weird hesitation

I

ianmatt74

Junior Member
I have a 1959 292 y-block, bored .030, pertronix 2, headers, mumert intake, avs2 500 cfm carb, original 4 speed T98. Also running autolite 46 plugs gapped .040. At around 2800 rpm under decent acceleration i get some hesitation. If i ease into that range it doesn't do it and pulls good on up. But put load on it and she falls on her face a bit. Any thought on what could be causing this? what is this a symptom of? Are the secondaries opening too soon?
 
Any backfire or cough? Almost sounds lean and that would likely be power valve or accelerator pump.
 
If the ignition is in good shape and advancing properly, and if it's not an issue like accel pump shot from the carb, then I guess it's possible the air valve over the secondaries has the spring set too light, since these carbs are used on a wide variety of engines.
If the hesitation is when you get into the secondaries, then maybe play with the spring tension on the air valve and see what happens. I would say slightly more tension for a first try.


Sal
 
DaleM said:
Any backfire or cough? Almost sounds lean and that would likely be power valve or accelerator pump.
Click to expand...



The AVS has no power valve to speak of. pretty sure it uses metering rods controlled by manifold vacuum.


Sal
 
Not that this might be related, but you mentioned you have the plugs gapped at .040. Shouldn't it be more like .035 ???
 
Thanks guys I will try a few things like tighten the 2ndary spring flap. I also am going to try autolite 45s at .035. I have played with the holes on the accelerator pump and the bottom hole (smallest shot) is they only one that runs good. the other holes give me bog off the line.
 
ianmatt74 said:
I have a 1959 292 y-block, bored .030, pertronix 2, headers, mumert intake, avs2 500 cfm carb ...

At around 2800 rpm under decent acceleration i get some hesitation. If i ease into that range it doesn't do it and pulls good on up. But put load on it and she falls on her face a bit.
Click to expand...

IF you are sure the IGN is 100%, the valves are adjusted properly (proper manifold vacuum), fuel pressure and delivery are 100%, then you may need to go into carb calibration. Your intake and headers are going to give you greater flow through the engine and you may have to enrichen the fuel mixture to get proper performance.

You need to find online the INTR SHEET for the kit shown below to guide you. Make sure you choose correct kit.
 

Attachments

  • Calibration Kit.jpg
    Calibration Kit.jpg
    54.8 KB · Views: 10
So I jetted in down one size jet and rods, adjusted timing, and have accelerator pump arm in lower hole and the hesitation is almost gone.
 
You must log in or register to reply here.
Back
Top