Need some help - vapor lock/fuel starvation issues

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ghsnu

ghsnu

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spedy7
I have a 1966 Mustang that my dad and I just finished swapping the motor in (now has a proper 289). We‘ve been having major issues with fuel delivery though - as soon as it starts to warm up, it seems as if the fuel just starts boiling off in the line - there's little to no fuel in the filter. We have a 570 cfm Holly Street Avenger carb and a little hotter cam along with a dual exhaust system, if that changes anything. I also live in Arizona near the border so its hot as 🤬 out here too.

We bought a new pump in hopes that that would be it (turns out our first pump was also the incorrect pump too). That didn't fix it so we put a 1" spacer on - still didn't fix it. Put a Holly fuel pump on thinking it'll help pull more fuel - nope. Discovered that our timing was too advanced and adjusted that - we thought that fixed it, but it didn't.

I don't know what to do know other than install a low prressure electric pump to pressurize the lines in hopes to keep the temperature from burning off the fuel. I don't know if the float is set yet ether, I'll check on that. We also have a cooler thermostat that we haven't installed yet (holding off in hopes of a better solution).

I've heard various solutions, the best being installing an electric pump and running a return line with a regulator. I've also heard installing a hood scoop to keep engine bay temperatures down (which is costly as I'd rather buy the '68 Shelby hood instead of some tacky scoop).
 
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The engine shouldn't be that hot that it boils off the fuel. I did install a Holley electric fuel pump with a pressure regulator and haven't had any issues on my 351W, no return line though. Do you have a heat shield under the carb?

Installing a hood scoop won't do much to keep the temp down. Might help a little bit but not much. Especially in Arizona.
 
Slashfan
The engine shouldn't be that hot that it boils off the fuel. I did install a Holley electric fuel pump with a pressure regulator and haven't had any issues on my 351W, no return line though. Do you have a heat shield under the carb?

Installing a hood scoop won't do much to keep the temp down. Might help a little bit but not much. Especially in Arizona.
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We just have a spacer, no heat shielding. We're planning on installing 3/8 lines and rerouting them away from any heat. There's a couple places where the lines are quite close to the exhaust: right after the tank the exhaust is about an inch or two away from the line and the muffler is a couple inches away as well.

If this doesn't work, we'll probably invest in an electric fuel pump.
 
Interesting. I ran my line right over the driver side valve over through and accelerator pump and an electric pump (pressure regulator as well) in the middle of the frame. Never had an issue.

Regardless of muffler location it should not be boiling off fuel. Has the engine overheated before? Do you have any insulator gaskets installed? Could be your carb is not tuned properly. I've heard of improperly tuned carbs boiling fuel off and then condensing and the engine acts as if it's flooded when you go to crank it over.

Is it boiling out of the carb or in the line away from the carb? If you can try relocating the line to somewhere else (run it along the firewall, down and out if you need to) and see if it helps.
 
Are you certain you are boiling the fuel in the lines and not simply running out of fuel? Check your floats and adjust as necessary.
 
Not sure if we adjusted the floats yet (last I remember we needed to), but the lines should be ok - although when I had the 200CI straight 6 in the fuel filter clogged up with a piece of dirt. We took the line off at the tank it just pours out though.

Letting it sit for a bit with a bag of ice on the pump results in fuel slowly trickling back into the filter.

Its been running hot, but that shouldn't be the issue. There's still gas in the carburetor when it vapor locks. It could be burning off at the pump due to the heat...
 
It shouldn't be running over 180*-195* even at WOT. What thermostat does it have on it? IIRC ford supplied 192* thermostats stock.

Also check the timing. If the timing is off that could be why its running how and why the fuel is boiling off.
 
I doubt you're burning up fuel at the pump. On the cooling note, there are standard and reverse rotation SBF water pumps. Mechanical or electric fan? Do you know what your actual water temp is?

Are you positive your pump actually pumps enough fuel? Do you not have a fuel pressure gauge on your carb inlet line? Are you using a Carter, Holley, BG pump? Any weird rattle noise behind the timing cover? I've seen a lot of the two piece fuel pump eccentrics break, I only use the Ford Racing one piece unit. Hardened fuel pump push rod? Check the pump push rod for wear on the eccentric side.

