Starving Under Load? Options

[Rand]

Never heard of "trigger points". Are we talking regular points...the ones in the dist.?

Not the ignition points, they trigger the FI. Doesn't apply with your carbs.
Let us know when you check/replace the fuel filter.

[crash914]

trigger points are used in fuel injection engines to "trigger" the fuel injectors to fire. They are located at the base of the distributor. Usually when these wear out you will get a miss at around3200 to 3500 rpm....

With carbs, these are not an issue.

[kenshapiro2002]

Well...she's doing it all the time now. The fuel filter was very clean. At idle she can rev up better than under load (of course?) but she's spitting and backfiring now as well. The air filters were filthy, but I ran her around the block while they were soaking and she didn't do any better without the filters. PO (Porsche tech) tuned her before she was sold. Does it sound more like tune or carbs?

Never heard of "trigger points". Are we talking regular points...the ones in the dist.?

Not the ignition points, they trigger the FI. Doesn't apply with your carbs.
Let us know when you check/replace the fuel filter.

[kenshapiro2002]

How difficult is this? Do I need a weber book to follow? I'm ready to do it, but need some guidance.
Ken

...next would be to disassemble the carbs and clean...look for the varnish. I just had to do this to my snowblower....

[Kirmizi]

http://www.carburetorclinic.com/weber_tech.htm
Try there, in addition to searching this site.
Mike

[nycchef]

http://www.carburetorclinic.com/weber_tech.htm
Try there, in addition to searching this site.
Mike

this worked for me..eventually





A copy of my carb tuning method post for Trekkor, a few years ago.

Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good.

Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist.
Start and warm up the engine.
Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off.
Turn the mixture screws all the way in and then 5 half turns out.
Turn the air bypass screws all the way in.
Turn the idle speed screws out til it just touches, and then in 5 half turns.
Put on your hearing protection and start the car.
Use your STE and find the barrel that pulls the most. We'll call this one baseline.
Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)
Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels.
Go to the other carb and do the same thing.
Snug the jamb nuts on the air bypass screws.
All six (or four)barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure.
Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance.
Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm.
Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest rpm, then turn it in 1/4 turn.
Do the same with the five other mixture screws.
If you have to turn the mixture screws more than two turns either way, you've got the wrong jets.
Recheck side to side and individual air balance, adjust as needed.
Road test the car.
If you get snapping and poping out the intake, it's generally a lean condition.
If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich.
If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets.

That's a rough, five minute draft of my carb tuning proceedure, hope it helps!

If it goes good it should take about 45 minutes, if not about three years.

PK

Another good tip: If you think you have a lean cylinder (idle jet plugged) you can back out the jet carrier a half to one full turn and the engine should stumble, if it doesn't change theres a good chance the jet is clogged. This primarily applies to the 3 barrel carbs, as the 2 barrel IDF's have a different type idle jet set up.

Don't diminish the value of correct ignition timing, and valve adjustment, it makes a difference. Also make sure your linkage is dead nuts the same length.


--------------------

Perry Kiehl

several mid engined Porsches
914 Network
914 Restorations, Repairs, Parts
Exclusive source for the 914 Umbrella Cover

[jmill]

After sitting for so long you need to go through the carbs. Junk builds up in the float bowls, fuel wells, accel pump and passages. I wouldn't be surprised if your float bowl and accel pump body is filled with all kinds of crud and corrosion. Running it after it sits for years will then spread that junk through your jets. Buy a couple of rebuild kits and the weber tech manual. You'll be glad you did. You'll know how they work and how to tune them.

[kenshapiro2002]

Thanks all.
Ken

After sitting for so long you need to go through the carbs. Junk builds up in the float bowls, fuel wells, accel pump and passages. I wouldn't be surprised if your float bowl and accel pump body is filled with all kinds of crud and corrosion. Running it after it sits for years will then spread that junk through your jets. Buy a couple of rebuild kits and the weber tech manual. You'll be glad you did. You'll know how they work and how to tune them.

[r_towle]

pull them off.
Box them up.
Send them to Art.

http://www.aircooledengineering.com/services.html

Rich

[kenshapiro2002]

Just drove it like I stole it and it ran better, at least for awhile. At about 4,500 RPM it often acts like I've hit a governor..it just goes flat. It wanted to "starve" especially in lower gears , until I nailed it and it seemed to get "beyond" that. All in all it ran much better. The can of Techron I threw in a few days ago might have helped too. I;m convinced that all other parameters are pretty good and that it's carb filth, or just bad adjustment / balance. The rebuild kits and synchro tool arrived today.

