backfiring around 2500rpm

Now that I have put the 4th starter on (new no more rebuilds!) I have been getting a very inconsistent backfire around 2500 rpm.
I checked the distributor to make sure I didn't loosen it up with messing with the starter.
The engine runs good the rest of the time and doesn't do it at any particular time like accel or decel just when it wants to warm or cold but it seems to be always around 2500 when I look down.

I have about 400 miles on the engine since the rebuild and didn't have this issue until i put on the last starter a week ago. I have a new distributor, coil, everything... ( I was holding out on the alternator, but it finally died too)

Weber 38DGES, timing is about 15 and vacuum works with no detected leaks. Plugs look good.

I've tried to adjust the carb some, both ways but it doesn't seem to make a difference on the backfire. And no I cant make it backfire it just does when it wants to.


What else can I look for?

Thanks!

Marc,

You have points? If so, i would closely inspect the set-up. Make sure everything is tight and in particular the little gound wire is actually doing its job in there. They fray and act intermittantly very easily.

Re-gap and then check the gap after a run. Points can wear quickly; I've had them go south in a few miles...speaking of the plastic piece that rides the cam. Are you sure about the condensor? Another weak point but one that would be evidenced by lots of contact point wear...pits and burns...use a maginifying glass.

Will it run OK above 2500? Or is this the top?

I doubt that it's fuel related. What's the dizzy cap look like underneath? Have you tried an new one?

Others here will have more ideas...hang in there. The last time I had one of these problems it was solved with installing electronics....it was a complete mystery solved.

Dan

BTW, are the valves adjusted according to specs?

Hi Marc,

I am running a DGES also but my timing is set at 30dgs @900 RPMs, I was instructed to start at 25dgs and advace it by 5 dgs till I got a ping then retard it by 3dgs.

Cheers,
Larry

Hi Marc,

I have DGES38's also but I have my timing set @30dgs @900 RPM's. My instuctions from Brit-Tek were to set the timing to start @25dgs and if I did not get any pinging to advance it by 5dgs each time till I got it to ping, then retard it 3dgs and I should be right on the money.

Cheers,
Larry

I am using points and visually it all looks OK but I am not sure what to look for other then obvious wear or burning. This is a new distributor and cap and wires. I was thinking of going electronic with a Crane but I want to figure this out before I start replacing everything.

I have no other issues running the RPM up to what ever.

You mention a ground wire? in the distro? I will look again tonight but I think everything is pretty secure. The gap is supposed to be .0014 when open, correct?

Try .015 mate

I try to set gaps at .016". That may be part of the issue.

What kind of backfire are we talking about? Descibe as best you can what happens. A loud bang? More of a popping with a surging feel?

If its ignition/timing related, advancing the timing should eliminate the problem. Try a higher setting if you can (18-20 BTDC?) as long as there is no pinging taking place. It may be as simple as your timing marks being incorrect!

That could be it right there! .0014 is a wee bit small!

I havent checked that gaps yet but i did add to many 0. I will try for .016.

The backfire is more of the popping and engine stutter not a overly loud bang. It was really bad this morning being on the cold side here.

Is there a proper procedure for checking the gaps?

Thanks!

The easiest way to check the point gap is to pull the distirbutor and do it on the bench. I know it sounds like a pain, but it really is faster, easier, and more accurate. Just use a .016 feeler gauge. Put it between the contacts, and rotate the distributor shaft. You'll see a slight movement of the feeler gauge if the setting is loose, no movement if its tight. I do this with the .016 gauge removed from the "deck" of other gauges so the points hold it in place. When the adjustment is perfect, you'll see the tip of the gauge just start to dance a little as the points open all the way.

Your stutter is more likely a lean setting on your carb than anything, but a small point gap will also cause issues. Reset the point gap, recheck your timing, and then go for a test drive. If the issue is still there, check your secondary jet and consider going one or two steps richer!

Naomi had coolant from the heater valve dripping on her dizzy, made her car backfire too. Worth a look.

Mike

I adjusted the timing to about 20 yesterday at lunch and that only had minimal effect.

So last night I too Jeff's advice and pulled the distributor to check the gap. It had almost no noticeable gap. I set it .016, which was an experiment in itself.

The engine runs sooo much better! I guess I will have to plan on an an electronic upgrade sooner then I thought.
I'm still getting a bit of run on when shutting the engine off but I think I have the weber to rich in my other adjustments but its idling nicely at 900 so I think I will leave if for a few days and see how she runs.

Thanks all!!!

marc, that's pretty typical - I actually recommend rechecking point gaps about 3-500 miles after new points are installed. Thre's a quick break-in period they go through, then the wear will stabilize. Your results are pretty common for this situation! Congrats!

Thanks again!

Is there a schedule that i should regularly check the points?

I actually hope to upgrade in a few months.

Now that you have them broken in, check them at oil change intervals, although you may only need to adjust at every-other oil change?

You'll notice when they start to close, and it could be sooner than later....PITA...Go with the Pertronix....Jeff might be able to help you. Lets you focus on other things, like driving it.

DD