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Late Qjet idle mix screw range?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

turbo camino
Posts: 77
Joined: Sun Aug 10, 2008 11:51 am

Re: Late Qjet idle mix screw range?

Post by turbo camino » Tue Oct 08, 2019 2:31 pm

No, I didn't do the threaded idle tubes on this carb, I just mentioned I have the ability to make them if it comes to that. I did the secondary tubes because I found one fallen out when I took it apart, and I had a spare set of tubes that'd already been modified so I stuck those in while I was there. Front half of the carb is still stock.

If it turns out the mix screw adjustment is an indicator of a real problem I'll for sure dig into doing the primary tricks. It may run OK, and that's all this one has to do, be 'just OK'.

It's been 10+ years since I messed with a carb of any kind, though I did tons of Qjets, stock rebuild/repair stuff, back in the early '90s when they were still common. Oddly, probably better than half of them were E4MEs, I know those better than the late non-electronic carbs. I just didn't remember ever seeing one that wanted 5-6 turns out on the screws.

Posts: 2390
Joined: Mon Jan 11, 2010 12:44 pm

Re: Late Qjet idle mix screw range?

Post by rfoll » Fri Oct 11, 2019 1:01 pm

I don't know where you live, but it could be related to cold weather and no carb heat. I recently ran in to a dramatic indication of how important it can be. My car is a 79 impala with a Vortec 350. To provide carb heat, I use an Edelbrock Performer
RPM manifold that has crossover bungs and a path under the manifold. The heater circuit is plumbed through the manifold and if the heat is shut off, there is no water circulation for carb heat. With the engine up to temp, and on a warm day, the circuit is closed. Our current temperatures are about 30 degrees overnight and 60+ during the day. I parked the car with heat turned off and drove the next morning with out turning it back on. When started the car ran and idled really rough. While sitting at a stop light 3 miles down the road I realized the heater was off, and when I turned it back on, the engine cleaned up and started running smooth before the light changed.
So much to do, so little time...

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