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Using my philosophy that a problem is quite often related to the most recent thing that was done to the engine, I would test the recently rebuilt fuel pump to make sure it is putting out enough fuel. That would account for idling OK but going flat on acceleration. Re-read Dick's post on the proper rebuild if it is not providing enough fuel.

David Jones wrote:Not any discernible difference between any of the capacitors used on all distributors except for packaging. They all perform the same function across the world. Total globalization of a product. Lucky for you the VW one is a direct replacement quite often in fitment. Lucas not quite so convenient.

Correct in my experience. If you can find one of the old Bosch condensers, they last a long time. The new ones less so IMO. Bruce Smith's comments in this thread are on the money. "a good capacitor should measure 0.27 - 0.32 microfarads" that is if you have a capacitance meter. Any way this is an easy check and when eliminated, you can move on. In my search, I even went to the trouble of 'potting' a modern solid state capacitor in an old Bosch 'can' and it worked well.

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Wes Bender wrote:Using my philosophy that a problem is quite often related to the most recent thing that was done to the engine, I would test the recently rebuilt fuel pump to make sure it is putting out enough fuel. That would account for idling OK but going flat on acceleration. Re-read Dick's post on the proper rebuild if it is not providing enough fuel.

I've been thinking similar after recent pondering. Isn't the pressure somewhat adjustable by the number of gaskets installed? How many gaskets were on the pump that was on the car, if any, and are they still installed?

Other than that - weak spring in the pump?

I would check the thermal spacer under the fuel pump if it is too thick it will no allow full stroke of pump. This is a common mistake with rebuilt pumps installation.

Re: condensers
Recently, I have given this subject a lot of thought.
The reason for the condenser in the first place is t provide a little reverse polarity voltage at the points. This REDUCES or eliminates the build up of material trnaference on the points. Without it, a little “tit” is left, thus closing the points, thus changing the timing, thus making for rough running.

So, the most common forms of failure are:
1. An internal short circuit. If this happens, the engine WILL NOT RUN AT ALL.
2. An open circuit, as if the condenser was not there or disconnected. This will not cause the engine to not run, UNTIL the points close up. (No back Voltage)

I realize that there a lot of people are pointing fingers at non-German sourced condensers. But, I can think of another cause ——. E85 gas causing numerous problems along with:
Long cranking time (caused be empty float bowls) that leads to dragging the voltage down, that leads to increased amperage draw across the points (and condenser). And bingo, that little tiny solder joint melts and the condenser circuit goes open. A little later, the points close up, and the car stops running.

This seems particularly prevalent with those who have not as yet installed a carb priming aux pump.
Get one, and I’ll bet your condenser problems will go away.
Also - don’t forget to keep up the voltage with a battery maintainer.

And NEVER forget: E = IR

Franny Brodigan wrote:

Harold Singh wrote:

Franny Brodigan wrote:Does the engine backfire when it looses power? Does it load up when it returns to idle?

If not, then probably just bad fuel. If it is backfiring, then the fuel is fine and you have ignition issues...

Franny

At Idle: From cold it fires right up and at warm up during idle I don’t notice much back fire right now.

Driving: I don’t know that I would call it loading up but, really any acceleration seems to make it feel like it’s stumbling or losing power. Even missing. It will backfire some. Strange that it starts and idles so well.

I don’t have any wear on the distributor. It’s tight. The cap rotor and wires have all been replaced now with new stoddard Bosch parts. Points gap was checked. No wear or burned spots on those. Condenser I have not changed. Maybe that will be the next thing and some additional coil tests?

Harold - That is what I was getting to. If the car is running lean under load (from your history), it is probably a fuel related issue, but it would need to be common to both sides (like bad gas, not one carb out of tune). If it is rich under load and backfiring a bit, then it is probably electrical, but, again something common to all four cylinders. The first thing I would look at is the condenser. Throw on a known good part and see if that is it. I had these exact symptoms out driving one day and a new condenser and 10 min and I was back on the road again (yes they do go bad and can be bad from new). As a rule, I don't change them anymore during an electrical tuneup as new parts seem to have a high failure rate (for me). If the condenser is known good, then take a look at the coil or other electrical connections.

Just try to box this in and think - is it common to all cylinders, or just one side? What do I hear out of the tailpipes, what out of the carbs? All these issues have a specific tell. Folks will tell you what worked for them but listen to the car. It will tell you who to believe. A bad/fouled spark plug and a bad coil have very different tells but are both electrical.

Listen, postulate, test, eliminate, repeat.

You'll get it!

