I've been putting a handful of miles on her every other morning or so (funny how I keep forgetting things on errands runs...). Pulled the plugs just now while lubing the chain, and I think this looks just about right--if I were tuning old school style.

Now, this is after idling down my 400' drive and then feathered throttle just to get off gravel up into garage, but still I think close enough for the El Cabezon run on the 15th, don't you think?

She's only getting around 38 mpg, but that involves a lot of in-town driving, so presumably will average out a little better on the highway.

The speedo is reading 7 mph slow at around 50 mph, worse as I go faster. This is actually reassuring because I was feeling pretty wimpy, wondering whether I'd be able to handle ~3 hour in the saddle at 65~70... answer is I'll be fine, since at an indicated 60 I am going nearly 71 according to one of those NM State Police radar signs by the side of the road.

I'm wondering if I need a different speedo drive gear...? The speedo itself is a 2:1 unit, which I was told is correct for a ratchet top 4-speed of this vintage. Perhaps it's the Michelin Commander radial, and the lower profile is dialing up the reading?

 

If the speed is reading low then chances are that the odometer is also..

I don't know much about shovel speedos but if it's off the front wheel, I suspect speedo ratio is determined by the diameter of the front wheel.. IIRC there are different ratios selected based on whether it's a 16 / 19 / 21 inch wheel. Speedo can also be different..

The only reason why I know this is that I've messed with EVO speedometers with both a 21 and 19 inch front wheels with mechanical drive speedos. .. I remember that they were different.

 

I had the same problem with my '77 FXE, I think they came stock with the 16-in wheel and when I bought the bike it had a 21-in and the speedometer was easily off 10 miles an hour at 65 mph.. What I did was I believe was 83 or 84 not sure what model with a 21-in, I bought the speedo drive gear for that and it got me really close. I actually checked my miles to the mile markers on the side of the interstate and I was within two tenths of a mile at 10 mi. So if you get a later model Speedo drive for a 21-in wheel, I want to say to Wide Glide, I think that'll resolve your issue It worked for me..

 

Thanks to both of you.

Max - Oh, crud... of course you're right that the odometer would also be off--and low at that. I will do the first oil & filter change early.

Everyone - This has an old ratchet-top 4-speed, so the speedo drive is in the front of the tranny. Accordingly, it'd be the rear tire throwing it off--but I think you're both right it may be as simple as doing some math. Sounds like I need to compare the O.D. of the Michelin to whatever balloon tire was originally on a '51 Panhead. Then, see if someone sells a variety of drives. Surely someone does, with all the chopper mods people do to these old wishbone frame bikes.

 

Trying to figure out whether a chest mount will work to shoot some video of the El Cabezon ride on the 15th, so took a (very short) clip. Looks like I'll have to add a little extension to lift the camera up a bit--all you see is handlebars--and also definitely need to add a remote mic with wind sock, as the camera auto-adjusted the audio and all you hear is wind. Hmmm... I guess I could put the lapel mic in my helmet, but I'd have to remember to keep from commenting on people's driving habits...

 

Yeah, if it uses the tranny, you'll have different issues.. Rear gearing changes also make the difference. Not sure how you fix it.. Speedo cable on the front wheel? A mini change using small timing gears?


https://www.mcmaster.com/synchronous...elt-width~1-4/

 

Did not know that you have a trans gear on that note the FL's and the FX'sb had different t trans gears.. I'll look to see if they also had different Speedo drive gears.. What year is your bike?

 

Everything in finding for the FX or FL is a 23 tooth drive for the speedo great... What is your trans gear and rear wheel gear.. and still need to know model and year.. FL's we're a 22 trans gear and FX's were a 23 tooth but the rear wheel sprocket was the same, a 51 tooth..

 

It's a 1951 FLL - thanks very much!

 

Oh, right - my rear combo drum and sprocket is 51-tooth, but I've got a much taller front sprocket so it's better on the highway... ah, my maintenance record says it's a 25-tooth. About the biggest I could fit on there without rubbing on the tranny housing...