Hey guys,

Been messing with my 71' k-10 trying to figure out why it is missing/chuggging at cruise.

Motor is a 78' 350 w/ edel 600 carb. Timing at 10*. Prev. owner said it has a diff cam, but i dont know the details of it. Has elec, ign. conv. kit .

It idles fine, but while driving/accel w/ light throttle, it has a good miss to it. Like a cyl or two is not firing. Give a lil more gas and it clears up fine.

Pulled off the vac. adv and it holds vac (mouth test haha ) and the rod moves in and out smooth ( kinda hard to push in tho? ) Replaced vac. line going to carb. Has an edel 600 carb, adjusted idle screws to what seems good, per edel intructions. Plug wires look good, but dont know the age. Havent looked under the dist cap yet to insp. that area.

Just ran some top engine cleaner w/o any change in problem.

What are your thoughts???

Thanks in advance - Jake

 

You said the plug wires look good but what I read was the plug wires need to be replaced. I went through this same deal with several GM engines and thats all it was on them. Its cheap insurance.

 

my bet it is the aftermarket cam, the prev owner most likly used a rv cam and they tend to "stutter" at cruse. try going 8*tdc on the timeing. is the vac advance hose connected to the intake instead? some make the mistake of installing it to the pcv port, or vac motor port on the carb. the 600cfm carb is just a tad on the small side. a 650-750cfm would help-are the secondarys on the carb working? try adjusting them to open slightly sooner. also over looked is the carb mounting gasket, check for vac leaks

 

Check the cap/rotor and points, also check plugs and wires, get a spray bottle and fill it with water, with the engine running spray the plug wires, listen for and stumbling and look for any arcing, you can't tell if a wire is bad by just looking and feeling it (unless it shorted through the jacketing). The point gap should be 18-22k. Is the engine pinging at all? Vacuum advance should be run to the pulsing port on the carb, not to the manifold. It sound electrical to me.


Tim

 

I would be leaning towards secondary ignition missfire (plugs, plug wires,coil, cap or rotor) You stated electronic ignition conversion. Some of the old mallory unilite conversion kits gave missfire issues. I would recommend changing to a factory H.E.I distributor (like 1975 & later G.M. vehicles) and factory style cap, rotor, coil assy. They are for cheap rebuilt or new from NAPA and with a new set of wires your ignition system would be good to go. Just remember to power the distributor with a 10 gage wire from a key activated source. Do not use the factory resisted wire that is currently powering the coil.

As for the 600CFM carburetor. That it fine for general use and better fuel economy. No need for bigger unless you start looking for better 1/4 mile times and hot rodding. A factory Q-Jet would be best for mileage and cruise performance.

If you have an adjustable timing light adjust timing for max of 34-36 degrees. All timing shoul be in by say 1200-1500 rpm. If it is overadvancing you may have to recurve the distributor with a kit. Mr Gasket or Crane makes and inexpensive and easy kit with full instructions. You could even go as far as an adjustable vac. advance unit. Again easy to install and instructions are easy to follow.

Good luck

 

Okay, thank you for all the input. Im going to try to answer all of these questions quickly.
Vac adv line is going to pass. side vac port on the carb.
Points on dist cap dont look burnt or corroded bad, all look even
Plugs all look uniform, dry, light brown
New plugs were gapped .35 100miles ago
Elec conv kit was done 2 yrs ago
No spark knock
Fuel filter may need a change, being i just dont know how long its been on there, fig if it was a real prob WOT would show that

Should i try running w/o vac adv hooked up? If so what should i see with out it?

 

in regards to the vac advance, use a vac pump(hand held) to see if it is moving. it may be seized or bad diaphragm

 

Ran w/o vac adv. hooked up just a min ago and nothing changed. Still missing at cruise and very light accel, cleans up and hauls at wot and med throttle. Noticed idle is getting a tiny bit erratic when i got back?