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#226 lctriples

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Posted 17 January 2022 - 06:29 AM

Re sealed manifold plug and clamped off rubber stoppers, same problem. I have also changed carby from manifold 1 to manifold 2, so must be a carby, not manifold leak/issue (weak air flow used to be cylinder 1, is now 3). Will remove entire setr up during the week as might be easier to problem solve on bench. Paul


Edited by lctriples, 17 January 2022 - 06:31 AM.


#227 jd lj

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Posted 17 January 2022 - 07:03 AM

From your previous post...
At the moment going from cylinder number 1 (front of engine) to 6, air flow meter at 1,000 reads carby 1: 7,5, carby 2: 2.5 (problem carby) 7, Carby 3: 5,5.

So what was previously carb number 1 with barrel number 1 flowing at 7 on the synchronisation tool and barrel number 2 flowing at 5 is now carb number and the discrepancy between the two barrels remains, correct?

Was the original carb number 2 reading at 2.5 for both barrels?

This must've been idling quite roughly with the variation you had between the cylinders ranging from 2.5 -7.

I'd try just removing that one carb for now and checking the alignment of throttle plates. Completely back off the throttle stop and hold it up to the light looking at the back of it and look for any gaps around the outside of the throttle plates. There should be almost no light visible around the outside of the throttle plates. If you see one area with noticeably more light than another that can be a problem or if one barrel has more light showing than the other.

#228 jd lj

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Posted 17 January 2022 - 08:56 AM

Chances are that you have a twisted spindle from people using an incorrect technique to tighten the throttle/spindle levers. This us quite common.

#229 lctriples

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Posted 17 January 2022 - 10:10 AM

James, very confusing i know, Carb no 1 (offending carby) which is now mounted to manifold two was flowing same when mounted to  manifold 1 ie: around 2.5 for throat one and 5 for throat 2. I'm tipping would read the same regardless whether is was mounted to manifold 1, 2, or 3, affecting cylinders 1, 3 or 5. I will start with removing offending carby first and check as you suggested, i just know that whatever cylinder that "throat" is feeding, engine wont idle for that pot (ie: when you take spark plug lead off, makes no difference to how engine runs). I will also post photo of discrepancy between maifold and cylinder head ports. Thanks in advance, Paul



#230 jd lj

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Posted 17 January 2022 - 10:34 AM

So once you moved that carb to the middle carb did you still have the cylinder not firing in the new position? Does the cylinder that wasn't firing originally now fire with the carb positions now swapped? The cylinder that wasn't firing is that the barrel with the high or low airflow?
How many turns open are the idle mixture screws? Does that cylinder respond to idle mixture screw changes?

#231 lctriples

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Posted 17 January 2022 - 11:02 AM

James, yes, whatever cylinder the offending (low air flow) carb/throat get moved to dosn't fire, and when you replace with a good carby, runs normally. At first i thought was a compression problem with cylinder one, as comp was a little bit lower, but now that i've done around 600k's, (with 350 holley) rings must have bedded in better as comp is consistant across all 6 cylinders. So i will concentrate on offending carby so see if i can see anaything obvious. I might even try swapping jets/tubes, butterflies ect from one of the other 2 carbs, as i think just a process of elimination now. I tried adjusting idle mixture, make a slight difference to how engine ran, but not to airflow reading. Idle mixture screws on other 5 throats were more definitive in response to adjustment. So just to clarify, the barrel/throat that only flows 2ish on air flow is the problem, no matter what location it is mounted to cylinders/engine, cheers Paul


Edited by lctriples, 17 January 2022 - 11:08 AM.


#232 jd lj

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Posted 17 January 2022 - 12:58 PM

The idle mixture screws won't change the air flow reading but I was curious about that same cylinder not firing.
Remove that idle jet and make sure that you can spray carby cleaner through it, through both the bottom hole (fuel inlet) and the side hole (air inlet). Then looking down the hole where the idle jet screws into the carb you'll see a passageway which leads to the progression holes and idle mixture screw. Spray some carby cleaner down the passageway by poking the straw from the carby cleaner down there. Make sure that the carby cleaner comes out through the progression hole port and the idle mixture screws hole. When refitting the idle mixture screws put some grease on the threads to reduce any air leaking past them. This won't change the air flow problem but if that cylinder won't fire it'd be worth while making sure that it's getting fuel.

