Symptoms of an Intake Leak?

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KnuckleDuster

KnuckleDuster

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Still fighting cooling issues, but everytime I set the idle and drive the car more than a few miles, the idle jumps up a couple hundred rpm's.
My theory is my intake is leaking slightly and when hot the metal is expanding to seal or reduce the leak. The vacuum guage needle is shaky and bounces 1-2hg also.
Looking for some experienced opinions before I pull the intake.
Thanks.
 
I think a small shake is ok if it's bouncing all over then you have an issue. Spray some carb and choke cleaner on the runners at the gasket and if it revs up you have got a leak in that spot.
 
Setting idle at 195° , but the engine is creeping up to 240°.
If the intake is pulling air, could the heat be coming from a lean condition?
Timing is 20° initial, 34° all in at 3000rpm.
 
If the idle jumps up that means something might be out of adjustment and the car is telling you it wants something different. Check your carb linkage/throttle return, make sure that works as it's supposed to. If it does not return all the way then you need to fix that first.

Like said above, check for an intake leak with carb cleaner. Spray around any suspected leak areas and listen for a change in rpm. If it goes higher, there's your leak.

Once you verify all the simple stuff, maybe take some initial timing out then re-set the carb to the new base line and see how it goes. Verify fuel pressure and float level before you start messing with the carb.

Could be a blown head gasket though, maybe just starting. 240 is too high. Notice any white smoke from the tail pipe? Might want to check your oil for milky color. When it's cool, take off the rad cap, start it up and check for bubbles in the coolant as it warms up. Have you noticed any coolant loss but no external leaks?

What kind of cooling fan do you have? Got a shroud?

Also could be a stuck valve. If the gauge is bouncing, that can indicate a valve issue. Might be a Guide, spring, rocker or the valve has carbon on it preventing it from sealing etc.
 
rmchrgr said:
If the idle jumps up that means something might be out of adjustment and the car is telling you it wants something different. Check your carb linkage/throttle return, make sure that works as it's supposed to. If it does not return all the way then you need to fix that first.

Like said above, check for an intake leak with carb cleaner. Spray around any suspected leak areas and listen for a change in rpm. If it goes higher, there's your leak.

Once you verify all the simple stuff, maybe take some initial timing out then re-set the carb to the new base line and see how it goes. Verify fuel pressure and float level before you start messing with the carb.

Could be a blown head gasket though, maybe just starting. 240 is too high. Notice any white smoke from the tail pipe? Might want to check your oil for milky color. When it's cool, take off the rad cap, start it up and check for bubbles in the coolant as it warms up. Have you noticed any coolant loss but no external leaks?

What kind of cooling fan do you have? Got a shroud?

Also could be a stuck valve. If the gauge is bouncing, that can indicate a valve issue. Might be a Guide, spring, rocker or the valve has carbon on it preventing it from sealing etc.
Click to expand...

Thanks.
TXDart and checked the radiator neck with an emissions sniffer whle the car was running, got zero readings. I think that ruled out a head gasket.
Tried three radiators, currently running a 26" 3 row brass I had rodded and checked. 7 blade OE vicious clutch fan with a factory shroud. Sealed the gaps between the radiator and shroud as well as hood to core support.
 
KnuckleDuster said:
Thanks.
TXDart and checked the radiator neck with an emissions sniffer whle the car was running, got zero readings. I think that ruled out a head gasket.
Tried three radiators, currently running a 26" 3 row brass I had rodded and checked. 7 blade OE vicious clutch fan with a factory shroud. Sealed the gaps between the radiator and shroud as well as hood to core support.
Click to expand...

Could be air pockets in there, might try and bleed the system?

Have a thermostat? What temp?

Do you have any under driven pulleys?

Could there be crud in the coolant passages?

Regardless of the cooling situation, I think you might want to take some timing out. Not sure how radical your combo is but 20 initial seems like a lot. As an example, I had a high strung 340/W2 with a .557" solid cam that idled at 1,100. Had 18 initial. If your timing was excessively advanced then you would be melting stuff.

It's worth a shot. It's easy to do and you can always put it back.
 
I second the initial timing you should be somewhere between 10-12 initial. 20 seems high will heat you up quick. My linkage was an issue to easy stuff to middle out before dropping any coin.
 
Torkmnstr said:
I second the initial timing you should be somewhere between 10-12 initial. 20 seems high will heat you up quick. My linkage was an issue to easy stuff to middle out before dropping any coin.
Click to expand...

10-12 is stock, I think he would need a little more, like 16-17.

