Walbro 990 tuning

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Top Jimmy

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Selkirk,NY
So I added a 990 for whatever reason. I can't get this damn thing to idle, or hold a decent tune. Has anyone else had this issue? What'd you do? I have an XT with the stock motor, Phat Dad stack, Aluminum intake, and Dominator clone pipe. I trashed my stock carb. , but wish I kept it now!!! :mad:
 
Oh yeah. I'm pulling on this for what seems like days to start! Seems like it's fuel starved. I have to cover the mouth of the stack in order for the gas to draw into the carb. REALLY MISSING THE CHOKE!!!!
 
Reset the needles. For the 990 I set the high and low speed needles to 1 1/4 turns out. Try that and see how it goes.

When did you install the aluminum intake and the ShreadStack? Did you make sure the carb bolts aren't too long? If they're too long, that'll cause an air leak.
 
Also, it shouldn't be that hard to start. Pump the primer bulb about 6 or 7 times and give it a few extra pulls. It should start up pretty easily.
 
Thanks for the response guys. I actually had it running yesterday and today. Yesterday I was running it up and down the street. Today I was trying to tune it on a block. It is REALLY hard to start. I had to cover the mouth of the stack in order for it to pull fuel. Then it flooded, so I held it wide open and it started. It won't idle or stay running long enough to get a tune. UGH!!!
 
what are you high and low needles set at? Either your needles on your carb are really off or you have an air leak somewhere, with a new carb and gaskets it should fire right up for you on stock carb settings and idle with no issues. If you have an air leak though this will cause alot of inconsistancy and next to impossible to tune.

Set the carb to factory settings and prime the fuel ball and try to start it. If it does not start there is a good chance you have an air leak. Another thing to do is vent your gas cap, if gas cap is not venting properly this will cause you some problems also.
 
Gas cap is vented. If there's an air leak, could it have ran decently yesterday? needle settings are at 1 1/4 on both lsn and hsn. I've adjusted all over from there. when I return to the 1 1/4 on both ,minimal improvement. If I can get ti to start, I'll WD-40 test for air leaks. I can't imagine a leak though, I used a teflon/rubber gasket and a paper gasket on the intake and paper on the carb. all of which are new. bolts didn't appear to be too long either. UGH! I'm suppossed to take 2 of my sons to the track today.
 
i've had trouble with my stock motor also with a different carb. the only way it'll run is if i have the stock carb on it. i tried a brand new 668 and just to get it to start i had the l at 2.5 turns out. put the stock one back on and no problem. for some reason that motor won't work right with any other carb. atleast mine anyway.
 
Gas cap is vented. If there's an air leak, could it have ran decently yesterday? needle settings are at 1 1/4 on both lsn and hsn. I've adjusted all over from there. when I return to the 1 1/4 on both ,minimal improvement. If I can get ti to start, I'll WD-40 test for air leaks. I can't imagine a leak though, I used a teflon/rubber gasket and a paper gasket on the intake and paper on the carb. all of which are new. bolts didn't appear to be too long either. UGH! I'm suppossed to take 2 of my sons to the track today.
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Yes it is possible for it to run with an air leak. It makes it unstable. The problem area is between the carb and intake and between intake and motor. Some times the bolts are too long. The bolts stops turning so it seems tight but they bottom out inside the hole and do not get tight enough to seal things up.
 
Well I went to the track with the boys in hope of one of the other guys being able to lend a hand. We discovered that the grommet that goes into the tank was ripped to poop. Also, the vent tube was on the very bottom of the tank. I need to replace the grommet and I think the fuel filter may be clogged as well. Any thoughts???
 
Which screws need to be shortened? The ones that hold the intake? Or the ones inside the filter? And by how much?

Thought I solved my air leak problem by replacing the gasket between the filter and carb. And now it won't even start... Couple drops down the spark hole and it turns over for about a second, but that's it. Both needles are at 1 1/4. Even if I still had the air leak it would atleast start up, right?
 
the 990

check the things they said- the bolts- the gas line goes into the bottom of the carb- the return line is on top- by the primer bulb. check the gaskets to make certan the carbs -intakes pulse hole is not covered.- this pulse hole makes the carbs fuel pump operate. the 990 feeds quite a bit of fuel-- set both needles @ 1 turn out. - just to start it- then set as required after the engine warms up-- i say your pulse holes are blocked- intake, carb, or both. just a guess-----
 
also, if the wt series carb is in correct working order, you can pumb the primer bulb forever and it will NOT add one drop of gas into the engine. in your colder area, add 7-8 drops of gas down the plug hole- with the spark plug still out- shut the radio off- move the throttle to wide open position, and pull the rip-cord 2-3 times. install the plug- move the throttle back to idle- turn the electronics on-- and try to start.
 
let me be more clear about the primer bulb. the primer bulbs there to remove trapped air- add fuel tru the carb. if you have a carb with a accelator pump, after the carb is bled -punped free of air, when ya move the throttle, it will give the engine a small shot of gas. on a carb with no accelator pump, -- my cars with the 990 can be ran, shut off on a 60 degree day for 1/2 hour. they will not start until i either add drops of gas tru the plug hole- or mist gas into the carbs intake side. People in hot climates will have diffrent results starting these non choke equipped carbs.
 
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