Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Race Job Progress

Race Job Progress

Post Sat May 14, 2011 6:21 pm

Posts: 42
I’ve been on here a few times in the last couple years asking lots of silly questions in my attempts to edu-ma-cate myself in all things 45 as I’ve been slowly putting together a bike for vintage roadracing. It’s getting pretty close to done so I thought I’d post a pic or two to let folks see what I’ve cobbled together.



It’s been running for a little while now & I’ve been tinkering a bit to try to make it run well. As we all have experienced, there is often a lot of room between “running” & “running well” ….
The bike seems to run kinda OK at lower RPMs & smaller throttle openings, but breaks up & backfires real bad & won’t make power at more throttle & higher loads. It seemed like it was running lean so I tried several different main jet sizes but that seemed to have little or no apparent affect. I was puzzled to the point I was scratching a bald spot on my head. Rather than just keep scratching until I wore through to my skull, I went to a local shop that specializes in old H-Ds & told them my sad tale & asked if they were interested in trying to figure it out for me. Clever boys that they are, they asked not about the carb, but my ignition. Well, it’s just an old F-B mag off an old iron head Sporty. It’s got new points, condenser, cap & wires, but otherwise is of unknown condition. So, it’s currently off & at the shop getting examined closely. Hopefully, they will find the smoking gun & we’ll be happy ever after, although the carb will certainly still need some degree of optimization, I’m sure.
So, thanks for all the help so far from a bunch of folks on here (but don't sigh with relief just yet - I'm sure my questions haven't ended yet!).

Post Sat May 14, 2011 7:36 pm

Posts: 332
Location: north central Ma.
One easy way to figure out if you have an ign problem vs fuel problem is close up the spark gap if the ishue moves up in the rev band you have weak ign if it stays the same its fuel.

Best of luck, have fun on the track! :P

"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars!

Post Sat May 14, 2011 7:52 pm

Posts: 767
Location: CA USA
Nice work. I see the 2 bolt gearbox, 1940 clutch arm, what year is the gearbox. How about a rundown on all the stuff you used. Motor, frame, wheel hubs, etc. Nice crossover for the rear brake. Do you have a closeup pic of that?

Post Sun May 15, 2011 2:50 pm

Posts: 141
Location: USA
Yeah man I 'm loving it ,really nice job,how about the details,anymore close up pictures.Its inspirational. :D :D :D

Post Sun May 15, 2011 2:57 pm

Posts: 42
Thanks for that advice, 44. Hopefully the shop I took the mag to will be able to find something. I'm confident they know what they are doing, so I'm just interested in whether they will find anything in particular with mine.
Lessee, a rundown, eh, 'dog? Well, as you noticed, it's a 2-bolt frame & the trans (at least the case) is a '40 (it has the date tag on it). I really don't know what vintage the parts inside the trans are, but I'd guess it's a collection of whatever works. Narrow clutch & fiberglass repop primary cover. The engine bottom end is a WL case with S&S flywheels & some NOS & some S&S shafts. Sportster rods & custom pistons. WR cylinders & heads. Moldthread's cam lobes on WL shafts, roller lifters in modified WR lifter blocks. Carb is M-53. The tanks are '59-60 Servicar, so I had to hack up a repop '47 & up solo shift gate so the notches were in the right places for the 3rd gear forward shift pattern. I have a pair of hacked up '41-46 tanks that someone had heavily modified for a chopper a long time ago. My plan is to eventually cut them down & make a set of pretend WR tanks. Front wheel hub is 8" BSA, I believe it's A65, so that's, what, mid-60's? The rear hub is 7" Yamaha Big Bear, which I believe is also mid-60's. Both hubs are laced to 19 X 2.15 Excel rims, basically modern MX rear rims (although the spoke count is different). The final drive is 520 chain, so I machined down a worn out trans output sprocket to use as a hub & bored out an MX 15 tooth sprocket & welded it on. I also have a good 16 tooth sprocket that I machined down to 520 width. Lots off little pieces, like the handlebars, the seat, the rear fender & more are just swap meet or Ebay finds of indeterminate ancestry.
That's most of the big stuff I guess.
Oh, & I don't really have much in the way of close up pics. I dunno if I want too much close inspection! I'm a hack, not a craftsman! I'll try to get a few closer shots that won't embarrass me too much...

