Random Backfire

[likeold]

But it is timed perfectly with 4*

[likeold]

Today once the car was hot I pull the throttle and let it run high rpm maybe 1500 or so. She would skip and run a little rough every once in a while. Nothing real serious but would not run completely smooth at the high rpm. At idle it does not skip. I have all new components, wires, plugs, rotor, cap - electronic points. 

[EmTee]

Do you have your sparkplug cover in place?  Are your sparkplug terminals insulated or bare?  Have you checked the coil tower for a crack or carbon tracking?

[EmTee]

2 hours ago, likeold said:

She would skip and run a little rough every once in a while. Nothing real serious but would not run completely smooth at the high rpm.

Try repeating this test in the dark and look for any external arcing.

[likeold]

Okay thanks more things to check.

Yes spark plug wire ends are booted.

Use to mist with a spray bottle back in the day looking for arcing. 

[likeold]

Misted the electrical components last night in the dark and ran at a high rpm and did not see any arcing.

[EmTee]

Well, I'm running out of ideas...

 

Could it be an intermittently sticking valve?  The condenser has been replaced (or eliminated), right?

[garnetkid]

It could very well be the valves may be adjusted to tight.  I found that out years ago when I experienced some backfiring on my 25.  I had adjusted them a little too tight in an attempt to quiet them down. Once I backed them off a little the backfiring stopped.

[likeold]

So I want to put the original points and condenser back in and see what happens. Right now with the electronic set up I have three wires hooked to the coil. The red (on pos) and black (on neg) from the electronics and another wire on pos I assume from the ignition. When I put the points back in I will only have one wire coming from the distributor which I assume goes on positive. What gets hooked to the negative side of the coil?

[Bloo]

On a negative ground Buick, the points/condenser wire from the distributor connects to the negative coil terminal. Voltage from the key connects to the positive coil terminal.

 

When the points close (or the transistor conducts), the points (or the transistor) ground the negative coil terminal through that ground wire we have all been talking about. When the points open (or the transistor stops conducting), the coil fires.

 

The black wire on the module is doing what the points and condenser did. The red is just power for the module.

 

 

Edited September 24, 2022 by Bloo (see edit history)

[likeold]

Yesterday I put the original points and condenser back into the vehicle and adjusted the timing to 4°. The car does run a little better, with less muffled backfire noise seems to be happening more now when I let off the gas. I plan on buying new points and condenser and the correct ground wire and clean up the other wires so everything is new and fresh. Something that came to mind that nobody else has mentioned could I possibly have a weak coil? I think I might buy a coil when I buy the other parts just to try and eliminate that possibility. I know from previous experiences coils can cause many different symptoms.

 

I have been trying to find a six volt tach and dwell meter on eBay and can't really find anything good or at a reasonable price, anybody else seen one for sale someplace?

 

After I finish cleaning up the distributor I do plan on moving on to the valves to check the adjustment. As somebody mentioned perhaps they are too tight. I do notice when I drive by a fence or something that can echo the sound of the car back, it sounds like the exhaust goes puff puff puff puff puff puff which does not sound right to me.

[EmTee]

Do you ever get a 'BANG' out of the exhaust when you let off abruptly, or is it always the muffled 'puff-puff-puff...'?

I tried a clip-on 'hot wire' from the positive battery terminal to the '+' coil terminal to rule-out an ignition switch or ignition wiring problem.

I'll be interested to see what your valve lash measurements are.  Check them cold first, as that's easier and you should be able to see right away if any are too tight...

[likeold]

I Never hear a big bang just a muffled type popping. I Ordered the points condenser and a new coil tonight I want to get the distributor all squared away. After that I will take a look at the valves. If I'm going to check them cold first, how the heck do you turn this engine over? There is only a small space between the crankshaft pulley and the radiator so I can hardly get a wrench in there. What would the go / no go spacing be for the valve lash when cold?

[garnetkid]

you should be able to adjust them running with a cold start. they won't heat up to make much of a difference in the time it takes to make the adjustments.  Do you know if there is much wear in the tappet arm and the push rod end, if there is it will be more difficult to getting it accurate with a feeler guage.  It is best to have a little tappet noise than none at all.

