View Full Version : primary throttle shaft wear?

02-04-2007, 05:27 PM
I got a 1975 750 fourbarrel Carb. Rochester Quadrajet 7045229. Before I decide to rebuild it I checked the primary throttle shaft for wear. It moves in the open wide position forward and back at the very most ten thou of an inch, maybe 15. At closed throttle it still has a bit of play but less than 10 thou. So is there a mechanic guru on this site that can tell me if I should toss it and buy a rebuilt one. A machine shop in Williams Lake told me they could re-bush it for $70 plus tax. Buying a rebuilt one is $280 compared to about 130 for me to rebush & rebuild. I am cheap what can I say;)

I had taken it apart because engine was flooding so I figured something was wrong internally with the carb. I discovered one of the brass tubes that is pressed into the top of the carb by the secondary tubes had fallen into the bottom of the carb. I guess that's why the engine was running so poorly. The carb worked fine until the flooding occurred. I have rebuild kit for that I bought for $25. I don't need to pass air care because I live way up your Hundred Mile House but I don't want to put good money after bad. I've heard that even brand-new carbs have some play.

02-04-2007, 11:14 PM
Too bad your so far away, I can rebush it for a lot cheaper then that. I think I paid $120 for the reamer and 5 sets of bushings.

While it's apart, check to see if the bowl is leaking, they are prone to leaks and when it sits for 15 minutes or so it is a hard start, seems flooded.

Quadrajet, one of the best carbs out there as far as I'm concerned. Simple design and they work.

02-05-2007, 07:07 AM

How much would you charge to rebush it? I could also greyhound the plate and shaft to you.

I found a bushing\reamer kit on the Internet but I wonder how often I would use it? My carb for my 454 needs new bushings too. Maybe I should just buy a kit off the Internet. Does Lordco sell it? I have an account with them. Do you have a part number for the kit so I could order it?

I have another carb of on my 454, #7045512, would it temporarily work on my 305? Maybe I could use it until my present carburetor is rebuilt?

02-05-2007, 07:36 AM
If it ran good before it started flooding, and the it returned to idle good, I would just rebuild it. Just obout every Q jet has worn throttle shafts, but they work well anyways, and a rebuilt will probably be worse the what you have.

02-05-2007, 07:53 AM
Righty on! That makes me feel better. As for the egr valve, from researching it, I can just disconnect it or take it off and put a cover plate on it?

02-05-2007, 08:28 AM
Unless its for cosmetics, there is no reason to remove the egr. It doesn't cause any power loss and allows a bit more timing without pinging, giving you more power and better mpg's.

02-06-2007, 06:16 AM
I needed to get my Jimmy back on the road![36] my wife took our daily driver down to the coast for a couple days. So I needed a set of wheels to drive the kids around;) :D . Anyways I rebuilt my 750 carb yesterday without re-bushing it based on pumpkins opinion. It runs really good[36] . Since this carb came off a 1975 400 v8 and it did not have any egr valve on it's manifold, I made a plate to cover the hole on my bagged 305. My vacuum is 16 at idle. Low but I guess okay. No pinging yet. I set the timing at 8 degrees since a friend told me it that would give it a bit more power. I still need to doublecheck my idle with my tac, adjust the two screws at the base of the carb, and doublecheck the timing. I know the compression is a little weak. I did a compression test and the rings are a little worn. Took four cranks up the engine for a compression to come up over 120. I'm not going to put any money into this engine. I got my 454 sitting in the garage waiting to go in and it may need to need to have the heads done. Just waiting for the right season to start:confused0006: . I do have three quarter ton 4:10 diffs waiting to go under. What do you think pumpkin?:confused0006: Start with the 454 or the lower geared diffs?:confused:

02-06-2007, 07:41 AM
I'm not a big fan of big blocks, due to the price, and weight. I like small block 400's. Its quit easy to get 400 plus horse, and 400 plus ft lbs of torque out of them and the are very streetable, with plenty of power. When you figure on the average price for just a core big block being $1000, it just seems more economical to go small block, unless your wanting 500 or more in the power numbers,,,,,,,,,, and 4 mpg's. 4.10's would be the place to start if your runing a 35" tire, and no overdrive. If you have bigger tires, I would look at a bit more gear, and if you have an overdrive you can get away with more gear. My Blazer is going to be running a 400, 700r4, 4.56 gears, lockers front and rear, on 35's.

