dead spot at full throttle... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

The Blue Pig · 07-19-2002, 02:47 AM

This is actually a problem we are having with my girlfriends 74 half ton. Cherry red, 4/6 drop, short fleet, 350, has an Edelbrock 650 manual on top, and I think that is what the problem is. It starts out fine, and it accelerates ok, until you get just before WOT, then it hits a dead spot and its like that all the way to the floor. At first I thought the weights on her distributor might be frozen and they were not advancing the timing, but that would be more of an RPM thing, not a throttle position thing, cause you can get it to 5000 on the tach, it just takes a while. So I was thinking the only thing directly related to the postion the throttle is in is the carb. I have never had an edelbrock apart, only hollies. Is there some sort of power valve? If it was the accelerator pump, wouldnt the problem be there at all throttle positions? Any help would be appreciated. thanks. gotta get it fixed. Just put an auburn pro series limited slip fitted with 3.73's, gotta try them out.

**MikeB** · 07-19-2002, 10:33 PM

Assuming the carb is a 600 or 750 Performer series, there are no power valves, just a tapered metering rod for each of the primary jets. As manifold vacuum decreases (like at WOT) the rods pull up to let more fuel go thru the jets. There are several different rod sizes and 5 different rod springs that determine the vacuum drop at which the rods lift. There's nothing but two jets for the secondaries -- no rods. The secondary butterflies are vacuum actuated -- the vacuum in the throttle bore pulls against a counter weight. The carbs are very easy to take apart. Just don't lose the little rod clips. You shouldn't need to replace the main gasket, but entire rebuild kits are fairly cheap. Edelbrock's website has some good tech and t-shooting info at: http://www.edelbrock.com/automotive/index.html Select "Carburetors" from the menu on the left, then "Carburetor Owners Manual." By the way, the problem sounds like fuel starvation. Maybe a secondary jet or the fuel passage that feeds it, is clogged.

Longhorn Man · 07-19-2002, 10:45 PM

Actually, I was thinkingaccelerator pump. The pump is only there to help in the transition from idle circuits to WOT. If you can spin it to 5 grand, the secondaries are open.
Look to the right of the carb. On the right hand (drivers side) ipper corner, there is a little rod going into the top of the carb. Look at the lever on it. THere are 3 holes, and another rod there.
You can see that each hole will give it a diferant amount of fuel, and at differant times.
Carefully try to remove the little clip that holds the rod. and for gods sake, don't lose it. (real PITA) Try moving it to another hole on the rod. Take it around the block. Do it on all 3 settings. Then pick the best ruinning hole. This may fix your problem, or it may make another problem liveable.
It'll only take yu 15 min to get all selections and trips around the block, hell., go try it now.

**MikeB** · 07-19-2002, 11:16 PM

If it accelerates OK until going to WOT, the pump is probably OK. I've always associated pump problems with bogs when accelerating from a stop (idle to main circuit transition). But, hey, might as well take a look at it. Please let us know what fixes the problem.

The Blue Pig · 07-20-2002, 03:58 AM

Thanks a lot for the info guys, its great to have such handy advice close at hand. I spent all day hanging her new rear end, mounting shocks, brake lines and all new brakes, rebuilding wheel cylinders etc. I will have the rotors turned tomorrow, put on new pads and then make my way to the engine. I will probably pull the carb off, and do a manual inspection, but go ahead and pull the whole thing apart and get myself into trouble. I will check the secondary jets like you said and see if anything is stuck, also play around with the accelerator pump a tad. But, if I got the whole thing apart, might as well get a kit for it anyways. I just hope this does not lead to having to replum gas line or something. I guess I could hook up shop air right before the inline filter and blow it all backwards. have you guys done that? Anyway, I will go and definitely let you know what I find in the next couple of days. thanks again for the help.

crazy longhorn · 07-20-2002, 09:54 AM

There is not a lot to the edelbrock carbs,pretty nice to work on.......you might check the float levels before you start jetting, 1 of the floats was off on my 1407. good luck......Al

