Re: 427/435 tripower hesitation on full throttle
The two end carburetors don't have throttle plate adjustment screws. The throttle plate is adjusted using the linkage. I followed the AIM to set the adjustment. They are both fully closed in the idle position but open slightly when I manually move the throttle slightly open (engine off). The end carbs don't fully open until the rpms increase significantly.
Yes, I did say the engine will idle with the center carb idle scew backed out all the way. However, I have since replaced one of the end carbs with a spare I had because I thought it had an internal leak. This didn't help the hesitation problem but I think it changed the idle setting on the center carb. I will check to see if it will still idle with the screw backed out all the way the next time I have it running.
I also think there may be an internal vacuum leak. The fact that increasing the shooter size worked up to a point indicates to me that the larger shooter was covering up some of the lean condition potentially caused by an internal vacuum leak. Seems reasonable that as the engine warmed up and reached operating temperature the vacuum leak was exacerbated. Didn't someone mention that there is a product that can be used to temporary seal a vacuum leak on the throttle shaft? Can anyone tell me who sells this product. I think it would be worth while to test.
I was also wondering if it is possible that the low manifold vacuum could be related to valve lash? If I adjusted the intake and exhaust lash to loose/tight would that casuse a low vacuum? I remember my engine builder recommended an OEM cam so that I wouldn't have to remember what the lash setting are since they would be the same as factory specs. What I don't remember, and I can't read the faded inventory list, is the manufacturer.
Thanks,
Ken
The two end carburetors don't have throttle plate adjustment screws. The throttle plate is adjusted using the linkage. I followed the AIM to set the adjustment. They are both fully closed in the idle position but open slightly when I manually move the throttle slightly open (engine off). The end carbs don't fully open until the rpms increase significantly.
Yes, I did say the engine will idle with the center carb idle scew backed out all the way. However, I have since replaced one of the end carbs with a spare I had because I thought it had an internal leak. This didn't help the hesitation problem but I think it changed the idle setting on the center carb. I will check to see if it will still idle with the screw backed out all the way the next time I have it running.
I also think there may be an internal vacuum leak. The fact that increasing the shooter size worked up to a point indicates to me that the larger shooter was covering up some of the lean condition potentially caused by an internal vacuum leak. Seems reasonable that as the engine warmed up and reached operating temperature the vacuum leak was exacerbated. Didn't someone mention that there is a product that can be used to temporary seal a vacuum leak on the throttle shaft? Can anyone tell me who sells this product. I think it would be worth while to test.
I was also wondering if it is possible that the low manifold vacuum could be related to valve lash? If I adjusted the intake and exhaust lash to loose/tight would that casuse a low vacuum? I remember my engine builder recommended an OEM cam so that I wouldn't have to remember what the lash setting are since they would be the same as factory specs. What I don't remember, and I can't read the faded inventory list, is the manufacturer.
Thanks,
Ken
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