The 5th 248 carb is cleaned out & going back together, but there's still some gunk in the bottom of the bore for the power piston. I've tried soaking it in B12 chemtool (plugged the hole at the bottom), but there's still enough there to make the power piston stick in the bottom a bit. I'll need to get it all cleaned out so that the piston will move freely after it's bottomed. Strange, since the piston polished up really nice, and the sides of the bore are clean. That gunk/varnish in the bottom is causing it to stick...and I can't have that when the carb is in operation. Stuck power piston is a non-starter...literally. The plastic cam on the secondary rod hanger was also shot...I cannibalized the Rembrandt carb again and used the cam/secondary air flaps as replacements. The ones on the Rembrandt were freshly plated, and looked a little nicer. I still have to try out the 4th of these carbs...I should be able to do that this week. So far, the ratty 248 is the winner. I may end up selling the 241s, since the needle/seat on the 248s seem to have better fuel control.
I thought you'd end up liking the 248 the best out of this generation q-jet.... Seems they were making a lot of "learning curve changes" thru out the '66 - '67 production run starting with the 240 and ending at the 248 just in '67 alone, continuing to refine it as the years progressed.. I was also looking at trying to fit a newer 800 cfm unit for a while, and also thought about swapping the '67 base plate or primary shaft to a newer model for the larger cfm, smaller float and leverage, but put it on the back burner as the 248 seems to work just fine for my 425 application... Some have mentioned in old threads that they preferred the 71 - 74 800 cfm 455 Buick models... Wished the base plate would just be a simple swap, as I refuse to grind the edge of my intake, block the exhaust crossover, or use a spacer... Glad it's running well for you... Your getting to be a PRO.... :gp:...
Still soaking the power piston bore, though the stickiness is getting less and less. The secondary well plugs (brass pressed-in cups) were leaking worse than ever. The soap-water test + air showed a HUGE mess of bubbles. I drilled out the leaky plugs with my 7/16" bit, and cut some fresh screw-in plugs from that anodized 1/2-20 bolt I had left over. I've tapped the wells, and screwed in the plugs with threads coated with gray marine-tex. Should hold up well. The primary wells weren't leaking, but I wire-brushed them clean with my Dremel and marine-tex'd them as well. Hopefully, I can get this one put together this week.
Okay, the gunk in the bottom of the power piston bore is finally cleaned out. I needed to use a no. 2 pencil with 1500 grit sandpaper taped around it to polish out the gunk & now the piston no longer sticks in the bottom of the bore. It pops up against the tension of the new blue power-piston spring I'm using. Here's some shots of the cleaned & re-assembled 7027248: Here's what it got from my other cannibalized cores: - baseplate from 7027146 core, new primary bushings installed (it had bushings already, but they were loose & leaking) - secondary cam, hot idle compensator & cover, lockout lever and air flaps from Rembrandt 7027241 - choke rod from 7027146 - new gaskets, float, 72 main jets and ethanol-resistant pump cup - new plugs -w- marine tex on secondary wells Still have to try out the other 248, then this one will be next. I've noticed that the accelerator pumps on some are shorter than others. Using a longer pump may decrease the travel of the pump cup in the bore, and shoot less fuel per stroke.
Looks like your going up 2 jet sizes on this one... Hope your keeping track of all the combinations... Have you compared if the New Blue Power Piston Spring your using is any longer/shorter - thicker/thinner than any of the others you've been thru so far... Nice Job on the Well Plugs... These castings are pretty thin in the cup area compared to the newer ones...