Overly advanced timing can cause pre-ignition and increased engine heat as well...
 
It should be the stock thermostat. I have a lower temp thermostat, but haven't installed it yet. We did install an aftermarket breakerless distributor (can't think of what it is, I'm away on vacation right now) and just retarded the timing a bit as it was too advanced. This could be the problem as we've been having a few timing issues with it.

It should be the stock (mechanical) water pump as well. Had to buy a new one though. I don't have an aftermerket water temp gauge, just the flimsy stock one. We put in a Holly fuel pump thinking it would help - and it seemed to at first - but resorted back to fuel starvation and eventually vapor locking later as it warmed up. Should be the stock ecentric though. We had the wrong fuel pump at first (due to the parts guy - got one for a 351W instead of the 289), but I don't think that caused much harm.

I think installing different springs in the distributer to get the timing right may help, but it's a completely rebuilt motor bored .060 over with new pistons, Edlebrock intake, Holly 570 cfm carb, Comp cam with a milder profile, and heads from I think a '68 - can't remember. Still far from broken in, but I was told it would run hot until it's fully broken in.
 
.060 over is a little too much for a 289. That has been known to cause overheating and cooling problems in itself. .030 over is generally considered to be the safe limit for any thin-wall cast Windsor from Ford. .060 over is still pushing it for the beefier 351W blocks though.
 
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I've seen & machined plenty of 289/302's to .060" over provided they'll still sonic test over .140" wall thickness at that over bore. Not a concern at max over bore if checked and machined correctly. Having a boring bar doesn't mean just anyone can bore on center on every cylinder. Respect to the old schoolers with boring bars who nail it dead on, cause we use Rottler F65A CNC's... :)

You have 68 heads with the slotted push rod holes like the HiPo heads? Perhaps your running warm issue is a mismatch of heads/block/head gaskets. Maybe someone forgot to drill some steam holes or perhaps your head gaskets don't have provisions and you need them...? Block and cylinder head casting numbers might shed some light in what you really have.

What I meant with the water pump is the the pump fins would not effectively push water if it's spinning the wrong direction. Standard (clockwise, typical v-belt pulley setup) rotation or Reverse (counter-clockwise, some serpentine pulley setups) rotation. So you'd will have a water pump running at less than 50% capacity if it was the incorrect water pump.

If your motor is the physical cause of heating up enough to vapor lock, your spark plugs must have heat showing way up on the threads! How do your spark plugs look?

If not try insulating the tank feed and carb feed near hot areas with Thermo-Tec sleeves or something similar. Re-curving the dizzy could help to. Keep us in the loop...
 
MaliciousMD
I've seen & machined plenty of 289/302's to .060" over provided they'll still sonic test over .140" wall thickness at that over bore. Not a concern at max over bore if checked and machined correctly. Having a boring bar doesn't mean just anyone can bore on center on every cylinder. Respect to the old schoolers with boring bars who nail it dead on, cause we use Rottler F65A CNC's... :)
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I believe it can be done safely but I've seen far too many go because of that. Personally I wouldn't go over .045 on any Windsor block. I considered taking my old 351W out to .060 (already .030) but the cylinders have so much taper that a .060 over bore wouldn't even come close to fixing it. Lots of hard, hard miles on that block.

I didn't even think of mismatched heads...would be a good idea to get the casting numbers so +1 on that.
 
Sorry for the late reply, haven't been able to get on in the past few days.

Don't know the year, but they're 302 heads. The other pair we have are 289, but one's a 65 and the other a 64 (also has a crack near where the valve cover sits, but appears to be somewhat welded over).

We just installed a new 3/8 fuel line and moved it away from the exhaust, but it's still locking up (temp rises pretty damn high when idling for ~30secs or more). The fuel filter is before the pump, and it appears ether not enough fuel is getting to the pump or its boiling off before it gets there - nothing is in the filter, although increasing the throttle leads to some fuel going though, but it never fills up unless it sits.

