More and more Batavus woes...

I wanted to post a word of caution. Watch out how lean your engine is if you switch to a very high flow air filter. As far as I can tell, that's where I got caught today. I tried a new foam filter and I had to feather the choke for about 10 miles on my way to work today. My best guess is that she's just too lean. Should I go from a #56 jet to a #58? My manual says to use a #58 during break in, and switch to a #56. Now, as for changing the jet....Can I use any jet from a motorcyle store, or do I have to get yet another manufacturer specific part? If a couple bucks and 10 minutes will solve this, I'm all for it.


Re: More and more Batavus woes...

Miniengine you have a foam filter and have you ever had any problems? Have you done anything else to your moped?

Re: More and more Batavus woes...

Miniengine /

Yes Nick,

I've done so many things to my Bat. that it would be hard to walk someone through them to acheive the same results. Problems? Hell yes I've had problems. We went through two cylinder jugs before we discovered just how far we could open the ports before going into the land of no return. When tinkering you will find more failures then success stories. I cringe when I see fellow members of this forum call my words gospel, because I've tried many a religion so to speak before I found one that worked for me. Fred, Ron, and Brian S. have the theories to why some of these things work while others will fail. I only know what worked for me.

On the foam filter deal, I kept jetting my carb. up until the engine started to babble. Then I removed the stock air cleaner and the babbling problem went away. That's when I went in search of a free flow air cleaner.


Lamborn's Miniature Engines

Re: More and more Batavus woes...

Ron Brown /


I have just finished re-jetting my Batavus Starflight. I de-carbed and cleaned the exhaust port and exhaust, set timing, cleaned carb and cleaned and lubed all the moving parts. In other words, I tried to get it back to original condition befor I started. I really need a new drive chain but it is not too bad.

I removed the air box/cleaner and still four stroked at max speed, which was about 20 mph on the speedo.

The carburetor had a reduced diameter between the slide and the manifold. The intake side of the carb and the manifold were the same size and larger than this "restricted" section. I drilled this section out to the same diameter as the rest of the intake. The immidiate result of this was that I ran really rich at idle. Besides smoking, the most obvious symptom of this was that if I turned off the gas at idle, as the carb gas level fell, my motor would rev way up before dying. Looking at the carb slide, it had a slot in it, positioned directly over the jet, which allowed the mixture to get past the "step" created by the restricted section of the carb. When I removed the restriction, the whole length of this slot was exposed and sucked fuel out of the jet like a shop vac. I filled the slot with epoxy gas tank repair putty and left it lean initially.

I have the advantage of owning a clock bushing tool and reamers which allow me to size jets easily so I proceeded as follows:

With the air box off, I reduced the main jet size and tested the mixture by opening the throttle wide and using the choke, fortunately the old fashioned flap over the intake, to control the mixture on accelleration. With too small a jet, I had to use some choke at whatever speed I peaked at. I increased the size of the main jet a little at a time until when I reached maximum speed, with the throttle wide open, any amount of choke would slow me down.

Then I opened up the slot in the slide a little at a time until the idle mixture was rich enough to maintain an idle.

I made a foam air cleaner and verified that the mixture did not change.

When I ride now, I get best acceleration by rolling on the throttle as rpms increase to maintain a good mixture. The ped tops out at 25mph on the speedo and when I go somewhat downhill, it will hit 30 without 4 cycling.

The Batavus is still a little slower than my Motobecane Model 7s which are also stock except for air box and jetting. I suspect the exhaust on the Motobecanes is a better design.

I hope this helps.


Re: More and more Batavus woes...

Now don't cringe when I say this, if you've only got one jet or can find only one size jet for your bike, you we go......drill it out to the next size. Mind you, be very careful and you've got to have a large selection of small wire guage drill bits. You must test after every drilling and remember, there is no going back unless you've got a spare jet the original size.

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