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Old 06-03-2010, 12:22 PM
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rochester q-jet information

Hi guys!
a question please...
can i bend some linkage of my rochester quadrajet to early open the secondary opening?!
time ago it has been modified, i think bending linkage and now it opens just a few of millimiters and only when i push down accelerator to the floor.
i'd like to have at least an opening of 45 not lus 5!!
it's a 305 engine and carb is a Rochester Q-Jet M4MC or M4ME, they are very similar but my carb has rear vacuum break connected to secondary opening so i don't know if it's possible bending linkage.
thank you very much guys!
Fabio

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Old 06-03-2010, 02:46 PM
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You can get the secondaries to open sooner by removeing some tension on the spring. There is a screw on the side of the carb with a allen wrench retaining screw at the bottom. Hold the screw and loosen the allen wrench nut then turn the screw counterclockwise and it will loosen the spring. Don't get it too loose. You might want to check where it is now before making an adjustment. With the carb off turn the screw until the spring no longer touches the rod. There should never be more than a turn on the screw. If you are running it with an automatic trans you can run looser than with a manual. You don't want the air valve flapping when shifting gears or you will get a bog.
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Old 06-03-2010, 03:39 PM
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oh thank you!
yea it's an automatic transmission. crew is on the right or the left of carb?!
'cause i saw that secondary opening is connected on the right with accelerator linkage and on the left with rear vacuum linkage
thanks again
fabio
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Old 06-03-2010, 03:47 PM
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Along with what Mertz stated there are some articles on the carbs in the Knowledge Base on this site, some will have diagrams of what you are asking for.
http://www.hotrodders.com/kb/carburetor-articles-2
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Old 06-04-2010, 12:46 PM
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ok!! thanks guys!

finally i found the little screw (really small and hidden!) and i adjusted it just 1/4 turn on. i think it's enough.

in the beggining i didn't see changes, but with truck running, sound of secondary opening is unmistakable!

i don't know how many degrees is opened, because with truck sitting there, as you told me, butterfly opens always for a little bit, but certainly faster.



if i can, i have another question about carb...



for idle adjustment, haynes manual says:

idle speed for 305 engine:

high 1600 and low 600 RPM



600 is final idle, right!? when i turn idle speed, after adjusting mixture screws at the maximum engine speed?

and 1600!? fast idle adjustment on the left!?



thanks again

Fabio
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Old 06-04-2010, 02:47 PM
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Set the idle mixture screws at about 700 rpm so it is only on the idle circuit. Use a tach or vacuum gauge or your ear and open the mixture screw until there is no change then turn them in a little at a time until you get a vacuum drop or idle speed change then back them out 1/2 turn. You might want to blip the throttle after each adjustment. Keep the idle around 700. When you have the best and leanest idle turn the idle speed screw to get to 800 with an automatic. Higher if you have a problem with idle quality when in gear. Mine likes 800. If you are running full manifold vacuum to the distributor it might help to disconnect it when making the adjustments but plug the carb then re connect and it will increase your idle speed. You are trying for best and leanest idle. This will help with throttle response and fuel mileage.
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Old 06-06-2010, 01:15 PM
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Hey guys!

maybe 305 engine is a junkyard engine as many people said me , but now i think it's running tremendly good!

i spent 2 hours to setting in the better way my q-jet, in the end this is the setting:



- mixture screws : 2 3/4 turns from zero point.

- idle speed : 600/700 rpm in D position.

- 1/4 turn for secondary opening adjustment screw

- just a problem with fast idle screw... i set the screw with cold engine because it works with cold engine, but i know maybe it's better with warm engine.



now when i start engine, it runs around 1500 rpm as spec., but if i push down accelerator, it's not smooth. i have to wait just 1 minute or push down again.



however it's fun to see how many new Fiat 500 "supercars" i can burn all together!

thanks!

Fabio
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