runs like a vac leak

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highflyer

highflyer

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Some time back I started a new motor..never has run well..runs like I missed the intake gaskets..iv did a comp test and came out with 155 pretty much across the board..runs bad cold and as it warms it gets better but still runs like a vac leak...in the garage or out it really stinks up the place..fowl unburnt fuel stink..when I started it months back I wrote about the pvc valve pounding ..iv replaced wires plugs dist ign box coil ..just runs like s#@t..so today I made up a leak down tester and did some testing..i made the one on the net with a .040 thru hole..first cyl number one with 100 pnds pressure it read 40 pnds plugged in...moved to 4 it read 36 pnds...both at tdc..thes are j heads with less than 1000 miles..so I moved to the rear and put my ear up to the e x pipe .no air escaping..pulled the oil fill cap on the val covers and I could hear air escaping..there wasn't a wind storm there, but I could hear the hiss of escaping air..what ya thiunk...all welcome
 
Im not familiar with your tool, but no matter. The pressures are too low to be useful. but the 10 % difference is somewhat telling. Somewhat because we are missing the rest of the cylinders so really have no way to make an accurate assessment.
air past the rings is mostly normal; 2 to 4 % is typical, unless you have gapless or really tight file fits in a hot motor then 2% or less is achievable.
I will throw my hat in with the others regarding timing being late. Thats the number one go-to with, stinky,makes your eyes water, exhaust.

Just to reiterate; what build specs and most importantly; cam and idle timing. Cant help you until you help us
 
262 comp cam 10 int about 38 total..carb is right from the box clean ..didnt feel any more cylinders were necessary since the first two were so low..float level is perfect.rings are new i dont think bad rings would give a 155 compression test...they are within a pnd or two of being the same..
 
What are you running for rockers, adjustable? If so, too tight?!? Hanging a valve open maybe??
 
Had something similar happen once, and it was a bad seal between carb and intake. It is worth checking. Also, and I am almost embarrassed to suggest it, make sure there are no unplugged 'holes' in the carb. It is within the realm of possibility that a new out-of-the-box carb could have been installed with a vacuum port open that needs to be plugged. I've seen it happen.
 
14-16 initial would be where I'd start for timing. That should clean up the idle.

You'll have to adjust the mechanical to hit your total number.
 
10 degrees initial. That's were I START with a stock engine. I have my 351M Ford at 22 initial and 36 total.
 
If youre trying to pressurize the chamber through a hole of .040 diameter, the rings will leak that away pretty quick.I mean the top ring gap has a bigger area than that. If you suspect cylinder leakage, procure a proper tool.
Well 10* isnt that far off, to cause as much stink as youre talking about. Have you verified the TDC mark?
I suggest you crank in some more degrees, maybe 3 at a time,and resetting the idle rpm each time,until the idle rpm stops rising.Adjust the mixture screws as may be required, then re-evaluate the stink and idle quality.If you get an off-idle hesitation, the T-blades may be too far closed or the pump may require resetting.You may have to sync up the transfer ports to the blades.There will come a point where you will find yourself running into too much idle timing, in as much as the rpm cannot be slowed down enough without getting a hesitation due to the transfer ports being too far out of sync.
Also; make sure the vacuum advance is not affecting the idle timing.And make sure both mixture screws are affecting idle quality.
good luck
 
How many old cars has he had? Some of these cats that have had nothing but new EFI stuff haven't a clue.
 
I agree with the timing being too low for initial. Should fall around 14-18. My 360 is 20 and 40 total, but I'm at altitude. Are you sure you're plugging the vacuum advance when checking total timing?? 28* of mechanical advance seems like a lot. Not sure on the .050 of that cam but even mild cams can be a little stinky and not want to idle low, cold, or out of time. How's it run on the highway??
 
