one idf not reading high enough
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grasshopper
- Posts: 206
- Joined: Wed Aug 13, 2014 10:25 pm
- Your car is a: 1976 Fiat Spider
one idf not reading high enough
Hi all. Ive got my idf's adjusted best I can on brand new engine.They seem pretty good. They are all reading around "6" on carb synchrometer except for carb closest to firewall. It is around 5. I can't seem to get it to rise to 6 like the others. Am I doing something wrong or is this typical ?
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sptcoupe
- Posts: 987
- Joined: Tue Mar 17, 2009 9:25 pm
- Your car is a: 1972 124 Sport Coupe
Re: one idf not reading high enough
When you balanced the bores, did you start with the air bypass screws lightly seated?
If you did that, and the #3 bore was reading the highest between 3 & 4, you should have set that screw with the lock nut, and backed out the bypass screw on bore #4 until the flow between three and four equalized. If you did this and the #4 bore won't come up to number three, it could be an internal issue in that bore.
I also noted that the flow was around 6 (they should be better than "around 6" BTW. Get them the same) . The usual flow is between 4.6-5.2. At six, it could mean that 1) the idle speed is too high - it should be set at 800-900 rpms. If it is too high, you will not get a smooth transition from the idle mixture screw system, to the idle jet system, and the draw at idle will be different and inconsistent between bores.
You may have a bent throttle plate shaft that causes the throttle plates to seat differently.
The throttle plates may not be properly adjusted on the throttle shaft and seated differently from one bore to the next. To adjust the throttle plates, remove the carb top, aux venturi and choke, and slightly loosen the two screws that hold each throttle plate in place on the throttle shaft, being careful not to loosen them so much that they could come off and fall into the intake runner. With the throttle plates slightly loosened (you should be able to move them a bit), snap the throttle plates open and closed two times, then tighten down the screws. That will center your throttle plates. Best don with the carb off the car, but perfectly doable if you are careful with the set screws for the throttle plates.
If your idle speed screw is out far enough so that it is not touching the throttle shaft lever and it the carbs are drawing "6", check your timing to make sure it is at 10 degrees BTDC at 800-900 rpms.
I honestly think you should re-do the balancing on both carbs. The most likely cause is a misstep in the process.
You can call or PM me if I have confused you. I'm writing this through the course of a busy day at the office.
If you did that, and the #3 bore was reading the highest between 3 & 4, you should have set that screw with the lock nut, and backed out the bypass screw on bore #4 until the flow between three and four equalized. If you did this and the #4 bore won't come up to number three, it could be an internal issue in that bore.
I also noted that the flow was around 6 (they should be better than "around 6" BTW. Get them the same) . The usual flow is between 4.6-5.2. At six, it could mean that 1) the idle speed is too high - it should be set at 800-900 rpms. If it is too high, you will not get a smooth transition from the idle mixture screw system, to the idle jet system, and the draw at idle will be different and inconsistent between bores.
You may have a bent throttle plate shaft that causes the throttle plates to seat differently.
The throttle plates may not be properly adjusted on the throttle shaft and seated differently from one bore to the next. To adjust the throttle plates, remove the carb top, aux venturi and choke, and slightly loosen the two screws that hold each throttle plate in place on the throttle shaft, being careful not to loosen them so much that they could come off and fall into the intake runner. With the throttle plates slightly loosened (you should be able to move them a bit), snap the throttle plates open and closed two times, then tighten down the screws. That will center your throttle plates. Best don with the carb off the car, but perfectly doable if you are careful with the set screws for the throttle plates.
If your idle speed screw is out far enough so that it is not touching the throttle shaft lever and it the carbs are drawing "6", check your timing to make sure it is at 10 degrees BTDC at 800-900 rpms.
I honestly think you should re-do the balancing on both carbs. The most likely cause is a misstep in the process.
You can call or PM me if I have confused you. I'm writing this through the course of a busy day at the office.
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grasshopper
- Posts: 206
- Joined: Wed Aug 13, 2014 10:25 pm
- Your car is a: 1976 Fiat Spider
Re: one idf not reading high enough
Thank you for the response. I will look into it as soon as I can. Thanks again.