Help!

RMartin · 09-29-2003, 01:20 PM

I want to thank everyone for their help so far but I still can't get my 68S to run right.
It still won't rev over 3500-4000 rpm. I've put on a new fuel pump,coil, did a valve adj. and just rebuilt the carbs. The car starts good, idles great. No funny engine noises. It runs good up to the point it starts backfiring(through the exhaust)and looses power. The only thing I've done to make any difference at all is to bump up the timing to about 35 BTDC. Then it will pull up to about 5000 rpm but the engine pings when I take off. It seems like the faster the timing is, the higher the engine will rev. The strange part is it only does it going down the road, in the driveway with the correct timing the car will rev to 6000 rpm and sound good.
I haven't been through the distributor yet. Could the cam timing be off? I'm running out of ideas.

dhoward · dhoward's Garage

Have you checked to see if you're getting full throttle at the carbs? THere are a couple of bellcranks in the linkage that can give less than full travel if the bushings are worn....

Early_S_Man · 09-29-2003, 03:09 PM

By all means, check the advance curve, because you need to know if the distributor needs cleaning or other work.

Most likely, though, is that your main jets are clogged because of debris in the fuel ... because under load your engine operates on the idle jet circuit up to past 3500 rpm under load! I recommend removing, disassembling and cleaning the carbs with a vat-type carb. cleaner such as Berryman's Chem-Dip.

RMartin · 09-29-2003, 03:36 PM

I just went through the carbs but I guess I could have missed some dirt. If it's dirt in the mains why would advancing the timing make a difference? Could the main jets be to small? I am assuming they are stock.

nigel911 · nigel911's Garage

What octane gas are you using?

Allenk · 09-29-2003, 05:06 PM

What do the plugs look like? Could you be getting too much fuel? That would explin why advancing the timing is helping.

RMartin · 09-29-2003, 05:54 PM

I'm using 91 octane. The plugs all look good, light brown color. I don't think it's getting to much fuel, but I could be wrong. I haven't smelled a strong gas smell.

Allenk · 09-30-2003, 03:46 AM

Doesn't sound it by the plug read.

Allenk · 09-30-2003, 04:21 AM

I would follow Early_S Mans suggestions at this point. Light brown seems lean. Does it have good pick up up until it won't go anymore? Or is it sluggish? A what point does it start backfiring through the exhaust, after idling for a while or while accelerating? That's a symptom of too much fuel. What are you mixture screws set at?

nigel911 · nigel911's Garage

I don't have as much technical knowledge as most of the other guys on this board - just trying to be helpful so humor me...

When I fill my car with anything other than 87 octane gas it runs like an asthmatic dog - coughing, spluttering and not revving cleanly. Bearing in mind most older cars were designed for the fuel available at the time of manufacture, todays fuel is considerably more refined and of much higher octane. When I collected my 'new to me' 911 it ran fine until I filled it up (can't remember which octane, but definitely 91+). With the higher octane fuel the car would do exactly as you describe: rev cleanly sitting on the drive but under load simply misbehave, misfire, not pull high revs etc. I rang the PO and asked what gas he used, "lowest available octane" was his reply - he is a Porsche racer and DE instructor with a few of Stuttgarts finest in his garage. I ran the tank out, refilled it with 87 and it was like a different car, behaving perfectly at all revs, under load etc. Apparently the octane when my car was built was considerably lower than 87...

Allenk · 09-30-2003, 12:00 PM

Leaded gas.

RMartin · 09-30-2003, 12:59 PM

The car runs good up to the point it starts cutting out, approx 4000 rpm, then will go no more. The mixture screws are two turns out. That was the recommended setting I got off of this board after a rebuild. The air screws are a half turn out. After I rebuilt the carbs and started the car up it idled so good that I didn't mess with the screws very much. I checked the air flow in each barrel with a synchrometer and they were all with in a pound of each other.

Allenk · 09-30-2003, 03:00 PM

Are you sure your throttle valves are opening all the way, letting the high speed circuit kick in? Otherwise, I find it hard to beleive that all your high speed circuits are clogged and nothing else is effected. It sounds more like your running out of fuel. Did you set your float heights? How about fuel pressure? Hopefully someone that has experienced this will chime in soon. I just have ideas of things to check.

RMartin · 09-30-2003, 03:47 PM

Allen, I just went out and had my daughter hold the gas pedal down while I checked the butterflies in the carbs. It looks like the butterflies aren't even opening half way! I don't know why I didn't check this before, someone even mentioned it already. Goin to play with linkage, I'll let you know how it turns out. Thanks

bell · bell's Garage

that'll be great if it is the linkage.......
let us know.......then let us know how much quicker it is

i'd also reset your timing once the linkage is adjusted.

Allenk · 09-30-2003, 04:42 PM

Sounds like good news. Lets us know what you find wrong. It's good info for the next person with a similar problem.

RMartin · 10-01-2003, 02:42 AM

It appears that somehow the bracket on the accel. pedal under the floor board got bent over to the right and was hooked under the tunnel where the cable comes up. After I popped it loose I had an additional 2 or 3 inches of pedal movement. After work tonight I'll finish readjusting the linkage.
This is why It would rev good in the driveway(working throttle by hand) vs. down the road(working throttle by stuck accel. pedal.
Feel like an idiot but at least I got a bunch of new parts and a carb rebuild out of the deal! LOL
I expect the car will be a whole bunch quicker. Can't wait! If anyone is wondering you can go exactly 70mph on the idle circuit.

RMartin · 10-01-2003, 04:30 PM

OK guys I got the linkage all adjusted and now the butterflies are opening all of the way. Set the timing where it should be and went for a test drive. Same exact thing happened! Would not rev over 4000 rpm. Backfiring and loss of power. Went back and tried to set the timing back up but never did find a spot where I could get the engine to rev up to 6000 in the driveway. There is someting screwy with the timing on this car. Can the distributor cause this?
If I set the static timing by the book that I have the car will start and idle fine. Then you're supposed to run the engine up to 6000rpm and set at 30 BTDC. The motor will not rev over 2500 rpm if I follow this procedure. I have to bump the timing up at idle to almost 30 BTDC before the car even has enough power to pull out of the driveway.

Allenk · 10-01-2003, 04:50 PM

That just s_cks. I'm just shooting from the hip here so please.... I'm assuming the distributor has a mechanical advance? or is it vacuum? Either way does the rotor advance by hand and snap back? How do the points look? Are they gapped properly? Have you tried to rotate cyl. #1 to TDC compression, to see where the Z1 and rotor alignments are?

RMartin · 10-01-2003, 06:56 PM

Yes it has a mechanical advance. Every thing looks free and snaps back. I've checked the points several times and the gap is correct. I've also went to top dead center and had the dizzy out a coulpe of times. This thing is driving me nuts. Got to be missin something here some where. Bout ready to send the dizzy off and have it rebuilt, its the only thing I haven't gone through.
Can the cam timing be off? How can I check that?