Distributor Vacuum
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inkpot
SILVER Star
Correct. What you are looking for is Ported Vacuum. Early 70s 40 series carbs had it near the front right corner of the carb IIRC. If your running an aftermarket unit, then you will have to search it out. John
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Okay- it's got a Motorcraft carb. Not a lot of ports on it... I guess the process would be to hook up a vac gauge and bring the revs up?
Thanks for the responses. I do have a port on the side of this carb that is "dead" at idle, but I haven't tested it further.
Thanks for the responses. I do have a port on the side of this carb that is "dead" at idle, but I haven't tested it further.
Pics??
Very likely candidate. Put a gauge on it.
Chamba
Too short. Too long. Just right: the 43
But this also depends on the dizzy. I have a GM HEI which requires that the vac advance be hooked to direct manifold vacuum.
Contrary to an earlier opinion, ported vacuum is zero at idle. Manifold vacuum is high at idle to part throttle, which is what you want in a vacuum advance distributor. The only reason to go to the carburetor port is emissions. I just "experimented" with switching my 1970 non-USA Aisan 1bbl from ported to manifold and immediately noticed improved starting, idle and low speed/hill performance. It isn't like a turbocharger, but noticeable improvement.
"Manifold vacuum is high at idle to part throttle, which is what you want in a vacuum advance distributor. The only reason to go to the carburetor port is emissions. I just "experimented" with switching my 1970 non-USA Aisan 1bbl from ported to manifold and immediately noticed improved starting, idle and low speed/hill performance"
Ugh, no, you are incorrect. If you come off a high vacuum port at idle, your vacuum advance will be fully advanced and, assuming your distributor timing is set correctly, you will be WAY too advanced while the engine is cranking. Not to mention the massive pinging you'll get when all the mechanical advance kicks in at high rpms. If your performance improved using manifold vacuum, then your dizzy timing must have been extremely retarded to start with.
Ugh, no, you are incorrect. If you come off a high vacuum port at idle, your vacuum advance will be fully advanced and, assuming your distributor timing is set correctly, you will be WAY too advanced while the engine is cranking. Not to mention the massive pinging you'll get when all the mechanical advance kicks in at high rpms. If your performance improved using manifold vacuum, then your dizzy timing must have been extremely retarded to start with.
Hate to hi-jack, but would a 1978 be vacumn or mechanical advance?
Doug, I did a lot of research here as well as on the net and 99% of the advice was to go straight to the intake manifold. I have not experienced any of the difficulties you pointed out. It quite simply has been one of the best things I have done to this old rig. I was unable to find a dwell meter or timing light down here and have both coming from the USA at the end of the month. If I see something untoward with regards to the timing I'll let you know.
I have some questions for you guys since your posts started me thinking about all this. There are vacuum advance, and vacuum retard distributors, and I have never really spent any time thinking out the difference between the two.
Toyota used both advance and retard. Weren't the retard dissy's earlier, and the advance later? What year did Toyota make the change?
If you had a vacuum retard dissy and hooked the dissy vacuum to manifold vacuum, would this increase the retard of the timing at an idle? Just wondering if this might be what makes the difference between what DougAustinTx and cuencanolenny are saying?
Don
Toyota used both advance and retard. Weren't the retard dissy's earlier, and the advance later? What year did Toyota make the change?
If you had a vacuum retard dissy and hooked the dissy vacuum to manifold vacuum, would this increase the retard of the timing at an idle? Just wondering if this might be what makes the difference between what DougAustinTx and cuencanolenny are saying?
Don
I would like to see the sources of the information you found in your research. I doubt anyone on this board who has built engines would recommend going to the manifold for dizzy vacuum. Now, in answer to Handcannon's question, it is theoretically possible that running the vacuum tubing from the manifold to the RETARD port on the dizzy (if you have a retard port) might make the engine run better if the dizzy timing had been advanced way over specs. The easy way to verify which port on the dizzy does what, is to remove the dizzy cap, and the dust shield, insert the end of the vacuum advance line into your mouth and suck a vacuum. If the dizzy baseplate moves counter-clockwise you are on the advance port. If the baseplate moves clockwise, you are on the retard port.
Doug, just entering vacuum advance did the trick. I'll try later and see what I can dig up and post.
