no use checking timing at various rpm's in regards to the vacuum can, you only need to worry about two things on the vacuum can - idle and total with vac advance when timing is all in. Anything else inbetween you will not be able to deal with unless you want to get a very long vacuum hose and run the gauge in the cockpit while your driving. The vacuum advance system is designed to operate based on engine LOAD and you will not get a load on the motor while having it sit in the garage and you rev it up, that's simply a function of rpm and taken care of by the mechanical advance.
For the correct vac. can you need to know what vacuum the motor makes AT IDLE ONLY and choose a can that gives you the amount of advance you need at a point that's at least 2"hg below the motors vacuum level at idle. So, assuming your motor is producing 10" of vacuum as you stated than you need a can that brings in the advance by 7" or 8" vacuum.
What concerns me though is your high initial timing at 22º. you may not have a starting issue currently but once you get a proper vac. adv can connected to full manifold vacuum your initial timing will jump up to 37º-38º and that's awfully high.
I'd have the distributor recurved to increase the mechanical advance to somewhere between 20-24º. this would allow you to have your total timing at 36º with your initial timing down between 12º-16º.
I'm not very knowledgeable on cams so don't know how mild or radical your cam is but if it's more on the hot side than it may prefer a somewhat higher initial timing, say the 16º rather than the 12º. This way once you connect the vacuum advance you won't have your timing too advanced at idle.

Even if your cam is very hot, 10" of vacuum is still low. If you plugged and capped everything and still are only getting that low of a level of vacuum I'd do more checking around your motor. maybe a small vacuum leak from the intake? or check the rings with a leakdown and compression test?
To give you an example, the factory stock 30-30 cam i have in my '65 L76 motor is considered a pretty radical cam for the street and probably one of the most radical cams GM ever put in at the factory and depending on the motor it still produces around 13" of vacuum.
I'd guess there is still a leak somewhere on your motor affecting the vacuum that you haven't found yet unless someone else chimes in and can confirm that the specs on your cam are typical for producing such low vacuum levels in which case you just need to deal with the vacuum as it is.

 

Thanks Barry. Appreciate the heads up on checking the timing and bringing to my attention the new very high initial timing number once I get a new can installed. Your post was very helpful. I am definitely going to find someone with a distributor machine that can get mine to where it needs to be.

All in all, it's looking like my 3 issues were mostly separate after all.

A new fuel pump should take care of the carb issues.

Getting the distributor recurved and vacuum advance replaced should allow me to set the timing correctly.

And while I will check, double check and triple check for a vacuum leak this weekend, I'm not hopeful of finding one so it looks like I am also going to have to find someone knowledgeable about cams and how they can affect vacuum at idle and what, if anything, I need to do about it. Anyone have any thoughts on the low vacuum issue?

DC

 

DC3, you might also want to borrow a different timing light from someone and compare the two just to be sure the numbers you're getting are accurate.

 

Frankly, I would go back to the basics. I would check the mark on the balancer and pointer by physically finding TDC. Make sure it is marked correctly. I would then look at the distributor and make sure it is installed correctly. Not a tooth off. Then you will know that what you are seeing with the light is correct. I would check the compression, and the valve adjustment. Frankly, I find it hard to believe that you can start it with hot with 22 deg. initial timing. It tells me that there is not much compression, that the cam is either not installed correctly or has a ton of overlap, or it`s flooding profusely. This would cause the low vacuum. Why havent you already installed a new vacuum advance? We have been on this for about a week now.

 

Good advice. I will do this. Of course, I've never done this before so will have to learn how. I'm sure it's old hat to you guys with tons of experience. Any tips or tricks I should know?

Several reasons. 1) I haven't been able to find the advance locally that was recommended in Lars paper and was my first choice and haven't had a chance to look for the adjustable can that was also recommended to me. 2) If I do have a low vacuum problem that can and should be corrected, it will likely change which advance is appropriate for my engine. 3) I works for a living, dang it. 4) I am in full throttle learn mode and am trying to determine which steps to take first. 5) The car is very drivable with the current distributor settings even though the vacuum advance is not working so the carb issue is a higher priority.

So, it looks like a good plan of action is:

1) Replace fuel pump, adjust carb as needed
2) Verify timing mark and pointer
3) Verify distributor installation
4) Find and repair any vacuum leaks
5) Check compression and valve adjustment
6) Verify camshaft is properly installed and dialed in and that timing chain is good
7) Confirm vacuum at idle
8) Select and install proper vacuum advance
9) Set timing
10) Have distributor checked and recurved if necessary

Anything I'm overlooking or have in the wrong order?

DC

 

Good for you DC We are pullng for ya. John

 

No vacuum advance is going to make much difference in the vacuum reading. If it really is that low, that is a healthy cam, or the cam is not installed correctly, or the valves are not adjusted correctly. Your 22 degrees of initial timing is a crutch for that advance not working.

