The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 12-17-2011, 06:30 PM   #1
shermro99
Registered User
 
Join Date: Nov 2010
Location: Salt Lake City, UT
Posts: 33
Question Sluggish at High Speed

1970 Chevy C-10 5.7L Gas 400 Trans.

Had the breaks inspected, bearings and alignment done. All is well. Gping 30-45 the truck runs well. Going about 65-70 it seems sluggish. I am not sure what could be causing it. New spark plugs and tune up done. Just seems as though it is trying to pull back when I am going that fast. Any ideas?


R
shermro99 is offline   Reply With Quote
Old 12-17-2011, 06:40 PM   #2
into69z
"brand new second-hand"
 
into69z's Avatar
 
Join Date: Feb 2007
Location: White House, Tennessee
Posts: 526
Re: Sluggish at High Speed

check the hose coming off "ported" manifold vacuum( on the carb) to the distributor for leaks and cracks. Also, check to see your vacuum advance is working on your distributor. If those are good, look for anymore vacuum leaks and then check your fuel filter,fuel pressure and float level on your carb.
__________________
Steve
69 3/4t custom camper
tilt,am/fm,speed warning,air gauge,buddy buckets,aux battery, big block,p/s,p/b,a/c
67 Camaro
96 Impala ss-sold
04 hybrid Honda-saving gas for the blue truck!:
b69:
into69z is offline   Reply With Quote
Old 12-17-2011, 06:45 PM   #3
72chevyk10
I built it
 
72chevyk10's Avatar
 
Join Date: Sep 2008
Location: Bakersfield ca
Posts: 744
Re: Sluggish at High Speed

did the truck recently start being sluggish? my truck is like a garage door on the freeway at all times haha
__________________
'72 k10 lwb 454, th400, 205, d44ft, 12b rear, 4in skyjacker, 35x12.5-15 superswampers, 4.56, blazer tank. painless wiring harness
'98 dodge 3500 12v 5sp 4x4. the truck that actually runs


Quote:
Originally Posted by prostreetC-10 View Post
I think the best and cheapest performance mod is to have someone that knows what the hell they are doing perform a tuneup on said vehicle.
72chevyk10 is offline   Reply With Quote
Old 12-17-2011, 07:04 PM   #4
ChevLoRay
Old Skool Club
 
ChevLoRay's Avatar
 
Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
Re: Sluggish at High Speed

Quote:
Originally Posted by 72chevyk10 View Post
did the truck recently start being sluggish? my truck is like a garage door on the freeway at all times haha
Aerodynamics are not the strong suit on these trucks. Add in a 3:73 rear gear and you are getting close to the limit of what may be doable. Still, it should run 70MPH without much effort.
__________________
Member Nr. 2770

'96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed.

'69 C-10 SWB; 350/TH400 - in limbo

The older I get, the better I was.
ChevLoRay is offline   Reply With Quote
Old 12-17-2011, 11:30 PM   #5
shermro99
Registered User
 
Join Date: Nov 2010
Location: Salt Lake City, UT
Posts: 33
Re: Sluggish at High Speed

It started about 2 months ago. Before that it used to run beautifully
Posted via Mobile Device
shermro99 is offline   Reply With Quote
Old 12-18-2011, 12:04 PM   #6
chopnchaneled
Registered User
 
chopnchaneled's Avatar
 
Join Date: Dec 2009
Location: Atlanta, Ga.
Posts: 1,050
Re: Sluggish at High Speed

Mine was doing that and it turned out to be trash in the gas and had the filter clogged.
__________________
I don't think we get smarter as we get older. We just run out of Stupid things to do.
chopnchaneled is offline   Reply With Quote
Old 12-18-2011, 12:06 PM   #7
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 13,731
Re: Sluggish at High Speed

Cam might be going flat. Pop off the valve covers and check the rockers.
geezer#99 is online now   Reply With Quote
Old 12-18-2011, 12:14 PM   #8
shermro99
Registered User
 
Join Date: Nov 2010
Location: Salt Lake City, UT
Posts: 33
Re: Sluggish at High Speed

I highly doubt it's the cam. It was installed brand new last year. It's a high performance can too.
Posted via Mobile Device
shermro99 is offline   Reply With Quote
Old 12-18-2011, 01:00 PM   #9
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 13,731
Re: Sluggish at High Speed

New springs too!!
geezer#99 is online now   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 05:13 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com