nitrohead5300

From top end performance point of view which one of these 2 carbs is better the 257 or the 813??

rckiwi

None of the above! go with a 990

nitrohead5300

rckiwi, thanks for your response but could you tell me why you feel the 990 carb performance is better than the 257 & 813?? From what I understand the 990 is a 813 minus the accelerator pump. Are you saying that this carb has more topend or is just easier to set up??

levi133

first off no carb is the perfect setup for every motor what motor do u have and what type of fuel do u run..

nitrohead5300

Zen 27.2 cc ESP modified and ported with a 771 carb . I believe 92 octane 24.1 oil mix.

rckiwi

Ok sorry more explanation!

257 I have only used on boats and they work very well! but no primer!

813 I have used on various cars off road from 26-29cc Zens to CY270 awesome carb until they get wear on the throttle shaft due to
A/ dirt getting between the shaft and body wearing the shaft out quickly
B/ also because the shaft has also tension spring for the pump also makes it wear quicker.

The 990 seems very easy to tune compared to 813, but still only needs small adjustments to get different results. as far as no choke or pump, once it is fully primed takes 3-4 pulls from dead cold to start.

I hope this helps you! Cheers

nitrohead5300

Thank you rckiwi !!

levi133

I would say stay with what u have or even port and get rid of the choke on a 668 and try it.. u would be surprised..

nitrohead5300

Levi133 my 771 does not have a choke on it , I have to cover the carb with my hand give it a tug or 2 to prime it. I kinda like the 771 carb because it has proved to be reliable but I am always looking for more performance.

splcrazy

i have once ported a stock 668 removed the choke and filled the holes, that carb ran excellent proberly had the same performance of an 813 or better than the 813 after i done that mod , i did that mod because ddm never had it in stock and then i think they just stopped doing that altogether . but now i just run the 813 cos its there to buy and its cheap , but after this i think i will give modded and ported carb another go .

nitrohead5300

How do you port a carb??

splcrazy

with a dremel , you can only do it when you remove the choke , and you port the hole where the choke was you just enlarge the opening on the choke side , and then you have to fill the holes from the removed choke pins with steel putty jb welb epoxy

nitrohead5300

Thanks for the tip on porting[sm=thumbup.gif]