[EmTee]

54 minutes ago, likeold said:

...how the heck do you turn this engine over?

With the plugs removed and a tight fan belt, I was just able to spin mine over using the fan as the 'crank'.  I set the rotor to point at #1 and checked each cylinder in order as I rolled the motor through the firing order.  Record the values and you can use them later when you make the hot adjustments.

 

I still have one (maybe two) lifters that tap when cold, but run quiet when warm.  I'm guessing that may due to wear on the rocker arm tips where they contact the valve stem.  It's on my non-critical 'to-do list'...

[likeold]

Yesterday I installed my new points and condenser and all the new necessary wires in the distributor. Took the car for a ride and she ran no different. So today I am looking at the valves, and before I screw this thing up totally I need to get some clarification. I want to check the valve lash cold just to get an idea of what they're set at. With that said I can barely get a .0012 or .0013 feeler  gauge in most of the valves when it probably should be .0017 or .0018.

 

I turned the engine over and aligned the rotor with cylinder #1 in the distributor and tweaked it to top dead center on the flywheel (which I'm assuming is UDC 1&8 on the flywheel). And then I referenced the document I found on this website, which sounded like it might be pretty easy. But what I'm finding is, if this document is accurate some of my valves are still open even though they should be closed.

[likeold]

Let me take that back, If I have the valves in the right place I'm getting readings from 0 to .0015 cold. (I was looking at the wrong valves) My gosh if I set them all to .0016 it should be a huge improvement, I have not turned the engine over to #8 yet. Please let me know if I'm doing this right before I start adjusting, thanks

[Bloo]

OK Here's the deal, when you are at TDC, two cylinders are at TDC. Only one of them is on the firing stroke. The firing stroke on #1 comes up only on every other crank rotation.

 

The traditional way to do it is to remove the plugs, and as you bump the engine over, look for number 1 to blow your finger off of the hole if you are on the correct "turn". If you are on the wrong turn you have 2 choices. You can run it around one whole turn, or you can start with the "opposite" cylinder in the firing order, judging by the pics that is #8 on this engine.

 

Since this engine has just been running and you know it runs, you can cheat. Just take the distributor cap off (and the spark plugs out so the engine turns easy, but don't lose track of where the wires go). Look at the rotor. If it is pointing at #1 you are good to go. If it is pointing at the opposite (#8 in this case), either run it over another turn or just start adjusting with #8. Check both intake and exhaust valves. Rotate crank about 90%. Watch the distributor rotor and point it at where the next tower would be, about 45% or half what the crank turned. Check that cylinder. Repeat until you have done all eight.

 

Keep doing this, either following the firing order, or just watching which plug wire the rotor will be pointing to next. Keep turning the crank another 90 degrees each time to get to the next cylinder.

 

You can turn an engine over easily on most cars with the spark plugs out, by just sticking it in gear and grabbing the front wheel and rolling the car while you watch the rotor. Higher gears roll easier, but sometimes using reverse and rolling the car backwards can be more convenient if there is a bench in front of you.

 

Edited September 29, 2022 by Bloo (see edit history)

[likeold]

Okay so each time the rotor points at a certain cylinder (cap tower) and the flywheel is it TDC adjust the intake and exhaust for that cylinder, right?

 

Seems the attached document is not accurate at all then????

[Bloo]

It probably isn't incorrect, although over the years I have has less than stellar luck using those type of methods that use less positions of the crank. About half the time I wind up re-doing it the way I posted above.

 

What you want is for each lobe you adjust to be on the base circle of the cam lobe, avoiding any clearance ramps, lobes starting to come in, or whatever. With my method you are adjusting both valves where the cylinder fires. You don't need any precision. Both valves have been closed since the piston was nearly at bottom dead center, and wont try to open again until the piston is way down again. You really can't miss. It's impossible. Best of all you can do it fast because you don't need to be too accurate about crank position, or even remember which valves to adjust. Just follow the rotor.

