truck runs bad - The 1947 - Present Chevrolet & GMC Truck Message Board Network

my70chevyc10 · 05-14-2010, 02:10 PM

I have a 70 swb with a 350 in it an it runs good untill the engine gets up to temp then it seems like it is low on power. Throttle responce is good before it gets to temp an wants its up to temp it just has no getup an go. Its got new plugs. MSD cap rotor and coil and MSD wires with a MSD street fire dist.Any help would be good

Thanks JOHN

71meangreenc10 · 05-14-2010, 02:13 PM

Possible headgasket leak?

Are you having to add coolant? Do you get white smoke from the tailpipe when it gets hot?

Smitty

68gmsee · 05-14-2010, 06:44 PM

Several things can cause the problem. Here's some things to check.

1. Fuel pump. It may work okay at first but may not be able to keep up with the fuel demand of the carb.

2. Check the choke to see if it runs better with it closed. Might be a vacuum leak somewhere that's causing it to lean up when the choke opens.

3. As mentioned, head gasket problems.

4. Worn cam.

5. Timing and/or vacuum advance mechanism. Make sure the vacuum advance is working properly.

BADPURPLE70CHEVY · 05-14-2010, 09:35 PM

Quote:

Originally Posted by 68gmsee

Several things can cause the problem. Here's some things to check.

1. Fuel pump. It may work okay at first but may not be able to keep up with the fuel demand of the carb.

2. Check the choke to see if it runs better with it closed. Might be a vacuum leak somewhere that's causing it to lean up when the choke opens.

3. As mentioned, head gasket problems.

4. Worn cam.

5. Timing and/or vacuum advance mechanism. Make sure the vacuum advance is working properly.

Sounds like timing...

martindc1 · 05-14-2010, 09:41 PM

I was thinking that either the choke is staying closed or maybe a vacuum leak or possibly the metering rods are staying seated under a load and its too lean.

BOOB · 05-17-2010, 09:38 AM

It's going to be fuel or timing.

You distributor should be pretty adjustable as far as curves and total timing go but most street SBCs like an initial around 8-10 deg. and around 30 deg total. Initial isn't as important as total. If you drive it hard, you basically slowly advance it in small steps until it pings and back it off a few degrees (generally). For street motors I use engine temp as an indicator as well. My 55 runs at 190 all day with 30 degrees total and no pinging. I know I could probably advance it a couple of degrees but I would most likely increase engine temp as well. Check your vacume advance if you have one as well as mechanical. Throw a timing light on it and suck on the vacume and see if it affects the timing. With mechanical you simply rev the motor a bit and see how it acts.

Cold motors love a rich mixture. Make sure you dont have a sticking choke, otherwise you may need to clean up the carb or tune it a bit.

Tynee · 05-17-2010, 12:10 PM

Have you made any changes recently, or you're just noticing that it has gradually become a problem?

05-14-2010, 02:10 PM	#1
my70chevyc10 Registered User Join Date: Jul 2007 Location: Covina Calif Posts: 172	truck runs bad I have a 70 swb with a 350 in it an it runs good untill the engine gets up to temp then it seems like it is low on power. Throttle responce is good before it gets to temp an wants its up to temp it just has no getup an go. Its got new plugs. MSD cap rotor and coil and MSD wires with a MSD street fire dist.Any help would be good Thanks JOHN __________________ "Your trucks fast! You must have been going 120 when I passed you." "Owning A 10 Sec Import Is Like Coming Out Of The Closet, In The End Ur Still Gay" If for some reason i loose to a import...At least i can go home knowing the vehicle i drive drops girls panties...

05-14-2010, 02:13 PM	#2
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,159	Re: truck runs bad Possible headgasket leak? Are you having to add coolant? Do you get white smoke from the tailpipe when it gets hot? Smitty __________________ 71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 71 C20 Longhorn/Ole Yellor 69 C30 Former Motor Home, Flat Bed time Last edited by 71meangreenc10; 05-14-2010 at 02:13 PM.

05-14-2010, 06:44 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: truck runs bad Several things can cause the problem. Here's some things to check. 1. Fuel pump. It may work okay at first but may not be able to keep up with the fuel demand of the carb. 2. Check the choke to see if it runs better with it closed. Might be a vacuum leak somewhere that's causing it to lean up when the choke opens. 3. As mentioned, head gasket problems. 4. Worn cam. 5. Timing and/or vacuum advance mechanism. Make sure the vacuum advance is working properly.

05-14-2010, 09:41 PM	#5
martindc1 Registered User Join Date: Jul 2009 Location: La Crosse, WI Posts: 218	Re: truck runs bad I was thinking that either the choke is staying closed or maybe a vacuum leak or possibly the metering rods are staying seated under a load and its too lean. __________________ Currently truckless, previous trucks: 67 K20, 87 K10 aka V10 & 72 C10

05-17-2010, 09:38 AM	#6
BOOB Registered User Join Date: Oct 2008 Location: Taylor, TX Posts: 95	Re: truck runs bad It's going to be fuel or timing. You distributor should be pretty adjustable as far as curves and total timing go but most street SBCs like an initial around 8-10 deg. and around 30 deg total. Initial isn't as important as total. If you drive it hard, you basically slowly advance it in small steps until it pings and back it off a few degrees (generally). For street motors I use engine temp as an indicator as well. My 55 runs at 190 all day with 30 degrees total and no pinging. I know I could probably advance it a couple of degrees but I would most likely increase engine temp as well. Check your vacume advance if you have one as well as mechanical. Throw a timing light on it and suck on the vacume and see if it affects the timing. With mechanical you simply rev the motor a bit and see how it acts. Cold motors love a rich mixture. Make sure you dont have a sticking choke, otherwise you may need to clean up the carb or tune it a bit. __________________ 1970 Short/Fleet C-10 (Project) -Slammed and Tubbed 1955 Cameo -Straight six, Turbo Hydro option 1955 BelAir 2 door post -All original down to the oil bath air cleaner 1964 Corvette -All power A/C 327 4 spd. tanker

05-17-2010, 12:10 PM	#7
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Re: truck runs bad Have you made any changes recently, or you're just noticing that it has gradually become a problem? __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.



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