Carburetored type IV engine problem diagnosis., Engine idling problem. Options

[Keith914]

Just completed very careful cleaning, installing, adjusting, balancing two Weber carbs on my recently rebuilt '72 1.7 type IV 914 engine upgraded to 2.4 L. Carbs are real Webers (Spain), and we're working well earlier. Balancing and setting idle at 1,100 rpm was done on cold engine - nice smooth idle and solid response to accelerator action. The carbs are 44's, idle jets are 55's, main jets are145's and the air jets are 200's. Sea level ambient condition.
Engine starts immediately and runs very well and continues to run very well above about 2,000 rpm. But once engine is approaching and then at normal operating temp - 190 F, it will not run smoothly below about 2,000 rpm, and at idle accelerator position, engine drops below 1,000 rpm and stumbles to stalling sometimes with pre ignition sounds as it stalls! Timing is set at 32 degrees at 3,000 rpm, and distributor is new with new Pertronix electronic unit, and no vacuum mechanism.

Welcome any diagnosis suggestions.

[injunmort]

all linkages and actuators are sync, try 34 degrees advance at 3000rpm, that is where my 40's run best.

[Keith914]

Just completed very careful cleaning, installing, adjusting, balancing two Weber carbs on my recently rebuilt '72 1.7 type IV 914 engine upgraded to 2.4 L. Carbs are real Webers (Spain), and we're working well earlier. Balancing and setting idle at 1,100 rpm was done on cold engine - nice smooth idle and solid response to accelerator action. The carbs are 44's, idle jets are 55's, main jets are145's and the air jets are 200's. Sea level ambient condition.
Engine starts immediately and runs very well and continues to run very well above about 2,000 rpm. But once engine is approaching and then at normal operating temp - 190 F, it will not run smoothly below about 2,000 rpm, and at idle accelerator position, engine drops below 1,000 rpm and stumbles to stalling sometimes with pre ignition sounds as it stalls! Timing is set at 32 degrees at 3,000 rpm, and distributor is new with new Pertronix electronic unit, and no vacuum mechanism.

Welcome any diagnosis suggestions.

Also I should mention on two occasions as the engine stalled from idle, there was a loud single backfire?

[Keith914]

Here is a pic of the linkage.

[Valy]

You should adjust carbs when engine is warm, not cold.
Sounds like the mixture is too rich at idle.

[Keith914]

Here is a pic of the linkage.

Here is a better pic.

[Keith914]

You should adjust carbs when engine is warm, not cold.
Sounds like the mixture is too rich at idle.

The air/fuel mixture "needle" valves are set at two turns from closed. I wil turn them in when the engine is hot as a trial tomorrow. Thanks for your comment.

[stugray]

Sounds like an ignition problem not carbs.
Is your advance mechanism sticking?

[flyer86d]

Clogged idle jet.

[Keith914]

Removed the carbs again and inspected the float adjustment. Both were above parallel with the underside of the casting - adjusted them back to parallel. This reduced the fuel level about 1/2 inch. Inspected all four idle jets - all were clear. Inspected the jet and diaphragm of the acceleration pumps - both were clean and in good shape.
Adjusted the air fuel valves leaner and richer ( in and out respectively) with the engine close to operating temp. Was unable to find a smooth idle position - each setting eventually leading to a stall at various idle speeds. Engine still runs well above 2,000 rpm - suggests ignition is firing all 4.
Checked timing - at 3,000 rpm, setting is on leading edge of large fan bar - 34 degrees (?). Fuel pressure is at 4 lbs/ square inch.

What should I try next?

[stugray]

Removed the carbs again and inspected the float adjustment. Both were above parallel with the underside of the casting - adjusted them back to parallel. This reduced the fuel level about 1/2 inch. Inspected all four idle jets - all were clear. Inspected the jet and diaphragm of the acceleration pumps - both were clean and in good shape.
Adjusted the air fuel valves leaner and richer ( in and out respectively) with the engine close to operating temp. Was unable to find a smooth idle position - each setting eventually leading to a stall at various idle speeds. Engine still runs well above 2,000 rpm - suggests ignition is firing all 4.
Checked timing - at 3,000 rpm, setting is on leading edge of large fan bar - 34 degrees (?). Fuel pressure is at 4 lbs/ square inch.

