76 912e 2.0 help needed
 

I have 1976 912e 2.0 (same as 914) switched over from FI to dual Delorto Carbs. Performed the following after failing state emissions and for better driveability. Car would backfire through left carb on occasion and some exhaust backfiring while coasting.

Day 1) Adjusted all valves to .006 (which I later found out was wrong on exhaust side) Engine Cold

Day 2) Adjusted intake valves to .006 and exhaust to .008 engine cold. Changed Cap and Rotor, adjusted points so that Dwell was at 50 on 4cyl scale, changed ignition timing to 34 degrees BTC at 3200 RPM. Performed leakdown test on each cylinder 1- 6% 2-5% 3-6% 4-5% after engine was warm. Changed plugs to Bosch Platinum gap set at .028. Balance carbs with Uni Syn and adjusted idle however didn't adjust linkage as I though it still seemed balanced. Didn't adjust air imixture on carbs. Took the car for a ride for about 30+ miles and it ran the best I ever had it, nince sweet spot around 3000 RPM,then on return trip I got loss of power and hesitation.

Day 3) Double checked the Points and the Dwell was the same, double checked timing still the same and double checked the airflow balance from carb to carb, still the same. Pulled plug on cyclinder #1 everything appeared perfect. Decided to adjust air mixture (2 screws per carb) I turned them in till cylinder ran rough, backed it out till it smoothed out and then 1.5 turns out from there. Did that to all cylinders and went for a ride. Same hesitation and lack of power.

Day 4) Pulled valve covers for 3rd time on cold engine, checked all valves, found exhuast on cyclinder 4 too loose, so I adjusted it. While turning engine manually for valve adjustment I noticed that the new rotor was loose and not seated correcty on the distributor shaft. I still had the old rotor and sure enough it fit correctly ( the inside guide on the New Rotor was not correct). Cleaned old rotor put cap back on and took test drive. Very slight improvement. Checked air mixture again and made slight adjustment, advanced timing to approximately 36 degrees BTC. I noticed that as I pushed down on the middle of the throttle linkage that the carb for the #3 and #4 cylidinder was opening before the other side. I adjusted the linkage and now they open exactly the same. The stumble off idle is gone and the engine revs better than ever with no hesitation or carb backfiring, however there is a little exhaust backfiring. I take the car for another ride, big improvement, but not quite 100% and now there is exhaust backfiring during any coasting in any gear, pretty much whenever I'm not giving it gas. There is still a light stumble when using the accelerator pedal, but not manually push the throtte from the engine compartment.

Sorry for the long post, but I'm out of ideas except for a carb rebuild. I've only had the car for several months, and no knowledge of when the carbs were new or ever rebuilt. I'm begging for help, because I don't know where to go from here.

Ryan
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Ryan
Riverdale, NJ

'68 911 Coupe
'76 912e

Howdy, Give a try over here............

http://www.912bbs.org/index.php?a=forum&f=13


CheersSmileWavy

Ryan, I don't think you'll ever get it not to pop or backfire occasionally whilst running carbs. Getting them balance perfectly will help, rejetting will also help, this is best done on a rolling road and somebody who know carbs. Air leaks on the exhaust side will cause some backfiring, also air leaks around the carbs/inlet manifolds will also cause some popping and poor running. I struggled to get the aftermarket inlet manifolds to seal adequately (CB Performance) there is little material around the flanges for the gasket to seal especially if some match porting has been done.

I ran my 912e with a pair of Dellorto DRLA 40s, whilst the throttle response was better and it had more power it was less driveable than with the original FI. After alot of work getting everything just so and rejetting it would still pop/backfire occasionally on the overrun. Webers will not be any better.

Mine ran better with a 009 dizzy, though I had it running on the original FI dizzy with vac lines plugged into the carb base.

Update: Carbs were rebalanced, but I found exhaust leaks at the flanges from the exhaust manifold pipes to the heat exchangers. I'll tackle that problem this coming week end. As for my distributor, it must not be original as there is no vacuum advance or any vacuum ports.

Ryan

Sounds like you have an 009 fitted, shouldn't cause you any problems. Deal with the leaks first, you may need to tweak things afterwards, timing and so on.

Ryan, you may want to get yourself a set of solid copper exhaust gaskets from Jake Raby http://www.aircooledtechnology.com/store/product.php?productid=16719&cat=352&page=1

They work great!!!

Fran

912E #224

They look good. The exhaust I had built for my 912e did away with these specific flanges and used Type25 ones instead. He also but off the existing flanges on the h/e's and replaced them with T25 also.