Hesitation/bog Problems on my 86

[454Man]

375/ 41center plate and weights. Google them.

[rockable]

Grrrr.  I have my truck running great except for when it is cold.  When it is cold and the choke opens and you blip the throttle to take it off fast idle, it dies.  Once the coolant warms up, it idles fine.  This indicates to me that I have done something wrong with the vacuum lines maybe.

I have disconnected and plugged the two bottom lines on the TVS that used to go to the ESC distributor.  I put a tee in the timed vacuum port and fed the new branch directly to the standard HEI distributor.  The only thing the TVS does now is close the heat riser valve when it is cold and open it when the coolant warms up.

What did I do wrong?

[454Man]

Is the heat riser tube in place from the exhaust manifold to the air cleaner housing? This will allow hot air and should cure the lean condition you describe.

[rockable]

No.  Right now, the air cleaner is off of the carb.  The heat riser on the. Air cleaner has not been functional for a long time.  I never had this problem before changing distributors and removing the two vacuum lines.

After thinking about it, it seems that I must have a vacuum leak AFTER the coolant warms up, which means it is switched by one of the TVS valves.  I know the one controlling the EFE is normally open and closes once operating temp is reached.  Got any ideas where I should focus my search?

[rockable]

Used one of those hand vacuum testers and could find no leaks.  Therefore, I used the vacuum gauge and adjusted my idle mixture.  It turned out quite a bit richer than I had it set but now it idles when cold or hot.  The hesitation is almost gone.  I'm pretty good with it now.  It's so much better than it was.

One question.  What should the manifold vacuum at idle be? 

[Fairlane514]

Depending on your cam, anywhere from 15-19 inches is about normal, the smaller the cam the larger the vacuum amount should be.

[rockable]

16" max. It's running pretty well but the accelerator pump has to be a little worn.  I may replace it with a different carb.

[rockable]

If it wasn't for bad luck......

Yesterday, I towed a uhaul trailer about 200 miles round trip on the interstate to help my son move.  On the way over, loaded, I towed in drive.  Since it was a small trailer and empty, I put it OD on the way back.  About thirty miles into the trip the engine started to miss.  Since there was nothing I could really do, I drove it home on 7 cylinders.

Today, I pulled the plugs and all of them looked really nice except number 8.  It had a chunk of metal or carbon welded to it.  After putting in a good plug, it still didn't run right.  I notice what seemed to be too much blowby comin from the crankcase, so I checked the compression.  There is almost none on number 8.  I may have holed a piston.  I don't know.  All I know is now I have to either rebuild the 305 or buy another engine.  What is my best option?

Will all my accessories fit a 350 crate engine?  I know I will have to change the intake and I want to change the carb.  Anything else?  Any other suggestions?

[bd]

Sorry to read of your trouble.  You probably have too much timing, causing detonation - you need to assess/correct that.  Limit your total advance (initial+mechanical+vacuum) to ~32° and make sure it doesn't come in too quickly. 

You'll need to tear the engine down to know for sure, but it will likely be cheaper to reslug #8 than replace the motor (if that's all you have to do), unless you find a complete, low-mileage, running engine for cheap that you can swap in.  All accessories on your 305 will bolt onto a crate 350. 

[rockable]

This engine has 90k miles on it, so I wouldn't repair one hole.  I would either rebuild the engine or put a new one in it.  It was using a little oil because I could see it smoke on startup occasionally.  If that hole was getting more oil, that could have caused it to have pre ignition in that hole only.  The other 7 plugs looked fine and I was at 33-34 total advance.  Sometimes stuff just happens.

[rockable]

I am going with a basic crate 350.  It's the easy way out and gives me more torque and hp than the 305.  I just can't see throwing good money and time back into an engine I never loved.

[454Man]

I will throw in my two Pennies... Search around for the hei 375/41 center plate and weights. This makes the perfect mechanical that a close to stock small block needs.you will see a big diff in the engine sound, tq, and HP all around it will run the best it ever has. Trust google them and them google other methods of getting 32° or 34° of mechanical. Nothing else is correct... When trying to achieve the correct admit of timing. If you need help finding them let me know ill look around here.

[rockable]

I have looked but have had no success finding the 375/41 plate you refer to.  If you find it, please post a part number.  Thanks.

[454Man]

No where to by them except the yards with suburbans.no one has mass produced them.read the thread provided pay attention to ignitionman then google him you'll find he is very knowledgeable on this subject.  If you can't find them near by ill look around here on my time off.

 http://www.chevytalk.org/threads/showflat.php?Cat=0&Number=1448054&page=0&fpart=1&vc=1

[rockable]

What year Suburban or truck?