Rochester one-barrel carb - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dick's 67 · 07-24-2011, 10:21 PM

I have a '67 235HP with a 3-speed Chevy with 55k originals. Will post pics when I learn how. My problem is: While cruising at any speed, truck jerks. If you accelerate, let off, or pull choke out, jerking stops. Was told to back off idle mixture screw and if that corrects the jerking, the problem is in the power valve piston.
Backing off the screw helped the problem, so I stretched the piston spring from 1 5/8" to 1 11/16". That helped, but still can't find that happy place.
I've exhausted about all the info. I've received. Unless anybody has other suggestions, I would like to know if anybody has used CarburetorsandMore.com.
Thanks,
Dick

Wrenchbender Ret · 07-25-2011, 03:59 PM

A 67 has either a 230 or 250 engine. Most likely a 250. It comes with a Roch. model B carb. First check that the accelerater pump is putting out s good shot. Take a look at the main metering jet & see what size it is. Often these carbs go through "rebuilders" & they mix up parts. It should have about a .058 jet size. You can increase it slightly to get it to drive better. Make sure the power valve piston Knocks the ball off its seat. They can get bent. Check the float level. It should be 1 9/32in. from the gasket to the bottom of the float. Its not good to tailor the float setting on this carb.

PanelDeland · 07-25-2011, 07:59 PM

You might also check the vac advance on the distributor.Mine did that and I found that the vac can(in the dist) was leaking and wouldn't hold advance.When I replaced the vac mod,it stopped most of the jerking you describe.Then when I did a HEI it stopped completely.
Don't forget to check the filter in the carb.It's behind the nut where the fuel line hooks to it.

Dick's 67 · 07-25-2011, 10:49 PM

Thanks for the info. I have a decent accelerator pump stream. I have a .058 jet; tried a .60. Ran worse. Piston spring seems to unseat ball okay. Will check float depth. Filter is a brass mesh. Seems to work fine. Will check the vacuum, and let you know the outcome. Thanks.
Dick

Bus Ted Knuckle · 07-26-2011, 12:20 AM

sure sounds like a bad vacuum advance to me.

Dick's 67 · 07-26-2011, 10:00 PM

I took a carb from a good running truck, and put on mine the jerking wasn't quite as bad, but still there. So I borrowed the vaccum advance also, no more jerking. My vac is really tight compared to the good one. Thanks for the advice, before I wore the carb out. My truck is on page 44 of Vintage Truck magazine,May/June 2010 vol.18-#2 Can anyone tell me how to add my truck picture to my profile. Thanks Dick

68 IRON · 07-26-2011, 10:21 PM

Join date 2006? Wow you've been here awhile (very few words)! I think adding the pic is under your stats page....just click your handle (name) and it should be somewhere on that page.
Found it.... Go to FAQ and click on the profile sudject. The next page brings up all subjects for that, including avatars. Just follow the instructions.

Dick's 67 · 07-27-2011, 10:28 PM

Thanks 68 IORN. My wife followed your directions, got the picture there in no time. I would still be working on it at sun up. That's why the few words! I'm learning
Dick

07-24-2011, 10:21 PM	#1
Dick's 67 Registered User Join Date: Nov 2006 Location: Fortville, IN Posts: 9	Rochester one-barrel carb I have a '67 235HP with a 3-speed Chevy with 55k originals. Will post pics when I learn how. My problem is: While cruising at any speed, truck jerks. If you accelerate, let off, or pull choke out, jerking stops. Was told to back off idle mixture screw and if that corrects the jerking, the problem is in the power valve piston. Backing off the screw helped the problem, so I stretched the piston spring from 1 5/8" to 1 11/16". That helped, but still can't find that happy place. I've exhausted about all the info. I've received. Unless anybody has other suggestions, I would like to know if anybody has used CarburetorsandMore.com. Thanks, Dick Last edited by Dick's 67; 07-24-2011 at 10:29 PM.

07-25-2011, 07:59 PM	#3
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Rochester one-barrel carb You might also check the vac advance on the distributor.Mine did that and I found that the vac can(in the dist) was leaking and wouldn't hold advance.When I replaced the vac mod,it stopped most of the jerking you describe.Then when I did a HEI it stopped completely. Don't forget to check the filter in the carb.It's behind the nut where the fuel line hooks to it. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

07-25-2011, 10:49 PM	#4
Dick's 67 Registered User Join Date: Nov 2006 Location: Fortville, IN Posts: 9	Re: Rochester one-barrel carb Thanks for the info. I have a decent accelerator pump stream. I have a .058 jet; tried a .60. Ran worse. Piston spring seems to unseat ball okay. Will check float depth. Filter is a brass mesh. Seems to work fine. Will check the vacuum, and let you know the outcome. Thanks. Dick

07-26-2011, 12:20 AM	#5
Bus Ted Knuckle Son of a gun Join Date: Jan 2007 Location: Hot Springs, Arkansas Posts: 1,636	Re: Rochester one-barrel carb sure sounds like a bad vacuum advance to me. __________________ Bill BEATERS ARE NEATER

07-26-2011, 10:00 PM	#6
Dick's 67 Registered User Join Date: Nov 2006 Location: Fortville, IN Posts: 9	Re: Rochester one-barrel carb I took a carb from a good running truck, and put on mine the jerking wasn't quite as bad, but still there. So I borrowed the vaccum advance also, no more jerking. My vac is really tight compared to the good one. Thanks for the advice, before I wore the carb out. My truck is on page 44 of Vintage Truck magazine,May/June 2010 vol.18-#2 Can anyone tell me how to add my truck picture to my profile. Thanks Dick

07-25-2011, 03:59 PM	#2
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,212	Re: Rochester one-barrel carb A 67 has either a 230 or 250 engine. Most likely a 250. It comes with a Roch. model B carb. First check that the accelerater pump is putting out s good shot. Take a look at the main metering jet & see what size it is. Often these carbs go through "rebuilders" & they mix up parts. It should have about a .058 jet size. You can increase it slightly to get it to drive better. Make sure the power valve piston Knocks the ball off its seat. They can get bent. Check the float level. It should be 1 9/32in. from the gasket to the bottom of the float. Its not good to tailor the float setting on this carb.

07-26-2011, 10:21 PM	#7
68 IRON Registered User Join Date: Sep 2010 Location: Olympia, WA Posts: 736	Re: Rochester one-barrel carb Join date 2006? Wow you've been here awhile (very few words)! I think adding the pic is under your stats page....just click your handle (name) and it should be somewhere on that page. Found it.... Go to FAQ and click on the profile sudject. The next page brings up all subjects for that, including avatars. Just follow the instructions.

07-27-2011, 10:28 PM	#8
Dick's 67 Registered User Join Date: Nov 2006 Location: Fortville, IN Posts: 9	Re: Rochester one-barrel carb Thanks 68 IORN. My wife followed your directions, got the picture there in no time. I would still be working on it at sun up. That's why the few words! I'm learning Dick



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