Solex twin PDSITs Fuel not atomising...

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jifop
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Solex twin PDSITs Fuel not atomising...

Post by jifop » Fri Apr 04, 2014 2:57 pm

Hey guys, I'm hoping someone can help me! I have twin 36-40 PDSIT carbs on my 914 engined ghia and the pick up is terrible, now I was looking down the barrels and noticed that as the fuel comes out of the brass tube it pours out like water out of a tap, there is loads of pressure but it doesn't spray.

Am I being mad or should it be a spray rather than a stream?

helowrench
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Re: Solex twin PDSITs Fuel not atomising...

Post by helowrench » Fri Apr 04, 2014 3:03 pm

What is your fuel pressure?

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jifop
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Re: Solex twin PDSITs Fuel not atomising...

Post by jifop » Fri Apr 04, 2014 3:56 pm

8 out into the king filter 3.5 to the carbs!

helowrench
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Re: Solex twin PDSITs Fuel not atomising...

Post by helowrench » Fri Apr 04, 2014 5:55 pm

http://www.thesamba.com/vw/forum/viewtopic.php?t=572107
Try reading through here, it may give you some pointers.

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jifop
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Re: Solex twin PDSITs Fuel not atomising...

Post by jifop » Mon Apr 21, 2014 8:19 am

Thanks for your help so far...

The engine is very healthy with no endfloat, its running an SVDA dizzy, stock exhaust and stock linkage, valves are adjusted correctly and timing is spot on.

Here is a video showing what I mean about the fuel running into the body https://drive.google.com/file/d/0B2yjK2 ... sp=sharing does that look normal?

Thanks in advance for any help!

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jifop
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Re: Solex twin PDSITs Fuel not atomising...

Post by jifop » Thu May 01, 2014 1:16 pm

Does anyone have an idea if this looks normal?

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sideshow
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Re: Solex twin PDSITs Fuel not atomising...

Post by sideshow » Thu May 01, 2014 3:40 pm

I'm an not sure what the videos shows.
With the engine off are your pump jets working ok? Sharp stream down the butterfly?
If you are concerned about the high speed circuit it is really simple to test off car (exuding the super dangerous part of atomizing fuel over the floor): Hold the throttle wide open and use compressed air into the air horn, this will pull fuel out of the bowl rapidity.
Yeah some may call it overkill, but you can't have too much overkill.

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jifop
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Re: Solex twin PDSITs Fuel not atomising...

Post by jifop » Fri May 02, 2014 12:32 am

Basically the fuel is a stream and I always thought it should be a spray?

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Marc
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Re: Solex twin PDSITs Fuel not atomising...

Post by Marc » Fri May 02, 2014 1:38 am

I see the normal stream of fuel that's squirted in through the brass accelerator pump nozzle when the throttle is cracked open. That's NOT the primary source of fuel, it's provided temporarily to compensate for the momentary lean condition which occurs when the throttle is opened suddenly and manifold vacuum decreases - a car will run without the accelerator pump if the throttle is opened ver-r-r-y gradually.
The reason that you aren't seeing any atomized fuel is that it is, well, atomized - it enters the carburetor through the main distribution nozzle (the cast part that protrudes from the side of the venturi) not through the brass tube of the accelerator pump system.

The accelerator pump nozzle typically aimed so that it squirts that stream very close to, but not touching, the narrowest point of the venturi wall - this gets it past the throttle plate the quickest and in most cases yields the minimum hesitation on acceleration. Sometimes if the local refinery makes their switchover to the less-volatile "summer" blend prematurely (or if you're just trying to use some old gas that's lost its volatile properties) you'll have less of a hesitation if you aim the pipe so that the stream just kisses the rim of the main nozzle so it fans out, but under normal circumstances that's not necessary. If you aren't experiencing a "flat spot" when you accelerate from stop I'd leave it alone.

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Re: Solex twin PDSITs Fuel not atomising...

Post by Clonebug » Sat May 03, 2014 9:42 am

The only thing I see is that you have throttle movement before any fuel comes out and that can cause a slight hesitation.

On a Kadron carb you have to adjust the pump stroke so you have fuel instantly as soon as the arm moves.

That involves adjusting any slop out of the pump arm and diaphragm.
Stripped66 wrote:The point wasn't to argue air temps with the current world record holder, but to dispel the claim that the K03 is wrapped up at 150 HP. It's not.

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Marc
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Re: Solex twin PDSITs Fuel not atomising...

Post by Marc » Sat May 03, 2014 12:24 pm

Clonebug wrote:The only thing I see is that you have throttle movement before any fuel comes out and that can cause a slight hesitation...
:oops: I was focused on the "atomization" and not paying attention to the throttle, but you're right - looks like at least the left one may have more than just an adjustment problem, too. Hard to be sure from that snippet but its checkball may be sticking. I agree, though, if the timing's good and response matters more than fuel economy he should adjust the pump links up tighter.
I do have to wonder what constitutes "spot on" timing with this carb/distributor combination on a Type IV engine - I'd want to see how the advance steps in when the throttle is first opened.

jifop, are you getting a sufficient vacuum signal from one carb's port or do you have it plumbed to connect them both? (I couldn't see any vacuum lines in the video). The latter may be worth a try if you haven't already.

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