VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt Weak spark

What does it mean to have a weak spark? When checking for spark I get a yellowish spark. It is not a snapping blue spark like I seen in the past. Its also makeing the engine hard to start, and every once in a while I get a slight back fire. Any suggestions?

I would start by checking your points. If the are pitted or burnt, time for a new set. The factory calls for .018" California Bills speed manual suggests .012" I have mine gapped to .012" With no complaints at all. Secondly, I don't know where you checked your spark. If it was at the spark plugs, I would definatly check the gap. If it is gapped to far, you will expirience weaker thinner spark, per Chiltons General handbook. And if that is no dice, check your coil. If it looks like it is leaking oil, its time to go. I don't know what the ohms/resistance is supposed to be, but I would imagine it shouldn't be more that .010 uF. Good luck.

Cheif, one of your symptoms the ocassional backfire and the weak yellowis spark indicates you may have a bad distributor cap, with some arcing inside. I would say to consider the ignition system as needing a tuneup.
parts you should replace :
Sparkplugs
Distributor cap
Distributor rotor
breaker points
condenser and any frayed or oil soaked plug wires and the high tension coil wire
with the problems you are having I would swap out the coil with a new one. Once you have done the complete ignition tune up you should have a good reliable ignition. just a word of caution. learn to check the condenser and coil electrically before installing them. I have found bad condensers and coils new out of the box.

Clean and regap or replace the sparkplugs you will need to regap new sparkplugs out of the box. consider the age and condition of the plug wires (raise the hood on a dark night and see if there is arcing between the high tension sparkplug wires). Replace the points and condenser, being sure the lead wires and the block insulator in the cap are clean and in good condition, check the distributor shaft and ignition point cam for sideplay and replace the old rotor with the new one. Also set the timing with a timing light and check the dwell, Chevrolet shop manuals don't consider using a dwell meter. i use one as a backup of my setting the point gap. Also do a physical check of the battery cables and terminals which will require you to remove the cables from the battery and clean the cables and terminals with a brush type cleaner. New 00 gauge or larger battery cables from a farm tractor supply store are a good idea for a 6 volt system if the cables are worn, corroded or frayed. This should help the starter and the charging system.
You may already know all this information but I just hope that someone that is new to the old car hobby may benefit from the info.

Stylemaster47, just tryin to get this straight, your checking resistance but getting a reading for capacitance when what you really want is inductance???
“I don't know what the ohms/resistance is supposed to be, but I would imagine it shouldn't be more that .010 uF.”

Mack, I’m interested in how you are checking your condensers and coils?
I have a bridge on the test bench to check capacitance and inductance but have never been able to find any values for the automotive electrical components. Do you know of a source for them???
“and just a word of caution. learn to check the condenser and coil electrically before installing them. I have found bad condensers and coils new out of the box.”

Denny Graham
Sandwich, IL

The correct point setting for a 1936 is About .021" for new points and .018" for used.The reason that new have a wider gap is to allow for a slight bit of wear on the rubbing block. A very light film of grease should be applied to the cam the points ride on. Do not set to .012" as it will cause rapid burning of the points.Setting used points with a feeler gauge can be a little "tricky" if the contacts have a "pit" on one side.
The 1936 coil will not leak oil as the original coil was not oil filled. If it has a much later replacement coil it could be oil filled.
I would advise that you always carry a spare fresh condenser with you. The condenser used in your 1936 is very available as its the same as a 1974 6 Cyl. condenser.
I would strongly recommend keeping a spare condenser,points,coil,fuel pump,dist, cap and rotor for emergencies.
For your present problem I would began by replacing the points and condenser and seeing if there is any improvement.I am sure that you will not have all the equipment mentioned for testing the components and they are not expensive items. The coil is also a very probable item.All lead wires (coil to dist.) possible cause.contacts in cap another .

The correct point setting for a 1936 is About .021" for new points and .018" for used.The reason that new have a wider gap is to allow for a slight bit of wear on the rubbing block. A very light film of grease should be applied to the cam the points ride on. Do not set to .012" as it will cause rapid burning of the points.Setting used points with a feeler gauge can be a little "tricky" if the contacts have a "pit" on one side.
The 1936 coil will not leak oil as the original coil was not oil filled. If it has a much later replacement coil it could be oil filled.
I would advise that you always carry a spare fresh condenser with you. The condenser used in your 1936 is very available as its the same as a 1974 6 Cyl. condenser.
I would strongly recommend keeping a spare condenser,points,coil,fuel pump,dist, cap and rotor for emergencies.
For your present problem I would began by replacing the points and condenser and seeing if there is any improvement.I am sure that you will not have all the equipment mentioned for testing the components and they are not expensive items. The coil is also a very probable item.All lead wires (coil to dist.) possible cause.contacts in cap another .

