Won't idle, surges backfires dies

[davis911s]

Ok here is weird scenario

I had to park my car a few years ago. ran when parked,

Now I can not get it to run properly. I drained all the fuel and replaced it.

When you try to start the engine it will start, but starts hunting and surging then dies, sometimes it backfires through intake before dying.

I replaced the complete CIS with a set of a known running car, same thing.

Frustrated and thinking carbs have less vacuum leaks etc to figure out. I replaced it with the single carb
http://forums.pelicanparts.com/porsche-911-technical-forum/357313-oh-yeah-buddy-kill-newbie.html

I personally took this off a running engine. I added a PMO regulator and it is set to 3.5 PSI

I have tried the original CIS fuel pump AND a working low PSI fuel pump for carbs.

Still exact same symptoms

So I am thinking it shouldn't be fuel related.

I checked distributor and all looks good. Spark is good from coil
I did cold compression test all were around 110-120 (bad gauge doesn't stay at highest)

Does anybody have any ideas??? I don't want this to turn into debate on CIS vs Carb, especially the single carb debate. I just want the car to run. ANYTHING is better than a non running car.

things I am wondering about
- I have not done valves. but like I said it was running when parked
- I am wondering if there might be a restriction of blockage in the fuel RETURN line? I read somewhere this can cause issues. How could I check that and does it sound like it would cause this issue?

ANYTHING???

[Bob Kontak]

Did you drain the gas from the float bowl and clean things out in there? I have had two pieces of equipment fail in the last two years just from letting gas sit in the carbs for a number of months.

Does you system run fuel back to the gas tank?

[davis911s]

Cleaned the carbs out. Drained the float bowls, checked float levels and blew out the jets. Cleaned mixture screws and blew air through the carb.

My system is set up through the PMO regulator to run fuel back to the tank. The CIS had the fuel return line and I used that. I do not know if it is returning fuel back or not. How can I check to see if the return is not blocked?

[Bob Kontak]

Disconnect, pucker up and blow I believe. Focus on ossiblue and boyt911sc's posts.

http://forums.pelicanparts.com/porsche-911-technical-forum/688508-wur-issues.html

[davis911s]

I read those posts. So can I use a compressor and blow air in or will that wreck the tank?

Should I hear hissing in the tank when blowing?

[HotRod]

I have the same problem with my 84 Carrera. No backfire, but under idle it hunts, surges, then RPM goes all the way to zero and stops. It's stock except for 964 cams, and cat removed. It seems to be fine under partial throttle, but pulling up to a stop sign it just quits when the RPM decreases.

Engine was completely rebuilt about 5K miles ago. This problem just started the other day. Any thoughts on where to start looking?

[davis911s]

Have you checked your fuel pressure?

[boyt911sc]

Originally Posted by davis911s

I read those posts. So can I use a compressor and blow air in or will that wreck the tank?

Should I hear hissing in the tank when blowing?

davis,

You need less than 5 psi. supply of pressurized gas into your engine to locate these hard to find air leak/s. What tank are you referring? Gas tank? You could not get air to the gas tank using this test even if you wanted!!!!! You're just injecting pressurized air into the engine's induction system and not to the fuel lines.

Tony

[HotRod]

No, haven't checked anything yet. I'll start with that. I would think that if it was fuel pressure, I would see the problem at higher RPM as well...but I guess that's a good place to start.

[davis911s]

Originally Posted by boyt911sc

davis,

You need less than 5 psi. supply of pressurized gas into your engine to locate these hard to find air leak/s. What tank are you referring? Gas tank? You could not get air to the gas tank using this test even if you wanted!!!!! You're just injecting pressurized air into the engine's induction system and not to the fuel lines.

Tony

I can't get my car to run. And I can't figure it out I read in a post somewhere that they couldn't get carb to run because of a block or kink in the fuel return line. I was wondering if that could be my issue. So I was wondering if I blew air into the return line if I would see or hear air in the gas tank to check for kinks????