Rusty why are you asking the club...ask me..yes I just replaced the injectors in my 99 v/6 tacoma,but in 1960s 1 ran a 426 hemi yellow plym satellite iv built a few chevys a few 351 Windsor industrial motors for boats.even a rambler motor once..young cat I don't think so..im a retired 43 year state of cal certified precision machinist..dum enough to leave a gaping hole in the carb.NO NOT LIKELY..68 years old and no dementia..iv built a number of holleys..afbs 4 and 2 barrels.iv completely rebuilt boat outdrives and lower units.IN THE 60S my uncle was a Chrysler trouble shooter that was very good..but im no expert.FAR FROM IT.some guys on this site are and some are like me and know just enuff to get into trouble lol.some of the responses got me to think...are my pushrods too long...or have the j heads been shaved enough to be keeping the valves from seating..Kit and bad sport I like your way of thinking..these heads could have been shaved to far and be keeping the valves open..i did a pushrod length test when I bot them.comp pushrods.checked out ok..the rockers are stock mopar ..I think ill make up some shims and slide them under th bars and see if there is any diff..Rusty,i noticed in the years you are sometimes a bit testy..please try to put brain in gear a LITTLE better before making derogatory comments..to you all thank you for helping me...
 
I was not being derogatory in the least. How do we know who you are or what experience you have? This site is inundated with young types that know nothing except how to jump in and turn a key. So forgive me if I ruffled your feathers.

You seem to forget, that I have been trying to help too. Just because you take something not as intended doesn't make that untrue. I am glad you have the experience. Much more than I it sounds like. Again, nothing personal was meant at all. Sorry you took it like that. Like we always say around here, my crystal ball is broke, so I cannot see through the internet who I am talking to.
 
What's easiest to do. That's the direction I'd go first.
 
Highflyer
Before you tear into it and start shimming the shafts, there is an easier way. A cylinder leakdown test will tell you all you need to know, in that direction.
And Im coming 62 in June, and as healthy as ever. When someone refers to me as a cat(not so much anymore), I consider it a term of endearment, and it carries a connotation of brotherhood. jus saying.
Im here to help as well. Im pretty much done projects. Im hoping to share my 45 years of knowledge with whom ever can use it.
 
AJ/FormS said:
Highflyer
Before you tear into it and start shimming the shafts, there is an easier way. A cylinder leakdown test will tell you all you need to know, in that direction.
And Im coming 62 in June, and as healthy as ever. When someone refers to me as a cat(not so much anymore), I consider it a term of endearment, and it carries a connotation of brotherhood. jus saying.
Im here to help as well. Im pretty much done projects. Im hoping to share my 45 years of knowledge with whom ever can use it.
Click to expand...

He did say in the OP, that he did a leak down test of sorts. No air from tailpipe, but could hear air escaping into the block.
 
Unless you use total seal rings, you WILL get some air through the crankcase......and might a little with total seal.
 
Thats right. And if the cylinders have been washed clean by a poor tune, it will be worse.
The compression test tells one PART of the story.
The cylinder leakage tells another PART.
Together, a pretty good picture emerges as to the entire state of the swept volume and chamber.
Consider this;
a leakage test will not see anything below the ringpack at TDC, but a compression test will find a wrist pin groove real quick.Or a compression test at 155psi might be fine, unless a Leakdown test shows every valve is leaking or every ring is worn out to the same degree.
I dont tune engines anymore for guys that refuse these tests as part of my tuning regimen.I have chased my tail too often in years gone by. This is particularly critical on small, highly stressed powerplants; like snowmobile engines.
 
Well now we are getting somewhere.i think.. I twisted it today and 16 seemed like a good spot it seemed to like it there..20 was too much and the starter was kicking back it still wants to kick back a little at 16...the stink got a little better the poor running is still there the timing adj didnt help it at all,im gonna do a leakdown test thurs [gone fishin ]tomorrow..this time instead of making a tester ill go buy one..Im still thinking leaking valves..tx for the help
 
Once you find your initial timing spot, then play with the curve.
 
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