johnsonm

Should the MCS dwell still be around 30 while cruising down the highway?

Could I use this to determine a lean or rich condition at cruise?

When I am cruising down the highway and give a quick, part throttle accelleration, I get a hesitation. It almost feels like the timing is going retarted. The engine will hesitate / flutter a little (keeps running, tone changes and power drops off) then will gradually catch up and accelerate like I would think it should. This hesitation lasts maybe 2 full seconds, maybe longer, especially in a higher gear.

Wide open throttle seems pretty good.

This is on a LG4 controlled, vortec headed 350. Still working the kinks out of.

I got the 350 knock sensor and ESC module, and have adjusted the base timing from -2* to 12* advanced with no noticeable, so I don't *think* it is the timing.

Thanks!

Matt

naf

iTrader: (7)

Nah, dwell should be set at 30 degrees in park/idle. You can connect the meter and run the wires into the pass seat to see what the dwell is doing while you're driving. This will let you know that the ecm is controlling mixture properly. If it's staying pegged (full-rich or full-lean) you'll know you have a condition that is outside of the range that the M/C can adjust to.

Verify spark advance with timing light. With engine warm (dwell wavering) and EST CONNECTED, make sure you're getting ignition advance when you rev the motor. You probably won't be able to tell how much as it will be past the marks but it's more important to verify that it IS advancing.

Disconnect KS and see if there's a diff when you drive.

Check your TPS. Verify that it's close to 0.40 volts at idle and increases to 4.0 volts at WOT. A bad TPS or missing plunger can cause your symptoms. Read voltage across the two lower terminals with the plug connected, ignition on.

Let us know what you find after you check the above.

johnsonm

Hooked up the dwell and threw it in the passanger seat. It stays around 38 +/- while at a steady pace down the highway. Shows lean (numbers below 30) on accelleration and rich on decel. Generally doesn't reach either extreme end of the scale, sound pretty reasonable, right.

Timing is advancing in neutral. Is it possible to check total advance like this?

I disconnected knock sensor and it immediatly set a code. I erased the code and hooked the KS plug to the old 305 KS and zip tied it, and grounded it, out of the way in the engine compartment. I didn't *feel* any difference. I advanced and retarded the timing between 0* and 8* and couldn't tell a difference or hear any ping or valve rattle.

When we first swapped the engine I broke the TPS. I know what the car feels like when that is not working. It is similar now, but not nearly as pronounced or dramatic. That sudden increase in trottle results in shudder, low power, hesitation, that gradually clears up. But if you ease into it, it acts ok. If you go WOT all is well. What I am experiencing and a bad TPS are very similar. I have checked and re-checked the TPS and adjusted it from .4 v to .6 or .7 to see if it would trick the computer to bringing in timing early, like the throttle is open further than it really is, but no change either.

Is there any more to tune on the primary side of the carb, like with the lean and rich stops, than just 4 turns out (lean stop) , then 1/8 inch of movement of the MCS (rich stop) and then set the IAB to get the dwell of 30.

naf

iTrader: (7)

Sounds like you're dead on with the primaries and mixture control. I'd start looking at your secondaries.

Check the choke pull-off. Pull the vacuum line off the nipple, press it in, hold your finger over the opening and make sure the plunger stays engage.

Play with your air valve tension some. You may be getting a slight bog as the secondaries come on-line. Start super loose tightening a little each time. See if it makes a diff. Didn't you already play with this?

You've had the air horn off, right? Are you sure the four tubes (emulsifier/pick ups) are in their proper place and still attached to the under side?

My other thought would be fuel pump shot. Not sure how to check other than to make sure fuel is squirting out when it is depressed. I've drilled a second hole on mine closer to the body to increase the amount. Helped with some cold weather issues but the difference is probably small enough so you wouldn't notice much. Perhaps your booster is shot and pumping little or no fuel into the carb on tip in.

johnsonm

Will start checking the secondary side and get back to you.

I messed with the AV tension, but only checked for "results" at WOT, I never put much thought into part throttle.

I guess the point at which the secondaries open, depends more on engine conditions, vacuum and load, and less on throttle pedal location? So for me to say to myself, "I wasn't getting into the secondaries, I was only at half throttle", may have been inaccurate?

When secondary plates and AV come open, do they pop all at once, or gradually ease open?

I will open the top of the carb back up. Could float height cause any problems like this?

naf

iTrader: (7)

The secondaries can gradually open. Vacuum secondaries are designed to provide only the metering required by engine load, not throttle position, so what you're saying is correct. Play with AV tension before digging into anything. It's easiest. Oh and check that pull-off. It's right there in front of you.

Float adjustment shouldn't be an issue. Your airhorn tubes are probably fine, I'd think one missing/dropped would cause more issues than you're experiencing.

Don't open the carb until you've checked the more likely, easier stuff.

johnsonm

Always check the easy stuff first!!! Story of my life.

Carburetor to intake mouting bolts were finger tight. Only the weight of the carb was sealing the carb to intake gasket.

I'm sure I got excited and only ran the bolts down by hand durring the cam, head and intake swap. Got tunnel vision worrying about flattening a cam lobe.

New gasket and carb torqued bolts. Now the car runs like I would have immagined it should have.

Instant throttle reponse, lots of pull throughout entire rpm range. Very fun!

I am an idiot.

naf

iTrader: (7)

Awesome.