Builds The Clustertruck Rides Again - Refurbishing a 1975 Chevota

[Weber Sarge]

The whole problem with using any adapter is a lack of meat under the center of the adapter itself on the manifold - it makes it a lot harder to prevent heat and cool cycles from causing leaks over time . The only way I've Q-jets work correctly is when they are installed on a proper manifold made for them - I think Edelbrock has a specific one or maybe it was Weiand or something...? Don't mess with Chebbies much anymore , bit fuzzy...
Sarge

 

[Cdaniel]

Still think the choke port is the likely leak. Your base gasket inspections have told you the gasket isn't the problem. And that 4 hole base gasket will take care of any possible mis match to the carb. I've run that carb, that gasket, on that style manifold for decades with no issues.

 

[RWBeringer4x4]

Still think the choke port is the likely leak. Your base gasket inspections have told you the gasket isn't the problem. And that 4 hole base gasket will take care of any possible mis match to the carb. I've run that carb, that gasket, on that style manifold for decades with no issues.

I agree that the choke port leak is present - pretty much proven by the fact that the engine stalls when I spray the choke. SuperBuickGuy brought up a good point though - about checking the internal vacuum passages on the baseplate to make sure they're covered properly. Figured I would start there, before I start RTVing or otherwise plugging vacuum passages. I'm going to wait to get the final word back in the baseplate from Sean at SMI. If he thinks everything looks OK, I may pursue the choke plugging approach and see where that gets me. If I still don't get improved mixture screw response, I'll buy a 4-hole gasket.

 

[SuperBuickGuy]

Edelbrock 2696

The most important part is that you buy an adapter with 4 holes rather then 1 big one. Most stores like O'Reilly's have these on their shelf (though, generally, a Mr. Gasket brand). The other thing to be aware of is the hole size can vary.... but with that said, it's just additional knowledge since I'm sure your carb is not a 875 cfm version.

whatever you do, do not silicone any vacuum passages...

 

[RWBeringer4x4]

Ok guys, the feedback I got from SMI:

1. The gasket fits the intake manifold fine. No adapter plate needed. I'm inclined to agree, since, as I said previously, It doesn't seem to leak.
2. The gasket fits the baseplate fine. It is apparently normal/non-harmful for that vacuum channel to be exposed.
3. As long as the mixture screws are responsive enough to kill the engine, they're OK. I find it strange that max vacuum is showing up at about 3/4 turns out, but the mixture screws will definitely kill the engine if I run them all the way in...

In short, I may hook this thing back up with what I've got and just run it; maybe plug the choke leak. Honestly I think I'm splitting hairs. Ive got a solid, low idle and good throttle response, and I'm not really detecting any stumbles on or off the throttle. Choke seems to function properly...Maybe I just have unrealistic expectations about mixture screw sensitivity...

 

[SuperBuickGuy]

and always follow the advice of the folks that took your money....

watch your spark plugs over the next few weeks - if you start getting specs on the insulator (the bit below the electrode), we'll need to revisit this.

 

[RWBeringer4x4]

and always follow the advice of the folks that took your money....

watch your spark plugs over the next few weeks - if you start getting specs on the insulator (the bit below the electrode), we'll need to revisit this.

When the folks that took my money build quadrajets for a living, and have a good reputation for standing behind their products, I'll give them the benefit of the doubt until I have reason not to.

That isn't to say I don't have five or six other valid opinions and options in the responses here. I'm certain the 4-hole gasket would work just as well. Better? Time will tell, if I can't get this one dialed in properly, that's the next step I'll take. I'm getting a bunch of different messages here - from different gaskets, to adapters to entirely different intakes. Can't try them all at once!

I simply can't understand how running an adapter is going to help in this case. The baseplate gasket mates the top of the intake perfectly, I have no external leaks at the base, and it's the base gasket provided by the rebuilder as a match for the carb he provided.

I'm a scientist - by nature I try to limit variables to one thing at a time. Aside from less mixture screw response than I'd expect, I really don't have any outward signs of a vacuum leak (eratic idle, stumbling, etc.) anywhere aside from the choke.