Also forgot one thing, did you check your rad cap to see if it is good?

Another thing to do might be to try another one with a lower pressure. I forget the formula but for every X degrees of pressure, the boiling point of the coolant is raised like 15 degrees. Or something like that.
 
System has been professionally bled. 16# cap. Initial timing set at 1000rpm with vacuum guage, it actually wants more. Idle and vacuum increase up to 30°
Comp XE285HL cam and Holley 750 vacuum secondary carb. Robertshaw 185° stat with a Flowkooler water pump. Can see plenty of flow when the stat opens and the temp is real close. Bottom hose does NOT collapse at high rpm.

Timing is limited to 34° total with an FBO plate, how could that be too much for this engine at 2400-3000rpm on the highway? Under that rpm it stays about 200-210° on a 100° day.

I will redo the distributor and lower the initial. I have to think the heat is either timing or lean related.

I don't have money to throw at it for a couple weeks. I will probably reseal the intake and get an A/F guage and o2 sensor when I do so I can see what is really what. Might try a new fan clutch or go to electric fans and a 4 core if all else fails...

I was hoping someone else had this same issue to save me some trial and error.
 
KnuckleDuster said:
Initial timing set at 1000rpm with vacuum guage, it actually wants more. Idle and vacuum increase up to 30°
Comp XE285HL cam
Click to expand...

I guess you might be in the ballpark with your timing, that cam has a lot of duration. I don't know, maybe set it at 18 and see if there is a difference.

Running vacuum advance? You did set the timing with it plugged, right?
 
rmchrgr said:
I guess you might be in the ballpark with your timing, that cam has a lot of duration. I don't know, maybe set it at 18 and see if there is a difference.

Running vacuum advance? You did set the timing with it plugged, right?
Click to expand...


Haven't hooked up the VA yet, it is plugged on the can and carb.
 
So...regardless of the cooling issues, does it sound like the wandering idle might be caused by an intake or some other vacuum leak?
Has anyone had the same problem and fixed it?
 
KnuckleDuster said:
So...regardless of the cooling issues, does it sound like the wandering idle might be caused by an intake or some other vacuum leak?
Has anyone had the same problem and fixed it?
Click to expand...

Take off the air cleaner and put a rag or shop towel over the carb., see what happens to the idle speed. If it goes up, you have a leak somewhere. Reducing the amount of air coming in should offset the leak by making the A/F richer.

Have you tried to find a leak? Have you checked for exhaust leaks as well? Hear anything that might sound like an exhaust leak?

Have you removed any spark plugs? Maybe take 'em out and compare 'em. Obviously a light one is going to be the lean cylinder.

Though you did not mention any braking issues, I saw a pic in your cooling system thread that you have a brake booster. Those vacuum lines are notorious for leaking, so is the little valve on the booster itself. Maybe look those over for cracks.

After that, I'm out of ideas.
 
I had that stat once flowed real fast so fast it did not stay in the rad long enough to cool something to think about.I switch it out and my cooling wos went away.
 
BIG thanks to TXDart!
We smoke tested the crankcase with and without the carb and found the intake is sealed, but my Holley was leaking at the throttle shaft. Swapped on an Edelbrock 850 and the idle fluctuation went away.
We ran the car and it ran much better until we got back to the shop. We initially used a standard thin gasket, and with the guage still getting to 225°, heat sink boiled the fuel. The fuel was puddling on the butterflys, then spewed out the bowls. We cooled it down and tore down the carb. Martins carb had only been used for break in and had been sitting. We found trash in the bowls and determined the boilng stirred it up, preventing the passenger side needle from seating and/or sticking a float. We cleaned and blew everything out, checked the float travel and levels, and added a very thick fiber gasket.
Took it back out and drove it about 15mi roundtrip under varied conditions, back road cruising, highway speeds, and hard acceleration. It peaked out at 225° and throttle response was great. The motor seemed much more tame and streetable. Very smooth lopey idle, and a monster when I gave it as much as half pedal. I didn't go nuts due to darkness and unfamiliar roads but no trouble breaking the tires loose at 30-40mph, and from a stop it will spin the 275's until I let off.

Not perfect but a HUGE step forward.
Next steps will be Countour fans with a Dakota Digital controller and then maybe a Champion radiator. Also will be adding a Wideband A/F meter when funds allow.

Really appreciate all the help and advice. Without all the good people on this site would have never gotten this far.

I have to really give Martin a big thumbs up! I met him here and over the last year we have become great friends and he has selflessly spent his time and resources helping me out.
 
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