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3.5 V8 SU Carb Issues

Discussion in 'It's A V8 Mate!!' started by hef19898, Aug 6, 2020.

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  1. hef19898

    hef19898 Well-Known Member

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    I got Facet one, Famous Four claims it's OEM.

    Good question regarding the pressure. The old one stopped, but that was due to a faulty relay and had the engine stall. With the new relay, both pumps ran continuously, something they didn't do before the stalling issues started.

    I am a total noob to engines, so that's maybe a stupid question. How exactly is the pump controlled? I assume it shouldn't run all the time right? So is that done by some kind of sensor in the float chamber of the carbs or via the ignition / vacuum? The car does have a transistor ignition system installed, the faulty relay is between the transistor box and the pump.

    Have a nice Sunday everyone, and stay safe!
     
  2. Hicap phill

    Hicap phill Well-Known Member

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    Pumps.
    Find the return from the carb to tank,pipe this to a container once you have flowing petrol squeeze the pipe. Pumps should stop if they are interrupter pumps.(just means they are up to pressure)

    have you tried pipes from a container to feed the carbs to prove the original pipes are good?
     
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  3. hef19898

    hef19898 Well-Known Member

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    Not yet. The plan is to throw out all the old tubes incl. the return one. Will test the squeezing as well once it stops raining cats and dogs over here.
     
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  4. Hicap phill

    Hicap phill Well-Known Member

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    Just make sure you put the correct ends back onto the carb as 1 has a smaller bore to cause a restriction on the return
     
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  5. hef19898

    hef19898 Well-Known Member

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    Unfortunately, I still didn't find time to check the carbs out, I tried my late grandfather's wood turning machine and am in the middle of producing a Christmas forest...

    Today, I tried something so. As the mixture is too meager at high revs, I restricted the snorkel intake. Amazing what you can do with duct tape. I also restricted the return fuel flow by bending the fuel line a little bit. The result is that it now revs up to 4k under load and I get 140 km/h on the highway. Until I have time to refurbish the carbs, I will make this semi-permanent. We are using it for weekend and day trips at the moment.

    I wouldn't be surprised by now if it is the swimmers that are blocked. But I am getting there, slowly but steadily...
     
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  6. hef19898

    hef19898 Well-Known Member

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    Long last...

    Today I managed to pull the first carb out, not sure if I will get it back in so... Anyway, carb is out and already more or less dismantled. And it is clean, not dirt or blockage to be seen. I cleaned all fuel inlets, and nothing but clean brake cleaner came out. Gaskets are solid, too.

    If the weather permits, I'll pull out the second one tomorrow.

    Maybe someone can help me out, so. The above mentioned solution, restricting the fuel return, fixes the issue. Now it seems the first carb should be getting enough, the float chamber is clean and the floats are moving freely. If the second one comes out clean as well, the only problem can be a blockage somewhere between the fuel filter and the carbs, right? The pump is new, the fuel lines from the tank to the pump and from the pump to filter as well. Or am I missing something here?
     
  7. kermit_rr

    kermit_rr Can't Remember Full Member

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    Have you checked you're getting a good flow from the pump? Is the float height adjusted correctly?
     
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  8. hef19898

    hef19898 Well-Known Member

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    Pump is giving a flow, didn't measure is so... Float hight is a good question. Any idea where I can find the right adjustment numbers for that?
     
  9. Shippers

    Shippers Well-Known Member

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    Dont know if its been mentioned before but youtuber Churchhouseclassics does some good carb tutorials...
     
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  10. hef19898

    hef19898 Well-Known Member

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    I am an idiot. Well, I'm like 85% sure I am.

    Today, I put the first carb back together. Everything is moving smoothly, I just replaced two gaskets anyway. And I decided to check out the o-ring in the damper, the one that is leaking. And while doing so, I realized something odd. No matter what I did, the needle rested at a very low position. So whatever I tried to get a richer mixture didn't work.

    And than I remembered. The car had a tendency to just shot down. Reason was a broken relay, but before I discovered that by chance, I already worked on the theory of fuel starvation. Well, I couldn't test it yet, but it is very well possible that I unscrewed the needle back than without realizing it.

    Once my ankle agrees to me standing, I'll put it back in and see what happens. And I also will check the needle on the other carb. Would be quite funny if all that hazzle, fuel pump and so on, wouldn't have been necessary.
     
  11. hef19898

    hef19898 Well-Known Member

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    Today was the big day! The carb is back in, throttle link is working, choke is working and she got a new throttle cable.

    She also is a non starter now. Well, she started once for maybe 30 secs and died. Both batteries were flat as well, so she's charging bow over night. Fingers crossed it's just the low battery that's the problem.
     
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  12. hef19898

    hef19898 Well-Known Member

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    She's starting again! It was either the low battery or the stiff diaphragm in the right carb. Funny ehat I find every time I go through the boxes that came with the car. A throttle cable, carb diaphragm...

    Card tuning will be done next week, I don't want to drive the neighbors crazy on a Sunday. A test drive is next, so!
     
