My Own Vice Grip Garage - Getting the 250 i6 Running Again

[Luke87gt]

Hi guys, some of you may be aware that I acquired a ‘69 c10 last year (250 i6, 3OTT). The truck sat for years with the previous owner before he decided to list it for sale. It was shipped from Washington to California and was able to get onto the trailer and off the trailer under its own power, but barely.

Since then, life happened and believe it or not I actually haven’t started it since it was driven into the garage last year.

Today I finally managed to remove the Rochester MonoJet carb for rebuild. It looks pretty rough as you can see from the pics.

Being new to carbs, I’m hoping you may be able to help me identify several parts of this carb. I’ve numbered the pictures for reference:

#1: what is this screw? It can’t be the idle screw as that’s on the back of the carb. Anyone know what it does?

#2: what is this capped vacuum line? Am I correct to assume that when I do power brake conversion, this is the vacuum port I will utilize for that upgrade?

#3: this port was connected to the vacuum advance. By the way, should I replace the vacuum advance? Do these have a wear out and go bad?

#4: what in the world is this? It looks to be a plate with 3 holes and it swivels. However, it wasn’t attached to anything. I wonder if that’s right or if I’m missing some connection?

By the way, one of the two nuts that holds the carb to the manifold was finger tight. That can’t be good :-)


Beyond the carb, I have a set of new plugs, wires, coil, cap, rotor, condenser, points, and fuel filter. I am about to order a new gas tank and replacement lines. I’ll get those items replaced, crank it, and see where we are.

I hope to utilize this as a progress thread to get this engine running again (I hope).

At some point I’ll ask for help with verifying timing, checking vacuum, and setting points.

Big thank you guys for the help!

[Steeveedee]

Not all parts in pic are on your carb.
https://www.carburetor-parts.com/mon...g1ElE4Y6XI5Her

[RichardJ]

#1 Idle Mixture screw. Not idle speed screw.

#2 Could have been available for some option such as auto trans. power brakes generally use a much bigger hose. Square head, tapered thread plug in manifold at very bottom, center of first image would be good for P. brake.

#3 Vacuum advance diaphragms do go bad and leak. Apply vacuum to test.

#4 High speed idle cam. Part of your manual choke. It may be missing a choke rod.

[HO455]

Here's a link to Mike's carburetor parts. It has good photos and descriptions of the choke system. Shows the missing linkage from your #4.

https://www.carburetor-parts.com/Mon...Tsm2VC1pqOgehf

[Luke87gt]

Great information, thank you all. Mike’s carbs looks to be a great resource, wow.

This total carb newbie now knows where his idle mixture screw is and that his carb apparently is missing a choke rod (fast idle). I’ll be sure to get that during the carb rebuild.

Question: what’s the procedure for setting the idle speed and the mixture? My understanding is that you warm up the engine with the choke engaged, then set idle speed, then tune the mixture to the sweet spot. Any tips on that?

Thank you

Luke

[MikeB]

Originally Posted by Luke87gt

Question: what’s the procedure for setting the idle speed and the mixture? My understanding is that you warm up the engine with the choke engaged, then set idle speed, then tune the mixture to the sweet spot. Any tips on that?

I welcome better explanations, but here's mine for a start!

• Start with idle mixture screw 1.5 turns out from fully CW
• Warm up engine to normal operating temperature with choke fully open and fast idle speed cam disengaged
• Set idle speed screw to desired idle speed
• Turn mixture screw CW until engine speed slows, and then turn
  it CCW until it picks up again. Shoot for max RPM, but don't go CCW past where you get the max RPM.

Reset idle speed screw as many times as you need to. It's kind of a dance between the two.

[Luke87gt]

Very good summary.

I assume this procedure only applies once timing has been set and confirmed stable vacuum?

[70STOVEBOLT]

Originally Posted by Luke87gt

Very good summary.

I assume this procedure only applies once timing has been set and confirmed stable vacuum?

Correct. If you have a vacuum tuning gauge, you turn the mixture screw out
(CCW) until the vacuum reaches it's highest point. You will have to reset the idle speed screw after this is done. Don't forget, disconnect the vacuum advance and plug the port on the carb while setting the initial timing.

