loose power on high end - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dmigura · 05-06-2006, 05:54 PM

This may not be the right forum to post this question, but this is where i always go. I have a 1970 4x4 with 71,000 miles original motor. I have had about a year and it looses power at about 65mph especially when I am going into the wind. the motor also starts to clatter a little. I replaced fuel filter, checked timing, and run medium otcane fuel and still the problem exist. Any ideas on what it might be.

1969K10 · 05-08-2006, 10:55 AM

Have you looked into your vacuum advance for your timing? Is it hooked up? If so, pull some vacuum on it to make sure it's holding vacuum... Just grasping at straws here...

Paul M · 05-08-2006, 07:04 PM

yea..hook a timing light up..and rev it a bit in and you should see the timing advance to like almost 40....if not,check vacuum diaphram and also check weights in the dist itself. if those are working,id do a compression check of all cylinders...and lastly, with truck off,make sure carb is opening fully,by taking air cleaner off and looking down into carb.butterfly has to be straight up and down,then check the linkage to be sure its opening correctly...ok shot my wad..hope you fix it

wibilly · 06-06-2006, 11:05 AM

it may also be a worn cam i had a 64 seemed to run great till i got in high gear then no power pulled valve covers and found valvs to be oppening very little

OLDCHEV4X4 · 06-06-2006, 12:13 PM

or weak valve springs too.

**special-K** · 06-07-2006, 06:12 AM

What size tires and what gears.There`s more to it,but this info would help get a baseline on the truck.In other words,could make your problem more pronounced.

dmigura · 06-07-2006, 01:17 PM

I am running 33s with stock gears not sure what they are it is a 70 half ton with a 4spd. I put a quadrajet from a 1980 ranch truck that I have just to see if that maid a difference, and it seems to be running better. I think something might of been wrong w/ the old carb.

220mph · 06-28-2006, 01:02 PM

I had the same problem. It wound up being the distributor shaft bushing was worn so the timing was going out under load.

05-06-2006, 05:54 PM	#1
dmigura Registered User Join Date: Jul 2005 Location: South Texas Posts: 17	loose power on high end This may not be the right forum to post this question, but this is where i always go. I have a 1970 4x4 with 71,000 miles original motor. I have had about a year and it looses power at about 65mph especially when I am going into the wind. the motor also starts to clatter a little. I replaced fuel filter, checked timing, and run medium otcane fuel and still the problem exist. Any ideas on what it might be.

05-08-2006, 10:55 AM	#2
1969K10 Senior Member Join Date: Jul 2004 Location: Clarks Hill, Indiana Posts: 733	Re: loose power on high end Have you looked into your vacuum advance for your timing? Is it hooked up? If so, pull some vacuum on it to make sure it's holding vacuum... Just grasping at straws here...

05-08-2006, 07:04 PM	#3
Paul M Junior Member Join Date: Jun 2000 Location: Oakridge, Oregon Posts: 138	Re: loose power on high end yea..hook a timing light up..and rev it a bit in and you should see the timing advance to like almost 40....if not,check vacuum diaphram and also check weights in the dist itself. if those are working,id do a compression check of all cylinders...and lastly, with truck off,make sure carb is opening fully,by taking air cleaner off and looking down into carb.butterfly has to be straight up and down,then check the linkage to be sure its opening correctly...ok shot my wad..hope you fix it

06-06-2006, 11:05 AM	#4
wibilly Senior Member Join Date: Nov 2005 Location: northwestern wi Posts: 2,111	Re: loose power on high end it may also be a worn cam i had a 64 seemed to run great till i got in high gear then no power pulled valve covers and found valvs to be oppening very little __________________ common sense isn't so common anymore

06-06-2006, 12:13 PM	#5
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: loose power on high end or weak valve springs too. __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

06-07-2006, 06:12 AM	#6
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: loose power on high end What size tires and what gears.There`s more to it,but this info would help get a baseline on the truck.In other words,could make your problem more pronounced. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

06-07-2006, 01:17 PM	#7
dmigura Registered User Join Date: Jul 2005 Location: South Texas Posts: 17	Re: loose power on high end I am running 33s with stock gears not sure what they are it is a 70 half ton with a 4spd. I put a quadrajet from a 1980 ranch truck that I have just to see if that maid a difference, and it seems to be running better. I think something might of been wrong w/ the old carb.

06-28-2006, 01:02 PM	#8
220mph Speed Limits...yeh right Join Date: Jun 2006 Location: So Cal Posts: 72	Re: loose power on high end I had the same problem. It wound up being the distributor shaft bushing was worn so the timing was going out under load. __________________ 1972 3/4 ton 4x4 LONG BED 1940 Chevy Pickup 1970 El Camino Pro Street 496BB w/NOS

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