I have also found coils that tested bad but installed them anyway. Ran one (original 29-32) for over 15 years without any spark problems. I removed it when I regapped the plugs to 0.040" because I was sure it would get fried with the extra resistance. So guess you can't rely on the testers as the final word. It maybe that the modern criteria is too high for the older coils and ignition systems with low compression, solid wires and narrower gaps.

Sorry about that, What I meant was ohms. I don't have the symbol for either of those on my computer, and my tired brain substituted uF for ohm horseshoe. I'll just stick to washing windshields from now on...

Denny, I check condensers with a 260 Simpson analog multimeter. On the highest ohm scale I check for leakage, you should get a capacitance kick. I then quickly switch the polarity with my lead wires and get another capacitance kick in the opposite direction, and the meter falls back to the infinity end of the scale. In a condenser no leakage is acceptable, the condenser will be considered to be "shorted" if the needle fails to fall back to infinity, and if there is no capacitance kick the condenser will be considered to be "open" either "shorted" or "open" is a bad condenser. You must have a good quality analog meter with at least a 100K ohm scale to do this check. (I don't know if a digitual multimeter can be used to check for a capacintance kick)It works because the meter puts around 25 to 30 volts across the resistor or condenser being tested on the high ohms scale, this voltage gives the capacintance kick. You can check a condenser bu holding the case with an insulated glove and touching the lead to a sparkplug lead on a running engine, then when the lead is shorted back to the condenser case you will get a good spark, you may also hold the condenser in your bare hand, and if you get a shock with the lead wire on the sparkplug the condenser is shorted, and if you touch the lead wire and hold the case in the other hand, a good condenser will give you a good shock.

I would not do this sparkplug testing of condensers if you have a pacemaker or can't take a high voltage shock!

I check the coils for resistance and leakage compareing the readings of the secondaries and primary values to a coil that i know is good, Like Chipper i have checked some coils that would be considered to have bad numbers that work, likewise coils with better than average readings perform poorly at times. I have around 8 or 10 coils of several differecne brands andvintages. It surprised me to find that several coils marked 12 volt check out with restivity readings very close to those marked 6 volts. The only really good testing I have been satisfied with is to switch the coils out on an engine that is running poorly because of a weak spark and see if there is any improvement.

After all, I consider my self to be a 'Shadetree mechanic" regardless of all the tools and equipment I use, I never worked a day in a real Chevrolet Dealers shop........

Thanks Guys for all of your advice. I will put it to good use this weekend, and Ill will let you know how it turned out. also If anyone out there has a spare original type coil for a 1936 Master that they wouldn't mind getting rid of please let me know, as Iam having troubble finding one. Thanks again.

Ken

I also use a analog VOM (just like the Simpson but cheaper) to check coils and condensors. Have a spark gap tester that I have used a few timea. It has this adjustible screw to set the gap. To test set the gap on the scale and see if the coil or condensor will produce a spark to jump between the poles. I know it is around here some where but those darn gremlins have hid it. It will be in front of my face when they decide to end the game and I am no longer looking for it. Sure is a problem when you have so much stuff that you can find it. What ever it is?

Been there, done that. Same results.

I have a new one.Its a genuine Delco of the later type oil filled .It will look slightly different from the original but is all that has been available since 1947.Your present Eletrolock will fit onto it OK.

Ok Mack, thanks.
I think I might just test a few new condensers on the bridge and see just what the actual capacitance is for a fresh condenser. Being a lo-voltage component I would bet that the dielectric is just paper, if I had an old one laying round I’d perform and autopsy. Paper capacitors are notorious for having a short shelf life. The dielectric absorbs moisture and then the foil corrodes causing a failure. Some of the new DVM’s like my Wavetek have a capacitance test function that is fairly accurate. Also, the Simpson 260 on the highest resistance scale puts all five batteries in series and delivers around 7.5v max at the leads.

Since the coil is, subject to high voltage I would think that one of the problems that probably causes them to fail is a breakdown of the insulation of the secondary coil. I suppose the only really accurate way to test one would be with a hi-pot tester. A continuity test could show that the windings are good but would not tell you if there was any arcing over. If the coil wire didn’t burn thru on the first failure of the insulation this could cause the spark to be weak, the wire would eventually fail and cause a complete lack of spark.

Stylemaster47, I know, you know, I’s just keepin’ ya on your toes. I don’t think there is an extended ACCII code for the Greek letter Omega. The charts show it as 234 but I have never been able to get any of the Greek alphabet to work on any of my confusers.

Denny Graham
Sandwich, IL

Denny, you are correct about the output voltage on the Simpson 260 meter, also it only has a 10K Ohms scale.

The best meter for checking condenser leakage for me is the Triplett 630A it is the one that puts out the higher voltage of around 25-30 volts, and it does have a 100K ohms scale.

