Sunday, August 27, 2023

Cute little baby Chopper with a mysterious secret…

I happened upon a posting for a 1979 CM185 TwinStar bike for sale just about 10 miles away. In FB chat messages the owner, a young 20-something woman, was going through a move and divorce and needed to move the bike along to a new home. The photos made the bike look well-cared for and complete, but the conversation about the details revealed that the ex-husband had tossed out the side covers, original carburetor, and license plate. Nice guy!

                                                          OEM FACTORY PHOTO

The bike was purchased a couple of years before, but the funds to get it going again were low, so it sat quietly. She did have the original CA title showing the miles at 3100 and mentioned that the tires had been replaced just before purchase. The date codes on the tires were xx21 so that verified the information. The battery had been purchased then but was now a few years old and not very high on voltage. These early bikes only had a 6-volt electrical system and a 4-speed transmission. They rolled on 17” tires and came with some seriously high 6-bend handlebars from the factory. highlights the introduction of the model.

The engine is based upon an original 125cc twin. I owned an early CB125T, which is a totally different animal with a 180-firing crankshaft, a tachometer that redlined at 12,000 rpms and had dual carbs, a 5- speed transmission, and 18” wheels, with a front disc brake. Plus, it had a 12-volt electrical system.That bike would go 80 mph right out of the box.

Unfortunately, Honda chose to de-content the CM series versions with no tachometer, a single carburetor, 4-speed transmission, small 17” wheels, uncomfortable stepped seat, a side stand only, plus the silly high handlebars. It was designed as an entry-level machine at a low price. The next version of the bike was enlarged to 200cc and acquired a 12-volt electrical system. After that the bike grew to become a CM250, then the CB250 Nighthawk and the ubiquitous 250 Rebel, all with the same engine platform

The engines split vertically with the center crankshaft bearing wrapped with a cast-iron holder that bolts the crankshaft firmly into the engine case half. The camshaft chain is a Morse-Hy-Vo linked chain and the whole powerplant is robustly designed for a long lifespan.

The bike’s original carburetor was no doubt full of old gunk but probably rebuildable. Unfortunately, the choice had been to install a cheap Chinese knock-off copy, of which there are many still listed on eBay as fitting the bikes, but they all lack the angled throttle cable guide that is part of the carburetor top. The cable winds up having to do a 90-degree bend, outside of the cable adjuster. There is a part number for the carb top, but the eBay pricing is in the $50-60 range, despite the fact that CMSNL shows them at $22. After trying an OEM carb top, it turns out that the Chinese copy carburetor has a 22mm slide vs. the 20mm slide of the stock carburetor.

I met with the owner, looked over the title situation and the condition of the bike and we made a deal that reflected the missing parts and the non-running condition. During inspection, I was amazed to open the gas cap and find a perfectly clean tank surface on the inside! That seldom happens when I go to look at almost any used bike now. The bike had been stored mostly indoors and the paint on the fuel tank was still in its lovely red condition. There was pitting on a lot of the chrome parts, but the worst was on the turn signal stalks. Too bad about the missing side covers, which seem to have a “value” of around $75+ each now. She helped me push the bike up into the Tacoma and off I went back home with this little cutie, not knowing that there were some interesting challenges ahead.

The first thing was to put the battery on a charger and see about getting the static voltage value above 6 volts. In the meantime, I extracted the carburetor and noticed that the large heat shield insulator had been cut off at the bottom. The insulator was designed to prevent engine heat from being transferred directly to the float bowl. While the remaining portion still insulated the carburetor flange from the cylinder head heat, the cut-off portion would allow more heat to warm the float bowl contents. More things to go hunting for on eBay and elsewhere.

So, the carburetor had a little bit of green slime inside, but nothing drastic. I cleaned the pilot jet, and main jet holder cross-drilled holes and checked the float level setting. It all looked close to OEM settings, although the main jet had no size marked on it. It was reassembled and reinstalled with hopes of the bike firing up once the battery was charged up some. The main jet was not marked, but according to the Honda tune-up book, the main jet was supposed to be a 105 and the one that came with the carburetor was more like a 100, so an OEM jet was installed.