[r_towle]

If you get a gallon can of carb cleaner so you can dunk them its about a two hour job to do it really nice and clean...
It can be done in one night.

Do remember...do one at a time so you dont forget what goes where...you have a live roadmap to look at.

Carb cleaner, toothbrush, compressed air and a clean tabletop...your good to go.
Dont set the carb cleaner on concrete or on metal...it starts a reaction in the can (read the can)
Dont drip the cleaner on anything...it will act like bleach in a few seconds and stain it.

Aside from that.....just work at a steady pace and clean every single part in the carb and the body itself...then put it back together.
You will be very happy you did it.

Rich

RIch

[jmill]

1 -Does it scream away in the first couple of gears and then fall on its face.

2- Does it fall off in any gear under load at 4500 RPM.

3- Is there any popping out of the carbs at 4500.

1 = fuel pump is junk or your fuel filter is buggered up
2 = mains are too big
3 = mains are too small or see #1

[kenshapiro2002]

1...No. In fact it does worse in first than any other gear.
2...It's erratic. Sometimes it falls off at 4,500, other times it's OK.
3...Not sure where the popping is coming from; probably carbs. Again, it's erratic and seems to be mostly on decel.

1 -Does it scream away in the first couple of gears and then fall on its face.

2- Does it fall off in any gear under load at 4500 RPM.

3- Is there any popping out of the carbs at 4500.

1 = fuel pump is junk or your fuel filter is buggered up
2 = mains are too big
3 = mains are too small or see #1

[seebobgo]

Let the spending begin. You got to find a good shop in Baltimore. My shop is in Annapoli$$$

[kenshapiro2002]

Shop my ass...anything a "shop" can do I can do. Usually better because I don't know what I'm doing so as well as the shop wrench does, I study the problem, take my time, work clean, and care about the results and the condition my car is stored in, worked on and returned to. Same with home improvement.

Let the spending begin. You got to find a good shop in Baltimore. My shop is in Annapoli$$$

[kenshapiro2002]

Alright...so I've had the rebuild kits for a week or so and was awaiting the Haynes manual...anxious to get started. Well, after reading chapter 12 on rebuilding the carbs, I have an ice cream headache. Surely I don't need to strip every single part out of these babies, do I?

[r_towle]

Alright...so I've had the rebuild kits for a week or so and was awaiting the Haynes manual...anxious to get started. Well, after reading chapter 12 on rebuilding the carbs, I have an ice cream headache. Surely I don't need to strip every single part out of these babies, do I?

Yes, and its simple.
Keep one carb fully assembled while you do the other.

All the parts only fit in one place....that is the beauty.

Rich

[jmill]

To do it right, yes. There isn't much to them.

[kenshapiro2002]

So...just went out to drive her hard again. I guess Im hoping she'll "heal" so I can avoid the carb rebuilding thing. Anyway, she runs well at idle (idle jets seem fine), and was running OK for awhile if I really floored it. Then she started bogging down around 4,000 RPM...completely starved (or sparkless; fuel starved it seems). I gave a better look into the fuel tank. The sock looks crapped up, but it's hard to tell for sure...just looked black. around the base of the tank...near the sock (inside what I assume is a round baffle surrounding the sock), there were many super small black specs...very small. I'm guessing this is crud that fell off the sock? Anyway, the tank walls look very clean and shiny. If the sock is my problem, it seems wasteful to do the carbs prior to replacing the sock. Am I right?

Also, will the tank come out without raising up the car? Is it simply an undoing of the strap, and taking off the fuel line once I lift it?

[jmill]

Yes it's that simple if the tank is empty. Don't forget about the access hole below the tank. That's right where the sock is and where your fuel line exits the tank. I pull the tank but others may have changed the sock through the access hole.

Explain this "starvation" you have. Does it just bog down or do you get pops out of the carb too. No lean pops and just bogging means too much fuel or ignition issues.

Starvation with carbs happens when the fuel supply can't fill the float bowl as fast as it's used. You suck down the float bowl and your mains run lean. You then get a bunch of pops and snaps from the carbs. The engine then usually dies because the idle jets get their fuel from the main fuel wells and those are too low already. You then can't start your car until the fuel system fills the float bowls up again.

Pull out one of your ETs and let us know what main and ac jet your running along with what ET you have. They are easy to remove. All you need is a standard screwdriver. Be careful when you reinstall it. Be gentle and don't cross thread it.