How to choose a monojet for 1967 292

[georgieb51]

When I bought my truck it was a project. I now have the engine back in it with some sort of monojet that came with a pile of parts and it runs extremely poorly even after cleaning it out. My mechanic says it is missing some parts. I would like to just buy a new one or a rebuilt one and know nothing about monojets. Are the ones for a 292 different from the 250s? The photo shows the one I have. It is not working and I have no idea what it really is. ( I apologize for the sideways photos).

[dmjlambert]

I had a Quadrajet that came on my truck that was not in good shape and needed more than just rebuilding. I was pleased with the replacement I ordered from National Carburetors. It was inexpensive and it works with gasohol. They have all carburetor types. I don't know if you're interested in customization, but for me they did not charge any extra to build one that uses 1969 throttle linkages and had an electric choke based on the 1985-86 year carburetor. It has been about 7 years, so you would have to call them to see if there's still options for something like that.

[indymachinist]

Good looking stepside!

I had a monojet that I attempted to clean and rebuild and everything else. Never got it working right.

[54blackhornet]

I had a 250 in a 68 GMC 1500. Pulled it and dropped a completely rebuilt 292. Besides the Momjet issues it destroyed the motor mounts often. Chinese rubber just couldn’t handle the torque. I was told GM had a retaining wire type restraint to prevent the mounts from ripping out. I ran it for a while with the 250 MonoJet and had no problems with the carb. The 292 is a beast..good luck 68Orange Sunshine should be able to help.

[georgieb51]

Someone on this link: https://67-72chevytrucks.com/vboard/....php?p=3644928 says that 1967 never used a monojet, but instead used a B carb from Rochester Does this sound familiar to anyone?

[georgieb51]

Someone on this link: https://67-72chevytrucks.com/vboard/....php?p=3644928 says that 1967 never used a monojet, but instead used a B carb from Rochester Does this sound familiar to anyone?

['68OrangeSunshine]

Originally Posted by georgieb51

Someone on this link: https://67-72chevytrucks.com/vboard/....php?p=3644928 says that 1967 never used a monojet, but instead used a B carb from Rochester Does this sound familiar to anyone?

My '68 had a MonoJet, once.
The B Carb was also a Rochester.
Carter made a single barrel YF. Not sure if that ever had Chevy applications.

['68OrangeSunshine]

Originally Posted by 54blackhornet

I had a 250 in a 68 GMC 1500. Pulled it and dropped a completely rebuilt 292. Besides the Momjet issues it destroyed the motor mounts often. Chinese rubber just couldn’t handle the torque. I was told GM had a retaining wire type restraint to prevent the mounts from ripping out. I ran it for a while with the 250 MonoJet and had no problems with the carb. The 292 is a beast..good luck 68Orange Sunshine should be able to help.

Well, thanks for the good word Black Hornet, but really, I gave up on the Rochester MonoJet in 1978 when I went to an Offenhauser aluminum intake and a Holley 390 CFM 4 barrel. In 2005, with a complete 292 rebuild, I upgraded to a Edelbrock 1404 500 CFM 4 Bbl.

In 1978, only 10 years after being new, I probably could have bought an NOS 292-set up MonoJet from a Chevy dealers' parts counter, but I was after high performance then. I never guessed I'd live this long, or still be running my '68 C/10 Stepside w/Factory L25 292 L6 fifty years later.

In the aftermarket, auto parts stores only carry a generic, Any-L6 MonoJet. I believe, back in the day, the Factory had a bigger bore, wider jetted, M-Jet for the 292. But I'm not expert there, sorry.

As for Motor Mounts, I got the Squarebody style Safety Mounts, on my machinist's advice. They have curved metal hooked edges, that interlock if the rubber parts. Same bolt holes, but threading the bolts is trickier. Great peace of mind.
The monster Torque is the reason the L25 required motor mounts forward instead of midships, like the 230/250 L6s.

[geezer#99]

That’s what it is!

[geezer#99]

I see a timing light on the ground.
What’s your timing set at?

[georgieb51]

Originally Posted by geezer#99

i see a timing light on the ground.
What’s your timing set at?

4 btc

[geezer#99]

Bump that up to 12.
Your poor running might be lack of timing.

Do you have stock points or an hei?

[georgieb51]

Originally Posted by geezer#99

Bump that up to 12.
Your poor running might be lack of timing.

Do you have stock points or an hei?