Thanks, this is the 2nd set of screw-in plugs I've done. I'm starting to get the hang of it. The blue spring is shorter & fatter than the stock long spring in the cores I've rebuilt, but the tension is pretty close...maybe a touch lighter. I'm not running a radical cam, and getting 15" of vacuum at idle, so I need a strong spring to push the rods up off-idle. At least this spring matches the blue Crane springs on my advance weights...I like blue stuff. Most of my Q-Jets are running 73 jets with 39 or 37 rods. Originally, my Rembrandt 241 carb had 71 jets and 41 rods, and it stumbled off the line all the time and had a lean-miss at idle. When I replaced it with my first 241 rebuild, I dropped the rods down to 39 and increased the jets size to 73, and the lean miss/stumble went away. I've also found that using new brass idle-mix screws with longer/sharper points has helped a lot in dialing in the idle mixture. Most of the steel screws in the cores are shorter & more blunt, and don't dial in as nicely. A couple of cores, though, have the steel screws with nice sharp & pointy ends...this latest 248 has nice steel screws installed. Because this is an early year, I need to use single-taper primary rods. The 7027146 which was installed when I bought the vehicle had dual-taper rods installed...42B. It ran really well...but leaked sometimes and using the wrong rods (too short) may have caused trouble later on. Earlier on, I also was fighting a fuel-delivery issue, and my ignition system (pertronix ignitor I) wasn't working well. Plus, I hadn't even tried the bushing fix yet. All of these things were keeping me from properly dialing-in the Q-Jet. Now, with the ignition/timing/fuel system improvements, the engine starts & idles really nice and lets me tinker with the carb as the single unknown in the equation. The only issues I have is some rough idle after a hot-soak, but that goes away after a couple of minutes. Could be my hot idle compensator isn't opening or is stuck.
I had good luck curing my off idle stumble by enlarging my idle channel restriction (and idle tubes) - I took it in increments, took me 4 tries to get it right, I went from .040 to .055.. Still dialing it in but the ICR has pretty much done the trick on the stumble,
I haven't tried monkeying with the idle tubes yet...maybe I'll try that with one of the 241s. I think I have a punch with a .093" tip to knock in the tubes & then pull the collars with a drywall screw. That's the one bit of the rebuild where I'm a little squeamish...messing with those little bronze tubes can get dicey. I had one of the secondary pickup tubes come loose one time, I just cleaned it off & tapped it back into the air horn with a little red loctite on the end.
I now have the 4th carb, my second 248 installed. The fat inlet nut I installed started leaking right off the bat, so I switched it to one of the more narrow ones and the leak is stopped. The primary shaft bushings are a bit tight, and the throttle is binding. I'm going to keep working it back & forth until it loosens up a bit, one of my other carbs had this issue before, and it went away after a few days.
Well, that sure didn't last long. First test drive, couldn't get the throttle to stop binding. Made for an interesting driving experience. Had to reach down & yank the arm under the gas pedal every time to get the idle back down. The binding got worse at higher RPM. At least my drive to/from work is only a few miles with minimal stop lights. If the primary throttle shaft needs to be worked on, I'll do that with the carb on the bench. Doing it while driving is neither enjoyable, nor is it safe. Off with it. On with number five. Vive la difference! Not just with the throttle now working as intended, but this one smokes all the others. Tons of pull off the line, smooth idle & no leaks anywhere. Looks nice too. I'm going to tweak it over the next few days as I drive it around town, still runs a little rough after a hot soak.
Just trying to keep track here... The Blue Spring and 72 Jets makes it happiest so far... Saw this tip on the net and thought I'd share it. To check the power piston spring with the engine running at idle and in gear (get someone to help or set parking brake for this) take a straw and slide it down the vent tube on the carb. (Note: this will only work on q-jets where the power piston is directly under the vent tube) If the power piston spring is to strong vs. engine vacuum, the power piston will bounce up and down raising and lowering the straw erratically with the engine idling in gear. With the engine idling and the correct spring for the engine vacuum, the power piston should stay down, only rising if the throttle is opened to reduce engine vacuum. This should be checked with the engine fully warmed up by running approx. 10 minutes to make sure that the choke is off. I haven't tried it yet, but sounds simple enough...
