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Vacuum advance and 44 IDF's
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Bug53
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PostPosted: Wed Nov 30, 2022 12:33 am    Post subject: Vacuum advance and 44 IDF's Reply with quote

Is anyone running a vacuum advance distributor with 44 IDF's?
I have a CB magnaspark which I'm pretty happy with now.
Im getting ready to start assembly on my 2095 and starting to purge some parts one of which will be a like new 034.
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oprn
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PostPosted: Wed Nov 30, 2022 5:24 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

It's been my experience that dual carbs do not generate enough vacuum signal to PROPERLY operate a stock vacuum pot. You may get some movement alright but is it enough and at the right time? I believe very few people that claim it works have actually tested it properly on the road in real driving conditions.

There are multiple threads on this subject by the way, use the search feature.
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Alstrup
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PostPosted: Wed Nov 30, 2022 9:07 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

oprn wrote:
It's been my experience that dual Chinese or Spanish carbs do not generate enough vacuum signal to PROPERLY operate a stock vacuum pot. You may get some movement alright but is it enough and at the right time? I believe very few people that claim it works have actually tested it properly on the road in real driving conditions.

There are multiple threads on this subject by the way, use the search feature.

Fixed it for ya Wink
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sallittjob
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PostPosted: Wed Nov 30, 2022 9:09 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

Options are limited with a traditional vacuum diaphragm driven advance distributor.

It's been a few years, but I had decent result by swapping an old 40hp distributor's vacuum can onto my distributor. The larger can on the old dizzy required less vacuum to operate. My Mallory Unilite had an adjustable vacuum can, but even turned to max sensitivity, the signal was too weak on my 40 Dells.

I finally ended up buying a digital distributor from CB. That setup was cool because they included spacers that went under the carbs and had vacuum ports which drew from all multiple cylinders and T'd into the sensor on the distributor. Since it was just a pressure/vac sensor and didn't need to do any mechanical work, I could just punch in the advance I wanted based off the vacuum available (on my laptop) and go from there. I don't think CB sells that setup anymore. Probably because it had a lot of buggy flaws (I can confirm through personal experience / roadside breakdowns).

You can at least use my input here as food for thought. My bug with that engine has been tore down for years now for rust repair. When I get it back on the road, I'll dive back into this problem.

Good Luck
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vwracerdave
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PostPosted: Wed Nov 30, 2022 9:14 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

It's the cam that produces the vacuum signal. The larger the cam the less vacuum you get.

I have a 2007cc with dual 44 IDF's and an Engle W-120 cam. That's probably the limit for using a 034 SVDA. I also run the anti-pulse valve from Aircooled.net
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Alstrup
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PostPosted: Wed Nov 30, 2022 11:30 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

OK. to clarify, once again. NO Spanish or Chinese IDF carbs deliver sufficient vacum for any SVDA out of the box. - Italian IDF´s and Dellorto´s do - to an extent. there is of course a upper line for cam duration ie intake vacum level at lower rpms. Intake vacum strength is cam related, yes, but it is also affected by CR, intake length and exhaust (type/layout) I kid you not.
chinese and Spanish IDF´s can be modified to deliver the same vacum as an Italian. If you know what you are doing you can evewn improve on the vacum pattern.
Several people claim that it does not make a difference. I beg to differ. If I use an SVDA distributor with IDF´s I always us the signal from both carbs, because at the end of the day it improves the signal strength so the vacum can actually advances the timing.
The solution with using a SVA can is good and will help improve the response with a weak signal.
I have run (hand picked) SVDA distributors on engines with 86b cams and 10-1 CR with full vacum advance (8 degrees)
If you wanna stay old school, and manual, there is also the trick with using an adjustable vacum can from the old pre 63 I believe bus distributor. I forgot exactly which one. You will of course have to have a certain amount of vacum in order to make it work.
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Bug53
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PostPosted: Wed Nov 30, 2022 12:30 pm    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

sallittjob wrote:



I finally ended up buying a digital distributor from CB. That setup was cool because they included spacers that went under the carbs and had vacuum ports which drew from all multiple cylinders and T'd into the sensor on the distributor. Since it was just a pressure/vac sensor and didn't need to do any mechanical work, I could just punch in the advance I wanted based off the vacuum available (on my laptop) and go from there. I don't think CB sells that setup anymore. Probably because it had a lot of buggy flaws (I can confirm through personal experience / roadside breakdowns).

You can at least use my input here as food for thought. My bug with that engine has been tore down for years now for rust repair. When I get it back on the road, I'll dive back into this problem.

Good Luck


That is the same distributor i use now with Kadrons. It performs hands down much better than the 034 I have.
I also have purchased the EMPI 44's so Im glad I have the dizzy from CB.
It worked well with the Kadrons but with the new build they will be on Ebay very soon along with the Treuhaft manifolds.

Thanks.
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jaket3
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PostPosted: Wed Nov 30, 2022 1:17 pm    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

Alstrup wrote:

chinese and Spanish IDF´s can be modified to deliver the same vacum as an Italian. If you know what you are doing you can evewn improve on the vacum pattern.#


Good to know, could you please share the modification. I've got Spanish 40IDF's and the vaccum signal from them is too weak.

Thanks, Jake
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earthquake
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PostPosted: Wed Nov 30, 2022 2:46 pm    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

Have you tried a vacuum can on it? go to a local wrecking yard and look at cars that had heavy emissions on them and look for a vacuum can with at least 3 ports [looks like a soup can or juice can] Hook both carbs to it and to the distributor and see if it helps. you could make your own too.

eQ
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PostPosted: Wed Nov 30, 2022 11:44 pm    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

I run a cheap 034 on my 2127 with dual 44 Webers. I ran vacum lines from both carbs to a T, last leg to the can. Works great! Has a 110 cam in it.
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94touring
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PostPosted: Thu Dec 01, 2022 3:28 am    Post subject: Re: Vacuum advance and 44 IDF's Reply with quote

My solution was run a black box, drive with a laptop and note which blocks it was pulling vacuum under light throttle, and adjust those blocks to the max advance I wanted. But you must be aware if you did the initial tune at sea level then went to say 8k feet you might be over advanced at WOT at the higher altitude. This will be dependant on how much vacuum your dual carbs are able to pull to begin with. Therefore I have a couple maps for various scenarios. My "mountain map" is advantageous also as it will slowly increase my WOT advance in increments as I climb in altitude and decrease as I go back to sea level. It's safe, does provide some vacuum advance in all scenarios, and provides the most power available at all altitudes.
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