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

nosoup4u · 10-10-2013, 03:22 PM

I have a 1968 C50 with a 327. This is a grain truck with a 4 speed and a two speed rear axle.
The old girl starts easy and runs good, but quite often when rolling down the hiway, after going through the gears and just getting to cruising speed, it begins to lurch almost like you were quickly stepping on and letting off the accelerator pedal.If you let off, and slowly speed back up it will come out of it.
It will happen if the the truck is loaded or not and in any of the higher gears.
Any ideas what might cause this?
I'll hang up and listen.

**Ol Blue K20** · 10-10-2013, 03:27 PM

Fuel filter, fuel screen in the tank, fuel delivery in general

nosoup4u · 10-10-2013, 03:56 PM

That was my first thought, but then why doesn't it do it when it needs maximum fuel like pulling a load out of the field?

**Ol Blue K20** · 10-10-2013, 04:07 PM

Maybe length of the time it's demanding that quantity, could be a venting thing too

BIG69GMC · 10-10-2013, 05:21 PM

definately air to fuel ratio issue. check your mixtures, you might be running to lean or too rich. best way is to adjust a little at a time and keep driving it. if it gets worse then adjust the other way.

Don Quixote · 10-10-2013, 10:41 PM

I had the same problem and fixed it by rebuilding the carb, it was just dirty so I took it apart and replaced the rods and jets and gave it a good cleaning with carb cleaner.

geezer#99 · 10-10-2013, 11:30 PM

If you have a tcs (transmission controlled spark) and it's not hooked up right you could have a vacuum leak in the top gear.
You got a pic of your motor with the air cleaner off?

nosoup4u · 10-11-2013, 10:34 AM

I bought it at an auction about a year and a half ago, so there's no telling how long it has been since the carb received any attention. I'll have to take it to a competent rebuilder this winter.
It's about 13 miles away right now but I'll post a pic of the engine ASAP.
Thanks for the replies so far.

*Mister-B* · 10-11-2013, 11:20 AM

In the meantime, some carb cleaner spray while everything is still in tact, and a good fuel additive like Lucas might improve things or maybe even fix it.

71K20chevy · 10-11-2013, 11:22 AM

Quote:

Originally Posted by Mister-B

In the meantime, some carb cleaner spray while everything is still in tact, and a good fuel additive like Lucas might improve things or maybe even fix it.

Yup ^^ or you could try some Sea Foam. Sounds like, without a doubt, a fuel problem. Not vapor lock is it? Doesn't really sound like it is, but it never hurts to be sure.

*Mister-B* · 10-11-2013, 02:08 PM

Quote:

Originally Posted by 71K20chevy

Yup ^^ or you could try some Sea Foam. Sounds like, without a doubt, a fuel problem. Not vapor lock is it? Doesn't really sound like it is, but it never hurts to be sure.

Just don't dump in two bottles of seafoam on an almost empty tank, right Andy? Inside joke lol

71K20chevy · 10-11-2013, 02:12 PM

Quote:

Originally Posted by Mister-B

Just don't dump in two bottles of seafoam on an almost empty tank, right Andy? Inside joke lol

Yes, she might run a little rough

10-10-2013, 03:22 PM	#1
nosoup4u Registered User Join Date: Oct 2013 Location: Seward Posts: 3	Lurching truck I have a 1968 C50 with a 327. This is a grain truck with a 4 speed and a two speed rear axle. The old girl starts easy and runs good, but quite often when rolling down the hiway, after going through the gears and just getting to cruising speed, it begins to lurch almost like you were quickly stepping on and letting off the accelerator pedal.If you let off, and slowly speed back up it will come out of it. It will happen if the the truck is loaded or not and in any of the higher gears. Any ideas what might cause this? I'll hang up and listen.

10-10-2013, 03:27 PM	#2
Ol Blue K20 Proprietor of Dale's Corner Join Date: Nov 2012 Location: Vacaville , CA Posts: 16,245	Re: Lurching truck Fuel filter, fuel screen in the tank, fuel delivery in general __________________ "Some Days Chickens And Some Days Feathers" Dale XNGH ECV Sam Brannan 1004 R.I.P. 67ChevyRedneck R.I.P. Grumpy Old Man R.I.P. FleetsidePaul

10-10-2013, 03:56 PM	#3
nosoup4u Registered User Join Date: Oct 2013 Location: Seward Posts: 3	Re: Lurching truck That was my first thought, but then why doesn't it do it when it needs maximum fuel like pulling a load out of the field?

10-10-2013, 04:07 PM	#4
Ol Blue K20 Proprietor of Dale's Corner Join Date: Nov 2012 Location: Vacaville , CA Posts: 16,245	Re: Lurching truck Maybe length of the time it's demanding that quantity, could be a venting thing too __________________ "Some Days Chickens And Some Days Feathers" Dale XNGH ECV Sam Brannan 1004 R.I.P. 67ChevyRedneck R.I.P. Grumpy Old Man R.I.P. FleetsidePaul

10-10-2013, 05:21 PM	#5
BIG69GMC Registered User Join Date: Jul 2009 Location: Albuquerque, NM Posts: 101	Re: Lurching truck definately air to fuel ratio issue. check your mixtures, you might be running to lean or too rich. best way is to adjust a little at a time and keep driving it. if it gets worse then adjust the other way.

10-10-2013, 10:41 PM	#6
Don Quixote Registered User Join Date: May 2008 Location: Woodlawn, TN Posts: 275	Re: Lurching truck I had the same problem and fixed it by rebuilding the carb, it was just dirty so I took it apart and replaced the rods and jets and gave it a good cleaning with carb cleaner. __________________ Rocinante: 1972 GMC C25, 292, SM465, 14 bolt, power nothing, 440k and still handles my PCS moves Jorge: Kia Roller-skate with lots of buttons for the wife Wovoka: 2017 Indian Chief Vintage, better on gas but not much So far, this is the oldest I've ever been.

10-10-2013, 11:30 PM	#7
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,731	Re: Lurching truck If you have a tcs (transmission controlled spark) and it's not hooked up right you could have a vacuum leak in the top gear. You got a pic of your motor with the air cleaner off?

10-11-2013, 10:34 AM	#8
nosoup4u Registered User Join Date: Oct 2013 Location: Seward Posts: 3	Re: Lurching truck I bought it at an auction about a year and a half ago, so there's no telling how long it has been since the carb received any attention. I'll have to take it to a competent rebuilder this winter. It's about 13 miles away right now but I'll post a pic of the engine ASAP. Thanks for the replies so far.

10-11-2013, 11:20 AM	#9
Mister-B Account Suspended Join Date: Oct 2012 Location: Salt Lake City, Utah Posts: 3,331	Re: Lurching truck In the meantime, some carb cleaner spray while everything is still in tact, and a good fuel additive like Lucas might improve things or maybe even fix it.



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