1970 LS5 Throttle Linkage

[Allen N.]

My throttle linkage is contacting a bolt on the intake manifold not allowing the carburetor set flush. Do I need to tweek the linkage in or out to clear the bolt? Or do I have another problem?

Here are a couple of pictures

IMG_20220131_151732907.jpg

IMG_20220131_151752783.jpg

Thanks,
Allen

[Howard H.]

Re: 1970 LS5 Throttle Linkage

Allen
The correct throttle arm does not have the part that is hitting the bolt, only the part that is pointing down. Yours looks like a small block throttle arm. I think the correct arm has RP 37250 stamped on it.
Howard Hiller 46797

[Mike E.]

[Allen N.]

Re: 1970 LS5 Throttle Linkage

Thank you very much for the responses. Thanks Howard for pinpointing my problem. I was afraid it was something like that.

I have sent emails to Vintage Muscle Car Parts and Cliffs High Performance to see if they have a 37250 throttle linkage.

Any other carburetor rebuilders you would recommend?

[Leonard M.]

Re: 1970 LS5 Throttle Linkage

PM sent with a link

[Allen N.]

Re: 1970 LS5 Throttle Linkage

It looks like I may have a restamped carburetor. I have been in contact with a Eric at Vintage Muscle Car Parts, and he doesn't like the stamping on my carburetor. Below is a picture.

IMG_20220201_115748652_HDR.jpg

[Mike E.]

Re: 1970 LS5 Throttle Linkage

Allen,
Not the same part number, but here is a stamping on a real 70 carburetor for comparison.
carburetor (1).jpg

[Mark E.]

Re: 1970 LS5 Throttle Linkage

Hi Allen,

Two differences I noticed between 7040205 and your carb-
- 7040205 has a fuel bowl idle vent at the front center of the air horn. The vent on this carb is plugged.
- Your carb has a vacuum port above the driver's idle mixture screw. 7040205 does not have this port (but does has its boss).

Your carb has the same configuration as 7040505 (plugged fuel bowl vent; added vacuum port), which is the NA9/ California variant for this car.

What does your vendor find suspicious about the PN stamping? It look okay to me but I'm not an expert (although the configuration of the carburetor itself is suspect).

[Allen N.]

Re: 1970 LS5 Throttle Linkage

Mike,

Thanks for the comparison. The 7 and 4 definitely look different on the two carburetors. And mine have alignment problems with the EH and date is not straight at all.

Mark,

The vendor didn't say what he exactly saw that was wrong, but he felt a good NCRS judge would likely see that it was wrong.

Thanks,
Allen

[Joe L.]

Re: 1970 LS5 Throttle Linkage

It looks like I may have a restamped carburetor. I have been in contact with a Eric at Vintage Muscle Car Parts, and he doesn't like the stamping on my carburetor. Below is a picture.

[ATTACH=CONFIG]110142[/ATTACH]

Allen------


This could be a case of 7040205 carb with an original float bowl assembly but a replaced air horn and throttle body assembly from another carb.

[Mark E.]

Re: 1970 LS5 Throttle Linkage

Allen------


This could be a case of 7040205 carb with an original float bowl assembly but a replaced air horn and throttle body assembly from another carb.

As noted above, 7040205 did not have a vacuum port above the left idle mixture screw.

[Joe L.]

Re: 1970 LS5 Throttle Linkage

As noted above, 7040205 did not have a vacuum port above the left idle mixture screw.

Mark------


Yes, I had not noticed that.

All 1970 Q-Jet carbs were unique to that model year. The carbs' major assemblies, including the throttle body, fuel bowl, and air horn were also unique to 1970. Non EEC carbs did not have the vacuum nipple on the lower left side of the carburetor. However, EEC carbs did have such a nipple in addition to 2 vacuum nipples on the right front side of the float bowl.

In addition, non-EEC carbs used an air horn assembly with the front "flapper" idle vent and cover while EEC carbs had this vent "blanked off" with only the casting "vestiges" present.