All signs point to a leak in the choke housing, but I'm not seeing a reason to suspect the baseplate.

As for the plugs - unfortunately they probably won't be too telling. The valve seals are toast so the plugs end up pretty black pretty quickly. Alternatively, some of the blackness might also be a result of all the futzing around I've done with the prior carb and timing over the past few months, plus loads of prolonged idling. I'll probably drop in a new (clean) set of plugs and see what they look like after a few tens of miles of driving.

Naturally, I mean no disrespect or offense to anyone who willing provide advice/insight as willingly as you all do...obviously I'm pretty green when it comes to this stuff and maybe I'll end up eating some serious crow, just trying to approach this one variable at a time.

 

[SuperBuickGuy]

it is easy enough to pull the choke off and put that cork seal in (presuming it's not there)... be careful with the linkage...

 

[RWBeringer4x4]

it is easy enough to pull the choke off and put that cork seal in (presuming it's not there)... be careful with the linkage...

Yeah, the only thing I remember that was a real pain when removing the choke was that little linkage the drops down into a slot in the main body of the carb - the choke's center shaft connects to it. I Can't imagine being able to get that lined up without completely disassembling it to guide it from the top of the slot...It's definitely a situation where I will really CONFIRM I have a leak there, as opposed to making the assumption and disassembling.

I wonder if just removing the screw that holds the choke on would allow me to back the choke housing out enough to drop the plug in without disconnecting that internal center-shaft linkage...

 

[RWBeringer4x4]

Ok, well, I bolted everything back up tonight, fired up the truck, and let it come to temperature. I sprayed all around the carb gasket. No leaks, no change in idle. Next, I disconnected the choke and removed the cover. I can now confirm beyond a shadow of a doubt that I'm missing the plug between the choke housing and the carburetor.

So, I'm thinking @Cdaniel was right:

Quadrajet Choke Housing seal and vacuum fitting

What Sean @ SMI had previously suggested likely won't work. Sticking some RTV inside the choke housing to cover the vacuum hole internally will stop the whistling, but what it WON'T stop, is the leak where the choke housing meets the carburetor body. As evidenced in the video below, it is leaking there, as well, since there is no plug or seal. Sorry, in advance, for the shaky camera work:



So, I think I'll send this video off to Sean and see what he says. I hate to consider sending this carb back to California for something this basic...then again, I also don't feel like I should have to disassemble a brand new (and pricey) rebuild and repair it.

 

[Honger]

So, I think I'll send this video off to Sean and see what he says. I hate to consider sending this carb back to California for something this basic...then again, I also don't feel like I should have to disassemble a brand new (and pricey) rebuild and repair it.

Good call. This guy has been talked up as if he's the Jim C. of quadrajets... And from what I've learned Jim C. would set things straight if he shipped you a carb with a vacuum leak for some reason.

Oh, and why don't you just get a 2F?

(Couldn't resist...)

 

[RWBeringer4x4]

Good call. This guy has been talked up as if he's the Jim C. of quadrajets... And from what I've learned Jim C. would set things straight if he shipped you a carb with a vacuum leak for some reason.

Oh, and why don't you just get a 2F?

(Couldn't resist...)

I wouldn't say he's quite "Jim C" level, but he has been helpful and responsive. I was able to back the choke housing mounting screw off enough to get a rubber plug into the leaking leg (which was absolutely open to atmosphere!) per Sean's recommendation. Spent yesterday morning getting it all dialed back in. I get better (still not great) idle screw response - they seem to want to sit at about 1 turn out, so that's where they're staying! I get a pretty consistent idle at about 650 RPM, notched up the timing just a tad to 14 degrees advanced at idle.

My only issue now is that the spring-loaded idle adjustment screw stripped . 100% My fault, but DAMN that thing is hard to move. For now, not a huge deal as I don't imagine I'll be fooling with the idle anytime soon.

