Vacuum issues dual Carburetor

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DumpRat
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Vacuum issues dual Carburetor

Post by DumpRat »

Hi all,

So im still working on these carbs and im having some success but we fired it up and it ran ok only to die out, had a look in the manifold under the carbs and one was soaking with fuel (front carb)in the manifold, and the other not. So i swapped the two carbs over to see if it was an issue in the carb, nope same again the front carb soaking the back one fine,.

When it runs i can feel the rear carb sucking really hard and the front carb almost not at all, so im thinking vaccum issues to the front carb,

I havent noticed any vacuum leaks anywhere but again this is not my field of expertise

Has anyone encounted anything like this, if so what are some suggestions for increasing the vacuum on the front carb toget the fuel tot the motor

Cheers again for any assistance
Remember : Manners Cost You Nothing but Get You Everything ....
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FRANK BASILE
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Re: Vacuum issues dual Carburetor

Post by FRANK BASILE »

Hi DumpRat. I must have missed the first instalment. What carby set up is it, on what engine?. From the logical steps taken that you describe it does already sound like a manifold/engine issue.
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steve the ford guy
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Re: Vacuum issues dual Carburetor

Post by steve the ford guy »

I had a similar issue with a 5litre Holden EFI, it was a poorly sealing intake manifold to intake port gasket losing vacuum, I think it's a design problem with those engines
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DumpRat
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Re: Vacuum issues dual Carburetor

Post by DumpRat »

Hi Frank

its a 265 hemi with dual carter BBD carbs, i have been going through some stuff trying to get it to run successfully but just isnt quite happening

origionally it was over fueling terribly as discussed in another thread

http://www.ozrodders.com/forum/viewtopi ... =5&t=65342

but now i have this issue, i will go looking for vacuum leaks soon,

the rear carb is sucking its nuts off and the front hardly anything, so i swapped the carbs around and same thing, back is good front not so.

years ago in my build thread i had photos of how i made the manifold and the internals (set it up with 2 seperate chambers and a ballance passage between them) unfortunatly all those pics are now gone and i cant get them back from imagecrap.

i am wondering if it was just one big open chamber would tht help resolve this but unsure

cheers
Remember : Manners Cost You Nothing but Get You Everything ....
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turns
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Re: Vacuum issues dual Carburetor

Post by turns »

Hi Dumprat

Firstly, it is super difficult to diagnose this stuff on a forum :shock:

I will assume that you have checked all the usual stuff like fuel pressure, float bowl levels and much more.................

Vacuum leaks are common and can be easy or difficult to find. Everyone has their favourite techniques but I mostly use a length of hose as a stethoscope i.e. one end in a clinched fist near my ear and the other end around possible areas of vacuum leakage on the engine. You will hear a leak quickly.

The red flag I saw when reading your post was "how I made the manifold and internals". It's hard without pics but I would be having a real close revisit on your manifold design and fabrication as a source of your running issues. If you still have the factory manifold maybe swap it back and see what happens.

Good luck with sorting it out

Cheers Turns
"Normal is an illusion. What is normal for the spider is chaos for the fly"...............Morticia Addams
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Sudsy
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Re: Vacuum issues dual Carburetor

Post by Sudsy »

Spray some brakeclean or similar on all the jointing surfaces while motor is running. Motor will pick up in revs wherever it sucks through the joint. That should tell you where it's leaking
Regards Bob
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FRANK BASILE
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Re: Vacuum issues dual Carburetor

Post by FRANK BASILE »

Did this get fixed?. Something else from my Valiant days had that carby particularly prone to air leaks due to warping distortion of the top cover when over zealous with tightening the screws. In this case though the carbs were swapped and the condition existed still in the same position. Me thinks still a manifold/engine issue.
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DumpRat
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Re: Vacuum issues dual Carburetor

Post by DumpRat »

update

we have it idling ok now just trying to get it to not die out under throttle, man these are some interesting carbs to work on

trial and error will find a solution eventually

hahah

cheers
Remember : Manners Cost You Nothing but Get You Everything ....
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