Bogging Down a bit at Startup HELP Please!
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Bogging Down a bit at Startup HELP Please!
I've been driving my newly assembled truck around and during startup and until it warms up it bogs down a bit during the bottom of acceleration. And for some reason until it warms up it has a tendency to idle really low and almost die when I'm at a stop. I'm guessing issues with carb but not sure which issues they are.
It's a 2brl Holly with Elec. Choke on a 400m.
It's a 2brl Holly with Elec. Choke on a 400m.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
What is the state of the choke plate, both when the engine is warming up, and already warmed up? For the warmed-up low idle issue, have you already gone through and adjusted the curb idle speed and idle mixture, the latter with a vacuum gauge?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
That may be too far for an engine that's trying to warm up. I'm not as familiar with the procedure on a Holley, but on the factory Motorcraft carburetor, the tension of the choke cap should make the choke plate snap shut completely, and a vacuum-operated pulloff keeps it open slightly (we're talking 16th's of an inch) when the engine is trying to start. As the engine warms up, the choke plate slowly opens.
Also, while a choke is partially closed, opening the throttle very far can make incoming air "push" the choke plate open causing a slight lean condition, which is normal - but if the choke cap spring is too worn out, the effect can be exacerbated. Also note that a subtle vacuum leak may not be strong enough to cause problems at idle, but can show up while the engine is warming up and is more susceptible to lean conditions. I'd check for those as well.
After the engine warms up and the idle speed is poor, is the choke open? You mentioned maximizing the vacuum gauge reading - what did the needle settle upon? Did you adjust the curb idle speed too? If you did, then why can't you just increase the idle speed?
Also, while a choke is partially closed, opening the throttle very far can make incoming air "push" the choke plate open causing a slight lean condition, which is normal - but if the choke cap spring is too worn out, the effect can be exacerbated. Also note that a subtle vacuum leak may not be strong enough to cause problems at idle, but can show up while the engine is warming up and is more susceptible to lean conditions. I'd check for those as well.
After the engine warms up and the idle speed is poor, is the choke open? You mentioned maximizing the vacuum gauge reading - what did the needle settle upon? Did you adjust the curb idle speed too? If you did, then why can't you just increase the idle speed?
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