I've just had to fix a twisted spindle on a set of carbs here today. These one's are 45dcoe9's that I bought a long time ago but haven't used yet. I've made a sealed box that I can bolt the carb to and a vacuum on the other end. I then attach the synchronisation tool to each throat and compare the results. I can also set the idle speed very close to where I want it on all three carbs.

#233 jd lj

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Posted 17 January 2022 - 01:03 PM

I find that if I measure from the rear face of the carb to the tdc of the throttle plates that if it reads close to 17.1mm +or- 0.05mm that that should be close to my idle speed.

On this carb that had a twisted spindle one throttle plate measured 17.05 and the other 17.15mm. This correlated with the air flow difference between the two barrels.

#234 lctriples

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Posted 17 January 2022 - 01:50 PM

Great advice james, will check that out tomorrow morning, when i say dosn't fire, it must fire at high revs as spark plug gets carboned up after running, as i always clean them thoroughly going through elimination steps of problem solving. When engine is running low revs (say 1,000rpm) you can tell by pulling each lead off that it isn't firing. Dont have the courage to try and remove lead's when running at 3,000rpm, and wont be as obvious. Do you have a photo of test unit you have made up??, might be handy if i persist with webers which i really want to do



#235 lctriples

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Posted 19 January 2022 - 07:45 PM

Hey james, pulled offending carby apart and looks like no jets, passages or air chambers are blocked, carby cleaner and compressed air flows freely. Checked throttle plates and dosn't appear a huge difference in how they sit against carby body to suggest a twisted spindle, when you shine light through. I tried to measure throttle plates against face of caby as you recommended but cant get a vernier or ruler against tdc due to spindle. What are your thoughts based on photos, and any tips on comparing one throttle plate against the other. Also had a really good look for cracks/flaws in alloy casting, once again nothing blatantly obvious 

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#236 lctriples

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Posted 19 January 2022 - 08:16 PM

Hey james, i tell a lie, now that it is dark, went out to garage and with a torch you can see more light showing through the throat that only flows 2-2.5 at idle, i would say visually around .5 of a mm top and bottom compared to right hand side throttle plate.  Does that seem right, or should that flow higher than the throttle plate that closes more?  How should i rectify this, new spindle or can i straighten the one i have? I presume are hard to fit into carby body as need to knock bearings out and re fit (press?) new ones, Cheers Paul, and thanks again for your help with this


Edited by lctriples, 19 January 2022 - 08:16 PM.


#237 jd lj

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Posted 26 January 2022 - 10:45 AM

Hi Paul,
Sorry for the late reply.
When I mentioned measuring from the rear face of the carb body to top dead centre of the throttle plates I do this at the top of the barrel well away from the spindle. I use the probe on the back of my verniers to get the measurements. The carb that I did last week only varied by 0.1mm left to right barrel/throat but that was enough to make a considerable difference. I straightened the spindle to fix this. New spindles don't come with the hole drilled for the pin for the pump rod lever/cam. To do this requires some jigs to be made to hold everything in the right place so that the timing of the pump shot matches the other carbs. As a side note the pump rod levers/cams seem to be drilled as a set as these components don't have the holes line up if they're swapped around between carbs. Taking the spindle and bearings out is a simple enough process, it's drilling the spindle as I mentioned above that's not for an amateur. Removing the throttle plate screws can be fiddly to as the ends of them get peened over once fitted so then need to be ground down to remove them without damaging the thread in the spindle. Quite often the slot in these screw heads is damaged too like yours and may need to be drilled out and extracted.

If the spindle is twisted it's most likely by a such a small amount that it'd be difficult to see just by looking at it. Twisted spindles can be fixed carefully. The throttle plates may need to be repositioned once it's done too. The throat that is flowing more needs to be closed more to balance them. It takes a lot of trial and error and having to take it on and off the engine to keep checking it until you get it right would be very tedious, that's where putting it on my vacuum box to test it comes in handy. I've heard of people drilling a small hole in the bottom half of the throttle plate of the throat flowing less air but this method shouldn't be necessary.

