1970 Cadillac 472, block off exhaust ports under carb on intake manifold

[Scot Minesinger]

Had to remove my intake manifold to resolve a "tic tic" sound, which will expound upon later after all work is done (head had to come off for valve stem repair/replacement).  Read the post on the 346, and maybe I should block of exhaust ports now.  The car is difficult to start (excessive cranking) when it is much over 70'F and it sits for 15 minutes to about two hours due to gas boil off.  The only detriment anticipated is that it will take longer for choke to warm up. 

Also read that it did not do much good.  I'm not into welding.  I was just going to use tin snips and cut up the old valley pan gasket to make a blockage, which would probably be 95% - sound OK?

The excessive cranking is annoying primarily and a little embarrassing.

[joeceretti]

I guess the key is keeping the fuel entering the carburetor cool enough to not instantly vaporize before flowing into the cylinder. I have zero knowledge of the 472 engines. I hope you can solve it.

[curly]

I have blocked the crossover passages on other (no Cad) engines before with mixed results.  Living in the AZ desert, I didn't notice problems in the warmer months, but in the cooler months the engines had flat spots on acceleration until the engine was fully warm. Cold starts were fine, but once the choke opened, the engines would stumble/stall any time the throttle was opened.  It was worse coming off of idle.  I wound up reopening the passage.
T Lewis

[76eldo]

Scott,

You should not have to do that on your car.  There is another problem, either fuel pump or carb related.  My 70 starts hot with a click of the key.

Brian

[Jon S]

Scott,

You should not have to do that on your car.  There is another problem, either fuel pump or carb related.  My 70 starts hot with a click of the key.

Brian

Agree - The problem with hot starts (especially in the hot summer months) is Ethanol.  The carburetor pre-heater is not causing the vapor lock problem . . . it is somewhere along your fuel line before or after the fuel pump.

[Scot Minesinger]

I will not do it then, after all my other 1970 starts perfect when hot.  Especially if there is a risk and it would be a pain to undo, will not do it-Thanks!

[The Tassie Devil(le)]

I blocked off the crossover port, and have never had a problem with it.   I like cold fuel going into the engine.   The cooler the mixture, the more power.

Created my own portable milling head and carefully milled the groove using a Battery Drill as power, and inserted a piece of cut tin into the hole.   Can be removed at any time if required (weather getting sufficiently cold enough, but that isn't going to happen down here)

Bruce.

[Scot Minesinger]

Bruce,

Did you notice an improvement in starting during hot weather after car was warmed up and was off for a half hour?  To improve starts under this condition, which is most common, would be worthwhile.

[Jeff Rosansky CLC #28373]

Well Scott, I seem to always be responding to your posts.
I also have a tic tic sound that I am trying to resolve and have been thinking about and intake issue.  Please keep us posted.  What made you think of the intake?
Jeff

[Scot Minesinger]

Jeff,

The tic tic sound I posted about last summer was cylinder # 7 where the rocker arm wore a hole thru it at the valve stem, ground down the valve stem that rides on rocker and the rocker compressed the spring directly on intake.  Car ran fine except for that noise.  Thought it was lifters on passenger side and when started replacing all 16 it was going well and they did not seem bad at all.  Then I got to cylinder # 7 and the problem was evident.  Not expensive to fix, a $75 valve and a $75 machine shop charge, plus head gasket, so under $200.  Should have noticed this when I took off valve cover, but seemed like it was either # 3 or #5 cylinder.  The head is back on and I'm just about to re-install intake manifold.

Back to the exhaust port at intake, I blocked it off by pressing in a folded five sided piece of sheet metal, which blocks off about 95% on each side.  Then I pressed the same type of sheet metal pieces into the head as well, so it is double blocked.  There is not undue force that may beak these pieces free is there?  The exhaust valve only opens during exhaust stroke so nothing would force the sheet metal to the valves as pressure is pushing away from valves.  The pieces could only be removed with a screw driver prying and a hammer.  Don't have the milling ability.

Thanks,

Scot

[Scot Minesinger]

here is the rocker arm

[The Tassie Devil(le)]

Did you notice an improvement in starting during hot weather after car was warmed up and was off for a half hour?  To improve starts under this condition, which is most common, would be worthwhile.

Hot weather?   We don't get it very hot down here, but then also not very cold.

All I know is that I don't have any problem starting it, so long as I remember it is carburetted and not fuel injection.   Call it lazy, but I always forget to give it a pump or two.

Bruce.

[TJ Hopland]

The 'band aid' fix for my hot start issues was an electric fan in front of the radiator hooked up to a mechanical timer switch.   I would just give it about 5-10 mins anytime I shut it off hot.   Never seemed to hurt the battery and never had issues with hot start.   Worked great for over 10 years.  Only got rid of it because I put EFI on that also solved the issue.