source within the USA here. They are $117 shipped on ebay. Thanks!

You can get it directly from Morgan (they make the Carbtune) with the case for $110 shipped:
http://www.ekmpowershop28.com/ekmps/shops/carbtune/carbtune-pro-4-column-and-toolpouch-24-p.asp

That's where I got mine and I was surprised when it arrived a lot sooner than I thought it would.
It took less than a week if I remember correctly.