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Heroez

Dellorto DHLA and Triple Talk

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It is easier to memorize the Enochian alphabet than to find a logic in the Dellorto emulsion tubes and idle jets. Des Hamill seems to be confused as well on page 67 of the PDF file "How to Build and Power Tune Weber and Dellorto..." In a paragraph he lists the idle jets in lean to rich, then the next column in a different paragraph states the leanest as the richest. Maybe it is just me. Does anyone else notice that? You former Dellorto owners, please give me some information you know please. Something to go on that you know! Tony, is my zx distributor idea good?

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Well then :)

 

I found my back ups of the files who died with the previous laptop, they have been sent to Heroez for uploading :) Des hamil book in pictures, not low quality scans :) Dellorto carb manual and some weber stuff....

 

I am reading the word document shared in this thread and i can't help to notice that the graph seems to sugest that dhla40 is too small for L24 never mind the L28? I am building my l28 and i am slightly worried? but not so moch as it seems the 40 are more than enough for the l24 by far. any thoughts or experiences?

Take a look at the update at datsunzgarage.com/weber for may 2012. His L28 is using 40s with 30mm chokes. Where highly modified strokers I see 45s with 38mm chokes selected for maximum high rpm loading power. I think we are on the right track for our engines Arnulf, in what we have selected for basic equipment. Maybe we can compare jet sizes when we get down to tuning them in.

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Most of the tables are for 4 cylinder engines. Some are for cylinder size. However all of them seem to be for maximum power, which means not the best match for driveability. For easy start ups, smooth off idle throttle transitions, we have to size down the results given in the graphs and charts. That is why I found the datsunzgarage write up so helpful. It more closely matched my engine and goal. If you look at the picture, he has the rubber fuel line with 3 Tee fittings supplying fuel. What do you guys think about that? Is it less prone to heat problems? Should there be a restriction at the fuel return line?

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Back pressure regulation. FPR after the "load" (carbs) - the pressure is controlled by restricting flow back to the tank. This allows full pump output to be put to the carbs during WOT when the floats drop.

 

Most charts are for street cars, not racing vehicles. Be sure you know what you are looking at in this regard. Almost any 40 mm Carb Guide will be for street use.

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I haven't made sending you that Dellorto book a priority. I'll try to get it done after the holiday. The Des Hamil book is worthless, as most of the books by that publisher are: pretty, glossy cover with nothing inside. How about you post the part numbers of your current venturis, main and idle jets? When I got my carbs from the junkyard (I got them in trade for the old Anson slotted mags that were original to my car), I replaced all the parts that had melted in the engine fire (which started in the aircleaner) , simply making all the part numbers the same for all three carbs. Then I cleaned and rebuilt them using new gaskets, accellerator pump kits and o-rings. If you look in any of the books I've found, all the calibrated part numbers that were in my carbs were wrong. Well, would you believe the darn thing started right up? But, it had that pesky little backfire. So, then I spent thousands of dollars on parts to find the "right" combination. Honestly, it was never really any better than it was on that initial start up. Why don't you just install them and see if you can get what you have to run? If it doesn't run, screw your idle jet adjustment all the way in and back out 2.5 turns counter-clockwise. With the new updated hybridz format I can't seem to put my youtube link in a post. To see my Dellortos running from a cold-start (not in the winter mind you-cause then you would see me cussing and having to jumpstart the car off my truck because in the winter trying to get the car started usually took more cranking than one battery could supply), go to youtube and search RebekahsZ + 240z + Dellortos and it should come up. I ran a stock distributor with the vacuum plate delete modification. The car had the little backfire before and after the vacuum plate delete. I think you can run any old distributor just to get it running. PS-once you have the carbs running, be sure to remove the venturis every couple of months and clean the corrosion off that builds between the venturi and the carb body - getting those venturis out can be a real bugger if they corrode in. But, boy, do those carbs look and sound sweet at full throttle! In this day and age where other alternatives exist (like fuel injection), triple sidedrafts are so much like porn (so I've heard): they look and sound good, but they burn up a lot of time are hard to live with.

Edited by RebekahsZ

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Back pressure regulation. FPR after the "load" (carbs) - the pressure is controlled by restricting flow back to the tank. This allows full pump output to be put to the carbs during WOT when the floats drop.

 

Most charts are for street cars, not racing vehicles. Be sure you know what you are looking at in this regard. Almost any 40 mm Carb Guide will be for street use.

 

That makes sense Tony. Its crazy how much logic I can overlook when thinking about a concept as a whole, and not looking at seperate functions individually. This leads me to think that no fuel return would cause the float bowls to overflow. So, does anyone have a recommendation for a type/brand of presrure regulator to be used after the carburettors? Should I just Tee off my existing S30 fuel rail at the rear outlet and use the restrictor that is already used on the return line?

Edited by Heroez

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RebekahsZ, you got it. The plan is to plug them in and see if they work. I just have to work out a couple set up changes like fuel feed and initial timing changes. Good tip on the corrosion! I appreciate your support. That is very big of you. It is very helpful to have your advice. It is ok to take your time sending the resources. Let me know what I owe you for that stuff. I will post the jet/emulsion tube sizes as soon as I am able. I have been meaning to send you a PM about that anyway. Talk to you later. Thank you, everyone, for your posts in here! I am learning!

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I have seen the stock rail feeding front and rear carbs using the stock mechanical pump and restrict or.

Never tested it myself other than for an informal transport or farting around car...but it seems to work fine.

 

Put a "T" in there and monitor fuel pressure. If it stays where its supposed to be...you're done.

 

Experimentation and documentation are recommended!