HEI. I tried it at 8 too. Sometimes it idles fine and sometimes it barely starts, But I can never get it out of my driveway. I can try it at 12

[geezer#99]

Do You have your vac advance hooked up?
Is it plugged off when you set timing?
Do you have a working choke?
Six bangers run cold at start up.
Have you adjusted your mixture screw on the carb?

[georgieb51]

Originally Posted by geezer#99

Do You have your vac advance hooked up?
Is it plugged off when you set timing?
Do you have a working choke?
Six bangers run cold at start up.
Have you adjusted your mixture screw on the carb?

Thanks Geezer. I installed a working choke. There is not much range of movement but it does work.
Adjusted idle on the carb.
I will double check with my buddy who is a real mechanic who was with me in my driveway to do the timing. I am pretty sure we had the vacuum advance plugged when timing. But I will check. He took the carb apart and soaked it clean and got a lot of stuff out but the told me there are interior parts that are missing that should be there but are not.
I think the carb is quite suspicious. I can use it as a core to get a replacement from one of these companies that rebuilds them and might actually know what a 292 is. Just not sure if I should get a Model B or a Monojet-- or maybe it does not matter as long as it is designed of the 292.

[Wrenchbender Ret]

That carb in the photo is not a monojet. It is a model B Rochester. Like posted earlier to MJ started in 68. The 292 carbs are different from the 250 & smaller engines. They look similar but the throat & venturi are larger on the 292.

George

[georgieb51]

Originally Posted by Wrenchbender Ret

That carb in the photo is not a monojet. It is a model B Rochester. Like posted earlier to MJ started in 68. The 292 carbs are different from the 250 & smaller engines. They look similar but the throat & venturi are larger on the 292.

George

Thanks for letting me know what I have > Until this posting I had never heard of a Model B. I wish I knew what you knew. I have no idea to tell what is a Model B vs a Monojet. But I will be looking for a Model B for sure.

[geezer#99]

Linkage will be different.
Best stay with the ‘B’.

[georgieb51]

Originally Posted by geezer#99

Linkage will be different.
Best stay with the ‘B’.

Makes sense to stick with t the Model B then.

[geezer#99]

Talk to Mike!
He’ll know what you need.

https://www.carburetor-parts.com/

[RichardJ]

>>The monster Torque is the reason the L25 required motor mounts forward instead of midships,<<

'68 sunshine ? You of all people.

They moved the mount, because they were forced to move the fuel pump. The 292 crank with 4.125" stroke interfered with the fuel pump lobe on the 250 camshaft. 250 - 292 cams are not interchangeable.
I don't know the time line for the 194, 230 and 292 production. This might be a chicken n' egg thing.

If you are staying with the stock intake and 1bbl, then I would agree the Rochester B will serve you well. For me, like '68orange, I went with a Clifford and a 4bbl. You need to make a bunch of changes to make 4bbl worth while.

I can't see a dist vacuum line in your photo. The vacuum port is a threaded port.
The vacuum port on the manifold appears to be correctly connected to the PCV valve . Is there a fresh air from air cleaner, intake on the valve cover?

Your dash probably has a manual choke knob so I wouldn't try to mess with a Rochester BC or BV auto choke version.

['68OrangeSunshine]

Originally Posted by RichardJ

>>The monster Torque is the reason the L25 required motor mounts forward instead of midships,<<

'68 sunshine ? You of all people.

They moved the mount, because they were forced to move the fuel pump. The 292 crank with 4.125" stroke interfered with the fuel pump lobe on the 250 camshaft. 250 - 292 cams are not interchangeable.
I don't know the time line for the 194, 230 and 292 production. This might be a chicken n' egg thing.
.

All the ''Late Chevy L6s'' [to use I-I's classifcation] first came out in Model Year 1963, starting Fall '62. They replaced the Stovebolt Sixes -- 218, 235, 261.
I did not know about the extra width of the L25 crank. I made a guess on why the 292's mounting was different from the 250's.

[CarolinaHD]

I got my replacement Rochester B from Rock Auto and it's been working fine for 3 or 4 years now.

['68OrangeSunshine]

Originally Posted by CarolinaHD

I got my replacement Rochester B from Rock Auto and it's been working fine for 3 or 4 years now.

I just scoped RockAuto for '67, 292 Carbs, and they are in stock. About $200.
Looking for '68 Rochester Monojets -- out of stock.
Good hunting.

[georgieb51]

Originally Posted by CarolinaHD

I got my replacement Rochester B from Rock Auto and it's been working fine for 3 or 4 years now.

Wow! That is good to know. I will check them out.