Post Sun May 15, 2011 5:18 pm
Pa Site Admin

Posts: 5843
Location: Ohio USA

I doubt we could find much in the way of hacking on that beauty. Pa

Post Sun May 15, 2011 6:15 pm

Posts: 20
Location: somewhere near Stratford, Ontario Canada

Hack or not, I wouldn't be too embarrassed if I were you. Nice bike!! Good luck as well!!

Post Sun May 15, 2011 9:49 pm

Posts: 767
Location: CA USA
Don't sell yourself short. What you did works. That's all that's important. Racing is surely the test. Some guys are better machinests and lay down prettier welds, but it doesn't make their stuff any better. Thanks for the details.

Post Mon May 16, 2011 7:16 am

Posts: 304
Location: Jonesville, Louisiana, USA
Good looking bike.

Post Mon May 16, 2011 12:32 pm

Posts: 349
Location: Champaign-Urbana, IL
Pull the number plates, add some lights, and have fun on the street as well.


Post Mon May 16, 2011 12:49 pm

Posts: 1654
I do like vintage racers.....
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Tue May 17, 2011 8:28 pm

Posts: 767
Location: Pa. , USA
She's a bute Bob, once you get it sorted out on the track you'll have lots of fun with it !
Vintage roadracing, Class C, AHRMA # 335

Post Wed May 18, 2011 3:56 pm

Posts: 42
Thanks for the nice compliments, fellers. I have worked with & hung out with some guys that really are craftsmen - artists in metal. I strive to make my work functional, but not too ugly.

Here are some closeups of a couple of the features that I thought came out pretty good. The first is the front brake. It was a bit of a challenge to get the backing plate to "float" with respect to the fork rocker. The triangular looking thingy is a bushing that rides on an inner sleeve. The inner sleeve is clamped between the rocker & the inner race of the wheel bearing. It works pretty good, nice & smooth & it keeps the backing plate nice & square to the drum.

This is a closer look at the cross over for the rear brake, as requested. I had no idea what the mechanical advantage between the foot pedal & the rear brake should be, so I made it very adjustable - as it turned out, it looks like I needed even more adjustment than I provided. There may be more holes in those arms' future...

Here's the handlebar. It's a ProTaper MX bar & the risers are just extra height risers for an MX bike. I made a couple little wedgie kinda thingies that go into the holes in the top of the forks & then a bolt goes down through the risers & clamps it all together. I thought it came out kinda clean & it works good. By the way, I know the upper clamp is backwards. That was intentional; I am planning on using the little ear in the center (that's supposed to face forward) to mount the steering damper. The damper I have doesn't have enough stroke, though, so I'm still workin' on it.

Last is my belly pan. It was made by a blind, spastic guy with a big, rough rock. Oh, no, wait, this is the one I made. It's so hard to tell them apart.

Post Thu May 19, 2011 4:47 am

Posts: 141
Location: USA
Yo Bob,your too modest,man I would let you work on my bike any day.That oil pan is great .I have got to to have one..It looks like you could take it off after the race and cook pancakes on it (its early morning here,I'm on a diet, forced to give up pancakes).Really ,you did a great job very inspirational for many of us. :D :D :D

Post Thu May 19, 2011 7:33 am

Posts: 304
Location: Jonesville, Louisiana, USA
Very nice work.

Post Thu May 19, 2011 2:46 pm

Posts: 1654
there was a long thread a little while ago about fitting BSA brakes in springers, but that's a very neat solution.

The rear brake crossover shaft arms look longer than you'll probably need in use. The original swing-arm BSAs had a cross-over shaft for the rear brake and the shafts were quite short ... tolatest=7 , as were the brake pedal arms

45s also had a cranked cross-over shaft in the rear linkage and again, the arms are only about 60mm long.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Fri May 27, 2011 1:48 pm

Posts: 123
Location: OH,USA
Soo what did you find out on the mag?Just wondering because I run the FM style mags on the Scout race bikes and have had similar issues.Haven't found a proper testing set up to trouble shoot these things and considering building something.