02-06-2007, 08:07 AM
I knew I should have kept my 400 small block core:( . Sold it to Fortins for $100. I was trying to downsize when we moved. I know I could sell the big block and put the money back into a small block:D . I wanted to at least try the big block to see what it feels like:cool: . I can always go back to a small block. If I really need to budget on gas in the future, I'll put the 305 back in. The 305 I have, the guy that sold it to me, told me there was a rv cam in it. How can I tell that there different cam in it versus the stock cam?:confused0006: Would I need to change the timing? A friend of mine does not use a timing light but just goes by ear. I've even been told how to power time my truck. Have one person sit in the truck with the truck in drive with the brakes on, give it a bit of throttle, and then the second person adjusts the distributor for the best engine response. You ever done that?

02-06-2007, 08:26 AM
Yup, sort of. but I do it while driving. Adjust it till it just starts to ping, then back it off a bit.

02-06-2007, 09:45 AM
How do you do it when your driving? You have a hole in the firewall? Or some kind of new tech ignition system?

02-06-2007, 02:18 PM
Drive, stop, adjust,,,,,drive, stop, adjust.

02-06-2007, 09:15 PM
How do you do it when your driving? You have a hole in the firewall? Or some kind of new tech ignition system?

He takes the hood off and get's one of his "good" buddies to sit on the engine and adjust the carb while he accelerates from 0 to 60mph. Works for me. :D

Good to hear you got it running ok. Usually you can get away without rebushing, but I like to do it when I rebuild my own stuff if it's worn.

02-06-2007, 09:23 PM
Reman carbs never have rebushed throttle shafts. It's a good idea anytime you rebuild a carb (unless you've already done it in the not too distant past). So basically, if you want a quality carb, don't buy...build. Or get it built, whichever.

02-07-2007, 07:32 AM
Thanks for the help everyone[36] . Kootenaycat, I will keep you in mind if I need to have my carb re-bushed. I can always Greyhound it to you. But now that the carb is running good I have two more problems:o :

1. When I back up, the truck really shakes, is that a bad u-joint? I have yet to crawl underneath and check.

2. In drive my automatic transmission shifts from first to second, but not second to third. If I let off the throttle a lot it sometimes shifts into third. Is that the adjustment on the vacuum modulator or maybe I have a minor vacuum leak down there. I will adjust the indent cable today and experiment with adjusting the modulator.

Any help you can give me would be appreciated.

02-07-2007, 07:24 PM
U-joints appear good. Slip yoke little up and down slop but very little.

As for shifting I took off the vacuum line that goes down to the transmission and attaches to that pod that I call a vacuum modulator. I took the adjustment screw out of the end of the pod and it was clogged with dirty black debris. There is also some dark looking liquid in the little bit of rubber vacuum line that was attached to the pod. I blew out the adjustment screw. Attach the vacuum line and tested the truck a few more times. The truck ships really good into second at about 50 to 60 km per hour. It will shift into third if I get over 80 and let the gas right off. But as soon as I put that title down a bit it shifts back into second.

Anyone experienced similar problems?

02-07-2007, 10:51 PM
Have you checked for vacuum at the end of the line? Without vacuum, it will shift exactly like you describe.

02-08-2007, 05:59 AM
There is vacuum at the line down by the tranny, but I haven't checked out how much. When it's idling I can disconnect the hose and it does not stall. Checking the vacuum at the carburetor, I'm just getting over 15. I have a few manuals and home, but the info on automatic transmissions is Chinese to me. I was told the kick down cable could be stuck in the engaged position. Come to think of it the end of the cable where it comes up by the carb is frayed a bit[16] . I think it's not sliding back down. I think it's time to replace that cable.

02-08-2007, 01:31 PM
Should'nt the tranny switch from 2nd to 3rd even if I push the cable all the way back and disconnect it off the carb. The pot on the tranny if it is shot what will happen. Also I now remember last summer I had to start manually shifting the tranny from 2nd to 3rd. Now that won't even work. What gives?

02-08-2007, 10:23 PM
If the TV cable is hanging up, it will not shift to third unless you're doing something like 120km/h, and with bigger tires/stock gears, that will be even higher.

Sounds more to me like the modulator valve, you mentioned a fluid when you pulled the hose off. It is probably leaking, which would act like no vacuum, which will make the trans think the engine is WOT all the time.

If all this is good, I'd guess maybe something sticky in the valve body? I'm not an auto tranny guy, so just going by memory from school, which was a loonnnnnnng time ago. :D

02-09-2007, 07:12 AM
You sound totally right. So based on my Internet research yesterday and reading a few manuals I got and info I got from the site, I decided to replace the pod and the TV cable. Going to see family in Kamloops today so I'll pick up a couple parts when I get there!! Thanks!