Regarding Handcannon's request, good question. I have read the FSM and know that I have this adjustment on the distributor for octane setting which advances or retards the distributor. Whether it is done by vacuum in operation I cannot say. I know that the vacuum advance is much smaller than the mechanical advance portion that takes over as rpm's come up which occurs at the same time the vacuum falls off to achieve the balance required for smooth operation. When I bought the MAF 6-1 header they offered a deal on a new distributor for $75 vs a normal $125. So I bought it. Haven't installed either yet. I had the header sent to Seattle for ceramic coating along with a good used, cleaned intake manifold. At some point I will also obtain a 2bbl Aisan from Mark's Off Road and fit this all up. The replacement distributor does not have the octane setting adjustment, just vacuum and mechanical advance as well as points. May swap that out for a Pertronix. Not a major issue, I don't mind the points and they are so easy to service up here in the mountains whereas I guess I would have to have two Pertronix in the event there was a problem. It is pretty remote here in the Andes and not a lot of stuff is available for these old rigs. Folks say you see them all over the place, I can count on one hand the number I see.
Merry Christmas to you all.
http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm
Regarding Handcannon's request, good question. I have read the FSM and know that I have this adjustment on the distributor for octane setting which advances or retards the distributor. Whether it is done by vacuum in operation I cannot say. I know that the vacuum advance is much smaller than the mechanical advance portion that takes over as rpm's come up which occurs at the same time the vacuum falls off to achieve the balance required for smooth operation. When I bought the MAF 6-1 header they offered a deal on a new distributor for $75 vs a normal $125. So I bought it. Haven't installed either yet. I had the header sent to Seattle for ceramic coating along with a good used, cleaned intake manifold. At some point I will also obtain a 2bbl Aisan from Mark's Off Road and fit this all up. The replacement distributor does not have the octane setting adjustment, just vacuum and mechanical advance as well as points. May swap that out for a Pertronix. Not a major issue, I don't mind the points and they are so easy to service up here in the mountains whereas I guess I would have to have two Pertronix in the event there was a problem. It is pretty remote here in the Andes and not a lot of stuff is available for these old rigs. Folks say you see them all over the place, I can count on one hand the number I see.
Merry Christmas to you all.
http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm
My vehicle has the manual choke with a solenoid that is supposed to keep it from running on after turning off the key. I quickly found that if the solenoid isn't connected the vehicle will not run. I don't have any emissions requirements on this vehicle here in Ecuador. However, I would not have had a requirement in Washington State either due to the age.
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1978 USA is the only year that is both vacuum advance & vac retard. There are 2 fittings on the vac can. The closest to distributor is retard, the one on the outer end of can is advance.
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For US market:
E-1968 are vacuum advance
69-mid 76 vac retard
77 vac advance
78 vac advance/retard
79-87 daul vac advance
For ROW:
E-200something vac advance.
Yes. It would cause the engine to start, but as soon as it was running, the vac retard would pull 20 degrees of timing out, causing the engine to barely run.
OTOH, if vac advance is connected to manifold vac, the result is an engine that starts, then revs up because it just added 20 deg of timing at idle.
Jim, I am not experiencing that condition at all. If I pull the hose off the distributor there is actually a very slight change in idle speed, barely perceptible to the ear. As I have said earlier, this change to manifold vacuum is quite simply the best thing I have done to this old beast. There are hills that required stopping and shifting into 1st that can now be pulled in 2nd. It is not a "major" improvement, but it is a low speed drivability improvement. This engine, of unknown mileage, does not burn oil, doesn't smoke, but it is really down on power in my opinion. But since I have never driven another LC I have no way of knowing if this is typical or not. It cruises fine on the highway, down here I rarely go over 50 mph, but it will run 60 with no problem, but then you hit a hill and you better be paying attention because if you aren't into the gas hard early it will bog pretty quickly. Granted, I am 8,300 ft, but it is weak.
Lenny, with due respect, your experiment is not very controlled and therefore not very useful. You are taking a LC with unknown timing settings (you admittedly don't own a timing light or dwell meter) and unknown equipment and you make a modification that results in your vehicle appearing to run better. The only valid conclusion you can come to from that test is that YOUR vehicle appears to run better. If you can verify the timing settings and the carb and dissy you are running, then your experiment might be meaningful to someone other than you.
