427 bogging down question?

[Bill S.]

i was going to test drive my 66 L72 today but found it bogs down under load. i have the timing set to 8 BTC and constant vacuum hooked up. i swapped the dist cap thinking we cracked it putting in the motor. i am begining to suspect the 3247 carb on it. it idles nice and revs smooth in the shop but as soon as you put it in gear and go to take off it has no power and bogs down. adding more advance helps it but does not solve it.i have a 650 double pumper to test it out but thought i would get ideas first, bill

[Mark #28455]

Re: 427 bogging down question?

Is 8 degrees with the vacuum advance disconnected?

Mark

[Bill S.]

Re: 427 bogging down question?

yes with line plugged off, i tried it with coventional vacuum line hooked up as well. this is a fresh L72 with cam break in and TI ignition valve lash has been set to specs after warm up (normalizing), bill

[mike valliant]

Re: 427 bogging down question?

Bill
If the ignition is advancing normally,may i suggest testing
fuel pump pressure and volume.Then fuel filter,float level
and finally accelerator pump operation as initial proceedures.
Mike

[Mark #28455]

Re: 427 bogging down question?

Are you flooring it from low RPM? Do you have a repro vacuum advance unit? What is the idle vacuum level? Do you have access to a vacuum pump (mityvac) to see at what vacuum levels the advance is starting and fully engaged?

If you bring the RPM up to about 3000 in 1st gear and then floor it, does it rev OK?

Mark

[Bill S.]

Re: found new issues

my starter started acting up, is a date coded original. while looking at it i found my new heat riser bound up and closed. until i get the starter working i cannot test further. when it rains it pours. how many cars can you remove the whole exhaust in 5 min? bill

[Bill S.]

Re: exhausting question

i suspect the frozen heat riser may be the issue but have not ruled out carb or a manifold leak. starter was the solonoid pin. snap ring was bad and it jambed. the irony is i would not have noticed the riser if i did not need to fix the starter. i guess every thing has a reason. is the donut on the lh side the same as right? it was toast. i have a solid metal one i can use.

[Joe L.]

Re: exhausting question

bill-----

"Donut" gasket is the same for either side. However, the heat riser side also uses a triangular shaped-gasket between the manifold and the heat riser (or, the spacer if you install that).

[Mark S. Lovejoy]

Re: exhausting question

Joe,

I didn't know a spacer was available for BBC exhaust. I'm not sure if I would install one, my concern would be the choke would not operate correctly.

[Bill S.]

Re: exhausting question

its not a spacer i have but a metal donut. are you supposed to lubricate the riser before installing? it was new.

[Clem Z.]

do NOT oil the heat riser valve as it will

cause it to stick. GM once sold a heat riser valve lube but i do not hink they sell it any more. powered graphite should work. i had a case one time with a corvette that would not rev up and i found the heat riser valve was installed upside down and would not open

[Terry F.]

Re: exhausting question

I believe lubrication would be a waist of time. It should move freely by hand. That is about it. Worked on many a car that had them and they were pretty far from being lubricated. You could wire it open and unwire it if you show the car. I could see where a new one could get stiff. Needs to open and close smoothly. No binding at all. Oil or grease will burn and leave a residue that may make it stick. Terry

[Gene M.]

Re: 427 bogging down question?

It may sound simple but fresh gas can make a world of difference. If it has old stuff like last year drain it before adding the new gas.

[Mike M.]

Heat Riser Lube

Clem, Gm did sell this as of 2 years ago I bought a can. I'm not sure if they still sell it. Part #992955 in a spray can now called GM Penetrating Fluid.
Mike

[Joe L.]

Re: Heat Riser Lube

Mike-----

That's a Canadian part number which is not available in the US. The US version of it is GM #1052627. This is the original part number which has been around for more than 30 years but I believe it has also been re-named as a "penetrating lubricant". That was actually a wise move since that's what it really is and what it's been used for a lot more than a "heat valve lubricant". It may not be sold by dealers in some states, though, due to state-specific emissions regulations.