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Finally figured out how to insert video. Dellorto DHLA40. Stock (Autozone) fuel pump, Holley bypass fuel pressure regulator to allow return line to tank set at 3psi on gauge, stock distributor with vacuum plate delete mod, dirty gas tank:( Sold on ebay about a 6 months ago for $1500 (I think). Wish I could remember who I sold them to so we could see what parts I had in them.

 

http://youtu.be/dZy8kg6K2Oc

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Now through the holidays I had time to read, study, search and ask questions. I got up the courage to take some parts out to examine the numbers. This is what I found- Main Air Correction is 180, Main Emulsion tube is 7772.5, Main Jet is 132, Idle Jet is 50. Idle Air Corrector/Jet Holder was marked 7850.1 (0 looked like C). This is in the middle of the range from weak-rich according to CB performance. From what I have read the Main Air Correction is good. Main Jet to Venturi size is a bit big. 30 x 4 = 120 so 132 Main jet is a bit rich but way better than too lean. Idle jet may be a litte small at 50. Main Emulsion tube... Umm, still unsure. Anyway, how do these numbers look to you folks?

Edited by Heroez

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I had either 125 or 135 mains. Best i could figure, the main jets only really matter at foot-on-the-floor wide-ppen throttle. Homestly, how often does that occur? And for how long? That is why the mains are selected pretty much based on venturi size. Most of your pain will be spent tuning the low-speed or idle corcuit. I think I ran 60s on the low speed circuit. I bought 55s and 50s-no real chang in how the car ran. Car ran rich with 60s, 55s, and 50s. Went down to 45s and it popped. Tried dropping venturis to 28s and it didnt help. Went back to 30 venturis. I think a pretty easy way to tell if you are in the ballpark on idle jets is this: if you can't make it stumble by screwing the bleed air screws in all the way, your jet is too rich. If it back fires you are too lean. Unfortunately, the "idle jets" control not only idle but they also control part-throttle operation. Think of this as everything between start up and full-wide-open throttle. You will spend most of your time selecting idle jets and messing with the bleed air screws. In order to not backfire regularly, I ran 60s and adjusted the air bleeds for fastest idle on each throat. The result was a car that drove smooth but was always a little on the rich side with a black tailpipe and pretty bad gas mileage. We chose between the main jets by using a stop watch to determine which jet gave us the fastest time full-throttle between two highway mile markers with a rolling start from a specified speed. My favorite: trial and error with a hillbilly dyno! Funny-my auto correct changes dyno to dunno-how appropriate!.

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Its OK. I have gained a lot from you already and your feedback is valuable. I was just testing the waters on what I have been studying, at least in theory with that question. That is why I threw out the jetting figures. To discuss in theory, if it seems within reason to work with the motor. I just want to be sure I dont mess up, damage the carbs or my engine, or otherwise have a bad outcome. The more things seem correct, I feel like the risk of a bad outcome is reduced.

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This may sound crazy but I am making a choice on how to run the fuel line by the number of hose clamps. Each carb has the single fuel inlet as of now. Using 3 T shaped fittings has the most hose clamps, more potential for leaks. Swapping in the dual fuel inlet part where the carbs are bridged together gives the least amount of hose clamps, beating out a triple fuel rail by 2, T connections by 3. The dual fuel inlets are less than half the price of a triple fuel rail, and twice as much as three T fittings.

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You can get banjo fittings that have an inlet and an outlet. That let's you basically make a fuel log with the carbs plumbed in series. Remember the needle valves just sip from your fuel supply line as needed to keep the float bowls full so the configuration of the fuel supply system is not critical. I ran both with and without return lines-it doesn't matter. Dead-heading the fuel lines didn't seem to hurt my fuel pump. Crap in the fuel tank will ruin your life. Be sure to run a fuel filter that you can see into ( I like the stock plastic one but some are made of clearer plastic than others). I also recommend t-ing in a gauge to help with trouble shooting in the future. The stock fuel pump makes just the right fuel pressure and volume so you don't need a regulator if you are trying to keep it simple, you can save a fuel clamps and bucks there. Your leaks if you have any, will come from flooded carbs, fuel standoff, wet backfires out the float bowl vents and maybe the accelerator pumps. I was thinking about somehow venting the floats to a little puke bottle just to keep the engine bay clean but I never got to it.

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Ok cool. Now the exhaust. Do you think going up to a 2.5 exhaust for good measure is in balance with the 40s? With 45s or 50s its a no brainer to go bigger. And is it necessary for a propper system to have a header? I have read that the mixture can hover in the mouth of the carb from an exhaust pulse. The long tube header has a scavenging effect that corrects this. Im not a big fan of the noise and heat of a header. Will a stock L28 Exhaust manifold be OK?

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The stock z motor makes 1hp per cubic inch. That means that the intake and exhaust are pretty well maximized right out of the box. Honestly, you will be doing well to make your new carbs function AS WELL as the stock SUs. I would base my exhaust decisions on what you feel is "coolest", not any performance concepts. Since the intake and exhaust share the same gasket, you will have some need to trim the flange on either the intake, exhaust (or both) and you may need some custom washers if the flanges are different thicknesses. I think the "Clifford" header is the best aftermarket header if you can find one. Hooker made a clone. If you are a 6-into one the MSA header is your only option. The pacesetter is ok as a 3-2-1 header but it hangs low and makes your feet hot because it gets close to the floor pan. The Nissan Motorsport header is probably the best with actual science behind it but it is a true race header and is super super thin metal to keep it light. Get ceramic because it looks best. Go 2-1/2 on the tail pipe.

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