Post Sat May 28, 2011 11:30 am

Posts: 42
Thanks for that link, 45Brit. I like the look of that cross over. Like I said, when I put mine together I had no idea what the ratios between the various links needed to be, so as much as anything I was just going for maximum adjustability. I should also probably mention that lots of things on the bike, including the rear brake mechanism, went through several iterations before I settled on something I was happy with. I think the version in the photo is maybe V4.0. I'd guess it will eventually morph into something more similar to what your link shows. I also like the splined shaft - mine is currently welded at both ends so it's not removeable or easily lubed. I will be thinking about V5.0 as I root through other folks old treasures at Wauseon & Davenport!

Not much of an update on the mag yet, Zooma. I was hoping to have it back by now so I could get the bike running this weekend. I did get a call about a week ago & they found a couple little things. They thought one of the shaft bearings was ready to be replaced, but it wasn't terrible. They also didn't like my spark plug wires - I had modern carbon core wires & they said they needed to be copper. I dunno why that makes a difference (but I don't know much about those things) - I will ask them about it when I go to pick it up. Other than that it was in OK shape & the magnets are strong.

I am learning that maybe my carb WAS the problem with the poor running after all. I found out that the air bleed holes in the M-74B main nozzle that I'm using are much larger than the M-53's (that I should be using). This will lean out the mixture, of course, & my understanding is that this effect will be seen any time that it's running mostly on the main circuit, which is right where I was experiencing it. I'm hoping to find out what the exact differences in hole size & location are between the M-74B & M-53 & then modify an M-74B nozzle to function the same as the M-53. More work to do!

Thanks again for the kind complements & interest.

Post Wed Jun 01, 2011 7:13 pm

Posts: 123
Location: OH,USA
Normally you will want to run copper wires and non resistor plugs.
The selection of non resistor plugs are not so good these days but you can still find them.
The carbon resistor wires and the resistor plugs put more load on the mag that you don't want.
Whom ever that you have working on it should run you through that if you ask or you can find
it on line at I believe the sites such as Morris and Joe Hunt in the tech sections and instructions.
Keep at and hope you can get out to some of the racing this year.

Post Sun Jun 05, 2011 6:37 pm

Posts: 42
Thanks for the explanation on the mag wires & plugs. They gave me the same explanation when I picked up the mag on Friday. So, the mag is all fixed up & pretty much perfect now, but I don't think it was the smoking gun in all this. The mag is back in & timed properly & the bike is still not running well at all. I'm kinda stumped. Road America is this coming weekend & besides not running well, I have zero time on the bike & RA is not the place I really want to be trying to figure out how to ride this thing.

So I did find out what the differences in the air bleed hole sizes & locations in the main nozzle are, so I soldered up one of my M-74B nozzles & re-drilled the holes. I think it went backwards. The bike starts reasonably easily & idles just fine, but now any kind of throttle increase causes it to backfire spectacularly out the exhaust & carb & it won't keep running unless the throttle is closed down again. When I re-drilled the holes in the nozzle I actually went a tiny bit smaller than the original size with the thought that it would richen the mixture a tad - worst case, I thought, was that I would get black smoke. It's running so poorly I can't even keep it running a little while to tune it. I have a CV carb that I'm thinking about adapting to the bike so I can at least get it running so I can spend a little time optimizing the other systems & then go back to the Linkert.

The next race I think I can reasonably make is Gingerman in August. I don't particularly like Gingerman, but it's the next best fit on the schedule. Work continues...

BTW, one little side comment on magnetos in race applications, Zooma. I have heard in the past that the condensers that typically come in your standard garden variety FB magneto tune-up kits are not appropriate for race applications. Something about the time spent at high rpms causes them to fail prematurely, I think. Unfortunately, I've never been able to find out what the correct condenser is for racing. Any ideas?


Return to 45 Flatties