Setting idle screws w vacuum gauge

[C&C Chevy]

Can use this line to hook the gauge to? Will it give a good reading?

[C&C Chevy]

OK, well that line is not a manifold vacuum line even though it was at bottom of carb. I found one on back of carb. Looked like it was hooked to window washer lines? Any way when I started the gauge was bouncing around between 14-15. I adjusted one side till it evened out at 17 smooth. Then I lowered idle speed cause it was racing pretty good. I then adjusted the other screw and got 18.5 dead smooth.

Do I keep turning screws till it bogs and then back it off till smooth?

[ont_guy_38]

Turn it till you start losing vacuum then adjust it back till it has the highest reading , do that for each screw...looks like you might already have it good with that reading though

[C&C Chevy]

I've read around the web that once I have the highest readings, I need to back down 1/4 to 1/2 turn or it'll be too rich. Is that right?

[ont_guy_38]

You wanna end up with the highest reading possible

[C&C Chevy]

Ok, thanks!

I lowered the idle set screw some more to what sounds around 500-600 RPM to me. Now, I'm getting 18 steady with the occasional blip. It sounds like its about to stall just for a 1/4 of a second then smooths out again for 6-7 seconds.

[Corts60]

If you have an auto trans, I would keep the idle at about 750.

18.5 is a great reading. That shows your motor is still healthy.

[C&C Chevy]

Ok, I did bump up the idle scew. Don't have a tach, but i'm guessing it's close to ~700 rpm. Seemed to help.

I checked the timing and the line was to the left of the timing teeth, so I turned the dizzy a 1/2" turn to the right and the miss in the idle I was describing went away. The white line is lined up on the first tooth. I'm guessing that's ok? Going to let it cool off and see how it starts cold..

[Corts60]

In the future, you always want to set your timing first before adjusting the carb. And I would double check what tab you are lined up with on your timing cover. If it is a stock set-up, you'll probably be good with 4-8 degrees BTDC.

[tucsonjwt]

Just a thought, I was never able to adjust my carb to my satisfaction so I took it to a shop which has an engine analyzer and works on classic vehicles and they finally got good adjustments on everything (not just the carb) after about 45 minutes of fiddling with it (2 mechanics). Very few people can fine tune these old trucks in this age of computerized vehicles - only old geezers with good tools can get it done.

[C&C Chevy]

Ok, took it out for a test drive. There are a couple of problems.

Start up is slow. The engine doesn't seem to roll over easily at first then starts up fine.

When I floor it high RPM there is some rattling, maybe pinging? Might be normal for a 4.3 pushing a TH400 in a full size truck though..

At normal driving it's running good, but it surges a bit when stopping.

[Corts60]

You are too advanced. That explains hard starts and pinging. You need to reset your timing as I mentioned above and then double check your vacuum settings after that.

[Corts60]

Originally Posted by tucsonjwt

only old geezers with good tools can get it done.

Nope. It's called basic mechanical understanding + reading and comprehension. If you understand all the components that make the engine go, and then you read as much as you can about that specific engine and it's traits, quirks, and recommended settings, tuning will not be an issue.

Newer shops, I find, are trained to do what the computer tells them to do. While they obviously have mechanical aptitude, their skills are not as sharp when computers aren't involved because they don't often get a chance to diagnose themselves, the computers do it for them.

[C&C Chevy]

I can't read the timing marks. I cleaned it with carb spray but it still dark brown and is hard to see. Which tooth is "0"? It has 4 teeth \/\/\/\/ not sure which tooth represents what degree mark. Off to google i go...

[Corts60]

Originally Posted by C&C Chevy

I can't read the timing marks. I cleaned it with carb spray but it still dark brown and is hard to see. Which tooth is "0"? It has 4 teeth \/\/\/\/ not sure which tooth represents what degree mark. Off to google i go...

The "V" with the deepest groove is zero. Every tooth to the left of that "V" represents (I think) 2 degrees BTDC each.

[C&C Chevy]

Ok, thanks! I'll get back at when I get home!

[C&C Chevy]

OK, I just found out from PO that he had to move dizzy one tooth over because of a stretched chain. Not sure what he means. Will that effect my timing marks any? Will I still be able to use "0" like the engine cowl sticker says for baseline or will have moved?

[Corts60]

Moving it over a tooth would only affect how much advance/retard you could get from moving the cap. 0 would still be 0. I would highly recommend replacing your timing chain though, if that is the case. After that, start all over with timing and go from there.

[C&C Chevy]

Whats all involved in replacing a timing chain? Sounds like a weekend project!

I got mine set at 4 BTDC according to this pic. I had to raise idle speed. It's at 18 steady on vacuum gauge. Going for a test dirve...

[C&C Chevy]

Ok, test drive went good! Pinging is gone and power is good.

The timing was set at 14 BTDC before I adjusted it down to 4. Going to leave it and work on other stuff. Just wanted a good baseline and I think I got that.

I will keep the timing chain project on the back burner, unless it wont hold the timing. Might wait until this fall, after I get the new trans in.

Thanks for all the help Corts60!

[Corts60]

You're most welcome. Glad you got it running right.