Rebuilt 351W starts, runs FAST, then dies - help wanted

[foothilltom 33]

Hi guys, I'm just at my wits end.  Swapped a rebuilt 351W for a tired 302 in my 69 coupe.  351W lovingly rebuilt by yours truly.  Installed in car after a brief 20 month project. 

Was able to run the motor for about 20 minutes at around 2500 rpm to achieve some kind of break-in, so I'm very glad about that.  But after that initial 20 to 30 minutes of run-time, something strange has crept in and I can't keep the motor running.

The vexing behavior that I'd love to get ideas for:

• She cranks/starts 100% of the time
• Motor runs VERY FAST (like 2000 rpm) for about 2 seconds, then dies quickly (no sputter like she's trying to keep going)
• If I goose the throttle, I can keep it running indefinitely, but it requires constant attention (makes it hard to get other diagnostics)

As this car had sat for several years during the project (with California gas), I suspected various fuel-related issues, so I replaced the 50 year old fuel cell, fuel lines, and replaced a suspect fuel filter.  I also pulled the carb (for the ump-teenth time), cleaned it up, adjusted the floats, etc.  Armed with a fresh fuel-delivery system, I was hopeful, but exact same behavior as before: quick start, runs SUPER FAST, then dies utterly.  

Since it just quits so suddenly, I suspected a fuel-pressure issue so I checked the sight plug on the carb and gas is definitely coming out easily, so the primary bowl is definitely full.

 

The fact that I can keep it running by opening the throttle is interesting.  Seems to indicate a carb/fuel problem more than ignition, wouldn't you say?  To me, that indicates the accelerator pump is delivering fuel on demand, but somehow the normal fuel circuits are somehow not doing their part?  The Holley carb has only about 20 hours of operation on it, but it did sit for 2 years while I slowly went about the engine swap.  I did not dip the carb, just sprayed it out after disassembly.

 

Some random thoughts:

* Am reasonably sure the timing is in the correct neighborhood (8B), but not 100% since I can't get it to idle long enough

* I meticulously found 0TDC on #1 during the build and my balancer/timing mark is dead on correct

* When installing the diz, I made extra sure I have #1 corresponding with 0TDC (not 180 off)

* Idle/Mixture screws on carb are in "default" position 1.5 turns out from closed

* Not sure if I have a vacuum leak, but I see about a reading of 18 on my vac gauge when I do have it running

 

The distributor is an "OEM" product I found on eBay.  I have a very old Petronix I unit in there and a 9V coil from the old days.  I do not have a spare dizzy to test.

 

Weird that it starts, runs fast, then dies.  Would really appreciate some ideas or similar experiences.

 

I really think I suck at this hobby.

Tom

[1969_Mach1 333]

For a Holley carb with only two idle air fuel mixture screws your preliminary adjustment sounds about right.  You might try two turns off seat for preliminary adjustments but the issue sounds more severe.  Sounds like you either have (1) a large vacuum leak, or (2) the idle passage or passages, or the idle channel restrictors are plugged in the carburetor.  The idle channel restrictors are in the metering block.  Typical idle channel restrictor sizes s in a Holley gas carb range from about 0.025" to 0.035" depending on the carb.  For a Holley carb, make certain every passage is clear in the metering block, main body, and base plate.  If you follow them closely you can determine where they enter and exit.  The last Holley I rebuilt for a neighbor that sat for a couple of years had idle channel restrictors in a metering block so plugged I needed to use number drills and a pin vise to clear them.  Soaking in carb cleaners and compressed air would not clear them.  Lastly, make certain the idle air bleeds in the main body are clear.  Looking down the top of the main body you will see 8 small brass bleeds, four on the primary side and four on the secondary side.  The outer four bleeds are for the idle and transfer circuits and the inner four bleeds are for the main circuit.  Let us know what you find.

