just when i think it all makes sense...350 SBC...lets say...Fact...im at tdc #1....dist. rotor pointing at #1....wires are in sequence..i have a mallory unilite no vac advance with the optical l.e.d.....the motor starts imediately when i hit the ****on....idle is great...vac***e is 18-20 at idle (which i understand is good with a tunnel ram)..throttle response is great....my issue is..i understand the timing should be 8-12 btdc at idle...but im like 20-22 ..when i retard it, it starts to run like ****...ive tried moving the wires one over in sequence in both directions...and ive moved the dist. one tooth forward of #1 and also the other direction.....it either stays the same, gets worse or wont start..............ok heres the kicker..why i tried this i havent a clue...but i moved the timing light plug lead around and obviously got different timing reading...but #8 was dead on 8 deg btdc which is just one over from #1.......what am i missing...could this be a cam timing thing....many advanced (haha) thanks
Is the vac advance hooked up while you are checking the timing? It shouldnt be. Also the cam size is a big factor.
Are you using a va*** port thats above the throttleplate? You are supposed to do that.... Start without the va*** connected, it should work OK before you connetct the va***. The va*** is "only" there for milage.ö
According to your post you have no vaccuum advance, so we can rule that out. What are your cam specs? I would verify that the timing marks are correct by using a positive stop in cylinder #1 (an old spark plug shell tapped for a bolt sticking into the combustion chamber) and rotate it gently in one direction until it stops, mark that on the balancer at zero, rotate it the other way until it stops and mark the balancer at zero. now measure halfway between those marks and you have Top Dead Centre. You need to verfiy this first, and then check your timing again.
What's your idle speed? 18"-20" vacuum is good for any stock or mildly cammed engine. Big cams - 280* advertised duration or so - usually idle 10" - 12". Once they come off idle - with idle rpm being 550-600 rpm - the engine unloaded vacuum levels will rise to 18"-20" or so. (Engine unloaded means 1500-2000 rpm with the car sitting in the driveway.) Do you have an ignition amplifier box? (MSD ETC.) What kind of timing light are you using? Some of the dial-back lights will show timing off by as much as 20*. Try a standard timing light and see what you get. A cam that is retarded will show very low vacuum levels, around 10" vacuum at idle one tooth retarded. Don't know what an overly advanced cam will show, but I'm guessing it would be low vacuum as well. Once you get your problems ironed out, get yourself a vacuum advance distributor otherwise the engine will overheat in traffic at slow speeds....
I would argue this point with you. Hot rods and the like are far better running vacuum advance sourced to manifold vacuum. As you noted, it helps mileage, but it also gives the lean idle mixture time to burn. Selecting ported vacuum to the vacuum advance system results in overheating and that's due to ported vacuum is zero at idle. GM developed the ported vacuum system to make engines run hot at low speed and added a thermostatically controlled vacuum switch to swap vacuum sources to manifold vacuum once a specific temperature is reached and then when the engine cools down, switches it back to ported. Check some of the recent overheating/vacuum advance threads to see what works and what doesn't.
I'm going to say that you have a ton of variables that you are not thinking about. Lets start with your timming pointer that may or may not be accurate. Now onto your mechanicle advance that is adjustable on the Mallory. Even though it may be right @ 12 degrees advance when it isn't running if your advance is adjusted to advance quicker it is going to show more advance @ idle. Now ask yourself what your idle speed is? On a stock motor you should be running @ 600 to 700 RPM but the fact is that your are running a tunnel ram and I have no idea what else. The truth is what you really need to be concerned about is your total advance. Which if memory recalls should be around 32 degrees. If it starts and runs good @ 20-22 then don't sweat it. Set it where it runs the best and forget about it.
MOOSE!!! Long time no see! We need to get together sometime. I want to hear that thing run. Is your wife still looking for an old pickup? I'm still trying to sell my '67 Ford F100. Hope to talk to you soon. Good luck.
Well Im not a Chebby guy. And what i tried to say was to establish a point when the engine is running good, I did not mean that you should run without the va*** in the long run. And i only repeteted what the MSD ready to run Dizzy instructuctions says. "The vacuum line should be routed to a ported vacuum outlet above the throttle plates." Taken under the heading of Timming Functions http://www.msdignition.com/uploadedFiles/MSDIgnitioncom/Products/distributors/8360_instructions.pdf Sio maybe you should enlighten them ;-) I have driven my 8BA flatheat thousands of miles without the va*** connected , without any heating or other problems. Except maybe a bit extra gas used. The reason for this is when i connected the va*** directly to the manifold i got 15-20 degree of advance at idle instead of the recommended 4 degrees. And it does not run good at all at idle, and i have not found a ported va*** Stromberg carb (This is not tru since the French 81 model have them, but i dont have any of them). And im not confusing it with the Ford Holley va*** port that give the difference between over and under the throttle plate, and should not me used on anything then the original Ford Distributor; The reason for the mechanical advance and the va*** advance, is to give the gas time to burn to the maximum at TDC. When you rev up an engine you get shorter and shorter time for the gas to burn , so you advance the ignition point with the mechanical advance system. When you are running part throttle the mix get leaner and it takes longer for it to burn so more advanced is added thru the va***system. When you are idling the mixture is fairly stable so a fixed ignition point should work. Regardless if you have valvecovers or what the name is on them
A fixed ignition setting will work, but not to the optimum. With no advance at idle and low speeds the engine will run hot. Flatheads are another story and I haven't had any recent experience with them so I won't comment there.
