Carb Tuning, and APEX arse kissing Options

[djm914-6]

Yesterday, I drove the 914 to NH to pick up some brake parts I ordered from APEX. These guys are great to deal with adn I highly reccomend calling them for you braking needs. (IMG:style_emoticons/default/smilie_pokal.gif)

I really enjoyed the ride north. The engine was pulling strong and the music was cranking (opened the muffler caps). I did notice one thing though...

When coming to a stop, the engine idles at 1500 RPM and slowly dies down to the normal 900 RPM. This takes about a minute or more. Why? What needs to be replaced or adjusted?

[ArtechnikA]

When coming to a stop, the engine idles at 1500 RPM and slowly dies down to the normal 900 RPM. This takes about a minute or more. Why?

could be that heat soak is temporarily boiling the fuel in the bowls making it run into the engine.

could be a vacuum leak.

a common cause is a sticky dizzy advance weight that's keeping too much advance in too long. this one's pretty easy to verify with a timing light.

[djm914-6]

I thought I read somewhere about measuring some amount of fuel too? I can't remember the specifics?

Also, I think the car may be running rich. When I uncapped the muffler, the inside of the pipes and caps were solid black. I can't imagine that's the way it's supposed to be.

[ArtechnikA]

I thought I read somewhere about measuring some amount of fuel too?

Also, I think the car may be running rich. When I uncapped the muffler, the inside of the pipes and caps were solid black. I can't imagine that's the way it's supposed to be.

not sure what you mean about measuring fuel...
if you mean setting the float level, yes - if they're too high, it can make this problem worse...
if that's not what you mean - what do you mean ? :-)

muffler isn't the best place to look for rich/lean...
pull a plug. better still check it with some kind of gas analyzer, but a plug read will get you in the ball park...

i can get you my carb setup but since i doubt sincerely we have the same venturiis and preatomisers, i don't know how close it'd be for you. also - i still have the open exhaust/track mains in there, they'll be w-a-y rich for the street - and i don't recall what i ran on the street. 110's maybe ...

i have renewed hope that the 911's engine may be okay after all, which means we may still be on for the ECR, and i can bring the Gunson gastester. i don't have much in the way of spare jets, tho - might be able to scare up the set of street jets i once ran ...

[JWest]

I thought I read somewhere about measuring some amount of fuel too? I can't remember the specifics?

You are probably thinking of measuring the accelerator pump quantity. Not really your issue.

[JWest]

a common cause is a sticky dizzy advance weight that's keeping too much advance in too long. this one's pretty easy to verify with a timing light.

Careful, because you can get into a chicken or the egg issue there. If the idle is high for fuel or other reasons, the dizzy will be spinning faster and have more than idle advance if working properly.

Sticking or jumping advance will clue you in that there are issues with the distributor that need to be looked at. A good cleaning of the advance weights never hurts, though.

[crash914]

Dam, if I knew you were in the area......

I have a wide band O2 sensor...we could hook it up and test...I don't know how to adjust carbs though....Matt or Jay could I am sure...

Look me up when you are next in the area...


herb

[balthazar]

Just my .02...

I had the same problem. The engine would drop to about 1500rpm and then slowly drop from that point to about 850 or so. I could tap the pedal to get it to drop faster.

The problem was a weak return spring on the linkage. Since my accelerator cable makes a few bends, the tension between the cable and its sheathing was enough to grab the cable and hold it a little.

Now that the spring has been replaced, the engine will SNAP back to around 650-700rpm them settle out at 850.

[djm914-6]

balthazar, that's an interesting comment. My linkage is rubbing against the aluminum pedal board. I try to bend the bottom plate (where the linkage goes from the pedal itself) toward the brake, but after a few pushes it goes back to the right again. It could very well keep the rpms up. Unlikely IMHO, but possible.

What about the black crap coming out the tail pipes? It's wet and very messy. (IMG:style_emoticons/default/huh.gif)