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Carby gasket Bendix carby

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  • Hilly
    Hilly
    11 days ago
    Quoting Hilly on 10 Oct 2025 09:47 AM

    One thing I did see was that there is an oring around the main jet that can/does perish and fuel can then get past making the mixture rich, maybe that could be part of your sooty plugs scenario if you haven't been there yet?

    Quoting Merv on 10 Oct 2025 09:56 AM

    Yes, new O ring in place.

    Was the old one ok Merv? Have you ran it and got sooty plugs since it was changed or did it get changed this time down, sorry I get like a dog with a bone at times.
  • Merv
    Merv
    11 days ago
    Sooty plugs since it was changed mate, but the old one would have had to been good and the new one no good for it to be the problem. Reckon the old one worked because it was probably in there so long it had stuck to the chamber wall. Anyway, fair bit of verdi grease it scrubbed past when removing main jet first time, so it came out a bit ratty. New one was in the kit.
  • Hilly
    Hilly
    11 days ago
    Right, gotcha, see how the accelerator jet sizes out, hopefully you find something, I did read it is a stream and not a spray, could it be the float chamber was flooding? I have no idea, genuine question.
  • Merv
    Merv
    11 days ago
    Quoting Hilly on 10 Oct 2025 11:54 AM

    Right, gotcha, see how the accelerator jet sizes out, hopefully you find something, I did read it is a stream and not a spray, could it be the float chamber was flooding? I have no idea, genuine question.

    More likely something I did removing and cleaning it before studying up on it a bit. I am a bit more confident it might go back right this time and run a bit better. I have installed the small spring too btw, altho still to get it to sit against the bowl wall when bowl is fitted. I'll check out the spray jet tomorrow and go from there.
  • obisteve
    obisteve
    11 days ago
    Gotta say Merv that you're past my direct experience with a Bendix too, which was just helping a mate install and then fine tune an adjustable main jet into a 1974 Sporty in 1980. So like Hilly I am following along hoping to learn something. But I do have 20 years of experience with Amals, Monoblocks, Concentric, and Mk 1.5 Concentrics (and one of them arrived new from the factory without the pilot air passage drilled completely through); 8 years experience with Mikuni VM28s off 1960s Kawa W2 650s, and the 35 years living with the CV on my 1200 Sporty.
    One thing that strikes me is that that if it's intermittently stopping the trike pulling into 2nd when road testing is that it's a big problem which you're trying to fine tune out. I'd encourage you to think big.
    Trying to pull hard against a load in 2nd is gonna need most of the air and fuel the carb is capable of flowing.
    Is there anything blocking fuel flowing  through the main jet and up to the venturi?
    When you were road testing did you try shutting the fuel tap and seeing if the motor ran any better before it sucked the last fuel out of the bowl?
    Did you try taking the aircleaner off for one run and putting a gloved hand over the carb intake?
    These bush mechanic methods can give you a good insight into whether the carb is running way too rich or way too lean under those throttle openings/revs.
    It's unlikely to be an accelerator pump issue, the pump shot helps smooth the transition to higher flow when you open the throttle fast, doesn't have much effect when you open it slowly. And was there any difference on road test between easing the throttle open, and slamming it open?
    Of the non carby possibilities, you've changed everything I'd have checked. I always go for spark plugs first, then the condenser.
    I've got points ignition on my Sporty too.
    Have you tried letting it idle with the points cover off,  and shining a timing light in there, looking for any of the connections moving around, sparks where there shouldn't be, that the advance is moving smoothly around and back as you rev it?
    Really bad manifold leak?
    Just chucking things in here, good luck with it, and I look forward to reading that you've solved it and learning what it was.
  • Merv
    Merv
    11 days ago
    Well Hilly, I have hit a hurdle. I originally used the Bendix main jet chart to back calculate the jet size of the accelerator jet at .0276", however AI tells me it is just .014", as it's a #14. I can in fact insert a .027" drill shank into it, which is not far from my calculation of .0276, however another session searching has not turned up any indication by Bendix on what measuring system they used for this jet. I'm told Industry Standard Practice would be .014. So what I need is for someone with a Bendix carby bowl to measure the jet. And if it's .014, then the nearest drill size I have is .0125. Might have to think for a while. Pic of spring in place, near as I can see it should be right. Stopped for now.
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  • Merv
    Merv
    11 days ago
    Quoting obisteve on 11 Oct 2025 02:57 AMedited: 11 Oct 2025 03:00 AM