[foothilltom 33]

Thanks!  Your point about the vac leak is well-taken.  I assembled the motor myself and remember feeling a bit hinky when I set aside the cork intake manifold gaskets and used RTV instead.  The connection point between the intake and the block just seems so...imprecise...and relying on a proper bead of RTV has me suspecting that I may have created a gigantic vacuum leak.  In any case, I wish I could keep it running long enough to adequately test for a vac leak.  I may try the "cigar smoke" method and do a static test.  

And yes, my Holley only has mixture screws on the primary side.  I've experimented with putting them all the way in and several turns out and have not noticed a change in behavior, so I suspect you're right that my issue is more severe.  I can't wait for the day when I can turn those screws to dial in the optimum vac/idle behavior.

I'm going to pull the carb again and get my 3x reader lenses on and get down to business looking for blockages.  I may also swap a friends Holley on a running car just to see if that grossly changes the behavior I'm describing while I'm inspecting mine.

I'd really like to find the culprit.  I appreciate the assist.  

 

[1969_Mach1 333]

If you are using an aftermarket aluminum intake manifold the RTV end seals should be fine.  That's typically recommended with aftermarket intakes because once in a while the cork end seals prevent the manifold from completely sealing to the cylinder heads.  If you can get your hands on a known good Holley carb from your friend, that might be the first thing to try.

Other than that, if the car has power brakes, disconnect and plug the vacuum port on the intake that it connect to as that can be a big vacuum leak.  The same applies to any vacuum lines feeding other stuff.

[barnett468 418]

start it up and keep it running for a few seconds then let it die.

remove the fuel level inspection screws on both float bowls and tell us what the level is. it should be around 1/8" below the front hole and around 1/4" below the rear hole. if some fuel comes out, the level is to high and either needs adjusting or the needle and seat are leaking.

as 69_mach1 suggested, plug all vacuum hoses including the pcv hose and brake hose and distributor hose etc.

what cam do you have?

what is your compression?

what is your initial timing set at?

 

 

[foothilltom 33]

An update.  I tried Scotty Kilmer's (youtube dork) "cigar test" and I can easily see a fairly huge leak where my Edelbrock Performer 351-W aluminum intake mates up with my GT-40 clone, Chinese-made aluminum heads.  We're talking a pretty huge leak, all along the entire edge.

So, I'm pretty horrified.  When I was intalling the intake (on the stand, months ago), I pretty much lovingly installed the gaskets, a tiny bit of clear RTV on the edges, and let the Felpro gaskets do their thing.  I torqued down each intake bolt in the proscribed order to the proscribed torque spec (which I can no longer remember).

Yet this thing is clearly leaking live the proverbial sieve.  What the hell.  Is there any reason to go back and apply a bit more torque to the intake bolts are am I just pissing up rope now?  It breaks my heart to think about pulling the intake off while the motor is in the car because it's just so dang hard to work on and it's dirty/windy out there.  

Ugh.  Thoughts, ideas,  etc. are very much appreciated.

[foothilltom 33]

And to answer Barnett's questions (I didn't see them until after I posted my latest).

• I do believe the float is too high...the fuel is right at the front hole after immediately shutting down the motor.  I will adjust that
• My "smoke test" revealed a pretty bad vacuum leak at the intake manifold to aluminum heads - ugh!  Not sure what to do there.
• Cam is a mild street cam from Comp Cams.  I can get the grind number, but it's just a skosh more duration than stock.
• Compression is really good.  Measured at 175 all the way around
• Initial timing was 8B based on the only time I could get a timing light going.  Since then I can't keep it running long enough.
• I was really careful about finding TDC on #1 during the build process, so I'd like to think my diz is aligned correct.  Wouldn't bet my life on the timing now that I've been messing around so much, but I'm erring on the side of too much advance if anything.  Using my ear more than anything now.

With regards to the vacuum leak I discovered (with a dang cigar, no less)...is it possible that developed during the break-in period when the motor got hot for the first time?  I'm hesitant to torque down on the bolts, but I'm wondering how much these two pieces of aluminum could have "altered" during the break-in.

