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Old 02-07-2011, 03:06 PM
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You are quite welcome. FWIW, there are a LOT of threads on working w/the Q-jet here on the forum. If you haven't yet done so, a search might be of some use to you.

There are a few tips and tricks, like placing a ~0.050" feeler behind the accelerator pump lever pin, so when you drive the pin towards the air horn lip it doesn't butt tightly against it- instead there's room to get a thin straight blade screwdriver in behind it to lever the pin back into position.

There are several different heads to the idle mixture screws: hex, flat blade slot, and one is an ovoid/hex affair that defies all logic- other than to make it difficult to turn. You'd have thought that capping the screws would have been enough, but I suppose this was extra insurance that they wouldn't be tampered with.

Anyway, these ovoid screws can be removed by using a crimped length of brass tubing, found at hobby shops. Once these bastard screws are out, use a dremel and a cutting disc to put a slot in them for a standard screwdriver. I do this to ALL my carb's idle mixture screws, because finding the right sized 1/4" drive deep socket is only half the battle- the OD of the socket has to be ground down in many cases in order for the socket to fit into the available space.

Early Q-jets had accelerator pump and choke linkages that were secured by small clips. If you can get your hands on these, they make dis- and re-assembly easier (especially the acc. pump link).

For some reason, I have found the base plate on many Q-jets to be missing a screw or two. While the base plate is "helped" being held on by the two long front bolts, it's still a good idea IMO to go ahead and add the missing screws. Just be sure to not over tighten these long bolts. If they're over tightened, it can warp the carb beyond use.

Check the base plate to be sure the throttle blades are exactly 90 when wide open. There are some who believe having the secondary throttle blades go "over center" helps w/A/F distribution w/some intakes. While this may be true, until you have a good grasp on the engine's tune and plug readings indicate a need for this, keep them @ 90.

I don't want to get you sidetracked w/a lot of tuning 'advice', this being a primer for dis- and re-assembly. But this is an easy cure for a common problem you might run into:

The idle discharge ports that are controlled by the idle mixture screws can be anywhere from around 0.050" to 0.080". If you find a lean idle condition that doesn't seem to respond to turning out the screws CCW, you can gauge the port size then enlarge it one size at a time until you regain control w/the screws.

This is providing that the throttle plates are not open too far due to a large cam- which will over-expose the transfer slot, just like on a Holley. The cure for that is the same as you'd do w/a Holley- start by using more ignition advance. This allows the primary throttle blades to be closed down some to lower the idle speed, which increases due to the advanced timing. Often, this is all that's needed, so be sure to do this FIRST, then enlarge the ports only if still needed.

A common problem on the early Q-jets especially, is leaky main wells.

The 'cure' for this has long been to use JB Weld, etc. to seal them over. This is just a stop-gap measure, I have seen personally how the epoxy will degrade over time and quit sealing as it did at first.

If a permanent fix is wanted, the wells can be resealed w/new plugs that are peened over to hold them in place.

The primary wells can be drilled and tapped for short screws that will cure them for good, although these wells seldom leak.

One last thing before this gets any more long-winded. On the secondary accelerator 'pump' discharge ports that are often located above the air valve- these are better located just below the closed blades. The upper ports can be sealed off w/epoxy on a clean, roughed up surface then the same size ports located under the blades, in line w/the existing holes.

Only do this if you are experiencing a lag or slight bog that doesn't respond to the usual fixes- like the air valve spring tension adjustment or the unloader orifice size.

The center two round gaskets are for the two different types of fuel filter housing/inlet fittings that were used. One uses the white nylon gasket on the very end of the housing, the other type used the orange gasket all the way to the end of the threads. If there's a lip on the end of the housing that will accept the white nylon gasket- use it, not both.

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