    Gotta say Merv that you're past my direct experience with a Bendix too, which was just helping a mate install and then fine tune an adjustable main jet into a 1974 Sporty in 1980. So like Hilly I am following along hoping to learn something. But I do have 20 years of experience with Amals, Monoblocks, Concentric, and Mk 1.5 Concentrics (and one of them arrived new from the factory without the pilot air passage drilled completely through); 8 years experience with Mikuni VM28s off 1960s Kawa W2 650s, and the 35 years living with the CV on my 1200 Sporty.

    One thing that strikes me is that that if it's intermittently stopping the trike pulling into 2nd when road testing is that it's a big problem which you're trying to fine tune out. I'd encourage you to think big.
    Trying to pull hard against a load in 2nd is gonna need most of the air and fuel the carb is capable of flowing.
    Is there anything blocking fuel flowing  through the main jet and up to the venturi?
    When you were road testing did you try shutting the fuel tap and seeing if the motor ran any better before it sucked the last fuel out of the bowl?
    Did you try taking the aircleaner off for one run and putting a gloved hand over the carb intake?
    These bush mechanic methods can give you a good insight into whether the carb is running way too rich or way too lean under those throttle openings/revs.
    It's unlikely to be an accelerator pump issue, the pump shot helps smooth the transition to higher flow when you open the throttle fast, doesn't have much effect when you open it slowly. And was there any difference on road test between easing the throttle open, and slamming it open?
    Of the non carby possibilities, you've changed everything I'd have checked. I always go for spark plugs first, then the condenser.
    I've got points ignition on my Sporty too.
    Have you tried letting it idle with the points cover off,  and shining a timing light in there, looking for any of the connections moving around, sparks where there shouldn't be, that the advance is moving smoothly around and back as you rev it?
    Really bad manifold leak?
    Just chucking things in here, good luck with it, and I look forward to reading that you've solved it and learning what it was.

    Hi Steve, my first thoughts were to think big, and the biggest problem was probably caused the minute I picked up the first spanner. Have studied up a little since then, and feel this next assembly might be better than the last (new needle, float, float spring, + a better idea of what I'm doing.) But to further define the symptoms for you, neutral, no load, idles great, great throttle response, flawless operation. In low, the second the clutch begins to put any load on the motor, dies, backfires, and goes nowhere. Back to neutral, no load, again flawless. I did try various settings of the choke, from full out to slowly full in without any improvement. Plugs black and sooty. No difference I can recall between easing the throttle open, and slamming it open. In any case, I will reassemble it now as it is and see what happens. Pretty sure this time will eliminate the "I did it" component, which means it should run good. Will let you know and appreciate your suggestions.
    By way of background, I had my first experience with an AMAL carb some 65 odd years ago, and my love of bikes using them continued until around 5 to 10 years ago, when I decided I needed a self starter if I'm to continue riding. That began my association with all things using Mikuni, and I still have about half dozen bikes in the shed, 5 of them registered for road use. Tho I haven't upgraded it for a long time, I believe my old Servicar is still shown on www.kroll.id.au 
    As a bush mechanic, I agree 100% with your Bush Mechanic methods. Will report back what happens.
  • Merv
    Merv
    11 days ago
    Tho it ran ok with the existing fuel hose, there is quite a kink in it from filter output to carby, so I am going to replace that with maybe a metal elbow or a piece of curved copper pipe. Will eliminate another potential problem. My butterfly is only 3/4 open when the pump bottoms out, and the last bit of throttle is very stiff, as the bucket moves up the shaft against spring pressure. The book says there are 3 holes in the pump shaft, and it can be adjusted between rich squirt to a lean squirt. My shaft has one hole only, and is the earlier type. I must remember however, the bike ran great with this setup before I meddled with it.
  • Merv
    Merv
    5 days ago
    I haven't given up on this bike yet, been busy on other things. Points I bought the other day were wrong so took them back today and fitted the replacement set this arvo, learning a lot along the way. Couldn't understand why the cam had 4 lobes (pics attached) and on measuring them, two opposing lobes had .100" lift from bolt while other two had just .075" lift. Testing for compression stroke on each cylinder, I marked with a white felt pent which lobes were used, and the same two fired the cylinders each time. A bit of research tells me that the other two are there to give a 'balanced' operation to the coil, which apparently is kinder to it than a series of two quick sparks widely spaced from the following two. Guess the lower lift is to create less wear on the points heel. So narrow cam is for rear cylinder and wider cam for front. I need to just confirm the cam wasn't slipped over it's retaining pin 180 out tomorrow before closing the points compartment up as done.
    Talking with the guy behind the counter today when exchanging the points, and he reckoned it must be sucking air somewhere. A quick look around each cylinder where the head mates showed no oil or signs of leaking, and besides each cylinder pressure tested to around 180psi with the compression tester (very high). Which rules out valves as well. So bit the bullet and pulled the manifold off, not knowing what I was doing. Came off easy enough, and the rubber O rings look in good condition to an untrained eye. Have new ones, and hope it goes back together as easy as it came off.
    This time will be the last time I reassemble this fuel system, as I really want to ride the bike. So if it still doesn't work for me, it gets the chop for a Mikuni. Will let you know what happenes. Hoping it's the manifold seals - that will mean I didn't cause the problem.
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  • Hilly
    Hilly
    5 days ago
    Close to kicking it in the guts are we?
  • Merv
    Merv
    5 days ago
    Quoting Hilly on 16 Oct 2025 12:01 PM

