What have I got?

[bonzo]

Hello all

I am a rookie 911 owner in need of some help. I recently acquired a '67 911 that had been a 20 year project for the previous owner. I am awaiting more info from the previous owner but would like to try this in the mean time. Engine was rebuilt in CA by former Andial employee(not sure when and to what spec). I am told it is a 2.2 liter(perhaps punched out from 2.0) and I am trying to figure out how to get the carburation set right. Engine# is 908047, type 901/05.

It has Weber 40IDA's with chokes that have been opened up to approx. 36mm( they are not size marked), auxillary venturis are 4.5, emulsion tubes are F3, air correction jets are 140, and main jets are 150. Given these modifications from stock, what do you suppose has been done internally to this engine?

I am at approx. 4200 feet above sea level. The engine starts and idles fine, but off idle to 3000rpm it has a stumble then smooths out above 4000rpm.

Any suggestions on which way to go with carbs settings? Any help would be greatly appreciated. Here are some photos. Have you seen my engine? Did anyone here build it?

Thanks,
Brian

[jluetjen]

Hi Bonzo. Welcome aboard! .

Here are my thoughts...

1) Your engine's serial model number (901/05) suggests that it is from a '66 or '67 911 "Normal" with Weber carbs and about 130 HP.

2) Given that the engine has been rebuilt, it's tough to even guess what the situation is with the critical internal parts like piston type and camshaft spec. These will come into play in chosing the correct carb jetting. For reference, here are some different jettings that I've come across as well as the results (if known).



On the other hand it could just be clogged idle jets.

To be honest it will most likely take some troubleshooting to isolate the problem(s) and fix them. But then that's why we're here -- isn't it!

[jpnovak]

Welcome Brian.

I agree with John. Looking at the carbs I see a lot of varnish from dried fuel. I would suspect a clogged idle circuit. This would explain why the car runs fine above 4K after the main curcuit takes over.

I would suggest that you remove the carbs for a good cleaning. Find a good stainless restaurant style pan that a carb body will fit into. Disassemble all jets and acc. pumps and immerse carb body in some Berryman's B12 Chemtool or similar solvent/cleaner. Let is sit overnight and then use compressed air to clean all the passages. This should solve your problem. You can also use concentrated citrus degreaser (purple stuff/simple green) in a plastic container.

If you are careful with disassembly you can reuse the gaskets. Otherwise buy a rebuild kit and replace them. These are available through our host.

Happy New Year!

[bonzo]

Thanks John and Jamie for the input. I won't be tinkering with it until monday but this gives me some more to think about. Much appreciated.

Brian

[john walker's workshop]

be sure the idle jets are 0.55. any smnaller and you get hesitation on acceleration and they spit and pop when trying to get it started cold.

[bonzo]

Let me add some info I left out initially. The idle jets are .50. When the engine is started cold, it does take a little effort. Not really coughing and sputtering horribly but maybe a few hiccups until it warms a little. Once running it idles smoothly and the throttle response is excellent and revs without any problem or hesitation. Under load though, that's when it's symptoms occur. Would changing the idle jets to .55 clear up this type of problem? I know these carbs would really benefit from a good bath, but I'd like to try few different settings before doing that. I have a set of 40IDS's with .55 idle jets I could swap out.

Brian

[jluetjen]

Once running it idles smoothly and the throttle response is excellent

You can't determine idle response while sitting in your driveway. It can only be felt when the engine is under load.

and revs without any problem or hesitation.

OK. But that doesn't really mean much since the engine isn't under load. The amount of fuel that an engine uses doesn't depend just on the rev's, but also the load on the engine. So the carbs may draw enough fuel under light or no load, but not under normal driving conditions.

I agree with Jamie, start out by getting a couple of carb rebuild kits and strip down the carbs and soak them to clean all the gunk out. Be sure to blow out the passages. Then reassemble the carbs and see if it makes a difference.

[bonzo]

I'm ordering carb kits and going to give these things a good cleaning. After partial disassembly it looks that they could be gunked up more than expected.

I'm still left with a few thoughts that may be harder to figure out.

1- I don't yet know exactly what cam spec and compression ratio I have. I know that makes it difficult and hopefully I'm on the right track to finding out(thanks to user skline).
2- What do you suppose they could be given the chokes/ main venturis are 36mm? I am told it is now 2.2 litres and according to engine#, it was originally 2.0.
3- We tried 125 main jets and it just wouldn't run, what size should I try next or should I try the 125s again after cleaning? I am at about 4200 feet above sea level, how does that play into it?

I feel like I'm forgetting something but I can't figure out what at the moment.

Thanks for the advise.