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914World.com _ 914World Garage _ Big backfire

Posted by: Trevorg7 Jan 18 2006, 12:16 PM

72 1.7 dual Weber 34 icts

Car was warm, in stop and go traffic.

3rd gear, 2100 rpm, 25-30 mph and the car seemed to lose power (no throttle response) for about 2-3 seconds and then boom! A large backfire with billowing black smoke.

Car has begun to buck a little at lower rpms and speeds in the past 1000 miles.

Plugs pulled 500 mph and are fine (gap, etc), solid state ignition.

Thoughts on where to start?

Thanks

T

Posted by: r_towle Jan 18 2006, 12:42 PM

take out the jets and clean them.

Sounds like some crap in the jets...

Lets say your idle jet is plugged, you would get no fuel at idle, and none till you transition to the main jet,,,which would shoot alot of fuel in based on the position of the throttle...

so then pow, you get a backfire...

you need to clean your jets, then changed your fuel filter.

Rich

Posted by: James Adams Jan 18 2006, 01:04 PM

QUOTE (Trevorg7 @ Jan 18 2006, 01:16 PM)
Plugs pulled 500 mph

The problem is that 914s are limited to about 0.6 Mach at sea level. You were going about 0.66 Mach (assuming it was a near standard day), and created a local shock at the back of the targa bar which disrupted the airflow into the carbs.

This is yet another reason you should have fuel injection, as it is typically good to 0.89 Mach (678 mph).

Actually, it sounds to me like you have an ignition issue, as you were still dumping in fuel but not firing it, then lit it all off at once (lots of black smoke) when the ignition came back. Throw some points back in for a test.

Posted by: joea9146 Jan 18 2006, 03:06 PM

QUOTE (James Adams @ Jan 18 2006, 03:04 PM)
Actually, it sounds to me like you have an ignition issue, as you were still dumping in fuel but not firing it, then lit it all off at once (lots of black smoke) when the ignition came back. Throw some points back in for a test.

I Agree I Think u have some type of Ignition problem.

Posted by: 914Jr. Jan 21 2006, 06:47 AM

Check timing.

Posted by: DNHunt Jan 21 2006, 09:18 AM

Bet the ricers would approve, nice long flame out the exhaust.

Dave

Posted by: lotus_65 Jan 21 2006, 10:01 AM

that happened to me once, what kind of damage does that cause?