FLHTC gas mileage

I recently purchase a 1993 FLHTC with 41.000 miles on it. (first bike in over 29 years). I use it to commute 150 miles round trip from 3,000 ft over a 6.368 foot pass and back down,weather allowing. I generally cruise at 75-80. The mileage is around 32-33 mpg. It has has Hooker mufflers and a K&N air filter. It runs really rough after a cold start-up using the mixture enrichment. Seems to have plenty of power after warm-up. It does have a rich smell to it while riding.

My question is, what mpg should I expect out of my bike and what if any modifications should I look at performing on the carb?

at that speed it sounds about right:devil:

Did it have new plugs put in recently, along with an oil change? Check that K&N as it may need to be cleaned..you can get K&N cleaning kits at most automotive parts places. This may help with the mileage, but your speeds upwards of 80 mph are gonna kill that mileage, especially blasting up that mountain pass. Slowing down will definitely help the mileage, but at 75 miles each way, it's tough to just cruise at 65 mph. I say take off for work 10 minutes early, slow down and just enjoy the ride. It was an occasional ride, it wouldn't make much difference, but you're probably doing this up to 5 days a week, eh?

Take the Time

SK,

So far all I've done to it is change the oil and clean the air filter. I'll check the plugs tonight or tomorrow. Too wet and cold to ride here yesterday or this morning. I guess leaving a little earlier to enjoy the ride wouldn't hurt. It's really funny actually enjoying going to work now that I have something to ride again.

Cool, don't forget to make sure your tires are fully inflated.

I think your mileage is a bit low - not drastic, but a bit. I doubt that the bike is tuned right - that gas smell is a big clue that your carb is not likely optimally tuned. Does your tailpipe look heavily sooted, too? Your plugs? You may have a bike that was set up for sea level, or never tuned for the 3000ft+ that you operate. If you don't know carbs I suggest ya take it to someone that does. You'll be alright if ya don't, but it sounds like it will run better if you do. Wouldn't hurt to have it dyno-tuned to your riding preference, since it is new to you.
:cheers:

Checked the plugs tonight and found that the foward cylinder plug is somewhat sooty and smelled of gas. Decided to do a compression check. The Back cylinder had 110 lbs. When I tried to screw in the compression tester into the foward cylinder it would not thread. It turns out that the front plug is only grabbing th last few threads in the cylnder. I think one of the main reasons the mileage is down os due to the fact that the cylinder is probably not completely sealed at the plug, although I didn't see any visible signs of leakage. With the 110 lb reading on the other cylinder, I believe that is probably low, I imagine that my bargin bike just got to be not such a geed deal.

I've done several automotive overhauls. With that in mind, does anyone have experience in doing a top end overhaul? Any helpful hints, other then having a dealer rebuild?

Dealer would be the last place I'd go & that's 'cause I've seen too many jobs that had to be done over again @ an indy shop in 6 months. Got a good machine shop in your area? I'll bet you do. Probably @ least one good independent bike shop too. The mechanics of pulling & re-installing the top end isn't all that difficult & your automotive experience will make it easier. But you'll want a machine shop to clean up the heads, do a valve job, replace valve springs & install an insert for the stripped out plug hole. And to bore/hone the cylinders right you must have torque plates, which a shop that works on H-D engines often will have - or certainly should.

Proper piston-to-wall clearance is crucial & the cylinders change shape as they're torqued down on the engine. You don't care if they're round or not sitting on the workbench (they won't be) but you do when they're installed & the only way you can be sure they will be is to duplicate the stresses put on them when they're installed - that's what torque plates do. I've cylinders change shape by as much as .004" & that might as well be a mile. Need a special bore gauge to measure top to bottom all the way around & most people don't have one of those in the toolbox - never seen one @ a dealer either. But a good machine shop will have one.

And different pistons need different clearances - using my Sportster engines as an example, with “Hypereutectic” alloy cast pistons, the proper PTW clearance is .0015"; with forged pistons it's .0025" & in the race engine it's .0045". That's because the forged pistons "grow" more as they heat up & the displacement is different in the different engines. We take measurements all the way around below the bottom ring groove, but the most important measurements are in line with the wrist-pin hole & then again perpendicular to it - they won't be the same.

You can go .040" over on most H-D cylinders & pistons come in .005" over increments, so if the PTW clearance is going to be too much just doing a clean-up hone on the cyls., get new pistons. Harleys are bad about the pistons trying to turn sideways in the cyls. just due to the basic V-Twin design & a "loose" setup will wear way too fast from the rocking action of the pistons. But if the PTW clearance is set *exactly* right & the rings gapped to the piston manufacturer's specs, you shouldn't have to do it again for 60,000 miles.

If you don't have a good shop in your area there's one I can recommend that you can send the top end to - Nallin Racing Head Service in Longmont, Colorado, just north of Denver off I-25 in the same business park as High Country H-D. Even though I'm in North Carolina, I know the owner 'cause our Sportster team stopped there 3 years in a row on the way to Bonneville to dyno tune & I know good work when I see it. Last I was out there they'd installed a new CNC milling center to do cylinder heads & FWIW, the 1st naturally-aspirated pushrod engine bike under 2000cc's to ever break 200 mph came from that shop. Attention to detail.

41k miles doesn't seem like it should be time for a top-end job. See if you can get those threads fixed and see it that makes things run better.

While I'd agree & H-D engines have gone over double that without a rebuild, with a used bike, unless you know the previous owner, it's not likely you'll know how those 41,000 miles were racked up, what service was performed & when. The stripped spark plug hole says it wasn't done very well & low compression ain't gonna fix itself. However, might get lucky with just a new set of rings & an insert in the head for the spark plug.

I'd still want to measure the cylinders with torque plates installed, as that will tell you quicker than anything if a complete top end overhaul is warranted, or if just rings & a bit of clean up will get the engine running right again. But while you've got the heads & cyls. off anyway, it just makes sense to me to do it all right then & there - after all, the engine is 15 years old & other items like lifters & valve springs can't be expected to work like new.