 

17 minutes ago, likeold said:

Okay so each time the rotor points at a certain cylinder (cap tower) and the flywheel is it TDC adjust the intake and exhaust for that cylinder, right?

 

It is TDC for each cylinder, yes. The flywheel mark will only be at a TDC (UDC) mark while doing 1 and 8 on this engine..... well.... unless it has similar marks for the other cylinders. Just start with 1 or 8, whichever the rotor is pointing at when your TDC(UDC) mark is lined up. After that, follow the rotor.

 

Edited September 29, 2022 by Bloo (see edit history)

[likeold]

Okay follow the the rotor, got it. I'm going to right down the measurements I found with the method I posted then do the adjustments the way you suggest. Will be interested in if they are about the same.

[Rock10]

I'd think hot running is the best.

It's a little messy and takes some practice, but you know you got the right clearance.

 

[Daves1940Buick56S]

What I do is run the engine (or preferably drive) until it is hot. Then pull the valve cover and follow the rotor, adjusting all to a tight 0.017. 0.018 should def be no go. Then put the valve cover back on and run again. The pull the valve cover and check with the engine running. Again a tight 0.017. Repeat until all are good.

 

I know some like to go tighter, like 0.016 or even 0.015, but after stupidly burning the valves on my Ford 289 when I was 19 I like to err on the loose side a bit.

[likeold]

Well I adjusted them all the valves to .0016 cold. Almost every valve was very tight. The car sounds and runs much different. I think all the muffled backfire noises are gone. Now the issue seems lack of power on the top end. Takes a long time to get up to 50 mph and its sluggish. I set the new points with a feeler gauge, cuz I don't have a dwell meter. Now I wonder where should the timing be with the higher octane gas these days? I feel I'm making progress.

[Larry Schramm]

Is the distributor the type that you can move by it's self?  I think it probably is.  If it were mine, I would start the car with a vacuum gauge hooked up to the intake.  Turn the distributor adding in advance until it starts to drop off from maximum. I would then back off the timing to just before you reached maximum vacuum.  This is with the spark lever fully retarded.

 

Go drive the car and see how it preforms.  Is there any spark knock?  If not that is where I would leave it.  This is way that adjusted timing on cars in the 60's & 70's before there was electronic ignition. Never had a problem.  Just my 2cents.

[likeold]

That's pretty much what the book says, I think they even say it's okay to knock a little. I will try that instead of the light. I also have a new coil and might put the electronic points back, but one thing at a time.

[EmTee]

44 minutes ago, likeold said:

Almost every valve was very tight.

I had several that were too tight on mine as well.  I set mine to 0.018" cold as a starting point.  I went back later and checked the hot clearance.  With that information I tweaked the valves cold as necessary to arrive at a 0.015" hot clearance.  In other words, if (for example) I measured 0.016" hot, when I reset the cold clearance I would set that one 0.001" tighter.

 

I have a couple of valves that still tap when cold after adjustment.  I think the issue with those is wear on the valve end of the rocker arm that is bridged by my feeler gauge.  To resolve that I'll either have to reset them using  dial indicator, or just replace the worn rocker arms...

[rodneybeauchamp]

On 9/30/2022 at 9:25 AM, likeold said:

 I set the new points with a feeler gauge, cuz I don't have a dwell meter. Now I wonder where should the timing be with the higher octane gas these days? I feel I'm making progress.

When I timed my ‘38 Buick with 6 Volt system, I used a 12v battery for the power source to set the dwell and timing from a modern timing light. You may need to use a resistor lead on the plug you use as a temporary measure as some don’t like solid copper wires. Great you are getting it sorted!

Rodney 😀😀😀😀😀😀😀😀

[likeold]

Well, I have done everything I can to get this car running well and I think it's all good now. After adjusting the valves hot, I set the carb with the vacuum gauge, put the electronic points back in and adjusted the timing to about 8 degrees advanced. She runs damn good now, no more random back fires or noises. Seems to have pretty good power and idles as smooth as can be, what else can one ask for? A lot was learned during this process, thanks for everyone's help and suggestions, now to move on to the next issue - drive drive drive!

[EmTee]

My experience: the more you drive 'em the better they run!