Scott,

Have you checked the vacuum advance diaphram for leaks? Also, might double check the vacuum advance and retard (if equipped) lines to make sure they are connected to the correct ports on the throttlebody.

Dennis

 

Dennis,

My shark is outfitted with the vacuum retard only. I have checked with mighty vac - it checks ok. Location on throttle body is correct as well.

Also,
I have confirmed that I have no screen on my Fuel Dist. inlet.

 

Scott,

Your 79 may have an advance only but it would be very rare to have a distributor with vacuum retard only. Sure you have it connected to the right thottlebody port?

Dennis

 

Dennis,

I may be a little backwards here:

When I remove the vaccuum line (car running) the idle speeds up. Timing is correct, by the way.

With distributor cap off, vacuum applied to the pot with mighty vac - the innards rotate ccw. Is this advance or retard? Must be advance.

The vacuum line is attached to a port on the front of the throttle body, I believe it is on the downstream side of the butterfly (between butterfly and plenum). Strong vacuum is observed.

 

I have only an advance port on my distributor and it is connected to the forward side of the T/B like yours Scott.
My idle slightly increases as well when that vacuum line is disconnected but not pluged, probably because of a leaning of the mixture.

 

OK - so air has been checked and is tight. You've minimized the vac lines and areas where air can leak.

If you recently pulled the motor, the fuel lines were disconnected for a time. Any chance a foreign object made it into the line, and is now creating a blockage? I know of one case recently where there was a flake in the fuel line that was not a problem at idle, but as more fuel was flowing, the flake caused blockage - at higher rpm - engine stumbling. Not on a CIS system, but I guess there is potential for it to happen. For this you would need to dismantle the runners and control lines and clear the lines. Probably do the main line too.

 

Scott,

The plate moving CCW will trigger the sensor and fire the coil sooner, so that is alright. The correct vacuum port is just left of front center on the throttlebody. There should be little or no vacuum at the line when the throttle is closed. When you set your timing did you remove the vacuum advance hose and plug it? The timing should then be set at 31 BTDC at 3K rpm. Once that is set, reattach the vacuum line and check the timing at idle (800 rpm). It should be at TDC +or- 4 degrees. If the timing is more than 4 degrees advanced you have the throttle plate blocked open or you are connected to the wrong port.

Dennis

 

Old school theory says that you have one of the following; not enough fuel delivery. not enough spark. not enough air. no exhaust flow. Vaccume leaks are usually worse at idle. When you put the rotor on, you also replaced the cap, yes? Air filter is clean, yes? All fuel filters replaced, yes? Try putting a gauge on the fuel line to check pressure and delivery. If you have checked all the above, and you know there is no vaccume leak, then it may be time to buy that fuel injection book that you always wanted.

 

DK,

I did recently find a flake (brass in appearance) in my old WUR inlet screen. I theorized that the flake may have come from my test gage adapter but is could have been from haviung my fuel system open while the engine was out. I removed the WUR inlet and outlet lines and cleaned - no blockages. I suppose that for a flake to make it into the WUR inlet screen it would have had to pass through the distributor - could be more trash in the distributor.

Dennis,

Timing was set per **** with vacuum line plugged. I have strong vacuum at idle - I'll need to double check my vacuum line installation. I'll also check timing at idle per your suggestion.

 

I think I'm on to something now. Apparently, I've measured the fuel delivery in the wrong spot. I had measured at the fuel supply fitting at the dist. and the correct spot for cars outfitted with a push valve is at the return to tank. Per spec. this should be 1360cc in 30s, I've measured 1100cc in 30s -- 260cc short.

My fuel filter is new, but one never knows what could have happened. My exterior fuel pump is new as well, but I can hear cavitation at the outlet - might have a suction problem. I'm going to assess the in tank pump by removing the leads on the external pump, turning the key and listening (with safety circuit bypassed). Perhaps this will tell me if I need a new internal pump.

 

Scott,

If you find the internal pump is deficient, try reversing the leads to see if it dislodges any crud or corruption. What type of external pump did you install?

Dennis

 

What does cavitation sound like? Just noisier than normal, or some specific type of sound? I wouldnt have thought that a 20% reduction in flow would produce that much of a power loss....
Checking the internal pump for working sounds like a good thing to do, as if it fails it seems to produce a big drag on flow.
jp 83 Euro S AT 49k, only one pump.

 

The external pump is OEM from 928 Intl. with no built-in check - I added a new check when I installed. The cavitation sounds like bb's rolling through the discharge. This is probably from the check chattering.

The more I read about the K-Jet (thank's to Sean79 for the PDF files) the more I'm convinced that my internal pump is bad and my external can't work hard enough above 2500rpm AND its trying to suck through a dead pump (nice flow restriction). I haven't had time to physically check, but I'm expecting a bad pump. Here's why: The Bosch manual states that fuel delivery for cars outfitted with one pump should be at least 1120cc in 30s, and two pumps should be at least 1360cc in 30s (measured at the fuel return to tank at distributor). My shark is outfited with two and I measured the delivery to be 1100cc in 30s - the math is not difficult here.

Pitman,
Such a power loss does seem drastic, but nothing suprises me anymore with this k-jet. It can be so delicate and so robust at the same time. Fuel flow and pressure are absolutely critical. To truly understand the power loss, I need to understand why some sharks require two pumps and why some don't. For example, according to the test sheets in the manual, some sharks have a single delivery test value: autos - 1 pump, 5-spd (USA and Japan) - 2 pumps. And some for both one and two pumps. So, why do some require 2 and some only one? I've heard that the second is required in hotter climates. Is this true and why? Apparently some work with the one pump with no issues, so why "potentially" is my shark affected so drastically?

 

hi i had a similar problem , with my 1988 928s4 auto, idle a little lumpy, would rev ok in park but under load over about 4000 rpm ....no power ,the mass air flow meter was at fault, got a new one quite expensive 400 pounds but she like a rocket now

 

Scott, My car is originally a UK delivery (opt C16) with one external pump. It spent 10 years in Saudi and still only had one pump when I got it, although it doesnt seem to be the original one (no surprise there). Never missed a beat in terms of fuel delivery (~1300cc/30secs at return line) at 100F +, only lost power due to crud in WUR inlet screen and rising hot control pressure. The two pump thing seems to cause as much problem when internal fails as just having one pump.
jp 83 Euro S AT 49k