Well, thanks to Matt (Plas76targa) I have my timing problem solved as he lent me his perma-tune while I am waiting for a replacement CDI box. I adjusted the idle stop screw and that fixed the crappy idle. And I have the fuel adjusted pretty close to perfect so far as I can tell (I went as lean as it could stand and richened it a little). I will get the shop down the street to use the CO meter to fine tune it later.

After all this it runs much better, can go to 6k parked (I'll road test it tonight), and idles just fine, BUT it still backfires out of the tail pipe when I hold the RPMs up a little. No fuel adjustment seems to affect this, and there seems to be sufficient power. Addition of the perma-tune has curbed the backfiring significantly, but it is still happening.

What might be causing my backfire?

Exhaust leaks?

Mike... Once again... you have missed the obvious Blinker fluid starvation problem.

Re-fill the reservoir and try it again. I find that if I use the Chinese blinker fluid. It has enough lead in it to stop the backfires. Also raises the octane level bout 3 points.

Or you can opt for the "Synthetic" animated pectron gas hydrolazation coupler that infuses pectrons directly into the combustion chamber. Thats an old Nazi trick they used when the realized they were running out of seal oil. (Don't get me started on that one)

Eiter one of the above solutions mixed with saliva should get you where you need to be with your engine.

If all else fails..... Move back to San Diego. PLEASE...!!!!!!!!!!!!!

Cheers,
Jo Moma

Ju clean yer plugs?? They had to be pretty nasty after all the mis firing that had been going on. Oh and enjoy the T-shirt. I don get one.....he sold out of larges If only I was a fat ass like you I could get a XL

I'm assuming that this is a 2.7L 6 cyliner with CIS?

If so, you are way too lean. CIS will run incredibly lean, dangerously lean. Lean CIS revs very quickly and willingly. (You can't adjust it like a carb, leaning it until its rough then richening it up.) You need to richen it up, clockwise slowly on the adjustment screw, 3mm by fuel distributor. When you are too rich, the idle will surge up and down. I would richen it a little at a time, approximately 1/8 turn, until the backfire goes away.

Also, you should not ever need to adjust the idle stop screw. With CIS you use the large air by pass screw on the side of the throttle body to adjust air bleed (controlled vacuum leak) to set idle speed. You need to adjust both the air by pass and the mixture(3mm) to get the idle speed and mixture right.

Good luck,
Ed

Ed, you are the man! I had to adjust the throttle screw because the DAPO had the whole system fuched up and this is why I am having fun chasing my tail
I have a manual from Scotty that covers the system pretty well, but doesnt cover this problem. I am going to recheck my mixture. I took it for a test ride and the first ride it had no low end and would kick in like a rocket. Second ride had perfect low end and would poop out at the top. I need to lean it out maybe. It got too late.

Scotty, I am wearing the shirt right now Maybe you should lay off the paint huffing and eat something so you can fatten up a bit and fit into the man size shirts

I will check for exhaust leaks tomorrow.

Thank you brain trust!

Clayton, I am looking into maybe doing primary care in an underserved area of CA so it is possible that we return.....we shall see. That is a ways away.

BTW you know the $50.00 a day storage starts Sunday right ???? One free week then

Dr Evil, it sounds like you are close. At this point, tune it as you drive. Remember, very very small adjustments can make a big difference. Just go a little at a time until it runs the way you want. I'll be doing the same to my 911 today after I put the new injectors in

Regards,
Evill Ed

Alright, I replaced the CDI box with a used one and it works like a champ as far as the timing is concerned. Odd thing, though, I started the car, richened the mixture and took it for a quick spin. It did great......then it warmed up and the power went to poop. WTF? Is my WUR shitting on me? What should I be goofing with now?

I also need to chase down a right lower valve cover leak as every time I make a tight left turn it smokes bad

Maybe just some shoulders.

Well, I just adjusted the timing AGAIN and I think it plus richening the mixture still has made it run much better.

-All 911 of the period this one is (74) were timed to 5*ATDC @ 900 RPM except for the Carrera 2.7 which is timed @ TDC (Z1) @ 900rpm

- Since I have SC cams I decided to time it to TDC. This also made it work better.

- @ 6K RPM the timing is supposed to change to the 35*BTDC mark. Mine was not getting close........SO, I did the second adjustment: 6K, vac hose disconnected, adjusted for he 35*BTDC mark. This made it run best overall. this and richening up the mixture. Now it has crazy power from 3k on, but is choppy and backfires below 3K. Probably need to give it more enrichment still. Now I am just waiting for it to cool down so I can chase the valve cover leaks.

Go Doc!!!

Also check for vacuum leaks, CIS is VERY picky about those. Steve came down from Canada one day and we just tore everything out and started from scratch. By the time we were done, his 3.0 CIS ran like new though. Check hoses, even breather hoses to the tank and such. One small leak can throw it all off. Make the engine "Pop" and "Fart".

Get your baselines down. Adjust the valves, stick a probe in the exhaust fix the mixture, clean the plugs, etc.

THEN drive it. If it STILL pops on decel, then it's an exhaust leak. Wet your hand and pass it over the pipes and if you feel a breeze, there's your leak.

Its not just on decel, its on constant as well. I have adjusted the valves. I also resealed the whole thing before installing it so I hope it is not a leak. I have to get the mixture closer, I am pretty sure.

More tweeking tonight and it is running better each time. I fixed the gasket I buggered up on the lower valve cover so the smoke signals are over. It still lags at lower RPMs, but I am wondering if it is due to the engine not being broken in yet?

How is the exhaust temps, left bank versus right bank, Is there a big difference left to right?

I havent gotten under there with my thermal gun, but I checked all of the valves, plugs and injectors so the only factor that would affect that would be the rings not having seated yet, no?

Yehaw! I am having a friend drop it by the local shop for inspection tomorrow It is pretty well sorted and just needs to be driven

Seriously, leaks on CIS can do bad things.

Of course that has already been said but I have to wonder dude why you're using CIS at all? You're not in CA so I can't imagine it's a smog requirement as you've already got the wrong engine in there...

Sorry, I'll go back to lurking now.

I am quite certain that the CIS is not leaking.

I am using CIS because of several reasons:
- It came with the engine
- I did not have to buy new pistons or cylinders when I rebuilt, I just reused the old CIS ones.
- I most likely will not need a front oil cooler as the engine is not maxed out with high comp pistons and carbs. This is cheaper and I didnt want to put a cooler in anyway.
- The CIS is a bullet proof system when it is tuned right and it will yield better gas mileage than carbs.
- I can always upgrade later when I am making fat doctor $$$

Oh, I did mean to imply carbs. HECK no, I was implying an aftermarket programmable FI.

Mine used to backfire as well but once we got it right now it only backfires a little when it is extremely cold - not very often where I am.

Oh, here is the reference that I use to adjust mine...

http://forums.pelicanparts.com/showthread....mp;pagenumber=1