100cc classic production build

[donpearsall]

Wow! I love that pic. The boat is not even touching the water, it's completely riding on the lower unit. Glad you did not catch a gust of wind!

Don

[Gearfinger]

Some easy help with engine breathing can be had by making a spacer for the cover over the mouth of the carb. Production bikes need to be somewhat narrow at the footpegs. Keeping the engine side covers tight over and around things make for nice packaging, but this also restricts airflow to the RV intake. Making a cover "gasket" 10 or 12mm thick and painting it side cover silver sounds to be in the spirit of the rules and not too obvious.

Search info on the Kawasaki G31M Centurian. A wicked little rotary valve 100cc MX bike from the early '70s.

[Koncretekid]

I just realized that the GP-100 is a rotary valve.  I cut the rotary valves on my Bridgestone 350 and ported the entrance inlet as well as milling the head.  Because I'm running it in MG at Loring, I naturally added bigger carbs (from 27mm to 29mm) and made my own expansion chambers, so it won't qualify for Production.  But I think the cutting of the rotary valves made a big difference.  The bike runs 113mph in the mile-and-a-half.

If I brought it to BMST, it could run in M-CG and that speed would easily be a record.  But spares are so limited, I probably never will.

[Gearfinger]

This is largely the same unit we got here as the Suzuki Gopher in the early '70s. Parts aren't too tough to find around the world...

[roflhat]

Wow! I love that pic. The boat is not even touching the water, it's completely riding on the lower unit. Glad you did not catch a gust of wind!

Don

Cheers  Hopefully going to Coniston again this year, see if I can top my own record

[roflhat]

I'll have a look at the carb gasket, would certainly be neat to make a sort of spacer that went in there. I guess even a thicker gasket would help some

Taking the bike down to a guy in England who is widely regarded as the best 2 stroke bike tuner in the UK, will blueprint the motor at least, see what he can do with it. Looking at that Bridgestone 350 online, from 95mph original top speed to 113 is a serious improvement, 19% which would see my Suzuki doing 83.3mph going by the quoted top speed of 70mph.

[rgdavid]

Who is the tuning guy in uk ?

[roflhat]

Who is the tuning guy in uk ?

Mick Abbey

[rgdavid]

Good choice...and he makes some lovely pipes too. (Hydroformed)

[roflhat]

Got the steering damper setup, changed the tires, cush drive and the rear wheel bearings. Still won't run, getting power to the spark plug but not enough to generate a spark. Get one strong blue spark followed by nothing. Changed the coil, HT lead, plug cap, plug, condenser, adjusted points and timing. Ordered a new stator, thinking the condenser isn't getting enough power to keep sparking

Think the bike will look a bit better with the white panels for race numbers hiding some of the gap above the rear tire

Bought Alpinestars leathers, proper gloves and boots. Leather are seriously tight, in all the wrong places! But they do fit so they'll do

[07R1LSR]

Love the bike!  Keep grinding...you will get it figured out

[Doc B.]

If you bought an old stock condenser it might be leaky. We got my teammate's P-PC Benelli to spark nicely last year by replacing the NOS condenser that he bought to freshen up the ignition with a modern polypropylene capacitor.

[roflhat]

If you bought an old stock condenser it might be leaky. We got my teammate's P-PC Benelli to spark nicely last year by replacing the NOS condenser that he bought to freshen up the ignition with a modern polypropylene capacitor.

It's a new one I got, are you allowed to update parts like that? You do get electronic ignition kits for these
Didn't realise the tires would be so skinny, none of the bikes in the Bonneville photos seem to be running such slim tires. Any reason for this?

[Gearfinger]

No spark with magneto is super simple to diagnose with a 12v test light, but the first step is even simpler.

Grab the spark plug in your hand, then kick the engine over. If you feel absolutely nothing, the secondary coil has an open in it's wiring or the primary coil has an open in it's winding. If you felt a bit of a tickle, it's time to employ the test light.

First, you must remember that when using the test light in line with the ignition wiring the system will not throw a spark even if everything is working properly. Spark cannot be made while the test light is attached in the electrical circuit.

Remove the points lead from the secondary coil, attach that to one side of the test light lead and the other to ground. When kicking over you should see a bright-ish light pulsing on to off to on etc.

If you see a bright light that does not pulse, the points are not making contact when closed. If you see no light, insulate the contacts of the points and try again. If light now, the points are grounded. If still no light, remove and isolate the wire from the primary coil to the points, try again. The primary coil should put out over 16v dc on a meter. Ohms don't really matter to me, dynamic testing tells all.

If you got a good pulsing light at the secondary coil lead, attach it back to the secondary coil, then perform the same test at the ground side of the secondary coil. You should see a less bright flashing light. If that's the case, re-attach the ground lead to the coil and place the test light between a ground and the spark plug lead. A working system will flash the test light.

I work on a lot of small magneto equipped engines. When I figured this test procedure out diagnosis became very simple, and my Fluke meter got kinda dusty...

[donpearsall]

The skinny tires are to your advantage over wider tires. The skinny tires have less rolling friction and less air drag. At your HP, traction will not be an issue.
Good luck with the ignition problem. You will solve it soon.

Don