Walbro carb on 100cc reedjet?

I knew people would say that. I know the tilly is better but I just want to run one for a personal reason. Just have a point to prove.

Are there any lean out issues I may encounter.
 
Remember what the WB3A was originally designed for; chain saws. They were designed to run very rich wide open to cool the engine. You can use it and it won't harm your motor.

DK
 
Don K said:
Remember what the WB3A was originally designed for; chain saws. They were designed to run very rich wide open to cool the engine. You can use it and it won't harm your motor.

DK
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Thanks a heap Don. Got guys here telling me a WB3A opened up to 28mm on a std reedjet in DD wont run as fast as a std ICA carb like an Ibea or HL360 at 24-25mm. On gas here.
 
Ya , arc a properly built WB3A should not only be as fast but faster, because of an increase in airflow over a std. 24mm carb. You will need to push the throttle bore to 28mm, that's close to the limit , and then bore the venturi to around 25.5mm . a Walbro at 25.5mm venturi 28mm throttle bore will more than make up for the superior flowing venturi shape of the IBEA or 360A at 24mm V. 26.5mm T.bore. You will want to build a high flow throttle shaft and butterfly assembly by reducing it's cross section to eliminate as much restriction as possible and still have enough strength to resist breaking. The step between the V. and T. bore should be eliminated by machining a slight angle from V. that will zero at the T. bore. When you bore it that far, the front side of the carb will need to be redone to get a nice radius venturi bump and then a properly shaped air filter adapter to maximize overall flow characteristics will be the finishing touch. Jon
 
I haven't fooled with the walbro much, but on a DD, I think I would be a little cautious of a off throttle lean., you may have to reach over and cover your airbox holes at the end of the straights.. I have never compared the circuits on the walbro to a ibea? to be on the safe side, I think I would put a external 3rd jet on it.. I am also a big proponent to running a larger t-b/venturi ratio.. you can get external 3rd jets by using R/C nitro engine remote needle.. I wold use a small pumper to feed it, if you can't tap into the backside of the carb pump cavity, the problem with that, is I don't know if you can get the extra fuel capicity in the walbro, (like you can by t-slotting the ibea or tilly.)

In other words, the 100cc reed is going to need different fuel requirements than a kt, and you need the fuel loaded up behind the shutter, for when you mash the pedal.. on dirt, clutched kart, a 3rd jet is not really required, if I run one, I normally set it at around a 1/4 out., and leave it..

http://www.hobbyking.com/hobbyking/...i_two_stroke_glow_engine_w_remote_needle.html

You could also use the remote needle and small reservoir with funny fuel???
 
Nice idea Mike, I never thought of using an r/c remote needle which is pretty silly because I have one on my outrigger .84ci boat. Its actually a 3rd channel servo actuated needle so you can adjust it once the boat is on the plane. Been a fair few years since I dug that out from somewhere in the back of my toy box. Was kind of waiting for my son to get a bit older.

Would you put the 3rd jet in front or behind the shutter. If its in front of the shutter its not going to feed any fuel off throttle. Maybe I can open up the idle jet to get some more fuel off throttle.

I was kind of going to run about V@27 and T@30. Maybe even V@28 and T@31. If I go that far I need to make and off-set fuel inlet nipple and also plug and re-drill the idle jets. If I stay with T@30 the idle jets should be ok.
 
For the off throttle lean condition, you can put a notch in the shutter right at the low side fuel port like an IBEA creating a signal boost off throttle. a third jet like in the IBEA is just a high speed enrichment and will be no help for off idle, if you need more down low you can pick up the idle circuit, that along with a shutter notch should be enough. Mike , there's not a lot of room in a Walbro to have a very large t.Bore to V. ratio if you want to increase the venturi any. Jon
 
Jon Brogden said:
For the off throttle lean condition, you can put a notch in the shutter right at the low side fuel port like an IBEA creating a signal boost off throttle. a third jet like in the IBEA is just a high speed enrichment and will be no help for off idle, if you need more down low you can pick up the idle circuit, that along with a shutter notch should be enough. Mike , there's not a lot of room in a Walbro to have a very large t.Bore to V. ratio if you want to increase the venturi any. Jon
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I'm so not with it the last few days. The notch in the shutter is a great idea.

You can go 30 or 31mm in the throttle bore if you make some alterations to the fuel inlet brass barb and also the idle fuel hole/jet. When I was boring the WB3A to destruction I found it just hit the step/taper where the Walbro tooling drills the small hole for the idle into the throttle bore. Also cut into the inside of the brass fuel inlet nipple.
 
I used one that was bore larger, and had an Alky kit in it on a TT21 once.
Ran good. Sold the TT21, kept the Walbro.
 
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