Truck stumbles when floored - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tim21391 · 08-13-2010, 12:23 AM

what did u gap your plugs to? i assume that one u just dropped in was hei.. did u gap them to .045? because with points i gapped mine to .035 and then with hei i gapped them to .045

1968CHEVYC10 · 08-13-2010, 02:03 AM

Quote:

Originally Posted by kevmic28

Id say change the fuel filter in the carb and run some seafoam through it. If it only gets run a few times a year that carb has got to be clogged up something good.

I took the fuel line off and I didn't see any kind of filter in there, is it kinda far back in the carb? I put some seafoam in there today and ran it for a little while, didn't notice anything but I figure it'll take awhile.

1968CHEVYC10 · 08-13-2010, 02:04 AM

Quote:

Originally Posted by tim21391

what did u gap your plugs to? i assume that one u just dropped in was hei.. did u gap them to .045? because with points i gapped mine to .035 and then with hei i gapped them to .045

Yeah gapped them to .045

72shortstep · 08-13-2010, 03:59 AM

On my Q-jet, the filter is where the fuel line enters the carb on the front. Good luck!

1968CHEVYC10 · 08-13-2010, 11:45 AM

Quote:

Originally Posted by 72shortstep

On my Q-jet, the filter is where the fuel line enters the carb on the front. Good luck!

Don't think there is one then, undid the flare nut and the adapter and didn't see nothin.

1968CHEVYC10 · 08-13-2010, 11:50 AM

Quote:

Originally Posted by Ticker

$20 says the timing is wrong - either the initial or the overall timing curve.

Where is the vacuum advance connected?

Here's a pic of where I hooked up the vacuum advance.
It's right below here the fuel line comes in.

youhaveamonkey · 08-13-2010, 12:14 PM

Ok, a few things here. RECHECK YOUR TIMING. Just do it. It is not hard. That is first.

Then the carb. There is a place for a fuel filter it is in the picture that you posted. It says "filter" on the front of the carb. Pull out the flare nut, then take a larger wrench (dont remember what size) and back off the part that the flare nut goes in to. If there is no filter in there, there needs to be one. That would be your first step. If your carb isnt getting enough fuel to allow the secondarys to work, you will effectively lean your mixture each time you push the accelerator down, and bog down the engine.

Check your mixture. Get a vacuum gauge. Set the mixture screw where you have max vacuum.

The carb may need to be rebuilt. There is a book about q-jets. I was not a carb guy either, however, the only way you are ever gonna learn is to do it.
There is a book about rochester q-jets. It is like 20 bucks or something at barnes and noble or borders or what ever. get it. it is worth its weight in gold. With the book and a good re-build kit, you can do it. It is not hard. Just be gentle, follow the directions and get it CLEAN CLEAN CLEAN. the toughest part for me is the end where you are trying to put the two halves of the carb together with the metering rods. It is a bit of slight of hand type of thing, but it really isnt hard. I guess what I am trying to tell you: just do it. Probably needs it anyway. MUCH MUCH MUCH better than a can of Seafoam, but I cant say I disagree with the other guys on here about it....

Good luck!

Cheers!

kevmic28 · 08-13-2010, 12:25 PM

Ok as fas as my carb goes, maybe this will help you out.
White circle is where the filter is.
Red circle over the vaccum tube is plugged on mine.
The yellow circle vaccum line goes to the choke.
Green circle: in this are is a vaccum tube that needs to be connected to the vacuum advance. also I have a tee from that tube to one under the choke that goes to the distributor advance.
Next is the clamps on your fuel filters, these have a tendancy to fail after some time and leak. Might consider changing to some screw drive clamps.
Now that is how mine is done. Mine could be wrong but it runs good this way.

1968CHEVYC10 · 08-13-2010, 02:01 PM

Wow thanks guys, yall are awesome! The vacuum advance is on the dizzy right? I was thinking that but you mentioned distributor advance, so I'm not sure.

