ApexGoblin Posted April 30, 2012 Share Posted April 30, 2012 I have lurked on this forum for awhile now, but haven't been able to find a solution to this problem... I have a 3/74 260z and I decided to get the motor in it running, (l28 n/a) I installed a set of weber 32/36 dgv carbs (not new) and got the motor to fire and run. However I cannot seem to get it to idle below the 2.5-3k rpm range, I can get a steady idle at around 3k rpm with the choke slightly on. If I take the choke off entirely the motor climbs to 3k and then slows to around 1k and then starts to "gasp" or shudder and then climbs itself back up to 3k. It repeats this process at a steady pace climbing and falling to rise again. I played with the idle speed and idle fuel mixture screws all day today thinking that this must be the problem, but there was almost no change to the engine response. I did get it to idle at around 1.5k for 30 seconds before it died (this was also achieved using choke manipulation with idle screw adjustment). I'm not really certain what may be causing this issue? Electrical? Vacuum? Everything seems to be hooked up and operational. Am I missing something? Has something electrical gone bad? I need a little help seeing as I am new to L series motors. If there's a thread on here covering this specific problem please direct me to it, I tried to find it but maybe the search function failed me. Otherwise any insight or tips would be really appreciated! Quote Link to comment Share on other sites More sharing options...
Leon Posted April 30, 2012 Share Posted April 30, 2012 Check for vacuum leaks. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted April 30, 2012 Share Posted April 30, 2012 I concur, vacuum leaks. Also, in your photos (in the old thread) it looks like you might have the vacuum advance connected to manifold vacuum rather that ported vacuum. If this is the case you will have too much advance at idle which will cause high idle. We just got a 260Z with the same DGV set-up and the vacuum advance connects to the forward vacuum port on front manifold, just behind the carb. The hose you asked about in the this pic http://i939.photobucket.com/albums/ad236/raukorist77/6fdb957a.jpg probably went to the air filter. It is likely the air inlet to the sir pump. You could put a little filter in it like the one on your valve cover. Connect it with a tee fitting to the gold port you asked about, which also should go to the air filter. Quote Link to comment Share on other sites More sharing options...
ApexGoblin Posted May 1, 2012 Author Share Posted May 1, 2012 I concur, vacuum leaks. Also, in your photos (in the old thread) it looks like you might have the vacuum advance connected to manifold vacuum rather that ported vacuum. If this is the case you will have too much advance at idle which will cause high idle. We just got a 260Z with the same DGV set-up and the vacuum advance connects to the forward vacuum port on front manifold, just behind the carb. The hose you asked about in the this pic http://i939.photobucket.com/albums/ad236/raukorist77/6fdb957a.jpg probably went to the air filter. It is likely the air inlet to the sir pump. You could put a little filter in it like the one on your valve cover. Connect it with a tee fitting to the gold port you asked about, which also should go to the air filter. ok i will try that. i was also thinking about having the carbs looked at? Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted May 1, 2012 Share Posted May 1, 2012 It could be something on those carbs is stuck or bent. Did you inspect them before just putting it all together? But mroe than likely a massive vacuum leak and/or bad sealing around the carb/intake/head. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted May 1, 2012 Share Posted May 1, 2012 ok i will try that. i was also thinking about having the carbs looked at? It might not be caused by the carbs. If you are going to take the whole car to a shop, ok. Don't take the carbs off and send them to a shop separately. Your symptoms suggest a lean idle condition that has been compensated for by turning the idle screw in too far in an attempt to get an idle. I would start by verifying all the basic settings and adjustments: Ignition timing set to stock Idle mixture screws at a base setting Idle speed screws at a minimal setting Valve clearance Make sure the throttle linkage moves freely and allows the throttle to close fully and easily. If it still acts the same disconnect all the vacuum hoses and plug their ports. If it is still the same check for vacuum leaks around the carb base gaskets, adapter to manifold gaskets, and manifold to head gasket. Check all fasteners for tightness, look for obvious problems such as missing or damaged gaskets. Next, run the engine and (with a helper if needed) spray carb cleaner around each joint. A leak will be detected by an obvious change in the way the engine runs. Typically, the engine will run better for a moment when you spray at a leak. Quote Link to comment Share on other sites More sharing options...
ApexGoblin Posted May 3, 2012 Author Share Posted May 3, 2012 well i just discovered that the intake/exhaust manifold gasket is absolute toast on the intake half, ordered a new one and will put it on friday, hopefully this will solve my problem. ill keep you updated! thank you very much for the help and troubleshooting tips theyve helped me a lot! Quote Link to comment Share on other sites More sharing options...
beermanpete Posted May 3, 2012 Share Posted May 3, 2012 Ok. Let us know how it works out. Quote Link to comment Share on other sites More sharing options...
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