Author Topic: 350 olds, runs bad when warmed up  (Read 317 times)

28chevyguy

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350 olds, runs bad when warmed up
« on: March 08, 2019, 10:02:49 AM »
been chasing a gremlin,   whenever engine is at full temp starts bogging losing all its power... runs like junk.

runs like a raped ape cold and leading up to operating temp.

carb is brand new ,  clear fuel filter is always full Im certain its not a fuel issue any more (swapped the Rochester for edelbrock)

Main question:  What are the main possible culprits for running bad when warm ?

Spark plug wires would do that, not the plugs them selves i would think?

Engine compresion ,   maybe worn valve seals not doing their job when engine gets up to temp ?

I want to stray away from replacing things that arent subject to change with temperature.

points wouldnt do that ?  conderser wouldnt ??     My spark plug wires are few years old but none of them shock me...

It seems my only options are to change the spark plug wires and do a compression test with engine warm.

can anything think of anything else ?

chopper526

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Re: 350 olds, runs bad when warmed up
« Reply #1 on: March 08, 2019, 11:13:11 AM »
I don't want to start asking stupid questions but, how does it idle when it's hot?
Throw a vacuum gauge on there, see if it changes as the engine warms up, maybe you have a crack or intake leak that only shows itself as the engine warms and expands. Also, check fuel pressure when hot. I have seen an old porous pump lose pressure when it got hot.....I'm trying to think outside the box :-\
Tighten it up til it strips, then back it off a quarter turn

sammons

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Re: 350 olds, runs bad when warmed up
« Reply #2 on: March 08, 2019, 11:41:25 AM »
Was it running the same before the carb swap? If it was, I would check coil or coil wire. A weak one tends to fail when hot. Like Chopper said, check fuel pressure hot. Sometimes even one year old fuel line hose colapse when under load, or a rust pin hole in steel line near frame.

If new problem since carb swap, I would check for choke not fully open at temp or possible float level too low. That's all I got ;)

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #3 on: March 08, 2019, 01:18:57 PM »
Seems like it may have lost about 3 psi of vaccum when warm . 

changes the plugs and wires... same thing.

yes this problem existed before swapping the carb,  no change at all.

fuel pressure is good, fuel filter as totally full at all times ,  I don't think its fuel related.

New Coil , Plugs, Wires, Carb , just swapped the pcv valve .  Still same problem , runs like crap under load .

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #4 on: March 08, 2019, 01:31:44 PM »
So.... The longer it runs the worst it gets,  now it wont even rev in neutral without coughin spitting, literally no power I might be able to get her up to 30-40 tops....

im leaning toward internal motor problem.... sucks too Ive been driving this 71 olds for 4 years as a back up car with great luck.

all good things come to and end I guess .

I never bring my car to garages but i do know a master tech ... he's rediculous  , if he can't fix it or tell me whats up , noone can.


Rattiac

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Re: 350 olds, runs bad when warmed up
« Reply #5 on: March 08, 2019, 01:50:21 PM »
Check the motor ground.
My dad's camaro ran like that. The only ground it had was a small wire from the electric choke. When revved up it would hardly run. A big black negative cable fixed that.
Maybe look at a vapor lock situation, fuel line getting hot.
My 2 .
« Last Edit: March 08, 2019, 01:52:14 PM by Rattiac »

sammons

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Re: 350 olds, runs bad when warmed up
« Reply #6 on: March 08, 2019, 01:51:37 PM »
Running out of guess's :(  Double check points and gap, usually condenser either work or don't, but not always. Check timing, wonder if chain is lose or jumping? Pull dist cap and turn crank pulley back and forth  and see if dist bug is moving tight with it.

Rattiac may be on there with ground situation. My Ramcharger drove me crazy with the vapor lock type thing. No power, bog on hiway after 10mins. Went thru all above, bout went insain! It was a pin hole in fuel line causing it to suck air under load.
« Last Edit: March 08, 2019, 01:55:32 PM by sammons »

chopper526

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Re: 350 olds, runs bad when warmed up
« Reply #7 on: March 08, 2019, 02:25:20 PM »
Did you do a compression test on the warm engine?
Tighten it up til it strips, then back it off a quarter turn

EDNY

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Re: 350 olds, runs bad when warmed up
« Reply #8 on: March 08, 2019, 06:30:53 PM »
Spark plugs can tell a story of being too lean, too rich or water.

I would pull a couple spark plugs and look at them..black and wet could be water in the fuel.  Car sits and water settles at base of carb and/or tank (runs good),  then is agitated when fuel begins getting pushed around and mixes with the fuel.
33 Chevy 5 Window, 34 Chevy 3 Window, 37 Chevy 4dr sedan

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #9 on: March 09, 2019, 12:05:19 PM »
Great suggestions. 

I did compression test all warmed up ,  120 psi across the board

I ran it down to empty practically twice and filled up half way with 93 octane

All my spark plugs visually seem all even ,  nothing black or fouled.

SO..... every time I touch the top of the cap  ( Points distributor)   I get zapped.

This didn't seem to happen the other day but maybe it does this once warmed up..  The wires going to the coil seem soft and broken down.   Think I might be on to something.   Driving it around cold im still impressed how much power the engine makes... does burnouts through second gear not bad for an old dog .    Going to continue from here.  good news I don't think my engine is bad.

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #10 on: March 09, 2019, 12:41:54 PM »
new cap and rotor.    Waiting to warm it back up now .  Still got shocked if I touch the coil wire boot on the center of the cap .

the wires going to the coil are really broken down looking and feel very soft rubbery . like they're smoked.


chopper526

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Re: 350 olds, runs bad when warmed up
« Reply #11 on: March 09, 2019, 01:01:56 PM »
I don't think you should be getting a shock by touching the top of the distributor ::) I might try replacing those wires, if that's not possible check out Rock Auto, you will find new distributors relatively inexpensive, if you decide to give that a try.
Tighten it up til it strips, then back it off a quarter turn

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #12 on: March 09, 2019, 01:06:27 PM »
Thanks chopper .   yes , going to replace the + and -  wirings going to the external coil, try to cut them back as far as i can.

    I think im finally onto something here.


chopper526

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Re: 350 olds, runs bad when warmed up
« Reply #13 on: March 09, 2019, 02:10:13 PM »
Keep up posted and don't give up!
Tighten it up til it strips, then back it off a quarter turn

28chevyguy

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Re: 350 olds, runs bad when warmed up
« Reply #14 on: March 09, 2019, 05:15:39 PM »
replaced the negative wire from the points inside the dist.  to the - on the coil .   No change .   

I still get zapped touching the top of the coil so im stumped at the moment.

also , part of me wants to think its starving for fuel because the plugs look white , not wet .  Doesn't look like unburned fuel .


 


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