Ground up: making a SuperHawk from scrap

[G-Man]

Dave

Nice progress!

The common problem with the advancers is that the neoprene buffers on the balance weights deteriorate to give you much more 'advance' range than you need. Also the pins and holes where the springs fit can become loose.

This all results in a rapid over-advance of the timing. You can check this with a strobe light and back off the timing accordingly if the advancer is in not too bad a shape. The timing light will save you having to strip th etop end is a better indication than just looking at the parts.

You will end up with a static timing that is off but something that will work better as the engine speeds up.

Another thought - have you got the carbs jetted correctly? I notice no air filters.

G


where the

Hi everyone,

Jumping ahead a bit here, but I've got the thing pretty much fully assembled, wired, oiled and fueled. Maybe later I'll tell you about my wheel drama, trying unsuccessfully to make exhaust headers, and various other steps along a crooked path.

I'm having a strange problem with ignition timing. I set the static timing and that seems to be right on. The bike starts and idles well. The problem comes when I try to give it throttle - it almost looks like the timing advance mechanism is working in reverse. It stumbles and eventually fouls the plugs if I try to open the throttle at all. Wondering if anyone has a clue - could there be something assembled backward? My next move is new points and condenser. After that I'm thinking I'll have to pull the engine so I can open up the top end and confirm the advance mechanism is assembled properly.

[dave_c]

Well, it's been a while since I checked in here. We built a shop in the backyard this summer, and the SuperHawk project has taken up residence. I made a gauge to rebuild and calibrate the timing advance mechanism, which meant the engine had to come out of the frame. So why not completely disassemble the bike and get serious about the finish work? Here it is coming back together after frame powder coating, and a period-correct single stage enamel paint job.

If anyone has questions on the timing advance gauge, let me know. The short version is I decided to remake the arm-stop pins with a 10mm diameter.

[Nick]

Simple way to check advance unit: Just grab it gently with pliers and twist it against the springs. If that movement advances the timing, it's advancing.

Of course, check timing with a strobe.

Shouldn't need to mention this, but since an earlier poster who was new to old Hondas had the same problem..... the chokes are off when the lever is down.

No air cleaners would generally make the engine run leaner rather than richer, but with stock jetting and needle settings it should still run okay without them.

Maybe try it without the mufflers?

[dave_c]

The advance was just way too sloppy. The low-end stops were worn to the point that it had too much range, so I had to advance the points plate all the way to one end of its travel to get the static timing right. With the rebuilt unit the points plate is roughly centered in its adjustment range with the static timing set correctly. The frame needed to be painted anyway, so this round of disassembly and reassembly was inevitable.

I know the perception is there's no air filters, but you will have to trust me. They're small, but they are there. No snorkels, just a self-contained filter pod to each carburetor.

[Nick]

One other thought: is the left slide in the left carb? I believe it's possible to install the left slide in the right carb, meaning the slide cutaways would be reversed, leading to rich running.

Tiny air filters can cause excessive richness due to too much restriction. Maybe try w/o air filters and straight pipes.

[dave_c]

Hi again,

Thanks Nick for the ideas. I verified the carb slides are installed in their correct carbs. I got the engine running nicely on both cylinders and was able to adjust the air (about 1.25 turns out) and idle screws. The timing is nice and steady, and when verified dynamically it is advancing about 25° with half throttle. With or without the tiny air filters on seems to make little difference.

Now I am seeking advice for a weak spark on the left cylinder. My points, plugs, wires and boots are all new. I suspect my 1960s coils and condenser are wimpy. I'll go search the forum to see if people have identified a good replacement option, but if anyone is inclined to comment here please go ahead!

Image links to a video of the bike running the best it has since I got my hands on it.

[sarals]

It does run nicely in that video! It looks nice, too.