Carburetored type IV engine problem diagnosis., Engine idling problem. |
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Carburetored type IV engine problem diagnosis., Engine idling problem. |
Keith914 |
Oct 21 2016, 07:00 PM
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#1
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Member Group: Members Posts: 248 Joined: 29-April 16 From: Laguna Beach, California 92651 Member No.: 19,948 Region Association: Southern California |
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. |
Keith914 |
Oct 22 2016, 08:51 PM
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#2
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Member Group: Members Posts: 248 Joined: 29-April 16 From: Laguna Beach, California 92651 Member No.: 19,948 Region Association: Southern California |
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 |
Oct 22 2016, 09:06 PM
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#3
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Advanced Member Group: Members Posts: 3,825 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
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 |
Oct 23 2016, 08:24 PM
Post
#4
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Member Group: Members Posts: 248 Joined: 29-April 16 From: Laguna Beach, California 92651 Member No.: 19,948 Region Association: Southern California |
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. |
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