I'm looking to gain some insight from the knowledge base here.

I have an '06 Deluxe. Engine is pretty much stock, with the addition of S&S 509 gear drive cams. Last winter, I did a top end rebuild. Multi angle valve job, .020" overbore on the stock barrels with KB pistons. Replaced the spring loaded tensioner system with 509 gear drive cams. And thank to djl for that advice.

I bought the bike with a Rhinehart 2-1 exhaust and the typical stage 1 type air filter. I don't consider these to be appreciably better than the stock equipment, and in regards to the exhaust, it may be worse.

The bike, since I've owned it has always exhibited a low speed, light throttle intermittent miss. I've had a few different tune-ups on it, and it's always there. The bike runs great.....except for that little intermittent miss. Like cruising through a neighborhood at 20-30mph.

The bike rarely sees the other side of 4000 rpm, and rarely, if ever full throttle pulls.Some tunes were way worse than others. I've not had it dyno tuned, and I'm not looking for every ounce of power I can get out of the combo. Decent fuel mileage, dependability, and smooth, fairly cool running is what is most important. I've got that with this combo.

Some might say, "Why the cams then?" To that I'd say, they were the mildest set of gear drive cams out there, and I wanted to eliminate the chain tensioner. Simple as that.

To deal with the miss, I was getting ready to buy a fresh set of injectors or having the existing injector professionally cleaned, and I still may. Then somebody mentioned reversion due to exhaust primary pipe diameter. It made sense. Sense enough to research more.

I know most of you fellers are after unlimited power. But, has anyone had any experience with trying different header pipe diameters to move the power band around?

The existing header is like many. 1.75" primary pipe diameter. In the automotive world, where most of my experience comes from, a header that big on a motor that small operated in this way is way WAY too big.

I'd be interested in hearing some opinions.

 

I have the '05 FLSTN Deluxe. It's carb.
I put in an S&S 510G gear cam kit. Had it professionally tuned afterwards at an indie shop.

Sounds like where you've not had it dyno-tuned, you probably never bothered installing an after-market powercommander (dyno-jet, screamin-eagle, etc.) or other such module to be able to remapp/tweak fuel injection for the increased airflow and leaner conditions of a stage 1? Seems like that's 1 that could be causing your miss. Retweaking fuel delivery ratios and timing whether in carb but especially in fuelie, afaik, is a must after changing the exhaust and aircleaner. Now, add the performance cam?....

An experienced tuner with dyno should dial it in, but they'll need a preinstalled module to do it. Or maybe they can sell you 1 and install it at the same time.
Seems like the exhaust diameter thing is a red-herring.

 

Have you swapped out the 8 degree injectors for the 25 degree ones per the HD service bulletin? After that, it needs a real tune— not just different maps thrown at it.

 

Perhaps you missed where I said I've had a few different tune-ups on it. I have the Dyno Vision gizmo, and got a few "canned tunes" from Fuel Moto. The tune that's in the runs the best.

It has the 25° injectors.

 

If your "Dyno Vision gismo" is the Power Vision, you have a good fuel management system; however, if the "few tune ups" don't include a dyno tune that addressed partial and wide open throttle, the state of tune is likely lacking. Canned tunes or maps are one size fits all which you know can be lacking. Just because the bike runs best on the current tune, does not mean the motor is "tuned". If the bike hasn't been on the dyno for at least a couple of hours, the tune is lacking. A map is a poor substitute for a proper dyno tune.

I think your comparison of primary pipe diameter with a "motor that small", i.e. 88" is apples and oranges. I think you have to look at a single cylinder volume for the head pipe size. For instance, a 5.0 liter 8 cylinder motor has about 40 cubic inches per cylinder and most headers for those motors have 1.625" head pipes that dump into a 3" collector. I know, over simplification, but you get my drift. Not an exhaust expert and not stating one way or another that 1.75" primary head pipe diameter is too large or not; could be but not sure that head pipe diameter is in any way related to your low speed hiccup.

I do believe that a good fuel management system and proper tune that addresses partial throttle as well as WOT operation will solve your problem as well as meet and possibly improve all your requirements for decent fuel mileage, dependability, and smooth, fairly cool running.

As usual, JMHO.

 

There is always wisdom in your opinions djl.

 

My experience: (others may vary) I paid a guy for a half assed dyno tune of a canned SEPST map when I swapped to 255 cams, bike ran considerably better. When I went to 107 I sought out a true professional dyno tuner and he was worth every penny and the 6 hour each way trip.

Like djl said if your Dyno Vision gizmo is a Power Vision, then you have a very good device for collecting data. You can create some logs of when this problem is happening and send them to Jamie to take a look at since your using a FM map. I have done this before with a FM tune and Jamie seemed more than happy to help out. Still not a substitute for a proper comprehensive dyno tune, but it may address the issue you are having.

 

If I remember your area has Chris Rivas vtwin who should be able to tune it.

 

As I was scrolling thru this, I was going to suggest basically what djl covered.
The partial throttle needs will be attended to on a dyno.
RC Cycles, in Hayward, has a great dyno man, Bob Lobenburg.
Cycle Tune of Fresno, Gary, is another outfit we know.
Scott

 

Thanks for the suggestions guys. I really do appreciate it.

I was really hoping for some conversation on the effects of intake charge dilution relative to header primary pipe diameter.