HarleyTechTalk

I've been working with my local shop to dyno tune my '78 XL. Have to say, am not real happy or impressed with the results. The bike:

Mostly stock 1978 XLH
S&S Super B with Thunderjet, and S&S and air cleaner
MAC dual shorty exhaust
Stock P cams

I don't know what is supposed to be typical for a 70s stage 1 Ironhead, but does 38HP sound about right to you guys? I was thinking it should be up in the low 50s or so, but maybe that is just wishful thinking.

What really through me was the A/F ratio plot. Down blow 3500, it was getting up above 15:1. That ain't good for old iron with no-quench hemi heads, is it?

I'll post the dyno chart when I can scan it. Not allowed to post in the AFR zone, they did not record the results the way that I had asked.

-JW

I think low to mid 50's is right where it should be.  What was the AFR above 3500 rpm on the main jet?  15:1 on the intermediate jet,  I think you need to go to a one size larger jet to richen it up a little.   How many turns out is your idle mixture screw?
Linky to some IH dyno runs and discussion:

http://xlforum.net/forums/showthread.php?t=951664&page=2

Yeah Gup, that was basically what I was expecting to see. Not the case, so it looks like I have a lot of work to do. And the starting point is, find somebody that actually knows how to tune an Ironhead! I might know a guy down in San Jose, he loves Ironheads, but is a bit of a pain in the ass to deal with. As long as the results speak for themselves, probably worth the pain.

Dyno sheet attached, sorry for the lousy picture qualtiy. I doctored it the best I could, the orignal was quite pale.

I think the number one concern is how the torque starts off OK, then quickly falls past 3000. And thus, so too will the HP. Real lean below 3500, but OK after that. So where is the power going?

-JW

[attach=0]

On the one run it looks like the main jet is too rich, maybe go down one size or turn off the Thunderjet.  Hows the engine health? Done a cranking compression test lately?  What kind of baffles do the MAC mufflers have in them?  You're a pretty savvy guy, I would think you could tune it yourself.  The S&S Super B manual and Mikuni HS40 manual have some good tuning info in them.
*edit* Are you running E10 fuel like we have to use in the midwest?

Actually, I think I'm going to start with going back to a CV. Yes the Super B is stylish, but sure comes with some baggage. I'm not sure what baffles are in those MAC mufflers, they're not exactly quiet so likely not that restrictive. So the journey begins...

-JW

The pipes don't look bad on the dyno. No ~3000 rpm dip

++ on the CV much better for the street.

Best is a Mikuni VM39 with a branch kit.
(no butterfly and shaft in the way provides more flow)
And the slide gives you a Variable Venturi at the fuel discharge port for better atomization.

And Dual plugs....

No dip, but that steady downhill decline after 3000 is a problem. Even stock P cams ought to be holding torque out past 4500. Something is wrong, I just need to figure out what. Timing?

I love the look of the Super B, but a really hate how twitchy they are just off idle. As in, when downshifting, and reaching for the clutch level and you move the throttle ever so little, and the motor surges. Hate that. CVs don't do that at all, in fact one of their "drawbacks" that I find a positive feature is the damping effect from the slider. They don't respond to minor movement on the throttle due to that slight delay in response. Much better street behavior if you ask me.

What is really strange, is that the behavior of the bike out on the road does not really correspond to what the dyno chart is saying. It actually runs quite nice, does not seem short on power at all, and pulls fine up to 6K. I'm tempted to go somewhere else and get a baseline on it before changing anything just yet, and this time with SAE correction.

-JW

What gear was that run in?

4th.

-JW

Still trying to sort this Ironhead out. I bit the bullet, and bought a Daytona Twin Tec WEGO iii. Before taking it back in to the dyno shop, I want to make a few changes to it, and try to tune it a bit myself with the WEGO. The changes:

Out with the Super B, in with a CV40 (done)
Out with the MAC exhaust, in with an OEM set HD "performance" exhaust (ala Cycle Shack)
Out with 23T trans sprocket, in with 22T

I need to weld a oxy sensor bung to the front pipe, am guess a few inches from the port? There's not much option, either close to port or down past the bend. The pipe hugs the frame tube pretty tightly. Then send them out for ceramic coating. Will swap the sprocket this weekend.

Stay "tuned".


-JW

Since tuning 1 carb for two cylinders is a compromise, gonna weld bungs front & rear?  Would be good to know you aren't too rich/lean on either cylinder. 

Yes that is true, but at the end of the day, what can you do about it? From my experience, the rear plug always seems to be a tad darker on a well tuned V twin, so get the front one tuned to the "optimal" condition and don't worry about the rear?

-JW

At minimum weld a bung in the back pipe too.  That way it's done already should you decide later.  I may even have a spare 18mm bung.   You should put the bung about 3-4 inches from the exhaust port if you can. 