This thread has been very helpful to me. I have a 67 GS400 with a 70 Q-jet off a GS455 and one off a GS350, both seem to have the same base plates and I'm having the problem that tech8 referred to about the interference the primary's have with the "smiley" channel and the edge of the manifold. Could you please post a picture of your base plate and the mounting gasket you use? This would be a great help while I try to figure a way to make the more modern carb's work on my GS. I really envy your having 4 correct 67 Q-jets I thought I was doing good getting some with in 3 years of correct. This Post has been very helpful and will be even more important when I get mine running, I've learned allot. Thanks
I'll take some pics soon. I actually use the steel plate (came with car when I bought it) and the gasket which came with one of my kits for the smiley channel in the intake manifold. Originally, the plate was installed flat on the manifold, then came the thick base gasket, then the carb. It made sense to me to use the gasket in my high-end (CARS) carb kit. Now, I have it installed as: --- Rochester Q -Jet --- --- 1/4" base gasket --- --- Steel Plate --- --- smiley-channel gasket --- --- Intake Manifold --- No vacuum leaks, and it runs smoothly. ---------- Post added at 12:01 PM ---------- Previous post was at 11:55 AM ---------- I also recall one of Cliff's earlier threads about re-manufactured (i.e. junk) Q-jets with the base plates having thin brass bushings instead of the oil-treated bronze bushings on the primary shaft. That's exactly what the original Q-Jet (7027146) had when I bought the car, and those are the bushings I ended up replacing. I was wondering when I took it apart: "okay, the primary shaft is loose & rattling...it needs the bushing fix." Then I took the primary shaft out & saw bushings already installed and thought: "wait...this one already *has* bushings installed. Why would it be rattling & leaking?" Answer: because these bushings are the cheap brass ones that don't cut it. Get 'em outta there! Put in the good stuff.
Here's some shots of number 5, plus a short video of the vehicle at idle. The audio on my camera is not too good, plus there was some wind & some beeping from some guy's car alarm, but you get the idea of the idle. It's at about 700 RPM in park.
Ah-ha. Glad I took those pictures. I noticed something I hadn't seen before: my vacuum line to the heater flow valve is missing. I could have sworn I'd put it back on. Just checked it: the line was cracked lengthwise and slipping off. Trimmed it and put it back on. All good now.
Number five is still going well, though cold starts are still a little tricky. My accelerator pump is functioning, but may not be shooting an optimal amount of fuel per stroke. My choke coil may not be pushing up as hard when cold. I got lucky and scored another thermal choke coil off of evilbay, used but in excellent condition. It has been blasted and primer-prepped, ready to try out. I haven't replaced the idle tubes yet, but I have a bunch in stock and did a test pull on one of my 241s. Only thing is tapping them back in without dinging/damaging them is tricky...I need to use a piece of wood or plastic to keep them pristine.
Interesting thread, I have a couple of those here. They have AY rods, my GS carb has AY rods. The parts book says AZ, but they are the same I think. I had the stock correct type 2 on my GS400. It ran so-so, it was supposedly rebuilt before I got the car. If the car sat for a couple days, it wouldn't start, no gas. I suspect the plugs were leaking. I bought another carb that was all super duper plated, it was supposed to be the right type 2, numbers matching. The carb ran pretty well until Spring. The car would not start easily. I had previosly adjusted the choke + cold starts were great. So...I'm trying to figure the prob, and I notice the throttle doesn't fully open. Look at it closer and notice the accelerator pump doesn't depress all the way, so it wasn't getting a full shot of gas + wouldn't close the choke either. This carb has like less than 2K miles on it! I take it off the car, and tear the air horn off it. My new hi-po gartered accel pump is jammed! I decide to look it over better, + the secondary rod hanger is different than my other carb. The choke bracket on my originals has like notches on it, this one doesn't. The hangers are different letters. The parts book says 430 + 400 use the same hanger, but it's a replacement 1 size fits all. It seems to have the right secondary rods, but the hanger is M which is pretty low on the totem pole. I know the holes elongate, so they change them sometimes. I have both major carb books. Put a new accel pump, it's running good now hot + cold. I'm not messing with in any more til Winter. I'll rip it apart then and check the jets. Anyways...I'm curious what hangers are on those 67 430 carbs. What are they? My other question is the inlet nut. Book says a paper filter..427...mine has a bronze filter and paper won't fit, diam is too large. Weird...all my carbs have different inlet nuts it seems. Maybe peeps had the same prob as you and changed them.
