Guest petrol Posted November 1, 2003 Share Posted November 1, 2003 Hey all... After fighting with firing order and getting everything else in order, I am now moving on to getting it running under its own fuel system ($1.99 per 20oz starting fluid is starting to get expensive) Anyway, I have the air cleaner assy all the way off. I have plugged every extra vacuum ref line from the intake manifold that I can find. The car will start and run high (fluctuating up and down, but around 3000rpm) ONLY with the choke 101% ON, and if you even bump it off by a mm or so it will stall out and die. The fuel pressure appears fine, and it flowing well to and from the rail...there dont appear to be any blocks in the fuel delivery path (i.e., I can blow lightly in the float bowl vent lines with the pistons removed..and fuel flows freely from the jet hole...but I cannot seem to find out why the thing wont fuel unless the choke is ALLLL the way on! I tried setting the adjustment screws all back to factory "starting positions" and making everything as neutral as possible. Fine tuning can come afterwards! Any ideas, hints, techniques?? I appreciate your help and your information so far...lets see it work now! -Scott Quote Link to comment Share on other sites More sharing options...
Guest ZmeFly Posted November 1, 2003 Share Posted November 1, 2003 but did you make sure your floats are at theyre proper hieght? id clean the needles and the pistons really well and make sure nothing inside the carb itself is causing the problem. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted November 2, 2003 Share Posted November 2, 2003 Sounds like you may have a major vacuum leak and the carbs can only supply enough fuel with the choke on. Tim Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 2, 2003 Share Posted November 2, 2003 Sounds like you may have a major vacuum leak and the carbs can only supply enough fuel with the choke on.Tim I was thinking about this...but I checked every possible source (to my knowledge) of a possible vacuum leak! There are no open ports at all on the crossover tube, where most of my vacuum references are...I even removed and plugged the brake booster vacuum line, just in case. I dont know (at this point...although I will look) how to check the float levels...so I will look at this next. I did start to look in the float portion before, but without actually thinking about it, I couldnt see how to detatch the float bowl portion from the carb body, and there isnt enough room to pull the float chamber top off (after you remove the 4 screws) because it bumps the main body... I'll go look again and see what i can find. Im sure its something stupid and small I am overlooking...like the firing order being CCW! -scott Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 2, 2003 Share Posted November 2, 2003 Also... I have a question for the old timers/experts...I have 2 sets of SU carbs, round-tops..whatever. The current ones have a different jet adjusting assy than on the carbs that just got yanked out. What is the difference between this jet adjusting assy which is on the motor I just pulled out: And this one, that I have on the L24 that I just dropped in... With that "lock clip" in place, I hesitate to think that they were messed with since they ran...plus I dont know how/where to start with setting them back to a factory.neutral setting. Anyone know? Thanks again, Scott Quote Link to comment Share on other sites More sharing options...
Drax240z Posted November 2, 2003 Share Posted November 2, 2003 Usually you start by turning them all the way in, then 2.5 turns out. There is lots of good info on the net about tuning SU carbs, and they are pretty basic really. Do some searches on the subject here and on zcar.com, look for "norm" and see what he wrote. To do it right though, you really need a uni-syn to balance the airflow. They are about $30 and are a worthwhile investment if you plan on keeping the carbs for a while. Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 2, 2003 Share Posted November 2, 2003 Thanks Drax... I thought they were talking about the screw on the topside of the carb being a "screw all the way in then back out a couple of turns"...at least thats what the Haynes book says. I appreciate the added info though...thanks! Scott Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 2, 2003 Share Posted November 2, 2003 I am also going to try to get those float bowl tops off again...does this require removing the carbs from the intake mani.? I just dont want to bend or tweak any of those fragile little parts in there, know what i mean? Quote Link to comment Share on other sites More sharing options...