Overall your tuning options are pretty darn limited as you know.  Maybe you should have bought an aftermarket EFI set up :-)   

Next thing to put on your To-Do List: Figure out how to wire those iron heads for a block heater and kiss those cold running blues goodbye. 

Well, in looking at the rear pipe, I don't see much chance of adding a bung and getting the sensor screwed into it, unless the bung is on the outside of the pipe. That wouldn't look so cool, right? Way too cramped on the backside. As far as where to mount it on the front, the Daytona book says "as close to the exhaust port as possible", which is quite easy to do on an Ironhead. Tons of room.

Limited tuning options? How many does an Ironhead need?

I think the CV has enough adjustments for a clever guy (If I can find one!) to dial it in close enough for good enough.

Regarding the cold bloodedness, I think the solution there is tighten that choke cable backside nut so the knob stays put, and....  lots of spare spark plugs!

By the way, it seems that Daytona Twin Tec is now Daytona Sensors.   

-JW

about 4" from the exhaust port is good for the sensors
try to get the outside of a bend
try to get both pipes
get plugs to blank them off when you are not tuning
once you have fished tuning you don/t have to live with the sensors

From the Daytona instructions:

[attach=0]

As it turns about, about 3 inches is as close as I can get it and have it somewhat not visible after it's removed, unless I put it on the front side of pipe. Which I'm not going to do. Will mount on the rear side of the front pipe pointed to the carb. And I can probably put a bung on the front side of the rear pipe, also pointed to the carb.

Seems like everything I touch, have to do a bunch of little things before doing the thing I'm trying to do. The bracket that came with these new exhaust pipes doesn't even remotely line up with the mounts on the pipes. So I need heat/bend it to fit the pipes. But alas, my damn oxygen tank regulator gauge is not working, so it's off to the welding supply...

-JW

there has been a lot of discussion over the years about optimal location for the sensors
generally pipe and bike manufacturers are oblivious to the requirements for gathering good data
sensor position being determined more by aesthetics and convenience
probably more important for fuel injection but applies equally to carb
for wide band sensors 3'' to 4" from the head is optimal
stay away from the inside radius
otherwise you are just going through the motions

Clean signal is what you want. Wideband sensor (bosch like Wego uses) wants to be close to the ex valve and can handle the heat.

Do the pipes have heat shields?  If so put the bung wherever.   A zit on the prom queen can be covered with make up :-)

Got the new pipes mounted, here is where I'll put the 02 sensor bungs:

[attach=0]

No shields on these pipes, so on the outside would not look so great. These will get ceramic coated after I get the bungs in place.

-JW

That looks like reasonable placement, but still might be a bitch on the back pipe.  I might install the front one 90 degrees from where your arrow is.  Tucked between frame and front of the engine.   You can get angled bungs if that would help.  Do you have the kit yet?

There is no room on the back, the pipe hugs the frame real tight. In fact, it has a flat spot pressed into the pipe to clear the down tube. I have the WEGO laying on the bench. Just swapped the trans sprocket today to a 22T. And now have to pull a link out of the chain, ran out of adjustment on the axle. Damn hot out there in the shop, yikes. I am kind of contempating dropping the heads off at RE Engineering and have him dual plug them. What the heck. What a better waste of money than throw it at an antique Ironhead, right?

-JW

   Back in the day when I was campaigning a stroked 74" cast iron, gave it to the ex and then she left & snorted it, I went though a lot of trial & error. The CV was one of the best things I did (was probably one of the first "CI" with a CV ever), along with Baisley roller rocker. Pipe wise I got along with MAC drags with some mode baffle, and eventually duel plugged heads with an HI4 single fire, Cam wise I was using Sifton GX's. But I think the P's really wake up with 1-3/4 ex valve, and can work well with strokers too. As for an DTT O2 port, alls fair & it'll get you closer damn near anywhere you put it, as long as you KNOW the clamp area is not leaking. I used one on my Bonneville bike.
    With the duel plugging, stock pistons don't leave much room, and can be problematic with it easy to burn though. You might be able to find a set of those old KB sloped pistons & then you probably wouldn't need the duel spark, but a single fire is almost a must.
   

Front cylinder runs leaner on a carbed H-D, use the front pipe for the O2 sensor. 

Get or make a long bung for the sensor so just the tip is in the flow.

A short bung will have the sensor stuffed into the header pipe and obstruct the flow.

If those mufflers are straight through I don't think they will work well, the ones with the flap work good.

Really if you want to get it in it's happy place grab a EVO pipe and fit it.

 [attach=0,msg1316284]     Heres my old  late '84 XLX. Yeah I tried one of those POS two throats, actually got it to work OK, the brackets weighed more than the carb. But the CV was hands down much better and more responsive . Sorry for the chitty pic, its all I have to remember that bike by is that plaque I made .  Some day somebody is going to walk in with a basket case & I'll recognize it immediately.