Q-jet jet and rod question

I have a 68 riv 430 with a 69 riv Q-jet that was on it when I bought the car. While I was rebuilding the motor I went through the carb to check it out and put a new kit in and rebush the throttle shaft. While it was apart I checked out what primary jet and rod combo was in it and it had a 70 jet with a 45 rod. The factory manual calls for a 70 jet with a 43 rod. I made note of it and put the carb back on the motor with what was in it since it was pretty close to stock, I didn't have any 43 rods and I wanted to fire up the fresh motor. Fire up went fine but it seemed a little hot and I chalked it up to being a little lean with the 45 rods and a TA112 cam pulling a little more air than stock. Got some 43 rods and now temp is fine and plugs look good.

Now to get to the point of my post after all that! I picked up a correct 68 Q-jet and guess what? It had 70 jets and 45 rods and the correct BG secondary rods. Did GM use different specs than what is in the service manual? I know it doesn't really matter since I will just use what jets and rods work, but it just seemed strange that the two carbs had the same set up which was different from what was supposedly stock. Anyone else find this with other Q-jets?

Keith

 

hey there 68 riv.. I have somewhat of a same thing going on with my 69 GS400.. The carb on it is from a 69 350 eng..it has 70 jets and 43 rods and the 400-430 all have 70\45 according to my '69 manual, all the other specs are identical except for carb #, secondary rods,{which are all the same for the 400\430}, and spark hole (whatever that is) witch :laugh: is the same on the 400\430...maybe this will shed some light o No: or maybe just more confusion.. :laugh:

 

Thanks faster eddie! If your 69 manual has the specs at 70/45 then that would explain the 69 carb with the 45 rods. I didn't have a 69 manual, only the 68, and it lists 70/43 for the 350/400/430 automatic, 70/44 for the 400 manual trans and 73/43 for a 350 manual trans. Secondary rods are BG for 400/430 and AK for 350. I know after 35 years that any of the parts could have been changed out by someone, but I just thought it strange how both carbs came up with 70/45 combo when the specs I had said 70/43. Looks like GM switched specs for 69 and maybe the 68 carb spec was switched at some point since there are two carbs numbers for early and late 68. I have the 7028240 which is the early carb and the only number for the 430 in the 68 manual so I was looking for 43 rods. When I found the 45 rods got to wondering!

Keith

 

67 400-430 jets and rods

i dont know if it will help but 67's had 71 jets and 40 rods in auto's.

 

Thanks Joe,

It always helps to know what works in similar engines. After some testing with the 45 rods I think they are too lean for my combo so 43 seems to be the ticket with my cam and exhaust. 42 seemed too rich. I did change out the power enrichment spring to a lighter spring since I found my idle vacuum is about 14 in.-hg in nuetral and 11 in drive @600 rpm. That really cleaned up the idle. I made a test fixture from an old q-jet body so I could test springs at different vacuum levels. If anyone is using the Edelbrock springs I highly recommend making the test fixture and checking the springs. I found the spring ratings to be about 2-3 in.-hg off from actual values. I think the weakest one is rated at 8 and didn't really close till 10.

Keith