Join Date: Nov 2001
Location: North Central Illinois
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Re: weber problems - daily driver -HELP
I need a "sticky post" for this , or learn how to copy it to the hard drive so I don't cause anymore undue wear on my totally wrecked fingers . First , always adjust the lean best idle with the speed screw backed off so it is NOT touching the linkage . Two, when setting the mix screw , only adjust it for the best and smoothest idle . Here's the trick: if your idle mixture screw is out more than 1.5 turns at this point , you need a bigger jet . The primary idle jet is located behind the choke housing on the side of the carb under a very large slotted brass screw . Most of these Webers have a 50,55, or 60 idle jet . A well set Sami engine will stand a 60 or so idle jet , some highly modified ones will take up to a 75 (max size) . My 38mm twin throat uses 75's in both sides , so guess how much $$$?? has been spent on this engine ? LOL .... Anyway, once the correct idle jet is installed , you should notice that the idle speed screw is very sensitive and will bring the idle up fast . This is due to the idle jet controlling the amount of available fuel VOLUME to the transition circuits . These circuits are what makes driveability just off idle clear up to 2k or so . If you ever try to adjust the speed screw and run into a flat spot , either the idle jet is plugged or the jet is too small . Those jets you mentioned on top are the air corrector jets for the main circuits . One for each respective barrel . Either that carb you have is jetted real lean , or someone has changed them . It should have a 160 primary , and 170 secondary air jets . Down in the bottom of the fuel bowl is the main fuel jets , most use 135-140 range for stock engines and 140-142 for modified motors . Be aware the air corrector jets will adjust the amount of air VOLUME available to be mixed in with the main fuel circuits at the upper range of each barrel . For example , if you find that you have to constantly keep opening up the secondary to maintain highway speed , try dropping down one size air corrector on the primary side to richen up the mix for a bit more power . If it gets worse , go up one size to lean that range out a bit . If at the point of opening the secondary there is a hesitation or balking , the secondary idle jet needs to be larger . Most use a 50, but could use a 55 or so . I usually try to stay within 10 points of the primary idle jet size , good point of reference to what the engine will use . Once properly set , the carb should seriously roar when the secondary is opened as you are feeding a lot of air at once . Open air cleaners will make it louder , so will 2" exhaust . BTW, unless you can figure out a way to jam more air/fuel into a Sami engine than I can , don't ruin that motor with an exhaust any larger than 2" , and run it the full length of the vehicle to get the best powerband and torque you can extract from it . A good flowing /medium back pressure muffler works well , cherry bombs won't help anything especially your ears . The stock fuel pumps suck , go with the electric Walbro and skip using the return system . Small block Chevy blockoff plates if I remember correctly work ok but need some mods to fit the Sami motor so you won't have any leaks in the future . Just remember to remove the pump pushrod or you'll be real sorry. Ok , enough for now , I think I forgot the original question anyway.....