The Little Girl Gets a Dyno Tune

February 17, 2009.
I’m not a sentimental kind of person, but I am quite pleased with being able to document the dyno tuning process of my little girl.
In 2008 I had the top end of my 1993 XL 1200 90th Anniversary Edition Sportster rebuilt. Along the miles, before the total rebuild, I have had the jugs bored out and new oversized pistons (+.30) installed. Shortly after having the work preformed, an ex-boyfriend went down in front of me, and I ran over both him and his bike with my little girl. In the process of rolling up and falling down on top of Mr. Elmer’s bike, some damage ensued. All kinds of little niggling problems…and I wasn’t happy with the performance of the bike.

After a season of riding the bike in a condition less than stellar, but still better than what it was, I took the bike to a professional to run through and fix. During that fix, I asked him to please pull the heads and check the condition of the pistons and the slide path of the metal against the jugs. Trouble in paradise, scoring…I couldn’t believe it. This shouldn’t have been, the work is less than a year old…oh wait a minute, it couldn’t be from me not breaking in the engine properly could it? I’ve always been very proud of how hard I can beat up an engine. Yes, dear…you bought yourself another top end.



Shannon, (my mechanic) was going through the bike, I also asked him to check my carb, as I wasn’t very happy with it’s performance as of late either. She had been spewing gas through the overflow tube. It was really messing me up while out on short runs here and there, I was too scared to ride it away from the area. Shannon took the carb apart, discovering a blown diaphragm, so he rebuilt the carb as well. Here in is my problem,not that the carb was rebuilt, but that the slow jet was replaced with an incorrect sized jet. For some reason he went smaller? I dunno…maybe that jet was in there all the time…maybe it wasn’t…but I never had the problems with the carb that I had been experiencing until the rebuild.

Well now we have the problem properly discussed, I guess I should get on with the dyno day at the dealer.

I arrived at the appointed time: 1PM. I walk into the service department, announce my arrival, and go back outside to change the air filter. I was running late again and didn’t get around to changing out my K&N filter for cleaning. I own two of these filters, no down time waiting for the filter to dry this way. While I was changing the filter, a mechanic comes out (one I haven’t talked to before,) who walks around the bike checking out the oil dripage that has accumulated at the top of my cam case and at the base of my pushrods. Yes, boys and girls, what a mess. I try to keep her clean, but it’s become one of those battles that just become such a bore. After I ride for a day, less then 500 miles, the accumulation of oil, road grime and gas in that area was a real drag.

The mechanic sees my James gasket has a place where it appears as blown out.

I’ve seen it before, it’s been like that forever I think. This guy thinks the gasket is blown and wants to get into the cam case to check it out. He goes behind the counter and we start talking about the bike, how many miles I have on it…and his jaw drops. I tell him the bike has 150K on it and the bottom end hasn’t been touched since I owned it. I bought the bike in 2004 with 1200 miles on it. So I should know about the bottom end. He REALLY wants to get into the cam case now! Tells me I should have the oil pump looked at, because in the early Evo Sportster such as this one, the oil pump had less than desireable traits, that will only become enhanced with age. Yeah, I know, I’ve read about these problems, I even kinda experienced one of them back in early ’06 (which is what led to having the first mini top end done). I ask him how much…sheet…of course I’m not gonna get outta there for under five hundred! No, I think I can get this bike to give me another season, and if I am lucky…(fingers crossed, knock on wood…) I want to get another 30-50K out of her this season.

He goes away, not gonna get any money out of me this trip. The dyno was a freebie, they owed it to me from the rebuild. I wait around, talk to the service desk guy for a while, walk over to the wash rack where they have led my bike to…the guys really like to work on clean bikes there…also, they wanted to check the cam case to see if it was blowing pressure out through that gasket. I don’t think so, and neither does my dyno tuner guy. So I’m leaving that be for a season.

Anyway, I snap a few pics of the bike as they hosed her down with the pressure washer, arriving just in time to hear them discussing the melted shit on one of my pipes, so I was obliged to inform them of the other blonde moment I had last week. I rode my bike to cover for my sister at her job, and wore a knit pants suit. Bad idea, as the right leg blew against the pipe and melted the material, sticking a nasty black crap to the pipes, which will melt off in time. The wash man did manage to get some of the crap off. I got a picture of the wasted material left behind on the pipe.



After the bike went through the wash process, she was left out in the sun to dry. So I waited out there with her….and I waited some more, and I kept on waiting until the dyno tune guy showed up from his EXTENDED lunch at 3 pm. Uhhhh, my appointment was at 1PM Mr. Prima Donna….I kept that to myself, I wanted him to not screw me over with a piss poor test and tuning. I believe that to be an excellent choice. He spent some extra time with my bike…and we talked tuning for some time during and after the tuning.

You know, Mr. Prima Donna gave me his name, but I’m lousy with names, I never remembered it. So from here out, he’s “Mr. PD” OK? Mr. PD arrives, rolls my bike up the ramp, ties her down till she’s trussed up like a 19th century whore, and he starts sticking stuff up her tail pipe…such indignities to be suffered while others watch. Ah well, these things have to happen if she wants to get better, and I so know she does!



Mr. PM starts taking her through the performance run. He likes the read outs. He runs her again, and is quite satisfied with her performance. I ask him if he felt the drag or what I was calling the “dogging” of the carb. It wasn’t bogging down it just didn’t have umpah at 2K. Once through the 2K point she sling shots through the RPM until we hit 3K. He puts her through the paces again, with the machine, and tells me he can’t feel what I’m talking about. We discuss it further, and it hits him that I am not talking about a decline in power, but rather a flat spot where no more power was available. He starts to thinking it’s the slow speed jet. He takes the bottom end of the carb off, (I’m impressed, the didn’t even have to take the air cover off…did it all by feel.)

Check out a few things before checking out the jet…and there it is. It’s a Mikuni Carb jet size 42. I need a 45 in there says he….”OK…do it” says me.



After he ran her through the torturous regime again, he shuts her down and we discuss the details of the run. Yeah, the low end is running a wee bit richer now between 3.0 and 4.0…and the bike is tits. Yeah…I like tits!
These are the numbers:
• Pre larger jet= Max power~66.17
• Pre larger jet= Max torque~63.29
• Post 45 jet = Max power~69.31
• Post 45 jet = Max torque~73.05



It was a great experience. Standing in the room with the machine, feeling the vibration from the engine in the air…so much, that my nasal cavities rattled, braking loose the snot drying from my cold assed ride into the shop. It was such a good feeling, and you know, I swear I could see the disturbance of the air molecules from the engine. Do you think that’s what it was? Or were my eyeballs vibrating in their sockets so bad, I could see waves in the air? Either way, it’s like a new kind of high for me…I really liked how it made me feel…you know what? Better yet was the ride home. The bike ran perfectly. No slingshot effect after the 2000 RPM mark…solid performance, steady pull and power increase throughout the ride, no matter what RPM I was riding at! I have a warm and fuzzy feeling again, just remembering the ride in order for me to write it down here.

One last thing: for the last few hundred miles, I have been hearing a vibrating plastic noise in back of me. I assumed it was the left rear turn signal, as it kinda has this way of wanting to rotate at the end of the extension. But as I was photographing the bike, and standing at the rear, I could see it is the brake light assembly. SHIT…SHIT…SHIT…I don’t wanna have to detach the shocks in order to tighten that fricken assembly. SHIT>>>SHIT>>>>SHIT!