Hugh Posted November 30, 2004 Share Posted November 30, 2004 If its really cold out (southern california cold) and I hit the throttle in the third or fourth gear around 50-75mph, it will kick and choke. Last night I was just cruising along, and it started cutting out on me, just momentarily.... like bucking as it loses power and then regains it. It did this a lot... and had me thinking. The car ran great in warm weather, but cold air is denser.. and requires a richer mixture. I don't understand how carburetors work (I'm a standalone EFI guy myself) so I don't know if they compensate for weather on their own. Do I need to richen the mixture a bit to fix this? If so, how can I just throw a little more fuel down on it? Quote Link to comment Share on other sites More sharing options...
Hugh Posted November 30, 2004 Author Share Posted November 30, 2004 Oh, and it works fine at low load, like high RPM in low gears, etc... runs great. It's mostly while cruising in high gears, and then I apply the throttle, or going uphill on the freeway. Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted December 1, 2004 Share Posted December 1, 2004 Doubt it is the weather. Sounds like fuel pressure, maybe, Like your bowls aren't filling fast enough. OR Perhaps other delivery problems like Power valve or Accel Pump. Need more info though. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 2, 2004 Share Posted December 2, 2004 I can say with absolute certainty that you don't have a bad power valve or accelerator pump. I'd suggest trying different weight oils in the carburetors. A lot depends on the carbs themselves. Mine ran great with ATF or Marvel Mystery Oil. Very thin worked great. Tried that in a friend's Z and the thing sputtered all over the place. She needed 20 weight oil in hers. If you haven't pulled the bells off and cleaned the pistons you should do so and dump the old oil out of the top of the pistons. Then you can try your new oil and see if that helps. If you don't have the Ztherapy video, it is cheap and informative. I haven't run SU's for about 5 years, so maybe someone with more recent experience will jump in to help too. Quote Link to comment Share on other sites More sharing options...
quicker240 Posted December 2, 2004 Share Posted December 2, 2004 May be jumping to conclusions a little bit as the symptom you described could be attributed to any number of things.But a quick inspection of the float chamber on both carbs is quick and easy.check that your floats hav'nt sank and the shut off valve is properly adjusted (about 14mm as I recall).Change the damper oil and check for smooth movement of the big pistons by pushing them up with your finger and releasing it.if all is well,you might have another problem(points,a bad plug wire,worn dist cap or rotor,etc,etc).these carbs are pretty sturdy and temp changes dont usually cause the kind of problems you are seeing.Good luck with it! Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted December 2, 2004 Share Posted December 2, 2004 Ok what is "oils in the carburetors"? That is a new one. I'm goin off of what I know about Holleys... k, I'll shut up now. Quote Link to comment Share on other sites More sharing options...
Hugh Posted December 2, 2004 Author Share Posted December 2, 2004 Thanks for all the responses. I'm looking for the ultimate in cheap fixes... I don't want to invest any money into this setup that won't be needed later. (I'm going SR20DET when my motor gets here from Japan) I will get out tomorrow and take a good look at the carbs, and follow all your suggestions. I also plan to change the fuel filter. Someone else told me it could be my aftermarket intake and header doesn't route any heat to the intake... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted December 2, 2004 Share Posted December 2, 2004 I ran my SU's with the coolant passages bypassed for years and it never caused me any problems. Quote Link to comment Share on other sites More sharing options...
BrandonsZ Posted December 2, 2004 Share Posted December 2, 2004 Well, I could say something about a certain part that you are using (Holley) but... It's electrical, look for the answer in the electrical system, I'd bet money on it. Could be a connection, or the fuel pump relay. I bet the cutting out at high load symptom is just a red herring. I bet your ignition is the culprit or a ground to the coil or something like that. Check all the major connections. Your electric fuel pump needs power to run, if you cut below a certain voltage it'll shut off the relay. One fun way of proving the electrical system is hooking a timing light up to the coil wire and running the light somewhere you can see it flashing, and when it cuts out, you'll see the light turn off, then BINGO. Of course if you dont' find any electrical problems then, fuel filter, or check out that think you call a carb. Otherwise good luck. Quote Link to comment Share on other sites More sharing options...
Hugh Posted December 2, 2004 Author Share Posted December 2, 2004 Why would the ignition only fail when its cold? Quote Link to comment Share on other sites More sharing options...
Guest 240zJake Posted December 2, 2004 Share Posted December 2, 2004 Well' date=' I could say something about a certain part that you are using (Holley) but... It's electrical, look for the answer in the electrical system, I'd bet money on it. Could be a connection, or the fuel pump relay. I bet the cutting out at high load symptom is just a red herring. I bet your ignition is the culprit or a ground to the coil or something like that. Check all the major connections. Your electric fuel pump needs power to run, if you cut below a certain voltage it'll shut off the relay. One fun way of proving the electrical system is hooking a timing light up to the coil wire and running the light somewhere you can see it flashing, and when it cuts out, you'll see the light turn off, then BINGO. Of course if you dont' find any electrical problems then, fuel filter, or check out that think you call a carb. Otherwise good luck.[/quote'] I'm pretty sure based on the title of this thread that he is not using a Holley he is using an SU Cold weather will not affect the electrical system's ability to function, but it will affect your battery. Check that the battery is putting out a good 13 volts, if the battery is not hot enough the coil will not charge completely in the short amount of time it has to charge. However that doesnt seem to be your problem. Maybe you could hook a fuel pressure gage somewhere visible and go for a drive, see if it drops. Hmm... the battery being cold could affect the FP... But then again SoCal cold... Quote Link to comment Share on other sites More sharing options...
Hugh Posted December 3, 2004 Author Share Posted December 3, 2004 It doesn't get THAT cold here. I'm using an Optima as well. I'm trying to imagine if the contacts in the distributor or the coil itself or something were cold... but thats not going to happen after the car has been running for 20+ minutes... It did feel like what happens when the spark blows out.. but a lot of things can feel like that. (lack of fuel, obviously) I was leaning towards a fuel problem. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted December 3, 2004 Share Posted December 3, 2004 When I drove my former daily driver 240Z up north to the frozen tundra of PA a few years ago, I had a similar issue when I reached a cooler climate somewhere around Virginia (less than 40*). I had no power and it would struggle to get going from a stop. I turned the knobs under the carburetors a half turn counter-clockwise (looking at them from the bottom) to drop the carn nozzles slightly, richening the mixture, and it ran a little better. I turned them another half turn and it ran like it was supposed to...no stumbling and plenty of get up and go... When I returned to Florida a week later, I just leaned the carbs back out. Regards, mike Quote Link to comment Share on other sites More sharing options...
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