DAW Posted November 2, 2003 Share Posted November 2, 2003 When referring to turning the idle mixture knurled ring (or notched ring) in then out 2.5 turns, this means clockwise in until it stops (as you would be doing if you were lying on the ground under the car and looking up at the bottom of the carbs), then back out 2.5 turns counterclockwise. Since you won't be under the car doing this, from above the turning action of your hand on the idle adjustment rings will be to turn the ring to your left to run the jet all the way in then to your right the 2.5 turns. Make sure the choke is not on at all and ensure that the jet is not hung up in its travel. Remember that when you do this idle mixture adjustment on an SU is actually raising or lowering the main jet and this will affect the mixture across the entire rpm range. Reach into the carb inlet with your finger, raise the piston, and let it drop. You want it to drop smoothly and easily. If it's sticking it will really screw up the way the engine runs. RE the fuel supply, run the engine, shut it off and remove the carb tops to see if the fuel level is the same. You could have a plugged supply line and even though the float level is right and the needle/seat are clear to flow, they may not be seeing adequate fuel flow or pressure. If the car has been sitting, put some fuel system cleaner in a fresh tank of gas before you tear into things. The engine will barely run with contaminated fuel. DAW Quote Link to comment Share on other sites More sharing options...
rags Posted November 3, 2003 Share Posted November 3, 2003 What weight oil did you put in the carbs? Too thick and vacuum won't pull the needle jet up. Try taking all of the oil out and see if that helps. Joe Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 3, 2003 Share Posted November 3, 2003 i put nice light, thin oil as spec'd by the book...then even tried the ATF everyone seems to like. I pulled the float tops off, and notice that the tabs the float hangs from are longer on the front carb...is this normal? They are not the same. when the float is held "flat"....the valve is almost closed on the rear carb, but barely touching the fuel valve on the front carb. I dont know what the heck to think now. I also checked again VERY good for vacuum leaks, and cant find any sources...as well as listening for "sucking" with my hands covering both carbs to see if I heard air sucking in from another place...nada. The air cleaner "back plate" doesnt have to be attached does it...to make the air/vacuum balance correctly? (the filter and filter cover off, of course) Thanks again for all the input..I appreciate it! -scott Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 4, 2003 Share Posted November 4, 2003 So anyone know how to tell what level of fuel is in the float bowls?? Is there some magic trick I dont know? (yet) I checked the floats themselves, and besides the differences mentioned above about the valve closure and/or the float mounts...everything else looks decent. The floats "float" as in they are still sealed and not taking on fuel or anything...I just dont know how you are supposed to check the operation of the floats while theyre installed, since the container is solid metal ! Unless there is a way to do it thru the float vent hole... any more of your top-notch assistance is greatly appreciated!! thanks, Scott Quote Link to comment Share on other sites More sharing options...
DAW Posted November 4, 2003 Share Posted November 4, 2003 Once again, you might try running the engine then promptly remove the float bowl covers and compare the actual fuel level between the bowls. As pointed out in a post above, you are not going to be able to sort out problems or set the carbs up properly without using a Uni-syn. DAW Quote Link to comment Share on other sites More sharing options...
DAW Posted November 4, 2003 Share Posted November 4, 2003 Petrol, with all due respect, you should be posting this thread in the Fuel Delivery forum. Also, go to Barnes & Noble and pick up a book on SU carbs. "How to Build & Power Tune SU Carbs" by Des Hammill is excellent. DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted November 4, 2003 Share Posted November 4, 2003 yeah, definitely get the book, and check out the z therapy web page /ztherapy.com/. Bruce knows more about su's than 99% of the world. btw, i assume the floats are moving freely, and the needles are straight... i went through a similar process on my 280 block, 240 heads a year ago. got fed up, broke down and traded in my old su's for a shiny new ztherapy set. the difference is truly amazing. oh, and i had two ignition wires switched around too... ...(he without sin shall cast the first laugh) Quote Link to comment Share on other sites More sharing options...
Guest petrol Posted November 4, 2003 Share Posted November 4, 2003 GOtcha DAW, thanks for the direction. I will go get that book...as well as try the "run then check" method. Thanks for the help, i'll give it another try, then I am off to ztherapy too. hehe. -scott Quote Link to comment Share on other sites More sharing options...
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