With the battery installed into the bike and the carburetor fuel system secured, I turned the key on and kickstarted the engine over…. and over and over. It started to sputter once, then died, and then went dead. I pulled the battery out for more charging and then removed the point cover on the left end of the crankcase to access the points. When I flashed the points with spark plugs in place, I got a meager tiny spark that was intermittent. I checked the spark plug caps and both seemed to be infinitely open according to my ohm meter. I rounded up some spare known good plug caps and picked up a set of plugs from O’Reilly auto parts, but the only options for these bikes are CR7-HS vs. the original C7-HS spark plugs. So, with resistor plugs and resistor caps, I was concerned that the spark intensity might be diminished.

I removed the point plate to better clean the point faces. I noticed quite a bit of arcing wear on the faces, which sometimes indicates a weak condenser. What I noticed was that the point arm, which is a phenolic material had a brass insert for the pivot function. For some reason, the points seemed to hang up before closing, due to some kind of roughness or wear in the pivot area. I dismantled the the point am and checked for areas of concern. There were two little wave washers on top of the point arm that seemed like they might be causing some extra pressure on the pivot point, so left one off. With that done, the points seemed to pivot more freely. What had happened previously, was that the engine would fire for a second then quit. When I checked the point's timing with a test light, the light would stay ON all the time, which usually indicates some kind of point face corrosion or dirt, but these were nice and shiny. After putting the point plate back on and going back through the carburetor one more time, the engine fired up and kept running even with the wobbly battery condition.

These bikes have auto-on headlights, so I removed it to lessen the current draw on the system while trying to get this thing to run. I must have kicked it fifty times expecting it to light up previously. What had been presumed to be a problem with the carburetor turned out to be a problem with the point set function instead!

I drove it up to the local 7-11 for a gallon of gas and rode it carefully around the neighborhood shifting through the gears and testing the brakes. There seems to be some chain snatch or perhaps an abrupt transition from idle to part throttle on the carburetor, but overall it was quiet and ran like it should. Even all the lights were working. The plastic tail light base had stripped-out holes, so a replacement unit was ordered from for a reasonable price.

You always feel relieved when your “bought-dead” bike comes back to life without any huge issues to remedy. New fork seals are on order, along with a new battery and a carb top with the correct angled cable receiver which should fit the carburetor. I have often had a small bike or scooter available to use to haul small packages down to the post office in Bonita, CA which is just a couple of miles away. Looks like this might be just the ticket to take the place of the last PO runner machine at a low price.

Follow-up repairs

The fork seals were replaced, and a new battery was installed which offered instant electric starting, but there was still a persistent oil leak coming from the left side. The shift shaft seal was replaced and finally, the countershaft seal, which looked pretty good when removed was also replaced. The engine case doesn’t have a stop machined in for the seal so in driving it into the recess it kept going in another 1/4”. I decided to install the second seal in tandem with the first one and now there are no leaks. I did drain the dark oil which had some aluminum swirling around and smelled somewhat like gasoline, so now it has a fresh 1.6 qts of Honda’s finest GN4 oil. The 4into1 rear tail light was installed, but the original screws and setting collars left the light assembly dangling. I peeled off the rubber cushion from the back of the original tail light and that provided the additional thickness to mount the light assembly correctly.

DrATV supplied some non-resistor spark plug caps and I purchased a backup set of points and condenser in case the originals start acting up again. So far, since these final repairs, the engine is oil-tight and the spark plugs are coming out clean. The engine seems to run up to whatever redline is without any signs of overheating. In checking the specifications in the Honda tune-up book, it appears that the upgrade from the CM185 to the CM200 included a camshaft change and carburetor change. The 185 camshaft shows 0/30 and 30/0 cam timing, whereas the 200 version is 7/27 and 27/7 specifications. Theoretically, this should give the engine a boost, although probably marginal given the whole design.

Other than searching for a set of nice red side covers that are less than $160 a pair, the bike is as good as it is going to be. A luggage rack would be handy for my eBay package run to the local post office, which is just a couple of miles away. This will take some of the unnecessary wear from my Tacoma, as the air-cooled engine heats up quickly and won’t sustain the kind of cold-start oil contamination of a water-cooled engine for short hauls.

The bike has a happy spot at about 45 miles per hour. The top speed is around 70 mph, but it gets really busy sounding as it strains to make enough power to move itself and my 200 lbs down the road at speed. It definitely has no place on the SoCal highways at all.

So, basically, for about $1,000 I have a fully licensed and registered, little runaround-town bike that is light and economical for local trips. These were certainly not on my wanted bike list, but sometimes an opportunity to buy something with promise and utility is too good to pass up.

Bill Silver

aka MrHonda


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