Walbro WT carb and Extended Intake

Akutey

Member
Joined
Dec 10, 2018
Messages
30
Decided to installed a Walbro carburetor on my 66CC Jet and toss out my petulant NT carb. Used two extend offset intake's joined at the male ends with RTV and a tight fitting copper tube to mate them internally. I finished it off quality half inch garden hose clamp. ( I ride on snow and trails) JB-Weld would work great too. A pulse line tap was added into the bottom of a new cylinder in the transfer ports. (Not drilling a 2009 era motor) I also added a tap into the carb and filled the existing pulse hole with JB weld to double seal it as it would be blocked by a intake manifold. I also *giggle* used the airbox the carburetor had been found with. (String Trimmer)

The carburetor itself is a WT-924-1 diaphragm style with a 19.05mm Choke Bore, 13.94mm 7.94mm Venturi and a 17.44mm 12.7mm Throttle Bore.
It has a choke, Low/High mixture screws and Fuel Primer. (Edited: Measurements were wrong, dont trust the internet)

The Venturi bore is 71.0002% size of the intake bore which match the range of a 70-90% that's shown linearly increase velocity with RPM. This in theory should slow down volumetric efficiency loss at high RPM caused by extended intake length. The intake length is a total 8.3 inch's from piston to throttle bore and should increase volumetric efficiency in low and mid RPM range by shifting its curve.

Results: I do run a 36T, I'm also tiny and 110lb so a 44T is already pretty torquey for me so it feels like I'm running a 44T now. There seems to be a idling issue (High idle or it cuts out) but other that I'm pleased.
 

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Arty

Active Member
Joined
Feb 12, 2015
Messages
316
Akutey:
Please keep us informed as to how you like the Walbro.
I am running one as well, but I have also incorporated a 40mm 4-petal RSE reed valve, and I really like it.
I also drilled and tapped into the bottom of the cylinder, and into the carb.
 

curtisfox

Active Member
Joined
May 13, 2010
Messages
609
Decided to installed a Walbro carburetor on my 66CC Jet and toss out my petulant NT carb. Used two extend offset intake's joined at the male ends with RTV and a tight fitting copper tube to mate them internally. I finished it off quality half inch garden hose clamp. ( I ride on snow and trails) JB-Weld would work great too. A pulse line tap was added into the bottom of a new cylinder in the transfer ports. (Not drilling a 2009 era motor) I also added a tap into the carb and filled the existing pulse hole with JB weld to double seal it as it would be blocked by a intake manifold. I also *giggle* used the airbox the carburetor had been found with. (String Trimmer)

The carburetor itself is a WT-924-1 diaphragm style with a 19.05mm Choke Bore, 13.49 Venturi and a 17.44 Throttle Bore. It has a choke, Low/High mixture screws and Fuel Primer.

The Venturi bore is 71.0002% size of the intake bore which match the range of a 70-90% that's shown linearly increase velocity with RPM. This in theory should slow down volumetric efficiency loss at high RPM caused by extended intake length. The intake length is a total 8.3 inch's from piston to throttle bore and should increase volumetric efficiency in low and mid RPM range by shifting its curve.

Results: I do run a 36T, I'm also tiny and 110lb so a 44T is already pretty torquey for me so it feels like I'm running a 44T now. There seems to be a idling issue (High idle or it cuts out) but other that I'm pleased.
Love the FOX..................Curt
 
Joined
Sep 26, 2018
Messages
130
Decided to installed a Walbro carburetor on my 66CC Jet and toss out my petulant NT carb. Used two extend offset intake's joined at the male ends with RTV and a tight fitting copper tube to mate them internally. I finished it off quality half inch garden hose clamp. ( I ride on snow and trails) JB-Weld would work great too. A pulse line tap was added into the bottom of a new cylinder in the transfer ports. (Not drilling a 2009 era motor) I also added a tap into the carb and filled the existing pulse hole with JB weld to double seal it as it would be blocked by a intake manifold. I also *giggle* used the airbox the carburetor had been found with. (String Trimmer)

The carburetor itself is a WT-924-1 diaphragm style with a 19.05mm Choke Bore, 13.49 Venturi and a 17.44 Throttle Bore. It has a choke, Low/High mixture screws and Fuel Primer.

The Venturi bore is 71.0002% size of the intake bore which match the range of a 70-90% that's shown linearly increase velocity with RPM. This in theory should slow down volumetric efficiency loss at high RPM caused by extended intake length. The intake length is a total 8.3 inch's from piston to throttle bore and should increase volumetric efficiency in low and mid RPM range by shifting its curve.

Results: I do run a 36T, I'm also tiny and 110lb so a 44T is already pretty torquey for me so it feels like I'm running a 44T now. There seems to be a idling issue (High idle or it cuts out) but other that I'm pleased.
I experience the same issue on my 21mm oko. You might want to try richening the idle. if that doesn't work, it may have to do with the carb being so much bigger. I can idle lower if I choke and close the throttle a tad but eventually it gets overly rich.

Also, the longer intake did that to me. I run a DIO Reed with low crankcase compression due to the large volume between the piston and Reed and Fred's machining work took alot off the crank.

Zeda has his Stihl 660 top end "Frankenstein" motor idle at 3500rpm and has a rev limit of 13500. It's the price he pays for more power.
 

Akutey

Member
Joined
Dec 10, 2018
Messages
30
Well long story short, fixed the idle by carefully adjusting the screws why testing the throttle but still had no high end. Then I bent a axel and in the process of replacing it I noticed the spoke's were badly stretched After replacing the wheel with the only backup a 20 inch freewheel I noticed it would pull me going from a deadstart with a bit of throttle. I got the carburetor to give me top end last night I'm hitting about 46.8km/h average.

fishingdog66 It's aluminum tape, use it to insulate my fuel filter as it sits between the frame and my leg with warm engine air blowing by.

curtisfox :giggle:

Hell on Wheels I try not to touch my choke, rarely need it even -5c.
 
Joined
Sep 26, 2018
Messages
130
Well long story short, fixed the idle by carefully adjusting the screws why testing the throttle but still had no high end. Then I bent a axel and in the process of replacing it I noticed the spoke's were badly stretched After replacing the wheel with the only backup a 20 inch freewheel I noticed it would pull me going from a deadstart with a bit of throttle. I got the carburetor to give me top end last night I'm hitting about 46.8km/h average.

fishingdog66 It's aluminum tape, use it to insulate my fuel filter as it sits between the frame and my leg with warm engine air blowing by.

curtisfox :giggle:

Hell on Wheels I try not to touch my choke, rarely need it even -5c.
I simply use it for testing purposes. Otherwise, I don't touch it.
 

curtisfox

Active Member
Joined
May 13, 2010
Messages
609
Best way to set them carbs is to open to about 1/3 rd throttle and hold it while turning high speed jet to max rpm's then open the let about 1/8 to 1/4 turn, will keep it for leaning out. Then jet the low speed jet so there is no hesitation when you crack the throttle, from idle to wide open throttle.........Curt
 
Joined
Sep 26, 2018
Messages
130
Best way to set them carbs is to open to about 1/3 rd throttle and hold it while turning high speed jet to max rpm's then open the let about 1/8 to 1/4 turn, will keep it for leaning out. Then jet the low speed jet so there is no hesitation when you crack the throttle, from idle to wide open throttle.........Curt
This is for diaphragm jets, correct?
 
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