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 26 2016, 08:50 AM
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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 |
More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests.
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Keith914 |
Oct 30 2016, 03:06 PM
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#3
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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 |
More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests. Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks. Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow. |
Keith914 |
Oct 31 2016, 08:41 PM
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#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 |
More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests. Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks. Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow. With damaged carb part replaced and minor final tuning, including volume metered balance, car is purring like a kitten cold and hot. (IMG:style_emoticons/default/piratenanner.gif) |
Localboy808 |
Nov 1 2016, 06:56 PM
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#5
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Member Group: Members Posts: 185 Joined: 17-July 16 From: Palmdale, Ca Member No.: 20,194 Region Association: None |
More good advice thanks. I have used/adopted all the advice. New gaskets for mounting the carbs and manifold to heads arrive today. Will order other main and air jet combinations for possible further tests. Other than a few minor carb adjustments, the problem was gasket vacuum leaks, primarily between the cylinder heads and the intake runners, where the thick (1/4") gaskets from FI were still being used. This is "known by those who know!" Apparently as the engine heated up this vacuum leak occurred and got bigger the hotter the engine got. Thus while tuning in a good idle with a cold /warm engine, the idle setting disappeared as the engine approached normal operating temp. with large vacuum leaks. Finally discovered one of the "needle screw adjustments" in an air jet had been screwed in too tight breaking a chip out of the casting where the needle extends into the carb barrel - which effectively eliminated it's effectiveness - too much air entering - equivalent to another vacuum leak. Will be replacing the lower casting of this Weber tomorrow. With damaged carb part replaced and minor final tuning, including volume metered balance, car is purring like a kitten cold and hot. (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/cheer.gif) gratz! I know how it feels to solve a problem like this. I think we all do! (IMG:style_emoticons/default/lol-2.gif) |
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