So, by part number the carb is a non-EEC carb but by air horn, float bowl, and throttle body configuration it's an EEC carburetor. Also, by throttle body configuration it's a small block carburetor.

Considering all of this, it now would seem likely to me that the 7040205 stamping is "not original" to the carb even though the stamping looks good to me. So, whoever did it gets a well-done for that feature. Is it possible that this could be a later SERVICE carb with changed features for the sake of consolidation? Not likely, at all, considering the late 1969 date code.

Something I find curious: the idle stop "dashpot" as noted by Mike E. is extremely rare. I rarely, and I mean RARELY, see these on original carbs. This is what I call a "mystery" part. I believe they were used only for some 1970 applications although it's possible they were also used in the 1971-72 period. I've never even been able to come up with a name for this part and I've never been able to come up with a GM part number for it, either. I also don't understand how it functions except to possibly delay throttle closing by some sort of non-vacuum means.

So, here we have what could well be a "Frankenstein" carburetor but one that includes a VERY rarely seen component.

One more thing: From the very beginning in 1970, the SERVICE part number (GM #7036811) for the float bowl assembly (i.e. the component that has the vacuum nipples) was the same for both the the EEC and non-EEC big block carbs. I assume that this SERVICE float bowl had the vacuum nipples since they would be necessary for the EEC carbs and could be capped for non-EEC applications. The SERVICE float bowls have no numbers stamped on the "stamp pad" of the float bowl (I know as I have an NOS 1969 float bowl [not for sale]. So, I suppose this carb could have been made up using a SERVICE float bowl. These were discontinued in 1976 so it's unlikely one would have been available at the time of rebuild of this carb unless the carb had a long-ago replacement.

[Mark E.]

Re: 1970 LS5 Throttle Linkage

I have four Quadrajets for my LS5: a service replacement with no numbers which came with the car when acquired in 1990; a configuration and date appropriate 7040205 I found a few years ago; and two 7040505 NA9/EEC carbs I also found and restored.

As Joe mentioned, the service replacement carb has the NA9 vacuum port. The one I have sports yet another vacuum port on the right side of the main body near the fast idle cam pivot. I've seen this port connected to the sensor for the thermostatically controlled air cleaner used on some models (not Corvette). 7040205 and 7040505 don't have this port. My 454 doesn't run as well with this service replacement. This may be due to an internal issue, but I believe it's because it isn't set up specifically for a 454. (For example, Q-Jets for big blocks typically have larger idle air bypass circuits, among other internal differences.)

If you have a 49-state variant LS5, 7040505 is a good performance choice. It gives the tuning option of full or ported vacuum for the VAC (7040205 does not have ported vacuum), it's set up specifically for a 454 (unlike small-block or service Q-Jets), and as a bonus, 7040505 is typically several hundred dollars less expensive than a 7040205 in similar condition. So if the PN isn't important or you're looking for a back up Q-Jet, 7040505 is a solid choice.

I have two "dashpots" used on some LS5 cars. All this device seems to do is dampen (slow down) closure of the throttle during its last 1/4" of travel. I don't know what this accomplishes... maybe Chevy learned this reduces emissions during these conditions? The problem is the two I have do not provide a consistent idle speed. Closing the throttle slowly causes a higher idle speed than closing the throttle abruptly. So these little gems sit in a box and are replaced by a normal idle adjustment screw.

[Thomas H.]

Re: 1970 LS5 Throttle Linkage

Hard to see in the pics, but do you have the thick base gasket installed? May give enough clearance - independent of correctness of throttle arm.

My early 71 LS5 throttle - CEC not installed in this pic.

Tom

[Allen N.]

Re: 1970 LS5 Throttle Linkage

Hard to see in the pics, but do you have the thick base gasket installed? May give enough clearance - independent of correctness of throttle arm.

My early 71 LS5 throttle - CEC not installed in this pic.

Tom

Tom,

Thanks for the suggestion, but I am too anal to install my Frankenstein carburetor. Now that I know how much is wrong with this carburetor, I am going to replace it.

Thanks,
Allen