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Center mount carb preheat question help
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Hnoroian
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PostPosted: Wed Feb 24, 2021 10:16 pm    Post subject: Center mount carb preheat question help Reply with quote

Been playing around with this for a little while and have almost found the answers but not really. Looking for anyone that has tried or experience.

Would this work with a insulated exhaust wrap to help the manifold from icing up? I do not live near the cold nor really plan trips in the cold with it (open top Baja) camping in higher altitude but never in a really big rush. Running rough for a little bit is okay. Have the battery and amperage to cover the drain.

100-200w 12v silicone heating wrap
https://www.ebay.com/itm/233873965627

I was gifted a cheap setup where the preheat ports in the manifold do not go all the away through to the other side. Yes I know exhaust preheat to the manifold is the best, efficient, and quickest and I can eventually weld the preheat tubes to the headers.
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PostPosted: Wed Feb 24, 2021 11:46 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Back in the previous millenium, in the UK mags, there was an add for what was called an IMDU, an "Inlet Manifold De-icing Unit". It was just about what you are envisionning. I'm not sure if they worked, but I haven't seen those ads in years...
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PostPosted: Thu Feb 25, 2021 6:54 am    Post subject: Re: Center mount carb preheat question help Reply with quote

It would make very little if any difference. You are far better off spending the time to get the factory one working correctly.
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PostPosted: Thu Feb 25, 2021 7:25 am    Post subject: Re: Center mount carb preheat question help Reply with quote

Yeah, I cant imagine 200W would be enough juice to make any noticeable difference.

Can you modify the manifold so that the exhaust gas can pass through? Drill through the manifold to Connect the two side of the heater tube, then trill/tap the hole on the outside with a pipe plug?
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PostPosted: Thu Feb 25, 2021 7:50 am    Post subject: Re: Center mount carb preheat question help Reply with quote

Hnoroian wrote:
Been playing around with this for a little while and have almost found the answers but not really. Looking for anyone that has tried or experience.

Would this work with a insulated exhaust wrap to help the manifold from icing up? I do not live near the cold nor really plan trips in the cold with it (open top Baja) camping in higher altitude but never in a really big rush. Running rough for a little bit is okay. Have the battery and amperage to cover the drain.

100-200w 12v silicone heating wrap
https://www.ebay.com/itm/233873965627


I've thought of such myself, but haven't tried, would be interested in the responses.

I have a single Weber 40DCNF on a matching intake manifold that never had any pre-heat tubes at all (purchased 1976 from Claude's Buggies/CB) on my 1835cc engine, and mine definitely runs better in the first 5 minutes in summer than in winter. Note that the 40DCNF has no choke either.
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Hnoroian
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PostPosted: Thu Feb 25, 2021 10:51 am    Post subject: Re: Center mount carb preheat question help Reply with quote

Thanks for the replies.

Im willing to try, but by the time I get to it it will be spring and summer again, so next winter it will be ready. I have a few more things Id like to do first and then worry about the preheat.

It is a cheaper 44IDF I have had for a while, cleaned and rebuilt and actually did pretty good. It is on a 1915cc. For the maybe once a year or so that I may need it seems like a bandaid alternative for free/cheap parts that will get by, and not out much money or length of time.

I have switched over from dual carbs which was nice, (both require a rebuild as they have clogged with silt dust). But the darn linkages (hexbar) had too much slop and always tinkering with them. Dont mind syncing them but getting covered with mud and whatnot always bugged me. After the rebuild considering putting on center pull as I continue to read about them.
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PostPosted: Thu Feb 25, 2021 12:02 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Best for a preheater set up is one that flows through all the way and one of the tubes is rerouted to the header collector so it actually pulls exhaust gas through.

With a header the air will not flow properly since the connections are at the #2 and #4 exhaust. There are many threads on this modification and aircooled.net used to offer headers with this modification (not sure if they still do). Here are some photos in the gallery of the modification to the header: https://www.thesamba.com/vw/forum/album_search.php...t_dir=DESC
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Hnoroian
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PostPosted: Thu Feb 25, 2021 1:22 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

I realize that the connection needs to go all the way though in the manifold (positive and negative pressure) but I dont think the one I have is capable of doing so, but will look again.

Might have solved my problem too. Some in thing that has crossed my mind is taking 3/8 or so stainless tubing and bending along the way to match the curves of the manifold and drilling/welding them in the header for a pressure and scavenger line. Then I would need to figure out how to attach to the manifold. Then again seems to be creating more work for my self for something I may never need/use.

My head spins sometimes from searching through forums, I have read and searched many...