07-19-2002, 02:47 AM	#1
The Blue Pig Thread Wizard Since 2002 Join Date: Apr 2002 Location: Fairbanks, AK Posts: 102	dead spot at full throttle... This is actually a problem we are having with my girlfriends 74 half ton. Cherry red, 4/6 drop, short fleet, 350, has an Edelbrock 650 manual on top, and I think that is what the problem is. It starts out fine, and it accelerates ok, until you get just before WOT, then it hits a dead spot and its like that all the way to the floor. At first I thought the weights on her distributor might be frozen and they were not advancing the timing, but that would be more of an RPM thing, not a throttle position thing, cause you can get it to 5000 on the tach, it just takes a while. So I was thinking the only thing directly related to the postion the throttle is in is the carb. I have never had an edelbrock apart, only hollies. Is there some sort of power valve? If it was the accelerator pump, wouldnt the problem be there at all throttle positions? Any help would be appreciated. thanks. gotta get it fixed. Just put an auburn pro series limited slip fitted with 3.73's, gotta try them out. __________________ --70 C-10 Longbed --71 C-10 Longbed --72 K-20 Longbed --74 C-10 Shortbed --86 Toyota Tercel (His Driver) --05 Chevy Trailblazer (Her Driver)

07-19-2002, 10:33 PM	#2
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,599	Assuming the carb is a 600 or 750 Performer series, there are no power valves, just a tapered metering rod for each of the primary jets. As manifold vacuum decreases (like at WOT) the rods pull up to let more fuel go thru the jets. There are several different rod sizes and 5 different rod springs that determine the vacuum drop at which the rods lift. There's nothing but two jets for the secondaries -- no rods. The secondary butterflies are vacuum actuated -- the vacuum in the throttle bore pulls against a counter weight. The carbs are very easy to take apart. Just don't lose the little rod clips. You shouldn't need to replace the main gasket, but entire rebuild kits are fairly cheap. Edelbrock's website has some good tech and t-shooting info at: http://www.edelbrock.com/automotive/index.html Select "Carburetors" from the menu on the left, then "Carburetor Owners Manual." By the way, the problem sounds like fuel starvation. Maybe a secondary jet or the fuel passage that feeds it, is clogged. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 07-19-2002 at 10:37 PM.

07-19-2002, 11:16 PM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,599	If it accelerates OK until going to WOT, the pump is probably OK. I've always associated pump problems with bogs when accelerating from a stop (idle to main circuit transition). But, hey, might as well take a look at it. Please let us know what fixes the problem. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!

07-20-2002, 03:58 AM	#5
The Blue Pig Thread Wizard Since 2002 Join Date: Apr 2002 Location: Fairbanks, AK Posts: 102	Thanks a lot for the info guys, its great to have such handy advice close at hand. I spent all day hanging her new rear end, mounting shocks, brake lines and all new brakes, rebuilding wheel cylinders etc. I will have the rotors turned tomorrow, put on new pads and then make my way to the engine. I will probably pull the carb off, and do a manual inspection, but go ahead and pull the whole thing apart and get myself into trouble. I will check the secondary jets like you said and see if anything is stuck, also play around with the accelerator pump a tad. But, if I got the whole thing apart, might as well get a kit for it anyways. I just hope this does not lead to having to replum gas line or something. I guess I could hook up shop air right before the inline filter and blow it all backwards. have you guys done that? Anyway, I will go and definitely let you know what I find in the next couple of days. thanks again for the help. __________________ --70 C-10 Longbed --71 C-10 Longbed --72 K-20 Longbed --74 C-10 Shortbed --86 Toyota Tercel (His Driver) --05 Chevy Trailblazer (Her Driver)

07-19-2002, 10:45 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Actually, I was thinkingaccelerator pump. The pump is only there to help in the transition from idle circuits to WOT. If you can spin it to 5 grand, the secondaries are open. Look to the right of the carb. On the right hand (drivers side) ipper corner, there is a little rod going into the top of the carb. Look at the lever on it. THere are 3 holes, and another rod there. You can see that each hole will give it a diferant amount of fuel, and at differant times. Carefully try to remove the little clip that holds the rod. and for gods sake, don't lose it. (real PITA) Try moving it to another hole on the rod. Take it around the block. Do it on all 3 settings. Then pick the best ruinning hole. This may fix your problem, or it may make another problem liveable. It'll only take yu 15 min to get all selections and trips around the block, hell., go try it now.

07-20-2002, 09:54 AM	#6
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	There is not a lot to the edelbrock carbs,pretty nice to work on.......you might check the float levels before you start jetting, 1 of the floats was off on my 1407. good luck......Al



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