Where does the vacuum advance line go on an old rochestor carb
I have a old rochester carb that I am putting on my old chev, I am trying to stay with an old style and have a 7019014 rochester 4 bbl.
there seems to be no vacuum port on the front of the carb for the distributor vacuum advance. I am trying to stay with the old look and this vacuum line is going to a 56 distributor with a hex diaphragm on the front. where would the vacuum advance line go in.
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Feb 23, 2014 - Uploaded by TheWhatisright Hopcorvetteman
It is a standard 350 Chevy with no real modification. .... missing something or can they be in a different location on my carb ( 81vette rochester quadrojet ). ... There are two fuel mixture adjustments on the rochester Carburetor.
To check the accelerator pump, with the engine off, move the throttle and look down into the top of the carb, You should see fuel squirt from the squirters at the front of the carb, into the venturis..If not, the pump is not working or there isn't enough fuel in the bowl. There is a filter in the fuel inlet of the carb. It's easy to replace but make sure that you don't loose the seal ring and be careful not to cross thread it when putting it back. The adjustment screws for idle mixture were often capped. Likely by now they have been uncovered. Attach your vacuum gauge to any port on the base of the carb or on the manifold itself and adjust them 'till you get the highest possible vacuum reading, then turn each about 1/8 turn back in. To test fuel pressure, attach the gauge to the fuel line with a "t" connector and read running pressure. You could just attach it to the end of the line and crank the engine but that isn't as accurate. You should have from 5-7psi pressure. Good idea to carefully check the fuel line also. It's probably very old and can have a pin hole in it somewhere. There also is another filter on the end of the line inside the tank. The carb itself is an easy rebuild. No "trick stuff" in there. As for the vacuum advance, if it's bad, it won't give you the symptom you are getting. You'd have a slight vacuum leak there and it may be down on fuel mpg but most times you'd never even notice it was bad unless you checked it. Test is simple...put your finger on the rod that goes into the distributor and attach the vacuum hose to the advance. You should feel the rod move.(running). Also check the spark timing. On most chevy smallblocks you can run around 8 degrees advance. The limiting factor is todays fuel....being not as good as it was when the engine was made, sometimes you need to back off on timing to match fuel. Using good fuel, you could power time most smallblocks at 38 degrees total timing at around 2,100 rpm and they should be perfect. (you'd need a programmable timing light or degree tape on the balancer to do that). Best guess??? Likely it's your accelerator pump. If you have an EGR valve on the manifold, make sure that's working as well. Also make sure the two wires that come from under the plate inside the distributor aren't broken or shorting.
Not sure which design carb you have but here's a rule that works for all carbs. Attach the vacuum advance hose to any port coming from the carb baseplate (bottom). If you don't have a free one, you can use a "T" in another line or if there's a fitting on the manifold you could use that as well. Just make sure that the line has full vacuum at idle. (check with a vacuum gauge or just put your finger over it and feel for vacuum) Since it's pretty old, it would be good to put your finger under the advance mechanism when you attach the line (running) and make sure the small rod that goes into the distributor moves when you do that. if it does not, then the advance diaphragm is bad and you will need to replace it. Use small rubber plugs to block off any unused ports. As for the fuel line. You should have a threaded inlet on the fuel bowl. The line attaches there. If you need to make a line, you can get one from any parts house, cut it to length and use rubber fuel hose to join it together with the one already on the fuel pump. When running new line, keep it away from exhaust manifolds, belts and pulleys. Best to put an in-line filter in the hose....that will keep the carb clean. If it's a four barrel (doubtful for that engine) you would need a fuel rail that joins both carb inlets to the single line from the pump. If you have a problem understanding this, just ask and I'll clarify it for you.
Check your ignition timing at 3500 rpm you should have about 40 degrees of advance If not, something is sticking in the distributor, either the vacuum or mechanical advance. This will cause a big reduction in fuel economy. Also, check your tire pressure. The cfm on a rochester is really not important. The primary bores are so small and they are the only thing allowing the mixture in most of the time.
Hookups vary from carb to carb. there are two kinds of vacuum: full signal at all times from the manifold or carb base, and delayed: vacuum that only is present with the throttle either closed or open (depending upon way the carb is internally ported.) I'm fairly certain that vacuum to the t case is full signal. vacuum to the advance is an either or thing. Some engines "like" full vacuum there, others don't. It's easy to tell though...if the engine wants to "lay down" when taking off from a standstill with advance attached one way, attach the other way and see if it makes a difference. Also you can check MPG in different positions and decide what works best if no "off the line" difference is observed. Make sure that the advance diaphragm is good or nothing will work correctly either way.
Injected or carb? If all emissions stuff is removed are you replacing it or just making stuff work? If usst making everything work, you need a hose from carb to vacuum advance on dist (if you have one) You can try putting the line above the throttle plate or below it and see which best suits your needs.. There is a large hose that goes to the brake power booster from the back of the carb (if power brakes, Another line goes to the vacuum system under the dash (makes heater controls operate) That line can go to a fitting on the manifold or any other full time vacuum connection on the carb base. All other connections can be blocked off.
The filter you chg. an inline filter? Is there a filter in the carb.where fuel line connects, some had a brass screan in the carb. you can chk. the fuel pressure without it running, just unhook line at carb. put it into a plastic bottle or something to catch it and have someone turn engine over if it squirts out good thats enought for it to run they only put out about 6 to 8 lbs. of pressure. I don't think that solenoid would keep it from running, when it will run on either. but maybe if you unplug it and see what happens. It suunds to me to be a fuel dilivery problem, either something restricting the flow to carb. or you got a bad pump.