Again, ideas are super welcome.

Tom

[foothilltom 33]

Cam specs.   Xtreme Energy™, XE262H.   

.493 lift

218 Intake, 224 Exhaust

[1969_Mach1 333]

What intake gaskets did you use?  Stock replacement intake gaskets will sometimes not seal up aftermarket intakes.  Since you have an Edelbrock intake, they have intake gaskets for it.  They are almost identical to the Felpro Performance 1250 intake gaskets.  Just a different color and I believe a slightly different material.  For Felpro Performance intake gaskets, the most common one used is the 1250.  Felpro also has a steel core version of the 1250, the 1250S3, which is a little thicker because of the steel core and also more durable.

[barnett468 418]

exactly what intake gaskets did you use?

what heads are they?

exactly what carb is it?

the gas level at the bottom of the hole is a little high but will not cause your particular problem but i would lower it a little anyway.

torque the intake bolts then do the smoke test again.

if it was leaking near the ends of the intake it may have leaked water into the oil.

the aluminum will not "move" enough to create a leak.

[foothilltom 33]

Hey guys, I used the gaskets that came with my 351 Felpro Gasket "kit" from Summit Racing.  It's been months, so it's fuzzy, but they were definitely NOT specific to the manifold.  As I recall, they were blue and NOT steel core.  I guess I can chalk that up to first-time-engine-build stupidity.    "A little thicker" would definitely be a good thing based on what I'm seeing.  I re-torqued the intake bolts a bit ago and it leaks from the save (several places) along the edge where it meets the heads.

Answering Barnett's questions (and I'm not trying to be withholding...just not always sure what is relevant).

• Aftermarket GT-40 clone heads from eBay.  The seller has a speed shop in Turlock, CA and I found out (much later after buying them) that he has about 80% bad reviews on Yelp/Google.  He keeps changing his eBay seller name, so I had no idea.    Here is a link that is current today of the same heads.  https://www.ebay.com/itm/Ford-289-302-351W-408-427-5-0-Mustang-Aluminum-Heads-GT40-EFI-OR-carburetor/372038104093?hash=item569f32f41d:g:LkoAAOxy~iJQ9irb:sc:UPSGround!94550!US!-1
• Holley 600 cfm carb.  The type with no idle-mixture on the secondary.  Nearly new but sat for a year or so during the project.
• Agreed I need to adjust the float.  Based on what you said, the gas is about an 1/8" too high
• Based on my Groucho Marx cigar test, it appears to be leaking all along the edge, but mostly in the middle.  I will drain the oil and see if there is water.
• Re-torquing the bolts made no diff, so you're right about the aluminum not "moving".  That was a pipe dream of mine.

I suppose its worth mentioning that the intake just came with the 351 block that I rebuilt.  I should have put some thought into it, but I just wound up using it.  Performer 351-W if that matters.

If this boils down to me putting the intake on w/out the proper gaskets, then I am an idiot, but I can live with that.  My fear is that the aluminum heads have some manufacturing flaw and I got swindled, but hopefully not.

Looks like I've got a whole bunch of re-work to do.  Thanks for your continued support.

Tom

[foothilltom 33]

Well, it's pretty much terrible news.  As Barnett prophesized, I have coolant in the oil.  I'd say about 10 oz of the stuff give or take.  The result was a slimy (unprotecting) mess.  My luck is I wiped my cam and everything else.

I guess the good news is I was watching the engine temp during the break-in and it stayed right around 180F.  Hopefully this leak developed after that and has just been a problem in the 40 seconds or so I've run the motor since.

I am going to go drink my sorrows away.  My attempt to rebuild a motor for a tired, but running Mustang is turning into an all out disaster.  I was so careful every step of the way, so I thought.

Bleh.