I'm guessing partially clogged sender/tank, but hoping that's not the case. My dad said get premium fuel when filling it up next time, but I doubt that'll fix it.
 
ghsnu
Sorry for the late reply, haven't been able to get on in the past few days.

Don't know the year, but they're 302 heads. The other pair we have are 289, but one's a 65 and the other a 64 (also has a crack near where the valve cover sits, but appears to be somewhat welded over).

We just installed a new 3/8 fuel line and moved it away from the exhaust, but it's still locking up (temp rises pretty damn high when idling for ~30secs or more). The fuel filter is before the pump, and it appears ether not enough fuel is getting to the pump or its boiling off before it gets there - nothing is in the filter, although increasing the throttle leads to some fuel going though, but it never fills up unless it sits.

I'm guessing partially clogged sender/tank, but hoping that's not the case. My dad said get premium fuel when filling it up next time, but I doubt that'll fix it.
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I'd take it easy on premium fuel unless you know what your compression ratio is. Don't run premium unless you have 10:1 or more compression otherwise you'll run into detonation problems.
 
Slashfan
I'd take it easy on premium fuel unless you know what your compression ratio is. Don't run premium unless you have 10:1 or more compression otherwise you'll run into detonation problems.
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Premium fuel has more knock-preventative octane than regular fuel. You won't get detonation as the fuel has less energy content due to the octane. Premium fuel will probably net you a little less power, but definitely not detonation. Please read this Slashfan and don't post misinformation:

http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/question90.htm

Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
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Eunos_Cosmo
Premium fuel has more knock-preventative octane than regular fuel. You won't get detonation as the fuel has less energy content due to the octane. Premium fuel will probably net you a little less power, but definitely not detonation. Please read this Slashfan and don't post misinformation:

http://auto.howstuffworks.com/fuel-efficiency/fuel-consumption/question90.htm
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I think I'll still try premium fuel, but I'm gonna pull the tank out today. I shook the car and I think I can hear some crud moving around in there. Maybe get a new filter and/or sender as well.

As far as I know - if the heads are 302 heads (we didn't have the cobustion camber size checked) - the compression should be back to stock specs.
 
ghsnu
I think I'll still try premium fuel, but I'm gonna pull the tank out today. I shook the car and I think I can hear some crud moving around in there. Maybe get a new filter and/or sender as well.

As far as I know - if the heads are 302 heads (we didn't have the cobustion camber size checked) - the compression should be back to stock specs.
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Depends on the year 302 heads. There were so many changes it isn't funny. Your compression (depending on the pistons) can range from 8:1 all the way to 10.5:1.

Though, the higher compression heads are hard to get a hold of, so I'd venture to say you are anywhere in the 8:1-9.6:1 range. If they are 1968 heads then (again depending on pistons and head gasket thickness) they are either early or late heads. All that means is that mid year there was a head change and compression dropped 5 points from 9.5:1 to 9:1.

That said, compression dropped considerably by 1970ish, and through the mid 70s all heads period were low compression. 302 and 351W heads were exactly the same (excluding head bolt diameter) from 1975-1985 when the introduction of both H.O. motors came around.

Also if they are 302 heads, they won't be back to stock specs. They might be close depending on the year of the heads though. Compression on early 289s was pretty high. The highest was the K code engines, being 11.6:1. That's a big difference. I doubt you'll have anywhere near that. You should be around 9:1 though, from what you are saying. Most heads were around there.
 
ghsnu
I think I'll still try premium fuel, but I'm gonna pull the tank out today. I shook the car and I think I can hear some crud moving around in there. Maybe get a new filter and/or sender as well.

As far as I know - if the heads are 302 heads (we didn't have the cobustion camber size checked) - the compression should be back to stock specs.
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Not uncommon to have the gas tank be rusted up or gummed up from old gas. I had to pull the tank from my RX7 and get it boiled/sealed.

Really should have had the heads checked. It's quite easy to do at home with a small square piece of lexan and a pippette dropper hole drilled in it. Not uncommon to have heads of the same casting number, but the chamber sizes be different (from unshrouding the chamber, surfacing, angle milling, valve jobs/changes, etc). But it would've given you an opportunity (heads off) to get some crucial figures to determine your actual compression.

