not enough vacuum

after rebuilding the engine in my lark i have a problemo with vacuum. after adjusting the valves three time and numerous timing adjustments i only have 15-16 pounds. i have an r2+ cam and springs and am sure thats not helping. my engine is bored 80 0ver with flat tops but i don't think that has anything to do with the problem. any ide'rs?

notsoslow64
1964 lark daytona
bd_marks@yahoo.com

[JDP]

Might be normal with a new engine until everything seats, but make sure the timing is advanced enough too. On a good day, a Avanti engine will only pull 20 inches.

64 Commander 2 dr.
64 GT Hawk R2 clone
64 Daytona HT
63 Cruiser
63 R2 4 speed GT Hawk (Black)
63 Avanti R1
63 Daytona convert
63 Lark 2 door
63 Lark 2 door #2
62 Daytona HT/ 4 speed
62 Lark 2 door
60 Lark HT
60 Hawk
59 3E truck
52 Starliner
51 Commander

[benny_64]

i advanced the timing as much as possible while watching a vacuum gage, highest it got was 16. i hope you are right though, the engine only has about 200 miles at most. but there is a huge flat spot at low idle. if i try to goose it at all it just dies down. and i am pretty sure its the vacuum issue. thanks guys.

notsoslow64
1964 lark daytona
bd_marks@yahoo.com

[bige]

My R2 bored .156 over and R2.5 cam only pulls 15-16 lbs. Runs GREAT. Look for other problems. Check the metering rods. Make sure they are moving freely in their bores. Check the accel pump and squirters, look for a strong spurt not a dribble at the slightest movement of linkage.

A cam with a little more duration will reduce vacuum at idle. But under acceleration or any movement of the carb plates vacuum will naturally drop down so low vacuum when you goose it is normal and the vacuum at idle reading will not correlate to off idle throttle response.

[Roscomacaw]

Hey! Benny! Good to hear from you again. I've wondered how you were and where you might be. (Benny's a Marine Helicopter tech)

What sorta carb are you running on this thing?

Miscreant adrift in
the BerStuda Triangle


1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe

[John Kirchhoff]

Not trying to sound like a know it all, but vacuum is measured in inches (of mercury) and not pounds. Old time vacuum gauges (including the one my dad made himself) basically consisted of a vertical tube with a hose attached to the top and at the bottom was a reservior containing mercury. This whole affair was attached to a flat piece graduated in inches. Attach a vacuum source to the end of the hose and it would lift the mercury up the tube where you'd note the inch reading. In the good old days (not really that long ago) high dollar motorcycle carb synchronizers had four of the tubes side by side while the cheapo jobs (like mine) consist or four gauges. Mercury being a no-no anymore, I doubt you can get the mercury ones anymore. Oh, water won't take the place of mercury because it's not heavy enough. I tried that when I was a kid and sucking a big tube of water into the carb kills the engine in a hurry.

[Roscomacaw]

John,

Fresh outta the service, I got a job at Continental Motors Division of Teledyne-Ryan. I had a job of building up jet eninge/turbocharger test cell control panels and running required cables and tubes to the cells from the control rooms.
The control room walls were one huge expanse of calibrated mercury tubes that they'd connect various test points to. The "techs" were forever spilling mercury out of the manometers and as a result there'd be big puddles of it in the area behind the manometer wall.[}] Once it was on the floor, it was considered "dirty" - it having been contaminated with dust and debris. The engineers considered the puddles a nuisance and so they were all too happy to let me scoop up and claim whatever was lying on the floors.
I'd get a quart bottle of the stuff and take it to a scrap metal yard there in Toledo. I usually got about $30 bucks for a quart! A nice little windfall in 1967!

Miscreant adrift in
the BerStuda Triangle


1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe

[GTtim]

Benny,
Your vacuum sounds like it is in the ballpark to me. My R2 bored .060 only pulls about 14 at idle. I'd suggest that the bogging down problem is due to the accelerator pump or a timing/distributor issue.

Tim K.
'64 R2 GT Hawk

[JDP]

One issue I've had with the Avanti carb is the metering rod springs. The Avanti engine does not pull enough vacuum to overcome the stiffer springs that are often installed and that allows the mixture to richen too early.

64 Commander 2 dr.
64 GT Hawk R2 clone
64 Daytona HT
63 R2 4 speed GT Hawk
63 Avanti R1
63 Daytona convert
63 Lark 2 door
63 Lark 2 door #2
62 Lark 2 door
60 Lark HT
60 Hawk
59 3E truck
52 Starliner
51 Commander

[GTtim]

Good point, John. I use the lightest springs in the kit, the blue ones.

Tim K.
'64 R2 GT Hawk

[Chicken Hawk]

If you have the lash set at .010/.012", try loosening them up to .020" and if it is still quiet enough for you (will have slight lifter clatter) that should help the idle some but the 15/16 inches is probably not too far off for the R 1 and 2.

Ted

quote:Originally posted by benny_64

after rebuilding the engine in my lark i have a problemo with vacuum. after adjusting the valves three time and numerous timing adjustments i only have 15-16 pounds. i have an r2+ cam and springs and am sure thats not helping. my engine is bored 80 0ver with flat tops but i don't think that has anything to do with the problem. any ide'rs?

notsoslow64
1964 lark daytona
bd_marks@yahoo.com

[wagone]

Hey Ted (and others),
I'm confused (of course, for me that ain't exactly hard to do). What manner of Stude engine are we talking about here? Lash set at .010"/.012", or even .020"? That is a wee bit TIGHT, or do I misread here--this sounds like a serious thread here and it's not April 1st yet. So what gives? If Benny has an R2 it must be a 289 (and more) and not a F**d engine, so what gives with this valve adjustment advice?

wagone and the OLD R2 Avanti

[benny_64]

well i dont think the problem is in the timing or distributor. i've advanced and retarded it into just about every position possible. i put a pertronix setup in it, so i guess points are ruled out. i am running a edelbrock carb, 600 cfm, i know i know its a bit over carbed but when i go through all the symptoms it seems like its not getting enough fuel. i went through the carb before putting it in and cleaned every spec of grime. i didn't replace the excelorater pump though. i will check it for healthy spurt and go from there. thanks a lot guys.

notsoslow64
1964 lark daytona
bd_marks@yahoo.com

[bige]

Which Edelbrock do you have? 1406 with the electric choke or the 1405 manual choke? Or, a 1405 with the electric choke installed. If you have a 1405, you may be dumping too much fuel when the car transitions from cruise to accel. They have larger jets and smaller rods. Is it new?
ErnieR

[benny_64]

not new, it is a manual choke. i checked the carb and i am getting a pretty weak spurt from the jets, i am going to change the accelerator pump and see what happens. thanks again guys.

notsoslow64
1964 lark daytona
bd_marks@yahoo.com