Question, where would it start to ice up? Right below the carb, downdrafts at the manifold curves, or the???
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PostPosted: Thu Feb 25, 2021 1:55 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Hooking up the preheat stuff as close to the factory design as possible will give best results.
As mentioned above... the aftermarket pipes with preheat flanges on #2 and #4 exhaust ports are worthless garbage. You need high pressure on one side and low pressure on the other for it to circulate. Two high pressure heat sources wont do it.
I found this out from personal experience.
I went from a cheap chinese muffler with preheat ports on #2/#4... to a nice German made Euro style stainless muffler with the crossover ports placed correctly.
The car ran 10 times better and it completely changed the jetting requirements too. A wideband O2 sensor was crucial in figuring all this out.
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PostPosted: Thu Feb 25, 2021 2:20 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Lost in my bookmarks

http://www.vw-resource.com/heat_risers.html

In the end there is no real way to work this out like I would want or should.

Am I still understanding correctly? Generally wetter weather and <50*F or so starts to create this problem or around there?
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PostPosted: Thu Feb 25, 2021 7:13 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

i know its been discussed but cant remember seeing or hearing whether anyone has done it or not, but what about running engine oil through the intake heat channel?
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PostPosted: Fri Feb 26, 2021 4:01 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

richardcraineum wrote:
i know its been discussed but cant remember seeing or hearing whether anyone has done it or not, but what about running engine oil through the intake heat channel?


I heard someone mention this somewhere.

I've been thinking of doing it as part of my rebuild. I've got a Weber Progressive and I hear it (like any centermount) needs heat.

Aftermarket header, so it's either take it to the muffler shop and get it welded or I route oil through the manifold. I'm cheap, and the oil routing is just a brass fitting and some hose, so what is there to lose?
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PostPosted: Fri Feb 26, 2021 4:29 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

stewartsoda wrote:
richardcraineum wrote:
i know its been discussed but cant remember seeing or hearing whether anyone has done it or not, but what about running engine oil through the intake heat channel?


I heard someone mention this somewhere.

I've been thinking of doing it as part of my rebuild. I've got a Weber Progressive and I hear it (like any centermount) needs heat.

Aftermarket header, so it's either take it to the muffler shop and get it welded or I route oil through the manifold. I'm cheap, and the oil routing is just a brass fitting and some hose, so what is there to lose?

I'm not cheap, but I'll save money where I can definitely. I've thought about this also. I was thinking of wrapping 3/8 tubing around the manifold. Exhaust is way hotter sooner....
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PostPosted: Fri Feb 26, 2021 5:03 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Wrapping the header and the preheat tubes will make a difference, but it is not really worth it unless you are in a very cold ambient.
If you have a header with the pre heat hook up on 2/4 which goes directly to the exhaust, the way to make it work the best is to drill a 12-13 mm hole im the right flange and a 10 mm hole in the left. By doing that you ensure that the exhaust is mainly moving in one direction instead of just pulsing back and forth.
An extractor tube like the ones [email protected] Aircooled.net sells (or used to, Im not sure he still hasm) is of course numero uno.
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PostPosted: Fri Feb 26, 2021 5:09 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

I did this a long time ago. It made a huge difference keeping the carb and the top of the manifold warmer.
Image may have been reduced in size. Click image to view fullscreen.


Brian
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PostPosted: Fri Feb 26, 2021 5:16 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Hehe Very Happy
Maybe you can start a new line of tupperware sales.

Im imagining the sales lady: "And this model also works very well for your husbands vintage VW in the wintertime." - Wifey thinks, Hmmm, good excuse for spending a little money Cool

But I hear ya! I have seen a couple of redneck solutions too, which actually worked well.
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PostPosted: Fri Feb 26, 2021 5:22 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

oh shit! that is awesome! i love the tupperware intake, thats the coolest thing ive seen in a while.
wheres the intake hose attached to?

also about the preheat tubes, i bought a dozen or so of the small hole copper gaskets a while back and run one on one side and a normal on the other. i have no idea if its better or not but it does make sense to me...
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PostPosted: Fri Feb 26, 2021 5:28 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

IMHO the hole in the copper gasket is too small.
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PostPosted: Fri Feb 26, 2021 5:31 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

richardcraineum wrote:
wheres the intake hose attached to?


It goes down through the stock pre-heat hole and sucks in hot air from the cylinders and header area under the tin.

Brian
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PostPosted: Fri Feb 26, 2021 5:56 pm    Post subject: Re: Center mount carb preheat question help Reply with quote

Brian_e wrote:
I did this a long time ago. It made a huge difference keeping the carb and the top of the manifold warmer.
Image may have been reduced in size. Click image to view fullscreen.


Brian


That is great! . . Thinking outside the box or maybe inside the Tupperware or . . . LOL
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