[1969_Mach1 333]

Sounds like the issue is simply that the stock Felpro replacement intake gaskets that came in the gasket set didn't seal the intake manifold to the heads.  With some luck no damage was done to the rest of the motor and a simple oil and filter change is all that is needed.  Then I think I'd replace the intake gaskets with either the Edelbrock 7220, Fel Pro Performance 1250 or Fel Pro Performance steel core 1250S3 gaskets. 

[DocWok 30]

5 hours ago, foothilltom said:

I suppose its worth mentioning that the intake just came with the 351 block that I rebuilt.  I should have put some thought into it, but I just wound up using it.  Performer 351-W if that matters.

You should check that the 'used' manifold has not been machined.

If it has been previously been machined excessively then this may explain your intake leak.

Plenty of information on the internet on how to check this.

[foothilltom 33]

Thanks guys.  Going to roll the Mustang into the garage today for the surgery to get out of the hot/wind/dust of the side yard.  It's no fun to take big leaps backwards, but that's how this game goes for the newbie, I suppose.

I'll take a good, hard look at the intake when it's off and figure out where my culprit is.  Just going to pray I did no real damage to the rotating gear.  I don't think it got over 180F the whole time.  Crossing fingers.

Update soon, I hope.

Tom

[DocWok 30]

Before you unbolt the intake manifold, it may be an idea to try and see if it's possible to slide a feeler gauge between the manifold and intake gasket.

It may give you an indication if you are getting any crush on the gasket.

Sounds like one hell of a leak if you have both coolant and vacuum leaks.

[foothilltom 33]

I'll do that right now.  Thanks!

And yes, based on my smoke test, the manifold was leaking pretty much from front to back, both sides.  Very strange.  I can't wait to see what the culprit is.

Update: I could get my smallest gauge through from front to back (.0025).  Color me ignorant.  I had no idea it could be so "off".  I wish I would have been more vigilant about that part of the fit.  I was hyper-concerned with the RTV gasket I made in the front and back.  Ironically, that didn't leak at all.  Just the Felpro gasket side.

The plot thickens.

[foothilltom 33]

Ok, so I'm still pretty well unsure of my next move.  Would appreciate some insights.  Recapping, I had a huge vacuum and coolant leak in my previous setup. 

Pulled the intake and have access to all numbers.

• Intake Manifold: Edelbrock Performer 2181
  • Came with block, have no history with it
  • Not sure to how tell if it's been machined
• Existing intake manifold gaskets: Fel-Pro 90103-1
  • bought as a kit from Summit many moons ago
  • research now clearly shows these are NOT for a 351W (but a 302)
  • Thickness mics out at .060"
  • Visually, these are a perfect fit for the manifold ports, so there was nothing obviously wrong with them
• GT40 (clone) aluminum heads bought from sketchy eBay guy, machine shop in Turlock, CA

Based on everything I've learned so far, the gasket is my #1 suspect, but I'm now wondering if this intake/head combo will work with any "standard" gasket.  According to the website, the recommended Fel-Pro 1250S3 set is only .065" which is just 5/1000th thicker than my existing.  I was able to get a .0025" feeler gauge through my old setup, which seems egregious.

If somebody could help me understand how to determine if my manifold has been machined, I would appreciate it.  If they've been altered, I'll just chuck them as I'm not going to pull the brand new heads and have them machined to match.  Also wondering if there is a much thicker gasket set...like 1/8" or something for this type of thing.  

I guess I am not sure how to proceed if the heads are somehow not to the same specification as cast iron heads or if my manifold has been altered.

Thanks for all your help!

Tom

[1969_Mach1 333]

1 hour ago, foothilltom said:

Ok, so I'm still pretty well unsure of my next move.  Would appreciate some insights.  Recapping, I had a huge vacuum and coolant leak in my previous setup. 

Pulled the intake and have access to all numbers.