    Close to kicking it in the guts are we?

    Not yet mate. Missus has me pegged for today, but blood test and medical crap first. Then still need to give manifold the smooth sandpaper on a sheet of glass treatment, then refit it, refit the carby and hook everything up again. Maybe late today if I'm lucky.

  • Hilly
    Hilly
    4 days ago
    Quoting Hilly on 16 Oct 2025 12:01 PM

    Close to kicking it in the guts are we?

    Quoting Merv on 16 Oct 2025 09:45 PM

    Not yet mate. Missus has me pegged for today, but blood test and medical crap first. Then still need to give manifold the smooth sandpaper on a sheet of glass treatment, then refit it, refit the carby and hook everything up again. Maybe late today if I'm lucky.

    Maybe today Merv 😁
  • Merv
    Merv
    4 days ago
    Quoting Hilly on 16 Oct 2025 12:01 PM

    Close to kicking it in the guts are we?

    Quoting Merv on 16 Oct 2025 09:45 PM

    Not yet mate. Missus has me pegged for today, but blood test and medical crap first. Then still need to give manifold the smooth sandpaper on a sheet of glass treatment, then refit it, refit the carby and hook everything up again. Maybe late today if I'm lucky.

    Quoting Hilly on 17 Oct 2025 08:59 PM

    Maybe today Merv 😁

    Got manifold fitted is all Hilly. And birthday party for 90yo mate today. I'll never get to enjoy this bike the way I'm going.

  • Merv
    Merv
    2 days ago
    Well, I admit defeat. Reassembled everything and still no different. Idles great, and responds to throttle blips great, but ask it to do any work and it throws the towel in. As have I. I have a Mikuni VM38-9 on it's way from the US, received the manifold adapter today, and have a piece of 16mm aluminium in the lathe, roughed out and waiting on carby to confirm fit, for adapter for air filter. 
    The Bendix is such a simple carby, and I can't understand what is wrong with it. And I guess if it's not the problem then I will find out when I fit the Mikuni, cause it will still run the same. But after new plugs, new leads, new O rings in manifold, new kit in carby, new coil, new condenser, new points, new float needle, added the spring which was missing, plus a good replacement float, I don't know what to do next.
    If after fitting the Mikuni the problem persists, I will give it to someone who understands this particular model to fix. One things for sure, it's a beautiful bike and I love everything about it, so it is a final keeper for me.
    Will report back on results. Cheers, Merv.
  • Hilly
    Hilly
    yesterday
    Well bugga Merv! I really hope the Mik sorts it, I just don't have enough real experience with the Bendix to offer anything other than encouragement, carburetors do get blamed for electrical issues though but you seemed to have that covered as well, I look forward to hearing how the next chapter unfolds.
  • Merv
    Merv
    yesterday
    Quoting Hilly on 20 Oct 2025 05:48 AM

