Fuel starve, or something Options

[arsprod]

Teeners,

I swapped out the single carb that came with my 74 2.0 for new to me dual Weber 40's. It took a bit to get them jetted and adjusted but it's at least very close. The car runs great - and then it doesn't. With no consistency, it will start to stumble, cough, and backfire. Most of the time it works itself out though seems to be getting worse. I'm befuddled. (IMG:style_emoticons/default/confused24.gif)
Here's what I know:
- carbs are jetted main 145, air 200, idle 65, venturi 28
- plugs look ok, if anything rich
- I don't seem to have any vacuum leaks
- steady 3psi fuel pressure
- timing and valves adjusted
- new plugs

Help! thanks

Aaron

[Superhawk996]

Sounds more like an ignition issue because of the randomness. Could be sticking advance plate assuming you’re using a traditional mechanical distributor.

Ignition and fuel issues are commonly mis-diagnosed one for the other.

Otherwise not enough info in your post to be of much help. No mention if RPM’s and load when this occurs. No photos of plugs. Have you verified bowls are clean and free of debris? Checked the jets for debris / corrosion?

The jetting you have is a little bit non traditional (main smaller, idle larger) but should be capable of running consistently and reliably.

On the fuel side, are you sure you have carbs properly tuned for best lean idle and synchronized properly?

[arsprod]

Sounds more like an ignition issue because of the randomness. Could be sticking advance plate assuming you’re using a traditional mechanical distributor.

Ignition and fuel issues are commonly mis-diagnosed one for the other.

Otherwise not enough info in your post to be of much help. No mention if RPM’s and load when this occurs. No photos of plugs. Have you verified bowls are clean and free of debris? Checked the jets for debris / corrosion?

The jetting you have is a little bit non traditional (main smaller, idle larger) but should be capable of running consistently and reliably.

On the fuel side, are you sure you have carbs properly tuned for best lean idle and synchronized properly?

I know jetting is weird but ended up there after trial and error. I feel comfortable saying they're at least very close to tuned. It's worse under load above 3k rpm. I'll pull the bowls again and check.

Interesting theory about ignition. It's an 009 that came with the car.

[Artfrombama]

It's worse under load above 3k rpm. I'll pull the bowls again and check.

My $.02
That screams fuel starvation but could be fouled plugs, narrow point gap.

[VaccaRabite]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

[arsprod]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

[Superhawk996]

Go smaller on idle (55) and maybe . . . Maybe . . . larger on main. Rule of thumb is main = 5x the Venturi. You’re already there. If it were me I’d just do the idle 1st.

Webers run off the idle about 70% of the time at light throttle, light load and 50-60 mph cruise. What you want is a seamless transition from the smaller idle circuit to the larger main (under acceleration and higher loads).

Once it’s running consistently then I would run some high speed high load runs where I know I’ll be in the main 100% and then re-read the plugs to decide if I need to go bigger on the main.

Post photo of plugs.

To reiterate my 1st post . . . Randomness leads me to suspect ignition more than fuel. I ran a 009 back in the 80s for tens of thousands of miles and could never make it work properly, there were always holes especially when accelerating from lower engine speed. Eventually had to have it re-curved to make it work properly. But having said that it was always reliable and drivable.

See post #12 to get an idea of how poor the 009 is vs ideal advance curve.
http://www.914world.com/bbs2/index.php?sho...370919&st=0

[Superhawk996]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

No, it would be rich misfire with the backfire coming from too much fuel being dumped in and it not lighting off until it gets dumped into the hot exhaust system.

This is why I’d like to see your plugs.

[arsprod]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

No, it would be rich misfire with the backfire coming from too much fuel being dumped in and it not lighting off until it gets dumped into the hot exhaust system.

This is why I’d like to see your plugs.

Well I pulled them to test for fouling and not pulling again! They passed the resistance test. I put 50 idles in and also ordered a cheap 009 clone from Amazon. It will be here tomorrow and an easy, cheap test. I'm going to check the bowls (again) for debris and float height. Stay tuned, and thanks for the input.

[ClayPerrine]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

No, it would be rich misfire with the backfire coming from too much fuel being dumped in and it not lighting off until it gets dumped into the hot exhaust system.

This is why I’d like to see your plugs.

Well I pulled them to test for fouling and not pulling again! They passed the resistance test. I put 50 idles in and also ordered a cheap 009 clone from Amazon. It will be here tomorrow and an easy, cheap test. I'm going to check the bowls (again) for debris and float height. Stay tuned, and thanks for the input.

