Do the Nutter Bypass

 

Thought of doing the Nutter bypass, but we have anual emmissions testing where I live, with both visual
inspection, and tailpipe. I'm worried it won't pass.

 

Frank

Fill out your profile when you get some time . I did the TRI and I have a new carb (2100MC) and I have a flat spot too .My timing is also right on 8 deg adv. I`m leaning towards the springs I put in the distributor . Now thats just a guess at this point . The carb is set properly too , a friendly shop owner did it as I watched and it looks good on the scope . At Aircare they checked only my gas cap , you might not get away with that being an 85 .

Jeff

Jeff /wwwthreads_images/icons/cool.gif

 

If the stumble only occurs when you are hard accelerating in traffic, and not when you rev the engine in the driveway...
If you let up on the throttle a little and the stumble goes away...
If you have a 'Bog' when you accelerate hard, (starts to pull hard, then bogs down, then takes off again...)...

The stumble off the line is your accelerator pump. (I'm giving 10 to 1 odds on this one...)

All carbs have an accelerator pump of one kind or another, and that pump is what 'Shoots' gas down the carb throat when you step on the throttle pedal.

When you try to accelerate, you need fuel 3 times faster than if you were cruising. That pump shot does the trick of adding the extra fuel.
My guess is you leaned out your idle mixture to an acceptable level, and now you are getting lean misfire on take off.
(With the crappy ignition, you just couldn't accelerate fast enough to find this problem before you did the ignition upgrade)....

All most all carbs have some sort of adjustment so you can get more fuel (bigger pump shot).
That pump shot is divided into two categories,

1. Duration, how long the pump shot lasts.
You can usually find a linkage arm outside the carb body that controls the pump shot duration.
You need to increase the duration of your pump shot. (have it last longer)
See if you can find adjustments on your accelerator pump linkage, and figure out how to adjust it.
(It's usually a dead give away it's a duration problem if you ever get a 'sneeze' or 'backfire' or 'pop' out of the engine when it stumbles, especially under a heavy load, like pulling out in traffic fast or mashing the throttle towing a trailer...)

2. Volume, how much fuel the accelerator pump shoots down the throat of the carb.
The only way to adjust volume I know of is to drill out the 'Squirters' that the accelerator pump shot comes out of.
(proper name, Accelerator Pump Discharge Nozzles... Squirters to the rest of us...)
It's only on rare occasions you will ever have to increase the volume of fuel delivered.

Drilling the Squirters will make the hesitation problem worse, by delivering all of the pump shot at once, then starving the engine even longer...

If you want to do something sneaky to see if it's the accelerator pump, back the idle screws out (richen the mixture) about 1 to 1-1/2 turn(s), and see if the stumble lets up or goes away entirely...

This is not a permanent fix, it's just a test...

If you leave the mixture too rich, you will waste fuel, contaminate your oil, foul out your spark plugs, plug up your catalytic converter, not pass emissions testing, and excessively pollute my breathing air...
It's just a test to see if you need to add a little duration to your pump shot...

Once you get the stumble fixed, then we can do the rotor phasing, then move on to the advance springs..
You will see this much of a dramatic difference again!

So many cats, so few recipes...