batavus speed and "4-stroking"

in regards to a previous message about 4 stroking where the moped makes a different sound at high speeds. my batavus hs-50 does that at about 23, which is the factory top speed. however, if i go down a hill, it will "4-stroke" and then run normal and keep goin faster. (ive had it up to 40 mph on a steep hill) Also, i put a dellorto tomos carb on it, and i had to put a rag on the outside, because it was getting to much air. Would changing the jet, or enlarging the manifold make it go faster? also, i have an extra 2-piece biturbo sitting around, that i was think about fabricating to fit on the batavus. would it help?

RE: batavus speed and "4-stroking"

I had the same thing on my Vespa Ciao, when it got to topspeed (wich wasn't much) it started 4-stroking. I took the entire engine apart and found there to be sand inside the cilynder because of the crappy airfilter Vespa designed. After having fixed that the problem was still there, I got annoyed by the bike; the whole design is crap and I couldn't find the problem. The problem probably had something to do with the crappy carburettor Vespa designed for it, so I sold it for a Honda PF50 Novio, wich is a very solid bike and has never given me any problems. Dell'orto carburettors are known to be pretty good so I think you'll be able to fix the problem, if it's getting too much air the mixture is too lean, changing the main jet size to a bigger one will fix this. Als make sure the carburettor is clean and the jets are not obstructed, and you really should get a good airfilter because having sand inside the engine is not something you're engine will like, in fact, it'll wear down to nothing in no-time.

Performance exhaust will almost always perform better than the original ones, provided that the exhaust DOES NOT leak, not even a bit. 2-stroke exhaust systems are very touchy about leaking, they have to have a good flow of gasses inside in order to work correctly.

RE: batavus speed and "4-stroking"

As for Batavus "factory" speeds. Most of the Batavus mopeds came in 20, 25, and 30 mph versions. You can tell the difference by the jet size (i don't know off hand the sizes) and the number to teeth on the sprocket of the pulley on the left side of the bike. The 30mph ones have 13 teeth, 25mph have 12, 20mph have 11.


RE: batavus speed and "4-stroking"

Erin Lassley /

I had always thought that 4 stroking was a self governing method to prevent over revving until I found out that it was actually a problem. How I've always over come the occasional 4-stroking is let the throttle go back to idle, and hammer it wide open. That usually cures it. If it doesn't, my carb is out of adjustment and I reach down while riding and tweak it a little. It's kind of fun doing adjustments and stuff while you are going down the road. It's like you have to keep monitoring stuff, tweaking this and that to keep yourself moving. Ahh - the joys of pedding! :-)


RE: batavus speed and "4-stroking"

Harry Bullochs /

I recently acquired a 1977 Batavus for the low low cost of "pick me up and take me away." The previous owner had obviously tried to start it and failed, because all sorts of bits were missing from it, not the least of which was the air filter.

After discovering that the problem was no spark (compression, spark, fuel), I traced the problem back to the taillight (far away from where he had been meddling), where some wires had fatigued off. After soldering those back together, the engine started on a few shots of starter fluid, and then she started smokin' the way she was meant to.

However, it ran like crap up hills. We had jury-rigged a u-tube to keep airborne junk from blowing into the cylinder, but we didn't have enough intake restriction, and it would bog out at open throttle. You almost had to nurture the spark, and keep the engine at the right revs to keep firing, no matter what it did to your speed. Not quite right.

I took a brass cap from some plumbing assembly that was a close fit to the carb air intake, and drilled a hole through it and stuffed it with a sandwich of brass screen (considered periphenalia in some states), filter material, and screen again. The engine ran a little better on this, but it began to stall out. I drilled the cap out almost completely, leaving just enough lip to hold the sandwich in, and I've been running that way ever since. It now beats my roomate's Yamaha QT50 up hills, where it had been losing sorely before.

Bottom line- get an air filter! That engine's tuned to have that intake restriction.

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