    Well bugga Merv! I really hope the Mik sorts it, I just don't have enough real experience with the Bendix to offer anything other than encouragement, carburetors do get blamed for electrical issues though but you seemed to have that covered as well, I look forward to hearing how the next chapter unfolds.

    Sometimes, encouragement is all that's needed mate. If you look at the two pics, one shows the fuel flow from the main jet, and the other shows the same from 4 jets up the top, circled in red. The book says that when the butterfly is closed, it is behind the idle jet, and that the needle adjustment will set the correct air/fuel mix for idle using this jet. Then, as you open the throttle, the 2nd. jet is exposed, followed by the 3rd. and 4th., as revs increase. And when you really flog the throttle, the main jet delivers, as in the second pic.
    Now opening the throttle enough for a normal take off, I sincerely doubt if I ever draw on the main jet, using the second thru to the fourth jet above, as well as the accelerator pump for initial revs. And I cannot see how you can check that these jets are all clear. If one or two of then are clogged then I'll get the initial spurt from the pump, then nothing. Which may explain why on 1/4 choke it pulls better as it's drawing more thru whatever jets are working.
    In any case, the Mikuni is going to be tested, Only change swapping from one to the other is the throttle cable.
    Idle jets.jpg
    Main jet.jpg
  • Hilly
    Hilly
    yesterday
    Right, well going by generalised carby operation those ports are your transition ports from idle to main so yeah if those aren't supplying enough fuel when the air rushes past as the butterfly starts to open and before the main kicks in then the engine is going to bog lean, you should be able to actually see fuel coming out of them as you crack the throttle you would think?
  • Merv
    Merv
    yesterday
    Quoting Hilly on 20 Oct 2025 09:13 AM

    Right, well going by generalised carby operation those ports are your transition ports from idle to main so yeah if those aren't supplying enough fuel when the air rushes past as the butterfly starts to open and before the main kicks in then the engine is going to bog lean, you should be able to actually see fuel coming out of them as you crack the throttle you would think?

    Ha! There's a 6 inch sheet of flame that comes out of there occasionally, and those jets are deep down towards the manifold end of the venturi so not easy to watch what happens when you wrap the throttle. The idle tube has holes in several places along it's length, so very hard to test with liquid when cleaning the carby. And to get enough air up there to blow them out sees' air going everywhere. Still a couple weeks wait for the Mikuni, so I might get keen again and have another go at it. But need to spend a couple days rebuilding an oil pump and lines for a 72 Suzuki Hustler so might have a change for a while. My 7th. Harley, and I've learnt more about the make with this then I did with all the previous six, so have enjoyed the exercise. Definitely different to the old British marques and old but more recent Japanese bikes I've had in the stable.
  • Hilly
    Hilly
    yesterday
    I got to admit a wall of flame would put me off looking as well, a welders mask perhaps 😁
    Seriously though, there must be a way of cleaning those ports out, got me looking at ultrasonic cleaners, I could sell it to the missus as a means of cleaning jewellery and such lol.
    Even after a session in one of those the ports would still need to be tested somehow, I'll see what I can dig up later, have to get sorted to go catch a plane right now.
  • Stuart
    Stuart
    yesterday
    Merv,

    you're well down the rabbit hole now :-) Here's some random thoughts that may have nothing to do with your issue(s).

    You mentioned you were going to replace the points earlier in this thread. Did you do this? Apologies if I missed where you said you did.

    Does the bike have a kill switch on the ignition? Is this a bit dicky and vibration at higher RPM is messing with power to the ignition? I have had a similar issue with a sidestand cutout switch on an old Jap bike I had years ago. But I'm guessing this is not your problem.
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