yoshi_w Posted October 15, 2015 Share Posted October 15, 2015 Hey guys, I got something out of the blue and hoping a random angel-sent individual will have some sort of assistance for me. I recently installed triple Dellorto dhla 40's on my engine via an SK manifold. The engine specs as follows: stock l28 bottom end with the exception of flat top pistons. The head is a rebuilt N42 head with a mild Rebello cam. The carbs have 38mm choke, 132 mains, 33 pump jets, 7772.8 emulsion tube, 210 air correctors, and 58 Idle jets. I should note that the engine ran with SU's (SU's were replaced with triples due to leaking throttle shaft) Replaced parts: plug wires, ngk bpr6es plugs, carbs were resealed, also rechecked all bolts With that out of the way, I am having much difficulty keeping the engine idling. I have tried backing out the Idle mixture screws 3.5 turns through 6 turns, and it still won't idle. If i give it a couple pumps, it will idle only for a second. I have checked for vacuum leaks but can't find any. I can keep it alive by giving it gas, which means its somehow not rich enough at idle. The idle jets seem pretty big, so is it just a simple vacuum leak that I am somehow missing, or is it something else? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted October 16, 2015 Share Posted October 16, 2015 (edited) I ran my Dells on a stock L24 with only 32mm venturies. I even considered going down to 28mm venturies. You may just not have enough vacuum at idle to serve ventuies that big. With that arranngement, I never ran my idle screws more than 1-1/2 turns out from the bottom. I don't have any info on my jets-all my books and charts went to the new owner when I sold them 2-3 years ago. The problem that I had tuning my Dells is that the emulsion tube and jet part numbers don't mean anything relative to how large or small they are. I had thousands of dollars in jets and emulsion tubes in a tackle box. I had them tuned really well for full throttle, cruise and idle, but I never could cure an intermittent lean backfire pulling away from stop signs at light load. I selected the main jets by trial and error, choosing the jet that produced the best flying mile time between a pair of mile markers on the highway. The car didn't smoke or stink from the tailpipe, but that lean backfire spit fuel out of the float bowel vents up on top of the carbs, so the garage always stunk of raw gas. The car was still slower in the 1/8-mile with the Dells than it was with stock SUs. But it sure did look and sound great! There is a venturi sizing chart out there some where. I think I got that info from a Des Hamil book-something like "Weber and Dellorto Power Tuning" or something like that. To size your venturis you had to know the volume of each cylinder, so 2800/6=467ccs per cylinder. Read across the chart from 467 and that gave you a venturi size recommendation. If the car is stock, I would go to the small side to improve driveability. Realize why you run Dells-its from looks, sound, and retro/performance style. Unless you are an expert with these and optimize cam and head to support the system, you will not produce as much power as you would with either a single carb, SUs, or fuel injection. If it weren't for the stinky garage and the lean backfire, I might still have them. Search my youtube channel "RebekahsZ" and you will find a video of the carbs and the car running-I think it is the very earliest video I ever put on youtube. Do you have a vacuum line to the distributor and brake booster? I don't know if failing to put a vacuum line on your distributor would make a difference in idle performance. I had mine set up with a solid plate in the distributor and the vacuum port on the intake manifold capped. A big vacuum leak anywhere will affect idle. Edited October 16, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
yoshi_w Posted October 16, 2015 Author Share Posted October 16, 2015 Yea, I have the Des Hammill book where I got the info about how many turns out the idle mixture screw should be. Given that its seems to be too lean at idle, I doubt less turns would help the situation. There is no vac line to the distributor, but there is no open ports on the manifold for that anyhow. The vac line to the booster is hooked up. I realized I could be wrong in regards to the choke so I'll have to double check that. In regards to power, its an L28 with flat top pistons and a mild performance cam, so hopefully I'll be able to take a little more advantage of them than just a stock engine. We shall see though. Thanks for the input. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 19, 2015 Share Posted October 19, 2015 The chokes are way to big for a stock sized stock configured engine. But that is not your problem. What is your throttle angle set at initially? Did you set up your throttle plates with a feeler gauge for initial idle speed then adjust down from there when you synched them? What is your manifold vacuum at idle, and has it been set to idle around 900rpms or are the throttle plates closed? Not making any difference from 3 - 6 turns means something is inactivating the idle circuit. You should be able to kill a cylinder at six turns out (by turns we mean 360 degrees from seat, not 180 degrees of the screwdriver slot.) When other carbs do this, I pull the carbs off to see if the PO has cranked the idle screws in so tight he broke the tips off in the idle holes. Then you gotta pop those tips out, and replace the needles... Lots of possibilities, vague if mostly nonexistent information. Hard to be specific. None of the basics were discussed as being done, or how they were done so it's all guessing at this point. Again, the chokes are way too big for a stock engine, but that has nothing to do with it not idling. Quote Link to comment Share on other sites More sharing options...
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