455man

I didnt realize the stock filters were that restrictive. I'll try that out when I get it back together.

GEARMAN69

Yep its just about any brand single snorkel closed (PCV) system air cleaner will kill it. On the PY forums I was trying to type through with a guy that had a rare 68 320 hp 350 HO tempest 4 speed car and he said it just wasnt that strong and didnt spin tires much yada yada. I went thru all the basics with him online and finally he took off the stock single snorkel breather I had told him in my first post and he was blown away at the power increase and tire smoking awesome improvement. Mind you I know you just have a 307 but also once that thing gets unrestricted cool open air supply those .09 rear rods are gonna make it lay down and bog out lean so just be prepared to swap ASAP don't force it too much up in the rev's just warm it up and hit and see the A/F ration change lean and adjust but the power should be tremendous improvement with the richer rod corrections and free cool flow air. We found those most hideous lean rods off all time in a mid 80's Olds 307 full size wagon a friends mom had and it literally did nothing if you flipped over the lid because it had no fuel. We swapped to much richer set of rear rods immediately and no other changes and it was getting it hard and sounding good pulling as hard as you could hope for a 150 net hp engine. But much much better. Other carbs that had horrible rear lean rods were like a 71 350 Buick too.

Here is the full chart of all secondary rods

http://www.hioutput.com/tech/qjetrod.html

455man

I've got a couple of sets of rods i can change to when I need to go richer. Keep in mind I'm very rich on the primary side. With the secondaries locked out its at 10.9. Is opening up the air cleaner going to provide that much more air for the 300cfm primaries? It's an easy check so I'll give it a try. I've been busy and have not put the carb back together yet.

GEARMAN69

Unlock the secondaries, and cooler available air will lean the primaries too. 69 jet is by no means rich on its own generally. A 50 rod teamed to a 69 jet on the primary makes for a lean part throttle condition. With a cool unrestricted air supply a 40-42 rod would be preferred if the engine remains with the cooler air and open breather. .

GEARMAN69

No update after open element air cleaner or lid flipped or just removed ?

455man

Sorry I've been lazy or just frustrated around the holidays. I put it back together and started it up. Gas came spilling out the top. So I'm taking it back apart to check the float and needle and seat. I'll also check the gasket for impressions.

shiftbyear

I had a similar problem, could not solve. Sent the carb to Cliff Ruggles. Turned out to be a warped main body and air horn. I could not see the warping visually. He sells and extra thick gasket to correct minor warping. Good luck.

455man

I have a warped body and air horn. The extra thick gasket might help solve the problem. Although I'm about ready to start over and buy a new carb. I'll get out to my cold garage soon to work on it more.

455man

Took the carb apart. Seemed to be some dirt near the needle/seat. Got it back together and have been tuning it. Setting the choke, choke pulloff and idle and APT. Got it close. I'll tune it more tonight.

Octania

FYI a QJET "can" run very well with a warped air horn and main body. Maybe not all warped ones do, but I had one that did.

On a very well behaved 455

And the warpage was not slight, it was on the order of 1/8" or more. Exceedingly obvious.

Yet the carb was perfectly well behaved.

I think I still have a photo of that. It was back in the "fuel line that don't fit right at all" days.

455man

I got the carb back together. Started tuning it. Accelerator pump ripped so i had to put an old one back in. Make sure you put a little grease on them if the bowl is dry. Adjusted choke, idle a/f and APT. Seems to run about the same as before. Still rich. I'll run an open element air filter this weekend to see if that lets more air in. Figured the 20 degree temps would lean it out but it hasnt.

455man

Shouldnt I be able to push the power piston down with this screwdriver from this vent hole? IMAG0173[1].jpg

With the car off this does not move up or down. No vacuum should allow the spring to push up the piston and the rods out of the jets.IMAG0177[1].jpg

Arms bent up too high causing the rich readings? With the top plate off the piston moves up and down. Thoughts?

455man

joesw31 Sorry i missed your post somehow. As far as mods go I've made the APT accessible, changed the jets/rod to lean it out and drilled out the secondary vacuum brake so the secondaries will open faster. Carbs been rebuilt but no other mods that I'm aware of. I might be interested in gaskets. Thanks. I'll pm you.

455man

Gearman69 I turned the top of the filter cover upside down allowing more air in. drove it around all day. Seemed to lean it out some but not much. I dont think that the stock little 307 is starving for air.