I took it out for a test drive Saturday afternoon. Runs great, but I had the choke wound too tightly. The choke would want to close completely, even with the engine hot, and then would take a couple minutes of heating the bimetal up before it would open enough to allow the fast idle to kick down. The result was a VERY rich mixture through a warm engine, and a truck stuck idling at 1300RPM in a parking space kicking out black smoke, that couldn't move until the kick-down responded. Long story short, I loosed up the choke, but haven't had a chance yet to see if I loosened it enough.

Honestly, I keep looking longingly at 2F's that come up for sale on craigslist... If I hadn't bought ALL the proper V8 conversion components already, I'd be a lot more inclined to go back...That said, now that the 283 is (mostly) properly tuned and running a good carb, it has some serious guts! The 40's back tires want to break loose pulling away from red lights, etc. particularly with the Aussie locker back there and the touchy clutch.

 

[SuperBuickGuy]

Oh, and why don't you just get a 2F?

(Couldn't resist...)

Because he likes twice the power, much better mpg, inexpensive parts, the ability to buy parts anywhere, lighter front ends, oil pressure... still, I don't get what the hubbub is - they're both Chevy motors

 

[Robs76fj40]

Because he likes twice the power, much better mpg, inexpensive parts, the ability to buy parts anywhere, lighter front ends, oil pressure... still, I don't get what the hubbub is - they're both Chevy motors

don't get it either....

 

[RWBeringer4x4]

In order to further beat the horse carcass - for me it's a simple matter of "it was there when I got it." It's cheaper and easier to move forward with a V8 than it is to move back to a 2F.

Plus, what SBG said is correct - parts availability for a SBC is ridiculous. The 2F, unfortunately, is going to be problematic in the coming years. If the 283 croaks, I can buy a brand new 350 engine for half the cost of a 2F rebuild.



Honestly, my plans for this truck are pretty tame - it will have a pretty easy life under my ownership. Power, torque, and fuel economy are secondary to running, driving, and stopping. It's a toy - something to mess with on the weekends. The engine will always be "whatever I can find that will keep it going for cheap(er)" at least until the day comes where I have nothing else to fix or a lot more money than I do now!

 

[subzali]

I still agree that keeping the v8 makes good sense, but parts availability is almost counter productive from what I've seen the past few pages. Quadrajet carb that could be from a truck, a Buick, or whatever, but they're all different but they also all fit with myriad adapter and intake manifold combinations seems to me to be such a headache since they don't all work.


Sent from my iPhone

 

[RWBeringer4x4]

I still agree that keeping the v8 makes good sense, but parts availability is almost counter productive from what I've seen the past few pages. Quadrajet carb that could be from a truck, a Buick, or whatever, but they're all different but they also all fit with myriad adapter and intake manifold combinations seems to me to be such a headache since they don't all work.


Sent from my iPhone

That's not so much an issue with the parts as it is that I am completely unfamiliar with carburetors and old engines. I was born and raised in fuel injection - so it's mostly my own ineptitude slowing me down!

 

[SuperBuickGuy]

if you can't tune a carb, you can't tune EFI... it all works on the same principles. In many ways, it's easier to learn tuning on a carb because it's so analog; efi requires the same inputs but adds a layer of complexity when parts don't work as they're supposed to. A plugged jet is really easy to see, a TPS that isn't working correctly in its mid-range is not. Not because it's not easy to test, but if you have a stumble from part to WOT, do you first get your testor out to see if the rheostat is outputting properly? heck, I do efi and that's rarely my first stop in diagnosis.

 

[RWBeringer4x4]

By "born and raised on fuel injection" I mean - Until I bought a 40 all I had to do to keep a car running was change the oil and put gas in it. This is yet another dead horse that could be beaten for hours - $hi+ Rick does not know how to do.

That's why I bought a basket case FJ40 frankentruck. That's why I'm here, annoying all you fine folks with incessant questions. Deciphering the mysteries of carburetion is just another step in the long journey of me figuring out what the hell I got myself into. I come to you guys in an effort to not break anything TOO expensive, but sometimes you have to break stuff to learn how to fix it. It's all part of the fun!

 

[SuperBuickGuy]

have you, actually, broken anything yet?

I get it, you're working back into the 20th century, you'll make 21st century in a few years... good