• Intake Manifold: Edelbrock Performer 2181
  • Came with block, have no history with it
  • Not sure to how tell if it's been machined
• Existing intake manifold gaskets: Fel-Pro 90103-1
  • bought as a kit from Summit many moons ago
  • research now clearly shows these are NOT for a 351W (but a 302)
  • Thickness mics out at .060"
  • Visually, these are a perfect fit for the manifold ports, so there was nothing obviously wrong with them
• GT40 (clone) aluminum heads bought from sketchy eBay guy, machine shop in Turlock, CA

Based on everything I've learned so far, the gasket is my #1 suspect, but I'm now wondering if this intake/head combo will work with any "standard" gasket.  According to the website, the recommended Fel-Pro 1250S3 set is only .065" which is just 5/1000th thicker than my existing.  I was able to get a .0025" feeler gauge through my old setup, which seems egregious.

If somebody could help me understand how to determine if my manifold has been machined, I would appreciate it.  If they've been altered, I'll just chuck them as I'm not going to pull the brand new heads and have them machined to match.  Also wondering if there is a much thicker gasket set...like 1/8" or something for this type of thing.  

I guess I am not sure how to proceed if the heads are somehow not to the same specification as cast iron heads or if my manifold has been altered.

Thanks for all your help!

Tom

See the post I left in your other thread you started where you posted pictures of the intake manifold and cylinder head.  At least by the pictures you can kind of tell what happened.  Basically, it looks like wrong intake gaskets.  At least that's what it looks like from the pictures.  Hopefully there is nothing else odd.

[foothilltom 33]

Oh man, you are so right!  Nice going!  I'm going to go measure the "height" of these and verify.  I'm such a stooge if that's what happened.

[barnett468 418]

if the gaskets are not the problem, the heads are most likely the problem because it is extremely rare that someone mills down an intake manifold.

You can do a few tests to try and determine exactly what part may be wrong. This will require a protractor which is cheap and a few spacers etc.

 

 

[foothilltom 33]

Alright, so without question, the gaskets are not correct.  As obvious as this to me now (thanks to you guys), it simply did not occur to me to measure the height of the ports on the heads.  I just ordered a gasket kit like a stooge months ago and never questioned it again even after going a different direction with aluminum after-market heads.

The port height on the cast iron heads is about 1.81" x 1" and my aluminum heads are 2.05" x 1.25".  As Mach1 pointed out from my photo, the top of the gasket did not even cover the top of the port, which clearly wouldn't be good. 

Now that I know that an intake manifold gasket has to match the head, I should be able to find what I need as far as port dimensions.

Edit: Wondering if this gasket may be my friend: Fel-Pro Intake Manifold Gaskets 1262R5 (2.25 x 1.4)

Now to Barnett's point...I will do the necessary geometry to see if this intake is "stock".  I also have trouble believing somebody would have machined the intake, but I suppose you never know.  The thing that still has me scratching my head was the fact that I could insert a feeler gauge along the edge of the intake and the head.  Maybe I was just getting lucky and poking it into the exact place where the port is, but I don't know.  It's now lost to history as I've removed the intake.

Last question: would it be useful to put some plastigauge (or some such crap) between the manifold and head and torque it down?  Will the resulting "gap" tell a story if these parts are going to ever live together?  

Thanks for sticking with me on this.  Nice going looking at the photo in detail, Mach.

 

Tom

[barnett468 418]

9 minutes ago, foothilltom said:

Now that I know that an intake manifold gasket has to match the head, I should be able to find what I need as far as port dimensions. 

No, it has to match the largest port. If the intake ports are larger than the head, it must match the intake port.

The  better gasket by far is the felpro steel core.

[barnett468 418]

Take the lifters out and look at the bottom. They should be perfectly smooth, if they are scored at all the cam is likely dead. Look at the cam as well. Put the same lifter back in the same hole it came out of.

 

[foothilltom 33]

12 minutes ago, barnett468 said:

No, it has to match the largest port. If the intake ports are larger than the head, it must match the intake port.

The  better gasket by far is the felpro steel core.

Roger that.  The ports on my head are larger than my intake, so I just made a bogus assumption that it's always that way.  Again, I learn something every time.