CIS rebuild - or PMO carburetors?

[JHanson]

Everyone -

My 1982 911 SC has around 105,000 miles on it, and lately the CIS has been finicky, resulting in an unplanned stop at a shop during a visit to California. Now, back in Tucson, it's acting rough until well-warmed up, so I might need yet another adjustment. I'm planning to buy an AFR meter so I can work on the system myself; however, I'm also planning further down the road.

What are your opinions on undertaking a complete CIS rebuild/renew, versus switching to PMO carbs? Overall, the cost seems pretty similar. I know I'd gain some power with the carbs; however, I'm greatly enjoying the 26 mpg I get on the highway with a properly adjusted CIS. I live in the county, so don't have emissions checks.

If carbs, would the 40mm PMOs still work if, (hopefully much) further down the road, I need an engine rebuild and go to a 3.2 SS?

Thanks for any input . . .

Jonathan

[Scott R]

The cost of a carb conversion is going to be a lot more than sorting a CIS issue. With a good diagnoses your CIS can be up and running again as it was before. Now if you want carbs that's another issue...

[Eagledriver]

Carbs are great for power and throttle response. Carbs suck for gas milage. Your 26MPG could drop to 15-18 MPG with carbs. It really depends on the mission you have in mind for your car. If you want to go on spirited country drives and track work without much steady state cruising then carbs are best. If you want a commuter or cruising car then stick with CIS.

-Andy

[tcar]

So your Overland Journal is "Environmentally Responsible" and you're talking about going to carbs?

Check with you state; many places (like here) will not let you switch to carbs and get the car licensed.

[RWebb]

Carbs are only environmentally responsible if you live where HC, NOx, and CO are not issues. Carbs are never going to have as low CO2 emissions as CIS (nor will they give you as good a cold start and initial driveability as CIS).

How much do you drive your car? If it is a low miles car, then the biggest impact on emissions is the fuel vapor (charcoal canister) system.

IF the cost is not off-putting and the above is allowable there and ok with you, then carbs.

Other options include EFI using a 3.2L 3.6L or even a 3.8L RS motor...

[trond]

If your CIS is getting old, consider tbitz EFI. A ready packaged aftermarket EFI system that bolts right up. It comes with fuelling map for the 911. After installing it in my SC last year I recommend it to anyone regardless of whether their CIS works or not. Great throttle response, good fuel economy and easy to tweak if you are so inclined.

[pcar9119]

A carb conversion can be very afforfably. Pmo isn't the only option. I have Zeniths on my SC, and I have about 600 into them. They work awesome. They will work on a 3.2 also, you'll just need the. Largest vents you can fit in it, probably 34 or 36 mm. They are a great carb for a fraction of the price of PMO.

[JHanson]

So your Overland Journal is "Environmentally Responsible" and you're talking about going to carbs?

I guess I figured since my wife and I live in a 350-square-foot cottage that is 100-percent solar-powered, and my daily commute is about eight feet, that I had some ethical leeway for installing carburetors on a hobby car . . .

Seriously, thanks for the responses. If the CIS can indeed be rebuilt for less, that's the way I'll go. I can start looking for parts now (I just missed an NOS Bosch fuel distributor).

I'll also look into that tbitz system; thank you for the tip.

[911st]

I love CIS.

If you want to have your fuel distribuitor and or WUR rebuilt check with Larry at

CISFLOWTECH

You also want to clean the injectors and verify they 'pop' at the same pressure.

Carbs increase throttle response and add about 10-15hp at the expense of MPG.

[JHanson]

Thanks for that link! I didn't know about Larry.

[JHanson]

Oh - one more question. Can the fuel injection system from a Carrera be retrofit to a 3.0? That would seem to be the best of all possibilities.

[euro911sc]

Correct me if I am wrong, but I think the intake stud spacing is different 3.0->3.2 so I do not believe that you can bolt the 3.2 intake on a 3.0. Even if you did you would be missing several sensors needed to run the 3.2 motronic brain if that is the direction you were thinking. These sensors are not exactly bolt on either

I would get your CIS issue diagnosed. Only then can you determine if it is economically feasible to swap to carbs. Could just be a loose or failing vacuum hose which is $10/meter at a VW dealer...

Carbs look a lot cooler though ITBs would be even better!!

-Michael

[RoninLB]

CIS is a great simple reliable system

fix your specific issues

some CIS nuance mechanicals can be removed like the deceleration valve etc that were installed for smog issues

[JHanson]

I kinda figured the Carrera F.I. swap was impractical, or there'd be a lot more talk about it.

Thanks for the further ideas, Ronin.

[RWebb]

CIS can indeed be rebuilt for less w/o question

re the 3.2L injection - you would be ahead in time, effort & $$ by swapping in an entire motor and its brain. that would give you more power, better emissions, and fuel economy.

but it will cost a few kilo$$ and you will have some electronics to deal with; more components maybe too

[RoninLB]

Originally Posted by OJEditor

Thanks for the further ideas, Ronin.

if my 1982 i'd probably recurve distributor and eliminate the vacuum retard canister

I'm not sure if all the SC had the dizzy turning the opposite way than previous years if you just want to get a used older version Bosch

[Scott R]

There was a thread a few weeks back with a guy that had a 3.2 motronic setup on his SC. He had to remove some material from each intake port to clear the injector correctly, but he did it. I believe he also had a spacer in between each intake runner as well.

I have also seen a 3.0 head that was machined to fit the motronic system as well. The studs were normal, it was again the indent for the injector that was changed by the machine shop.

I would have to agree with Randy though, may as well get a 3.2L engine at that point.

[JHanson]

Yeah, sounds like it.

Thanks again very much for the advice.

[Rasta Monsta]

FWIW, I would stay away from an NOS fuel dizzy. . .there's quite a bit of rubber in there that would die in long-term dry storage.

[JHanson]

Ah - good point, thank you.