According to google so is a Thermostatic vacuum switch "A temperature sensitive switch which allows spark advance when engine idles for long periods" And i guess it has something to do with exhaust emissions. And since i dont work with so new cars ive never heard of one until know. And I think this prove my theory. http://en.allexperts.com/q/Cl***ic-Antique-Car-2542/Thermostatic-vacuum-switch.htm "Question 1970 Olds delta 88 455. How can I tell if the thermostatic vacuum switch is operational, and if so, is it really needed? I recently got the air conditioner working, and since have experienced overheating, the vacuum switch has three tubing/hose outlets with nothing hooked to them, I do have a shop manual for this car, but it doesn't state how to check the switch. thanks Answer Kevin, the thermostatic vacuum switch that you have is an attempt by the car makers to meet emissions standards. Originally the switch interrupted the vacuum to the distributor vacuum advance and advanced or retarded ignition timing relative to engine temperature. This did reduce tail pipe emissions but under certain conditions reduced engines power and also increased fuel consumption. Most of these switches were soon byp***ed in an attempt to get the engine to run better with better fuel economy. It does not control engine temperature. If you started having engine overheating after getting the air conditioning working you might want to check the fan clutch on the cooling fan and make sure that the radiator is not partially plugged. Remember that the heat that you remove from inside the car is added to the air flow coming into the radiator. Brad" For people interrested in Ignition and timming this is good reading. http://www.btc-bci.com/~billben/navarro.htm And remember we are talking about physical laws here, and not what name its on the valvcovers. And there is millions of bikes out there without thermostatic vacuum switch, acually without any va*** adcvance at all. And they dont overheat. This not saying if an engine setup is designed to use a thermostatic vacuum switch and you remove it you may need to do something else to get it running OK.
Nothing like highjacking Moose's thread, but.... Here are the basics for me. Hundred degree F. day. 462" Buick running ported vacuum to the vacuum advance can. About five minutes of idling on an engine that was fully warmed up (182*) to start with and the temp gauge is running at 220* F. when slow traffic is encountered. With a 7# cap it will release at 234* F. When the engine hits 220* it's on the edge of thermal runaway and the point where I shut things down. Swapping the vacuum advance source to manifold vacuum with everything else the same, it will gain 7-8* after five minutes and settle in there. About 190* and if it's a long time it may go to 192-198* if the car has come in off the highway and entered slow traffic right away. An easy fix that works for me and the best part is, it doesn't cost anything. Along these same lines I'm watching my pal spend over $500. for a new radiator, bigger fan and making some shrouds to cure his overheating problem. All he really needs is a $20. junkyard distributor with a good vacuum advance can and toss the big time race-o distributor that's in there now. He can be a hardhead at times. I offered to demonstrate what would happen if I swapped my roadster to no vacuum advance at idle and then to manifold vacuum. He demurred, a guy thing I think. He doesn't like to lose arguments and if he wants to spend over five bills on an easy to fix problem, that's his right. I am curious to see what he does when the new stuff doesn't cut it.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I shouldn't be any problem to check the thermostatic vacuum switch. They are labeled as to what goes where and the checking can be done with a vacuum gauge (easiest) or timing light. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ I've read the Navarro treatise on advance mechanisms and methods for flatheads. An excellent read and a whole other ball game for OHV guys swapping to flatheads. I understand that more than a few guys have set up an SBC distributor on a flathead. Strikes me as a good move. Less complex than a flathead setup and probably better performance overall....
If you know that everything is correct I wouldn't worry about a timing light. Set it to where it runs it's best and still starts when hot. I not saying that I'm right but I do know that with my tunnelram , cam and ignition combo, that's what has worked best for me. Set it and forget it then set you carbs and have fun
man...not trying to be funny...but i have learned a **** load from you guys in this post.....and how ironic that once again i have a case of the WTF.....one of you guys hit it right on the head....ok fellas dont get mad at me..this is my first build....and i seem to have the wrong balancer on the engine, its for a sbc, but i pulled it off..took it to the store and it has 13 deg. difference from woodruff to tdc mark than the one off the shelf...apparently 2 bolt mains and 4's are different...mine being 4...anyway sorry for the trouble and many thanks ....i learned alot today...Moose
So I guess they are telling you that you can not run their distributor with the vacuum advance on a Rochester 3 deuce set up. Unless they can tell you where to drill the hole into the carb body to get the proper ported signal. There is no port for "ported vacuum" on a Rochester carb that came with the factory vacuum advance distributor. The GM factory distributors used manifold vacuum. You don't have to run a vacuum advance but I don't understand why you would not want to for a street engine. It's not like it hurts performance. I would think that running a vacuum advance distributor without the vacuum hooked up would hurt performance unless you modified the mechanical advance to make up for it being missing. Here is some more interesting reading on the subject. Someone should tell them that vacuum is expressed in inches of mercury and not LBS
There are at least three different Chevy balancers with the timing marks in a different place relative to the woodruff key. On top of that they are known to slip with age throwing the marks even further off.
this is the best idea and also after marking you true top dead center on the crank pulley,also mark the pulley at 32 degrees and then set your timing to this mark with all advance in,should be all in by 2500.rev it higher to be sure timeing is all in after setting at 32 degrees.now you can adjust timing up or down a couple of degrees if you get pinging or hard starting but you will be in the ballpark.
Here is one way I set up my car.It may not be correct but the car ran.Start up car rotate distributor until highest va***n is reached back off 1 inch of va***n .Or 2 Depends on starter working.Turn idle screw down when you do this .This worked on my motor without a timing pointer. All after markets are off.
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