Our 1973 Solex 3800 "tornado-freezer bike"

Daniel Woodard /

Just a little over a year ago, our house was hit by the 2019 Memorial Day Tornado. Thankfully, it mostly damaged the roof and siding, and the electric was out for most of a week, but everyone was safe. After cleaning our huge chest freezer out in the garage, we never got back around to plugging it back in. Eventually, I sold it a couple of months ago to free up some space in the garage.

A couple of weeks ago, I saw a Craigslist posting for a black Solex 3800 moped, "runs and drives ok - $300". I had never seen a moped with the engine up there by the handlebars, and was intrigued. My oldest son and I went up to take a look, watched the guy start it up and whiz up and down his driveway and the road a bit, then traded the tornado/freezer money for the motorbike.

We got it back home, then we took turns starting it up and riding it a bit. Initially, it seemed to alternate between running rather slowly for about 20 seconds to running quite well for about 20 seconds, and then it would sometimes die. Figuring that this fuel might be years old, I dumped out the old fuel. (heck, the guy might have had alcohol gas in there) I replaced that with alcohol free gasoline, mixed with Sta-Mix Smokeless semi-synthetic 2 stroke oil I picked up at Tractor Supply.

My son took it for a spin of about 3/4 mile last night. I took it out for about a mile and a half this morning. It definitely seems to run a bit more even than before, but I noticed that most of the time it still seems a bit "bogged down", and sluggish. Still, it was fun to take it out on the road.

Now that I've replaced the gasoline, I'd like to replace the spark plug. However, I have found various websites listing about a dozen different spark plugs as a best choice for this Solex 3800. I'm not sure what to order! If you have any suggestions for that, I'm all ears. Thanks!

Re: Our 1973 Solex 3800 "tornado-freezer bike"

Best spark plug will be a ngk or a Bosch. Which one will depend on what thread length you need.. most likely it is a ngk B6hs

Also, it is a solex. 20mph should be about its max speed. Not sure I would want a friction drive going much faster. The thing runs by moving a wheel against your front wheel which turns it to move.

Re: Our 1973 Solex 3800 "tornado-freezer bike"

Google Brian Solex

Re: Our 1973 Solex 3800 "tornado-freezer bike"

Obviously, you are mixing 2 stroke oil with the gas, right? 20mph is usually your lot.

Re: Our 1973 Solex 3800 "tornado-freezer bike"

20mph! No way. I hit 18 mph on mine down a slight hill and I felt it was going to fall apart. The other one I have with the wide open motor hits a solid 12 on flats. 20mph is a lot for a solex. If your looking for more speed get that one running and sell it. Buy a Puch or TOMos.

If it is not staying running, the carb could be clogged with its tiny passages or the fuel pump might need a new diaphragm. If those are clean it my need the points cleaned and re-gapped and new condenser.

But if it is running pull out the old phone and use a gps app. You should be between 12-14 mph or slightly higher of your lucky.

Re: Our 1973 Solex 3800 "tornado-freezer bike"

> EH FCC of the QCB Wrote:

> -------------------------------------------------------

> 20mph! No way. I hit 18 mph on mine down a slight hill and I felt it

> was going to fall apart. The other one I have with the wide open motor

> hits a solid 12 on flats. 20mph is a lot for a solex. If your looking

> for more speed get that one running and sell it. Buy a Puch or TOMos.

>

> If it is not staying running, the carb could be clogged with its tiny

> passages or the fuel pump might need a new diaphragm. If those are

> clean it my need the points cleaned and re-gapped and new condenser.

>

> But if it is running pull out the old phone and use a gps app. You

> should be between 12-14 mph or slightly higher of your lucky.

Yeah I thought they would be pretty slow. Every time I see one of those I'm like....yeah I dont have any desire to ride that.

Re: Our 1973 Solex 3800 "tornado-freezer bike"

The two I got going were fun to get brought back to life but after that I lost interest. Couple hot laps(at12mph) around the block on Friday night are fun tho.

Re: Our 1973 Solex 3800 "tornado-freezer bike"

Daniel Woodard /

Yes, I'm mixing semi-synthetic "no smoke" oil in, at a rate of 3 ounces per gallon.

I did notice a lot less smoking once I dumped out the old fuel and put new fuel in. (who knows how many years old it was, or whether it had alcohol or not) However, I also noticed that it seemed like I needed to keep the choke over a lot closer to "choked", even after it had been out on the road running for 10 minutes. Previously, I had been able to edge it on over to the right, away from the start position.

I have a new spark plug we can put in tomorrow. Maybe I'm just expecting a bit too much pep from it. I guess I'd have to compare it to one running at tip top shape to know for sure. I do have an app on my phone, and I'll start it up and ride it on a road with few/no stop signs for 30 minutes after we get the new spark plug in. That should tell me roughly how many miles per hour it is going. If I fill up the fuel tank first, then find an accurate ounce measuring cup, I could also do a test to see how much fuel it is using, by filling it back up after I finish. I would guesstimate that it should use about 9/10 of an ounce of fuel per mile driven - would that be close if everything is working well?

Re: Our 1973 Solex 3800 "tornado-freezer bike"

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Sorry to hear. We got lucky. I didn’t lose any bikes. It was a close call. I had a guy from Clayton take test drive on a moped today. He’s trying to talk his wife into it.

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