Mark, Quadrajet Question

[pontiacgp]

If you don't mind, do you like the stepped primary rods or the taper rods.....and why

Thanks

 

[Bonnewagon]

Steve as far as that goes I have no preference, they work the same for their respective application. I do however prefer the '75 and up Q-jets, which I believe have the stepped rods you are asking about. The old and new rods have different lengths so are not interchangeable. I have used both series, pre-'75 and post '75, and I find the later models are somewhat more fine-tunable, what with the APT and all. They also accept the electric choke which I use exclusively. The pre- '73 models have a divorced choke that is useless without a matching intake manifold. I have not successfully mated an electric choke to those models yet. The pre-'72 models are usually equipped for the old performance minded motors and thus have better idle circuits that can better accommodate more radical camshafts. The post '75 models usually need the idle ports drilled out larger to get a decent idle with such cams.

 

[pontiacgp]

Thanks Mark, the reason I asked is I have the #48 tapered in my quadrajet now. The carb is post 75. I have similar number carb that I picked up for parts and it has the #48 stepped primary rods and was wondering which set would be best but if they work the same then I will leave it alone...🙂

 

[Bonnewagon]

Steve, I looked in Roe's book and he describes the rods as having either a single taper or a double taper. Is that what you mean by "step"? The single taper would have the number 48, while a double taper would be a 48B.

 

[pontiacgp]

I highlighted the numbers with a black marker to make them more clear with a good magnifying lens, the numbers and letters are more clear ...it sure looks like a 49V but it must be a 49M......

 

[Bonnewagon]

I 've never seen those, only B or K. Is it single or double taper? It should be obvious, but if not, take a micrometer and see what you have. The tip should be .026". Remember the rod size and taper was chosen per application. For performance, all that goes out the window.

 

[pontiacgp]

measured, It has a 36 tip and then I found that rod on this list....the jets in that carb with the 49 rod are 72, must have been a real lean running carb.

http://www.gmcmi.com/wp-content/uploads/2014/05/Quadrajet-Carb-Primary-Metering-Rods.pdf

 

[Bonnewagon]

Not really. #70 and #71 are the most common jets I have found and mostly on 350 and smaller engines. Couple those with # 56 or #58 rods and then you have a lean, emissions set up. Here again I will quote from Doug Roe's book- "All rods have a 0.026" diameter tip at their smallest point, except rod 50D, which has a 0.036" tip". Then a footnote explains- 50D- "Special rod used in GMC Motorhome- has a 0.036" power tip". Your awesome chart (thank's for that!) shows only a handful of those 0.036" tip rods with all others being 0.026". I would be curious as to what the application of your carb was originally. You may have a rare beast there. But I still don't know what is meant by a "step". Is it a sudden rapid decrease in diameter as opposed to a smooth gradual taper? If so then I understand. Check out this site and you can probably find out exactly what that carb was from. http://www.newagemetal.com/

 

[pontiacgp]

I checked the carb number to see what application it had and it was an 80-85 Chev/GMC Truck

http://www.carburetion.com/CarbNumber.asp?Number=17080213

 

[pontiacgp]

I thought I found a nice carb for $125. It's from a 454 Chevy pick up, 76-77. They said ti was in good shape and asked for pictures. I guess good shape is in the eye of the beholder....