 

Remember that I got the 22 degrees of initial timing by setting the timing at the all in point of 2500 rpms to 36 degrees. This means the distributor is only providing 14 degrees of mechanical advance. Once I put in a new vacuum advance, I assume I can set the initial timing lower, but then will 14 degrees of mechanical advance be enough? I thought I was supposed to be shooting for 50-52 total all in with the vacuum advance. 14 of mechanical plus 16 from a vacuum advance still leaves me needing 20-22 of initial to get to 50-52 total. Your thoughts?

I doubt the cam is anywhere near radical enough to cause the low vacuum but that assumes it is installed correctly. Assuming no vacuum leaks, your thought that the cam is not installed correctly keeps playing in my brain too.

If the valves were not adjusted correctly, what symptoms should I be looking for other than a low vacuum reading? The car seems to run fine and I did get 14.5 mpg on the trip back from Arizona. Don't know if that is good or not. Don't hear anything out of the ordinary from the valves when using my not-so-trusty stethoscope (big freakin' screwdriver pressed to ear).

Thanks for the continued input. This has been a good learning experience.

DC

 

I'm no expert on this like a lot of the guys, but I keep thinking your vacuum is too low given the cam you have.
Yours is:
Duration @ 0.050” lift: 222/222
Valve lift: 0.447”/0.447”

Mine is:
Duration @ 0.050” lift: 214/224
Valve lift: 0.442”/0.465”
My engine pulls a nice steady 15" of vac. @ 775 rpm idle, with <1" fluctuation.
Would 8° less intake duration give 5" more vacuum at idle? I don't know, but my gut says that's too big a difference in vacuum for the seemingly small difference in cam timing. Anybody have an answer?

My 600CFM Holley DP had leakage problems out of the box. Crappy idle, and fuel dripping down the secondaries. I bought the new non-stick Holley gaskets, pulled it apart, cleaned out all orifices with a spray carb cleaner, and put it back together. Fixed the leaks. Just recently I had a flooding problem and discovered the hollow plastic primary float had a small leak at the mold part line. I replaced it with a brass float and fixed that problem.

With mechanical and vacuum timing set up the same as Lars and Barry recommend, the engine runs like it was designed to. Good idle, great pull off idle all the way up with no flat spots or other issues.

Cheers,
Pete

 

Hey Pete,

Thanks for the response. Good info. I'm with you. Don't know much about cams but yours doesn't seem too much different from mine. Maybe a cam guy will chime in.

I'm awfully tempted to just drive this car to Lars and say "hep me hep me, please Lars hep me".
Hell, a good tune might be worth a 10 hour drive.

DC

 

Replaced the fuel pump yesterday. What a pita. 8 hours. 15 minutes to remove the old one. One hour to install the new one and make the connections. Spent the rest of the time chasing and returning parts and fittings. Still couldn't find all the fittings needed to build a new hard line from the pump to the carb and ended up using fuel injection hose to get me by until I can find everything I need. The previous owner had used braided stainless hose with AN fittings and then cut the hose and used a regular clamp on a hose barb at the fuel pump. The old pump consistently showed 8 to 9 psi on the gauge. The new one shows 4 to 7 but the needle swings back and forth quite a bit which didn't happen with the old pump. Is that ok? There is an existing inline filter back near the tank. When I build the new hard line, do I need a filter between the pump and carb?

Checked the compression today. It doesn't look like good news. Here are the readings:

#8 - 142 . . #7 - 167
#6 - 163 . . #5 - 138
#4 - 175 . . #3 - 155
#2 - 165 . . #1 - 110

I put a squirt of oil into #1 and the compression came up to about 118. Also noted that it took 5 compression strokes to reach maximum pressure on each of the cylinders. I didn't write down the readings for each of the 1st 4 strokes. I wish I had. I'd say the 1st compression stroke produced no more than 80% of the final pressure and probably less than that on some cylinders. How bad are these readings?

The spark plugs were Autolite 145. Are these correct? All of the plugs looked identical. Jet black with soot. The gap was around .040. I cleaned the plugs and increased the gap to .050.

I didn't figure the valves were deposit free so decided to run some Seafoam through the carb. Followed the directions on the can and drizzled 1/3 of a can into the carb while the engine was running, then shut it down for 5 minutes. Then started it up and watched it belch smoke for another 5 minutes. Took it for a spin and could tell the difference. The idle was better and the engine just seemed to run smoother.

Still need to adjust the carb again and I plan to add some Seafoam to the oil. Figure it can't hurt at this point.

I was hoping to verify the timing mark and pointer but couldn't find a piston stop tool locally. Might have to order one.

DC

 

If those compression readings are right then all the Sea Foam in the store will not fix it. The compression readings should be within a 20 PSI range if it is ever to run well. Nothing short of an overhaul will help here. You might as well start saving up for a crate engine.

-Mark.

 

Thanks Mark.

I forgot to mention in my previous post that I tried again to find a vacuum leak and could not. I used starter fluid this time and really went over all the possible leak points thoroughly.

Given the low vacuum readings, the carb issues, the distributor, and now the compression numbers, I have to agree with your assessment. I think the bottom line is that this is not a healthy engine. This is further confirmed by one of the very first vacuum tests I did. When I blip the throttle the vacuum drops completely to zero and then rebounds to about 20” before returning steady to 10”. All of the vacuum diagnostic info I found suggests this is due to poor rings.

