Better informed with problems on 3 YFAs
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Senior User
Joined: Jun 2004
Posts: 106
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From: Scottsville, VA
Better informed with problems on 3 YFAs
First off I know that by many YFAs are viewed as junk and I understand full well but I'm not playing with a full deck, I refused to pay the tax on the ace of spades. This time I come to the forum well informed though.
This excerpt came from a Stromberg rebuild page http://www.btc-bci.com/~billben/fuel.htm: When using multiple carbs the manifold vacuum is usually low... . which contributes to premature opening of the vacuum controlled power valve. It’s not uncommon to find these valves opening with less than ‘A throttle applications since almost any drop in vacuum is enough to make them operate. As can visioned, this leads to a rich condition when it’s not needed. It’s impossible to compensate for this over rich condition by reducing the main jets because when these vacuum power valves open it’s the same as increasing the main jet size 10 whole numbers~ No wonder they always run rich. Stromberg’s mechanical power valve operates mechanically and is relatively unaffected by low vacuum. This eliminates the over rich conditions that are caused by the power valve opening too soon or when it’s not needed. Also, the Stromberg power valves can be drilled to suit your needs and driving habits whereas the vacuum type cannot since they are sized during manufacturing.
okay with all of that now known to me and in mind I can understand what spkytr and others were saying that it is more then jets and synchronizing the idle. There are also off idle conditions which must accounted for and that does include less vacuum at each carb. so here are my questions since I'm not knowledgeable of the internals of the Carter YFA. Does the YFA have a power valve? Is the metering rod the same as the power valve? I've heard of kits for Holleys that did away with the vacuum power valve and use a mechanical one as used by the Stromberg but never seen one used, only hearsay. If the power valve is an issue on a YFA, I believe that can be gotten around with a little engineering and small tooling machine shop work. I want the same effect as 3 stromberg 97s on my 300 without having to use 3 rare carbs. 3 Strombergs would give me strong torque and power off idle to about 4500 rpm which for me is more than sufficient. Any help with my continued trek into insanity and the bowels of carburetion infamy would glady be appreciated.
Spyktr I appreciate your input last time and I'm sorry for my poor choice of reaction. You've helped me research my project better. Today I found the answer finally remembering the name Stromberg. Thank you very much.
This excerpt came from a Stromberg rebuild page http://www.btc-bci.com/~billben/fuel.htm: When using multiple carbs the manifold vacuum is usually low... . which contributes to premature opening of the vacuum controlled power valve. It’s not uncommon to find these valves opening with less than ‘A throttle applications since almost any drop in vacuum is enough to make them operate. As can visioned, this leads to a rich condition when it’s not needed. It’s impossible to compensate for this over rich condition by reducing the main jets because when these vacuum power valves open it’s the same as increasing the main jet size 10 whole numbers~ No wonder they always run rich. Stromberg’s mechanical power valve operates mechanically and is relatively unaffected by low vacuum. This eliminates the over rich conditions that are caused by the power valve opening too soon or when it’s not needed. Also, the Stromberg power valves can be drilled to suit your needs and driving habits whereas the vacuum type cannot since they are sized during manufacturing.
okay with all of that now known to me and in mind I can understand what spkytr and others were saying that it is more then jets and synchronizing the idle. There are also off idle conditions which must accounted for and that does include less vacuum at each carb. so here are my questions since I'm not knowledgeable of the internals of the Carter YFA. Does the YFA have a power valve? Is the metering rod the same as the power valve? I've heard of kits for Holleys that did away with the vacuum power valve and use a mechanical one as used by the Stromberg but never seen one used, only hearsay. If the power valve is an issue on a YFA, I believe that can be gotten around with a little engineering and small tooling machine shop work. I want the same effect as 3 stromberg 97s on my 300 without having to use 3 rare carbs. 3 Strombergs would give me strong torque and power off idle to about 4500 rpm which for me is more than sufficient. Any help with my continued trek into insanity and the bowels of carburetion infamy would glady be appreciated.
Spyktr I appreciate your input last time and I'm sorry for my poor choice of reaction. You've helped me research my project better. Today I found the answer finally remembering the name Stromberg. Thank you very much.
Thread Starter
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Senior User
Joined: Jun 2004
Posts: 106
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From: Scottsville, VA
I answered most of my own questions with further research. A metering valve and a power valve are similar in that they both work off of vacuum. A metering valve though is more tuneable even in a simple carburetor like a YFA. A less stiff step spring will prevent the overdumping created by low vacuum on a multiple carb setup. The metering rod that is factory is the reason YFAs are known to not be fuel efficient. The rod is thin and there isn't that much difference between its two steps, cruise and power. A thin rod makes for a rich mixture and a thick rod for a leaner one. I'll solve this problem by searching for the correct metering rods. Most people think this isn't possible but one has to remember all the various applications the YFA experienced over its years of performance including 2.0 and 2.3L 4 cylinders. Each different application used a different metering rod. I'm betting that the rod from the 2.3 would have the best cruise and power step for my insane 3 YFA intake idea.
