4ac carby vacuum lines

[skit]

Hi all,

I posted this problem as a pic request in the media section also, but essentially its a tech question.

Can someone with a running 4ac please take a few pics of the vacuum lines around the fuel preheater?

Long story short, I bought a 32/36 weber for my gf's sprinter, but it was sold with an incorrect adaptor plate & I could never get it to seal properly against the 4ac intake manifold. So for now I have resorted back to the standard carb. Of course, in my haste to get the weber on, I didn't label all of the vac lines.

The rest of the lines I have sorted out ok, but I think I've cocked up the vac lines on the "drivers side strut tower" side of the carby (as opposed to the "engine side" of the carby). It runs a little rougher down low, especially when cold, and now backfires occasionally under a bootfull of throttle when it never used to.

Hope someone can help.

Cheers,
Scott

[Jonny Rochester]

The easy and simple solution to this: Remove all hoses and block off the holes. Run a single hose from the distributor advance to a port at the base of the carby. Use a timing light to check vacuum advance. Done.

[skit]

<div class='quotetop'>QUOTE (Jonny Rochester @ Apr 15 2008, 11:11 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=518605)</div>
The easy and simple solution to this: Remove all hoses and block off the holes. Run a single hose from the distributor advance to a port at the base of the carby. Use a timing light to check vacuum advance. Done.[/b]


Yep I had considered that - given that the weber only has one vacuum port to run the dizzy advance. But then, the weber has a mechanical secondary, while the 4ac aisin has a vacuum secondary. I'm not certain if it draws the vacuum from an internal port within the barrel, or from one of the vac hoses. From memory there is no port for a vac line on top of the secondary diaphragm - so I presume its internal, but I'm not sure if its linked to another inlet hole.

I can't seem to find any tech info on the aisin carby to confirm either way.

Your idea of blocking of all the holes except the dizzy advance - have you done this yourself, is it a general practice that everyone does, or is it just an idea?

Does the fuel pre-heater noticably improve cold performance (as the name would suggest!)?

Finally - the other thing I may have got wrong was where the charcoal canister tube connects back to the carby. Where should this go?

Cheers.

[F31N7]

there should be a vacuum diagram sticker on the inside of the bonnet

[Jonny Rochester]

The one vacuum hose to the dizzy will work best, and I have done this many times with older cars that would not otherwise run, and they have missing/broken parts.

But if you follow the original hoses, and understand what they do, and test how they work, then its fine to leave the standard setup also.

The vacuum line to the dizzy may normaly be bypassed by a head activated switch in the coolant thermostate housing. This changes your advance when the motor is hot/cold to help cold start and emissions. Not really needed. Some distributors have a double diaframe. One is for advance, one for retard. You only want one vacuum hose on the advance side, leave the retard one open.

You may have a few vacuum electric switches, controlled by 4th and 5th gear at the gearbox. THis helps to motor run leaner on the highway for ecconomy and emissions. Not needed.

The charcole canister line should run to the base of the carby. There are a few different ports at the base of the carby. The chcarcole one should be pulling some vacuum with the throttle open, but not too much air with the throttle closed. THe motor will run best without it, but you are ment to have it.