The Stovebolt Site Forums The Shop Area Engine Shop 235 time, tune, idle questions

Hello everyone,

I've finished the initial cam break in on my 235, and now I need to tune it. It is a 56 block, with a carter YF carb. After the cam break in, I tried to lover the idle to 425, but it started to sound pretty rough about 800 rpms. I never heard a good running 235 at idle, is it supposed to sound kinda like a diesel?

Second, do you set the idle, timing, or adjust the carb first? I was planning on adjusting the carb with a vacuum gauge, and the timing with a light. I assume all changes should be done on a warm engine, correct?

Thanks for the help,

Vince

After 500 miles of operation of the rebuilt engine:

Warm up the engine, and then run it for 30 minutes at operating temperature.

Re-torque the head bolts and the rocker-arm assembly bolts.

Set the valve lash.

Attach a vacuum gauge to the wiper port on the intake manifold. Attach a tachometer, if you have one.

Start the engine and set the idle as close to 500 rpm as you can get it to idle smoothly.

Adjust the carburetor mixture screw to obtain maximum vacuum.

Adjust the distributor timing to maximum vacuum (or, follow the procedure in the Shop Manual).

Adjust the idle to around 2000 rpm. Adjust the timing/distributor to obtain maximum vacuum.

Reduce the idle to around 450-500 rpm (manual transmission) or 400-450 (automatic transmission). Check the mixture adjustment again - maximum vacuum.

http://www.1954advance-design.com/Documents/Adjustment%20of%20valve%20lash.htm

http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0607.htm

http://chevy.oldcarmanualproject.com/shop/1955truck2/55ctsm0620.htm

Hey Tim,

I would really like to avoid waiting 500 miles to tune the motor, is there any reason why I can't do all of those things with a warmed up motor now?

Also, does everyone generally set the timing to the ball, with no extra advance?

Thanks again, Vince

No problem at all. How many miles do you have on it? If it less than 300 miles, you might want to do it again after another 500 miles?

As I described above, I do not use the ball to set timing. The ball will get you close. Maybe someone will post a link to previous posts that describe the "ping" (engine knock) technique for setting the timing?

Sure set the timing now. You can set it again at 500 miles. Set the ball to the pointer. Then tweak the timing as Tim outlines.

Kurt

Well, I've started it, ran the cam break in, and then drove around the block. So probably 5 miles total. LOL

It's 105 here today, so hopefully I'll get a chance to work on everything tonight after the sun goes down.

Thanks guys!

Hey Tim,

One more question, do you leave the vacuum advance attached to the distributor the entire time you adjust timing/carb mixture?

Thanks, Vince

Yes

Good luck.

Keep us informed on how the break-in and tuning goes.

OK, I have my vacuum gauge hooked up, and the needle bounces between 13 and 15 PSI. It'll smooth out if I raise the idle to 1kish, but doesn't seem to like to be below 750. Also, if I raise the rpms above 1200 it'll jump to 20ish and stay there, very steady. I've tried to adjust the carb mix, and it doesn't seem to have much of an effect. The carb was dry for about 2 months while I rebuilt the motor, maybe it needs a cleaning?

Any ideas?

Well, after doing some searching on the web, I found this site: http://www.secondchancegarage.com/public/186.cfm
It confirms a poor idle mixture cause the needle to bounce between 13 and 17 inches, (scenario 15). The site also said that a high performance cam (I have a Patrick's 264 cam) will cause a lower base vacuum reading (scenario 3). Is the 264 high performance enough to cause a drop in idle vacuum? I'm going to rebuild the carter, and hope that all is well.

Any other ideas?

Thanks, Vince

This may be to far OT or against rules somewhere so no worries if it gets deleted...
I was just about to post a link to that vacuum gauge site as well. It's a good un for folks trying to sort things out.
I also saved a link I stumbled across from 2002 by a guy banned from the M_P_R forum that walks you through the timing/carb set up for a 4V Eddy/Carter using the vac gauge. One of the better guides I've run across searching the web looking for nuggets of knowledge. I used it a lot getting a Stud 289 with a Carter AFB running a couple years ago. so for reference purposes only Tune up steps

Hi all,

I think I've fixed the problem, and I wanted to follow-up in case anyone else has this problem in the future. I ordered a carb rebuild kit, and when I took the carb off, I noticed hairline cracks in the insulator/spacer. I rebuilt the carb, and re-installed it with the new spacer. I also left off the base gasket, because I found a post here somewhere from a guy with an NOS 3211s like mine that came with instructions to NOT use a gasket.

I bolted everything back together, and I'm getting a pretty steady needle at 15 in/mg, maybe bouncing half an inch (pressure, not distance) either way.

I then called Patrick about out his 264 cam to see if the 15 in/mg was normal, and he said he wouldn't worry.

The truck seems to run pretty well now, I'm going to take it to work tomorrow on it's first voyage more than around the neighborhood. Here goes nothing!

Thank again to everyone here for the tuning and vacuum reading tips.

Vince