RedNeckZ Posted November 30, 2003 Share Posted November 30, 2003 I need some advice with a problem I am having. To begin with, I have a 1972 240Z with an L28 engine. It had triple 45 DCOE webers, 3/4 cam and header. We took off the webers to rebuild them and put on a holley carb setup for a temp. replacement. Timing was set at the normal 15% before TDC. It will start up and not idle. It will startup and run if we push on the gas a little. But every now and then it will backfire thru the carb. It looks like we have to much timing for this setup. Can I retard timing a little with out hurting performance. Off idle it runs great. Haven't work with the holley setup before and at a loss on what to do? Can anyone give me a hand? Quote Link to comment Share on other sites More sharing options...
Guest Nic-Rebel450CA Posted November 30, 2003 Share Posted November 30, 2003 You and jeff1216 should compare notes. He has been having a lot of trouble with his 4 bbl setup, some of which are problems like what you are describing. Try searching for his posts. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted November 30, 2003 Share Posted November 30, 2003 I ran a 4bbl setup on an L28 motor for a long time... I hated the Holley 390... It was horrible... Reduce the timing, then get down in jet sizes... I'd also get the quickchange spring set and start playing with that... The 390 carb is almost too big AND the intake is crappy... It dumps most of the fuel into cylinders 3&4 and leans out 1&6 real bad... Hard to balance... You might think about going back to a stock carb setup or swapping to a factory fi setup. I was running high 15s in the 1/4 and swapped to fuel injection and flat top pistons and jumped into the mid 14s... That was with headers, a scheider cam, and 3:70 gears W/ LSD... Mike Quote Link to comment Share on other sites More sharing options...
RedNeckZ Posted November 30, 2003 Author Share Posted November 30, 2003 Thanks for both of your replies. Will try to contact him and see if we can compare notes to see if we can find a fix. Don't plan on keeping it on the car long. I love the triple 45 DCOE's that where on it. They run great with the cam/head work that I have put on it. The new engine, we have started on, will have flat tops and 40 over size. The E-31 head already has bigger valves and porting. Should have body work and paint job completed by then. Thanks again, Rich. Quote Link to comment Share on other sites More sharing options...
Clifton Posted December 1, 2003 Share Posted December 1, 2003 A few degrees of timing isn't causing the back fire. If it's though the carb and the valve timing is on which it would be if it ran good before then it's lean, shouldn't do it at idle though. It may need a little more fuel at idle or throttle angle to rev higher. I would richen it up, if it doesn't help just turn it back to were it was. Also if you retard the timing at idle it will be retarded the same amount at at high rpm. Quote Link to comment Share on other sites More sharing options...
Zsane Posted December 7, 2003 Share Posted December 7, 2003 Backfiring through the carb is a lean condition, check for vac. leaks, fire it up and spray carb cleaner anywhere it could be leaking, throttle shafts included, be carful with the carb cleaner on a hot exhaust, if you have a leak, the idle will jump right up when you hit it with th e carb cleaner, I've heard propane will do the same thing, but I never tried it, I always use carb cleaner, never fails! Quote Link to comment Share on other sites More sharing options...
RedNeckZ Posted December 7, 2003 Author Share Posted December 7, 2003 We found the problem. It needs bigger jets in it. The carb was bought in Colorado and is setup for high altitude. So it is running a to small of a size jet in it for this place. Thank-you all for your replies. They helped a lot. Rich. Quote Link to comment Share on other sites More sharing options...
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