Franny

New condenser installed and insulation verified at the bolt so, it cannot touch the distributor body. New points installed and gapped. Retimed distributor and no change in running under load. I had high hopes after the other stories of bad condensers.

Sean M Rooks wrote:

Wes Bender wrote:Using my philosophy that a problem is quite often related to the most recent thing that was done to the engine, I would test the recently rebuilt fuel pump to make sure it is putting out enough fuel. That would account for idling OK but going flat on acceleration. Re-read Dick's post on the proper rebuild if it is not providing enough fuel.

I've been thinking similar after recent pondering. Isn't the pressure somewhat adjustable by the number of gaskets installed? How many gaskets were on the pump that was on the car, if any, and are they still installed?

Other than that - weak spring in the pump?

Wanna swap pumps and see?

Thomas Sottile wrote:I would check the thermal spacer under the fuel pump if it is too thick it will no allow full stroke of pump. This is a common mistake with rebuilt pumps installation.

Same spacer was used?

That's a shame Harald. Still a relatively easy check. I have an electric carb priming pump as Roger outlines and also a 6V CD (Winterburn) unit that is the best thing I ever fitted to my car, bar none (no real need for condenser, no points deterioration, higher voltage at start). Brilliant starting and seemingly more low rpm torque.

However, none of this helps you. I assume you have checked the coil resistance values, plug leads, etc. You also had the distributor built, you were saying. I assume when that was done they spun it up and checked the curve on a Sun machine or similar. No shorts inside the dizzy either. Any chance you can borrow another distributor and drop it in?

So, fuel or electrics? Folk on here are far more expert on these cars than I am. My money is mostly on electrics, but fuel flow is also a high probability. Not sure if you have mentioned the fuel lines. I had a problem with my early 911 and it seemed to get fuel starvation at around half throttle. Spent weeks trying to cure that and then cleaned/blew out my fuel lines from carbs to tank and found - a 3" piece of straw that was lodged in there acting as a floating deterrent to flow when I pushed the throttle! Instant success. Not saying that is an issue but check the fuel lines (through to the tank) also perhaps.

Mervyn Hyde wrote:That's a shame Harald. Still a relatively easy check. I have an electric carb priming pump as Roger outlines and also a 6V CD (Winterburn) unit that is the best thing I ever fitted to my car, bar none (no real need for condenser, no points deterioration, higher voltage at start). Brilliant starting and seemingly more low rpm torque.

However, none of this helps you. I assume you have checked the coil resistance values, plug leads, etc. You also had the distributor built, you were saying. I assume when that was done they spun it up and checked the curve on a Sun machine or similar. No shorts inside the dizzy either. Any chance you can borrow another distributor and drop it in?

So, fuel or electrics? Folk on here are far more expert on these cars than I am. My money is mostly on electrics, but fuel flow is also a high probability. Not sure if you have mentioned the fuel lines. I had a problem with my early 911 and it seemed to get fuel starvation at around half throttle. Spent weeks trying to cure that and then cleaned/blew out my fuel lines from carbs to tank and found - a 3" piece of straw that was lodged in there acting as a floating deterrent to flow when I pushed the throttle! Instant success. Not saying that is an issue but check the fuel lines (through to the tank) also perhaps.

Hoping to borrow Sean’s spare 6v electric pump to cut that out of the mix. He mentioned offline that I might have a window to try it before he reinstalled it as a prime/back up.

Roger, an open condensor very frequently will prevent a car from running at all, it is not merely to make the points last longer. Some cars will still run, but very poorly (immediately) with no condensor.

Good Harald. Also check the flow from the pump into a bottle or similar. There is a filter of sorts in the petcock. I assume that is clean?

Roger: your analysis of condenser function ignores the key role as part of a resonant circuit. When they fail open my car won’t run. Spent a night in Reno on the way back from Utah meeting till store opened. And they really do fail a lot these days. Like many others I have now opted for condensorless ignition (and have previously posted the details.)
Regards
Bill

Bill, ok.
You’re saying that if it fails open OR closed, the engine will not run.
Seems counterintuitive but I’ll take your word.
Thanks for the correction.

Harold, A question: Does the engine run fine at 3K rpm with no load? Does it only falter under load?

Do you have a cut fuel line from the pump to the carb? Can you splice in a fuel pressure meter there? It can be done with the original steel line, but You'll need a double banjo bolt and fuel line connector.

If it is faltering both under load and not, see if your fuel pressure is dropping at speed. Just have an extinguisher at the ready whenever modifying fuel lines. I bought a very useful low pressure/vacuum meter for not much money and have used it quite a lot actually.

You eliminated the condenser so that is a big data point. Now you need more information.

You'll get it!

Franny