Popping (mini-backfiring?)

[Vancouver '66]

Hello,

I'm a brand new proud owner of a 1966 912. Just had the carbs (dels) rebuilt and have been driving it for the first time. Performs well, but there are frequent little "pops" when idling or driving. They almost sound like mini backfires.

Does anyone have an idea how to correct? I'm hoping its just a simple adjustment.

Cheers,
Michael

[WFBowen]

Michael:
Congrats on your 912 acquisition!
I'd first check for any vacuum leaks at the base of the carbs, then:
Sync the carbs again & check the float levels; adjust the valves; double check your ignition wiring, points & cap & timing; re-adjust the idle mixture. The list goes on and on .
Did the car do this prior to the carb rebuilding? Sometimes a bad exhaust flange gasket can cause a "spitting" sound .
Bill.

[Vancouver '66]

Bill,

Thanks for the guideance, at least I have astarting point now. As perhaps the most un-mechanically inclined person on the plantet, I have a steep learning curve in my very near future. Checking for vacuum leaks will be the furst hurdle... what the heck's a vacuum leak (kidding)!

Sincerely,
Michael

[dimps8]

Michael head over to here. www.912bbs.org

[lep]

It's probably the Solex carbs, which, when out of adjustment cause the fuel-air mixture to interact differently with the ignition timing (spark plug firing) resulting in small carb backfires. Those are actually dangerous since the backfires are like a flamethrower 50% of the time in your engine compartment. I'll bet the top of your air cleaner is quite black from the burn pattern.

As long as you have Solex carbs, you will need to get them adjusted by someone who knows what they are doing. The alternative is to use Weber carbs which won't result in backfiring when out of adjustment. There are other parameters -- so you will need to weight these in.

lep

[aijf197]

I think I read in Duane Spencer's book that Delatori carbs have a tendancy to catch fire!

Sounds like they're just a little lean though. You could try backing off each mixture screw 1/8 or 1/4 of a turn and see if this helps. If not put them back! Messing with the carbs on these cars is one of the pleasures of ownership. If you get a syncronometer (basically a mass flow measuring device) you can spend hours balancing and tweaking the things!

[Nige-912E]

valve clearances and a lean mixture will result in popping back through the carbs.

I've never heard of Dellorto carb's catching fire, usually other factors that result in a fire, too high fuel pressure, badly installed fuel lines and so on.

I'm running Del's on my car, perhaps I ought to invest in a fire extinguisher, be a good idea anyway.

[aijf197]

I knew it was Dell... something!

Small world - I'm from Wirksworth in Derbyshire. I now work in Southampton, but I'm often up North visiting my parents.

I keep on meaning to buy a fire extinguisher anyway - I think you're actually required to have one by law when driving in Europe. I suppose a CO2 one would be best. I'm on Webers, but I want to go to Solex so I can adjust the accelerator pump.

[912UK]

Hi'er I live in Southampton and Vist Derbshire as my other half has friends up there.. although I avoid Nige when I am up there... te he... :-)

he has never invited me for a cup of tea or nothing ..... ;-)

[Nige-912E]

From Belper myself so not far away from sunny Wirksworth at all. Nearly moved house there a few years ago.

Mark you wouldn't be welcome anyway

[912UK]

Nor will you be now cos you don't have a 912 any more