Carburetor Central
If you have questions about the SU Carburetors, this is where you can find the answers.
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Just found this great graph. It plots A/F at down pipe of a Subaru as well as the simultaneous tail pipe A/F. It seems to show: Tail pipe A/F accurately represents manifold A/F Tail pipe follows manifold by pipe-propagation-delay time. Manifold more accurately captures fast transients. These transients are reduced in amplitude at the tail pipe. So for carb a/f monitoring, use the manifold for accelerator pump transient tuning. The tail pipe is fine for all other carb tuning.
Last reply by Stanley, -
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I have a 1971 240z, I think the fuel mixture is leaning out. During checking for vacuum leaks, I sprayed carb cleaner between the intake manifold and the head and the RPM shot up. I assumed the gasket was leaky and naturally replaced it, but even with a brand new one it's still doing the same thing. Mixture nuts are turned all the way up and float levels checked, fuel lines and filters double checked, all is well. It's truly a mystery. The leaner I set it, the easier it starts up, but it also backfires much more and consequently dies right after. The richer I set it the less it backfires, but the idle feels far more rough and much lower. Raising the rear suction piston do…
Last reply by cbuczesk, -
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Took the car to the shop to get it safety inspected. Inspection came back almost clean just a brake booster problem that they fixed, and some small electrical tweaks and an alternator belt change that I elected to take home and do myself to save shop labour. Halfway home the car all of a sudden felt like it lost power and died. I restarted it, it ran for 3 seconds and then died. After that it wouldnt start. Through the choke on and got 1 last second of engine running before sputtering and dieing. I noticed I wasnt hearing a familiar noise. Normally with the key in the on position I hear the fuel pump running. This time, nothing. At first I missed it cause of the traffic…
Last reply by Wingsuit, -
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observation: 2 to 3 turns on idle enrichment changes idle A/F 7 points 2 to 3 turns on idle enrichment changes cruise (3000rpm) A/F 3 points A/F at cruise and idle is balanced ~ 2.5 turns but rich at ~ 12.5 A/F is richer at idle than at cruise at greater than 2.5 turns out. My goal is get idle and cruise balanced ~ 14 to 15 A/F....waiting on 45 idle jets as next step.
Last reply by 240260280z, -
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I know there's lots of threads about this...and I think I've read them all. I installed my triples last year and decided to keep the stock mechanical fuel pump. It puts out quite adequate volume and pressure for the triples. I have a pressure gauge before the carbs and regulator on the tank return line which keeps the pressure at 3-4 psi. The car runs great even under heavy acceleration...no fuel starvation. My question: why does it take so much cranking to get fuel to the carbs for the engine to fire when cold and the car has sat for a while? The pump is supposed to have a check valve to prevent draining of fuel back into the tank.....correct? It seems I'm pumping…
Last reply by zKars, -
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Looking for 1 su car damper with a brass knob instead of the plastic. Anyone have one?????
Last reply by az240z, -
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Yup.... got 30mpg (Imperial Gallons) cruising at ~ 3,000 to 3,500 rpm on a 240z. Idle jets significantly impact cruise fuel efficiency. I was experimenting and used two sets of idle jets: 1) 55F11 2) 55F9 with air drilled from original 1.0mm to 1.5mm (picked up some metric bits in Lisbon) I installed bolts in place of the spill jets to rule out accelerator pump leaks clouding the results...btw it is not so bad driving w/o acc. circuit. The 30mpg was attained with 18.5 a/f at idle and 14.7 to 15.5 at 3,000 rpm over flat road. The idle was rough and difficult to maintain at ~ 800rpm and 2 turns out on the mixture screws. I drove ~ 300km and eventually developed som…
Last reply by siteunseen, -
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presently 40DCOE151 125 main 170 corrector F11 emulsion 30mm Choke 4,000 RPM 11.5 Air/Fuel 6,000 RPM 10.5 Air/Fuel 240z L24 270 cam I am thinking that a switch to 115 may lean it towards 12.5 at 4k and at the same time tip the the high end back at 6k. Any suggestions?
Last reply by Lazeum, -
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I am starting to look deeper into the claim that later DCOE's Idle Enrichment Screws are typically turned-out further. The details in the screw interface to the carb body distill to: 1. For the same flow: A narrow tapered needle needs to be tuned out further than a wider tapered needle if the orifice size is the same. It is proportionate to 1/tan 2. For the same fuel flow, a needle with the same taper needs to be turned out more from a smaller orifice than for a larger orifice. So to compare an early carb's Idle Enrichment Screw turn-out to a later, one must know the taper of the needle and the orifice size. In another post I measured the threads on early and…
Last reply by Zedyone_kenobi, -
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I just tried the choke on triple DCOE 40 151's with the default choke jets/tubes/air that came with the car. It seems to be too rich and no fast idle. Can someone describe how 3weber chokes are supposed to behave when properly set up? What will the idle jump up to when engaged? What A/F should I aim for? Thanks
Last reply by Lazeum, -
- 4 replies
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Hooked up my new FP gauge today, like the gauge it's a 0-10 psi McDaniels, easy to see under glove box from driver seat. Line is steel braid over Buna-N with black braided Dacron cover good for 3025 psi, all OK. Got steady 3.8 psi at idle which is ok I guess. Bled out the air, think I got most of it. One question though, when I shut down the engine, FP drops fast to 3 psi, then very slowly to 1.5 or 2. After a minute or two, looked at it again - it went back up to about 4 psi again. Whaaat? Then it dropped off again. After 15 minutes it was down to 1 psi. Doesn't seem like much of a problem, but I don't get that strange behavior at all. Any ideas? I got zip.
Last reply by Stanley, -
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I bought these from a acquaintance type who said the car was running fine with these carbs. They have been sitting for two years. I am getting ready to install them and came across the linkage issue. My question is how come two of three carbs don't have the throttle linkage no where near the idle speed screw? The throttle plates of those two are open as far as the linkage is from the screw. I can't find the adjustment procedure in all the literature I downloaded from this site. All I have figured out is the throttle shaft hits the accelerator pump rod. I appreciate the help!
Last reply by 240260280z,
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