Bogging off idle

[Doug&Deb]

I try to drive my Coronet once a week weather permitting. Today it started bogging badly under acceleration. I’m not sure if it’s fuel or spark. It still idles normally. Cold startup was normal. I ran to town for an errand and this started on the way home. Recent carb rebuild and tune up (within the last 1000 miles). The car has been running great until today. Nothing looks amiss under the hood. Any idea where to start looking?

[keithb7]

Pull air filter. Get flash light. Engine off. Look down carb. Cycle throttle linkage. Can you see a raw stream of fuel squirting inside carb? This comes from the accelerator pump. An easy first check. 

Edited December 19, 2021 by keithb7

[Bryan]

Read a recent post about point gap closing causing weird symptoms without affecting starting.  Easy to check without a lot of work.   Later check vacuum on distributor. Start with the easy stuff first.

[Doug&Deb]

While running I cycled the throttle. A quick blip gives a good stream of fuel. At normal throttle not much and the engine chugs and bogs. Point gap is correct and dwell is in spec. Seems like the accelerator pump but I’m not sure how or why.

[Plymouthy Adams]

don't overlook the possibility of a faulty/failing condenser....

[Doug&Deb]

Didn’t think of that. Would that cause the lack of fuel squirt in the carb? Probably a dumb question but I’m not good at diagnosis.

[keithb7]

If you slowly open the throttle, don't expect to see a stream of raw fuel. It comes out slowly and dribbles down the internal center wall in the venturi.

There is not really a bulls-eye we can hit to get this right, from afar. You have to check several things

We can only assume:

 

Condenser is good

points are set right

spark gap correct

coil is working properly

all ignition system connections clean and tight. No stray electrons

vacuum advance it working properly

fuel pump pressure is good

carb float level correct

nothing impeding the flow of fuel into the carb bowl?

no air leaks anywhere in fuel delivery from tank to carb bowl

choke is fully opening properly (if choke is partially closed does bogging improve?)

all carb sections are sealed up properly, no air air leaks. Air must only come down thru the top opening of the carb. No other entry permitted

 

Perform vacuum test on intake, engine running. Analyze results.

 

 

Edited December 19, 2021 by keithb7

[Greg51T&CWagon]

An odd one that I've experienced. make sure the distributor is snug if you messed with the timing on that tuneup. I've had one slowly, a little at a time, creep out of time b/c it had not been tightened down correctly.

[Doug&Deb]

Thanks for all the info. I have some checks to make. It came on so suddenly and that threw me. 

[Sniper]

There is a transition slot that covers the, well uh, transition from the idle circuit to the cruise circuit.  I have seen a bit o' crud in those on occasion.  That could be the issue.  The following pic is not from a Carter BB, but does show the slot and might help.

 

[Sniper]

Here's a poor resolution line drawing showing the slot (sort of) on a Carter BB. It is right above the throttle blade on the left side.

 

 

 

Edited December 19, 2021 by Sniper

[JBNeal]

On 12/19/2021 at 10:19 AM, Doug&Deb said:

While running I cycled the throttle. A quick blip gives a good stream of fuel. At normal throttle not much and the engine chugs and bogs. Point gap is correct and dwell is in spec. Seems like the accelerator pump but I’m not sure how or why.

What is the condition of the accelerator pump?  Is the leather intact?

[Plymouthy Adams]

quick blip you need the stream and the sudden movement of the spring will provide that....however slow and easy opening much less of a stream (often a dribble) as the fuel to transition from idle to run is less....and when above a certain point you will draft that fuel from the main jet....and why bog at upper end is not as noticed....

[soth122003]

What's the calendar time of the last carb tune or rebuild/cleaning? If you use ethanol gas, you could have the greenish residue from the gas partial clogging the ports of the carb. Since you say you drive it once a week weather permitting, you might use a tank of gas about every 2-3 months which is about the life cycle of ethanol fuel. Just something to check as every time I clean my carb (which is not that often) I find a decent layer of greenish mold/algae/crap lining the float bowl and I run or drive my 48 about once a week as well for at least 30 minutes or more.

 

Joe Lee