The $20 mystery Q-Jet (back to looking at it again)

[Rktpwrd]

Also, who's a good source for drill bits for enlarging jets?

Jack, I’ve just gone through all this with trying to get my QJ to idle on the idle circuit rather than the primary circuit. To add to Mark's suggestion of picking up that drill bit set (which I have as well), I found that some of the things that needed to be drilled out in the idle circuit required bits smaller than what’s available in that bit set.

Your local hobby shop should have pin vices (tiny hand drills) and tiny drill bit assortments to go with them. Just make sure to measure the bits with a caliper before you use them.

(Sorry for the thread-jack Mr. Grunt!)

 

[Bonnewagon]

Rktpwrd- did you do the mods all at once or one at a time? The reason being that if you do more than one thing at a time you have no idea what worked and what didn't. I have never found the need to touch the idle bleeds or any other part of a Q-jet beyond the jets, rods, and idle discharge ports. I find the tiny idle discharge to be the single biggest handicap to tuning an emissions carb. Even a bone stock 1980 Pontiac 301 responded well to that.

 

[pagrunt]

(Sorry for the thread-jack Mr. Grunt!)

No problem, I'm learn about the add on topic as everyone adds. If my Q-jet has the restricted sized parts when/if I rebuild it I'll have an idea of what to do about it. Carry on.

 

[Rktpwrd]

Rktpwrd- did you do the mods all at once or one at a time? The reason being that if you do more than one thing at a time you have no idea what worked and what didn't. I have never found the need to touch the idle bleeds or any other part of a Q-jet beyond the jets, rods, and idle discharge ports. I find the tiny idle discharge to be the single biggest handicap to tuning an emissions carb. Even a bone stock 1980 Pontiac 301 responded well to that.

Mark (if I may call you that, and it’s Donovan, we’re all friends here), I used Cliff’s entire section on modifying the idle circuit as a guide on mine, starting with measuring what I had to begin with.

In that section, Cliff has several “recipes” as he calls them, for modified engines with different camshafts and characteristics. I simply picked the recipe closest to mine and compared his modification recommendations and sizes to my carb. Some of the components didn’t need modifying like the upper and lower air bleeds, but others like the idle down tubes were so horribly restrictive, that they absolutely had to be opened up.
In fact, I didn’t even have a drill bit small enough to accurately gauge what size the orfice in the tubes were!

If you’re more interested, I can grab the book out of the garage and post up here the components that were modified and the before and after sizes.

(And as a footnote, it now idles like an absolute top and runs like a champ!)

 

[Longroof79]

Jack, I’ve just gone through all this with trying to get my QJ to idle on the idle circuit rather than the primary circuit. To add to Mark's suggestion of picking up that drill bit set (which I have as well), I found that some of the things that needed to be drilled out in the idle circuit required bits smaller than what’s available in that bit set.

Your local hobby shop should have pin vices (tiny hand drills) and tiny drill bit assortments to go with them. Just make sure to measure the bits with a caliper before you use them.

(Sorry for the thread-jack Mr. Grunt!)

D.
Thank you for that suggestion. I didn't even think about checking out a hobby shop. Honestly, I wouldn't enlarge the jets...I would just obtain a variety of a few sizes larger.
I have done no mods to my current carb. It seems to run pretty decent. The idle is a little on the high side and I haven't tried it yet to see what response I get from the secondaries.

 

[Longroof79]

Jack, I’ve just gone through all this with trying to get my QJ to idle on the idle circuit rather than the primary circuit. To add to Mark's suggestion of picking up that drill bit set (which I have as well), I found that some of the things that needed to be drilled out in the idle circuit required bits smaller than what’s available in that bit set.

Your local hobby shop should have pin vices (tiny hand drills) and tiny drill bit assortments to go with them. Just make sure to measure the bits with a caliper before you use them.

(Sorry for the thread-jack Mr. Grunt!)

D.
Thank you for that suggestion. I didn't even think about checking out a hobby shop. Honestly, I wouldn't enlarge the jets...I would just obtain a variety of a few sizes larger.
I have done no mods to my current carb. It seems to run pretty decent. The idle is a little on the high side and I haven't tried it yet to see what response I get from the secondaries.
The drill bits would come in handy for measuring jets and port sizes.
It's refreshing knowing that we're able to learn from each others knowledge and mistakes.

Mark, I thought you and Donovan were informally introduced. I know we're all friends here, even though some are embarrassed to use their first names. 😛 I don't know why.

 

[Rktpwrd]

D.
Thank you for that suggestion. I didn't even think about checking out a hobby shop. Honestly, I wouldn't enlarge the jets...I would just obtain a variety of a few sizes larger.
I have done no mods to my current carb. It seems to run pretty decent. The idle is a little on the high side and I haven't tried it yet to see what response I get from the secondaries.

No problem, you’re very welcome Jack. It can be a challenge trying to find bits that small and the hand drill to go with them. The bit index that Mark posted earlier got me through 95% of the drilling I had to do, but having those tiny ones left over from my toy car modeling days came in especially handy.

I’m with Mark, I wouldn’t advise drilling the jets either, just replace ‘em with the right ones. (Assuming we’re talking about the primary jets).

 

[pontiacgp]

Lee Valley has number drill sets if anyone is looking for them....🙂

 

[pontiacgp]

Mark, I thought you and Donovan were informally introduced. I know we're all friends here, even though some are embarrassed to use their first names. 😛 I don't know why.

I don't mind people using my name, at my age I need some help to remember who I am....🙁

 

[Longroof79]

Jack, the pre-emissions hole size is .095. Before drilling anything measure yours with a drill bit and see what it is for a baseline. Some are extremely small and meant for super lean emissions. I have found that opening up those discharge ports even a little can solve a crummy idle situation with no other modifications. Plus, if it was not the problem, you can still tune for a smooth idle by simply turning the screws back to a lean mixture. As for a drill bit set that is complete and cheap the 115 piece Cobalt set that harbor Freight sells is pretty hard to beat. I can usually snag it for under $100 and it is drill-through-anything COBALT man!

Mark,
Thank you for all your suggestions....and your drill bit recommendation. I'm poor in drill bits lately. Between wearing them out and breaking them...you can never have a good complete set of bits.