Topic: Vaccum at idle?

ibshane	-- 02-02-2018 @ 11:23 PM
	So I put a vaccum gauge on my '37 V8/85 and with the idle mixture screws I can not get the vaccum in the "Green Zone" on the guage or even get the needle to steady out! Would the timing be the issue?
ibshane	-- 02-02-2018 @ 11:31 PM
	The video didn't upload.., so below is a picture of the vaccum gauge reading. And keep in mind that the needle is not very steady. It's rapidly jumping back & forth between 12 & 14.
Yokomo99	-- 02-03-2018 @ 4:52 AM
	Your movie worked for me. I just had to wait for it to download. My first question would be where is the timing set. The needle is moving around but not too much. This would indicate a lack of timing as a possible culprit. Is the vacuum advance connected? Be sure to check out my YouTube pages at: https://www.youtube.com/user/MatthewBergin1 https://www.youtube.com/channel/UCJCdOfmXtM8xO9nXeQ-iSQQ This message was edited by Yokomo99 on 2-3-18 @ 4:57 AM
40 Coupe	-- 02-03-2018 @ 5:30 AM
	If the timing was off the reading would still be steady but low. I suggest you look on line for a chart of various vacuum reading and compare your results. The idle mixture screws should be ABOUT 3/4 of one turn out from full closed. minor adjustment should make a big difference. The vacuum gauge should be in the rear vacuum port on the intake manifold, usually used for the vacuum wiper motor. The front port should still be connected to the distributor vacuum brake.
Drbrown	-- 02-03-2018 @ 8:30 AM
	My 59AB engine, which has 35,000 on its rebuild, shows a steady 19 when the carb is adjusted right. A jiggling needle on the gauge often indicates sticking valves or maybe a defective head gasket. Low readings may generally indicate timing off, intake manifold leak or leaky carb gasket. This message was edited by Drbrown on 2-3-18 @ 8:34 AM
TomO	-- 02-03-2018 @ 9:21 AM
	Your idle speed may be too high and the air mixture not adjusted correctly. The idle speed should be 450-500 RPM. Turn the idle mixture screws in until they seat, (do not force them), then back out 3/4 turn. Slow the idle down until the engine starts to stumble and then turn the idle speed screw in about 1/4 turn. Now turn in both of the mixture screws in 1/8 turn at a time, if the vacuum reading increases, turn another 1/8 turn. Keep this up until the reading drops, then back off 1/8 turn. If the vacuum decreases when you make the first adjustment, back out both screws 1/8 turn until the vacuum increases then decreases. The final adjustment should be 1/8 turn from where the vacuum stopped increasing. I would try dribbling some Marvel Mystery Oil down the carburetor to see if that smooths out the idle. Do this with the engine RPM at a fast idle and then adjust the idle. The needle vibration could be caused by a sticky valve, weak valve springs, dirty spark plugs, weak spark, varying timing, or just a worn engine. If you have a dwell meter, connect it to the condenser tab on the coil. he reading should be 36 degrees and steady at all engine speeds. If it is more than 38 degrees, or varies, you should have the distributor serviced. You can check the idle RPM with this set up. If none of the above help, you should perform a compression check. The low readings could be caused by rings that are letting the combustion gases blow by. If your engine does not have the stock camshaft, the readings will be low and there will be some jitter. Tom
shogun1940	-- 02-03-2018 @ 10:52 AM
	A steady reading at idle, and at higher engine speeds indicates a good engine , a steady drop is usually a misfire or a valve not working properly. Low steady readings are usually a vacuum leak or the wrong timing. If you bring the engine up to 1500 rpms and snap it open, the vacuum should jump to 5 inches over what you had at idle this indicates good rings. Waving non lit acetylene torch over the carb should speed up the rpm, then wave it around the intake gaskets and carb base to find a vacuum leak. Good luck
ibshane	-- 02-04-2018 @ 2:09 AM
	Well I cured the shakey needle by about 90% by just holding the gauge in my hand instead of hanging it on the Radiator to Firewall support rod and picking up the engine vibration. Still a slight jitter in the needle.., but very little! So now I have a relatively steady needle, but it's still not in the green zone. Next up.., I will attempt to advance the time a little & see if that gets me anymore vacuum? My rig is 1937 so the distributor is the "Divers Helmet" type. Do I move the timing shaft up or down to advance the timing on these?? I'm thinking that moving the timing shaft down would be like rotating the distributor body clockwise if it rotated, which of course it does not!
39 Ken	-- 02-04-2018 @ 6:22 AM
	Here is another tutorial on the readings and meanings of vacuum gauge. Ken http://www.secondchancegarage.com/public/186.cfm
Ritzy1	-- 02-04-2018 @ 11:12 AM
	Nice resource! Thanks Ken!
ibshane	-- 02-05-2018 @ 12:08 AM
	Yes... Thank you Ken.., I had no idea of just how useful a vacuum gauge could be!
ibshane	-- 02-05-2018 @ 12:08 AM
	Yes... Thank you Ken.., I had no idea of just how useful a vacuum gauge could be!
oldford2	-- 02-05-2018 @ 5:02 AM
	Here is a test procedure for vacuum checking. Click on this Fordbarn thread and go to post #3 https://www.fordbarn.com/forum/showthread.php?t=7143&highlight=vacuum
40 Coupe	-- 02-06-2018 @ 4:12 AM
	Moving the timing screw downward (CW) will advance timing. Each mark on the timing plate is 2 degrees. Is your distributor vacuum brake line connected? Raise the vacuum brake setting all the way out by hand and then screw in back down 1-1/2 turns. If you remove the vacuum brake adjustment (large hex nut) you can add a couple drops of very light oil and get the brake cylinder moving smoothly in it's bore. You will have to disassemble the distributor to free up an sticking mechanical advance weights, if this is the problem.

EFV-8 Club Forum :	https://www.earlyfordv8.org/forum
Topic:	https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=18&Topic=11619