76 911S Backfire

prattrc · prattrc's Garage

Hello, All,

I am an old member of the 914 board here at Pelican, though I've been absent for some time. Wanting desperately to get back into the Porsche game, I recently bought a 1976 911S (Continental Orange). I've had it about a week, and things have been going well.

The car was bought from a Porsche dealership where the mechanic (whom I trust) gave the car his blessing. It cools well with an updated 11-blade fan. In fact, until this weekend, it barely ever warmed up above 200 degrees. This weekend, though, the weather has turned to spring and we're now about 20 degrees warmer outside, so it warms up to about 210 after 20 minutes of driving.

Anyway, I've had my first mechanical problem. After driving a short distance, letting the car sit for a few minutes, restarting and driving off, the tach will become erratic, kind of bouncing or ticking. The car doesn't buck or anything, and the engine itself doesn't seem to rev or hesitate as the tach bounces around. Eventually, the tach will drop off to zero. If I step on the gas at this point, the car will backfire loudly, then work as normal for a few minutes, and do it all again.

I looked through the archives, and couldn't find anything definitive. I also looked at PCA's tech section and found a Q&A seeming to match my condition. In that response, the in-tank fuel filter was diagnosed as clogged.

Any ideas?

Thanks!

prattrc · prattrc's Garage

Forgot to mention...

she does have the airbox pop-off installed and it looks to be seated well.

prattrc · prattrc's Garage

Dangit!

One last thing (hopefully), the idle is kind of high, around 1200 even after warm up.

Jim Sims · 03-12-2006, 09:51 AM

For a '76 911S (I also have one) those are classic symptoms of the points being bad/dwell being off. If you have no records of the last points replacement, change them. Check timing and set point dwell and then recheck timing. Idle and mixture then could be checked and adjusted. Cheers, Jim Sims Minerva blue California spec 1976 911S.

2.7S · 03-12-2006, 10:05 AM

prattrc,

I have a 1976 911 S as will and have experenced the same problem. Jim Sims has it right change the points. By no way am I an expert, but from all I've read and be told, when the tack starts acting like this, change your points.

Post pics and you may get a response from Dan as well.

Mid-yrs rule, what I don't know, but they are very cool IMO.

Regards,

Larry

Howard M · 03-12-2006, 11:36 AM

Third vote for points, though the backfire may also indicate a need for a distributor cap. Look at the bottom of the cap for anything suspicious.

Howard

prattrc · prattrc's Garage

Well, you guys rock.

I ran up to FLAPS and bought points. All fixed. No more dancing tach, no more back firing, and it seems to have a bit more oomf, too. That may just be me, though.

I'll post pics soon.

Thanks!

2.7S · 03-17-2006, 09:06 PM

prattrc

Glade you girls feeling better and yes, IMO, they do run a lot stronger with new points. By the way, mine has come down with the CIS bug like some of the kids on the block. I hope to take her out for spine this weekend before taking her to the doc on Monday.

Regards,

Larry