By the way, the last time I had to have the Triplett repaired it cost $270 plus shipping, I have since then quit hauling it around in the toolbox. That is where the old Simpson 260 roll top is now. along with a few Harbor Freight $4.00 ones that are my loaner-outers. I need to see if they are any good for condenser testing, I doubt if they are. That will be added to my to do list.

Mack, bout the only ones that check capacitance run around a hunddred bucks or more. The old capacitor testers always come up on ebay. Most you can usually get for $10 to $20 and they are more than adiquate for testing an automotive capacitor/condenser accuratly.
Denny Graham

Denny,I have a rack full of multimeters, O-scopes and even an operating Heathkit Ignition 10-20 analyser scope with al the leads I have collected these for the last 40 years and they come in handy and usually only use the old Simpson 260 and a dwell meter Tachometer on the cars.
I like the Triplett 630A and the O-scopes for checking out some old special analog electronic projects, Acoustic Velocity measureing devices, Radiation detection monitors, Ratio detectors, FM, pulse modulation and multichannel transmission systems. Many of them run on 400 cycle AC 400 volt power supplys. It is something I like and make a little pocket change with. I threaten to junk it all out when I have a unit go down and I can't find good parts replacement for it.

Well there ya go, of course not knowing you I was unaware that you were into electronics that deeply. I got into old electronics stuff about 15-16 years ago and ended up with my entire 40x42 foot building jammed full. 300 tube radios, 25,000 tubes a full set of Riders and Sams. I like collecting and restoring the old test equipment also. I think I have a Triplet 630 round here somewhere and I might be wrong but I thought they had one of those weird oval shaped 15v batteries with contacts on the opposite ends.
I think ignition components are often approached as though there were some black magic associated with them. In reality coils are coils and condensers are simply capacitors and they suffer from the exact same problems in an automobile as they do in an old radio.
Interesting subject, hope it helps out some of those guys that haven't dabbled with electronics in trouble shooting their ignition problems.
Denny Graham
Sandwich, IL

Yeah, I agree, I collected the test equiptment because I worked on a lot of analog stuff relating to oil well wireline logging and some of the other associated stuff. I feel that many times I go too deeple into the automotive stuff when I forget that the usual hobbiest has a shop manual and maybe a test light or maybe a pocket Multimeter, but then the next guy has retired from NASA's space program. He wants to talk in Farradays? Faradays? Amps, Micro amps and multichannel tracking. Then we get the Universary Profesor with a DR. in English Grammer that pays more attention to my spelling and syntax than the content, I guess it is good that we have all kinds here.

Ok JYD, how do YOU spell Farradays?

Macky Wacky: You should know how to spell the word since you are the professional technical writer here and your grammar and spelling should be perfect.

Gentlemen, great discussion on the technical aspects of ignition testing but it would surely scare off those with out a technical back ground. And for the price of new condesers at swap meets (.50 to $1.00) you can replace a lot of condesers for the price of those fancy testers. But I must confess to having a small shelf full of vintage auto testing equipment as well. Find it a lot more comfortable to test vintage ignitions using this equipment than the old lick the fingers and touch the wire metheod. I do have a question for Mr Mack or Denny. My old green tube periscope type (branded Champion)ignition scope is malfuntioning. I can no longer get my ignision trace to spread. The trace just stacks up to the L. side of the scope. Any hints to were to look for a probable cause would be appriciated.

That means to me that the beam isn't sweeping do you have a selectot swithh that spreads the pulses, or has a different time? In my Tektronics scopes the ceramic insulation boards often get dirty and arc the high voltage I have had some luck scrubbing them out unless the ceramic is cracked.

Post the model and make with the serial number and I will see if I can find a schematic and circuit diagrams here or on the internet and maybe I can pick a couple of items to look at.

Evening Mr Mack. My scope is a PLug-Scope Model 2000. Manufactured in Toronto. Don't have the year of manufacture but it automaticly adjusts for 6 or 12 V systems. To spread the trace there is a dial that you turn to spread the trace out. Haven't opened it up but I'll bet its either a variable resistor or potentiometer. THe traces are diffinatly there you can see the differances between the curves so I'm pretty sure the scope is creating trace patterns for each plug. I don't know if you get over to the old MSN site much, but I posted some picks of another old wrecker find. THanks

hey , Ron, Eh! Yes I check in there ever so often, I like the pics of those wrecker yards. I don't know your scope or how complex it is I'll see what I can come up with. Maybe some of the guys I worked with that have the Northern Exposure stuff will help, if I can catch them away from the cow pasture pool field. Don't know if can read a schematic in French though.

Mr Mack, THanks. I'm sure there is nothing exotic as far as electrcal inside. Just the finer points of Electronic diagnostics are beyond my training or experiance.