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Jul 21st, 2025 | | | | Joined: Mar 2015 Posts: 57 'Bolter | | 'Bolter Joined: Mar 2015 Posts: 57 | i have a 250 6cy in my 51 3100 there use to be a vacum pod that operaded a internal heat riser , by the lever on the out side of the exhust manifold any idea how to tell if its open or closed | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Doesn't matter- - - - -all that head is good for is an anchor for a medium-sized boat! The way it's supposed to work is the flap valve will be in the "hot" position pulling against a spring when vacuum is applied, and a thermal valve cuts the vacuum off when the thermostat opens and vents the line when the engine reaches operating temperature. The default position is "cold" to prevent detonation if there's a vacuum loss for some reason. That vacuum valve will not function properly without at least a 195 degree thermostat. The whole mess was a Rube Goldberg method of trying to meet EPA exhaust emission standards during warm-up. Installing an earlier cylinder head/manifold assembly with a regular thermostatic coil heat riser would be a much better option.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Mar 2015 Posts: 57 'Bolter | | 'Bolter Joined: Mar 2015 Posts: 57 | thanks just trying to have it open there is no vacum pod spring or anything other than the lever that controls it | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Shine a light up into the open end of the manifold where the exhaust pipe bolts on and watch the valve move. Then block the linkage in whatever position gives the best gas flow. It's been a lot of years since I worked on one of those emission-control engines, so I don't remember which way to move the lever for "open".
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Sep 2011 Posts: 1,363 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,363 | Doesn't matter- - - - -all that head is good for is an anchor for a medium-sized boat! The way it's supposed to work is the flap valve will be in the "hot" position pulling against a spring when vacuum is applied, and a thermal valve cuts the vacuum off when the thermostat opens and vents the line when the engine reaches operating temperature. The default position is "cold" to prevent detonation if there's a vacuum loss for some reason. That vacuum valve will not function properly without at least a 195 degree thermostat. The whole mess was a Rube Goldberg method of trying to meet EPA exhaust emission standards during warm-up. Installing an earlier cylinder head/manifold assembly with a regular thermostatic coil heat riser would be a much better option.
Jerry X2 integral head / manifold 250 tend to like to crack, & the Vari-jet carb is a pain (IMHO),
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | The vara-jet secondary metering rod has a nasty habit of wearing out the ball joint where it attaches to the air valve and falling into the intake. It usually gets imbedded in a piston crown and makes some interesting knocking noises as it batters the cylinder head.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Mar 2015 Posts: 57 'Bolter | | 'Bolter Joined: Mar 2015 Posts: 57 | well im guessing its time to look for another head along with intake and exhust manifold thanks for the heads up | | | | | Joined: Mar 2015 Posts: 57 'Bolter | | 'Bolter Joined: Mar 2015 Posts: 57 | well im guessing its time to look for another head along with intake and exhust manifold thanks for the heads up | | | | | Joined: Mar 2015 Posts: 57 'Bolter | | 'Bolter Joined: Mar 2015 Posts: 57 | i just had a new exhaust system put on the truck while it was on the houst i looked couldnt see it as it only afex the number 1 and 2 cyl the reason im asking when i run the truck about 55 or 60 for a while it starts acting like its loading up and i was thinking that flapper was closing and causign the problem... i guess ill have to split the exhust so i can get to it thanks for all the great info on this motor | | |
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