datsunlover Posted August 15, 2004 Share Posted August 15, 2004 Ok Im having a little problem with my 75 280z. Im running 240z SU's and normaly, I have no prob with them.. but recently, after I start it cold, it runs like poo.. It starts fine evry time, revs good, and seems to be running well.. but even after the temp guage comes up to where it normaly sits, If I try to drive it, it will still bog/backfire for 10-15 mins. Ussualy, after I see the temp guage read normal, I pop the hood and push up the choke on the fron carb and it smoothes out.. but then it still takes several minits to run well... it's like the carb bodies/manifold have to get warmed up to work properly!?! Anyone had a problem like this? Quote Link to comment Share on other sites More sharing options...
dot Posted August 15, 2004 Share Posted August 15, 2004 Just a thought. Your car sat for a while outside. It might have some water in the tank that made it's way to the fuel bowls. You could try some fuel de-icer to get rid of it. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 15, 2004 Author Share Posted August 15, 2004 I supose.. but wouldnt it act up like this all the time? It's like a heat realated problem caus after the car is compleatly warm, it NEVER does it. I can drive around for hours without a hick-up at all.. Quote Link to comment Share on other sites More sharing options...
dot Posted August 15, 2004 Share Posted August 15, 2004 Ya, your right there. I'm out of ideas. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 15, 2004 Author Share Posted August 15, 2004 Oh well.. I can live with it for now! I'll be riping the car apart again this winter (grr.. only a few months left of summer.. ) so maybe I'll get the carbs from Ztherapy.. or something! I was thinking of playing copy cat.. I found a V12 Jag for sale prety cheep.. but I got a free 280zx.. so I'm gona put my head on that engine to bump CR up, open the exhast and keep the SU carbs. I get a 5 speed out of this to so.. Quote Link to comment Share on other sites More sharing options...
e_racer1999 Posted August 23, 2004 Share Posted August 23, 2004 thought about reviving an old post... i have that same problem. are your carbs tuned perfectly? check your choke levels as well.... also, make sure that your carb damper oil is topped off.. some say 20W is the best. i'm running 30W and it's too thick, but i've been diluting it with 10W-30. also, make sure you don't have any vacuum leaks. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted August 24, 2004 Author Share Posted August 24, 2004 Heh.. thats funny.. tonite actually, I went out for a spin.. on startup, it did the same old 'blah blu.. bla blu..' ect... So I pop the hood and start messing with the choke mechanism (where the cables get attached) and HEY! It smothed right out when I opened the rear choke more! Hmm.. well, I just left it for now (the air cleaner is on and blocking the way to unscrew the lock bolt) but I think I solved the cold start burble.. and also found that the front carb choke sticks down a bit after I turn it off in the car. A little 'pop' up and it's fine.. oh well.. I'll live with it like I said, as the car is getting 'overhauled' in a month or so anyway! Quote Link to comment Share on other sites More sharing options...
DAW Posted August 24, 2004 Share Posted August 24, 2004 I'm a little perplexed...your problem is described as if your chokes are not working properly and when you pop the hood and manually activate the chokes the problem goes away- - have you tried adjusting the chokes according to the Datsun service manual (including fast idle adjustments by bending linkage rods the proper amount, etc.)? At any rate, the SU chokes are troublesome even when properly set, and if they stick they will throw the mixture off on one or both carbs through out the entire rpm range once it's warmed-up. On one of my dual SU cars I eliminated the mechanical chokes altogether and configured a primer line system like some aircraft engines use (they don't have accelerator-pump carbs either). It can be activated from inside the vehicle (the planes are this way too). Fast idle is by throttle cable (or by your foot if you don't want to set up a separate cable) if you don't use a check-valve in the primer line, the engine vacuum will draw in extra fuel but this isn't necessarily a bad thing because with a manual fuel shut-off valve in the cockpit (interior of your car) you can modulate the extra fuel during warm-up. A non-butterfly valve manual choke. This setup is also good because SUs can leak down the fuel bowls a bit while sitting and they may collect condensation inside once they do and with a mechanical fuel pump it may take a bit of cranking to get useable fuel to the intake manifold; whereas with the primer setup configured with a small electric fuel pump - - once you open the valve and tap the pump button for a few seconds, the engine fires instantly...a nice feature in battery-killing cold weather. I've never tried setting up an ether-filled reservoir for this primer...let me know how it works out if you try it. DAW Quote Link to comment Share on other sites More sharing options...
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