Is there any reason I would want to consider having this engine rebuilt? My goal is 350-400 HP, fuel injection, reliability, and with an OD tranny, decent cruise mileage.

Are the compression numbers bad enough that I need to be concerned about this engine failing soon or could I get several months out of it before rebuilding or putting in a new one?

Oh well. I may still tinker with it a bit. The engine and this thread both have been good learning experiences.

May be time to start a new thread titled "What Engine Should I Buy?". Bet that's never been discussed before.

DC

 

I got a 69 coupe with a 71 454/365HP, that pulls 10" of vacuum, in gear at idle. I'm running a 750 vacuum secondaries dual line carb. I finally, after 2 months of tuning, put the fuel pressure on my Carter electric fuel pump at 4.5 lbs. I lowered the fuel bowl levels to below what Holley says. That fuel bowl adjustment is for drag racing, not street driving. My floats are now set to "bump" the car decently to get fuel outta the site window. I jetted down from the Holley installed 70 jets to a set of 65's. I run a MSD distributor and 6AL box, with 39 degrees of total timing. Initial timing is 23-24, I think. If the motor is happy with it, give it to it. I had a real bad gas smell in my car too, that's all gone now. Your plug gap @ .050 is too wide, I think. Go down to .045 or back to .040 even, after all the initial grass roots checks. I'm really tired, but I think that makes sense.
Compression tests are ok, but a leak down tells the real skinny on the motor. Think about installing an O2 sensor and hook it up to a wide band, that will tell all, right there.

I'm getting a new 4150 Holley tomorrow, there has been plating problems inside the fuel bowls of a few Holley's. Mine looks like it was in the ocean water/sand for 10 years, it's less than 2 years old and 1 whole year was on jackstands. Good to know your hot rod shop owners!!!
Good Luck

 

DC3,you probably have checked this for vac leaks....but in case you haven't...look at the inlet mating surfaces particularly at the rear of the engine...sometimes the water crossovers in the heads aren't blocked properly and you can get excessive heat which warps the inlet and stuffs up the seal to the heads...i chased all sorts of vac leaks till i found that one and it really stuffs up the idle...i hope you get your issues sorted but i concur that 10" is very low for what is a pretty mild engine...john

 

As for rebuilding - if you can do it yourself it is worth doing. If you have to pay someone else you might as well just get one off the shelf. The big exception would be a numbers matching engine. With an original engine it makes some sense to rebuild them rather than buy a crate engine.

I would suggest that you drive the one you have, set up your distributor now and tune the carb. This engine will run for quite some time as it is now. Once you have time to pull the engine you can dissasemble it and evaluate the condition at that time. If you luck out and the bores are still serviceable you could re-ring it and save a lot of money. If the bores are trash and the block is not original them go straight to the GM crate engine shop and get you a new one. That is what makes the most sense at this point.

I usualy do my own rebuilds but not everyone has the tools or the time for that.

-Mark.

 

It's not original and not even likely to be a Vette motor. I will go ahead and tune the carb and work on getting the distributor set. BigBlockTank recommended I return the spark plug gap to 0.040 or 0.045. Given the HEI ignition, what do you think?

I've never rebuilt an engine and don't want to be without the car while I learn so I will drive it for awhile until I can arrange for a new engine. Then, I'll get a buddy of mine who has done some engine work to help me tear this thing down and see what's there. Is there anyway to verify if the bores are still serviceable without tearing it down?

I was going to install fuel injection and an O/D tranny anyway so I might as well dig a little deeper into the pocket to get a new engine. I figure I can get some cash back by selling the old engine or the parts from it. Surely somebody will want the camel hump heads if nothing else.

I am a little curious about something I read up on regarding engine compression numbers. My Haynes books says that the "standard" compression spec is 150. It also said that unusually high compression numbers could be a symptom of carbon deposits in the combustion chambers. I know my engine isn't standard but does the cylinder I have at 175 qualify for "unusually high" compression and thus is a problem also, or is it close enough to be considered good? Just curious.

Thanks to you and everyone that has helped. Appreciation the education. Hope I can return the favor someday.

DC

 

I told you that because I'm running a MSD ignition and have VERY recent experience in this. Recent as in just last week, mine wouldn't run well, or pass gas, let alone pass another car.

 

You can close the spark plug gaps down if you want. No harm there.

Doing a tear down is a good idea if only for the experience. You can have the bores checked by a good machine shop for little money. Be sure to mark where all the bearing caps are now before you disasemble them. They must go back where they came from in all cases. You can get the book "How to rebuild your small block Chevy" by David Vizard and read it cover to cover. I have one and it is just about worn out.

I would not get too wrapped up in the old engine. One thing I would advise you to do - be prepared to purchase a crate engine before you start tearing the car apart. Pull the engine and have it checked for bore wear first. If the bores are bad, order the crate engine. The time required for a rebuild is more than you expect so you might as well get it back on the road as fast as possible. The carb and distributor will be all ready to go so that will be a huge help there.

-Mark.

 

That's strange. Mine seemed to run better. But then, nothing about this engine surprises me anymore.

DC