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67 1500 Engine - carb & Distributor Upgrade
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thunderhead289
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PostPosted: Wed May 23, 2018 7:12 am    Post subject: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

First off, I want to say that this forum has been very helpful and i appreciate all the insight. im thunderhead289 on youtube and am relatively new to the beetle stuff.

Q1
so we have been able to determine that we have a 1500 engine in the 67, but it has a 28 carb and matching era distributor. Its my understanding that this carb will be richer due to the smaller bore and added vacuum signal - does that make sense when using the stock 1300 set up as reference? (i plan to play with the air and fuel jets if i keep this - i dont like that it doesnt have the top end jet - forgive the terminology)

Q2
I have a pertronix billit unit that has both mechanical and vacuum advance. iv been advised to use this only with the 34-3 carb. from my memory of our last beetle, the 34 will not fit on the 1500s intake design. Am i mistaken? i know the h30/31 will fit and it seems that these are readily available.
is there a way to mod the 34 on, or would i be just fine with running the h30/31?

Q3
can someone explain to me how the vacuum works on these carbs? im used to holley stuff, where when you get the engine under a load, manifold vacuum drops, and the vacuum advance is no longer adding timing (v8 knuckle dragger stuff so bear with me)
this is needed because the richer mixture along with the cylinders volumetrically being filled more will result in a faster burn where less timing is required for the mixture to ignite at the right time- in the v8 world the mechanical timing is the only advance under these situations. go back to cruising - less cylinder filling, leaner mixture, and the vacuum advance is adding timing again due to the longer flame front/burn time.
>>>> do the beetle carbs work the same way ported/manifold vacuum, or are the vacuum ports variable and thus timing is varied via vacuum advance?
i ask because my current distributor only has vacuum advance.
will i run into issues with the vacuum aspect of the h30/31 with the petronix unit? can someone explain the vacuum functionality to me?

alright book over - knuckle dragger out!
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thunderhead289
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PostPosted: Thu May 24, 2018 5:42 am    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

bump

Come on guys, dont make me have to figure this out myself Wink
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fl59bug
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PostPosted: Thu May 24, 2018 6:43 am    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

I'm not going to be much help regarding the 34-3 and 30/31 carbs with which I have no experience, but definitely the 28 carb doesn't sound right for your 1500. The 28 pict and 28 pict 1 carbs are from the 40 horse era.

I imagine moving to the 30/31 when paired with the correct distributor will improve the engines ability to get fuel into the works.
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PumaVW79
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PostPosted: Thu May 24, 2018 8:54 am    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

thunderhead289 wrote:

so we have been able to determine that we have a 1500 engine in the 67, but it has a 28 carb and matching era distributor.


What's the problem you are experiencing with this setup?
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Bugsy61
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PostPosted: Thu May 24, 2018 9:16 am    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

I’m going to take a wild guess that your 1500 is now a 1600. Just about everyone replaced the 1500 jugs with 1600 jugs over the years as they are a direct fit.
Any of the carbs will work if rejetted correctly. As you go up in size you’ll gain about 3 horsepower per size. The 28 is really small for a 1600, though. A lot of people prefer the 30 over the 34 because of it’s simplicity of operation, which makes it easy to tune. You’ll give up a little power with a 30. There are adapters available that let you switch from one carb to the other, and if you run an alternator, you’ll need one anyway to raise the carb to clear it.
If you want to use the aftermarket distributor, you’ll have to experiment a little bit. I may get corrected, but the vacuum on most of these stock carbs appears to me to be venturi vacuum, which continuously increases with engine speed. I would think that at some point during wide open throttle, you’re going to have too much advance, and the engine will ping. But I’d try it, and Tee off a vacuum gauge so you can see what is happening. You may have to run on the centrifugal advance alone, or use a lot of initial advance. Sorry I can’t be more specific.
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thunderhead289
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PostPosted: Thu May 24, 2018 11:12 am    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

Bugsy61 wrote:
I’m going to take a wild guess that your 1500 is now a 1600. Just about everyone replaced the 1500 jugs with 1600 jugs over the years as they are a direct fit.
Any of the carbs will work if rejetted correctly. As you go up in size you’ll gain about 3 horsepower per size. The 28 is really small for a 1600, though. A lot of people prefer the 30 over the 34 because of it’s simplicity of operation, which makes it easy to tune. You’ll give up a little power with a 30. There are adapters available that let you switch from one carb to the other, and if you run an alternator, you’ll need one anyway to raise the carb to clear it.
If you want to use the aftermarket distributor, you’ll have to experiment a little bit. I may get corrected, but the vacuum on most of these stock carbs appears to me to be venturi vacuum, which continuously increases with engine speed. I would think that at some point during wide open throttle, you’re going to have too much advance, and the engine will ping. But I’d try it, and Tee off a vacuum gauge so you can see what is happening. You may have to run on the centrifugal advance alone, or use a lot of initial advance. Sorry I can’t be more specific.


ah yes, ye ol' venturi vacuum.
that would not be good for advance timing since it would not drop out under hard throttle like manifold/ported vacuum does on a holley. just as you say, vacuum would continue to increase - this is how the secondary throttle blades function on a vacuum secondary holley 4 barrel. this also makes sense with how a fully vacuum operated advance curve can work on the beetle (like the distributor i have)

Im assuming there is no such thing as ported vacuum on a beetle carburetor?
thats about the only way i could see running the pertronix unit.

nothing is wrong with the current set up other than it seems completely gutless - and i dont like that it doesnt have that top end jetting to prevent a lean condition under high rpm high load. (28 carb)

it could be a 1600 - it doesnt smoke at all, so it must be fairly fresh - it has been sitting since 94.
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PumaVW79
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PostPosted: Thu May 24, 2018 1:10 pm    Post subject: Re: 67 1500 Engine - carb & Distributor Upgrade Reply with quote

thunderhead289 wrote:

nothing is wrong with the current set up other than it seems completely gutless


In this case, the next best thing to do is to install a dual carburetor setup...
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