Piston dish/valve relief/dome effects compression, but will not give you the piston crown orientation to the deck. This figure is critical. Same for head gasket bore/thickness. Optimal quench can only be had with the crown @ zero deck and using your head gaskets thickness (.039-.045" is pretty common) as your quench area. Added with an actual combustion chamber cc, you'll have info needed to make adjustments/upgrades without being detrimental to the driveability.

Just a suggestion. :) Having cool cars you can't drive or fiddle F'n with is no fun... 👎
 
^^^Which is exactly why I would have (had I built the engine) bought brand new aluminum heads instead of screwing with, lets be honest, rather 🤬 factory heads. Nice performance increase as well. With as much aftermarket as there is for Windsor engines, heads are pretty cheap. Don't get me wrong, they are still expensive, but most are only a few hundred for a set. Some go well into the $1,000 range but that is talking high end, race spec motor. A nice Edelbrock top kit isn't too expensive and the gains in horsepower/torque are well worth it. Depending on the build you can can actually improve gas mileage as well, which is always a plus.
 
Slashfan
^^^Which is exactly why I would have (had I built the engine) bought brand new aluminum heads instead of screwing with, lets be honest, rather 🤬 factory heads. Nice performance increase as well. With as much aftermarket as there is for Windsor engines, heads are pretty cheap. Don't get me wrong, they are still expensive, but most are only a few hundred for a set. Some go well into the $1,000 range but that is talking high end, race spec motor. A nice Edelbrock top kit isn't too expensive and the gains in horsepower/torque are well worth it. Depending on the build you can can actually improve gas mileage as well, which is always a plus.
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I would've bought a pair of new, good heads, but money is an issue. After I get myself situated in the military and get a decent flow of money, I'm planning on going through it and replacing parts as necessary.

Anyways, no luck. Gas is clear as water and I could barely feel any sediment in the tank. I just moved the fuel filter to the push side of the pump and covered the lines around the carb with heat shielding - even put on a cheaper plastic filter in hopes our faux glass filter was a problem - but it still seems to be struggling to get fuel.

I don't know if the Holley pump may be demanding too much fuel? If the carb could be demanding too much fuel? It's just odd trying just about every possible remedy, but nothing seems to be working.

The only thing I could think would be the cause of it is the pump heating up too much and losing effectiveness. But its a rebuilt engine...unless a bigger radiator/cooler thermostat would fix it.
 
ghsnu
I would've bought a pair of new, good heads, but money is an issue. After I get myself situated in the military and get a decent flow of money, I'm planning on going through it and replacing parts as necessary.

Anyways, no luck. Gas is clear as water and I could barely feel any sediment in the tank. I just moved the fuel filter to the push side of the pump and covered the lines around the carb with heat shielding - even put on a cheaper plastic filter in hopes our faux glass filter was a problem - but it still seems to be struggling to get fuel.

I don't know if the Holley pump may be demanding too much fuel? If the carb could be demanding too much fuel? It's just odd trying just about every possible remedy, but nothing seems to be working.

The only thing I could think would be the cause of it is the pump heating up too much and losing effectiveness. But its a rebuilt engine...unless a bigger radiator/cooler thermostat would fix it.
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Small glass and plastic inline fuel filters should always be post fuel pump and pre-carb. Can you give us the part number for the Holley fuel pump and carb that you have? Holley 570cfm you more than likely don't have adjustable air bleeds and more than likely a rather low cc accelerator pump.

Honestly, this is the big problem with mystery motors where there is little to no information about combination. You have yet to attach a wideband air/fuel meter to the engine. You have yet to verify any actual engine running temperatures. You have yet to acknowledge the condition of your spark plugs. Thermostat opening temp? Mechanical or electric fan? If mechanical is it clutch type? Solutions don't grow on tree's, and the ones that do usually cost $100 per/hr minimum and an over night stay at a shop for them to investigate all the things I've just asked you several times.

I'd rather help than see you spend the $100 per/hr plus parts somewhere. If you can't trouble shoot it with a rebuilt engine, it will be hard down the line when it gets some miles under it belt and needs up-keep or improvements.
 

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