HELP Dualjet vacuum pull off ruptured twice in 6mos?

[Uncle Dan]

(1979 MC, LG4 305, dualjet w/hot air choke, carb rebuilt by me 12/17 with new choke housing/coil, new primary pull off, deleted secondary pull off.)

So this carb has been doing great since I brought it back to life with one exception: choke and pull off adjustment. I've gotten it squared away twice now, and each time after a few weeks or months it'll come down with a hard start condition. It will turn over & fire but immediately stalls out; no amount of throttle pumping or feathering will keep it going.

Both times, my Pink Panther-style diagnostics revealed a choke butterfly that wasn't opening at all after the engine fires up & creates vacuum, leading me to put a MityVac on the pull off & find that the diaphragm has ruptured. Well, let me back up. That's what happened the FIRST time. Second time, after a few weeks with new pull off #2, the shenanigans started again this morning. I suspected the same thing & pulled the air cleaner housing. Sure enough, butterfly was staying 100% closed. I dicked around with things a minute & spun the choke around until it would stay open & running when cranked, then I accidentally tapped the adjustment screw on the pull off and it dropped like the hammer on a pistol. POP! I re-set the choke butterfly to closed, cranked the engine over, and the pull off wouldn't open the butterfly. Same no-start condition. MityVac now says pull off #2 is ruptured.

Spidey sense is telling me something could be sticking, or bent, or misaligned? Pics attached for reference. I did lube the fast idle cam a bit with WD40 but it didn't help. Maybe its just crappy aftermarket parts? Any clues what it might be, given my description? Would I be better off just converting to a manual choke? I'm about ready to.

 

[Bonnewagon]

Any backfires? That would kill them quick. But I think you nailed it- cheap crappy parts. Try getting an original off a parts carb or at least a good national brand. A working automatic choke is a beautiful thing and you should keep it by all means. Don't lube carb linkage- it just attracts dirt. EDIT: Check the hole in the end of the pull-off that the hose attaches to. It should be tiny like a pinhole. That is so the thing retracts sloooowly. Too big a hole lets it slam and maybe break.

 

[RegalBegal]

Try here....
https://quadrajetparts.com/rochester-choke-pull-fits-1975-1985-chrysler-p-223.html

 

[Uncle Dan]

Any backfires? That would kill them quick.

None noticed.

But I think you nailed it- cheap crappy parts. Try getting an original off a parts carb or at least a good national brand. A working automatic choke is a beautiful thing and you should keep it by all means.

Both were "Standard Motor Products" from RockAuto. I don't really know where that puts them in terms of relative quality. My next move was going to be NAPA, but I see from a little internetting that they make a lot of fuel management parts for NAPA.

Don't lube carb linkage- it just attracts dirt.

Wondered whether I was making a mistake. Usually when I catch myself wondering that, its enough to get me to stop & back up. This time I squirted it.

EDIT: Check the hole in the end of the pull-off that the hose attaches to. It should be tiny like a pinhole. That is so the thing retracts sloooowly. Too big a hole lets it slam and maybe break.

This one looks a little bigger than that...see pic. My brother suggested that the vacuum diaphragm may have been somehow forced too far in the opposite direction and hung there, then dislodged and slammed shut when I nicked it with the screwdriver while the engine was running. Either way, I'll be looking for an OEM unit or using RegalBegal's link.

Fileff

• Uncle Dan
• Jun 19, 2018

 

[79 USA 1]

Uncle Dan,
Where are you located? I still have the carb and intake from the blue Monte Carlo in my avatar picture. I put a Q-jet on the 267 when I bought the car with 13,400 miles so I'll check to see if its any good and if so you can have the choke pull off for the price of shipping.
I have to ask... 79 Monte Carlo with the LG4 305 should have a Q-Jet (4 barrel) VIN letter H in the 5th position. The Dualjet came on the 267 engine VIN letter J in the 5th position. Is the engine original to the car or was the 2 barrel swapped on to it?

Bob S.

 

[Bonnewagon]

Standard is no longer the standard. Pun intended. I just went through hell with Amazon about 3 Standard oil sending units, all failed less than a year, Amazon was crappy about warrantying them. I finally digged deep and bought an Airtex-Wells unit. Three years old and doing great. That hole looks kinda big. As I said, when in use or tested with the Mity-vac, it should pull slooooowly, not fast. The hole is usually so small you almost don't see it.

 

[Uncle Dan]

Uncle Dan,
Where are you located? I still have the carb and intake from the blue Monte Carlo in my avatar picture. I put a Q-jet on the 267 when I bought the car with 13,400 miles so I'll check to see if its any good and if so you can have the choke pull off for the price of shipping.

I'm in northern GA. That's a generous offer, and I would take you up on it had I not just picked up another from NAPA. This one is made by "Echlin". We'll see. Thank you, though.

I have to ask... 79 Monte Carlo with the LG4 305 should have a Q-Jet (4 barrel) VIN letter H in the 5th position. The Dualjet came on the 267 engine VIN letter J in the 5th position. Is the engine original to the car or was the 2 barrel swapped on to it?

Bob S.

Eagle eye..... The car's a J-code, but the engine appears to be a swap. I believe it to be about a 1980 model 305, maybe from an Impala or Caprice?? The number stamped on the block is 14010201. EID is F1015CUA, and the VIN code/assembly stamp is 1AS108229.

The 2-barrel carb came from who knows where. casting number is 17059140, and I remember digging around on the net and finding somewhere that it might have originally graced a 1979 Buick with an A/T.

 

[79 USA 1]

I'm in northern GA. That's a generous offer, and I would take you up on it had I not just picked up another from NAPA. This one is made by "Echlin". We'll see. Thank you, though.

I've had good luck in the past with Echlin brands through NAPA. Let us know the results!

 

[Uncle Dan]

Interim update: this part has just as big a hole as the last one. It'll open just as fast as I can put the vacuum to it.

Got me an orange & white EGR delay valve (BWD part # EC314) & put it inline between the Mityvac & the pull-off. Slows it down & modulates it perfectly.

We'll see how it actually works on the carb when I get a minute.