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  13. hef19898

    hef19898 Well-Known Member

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    Ah, the test ride was short. Once around the block, idle revs of 2.2k are a tad to high. With some luck, it's sorted tomorrow, so.
     
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  14. v8250

    v8250 Well-Known Member

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    @hef19898 , have glanced through your thread + I've been building/running SU's for a few decades. If not fully stripped and carefully inspected SU's can be quite troublesome. For starters you need to check the following:

    1. damper pistons + correct type/level of damper oil
    2. springs correct type and equal spring rate
    3. floats - you can buy non-sinkable floats - set up to ensure float chambers do not over fuel/flood
    4. spindles and bushes - if the bushes are oval they need replacing/reaming out to ensure proper seal
    5. needles - assuming they're the correct fueling, be sure they're decked to underside of piston + they sit central to jet
    6. set static jet height
    7. set up choke
    8. SU's should be set up independently to idle correctly [with correct fuel-air mixture using an air flow meter**], then linkages fitted/set up, then set up off idle and recheck mixture. If all okay then recheck at ~3000rpm for mid range mixture.

    **A Gunson manual carb flow meter is ideal

    Follow the above and they should be "on song" throughout rev range + I can 100% recommend Des Hamill's book, How to Build and Power Tune SU's. Hamill's a highly respected engineer and the book is the SU bible

    https://www.google.com/search?source=univ&tbm=isch&q=How+to+Build+and+Power+Tune+SU's&sa=X&ved=2ahUKEwjng4v-xNPvAhU_SxUIHR7rDIwQjJkEegQICxAB&biw=1536&bih=722&dpr=1.25
     
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  15. hef19898

    hef19898 Well-Known Member

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    @v8250, my bad, I mixed up the carbs in the thread title, the engine is running Zenith Stromberg's.
    The one I dismantled looked good, it was the first one I looked at so could have easily missed something. All valves worked, float was clean. I replaced two gaskets so. And the diaphragm today. The springs are the same it when I bought it, and never had any issues the first one and a half years. So I assume they are the correct ones.

    We'll see how the carb setting goes tomorrow. I have, theoretically, the whole day, so... I am cautiously optimistic! It's funny the the revs drop with the choke pulled out, no idea were that comes from.

    This forum is great by the way! Very useful replies and a load of encouragement, especially for newbees like myself!
     
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  16. kermit_rr

    kermit_rr Can't Remember Full Member

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    When you use the choke, you are changing the ratio between the fuel and the air going to the engine. With too much fuel, or not enough air, the mixture doesn't burn so well, as a result there is less power and the revs drop
    The choke works in a cold engine because the fuel doesn't vaporise properly, effectively changing the ratio of burnable fuel
     
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  17. v8250

    v8250 Well-Known Member

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    Okay, Stromberg's are straight forward too. Where carbs of a certain age some components are never guaranteed to be correct :. it's worth buying new pair balanced springs + any other components of unknown certainty. Revs shouldn't drop when choke engaged, this is either too much fuel or a little lean on air as more fuel is fed. For any carbs it's really worth buying/using 1. Gunson Carb Balancer, and 2. Gunson Colourtune fuel/air mixture inline spark viewer. Once air flow balanced at idle, off idle and mid range the Colourtune is a ready reckoner to identify any difference in fuelling which means one carb can be very finely tuned. Here, it's common for one bank to run slightly richer than the other [same with front to rear cylinders on a 4-6 block engines]. Once all set up be sure to Loctite the linkage nuts as they have a habit of easing up. Good luck for trow.
     
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  18. hef19898

    hef19898 Well-Known Member

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    I have to agree, setting them is straight forward. The reason for the 2.2k idle rev was the new throttle cable. Among other things, she was fitted with cruise control. Part of that was a changed mount for the throttle. A bracket solved that problem easily.

    I don't have a CO gauge and had to rely on listening to the air flow, so maybe the MOT has one or two things yo say later. Air flow sounds in sync to my ears. Mixture is good as well, no rev changes when lifting the piston. The left carb seems yo be running a tad richer than the right one with the needle base touching the piston base. Roughly one turn of the needle solved that.

    Now she's idle reving at a steady 700ish, hard to tell with a rev counter only showing 200 rev steps. After lunch I'll put the air filter back in and take her for test ride to see whether or not the power loss around 3.5/4 k revs is gone as well. So far so good!
     
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  19. kermit_rr

    kermit_rr Can't Remember Full Member

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    sounds perfect!! fingers crossed
     
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  20. v8250

    v8250 Well-Known Member

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    That's great news, it's incredibly satisfying setting up carbs :) Re' CO and air-fuel mixture, every carb'd car owner needs these simple tools

    https://www.gunson.co.uk/products/Colortune

    https://www.ebay.co.uk/itm/STE-Sync...r-SU-Solex-Dellorto-Carburettor-/273030912387

    eta: if you'd like to really see running improvement replace std air filters with K&N's and re-route the head breathers from the air intake into a catch tank [K&N also have very effective rocker breather filters too]...every little helps
     
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