[hewittca]

Nice! I am in to follow this thread since I too have an old i6 that I will attempt to revive. Good luck!

[Luke87gt]

I debated rebuilding the carb myself but given that I’ve never done that before and I’m trying to get this old engine running, I decided to send the carb out to CarburatorUSA in New Jersey. Should have it back in a couple weeks.

[Steeveedee]

Do you do any kind of model building, such as scale plastic or some such? You'd be able to rebuild that carb, if so. That monojet is dead simple, as is a Quadrajet, believe it or not. I'm really a 2-pound hammer kind of guy, but even I can rebuild a Q-Jet carb and make it work properly.

[Rust_never_sleeps]

Originally Posted by Luke87gt

I debated rebuilding the carb myself but given that I’ve never done that before and I’m trying to get this old engine running, I decided to send the carb out to CarburatorUSA in New Jersey. Should have it back in a couple weeks.

Gotta pick your battles if you want to stay on schedule

[Luke87gt]

Thank you for the encouragement.

Given that this engine is tired and needs no shortage of help, I want to take the carb out of the equation and leave it to a pro this time.

Next time, I will rebuild it!

[MikeB]

Originally Posted by Luke87gt

Thank you for the encouragement.

Given that this engine is tired and needs no shortage of help, I want to take the carb out of the equation and leave it to a pro this time.

I understand completely!

Be sure to send us pictures and tell us how well it works.

[Luke87gt]

Carb shop called and said that the carb was in really bad shape but looking new and back in transit to me.

When I replace the spark plugs, should I give the spark plug holes a spray of any oil since the car been sitting for so long? If so, what oil and amount is advisable?

[68 C10 Driver]

Definitely share pics of the rebuilt carb when it gets back to you.

[MikeB]

Originally Posted by Luke87gt

When I replace the spark plugs, should I give the spark plug holes a spray of any oil since the car been sitting for so long? If so, what oil and amount is advisable?

I'd just make sure the oil looks good on the dipstick. I guess spraying some kind of lubricant into each cylinder would help, but I don't know what to suggest.

[RichardJ]

>>carb was in really bad shape but looking new<<
Not sure what that is supposed to mean.

Be conscious, that rebuilt carbs ARE NOT PLUG-N-PLAY . You still have to adjust the mixture screw. You still have to adjust the idle speed. You still have to adjust the choke cable so that you have full choke on-off and check that high speed idle works properly.
Bench adjustments on a carb only go so far. It then has to be adjusted for your engine, running and warmed up.

>>give the spark plug holes a spray of any oil<<

If the plugs are already out, what is that supposed to do. If the plugs were really carboned up or hard to get out you probably should run a plug thread chaser.
Aluminum heads call for Anti-Seize compound, but that is controversial.
Be sure you have the correct plug type. Some heads use tapered plugs and earlier have gasketed plugs. Various reasons why you could have the wrong ones, so it doesn't hurt to check.

For reference - https://67-72chevytrucks.com/vboard/...t=tapered+plug

[MikeB]

Are you asking if you should lube the spark plug threads or cylinders?

[Luke87gt]

Originally Posted by MikeB

Are you asking if you should lube the spark threads or cylinders?

Cylinders

Sorry for not being clear.

[Luke87gt]

Here are some pics of the rebuilt Monojet.

Thing looks new, will install it soon.

After that replacing the tank, sending unit, and lines…

[Steeveedee]

Nice plating job! May it extend to the operation, thereof.

[Luke87gt]

Originally Posted by Steeveedee

Nice plating job! May it extend to the operation, thereof.

Thank you sir, let’s hope

Still have the plugs, wires, coil, cap, rotor, and points to replace.

Just not sure what the health is of the engine itself yet. The truck did get off the trailer and into the garage on its own power, but barely… I guess that’s promising right?

[Rust_never_sleeps]

What was it, 3 weeks turn time on the carb? Seems pretty good

[Luke87gt]

Originally Posted by Rust_never_sleeps

What was it, 3 weeks turn time on the carb? Seems pretty good

Just over 2wks