68 50th · 08-13-2010, 03:15 PM

I had the same problem, it turned out to be a secondarie metering rod that had slipped off the rod hanger and plugged one of the secondarie jets.
See this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=155657

08-13-2010, 12:23 AM	#26
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Truck stumbles when floored what did u gap your plugs to? i assume that one u just dropped in was hei.. did u gap them to .045? because with points i gapped mine to .035 and then with hei i gapped them to .045 __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

08-13-2010, 03:59 AM	#29
72shortstep lovin' the lowcountry Join Date: Apr 2010 Location: Moncks Corner, SC Posts: 138	Re: Truck stumbles when floored On my Q-jet, the filter is where the fuel line enters the carb on the front. Good luck! __________________ Chris 29461 72 SWB stepside 71 SWB stepside DRIVE IT LIKE YOU STOLE IT!

08-13-2010, 12:14 PM	#32
youhaveamonkey Registered User Join Date: Mar 2009 Location: Oakland, Ca Posts: 39	Re: Truck stumbles when floored Ok, a few things here. RECHECK YOUR TIMING. Just do it. It is not hard. That is first. Then the carb. There is a place for a fuel filter it is in the picture that you posted. It says "filter" on the front of the carb. Pull out the flare nut, then take a larger wrench (dont remember what size) and back off the part that the flare nut goes in to. If there is no filter in there, there needs to be one. That would be your first step. If your carb isnt getting enough fuel to allow the secondarys to work, you will effectively lean your mixture each time you push the accelerator down, and bog down the engine. Check your mixture. Get a vacuum gauge. Set the mixture screw where you have max vacuum. The carb may need to be rebuilt. There is a book about q-jets. I was not a carb guy either, however, the only way you are ever gonna learn is to do it. There is a book about rochester q-jets. It is like 20 bucks or something at barnes and noble or borders or what ever. get it. it is worth its weight in gold. With the book and a good re-build kit, you can do it. It is not hard. Just be gentle, follow the directions and get it CLEAN CLEAN CLEAN. the toughest part for me is the end where you are trying to put the two halves of the carb together with the metering rods. It is a bit of slight of hand type of thing, but it really isnt hard. I guess what I am trying to tell you: just do it. Probably needs it anyway. MUCH MUCH MUCH better than a can of Seafoam, but I cant say I disagree with the other guys on here about it.... Good luck! Cheers!

08-13-2010, 12:25 PM	#33
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	Re: Truck stumbles when floored Ok as fas as my carb goes, maybe this will help you out. White circle is where the filter is. Red circle over the vaccum tube is plugged on mine. The yellow circle vaccum line goes to the choke. Green circle: in this are is a vaccum tube that needs to be connected to the vacuum advance. also I have a tee from that tube to one under the choke that goes to the distributor advance. Next is the clamps on your fuel filters, these have a tendancy to fail after some time and leak. Might consider changing to some screw drive clamps. Now that is how mine is done. Mine could be wrong but it runs good this way. Attached Images __________________ 1970 GMC truck 1988 Harley 1200 Sportster Last edited by kevmic28; 08-13-2010 at 12:30 PM.

08-13-2010, 02:01 PM	#34
1968CHEVYC10 Registered User Join Date: Aug 2009 Location: Tomball, TX Posts: 578	Re: Truck stumbles when floored Wow thanks guys, yall are awesome! The vacuum advance is on the dizzy right? I was thinking that but you mentioned distributor advance, so I'm not sure. __________________ '68 C10 LWB 6.2NA/NP833 3.73's

08-13-2010, 03:15 PM	#35
68 50th Senior Member Join Date: Jul 2004 Location: Sweden Posts: 833	Re: Truck stumbles when floored I had the same problem, it turned out to be a secondarie metering rod that had slipped off the rod hanger and plugged one of the secondarie jets. See this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=155657 __________________ Mats.. ---------------------------------------------------- 1971 Cheyenne Super Custom Camper 475CBB/TH400/AC 1992 Silverado Sport Truck 1988 Silverado 2500 Ext Longbed 4x4 2001 GMC Sierra SLT 4x4 1990 Chevrolet K3500 1965 Pontiac Grand Prix 1980 Z 28 350/4-speed/AC/T-top 1980 Camaro Coupe V6/3-speed 1979 Buick Century Wagon



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