I just figured I would share a little trick I did to increase my venturi size on my weedy conversion. Same deal as some out there. Little to no money to spend. Received a free weedy and love to fly SPADS for almost no money. Any way, I got this Weedy but was discouraged at the carb performance on the stock 1 needle 7.3 MM venturi. It would've probably flown but with limited power on hand. Nothing like having a little more power to use if needed. I really didn't have the time to go out hunting for a used carb and Momma wasn't releasing any funds so what to do. I had just picked up a 5/32 chainsaw file to sharpen my chansaw(not converting but have thought about it) so I figure what the heck, pull the carb and throttle plate and start filing that lump in the venturi to open her up a bit. I stayed away from the ports/tiny holes and filed slowly tring to keep the venturi shape. After about 20 minutes I had it opened up to about 9.4 MM. Gave it a run and what a difference. I have a 21 CC weedy spinning a 15X6 APC and gained almost 900 RPM (Up to 7350)but the best is the response and idle improvement from the stock venturi size. The high end was not effected in fact it spun up higher. I would imagine there would be a limit using a non adjustable, high end needle carb, but my 9.4 MM was not it. This may sound silly to some but for me with little to no money to spend, it is a viable alternative to spending $20-$40 on a new larger carb.

Hi 6414,
Good job. I am converting a Mac 21 and it needs a 9.5 venturi. I do the hand me down method, I took a 9.5mm Walbro from a Mac 28cc that I havn't touched yet. Let us know how well it flies.

Dave

I am collecting engines pretty fast now. !3 engines in about 10 days. I have noticed some of the carbs have a built in restricter. Looks like they could be opened up much larger. I may try that. If I ruin one...no biggie....got 12 more!!!! Capt,n

I did a similar trick while messing with a ZAMA carb on my Homelite 25cc. I took a good, hard look at the venturi and discovered a drill would easily pass through without hitting any small ports etc. So I put it into my bench drill and carefully ran a drill through the venturi (not going to the butterfly though). I went just one size up....only drill I had that suited.

I had already modded the carb somewhat but managed to pick up about 500rpm, however; with a fixed high end needle it only made the high end run leaner than before.

Raven,
I have found that the high speed needle is hidden on some carbs. The sloted head of the needle is recessed and covered with soft epoxy etc. I removed the potting and exposed the HS needle. Look for this trick.

Dave

I removed the plastic cap unit from the ZAMA which now allows full adjustment of the low end needle. Alas, the high end needle is pressed into the carb body. There is no thread for the high end "needle" and the screwdriver slot is not cut.

If I was adventurous I could pull the needle out, tap the needle shaft, and then tap the hole in the carb body. This wouldn't work though as all the shaft diameters would then be out and the slightest mis-taping would ruin the carb.

I have since obtained a WA-167 (or is that WT) which makes the engine run a lot better with full adjustability. 8000+RPM is easily achieved, which should be more than adequate for my application. If it's not enough then it's time to start porting.