New to me 3.3ss - couple questions

[pnut_lee]

Purchased a car that just arrived yesterday. It's a 1982 911 with steel turbo flares. It's a beautiful machine, but have some questions on the engine.

Engine was rebuilt 4K-5k miles ago. Specs as follows:

Original Euro 3.0 case
Upgraded pistons and cylinders 100mm slip fit LN/JE 9.8:1
Billet mod s cams
70.4 stroke
PMO carbs
1.75" headers with M&K 2 in 2 out exhaust
MSD ignition - single plug
Wideband AFR kit with LCD display

Now my questions:

1) My two banks are reading different AFR.......one is consistently at 14.2-14.7. The other jumps around, but usually between low 12s and high 13s. I'm guessing one set of carbs is just adjusted to run a little leaner than the other. Is this acceptable or should I make an effort to adjust?

2) Engine has a huge flat spot in the power band after 5600 RPM. The engine has wonderful low RPM torque, but my understanding with mod s cams was that it should pull like crazy up beyond 7,000 RPM. The drop in torque is very noticeable from 5600 on. Is this normal or expected with this kind of build?

3). What should I set rev limiter to? I know this engine should love to rev, but what is a good safe number for longevity? Not getting much benefit after 5600 anyway, so I was thinking 6800.

4) Getting harsh vibrations through the car in any gear between 3000 and 3600 rpm. Only becomes really noticeable when letting off throttle in this range. I can tell it is there when powering through during acceleration, but not as bad. Any thoughts? Engine mounts?

I'm coming from a 964 And the difference is astounding. The 964 pulled strong up to redline, but low end torque was lacking. This engine is completely opposite.

Appreciate any insight.

[mreid]

The carbs are out of sync. Either due to adjustment, tune, or malfunction. It is very important that the air flow and mixture are balanced side to side. Have you compared banks with a unisyn? Is the flow balanced?

[pnut_lee]

Thanks for the info. Mechanic for PPI said carbs were set up properly.........

Do you attribute the difference in adjustment also to the flat spot in the higher RPM range? Could that be fuel related?

I should also mention that at idle the difference is far greater. AFR from one bank is registering 14.7 other side as low as 10.5.

I'm a newbie with carbs. I guess I need to find a local carb expert to help me out unless you guys can walk me through it.

[jpnovak]

Well, they may be physically connected properly but they are NOT setup properly.

You should not see much difference in L/R banks if the airflow and mixture are balanced across the entire engine. It takes about an hour to balance the mixture and linkage.

What does the AFR do when you pass 5600? I have seen early PMOs with a flat spot on transition from idle to main jets (easily remedied) but that is not you problem. Does it go Lean or rich? Do you have any documentation as to the jetting of the carbs? Would need to know idle jet, main jet, emulsion tube, air corrector sizes. Then we can help make suggestions depending on the baseline value and if it goes lean or rich.

It could be your fuel system is not up to the delivery requirements. Usually this is a clogged tank filter sock or other similar issue.

yes, MOd_S cams should scream to redline. 7K should be safe for the engine.

[pnut_lee]

Jamie,

Thanks for the info. I'll have to have my wife take a video of the AFR gauge while I run up past 5600. I'm too busy watching the tach to peek at the AFR when I'm screaming toward redline. I assume you want WOT readings?

The previous owner has a bunch of handwritten notes, I assume from the mechanic when they were tuning the system after the rebuild. Here is the last page in the book, along with a little cardboard strip with specs written on it. I believe the notes on the yellow pad to be the latest unless other changes were not noted.

[mreid]

Please take pictures of the engine with particular focus on the carb linkage and where it connects to the carbs on both sides.

[pnut_lee]

[pnut_lee]

Originally Posted by mreid

Please take pictures of the engine with particular focus on the carb linkage and where it connects to the carbs on both sides.

Sure thing, thanks for asking. Will do in the morning before I leave for work.

[jpnovak]

Where are you located?

[pnut_lee]

Wells, Maine

[pnut_lee]

Forgot to take pictures this morning. These are from the seller. I can get better pics tonight if these don't show what you want to see.

IMG_4436_zpsmubz7bpu by HKnut, on Flickr

IMG_4446_zpsisytt3de by HKnut, on Flickr

IMG_4439_zpsprhlbdjy (1) by HKnut, on Flickr

IMG_4440_zpslyzlp9nc by HKnut, on Flickr

IMG_4438_zpspoxoyftk by HKnut, on Flickr

IMG_4437_zpslwgvxyno by HKnut, on Flickr

[pnut_lee]

Just went for a drive. So bank one is running very consistent mid 14 from idle to redline. The other bank is very erratic from low 10s at idle to mid 12s and mid 13s through rpm increase up to about 5500-5600 where it goes very lean, over 17. Guess the lack of fuel would explain the loss of power above that rpm range.

Why would this bank run rich all the way up to that point and then magically go lean so suddenly?

