Co0ke Posted September 16, 2011 Share Posted September 16, 2011 Here's what I have: 260z with E88 head, Mild Cam 460 lift 280/280 duration Guessing the block is stock or from a 240 PO was unhelpful when i bought it last year. And i dont know how to check Dual downdraft webers 32/36 2.5" pipe from downpipe back and some big ugly muffler Everything else stock I have been just fixing problems, brakes, bushings, rust, gaskets, hoses, etc, ... most recently I reground the cam due to a wiped lobe from a broken oiler bar. Went with the grinders suggestions and got the max for stock springs, resurfaced the rockers and got new lashpads. I feel now like im ready to tackle the lack of power problem. Butt dyno is telling me it has less than 100 hp Here's what i've done so far... Checked compression...150 across all cylinders Cleaned points on dizzy...smoothed out nice after that New plugs Timing is at 10 deg advanced Havn't touched the carbs yet other than to set the idle screw to get me to 850....maybe to high. I have no experience with carbs whatsoever and am not a mechanic either I just enjoy doing everything myself and learning as I go. Guess I'm just asking for some guidance. What to do next? Should I mess with advancing the timing? Dive into the webers? Try to locate some round tops since i've read only bad stuff about the webers I have? Engine doesnt really pull until 3500 and at 5500 sounds like WHAAAAAAA!!!! till redline....actually sounds awesome, not sure if there's more power just sounds awesome Quote Link to comment Share on other sites More sharing options...
getoffmyinternet Posted September 16, 2011 Share Posted September 16, 2011 There is really no correlation between sound and power, just go by the feel when you stomp on it, ie. where the dead spots are. Do you have the dyno printout? Live readings of fuel flow etc would be very useful. I don't know what typical timing is for those, but 10 strikes me as way too low. I'm thinking at least 15 to 20, but I'm not sure. Nothing wrong with downdraft webers. I don't have practical experience so perhaps someone will step in, but my impression is that they can be great for performance but are more finicky than others and need to be precisely tuned to live up to their potential. You get what you pay for type of thing, great if tuned right, otherwise a nightmare (in other words it doesn't "just work") The most negative things I've heard all have to do with altitude sensitivity. They also have to be tuned to each other. On my old SUs someone just flew by the seat of his pants and got the engine running seemingly normal by messing with everything independently, the result being that one carb was set way too rich and on the other you basically couldn't get it off choke. Miraculously the engine sounded fine, but as expected, no real power. Quote Link to comment Share on other sites More sharing options...
Co0ke Posted September 17, 2011 Author Share Posted September 17, 2011 Lol....In reading other forums I always assumed the butt dyno was literally how the car felt in your butt as you stomped on it. *feels stupid. Definitely showing how much of a newb i am. At any rate, I will look into the timing, gotta borrow a light. I just had a friend help me and he just set it to what he thought was stock and left it. I'd like to find out what the total advance is and try to get the optimal setting. What are my options for measuring AFR and such? Can tuning up the carbs if they are working properly be as simple as adjusting screws? Or will i need to do jetting and/or replace parts? I really know almost nothing about carbs and am somewhat intimidated. I don't want to start messing around then get them to a point where i can't get them back in order to keep my car running. I'm simply looking to get the best preformance from what I have atm before doing any bolt ons. Quote Link to comment Share on other sites More sharing options...
the_journeyman Posted September 30, 2011 Share Posted September 30, 2011 What are my options for measuring AFR and such? Can tuning up the carbs if they are working properly be as simple as adjusting screws? Or will i need to do jetting and/or replace parts? I really know almost nothing about carbs and am somewhat intimidated. I don't want to start messing around then get them to a point where i can't get them back in order to keep my car running. You can get a gauge that uses an O2 sensor to show your AFR. Ones I've found online are around $200. Gotta either have a O2 bung on the collector/header or prep & drill for one. Depends on how far 'off' the carbs are. Proper fuel level is easily adjusted, depending on the carbs. I don't have any Weber experience, BUT on Mikunis there are idle or pilot screws. This helps idle & pilot mixture (idle to small throttle openings). The rest of the mixture (when you stick your foot in it) is managed by the emulsification tubes (needle jets on some), the fuel jet & the air jet. Hope this helps. Carbs are simple, but ONLY make a change to one area at a time. IE only change fuel jet, then see how it runs. Don't go changing fuel level AND jets at the same time or you won't know which caused the difference (good or bad) in performance. JM Quote Link to comment Share on other sites More sharing options...
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