What should I try next?

Based on some of your explanation I think you should read the instructions again of how you set the float valves.
Running poorly once warm could be an intake manifold air leak.
Had one this morning at the track because I had just reinstalled both carbs with phenolic spacers and double gaskets. Ran great on all of the 5 minute loops around the neighborhood.
The car had never been solidly heat soaked so when I checked the carbs after the first race they were both loose

[Keith914]

Removed the carbs again and inspected the float adjustment. Both were above parallel with the underside of the casting - adjusted them back to parallel. This reduced the fuel level about 1/2 inch. Inspected all four idle jets - all were clear. Inspected the jet and diaphragm of the acceleration pumps - both were clean and in good shape.
Adjusted the air fuel valves leaner and richer ( in and out respectively) with the engine close to operating temp. Was unable to find a smooth idle position - each setting eventually leading to a stall at various idle speeds. Engine still runs well above 2,000 rpm - suggests ignition is firing all 4.
Checked timing - at 3,000 rpm, setting is on leading edge of large fan bar - 34 degrees (?). Fuel pressure is at 4 lbs/ square inch.

What should I try next?

Based on some of your explanation I think you should read the instructions again of how you set the float valves.
Running poorly once warm could be an intake manifold air leak.
Had one this morning at the track because I had just reinstalled both carbs with phenolic spacers and double gaskets. Ran great on all of the 5 minute loops around the neighborhood.
The car had never been solidly heat soaked so when I checked the carbs after the first race they were both loose

Thanks for all the feedback. Have checked for vacuum leaks and when engine is running will use some carb cleaner to double check vacuum leaks.
Will install a fuel pressure regulator before start up to bring the pressure down from 4 to 2.5 lbs/square inch.

[McMark]

What's your advance at idle?

Get a modern adjustable timing light. They're cheap and you'll use it regularly.

[porschetub]

That fuel pressure is very high,that would cause the stalling,try to regulate it back to 3 psi,I think Jake Raby mentions he uses 2.5 psi. which ever pressure you use it will improve.
Choose a quality low pressure regulator not the cheap crappy one the VW shops sell.
You can never tune carbs with high fuel pressure as you will have fuel spilling over from the fuel bowls down the throats,raw fuel doesn't burn well.
These are large carbs for a 1.7 what size venturies are you running? .
Good luck.

[ChrisFoley]

These are large carbs for a 1.7 what size venturies are you running? .

He said its a 2.4L now.

[Mr Pharmacist]

I had idling issues for ages on my 2056 with 40 IDF's. I eventually fixed it by balancing the carbs using a carb air flow meter and a youtube video - its never idled so smoothly!

[Keith914]

One more issue identified. The gaskets between the heads and the intake are thick (1/4") which are prone to causing vacuum leaks with carbs. I will be replacing them with typical thin gaskets today and will report back.

[rhodyguy]

Don't tighten one carb to intake nut fully. Bring the torque value up in stages in a x pattern.

[Eric_Shea]

You have to use a syncrometer.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.partsklassik.com-1110-1477416745.1.jpg)

Valves and timing must be set.

Tune with the engine warm and at 2000 RPM

Without a syncrometer, you're just pissing in dark pants. (IMG:style_emoticons/default/wink.gif)

http://www.partsklassik.com/p-703-synchrometer.aspx

[Elliot Cannon]

My type IV is 2.2. I also have 44idf Webers. I've had them on the car for about 13 years and just recently rebuilt them. After rebuild it still ran like crap. I again checked the idle jets and found the jets on the passenger side carb were hopelessly clogged. Even after a thorough cleaning and rebuild. Cleaned them out, car runs great. I use 130 mains, 175 air jet, 55idle jets and 34 venturis. What size venturis are you running? Maybe try a different size vent. My experience with Webers is, you need to start with a jet combination then trial and error from there. I tried different combo's till I found what works for me. Try using smaller mains and air jets. You may also find your venturis are too large. (or too small) The syncrometer is a must have for balancing the carbs. I followed this advice for float adjustment. https://www.youtube.com/watch?v=54uPwTZ3DJw