Brain fart question 914-6 Options

[mb911]

I also wonder if the builder put pistons in upside down which would drastically effect the whole deal

We rebuilt an engine after a well known builder rebuilt it with upside down pistons and a half dozen base gaskets under each cylinder. Without the additional base gaskets, piston would have hit valves, with it, it had super low compression and ran poorly. Hack job rebuild from a well known (and infamous) shop.

It just was not built by an experienced builder they “ported” the intake ports in a way that I am not a fan but used stock cams and pistons so the story goes.

[technicalninja]

Evidence of monkeys...

[mb911]

Evidence of monkeys...

Yes

[Justinp71]

If fuel pressure is good and spark is good and in the correct order then-


Are all the carb jets correct? Don't forget to check the air jets and emulsion tubes those all play a big role off idle.

What RPM does the hesitation start? May need larger idle jets or smaller idle air jet if it's lean.


Also I heard you want to have 3.5 psi at the carb. I actually run a 4.5psi fuel pump and bleed a little return to get the idle pressure to 3.5psi at the carb.


Also make sure all the fuel filters are in good shape. When jumping down in pressure then you need to be cleaner than with an injection system.

Hope this helps

[rick 918-S]

Question: does the 2.7 have the FI heads from a CIS? What intakes are you using for the carbs? Are they properly covering the notch in the head for the fuel injector? Could just have a vacuum leak at the intakes

I had some Alien adaptors made to allow the use of early intakes to work with FI heads. I will see if it came find a set and post a pic.

[infraredcalvin]

Interesting on the cam timing 180 out…. Ive read numerous tales on the bird turbo forum about cams installed 180 out.

My track car runs seemingly well but for a 3.4 with s cams, 0-2% leak down - multiple tests, multiple gauge sets. it should be making at least 100 more hp than it shows. I posted on the 911 rebuild forum, cam 180 out was one of the first and many responses to my issue…

I’ve come to belive it’s “a thing” on 911 engines…

[mb911]

So after some PMs from a member I think this should be added to the equation. When throttling up slowly there is no issue it’s just when you jump on the throttle. That screams sparks fuel. Plan is to get the MSD wired in, change out the 123 coil and change to a traditional spark plug and go from there.

[rick 918-S]

I suggest a vacuum gauge. You can balance the individual throttles at idle and suck air between the gasket and head with the wrong intakes when you crack the throttle.that will produce the same issue you are having. This covers the injector notch without restricting the port flow.

[mb911]

I suggest a vacuum gauge. You can balance the individual throttles at idle and suck air between the gasket and head with the wrong intakes when you crack the throttle.that will produce the same issue you are having.

Interesting will check that.

[mb911]

Update.

No vacuum leaks,changed plugs, compression check with 1,5,6@90 psi and 2,3,4 100 psi

Looking like cam timing to me or bad valve job

[Justinp71]

Could use a spark tester and see the spark strength? or is spark ruled out with the MSD?

I also had this weird problem once where two of my idle jet holders were short, so the idle jets were not seating in the carb all the way. Car ran OK from memory though just insanely rich. It's just how I got the carbs back from the rebuilder, they must not have noticed.

If they had an AFR gauge would be interesting to see how the two banks compare.

[Justinp71]

Also I would still replace the fuel filters too. I went round and round on a car once that had one of those small bronze element fuel filters it didnt look dirty until you got it under a microscope and you could see all the small pores were clogged.

I'm thinking maybe its rich at idle but when you let it eat at high throttle the fuel flow can't keep up, that's what was happening in the above example. Just thought...

[Root_Werks]

Update.

No vacuum leaks,changed plugs, compression check with 1,5,6@90 psi and 2,3,4 100 psi

Looking like cam timing to me or bad valve job

Zoinks those are low numbers.

Agreed, it's something internal with the build at this point you'd think.

That sucks.

[mb911]

Update.

No vacuum leaks,changed plugs, compression check with 1,5,6@90 psi and 2,3,4 100 psi

Looking like cam timing to me or bad valve job

Zoinks those are low numbers.

Agreed, it's something internal with the build at this point you'd think.

That sucks.

Yup 100%

[mb911]

So I completed what I could. I don’t have time to drop the engine and retime the cams along fix all the leaking rocker shafts and the migration of rocker shafts. I suppose it’s a good lesson as you can’t trust a fresh build from someone that really is not in the know on these engines. The cam timing is not very basic, the rocker shaft procedure is also almost black magic sucks for the owner and for me to have not been able to wrap the project up myself