GEARMAN69

Also would like to know all the rod and jet numbers but did you unlock the secondary side linkage since before you said you did WOT testing with it wired shut.

wr1970

Swap meet is coming up! Just a heads up in case you need some parts.

455man

The power piston moved up and down before assemply. I pulled the top and it moves up and down. Put it back together and its moving up and down now. Took it for a test drive and it idled about 12.8 accelerated at 16.8 so it was really lean. On trip back home it flooded out and ran about 9.9 at an idle. Intake had gas all over it. Adjusted the APT and acceleration was better at 16.0 but eventually carb flooded again. Flooding seems random though. I might change the float and see if that solves the flooding. Rods are 50M and Jets are 69. I believe rods are stock. I changed jets from 72 to 69.

455man

I put the rod/jets in prior response above. I unlocked the secondaries. I'll lock them out again to see how the primary side runs at WOT once I get the flooding figured out. For once I had it lean so maybe I'm making progress. Float, needle and seat were new about 2 yrs ago when carb was rebuilt. nitrophyl float better than brass?

455man

I know, i might have to walk through and look. I'll give you a call when I get this carb figured out.

GEARMAN69

a 50 rod and 69 jet is an awfully lean part throttle. How many rotations off the bottom is the ATP at ? Once float is figured out and what fuel pressure has been getting to it BTW? I would still swap to a much better balance of rod jet combo like 41-45 rod with a 70-72 jet.. Even a 307 needs a balanced primary setup. You have headers with duals and hopefully soon an open air style cleaner. Something else is involved here. I would do brass float why not.

455man

I agree something was not right when that rod/jet combo gives me rich readings. I'll have to check the APT settings. I forget where its at now. I tested the fuel pressure recently and it was 5psi.

Octania

"a 50 rod and 69 jet is an awfully lean part throttle"


I noticed in going thru my 403's rich phase that IN GENERAL, the difference between the jet and the needle is about 0.030" aka thirty in the numbers.


I had fat rods in the Toro 403 carb but a C type parts carb had the right shiner needles and now it runs fine. Not sure what all ELSE took place to cure all that, but the needle/jet diff of ~30 was part of it.


How is you vacuum at idle? When I had poor vacuum, it ran really rich- I think the power piston was opening at idle, making things worse and worse. Bumping the timing WAY up was a large part of the solution. Then limiting the vacuum advance with the aftermarket limiter VA can. Or your other favorite welding or spacer trick.


I advise against modifying the vacuum break to allow faster secondary opening. No good can come from that.

GEARMAN69

Yep the 30 rule is right way to baseline a Qjet primary on a typical hiperf street and or strip car (duals , headers open air cleaner, cooler T Stat)

I run 74 and 44 in my 1977 800 carb

455man

Octania vacuum is fine. About 18 in. at idle.

Joesw31 i havent gotten that far yet.

Just replaced the float. No flooding on my trip. Seemed to run rich still. Came back and leaned the idle a 1/4 turn cause it was about 13.4. Noticed APT was all the way down. Then noticed that the power piston arms were not all the way down and could only be pushed down about .010. Before my test drive I made sure I could push the arms up and down. Seems like the rods came out of the jets and now wont line up to go back in. Bent arms?

455man

http://www.corvetteclub.org.uk/files...wer_piston.pdf

Found this PDF that shows how to adjust the power piston. Arms were bent up too high and rods were coming completely out of the jets. Measured it out and bent them back down about .200. Now I'm too lean. Set idle at 14.5. Part throttle gets up to 17.5 after turning the APT out 6 turns. It's late so I'll adjust it more tomorrow. Now that I have the rich problem fixed I probably need to put the bigger jets back in. Someone mentioned bent arms earlier in the thread but I didnt know what to look for.

455man

Did some tuning. Had to change jets to 72 from 69. 51M Rods. idle is at 13.4, part throttle is at 15.8 and cruising is about 15.6 WOT is 12.6-13.0. Checked WOT with primaries only and with secondaries. Seems a little lean at part throttle. I have APT turned out 6.5 turns. Accelerator pump is on closest hole. Might need a size smaller rod. It's running better than it ever has though.

olds 307 and 403

The factory non CCC carbs on the 307's up here were crazy lean. My 88 CSC had an 83 Tornado 307 non CCC. When I dumped that 307 in my 1/2 ton with headers, it developed a part throttle, lean miss. Throw a lot of timing and read the plugs, I bet it will be fine. If you want it slightly richer, you can probably adjust the APT a bit.

455man

Thanks. I'll try that.