Sluggish up hills

Sorry to keep pestering with questions.

My inline 6 300 has good compression and oil pressure but has a hard time getting up hills without bogging down and I'm going to re-check my timing.  I'd like to do it with the vacuum gauge but would like to ask the experts foist!  
I will disconnect & plug the advance on the carb... maybe use the brake boost vacuum source for the gauge... warm the engine and find the highest vacuum reading.  Do I need to back it off a tad once I get the best reading?  And is there a better way I should be doing this?  

Many thanks!

BTW, it has a knock-off Carter YF evil-bay carb.

I'd suspect the carburetor for your performance problems, due to it not controlling the vacuum advance properly, or there is something wrong with the advance, vacuum or centrifugal.

I like using a timing light myself for checking timing. It's easy to check vacuum advance with a timing light as well by just disconnecting the vacuum.

My 2 cents ...  

I used the vacuum line which goes to the temperature sensor mounted on the air intake snorkle and connected it to the vacuum gauge. My 1986 4.9L would pull approximately 21 inches of Hg at about 750 RPMs. I had to retard the timing [on 4.9L/300 engine this is when the distributor is rotated clockwise] to the point where the vacuum measured 18.5 inches of Hg.

Take it out for a drive and if it does not ping, advance the timing just a little.

Did this happen all at once or a little at a time?
What size tires, rear gear ratio and transmission you got?

You still running a cat on the truck?
Dave ----

Dave - Not really sure when I first noticed it.  It was subtle enough that a shift to second got her up a hill.  Guess it occurred to me fairly recently that I should be making it up gentle hills in third.  If the engine were tired, I'd understand.

My tires are 235-75R-15 and the door post tag says the transmission is "A".  Granny low 4 speed.  I most always start in 2nd.

Axle "18" and the metal tag on the 10-bolt cover reads: S806A  3 08  8 8 5B04

Well there is something going on that is not right as you have a lower rear gear (3.08) than me (2.75) but the rest is the same.
Not really knowing how steep this hill is and the speed you should be able to go up it even at 35 MPH in 4th and for sure 3rd gear. I can idle up my drive in 2nd, granny first and also start in 2nd gear from a stop.

I can tell you in 4th gear at 40 MPH is 1300 RPM.
I also have over drive and 4th gear OD at 40 MPH is 1100 RPM and it will pull.

So to your issue, you should have a feed back system on your truck.
A computer controls the timing & carb to lean it out.
To check timing you will need to pull the jumper so the computer cant adjust the timing and see what it is at. If off from factory then set it to factory.
Put the jumper back in and see where the timing is. Also bring the RPM up and check timing again, it should advance.

With timing set and hope advancing use a vacuum gauge to check what the vacuum is at normal temp & idle. Then bring the RPM up to 1500 and hold it noting the vacuum then RPM up to 2000 RPM and hold it.
What happened to the vacuum reading with the RPM hold at the 2 setting?

Report back the timing and the vacuum reading as we can move on from there.
Dave ----

Dave - Sorry, I neglected to mention the previous owner removed all computer stuff and installed a GM type HEI distributor.  Simplicity!

either the timing is off, or the carb is. this may be a good time to replace the fuel filter to see if you get a response. keep things simple and know that bases are covered.  clogged fuel filter or weak pump in general will leave the carb level low and lean it out causing a lack of power yet still run decent on level or light demand driving. checking fuel flow will also be smart to prove the tank screen is clear. old trucks, especially ones that had to be revived or brought out of retirement often have fuel issues. then it may be time to look in the carb but " start at the source of fuel" just something i do before going too far off track.

IowaTom wrote

Dave - Sorry, I neglected to mention the previous owner removed all computer stuff and installed a GM type HEI distributor.  Simplicity!

LOL ok so HEI dist. this carb you installed was it for your year truck or 83 and older that did not have feed back?
Think it was post #2 he thought the carb was the issue because it did not have vacuum for the dist. advance. If it is for your year it can cost power but I dont think you would feel it drop off, it would be down from the start.

When you can run the tests I posted above you dont need to pull the jumper to check timing but if you have vacuum to it pull the hose & plug it.
But the vacuum reading at idle and rasied RPM
Dave ----