Edit: Those carbs sound so lovely......... I'm excited to get this figured out. What an awesome car!

[jpnovak]

I would start looking at the sight glass to see if the float levels are correct. I would also disassemble and clean the carbs before making any changes.

Then spend some time to balance the carbs correctly.

The mid-14 on the one bank is not ideal for max power. I would prefer to see you just below 13.5 all the way up at WOT. However, The fact that it runs consistent means there is nothing especially wrong here. Start with something simple.

[Gordo2]

Good recommendations above.

I would start by assuming eveything was setup and adjusted correctly at some point. Carbs settings don't get that out of whack unless adjusted wrong to begin with. In other words - don't make any adjustments just yet...

Start by giving the idle jets a good cleaning - they can clog easily and are quick and easy to clean. A clogged jet could cause the different AFR's you are seeing. If you have a laser thermometer you can point it at each header pipe (close to the head) to quickly ID which cylendar has a clogged idle jet (much cooler temp).

If that doesn't fix the problem I would then move to idle mixture adjustment - first ensuring your idle screws / settings are balanced side to side and then adjusting your idle mixture screws to lean best.

The PMO's are pretty tight so your mixture screws should have a close number of turns needed to get to lean best. I've adjusted mine starting at 1.5 turns out for each screw and then adjusted all the same amount slightly to hit a certain AFR. This will put you very close to lean best.

From there I would check the balance at 3k RPM (using a unisync) - if you are getting different readings then your linkage may not be adjusted correctly.

Lots of possibilities- start with the simple and most likely stuff.

Good luck, Gordo

[pnut_lee]

Thanks gentlemen. I appreciate the time you've spent responding. Looks like I am going to get to know my carbs very well right out of the gate.

I'll do some searches for cleaning and disassembly instructions, but since this all Greek to me any tips or words of wisdom are welcome.

[pnut_lee]

Originally Posted by Gordo2

If you have a laser thermometer you can point it at each header pipe (close to the head) to quickly ID which cylendar has a clogged idle jet (much cooler temp).

This is a great idea. I'll start here first to see if I can isolate the particular cylinder(s) that might be causing the problems.

[jpnovak]

Pnut. Read and understand both of these threads.

New Webers - Adj Help Needed

Weber rebuild

Once you read these the suggestions made here should be perfectly clear.

[pnut_lee]

Thanks Jamie. I'm working up the courage to tear into these myself. All of this info is great, thank you.

[pnut_lee]

Don,

I was reading through your PMO thread, which is very helpful (thank you), and noticed that you abandoned your 1.75" headers. It seems Richard is not a fan of these?

I failed to mention that my car has 1.75" headers with M&K 2 in 2 out. When I read your post I started thinking this might be my problem. Previous owner has pages and pages of notes from carb tuning and adjustments trying to sort this out I'm starting to wonder if he ever really got it to run to his satisfaction. Could the headers be part of the problem?

The other side of the argument is that bank 1 though may not be ideal at 13-13.5 but it is 14.7 and running very consistent from idle to redline at WOT, so to me that tells me that the headers aren't the problem.......or at least not the specific problem with bank 2.

[Gordo2]

Originally Posted by pnut_lee

Don,

...you abandoned your 1.75" headers. It seems Richard is not a fan of these?

I failed to mention that my car has 1.75" headers with M&K 2 in 2 out. When I read your post I started thinking this might be my problem.... Could the headers be part of the problem?

The other side of the argument is that bank 1 though may not be ideal at 13-13.5 but it is 14.7 and running very consistent from idle to redline at WOT, so to me that tells me that the headers aren't the problem.......or at least not the specific problem with bank 2.

It seems unlikely that your headers would cause the issues you are experiencing. Richard recommended the smaller / 1.5" SSI's for my 3.2L - as it appears you have a short stroke 3.4L, I would think the 1.75" headers would be right sized.

Also, I was able to get the engine running pretty good with the B&B's. I had some nagging problems with hesitation from idle circuit to mains (~3.5K RPM) - Richard was convinced it was due to the headers.

I ended up going Richard's recommendation to reduce my headers from the 1.75" B&B's to the 1.5" SSI's primarily because I was convinced that the 1.75" headers weren't sized for what I was trying to achieve - more midrange torque. I changed a few things (venturi/jets) when I the headers, so I can't really put a finger on if the change had any impact on AFR's.

The PMO's will run pretty good even when not optimized with the right jets and settings. I would assume the previous owner was doing something similar to me - trying to resolve a hesitation issue, or get the AFR's as good as possible across the RPM range and various driving conditions. I too have loads of notes...

BTW - If your carbs were causing a huge flat spot at 5,600 RPM, I would think you would be seeing this in your AFR's (really lean or rich). Meanwhile it seems like an odd RPM to hit a flat spot - you are well into running on the mains at that point. Flat spots seem to normally appear coming off idle or during idle to main transition.

Good luck,

Gordo