<VV> Spyder backfire problem

Wed Dec 3 13:13:31 EST 2025

Sorry, I meant to send this Nov 18, but it was sitting in my drafts folder...
Appears to be exhaust side, big bang and huge cloud of black smoke out the tailpipe. I observed while goosing the throttle from the engine compartment and there was no evidence of backfiring through the carb.
-- Doug Mackintosh Corsa member since 1996 Corsa/NC member since 1996, Virtual Vairs member Corvair owner 1969-1971 and 1996-on 

    On Tuesday 18 November 2025 at 16:40:57 GMT-5, Michael Kovacs <kovacsmj at yahoo.com> wrote:  

Do  you mean a backfire through  the carb, or an after fire from the muffler. Two different diagnosis. 

    On Tuesday, November 18, 2025 at 08:02:13 AM EST, larry--- via VirtualVairs <virtualvairs at corvair.org> wrote:  

 Hi Doug,

My motto is "If in doubt, swap it out!  The ignition coil, that is."  
Ignition coils can have very weird and intermittent failure modes.  I 
nearly always carry a spare to swap out.  It only takes a minute or 
two, so no real risk of difficulty.

Another item that can make weird symptoms:  The lack of accelerator pump 
shot on only one side can be frustrating.  Check for a proper 
accelerator pump shot to verify or eliminate this as a possibility.  Oh, 
wait, I was thinking of a two carb power train.  Nevermind for this one.

Good luck,

Larry

On 2025-11-17 3:09 pm, Doug Mackintosh via VirtualVairs wrote:

> Hello, Corvair friends!
> I have an intermittent engine problem that has me stumped. I hope your 
> collective wisdom can help me!
> It is an intermittent problem with my daily driver 1964 Spyder. It 
> starts fine from cold, regardless of ambient temperature (recently 34 
> to 75 deg F). Up until last week it also ran fine and could be relied 
> on to get me there and back. The only exception was a very consistent 
> rough running / bucking / occasional backfiring the first few minutes 
> of driving for the first time after a rain, particularly under moderate 
> to heavy acceleration; after a few minutes it would smooth out and run 
> normally, and when restarted later there would be no problems.
> The problem I need help with started about a week ago. I started the 
> car (it was about 34 deg F), backed out of my driveway, and drove about 
> 5 minutes to my destination. Shortly after I headed down the road it 
> started to putt-putt, blubber and backfire and ran rough enough that I 
> was only able to go about 35 MPH on the 45 MPH highway. By the end of 
> my 5 minute trip it had smoothed out and drove normally, and when I 
> restarted it a few hours later and drove home there were no problems. 
> This was very much like the behavior I am used to after a recent rain, 
> but in this case it was bone dry and had not rained for some days.
> The next day, it behaved the same way, except I only made it about a 
> half block down my street before it stalled and would not restart. An 
> hour later, I was able to restart it and drive it back into my 
> driveway.
> The next day (about 50 deg F) it started and ran fine (just a little 
> roughness at first, but no backfiring, and was running well within a 
> couple of blocks from home). I drove it 5 minutes to my destination. 
> After several hours it started and ran fine as I drove it back home. 
> Later that day I drove it for about 15 minutes mostly on the highway 
> and it ran fine, including high RPM acceleration and under full boost.
> The next morning it started, then ran rough, bumbled, backfired then 
> died less than half a block from my driveway, and would not restart. 2 
> hours later I was able to start it and drive it back into my driveway.
> Here is what I have checked so far:- Cleaned and inspected the 
> distributor cap for cracks or tracking- Twisted the rotor to verify the 
> mechanical advance is working- Verified the correct firing order- 
> Checked that points are opening to a reasonable gap- Checked dwell 
> angle (32.5 deg at 1800 RPM, 30 deg at 4000 RPM)- Removed air filter 
> cover and verified air filter and carb look OK- Verified the choke 
> setting has not moved and the cover is tight
> I then started the car and did the following tests:- Let it idle a few 
> minutes (CHT gauge starting to register) then revved it quickly, which 
> resulted in backfire and black smoke out the exhaust; intermittent 
> backfires and black smoke clouds continued as I held the throttle open 
> to maintain high RPM. Repeated quick revving would sometimes be clear, 
> and sometimes produce black smoke.- Continued to let it idle for 
> several minutes and it eventually stalled (which it sometimes does 
> after extended idling)- Restarted it immediately (started on 2nd crank) 
> and it ran OK, revved fine and had no backfires or black smoke- Let it 
> idle a bit, then popped the throttle open and got some black smoke (no 
> backfire), but then it cleared up and revved fine on repeated quick 
> throttle pops- Let it idle a bit, then revved, then idled a bit, revved 
> again - no problems- About 6 hours later (57 deg F) I started the car 
> (1st try), then revved (revved fine). Let idle 5 min, revved again 
> (OK). After another 20 minutes idling, popped the throttle and it 
> stalled. Restarted (took a little cranking with throttle held open), 
> then it revved and idled fine (no backfires, no black smoke clouds)
> As you can see it is not consistent. I have not figured out how to 
> "make it do it", but I know there is a fair chance it will do it after 
> running just a minute or so.
> Anyone experienced this problem and know what fixed it? Or have a 
> suggestion to help me diagnose the culprit? Any help will be greatly 
> appreciated!
> -- Doug Mackintosh Corsa member since 1996 Corsa/NC member since 1996, 
> Virtual Vairs member Corvair owner 1969-1971 and 1996-on
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