boese1978

Double checking everything as I continue to drive the rebuild. Pulled these two plugs ( #2 & #4)- no time to pull others right now, opinions? Car idles a bit rough and sounds grumbly but it idles in gear albeit rough which I think is the cam....no back fires or popping...... and boy does it go

droldsmorland

One looks a tad lean one looks a tad rich. But normal fuel distribution and short runs can cause this. Also a vacuum leak can cause this unevenness. Use a vacuum gauge and start disconnecting things. PCV, Brake booster, vac advance etc. Once you've corked off all of these items with no change in RPM that points to carb or intake gaskets. Spray WD40 at the carb base. Does the RPM increase? If yes theres the leak. The base gasket or throttle shaft. If no results go around the intake. After that Id be looking at valves with a leak down test. What is the highest vacuum reading you can obtain with timing and carb air fuel screw adjustments?

oldcutlass

Its a fresh rebuild and everything needs to settle in. Looking at plugs just cruising around is not going to tell you much. Make sure the blacker one has the spark plug wire solidly attached.

boese1978

Thanks for the info- I did pull all the other plugs, only the one darker one, all others are the same. I think that dark plug did have a loose wire at one point that I pushed on all the way. Thank you for the input. DR- thanks, I'll do these things this weekend and report back. Eric- I have had the car out on the highway etc for a cruise at 60 or so for an hour or two plus lots of hours cruising the streets, is that still condsidered just cruisin around? Also- I think I am supposed to go one step cooler on the plugs per Mondello after break in, how long is break in?, suggestions on a 5/8 plug are welcome....

boese1978

http://www.harborfreight.com/fuel-pu...ter-62637.html

DR- this cheapo version work ok for my vacum testing? benefits of a better one?
thanks

droldsmorland

I'm not a fan of harborjuink; single use before the needle falls off. Look at Lisle, KD or Sears. Those are likely chineasium to, but slightly better quality. One bad plug could be a wire, a plug, a valve seal etc...
Agreed the secondary AVS valve should be tightened up. Google it if you're unfamiliar as to its location. It's a PITA to do on the car. Need a real short slotted screwdriver think Chapman set. Mark or keep track of where you start. Then tighten up in 1/8 to 1/4 of a turn. Keep going until you get a negative response. Then back off. It's counter intuitive but the tighter the door is the better the secondary response is. But there is a too-tight too. This is one of the reasons a Qjet got the name Quardabog. The spring loses its spring as it ages. Try that. What does the timing curve look like? Try 12* at hot idle without the vac advance. Then hook the advance up. It should bring in another 8-10-12* at idle for a total of 20-24ish. The remainder should come in around 2800RPM for a grand total of 36-40. This is with good gas 93 or better, mild ambient temp ~80* and is sea level dependant. Back off the higher up you are.



http://www.lislecorp.com/divisions/products/?product=77

boese1978

DR- No QJ, Holley 750 vacum secondaries. Bad valve seal on a completely new build?

11971four4two

HI MISTER
Glad you are up and running!

You may want to do a compression test to see if any problems with rings or valves

cheers
b

boese1978

Thanks Brian!! A far cry from the 68 vert I bought from you some 20+ years ago!! I'll be digging in this weekend...thanks for the suggestion!

11971four4two

Time sure flies when we are having fun! I think I sold you that 4 speed drop top in 1989 or so

I hope nothing too serious is wrong with the power plant in your current olds.

All the best of luck

droldsmorland

Boese, give us a little more background. I may be confusing two different postings here. I think I've responded to you a few times. Or you may have a couple of related threads going here? What have you recently changed? What exactly is the problem again besides questioning the plugs and idle quality?? Yes, bad valves on a fresh rebuild, a remote chance but I've seen it. Bad cam, guides and seals too. Not familiar with Holly vac secondaries. But a carb is a carb. You may need to play with rods and jets. Has the car ever backfired through the carb since you've installed it? Get that vacuum reading and adjust like I mentioned to obtain the highest possible vacuum reading. It should be a fairly steady vacuum reading as well.

boese1978

Olds 350 Bored to 4.155 and stroked- about 388ci. Full roller set up with stiffer springs, ProComp heads worked by Mondello, Edelbrock 7111, Holley 750, th350...basically everything from the ground up is new. Nothing has been changed recently , this is a new engine that I rebuilt and have had running and been driving now for about 3 weeks. No real "problem" I am just new to this kind of engine and was wondering how to get it a bit smoother.- Again, could be the cam mark sold me- it does run strong and it has never backfired from carb or exhaust. What else can I share? Thanks!!

olds 307 and 403

It does look a tad lean on the one plug. What are you running for timing?

boese1978

At this point I am timing by trial and error with road tests. The damper marks are no where near the tab so I can not give you a number.......I know, I know...

oldcutlass

You need an adjustable timing light. Bad timing settings will destroy an engine over time.

olds 307 and 403

I had a low compression 350 run a little rough, it was at 72 degrees! Find your 0 and mark it. Why are the balancer markings off? I like my Equus timing light with digital rpm and timing degrees.

droldsmorland

Has the distributor been dropped in at TDC on #1? I'd verify that for a sanity check. You have to know where TDC on 1 is to get it base timed. Apply timing tape to the damper if the factory marks won't work.

Super tuning is a method of extracting the best possible results from all the engines/trans and final drive systems. This is what you're trying to do.

Optimize the spark curve. If you know the cam, converter and rear gear specs you can have the distributor set up to optimize the cam profile. Have someone with a SUN machine do this. You will definitely feel the difference with a well-tuned distributor. Smoother acceleration and possibly a pony or three.

Are u running HEI, MSD or Points?
What's the advertised compression ratio of this engine?
What Converter and rear gear do you have? The converter stall needs to play nice with the cam timing and spark timing.


The carb is the next device that needs to be dialed in. You want idle, off idle transitions, mid and WOT circuits to all play where the engine wants it to play. Hard to precisely do without a dyno and O2 sensing. An O2 meter is a nice tool to have. The O2 meter will tell you exactly which side of Stoichiometric you are, (lean or rich).

You may need less carb? Do the math. For 100% Volumetric Efficiency the math says a 388 CI engine shifting at 5500 RPMs requires a 679cfm carb. If your shifting at 5000rpms, 617cfms. 6000rpm put it right there. Of course, that's at 100% VE. And a carb is a giant compromise. What I'm getting at is if you are struggling to get where you want you might try a fresh Q-Jet tuned specifically for your application. Or send the Holley out to get the same treatment with your cam, converter and final drive data. More super tuning....

A chassis dyno is the best as it will tell you which side of "Stoic" the engine likes by the greatest HP and Torque numbers. It's easy to extract the most from your set-up with a chassis dyno. Look around for a facility in your area. For a couple Benjamins, you could have an experienced dyno tech dial you in. Bring a plethora of distributor weights n springs and carb jets n rods.

Head spinning yet???
So if you don't want to go the dyno route the next best thing is the seat of your pants, patience, a vac gauge, spark plug and tailpipe reading. This will get you in the ballpark at least.