Hi Guys,
I've been working on my 79 truck a bit - it had some rough idle/start-up problems, so I've replaced the carb and gasket (which had never been touched since the truck was new) - seems to make quite a difference.
Now - one issue that wasn't solved was power/stuttering issue it has. It was doing it before I replaced the carb, but more noticeable now as the new carb is performing better.
To better explain - if I bring it up to speed slowly, no problems, but put my foot down, it stutters it's way to power.
Combined with this the fact that the motor (302) really bogs down when put into gear and the truck will cruise right along when in Drive (automatic C6 tranny) without touching the peddle.
I think I have a Vaccuum problem some where - but not sure where or how to detect.
My suspects are:
1) Vaccuum Advance
2) Vaccuum Sensor
3) Improperly adjusted Vaccuum Modulator

Any and All input is greatly appreciated - keep in mind I am not a master mechanic, just a week-end warrior with some mechanical aptitude.

 

Carb throttle pump shot? Either too much or too little will cause that problem.

A bad distributor pickup module will do it also.

 

Carb Throttle pump? - I assume you are referering to the Accelerator pump - I don't believe this is the problem as I just bolted on a fully rebuilt carb and it was doing this before I changed the carb.

Distributor pickup module - I'll be honest - you've got me on that one - What is it and Where is it?
Will this also cause the truck to bog down when in gear as well?
Thanks Torque1st!
Cheers,

 

It's in the distributor Alex,.

What slot is the rod in for the accelerator pump?

Position 1= closest to the end
2= Middle
3= closest to the swivel

 

Have you got the right carb and what's the ID? (And the calibration? How did you adjust the idle? If it takes off in with pedal pressure, the idle is too high and/or you have too much advance.

Have you got a vacuum guage? If so, run the engine until it's in the normal heat range, and run a hose to the manifold vac fitting. It should read at least 18, preferably 20. If it says 10, that's part of the problem.

Do you have the right vacuum hose hookup AND have you gone through and checked/replaced the hoses? In particular, have you tied the vacuum advance to manifold vacuum? If so, when you step on it, advance will be reduced, and if it's tuned at idle for full advance, that'll cause some bogging.

Have you checked/replaced the EGR? If the EGR is leaking or is opening too wide, when you step on it, it'll gas the engine to death and you won't have no pooky.

If all of the above is ok, you can hook the guage to the vacuum advance line (source port --> tee --> advance : tee --> guage) and accelerate the engine (in park, man, park! :> ) and see how much vacuum you're getting at the port. You can shut the engine off and compare that to how much the advance arm moves at a given vacuum. You can also do the same thing with the timing light.

ash
['You looked at your spark plugs lately?']

 

Hi Dennis -
Thanks.
And it is in the middle - same as the original setup.

 

Hi Ash,
Yes - the carb is correct - I verified all the numbers and such - but I do need to set the idle down.
Don't own a vaccuum gauge, but I suppose I should get one and do the check throughs as you have suggested.
Some of the hoses have been replaced, but not all - I suppose it's a cheap fix and should be done.
Will check the EGR as well.
Thanks!

 

OK -
Truck is getting worse -
When in Park - It does rev up OK, a bit of minor stuttering, but seems to have power.
When in drive - it barely has enough power to pull its self, occaisionally reving to life.
Going to see if I can locate EGR and check all hookups.
If anyone has any thoughts, feel free to let me know.
Cheers,
Alex

 

I suspect you are not getting any advance. That implies the box.
OTOH, I suspect you've got two different problems.

Before you drop 60$ (80 loonies?) on a new box, take a piece of vacuum hose, hook it up to the EGR, suck on it, and see if it holds vacuum and/or moves. Do the same thing with the vacuum advance on the distributor. If those are both ok, route a vacuum hose from the EGR port on the carb (drivers side front) directly to the vac advance, if it isn't already. Disconnect the hose to the spark port (underneath the choke heat shield) and cap the spark port. See if that helps. If you have a cat (I expect not) take a good long look at it - an elderly plugged cat will certainly make it run funny. Then I'd check the continuity between the e-box and the distrinutor/coil and look for any melted wires.

If all the above of the above is ok, spring for the box.

 

Thanks Ash.
Will try that.
One silly little question - I've seen what the EGR looks like, and I know it should be located on the intake manifold, but I can't seem to find it. I have noted that in some applications it is located on the spacer below the carb - but all I have is intake manifold, gasket, then Carb.
Maybe I should post a picture.
Would there be any difference on trucks built in Ontario????
Cheers,
Alex
BTW - No Cat. on this truck. Manifold to pipe to muffler to tailpipe - factory.