wtb walbro 990 carb

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Rsaint

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hi there anyone selling a walbo carb 990. also, want to know difference between 998,990,771? also wtb msd ignitionwires, air filter and velcity stack thanks
 
Never heard of a 998. The 990 is the same as an 813, but it doesn't have an accelerator pump. The 990 is the same as a 771, spec wise. Might have different metering springs, etc. Performance wise, they're going to be about the same.
 
I don't understand where the 813 carb is supposed to have an accelerator pump ,looks the same as my other carbs. it does have a pop off type main jet where some have only a fixed drilled hole for a main jet , but accelerator pump ???my favorite carb is the 19a it has a 36 bore /choke shaft /pop off main jet/ the 813 has no choke shaft and has the smaller venturi 32 same as the 990 .if you are going to run a pipe and the motor has some displacement 29-30.5 go with the 19a carb .the 19a has a straight through bore,you simply cant get the carb any bigger with out changing the manifold,and it's one of the good carbs .

the main difference in the carbs is the main jet ,if it has a simple drilled hole for the main jet the carb has no way to shut off the fuel when the air flow in the carb slows down (during deceleration) this causes a bog when working the throttle , the pop off style main jet delivers or shuts off fuel flow to the carb at a given air speed so the carb can switch effectively between hi & low speed without a bunch of unwanted raw fuel .this gives the engine a more snappy or punchy feel . Roger
 
I have a 990 that I am not going to use, I ran it for about a tank, but I like having a choke. I got it from gizmo motors and will ship it to ya for 45.
 
RAMJET said:
I don't understand where the 813 carb is supposed to have an accelerator pump ,looks the same as my other carbs. it does have a pop off type main jet where some have only a fixed drilled hole for a main jet , but accelerator pump ???my favorite carb is the 19a it has a 36 bore /choke shaft /pop off main jet/ the 813 has no choke shaft and has the smaller venturi 32 same as the 990 .if you are going to run a pipe and the motor has some displacement 29-30.5 go with the 19a carb .the 19a has a straight through bore,you simply cant get the carb any bigger with out changing the manifold,and it's one of the good carbs .the main difference in the carbs is the main jet ,if it has a simple drilled hole for the main jet the carb has no way to shut off the fuel when the air flow in the carb slows down (during deceleration) this causes a bog when working the throttle , the pop off style main jet delivers or shuts off fuel flow to the carb at a given air speed so the carb can switch effectively between hi & low speed without a bunch of unwanted raw fuel .this gives the engine a more snappy or punchy feel . Roger
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the pump bore on the 813 is inside the carb on the return side of the butterfly shaft . there is a c shaped machined out of this shaft-a steel ball rests in this-after the ball- the pump plunger with o ring-then the plunger return spring. yes, the pumped fuel discharges out the main. I suppose this way, Walbro was able to get away with just 1 check valve-the mains. The only visible diff eyeballing this carb- is the small steel plug on the carb body -where the cnc had to drill a passage, then plug up the hole. This carb still had a slight hitch -not really a bog- Stripped it down to bare bones, installed a notched butterfly valve- i have a bunch of these made up- with assorted styles of notches- bolted it up- fired up the cy29-problen sloved.
 
walbro carbs.

Ram-Jet. looks like you have lots more working time on these carbs than i do-- never new about the 19a. I am alone at my location- its all trial and error for me- The idea behind the notching of the butterfly is to give the lo-speed outlets a stronger signal- Some carb-engines it makes one hell of an diff for the better- others? not so much.- I bought the Walbro pressure spring kit- as u know- all the circuts in these carbs overlap- when the mods click together correctly- it really makes these engines run hard-
 
love the 990.. so far flawless flow , nice snappy topend . delivers without drowning the bottom half and easy tune sweet spot . very stable through warm up and no fade even after super long full bore sessions. nice, easy basic performance.

easy start 2 slow FULL pulls, TDC, first snap--->POP!
 
RCDAD said:
1&1/4 on the low1&1/2 on the high

This should get you started.
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I actually tried that and cannot get it to run. When I first installed it it was running too rich on both setting so I turned in both needles and back each out at 1&1/4 on the low 1&1/2 on the high to use as a starting point for tuning now it will not start at all and like a dummy i forgot to record the original settings
 
First pull the plug to make sure it's not wet. (Wet = Flooded)

The low need should be 1 1/4 out. High won't matter to get it started.

Set the idle stop screw so that the throttle lever is midway up the tapered part of the screw.

Push the bulb a good 5 times.

Pull the starter a few times real slow.

Now a couple regular pulls and it should fire right up.
 
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