• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Question -- 25D-4 vac hose connection with HIF-4s

Share this page

PAUL161

PAUL161

Great Pumpkin
Silver
Country flag
Offline
The rear carb on my 72 has a vac port on the bottom. I assumed it was for the vac advance on the dizzy. Yet, I have seen them hooked up to the vac manifold also. When I took the engine out originally to overhaul etc etc, this port was plugged. After rebuilding the carbs I assumed that this was the place to draw the vacuum from. Is this the proper place for the vac advance hose? That's where I have it hooked up but get no reading from it at any RPM. How about a clue??? /ubbthreads/images/graemlins/crazyeyes.gif /ubbthreads/images/graemlins/nopity.gif PJ
 
HIF4s get connected to each other via a steel C-shaped tube. A short rubber hose then connects them to the charcoal cannister via the hardline above the heater.

The dizzy advance goes to the manifold.
 
Re: Question -- 25D-4 vac hose connection with HIF

Thanks Scott for that info. Do you know what the port on the bottom of the rear carb is for? I'm not talking about the side ports that go to the canister, but directly on the bottom next to the intake manifold. Only the rear carb has it. It was plugged when I took them off the old engine with a rubber cap. I haven't been able to get any info on it's pupose. I've looked through Haines and found no info. My assumption was it was for the dizzy vac. /ubbthreads/images/graemlins/confused.gif PJ
 
Re: Question -- 25D-4 vac hose connection with HIF

Can you post a photo of said port? Also, what AUD# is on the tag for the carb? I have never heard of an HIF4 using ported vaccuum.
 
Re: Question -- 25D-4 vac hose connection with HIF

Scott, the carbs are on the car and to take a photo I would have to take it off. The tag no. is AUD 493 R. I have another set of AUD 434s and the rear carb in that set has no port on the carb. I think, but not sure, that the 434s had a solid butterfly while the 493s have a run on valve in the butterfly. Don't quote me on that as I'm not positive that's the case. The 493 has a port directly on the bottom towards the rear of the butterfly section on the firewall side. PJ
 
Re: Question -- 25D-4 vac hose connection with HIF

Ok, I know the port in question. Should be located underneath the carb body, pointing to the ground. This is actually manifold vaccuum, as it is ahead of the throttle butterfly.

If this were my car, I'd pinch it off and/or solder it shut and use one of the connections on the manifold instead.
 
Re: Question -- 25D-4 vac hose connection with HIF

Depends on what kind of vacuum cannister he is using. If the cannister is set for manifold vacuum, then use the connection at the manifold. If it's set for ported vacuum then use the connection at the carb.
Personally, I wouldn't pinch off the carb port. Just use a blind cap. There's a bunch of them on the Help! aisle of your local autoparts store. If the next owner wants to use the port, then he doesn't have to repair the port first.
 
Re: Question -- 25D-4 vac hose connection with HIF

I agree with not damaging the carb or changing its configuration. I used a blind cap and plugged it off and then went to the manifold vac port. The vac advance on the dizzy now works like normal. /ubbthreads/images/graemlins/thumbsup.gif /ubbthreads/images/graemlins/thumbsup.gif PJ
 
Back
Top