Am 009 distributor is terrible in a Type IV. The advance curve is all wrong. Get a 1-2-3 Distributor or find the distributor from a 1.8 914. Both will work Way better than an 009.

[rhodyguy]

Turn one idle speed adj screw in increasing the idle pretty high. Leave the other ISAS alone. Now measure the flow too see how closely they match. The 009 will work but the system is not optimized. Are points inside of the distr or something solid state? Any sort of snapping or popping back thru a carb?

[arsprod]

Turn one idle speed adj screw in increasing the idle pretty high. Leave the other ISAS alone. Now measure the flow too see how closely they match. The 009 will work but the system is not optimized. Are points inside of the distr or something solid state? Any sort of snapping or popping back thru a carb?

OK, did that - other carb is within 3 ticks of the fast idle one. What does that tell me? It's points, and yes getting snapping and popping through carb.

[rhodyguy]

I’m not familiar with 3 ticks. Of what? You mean a snail gauge and one carb reads 6 and the other 3? Snapping back on the lower reading carb?

[arsprod]

I’m not familiar with 3 ticks. Of what? You mean a snail gauge and one carb reads 6 and the other 3? Snapping back on the lower reading carb?

Yes, sorry - exactly that, snail gauge fast set carb is 6 other is 3

[arsprod]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

No, it would be rich misfire with the backfire coming from too much fuel being dumped in and it not lighting off until it gets dumped into the hot exhaust system.

This is why I’d like to see your plugs.

I think I figured it out and Superhawk you were right - ignition. Of course it's something simple and embarrassingly stupid. The points weren't opening, somehow lost the gap. After gapping correctly and readjusting the carbs it's running again. Argh!

[930cabman]

with 65 idles you are overjetted for a 2.0. At 3K you have both idles and mains pushing fuel to the engine. You may be fouling plugs. BTDT.

Zach

Easy enough to try smaller idle jets. I'll actually test the plugs. You're saying that too much fuel going through the transition shows like too lean?

No, it would be rich misfire with the backfire coming from too much fuel being dumped in and it not lighting off until it gets dumped into the hot exhaust system.

This is why I’d like to see your plugs.

I think I figured it out and Superhawk you were right - ignition. Of course it's something simple and embarrassingly stupid. The points weren't opening, somehow lost the gap. After gapping correctly and readjusting the carbs it's running again. Argh!

Great, you found it. Could be as simple as the screw holding the points was not tightened.

I have an 009 in my fresh 2056 with twin Weber 40 IDF's. Runs great. Not sure what all the hub bub about 123?

[arsprod]

[/quote]

Great, you found it. Could be as simple as the screw holding the points was not tightened.

I have an 009 in my fresh 2056 with twin Weber 40 IDF's. Runs great. Not sure what all the hub bub about 123?
[/quote]
Hey, I get it and if I had an extra $700 I'd get one too!

[Superhawk996]

I’m not familiar with 3 ticks. Of what? You mean a snail gauge and one carb reads 6 and the other 3? Snapping back on the lower reading carb?

Yes, sorry - exactly that, snail gauge fast set carb is 6 other is 3

Glad you found the ignition / points issue.

While you are in there doing a tune up, synchronize the carbs. You should be ably to get both sides pulling the same amount of air.

The car will transition better if the carbs are synchronized.

[arsprod]

I’m not familiar with 3 ticks. Of what? You mean a snail gauge and one carb reads 6 and the other 3? Snapping back on the lower reading carb?

Yes, sorry - exactly that, snail gauge fast set carb is 6 other is 3

Glad you found the ignition / points issue.

While you are in there doing a tune up, synchronize the carbs. You should be ably to get both sides pulling the same amount of air.

The car will transition better if the carbs are synchronized.

Yep! And I still need to put smaller idle jets in (ordered). It's still loading up after about 30 minutes, stumbles, backfires, then fine.

[dr914@autoatlanta.com]

agree replace the condenser

Sounds more like an ignition issue because of the randomness. Could be sticking advance plate assuming you’re using a traditional mechanical distributor.

Ignition and fuel issues are commonly mis-diagnosed one for the other.

Otherwise not enough info in your post to be of much help. No mention if RPM’s and load when this occurs. No photos of plugs. Have you verified bowls are clean and free of debris? Checked the jets for debris / corrosion?

The jetting you have is a little bit non traditional (main smaller, idle larger) but should be capable of running consistently and reliably.

On the fuel side, are you sure you have carbs properly tuned for best lean idle and synchronized properly?