Inline 6 help-smog?

[bretcopsey]

We put a deposit down on a 68 C10 with inline 6 yesterday, supposed to finish up the deal this week. The owner said he removed a "rusted through pipe" from the head years ago and plugged the holes with bolts. Since removal, there is a hesitation at about 1/4 throttle. The best I can tell, this would have been an A.I.R. Manifold (smog), but there was no pump? I'm thinking I should be able to get this to work without sourcing all of the smog equipment, but what should I be looking for to eliminate the hesitation? Just carb/timing adjustment?

[nascarguy320]

I would check timing and carb first. that's a good place to start at.

[Wrenchbender Ret]

With a little tuning & carb work it should be easy to fix. Try advancing the timing a few degrees. You can adjust the metering rod on that Monojet carb to give a little more fuel in the intermediate range. Check the float level.

[bretcopsey]

Thanks guys. Any vacuum ports I should be looking for leaks that were part of that system?

[davepl]

Remember AIR pumps into the exhaust to complete combustion of unburned fuel, so should not affect the calibration of the engine... I think.

[PanelDeland]

IIRC there wouldn't have been any smog equipment on a 68. There are several palces you could have a vac leak. Get a can of WD and spray, around the base of the carb, around any intake plugs, and check vac hoses for cracking.

['68OrangeSunshine]

My '68 C/10 Stepside w/292 L6 was built in Fremont and sold in LA by Felix Chevrolet, so it was originally equipped with the AIR smog system. I joined the Marines, my parents moved to Arizona, so when stationed [c.'74-'75] in Cherry Point NC, I was talked into deleting the AIR system and plugging the head holes, as I figured I would never need California compliance again.
IMO the AIR system never was any good anyway, merely a political construct without any performance advantage. If you don't need it to pass emissions, drop it.
I did, and never looked back.
[Save the brackets, as they may be useful for fabricating A/C or P/S mounts.]

[EDIT] Sorry I didn't read the first post clearly. The PO beat you to it -- dropping the AIR. Sounds like a timing/vacuum advance gripe. Carb should be looked into as well.

[bretcopsey]

Thanks again everyone. I was pretty certain I should be able to get this sorted out without reinstalling the "pipe" that was described. This truck is in pretty good shape with only 56k on the odometer and is going to be our oldest son's first vehicle. I need to make sure its in reliable shape for him.

[bretcopsey]

Just to close the loop on this, the truck is home now and I replaced 6 bolts in the head that were little more than finger tight with 6 brass pipe plugs(3 are visible in the second pic). There was also a vacuum hose coming off the base of the carb that was cut and plugged with a screw that I replaced with a rubber vacuum port plug (also in the second pic).

Just these changes and the hesitation seems to be gone. For what it's worth, this truck does appear to have come from the factory with the smog equipment, based upon the empty bracket above the alternator, double groove pulley setup and the sticker on the rad support.

[Jason Banks]

Your setup looks exactly like mine. 68 - 250 6cyl Built in Freemont sold new in San Diego(National City) A.I.R. tubes removed and plugged with brass, pump removed and bracket looks exactly like yours.

Mine runs amazing. So if what you did makes it work right, I wouldn't worry about it.

I used to have a 402 BB with A.I.R removed and it tuned and ran amazing too...

[matt_field]

Air pump on my 68 250, sold in mn when new

[Steeveedee]

The A.I.R. system was installed to help oxidize the rich mixture exiting the engine when the choke was engaged during warm up. This helped to reduce HC during warmup. Of course, the carburetor would be calibrated for this equipment, as well as for any other option, such as A/T, M/T, A/C or not, etc. Once the choke is open, and the thermostatic switch controlling vacuum to the pump is operational, the pump will just freewheel, consuming very little horsepower. That pump draws very little power from the engine, that can be seen by the tiny V-belt used to turn it.

If you have replaced the bolts, you may have noticed that the plugs should be straight pipe, not tapered pipe, since the A.I.R. system employed inverted flared fittings on the tubing. If you used tapered pipe fittings, there is only a small amount of thread engagement, and leaks can result. I never made this conversion, since back in the day I was a state-licensed SMOG mechanic, and would have potentially served time for violating the law.

[Tony]

First vehicles with AIR pumps were California 1966 models of some cars...The original carburetors had lean part throttle jetting that needed the hot air tube and vacuum operated flap on the air cleaner for best performance. These were often removed resulting in a part throttle hesitation... Over the years the main jet and needle wear and richen the mixture slightly and the hesitation might disappear...

[bretcopsey]

Well, the hesitation problem seems to be solved. We took it for a short spin to get some gas and two additional "drivability" issues cropped up. I'm normally a V-8 with headers and Holleys kind of guy, so forgive my ignorance. The first issue is that it seems to take too long for the engine to warm up and the idle speed to drop down. I noticed that the heat riser valve is frozen and the spring is missing. Would this be the cause of the warm-up issue?


I'm also not familiar with column shift manual linkage. It goes into reverse, second and third very well but is difficult, if not impossible to get into first. Any tips on what I should be looking for?