I am really confused and frustrated with my car

[boyt911sc]

Originally Posted by davis911s

I can't get my car to run. And I can't figure it out I read in a post somewhere that they couldn't get carb to run because of a block or kink in the fuel return line. I was wondering if that could be my issue. So I was wondering if I blew air into the return line if I would see or hear air in the gas tank to check for kinks????

I am really confused and frustrated with my car

davis,

In this case, you could simply run the FP and check the return line's flow rate. Blowing air through the return line to the gas tank could help you identify if the return line is blocked or not. However, if there is just a restriction that allows limited amount of fuel flow, compressed air would still go through the fuel line and make bubbles in the tank. Measure your fuel pressures.

Tony

[davis911s]

I checked fuel with the CIS installed and it was good TO THE ENGINE, also now I have the PMO regulator with thecarb and I can adjust it. I have it at 3.5 PSI to the carb, right where it should be.

How do I check return line flow rate?

[timmy2]

For your carburated system:
Blow a little air through the return line and listen for bubbles to confirm it is at least partially clear.
Put your gauge in line with the return circuit run the pump, close the gauge valve and see if the pressure goes to 3.5 psi. Then open the gauge valve and see if the pressure drops.
Which pump did you end up keeping on the car?

Your troubles almost sound like points are carboned up or timing is off. Fouled or wet plugs?

[davis911s]

I will do that test

I tried it with a smaller 12V pump from a VW, that only put out around 4-5 PSI. But when it didn't work I went with the Stock CIS fuel pump and the PMO regulator as everyone here was doing on the CIS conversions.

The pump had the internal check valve in it for the supply line. Years ago I had a hard start issue and put in an in-line check valve. I looked at that and it seems to be working fine.

I just can't figure out what could be causing the poor start/ no running issue with both CIS AND carb now.

I can't even get it to run long enough to double check timing, but it starts right up if I prime the carb. then it runs like poop and dies

[timmy2]

What are you using for a choke?

[davis911s]

electric choke. The carb was running on a 2.4 and I personally pulled it of, I have not touched the choke. I have tried to run it with the choke connected (verified 12V) and also tried it disconnected. No difference

[timmy2]

So, absolutely no air leaks at intake gaskets or rubber isolators on airbox or base of carb?
Float levels are set correctly and all jets have been cleaned. Fuel delivery to the carb is good. Choke system appears to be working.

Have you pulled all the plugs, grounded them and watched to see that each one has good spark when you crank the engine? (Check ignition coil ohms if weak spark)

Have you done a dwell meter test on the points when cranking to see they are set correctly?

Take a look at where the Dizzy bolt is located on the lock down, does it look right or has it moved? Are the vacuum pod(s) on the dizzy hooked up? Can you feel the advance mechanism in the dizzy working (Rotate rotor and it snaps back)
Are the wires, cap and rotor in good shape.

Compression is ok as per your earlier statements.

Hmmm, you need spark, fuel and compression to run... Something is missing.

If everything checks out I'd try minor adjustments to my timing in the advanced direction. It's what I had to do with mine when I redid my head studs last fall.

[wasserkuhl]

Does the car have any form of alarm/Immobiliser installed? If so, rip it out!!!

[davis911s]

Timmy

- There are no leaks
- Float was checked and correct,jets all cleaned and blown out
- vacuum is NOT hooked up to distributor, I have port plugged, It was never hooked up.
- Cap wires and rotor all "looked good". I will have to take a better look I think.
- Did minor adjustments to advance to a point that engine would not start at all them back to "original"

- I will do resistance test on plug wires, check for spark at each cylinder and clean reset dwell.

Originally Posted by timmy2

Hmmm, you need spark, fuel and compression to run... Something is missing.

exactly. That is why I pulled the CIS. To really simplify everything, there are way less things to check right now with this carb and still not working.

Wasserkuhl - there is no alarm or immobiliser, thanks for thinking of that.

[davis911s]

One thing that I thought of last night.

The PMO regulator has two "outputs". Obviously set up for dual carbs. I have one of the outputs blocked off since am only running one carb. I wonder if this is creating a "loop" of some sort and messing with the mixture????

I will send PMO a message asking about design