998/813 probs?

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The part number is Rovans. That carb comes on their cars. I'm not sure of any possible differences from the 813. Should be a good carb.
 
It is made by Walbro for Rovan. But like I stated, I'm not sure if changes were made in the design.
 
i don't know either as i've never had an 813 before to compare. i will be installing the 998 on my xt & putting my 990 on my son's xt tonight. when ido i will look for the hole that needs to be shoe goo'ed. that's why i was hoping alfred would put up a pic of this hole. that way i know what to look for & can confirm to all of y'all that there is a difference or not. :)

also, i noticed while playing w/the actuation that while opening the butterfly from idle to halfway it's easier to open than from halfway to wide open. is that bc from half to wide open is where the pump is activated?
 
i have no photo at the moment. assuming that this new carb has the same design as the 813, on the side of the carb that bolts to the intake manafold there is a hole where you can see the pump plunger, throttle shaft with a notch to operate the pump. I use the ada manafold.- rember what side of the carb this hole is. assemble as usual. after its all tightened up, look real close where the carb-gasket-manafold is-on the pump side. you should be able to see that about 1/4 of this pump plunger hole is exposed. Use shoe-goo. silicone is useless. first- do not press the shoe goo into the hole. all ya gotta do- get a small flatblade driver- put a little goo on the blade- stick the goo not on the hole- stick the goo on a outer edge- then sorta lift and pull the sticky goo over the hole- and stick it on the other side of the hole.- let it set a while- and do this agan. until its covered with out actually getting any goo down into the hole. - if its built like the 813- theres gonna be a hole-you just gotta look real close under good lighting conditions the see it. hope this is understandable.
 
found this little photo of the 998. on the right hand side of this carb - you may be able to see 2 holes.- the hole that is alinged with the brass throttle shaft you see on the outside of the carb is the hole that should be gooed up as i said in the above post.- its a modded 813- claim to have improved the metering circut. bet ya 20 bucks that they tru trial and error - installed assorted high speed check valves in this carb- a valve that releases at somewhat lighter pressure than the hs nozzle- check valve on the 813.- this high speed nozzle is the little round brass device you see inside the bore on either the 990- or 813. if this is the case with a somewhat lighter release pressure on this nozzle--- it should give a shot of gas tru the pump circut sooner than the 813 does--- just a alfred guess---lol.- yea, bolt that puppy up and let us know the results.
 
Here is a larger pic.

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yea, if my hunch is correct this would be a kick ass carb. the reason why is cause the stock 813 pump assembly has to overcome the high speed nozzle check valve before it can add fuel. it squirts plenty of fuel- the accelator pump has more than enough volume- but its delayed too much- a lighter pop off on the h s nozzle would enable it to inject fuel with less throttle applaction and right off idle too!! sayy- nice spelling huh? cripe, where i went to school the dudes that could bounce and hit assorted shapes and sizes of rubber balls were b and a students- but even after graduation they could not hardly read a comic book-let alone spell--- no kidding.
 
lol alfred. i got you man. i'm no grammar nazi so you'resafe w/me bro! i had a hunch tht hole as the culprit as i looked the 2 over side by side to compare. i went ahead & put some shoe goo ove that hole care too make sure i didn't gob it all up in the hole to affect the throttle shaft. i'm a look over it again now that it's bolted up to see if i can see the hole & goo it up if need be.

i can't say how it will compareto the 813 as i never had an 813. i will say that midway to full thottle it gets a lil stiffer to push tho. thank you alfred & brian. :)
 
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