Any time that you tighten the spindle nuts use a piece of alloy about 1.5-2mm thick folded into a U shape and position that over the throttle plate and spindle hard up against the side of the barrel closest to the nut that you are tightening. Using long nose pliers hold the spindle and throttle plate steady whilst nipping up the spindle nut. These nuts don't require much force to tighten them as the locking tab holds them in place. I use a nyloc nut on the end of the spindle without the lever. But the end with the lever won't have enough thread available for these so a little bit of loctite and the locking tabs is sufficient. I believe that spindles get twisted when people over tighten the spindle nuts but just let the throttle plates close against the carb body whilst being over tightened.

#238 lctriples

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Posted 27 January 2022 - 07:59 PM

hey james, thanks for getting back to me, now that i have the webers off car and on the bench i will compare all three throttle positions ect. can you straighten spindles insitu (still in carby) by carefully gripping either side as suggested with alloy strips, and try and get both closing at exactly the same time? thanks paul 



#239 jd lj

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Posted 28 January 2022 - 04:20 AM

Yes, you can straighten the spindles whilst they're still in the carb. I put a piece of plastic in the top of the barrel of the carb that's flowing less to hold it open somewhat and then push on the bottom of the throttle plate of the barrel that's flowing too much to try to close it further. It may take a bit of effort but proceed carefully. You have steel spindles which are fortunately stronger than the early brass ones.

#240 lctriples

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Posted 30 January 2022 - 07:55 PM

Hey james, had a really good look at carbs over the weekend and i dont think the problem is a twisted throttle, as compared to the other two, the offending carb is the better of the three (when you shine a torch through, the other two are more mis-aligned (throttle plate compared to its mate in the same carby if that makes sense) plus the offending barrel appears to be slightly more open which should flow more air, not less shouldn't it?. I swapped all jets/emulsion tubes, venturies ect ect from offending to good barrel, swapped soft mount gaskets, all to no avail. (cleaned everything with carb cleaner and compressed air again including all passageways i could see in carb body) synched and tuned them the best i could in the garage (5 cylinders) and when i went for a spin around the block, got 100mtrs and stalled, really hard to get running again, and limped home with my tail between my legs, back in the garage of shame!. Am wondering if there is a blockage somewhere in carb body, restricting air and or fuel flow? have put trusty old holley back on as car is being used as a wedding car in a few weeks. I might even try running webers on a hr wagon i own with my brother which has a fairly warm red motor as manifold should fit a holden red six. Any thoughts or ideas? thanks paul



#241 jd lj

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Posted 02 February 2022 - 11:10 AM

I still suspect a twisted spindle. In the past I've experimented with deliberately mis-aligning a throttle plate on a carb with a similar problem to try to get that barrel to flow more air but that experiment was unsuccessful. Because the twist is on a different plane to what is visable from the rear of the carb it's unlikely that you could see it.
Since you're taking the carbs off for the moment if you'd like to send it to me to check over and possibly rectify send me a PM and we'll arrange for that to happen.

#242 S pack

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Posted 02 February 2022 - 11:32 AM

I don't know much about tuning weber carbs but 1st thing I would do is replace all the rooted throttle disc fixing screws and see if adjusting the discs might improve the situation.

If that doesn't remedy the problem then a twisted throttle shaft is a high probability.



#243 lctriples

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Posted 10 February 2022 - 08:17 PM

Hey James, sorry for taking so long to get back but have been flat out with work. I appreciate your offer, but am in Melbourne so would be reluctant to send up to Sydney as don't trust aus post or couriers as have had thing go "missing" or damaged in the past. I will try my experiment on HR red motor and install a new set of throttle screws as Dave suggested and let you know how it goes. Am running a Holley ATM as car will be used in two weddings soon for family friends.



#244 jd lj

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Posted 11 February 2022 - 03:36 AM

In that case have a talk to Phil at BOI Performance and ask him if he'll have a look at your carb.

#245 lctriples

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Posted 12 February 2022 - 07:35 PM

James, will do, ill call him on Monday.






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