4 BBL Rochester

[TORQUE THIS]

Anyone ever rebuild one?? Difficult, things to look out for?? This is on a Mercruiser 5. 7.

 

[BQuinones]

I've rebuilt my Rochester Quadrajets a few times many years ago (in college; 74 Chevy 4X4; 350 engine). I personally thought the rebuild job was very simple and straightforward. I still have a spare sitting around just in case I decide to do another rebuild and want to avoid down-time. I can’t think of anything to be aware of. Good luck!



Ben

 

[massdiesel]

Very simple Mark and straight forward. If you need any help give me a yell i could blast down and help you with it

 

[fest3er]

As the others said, the Bogjet is really easy to rebuild. I tore down a spare one I had, set the parts to soaking in Gumout, went out and had a few drinks, came back and assembled it, then installed it on my '66 Gutless in the morning before going to work. (Geez; that was 23 years ago! When did I stop having such fun? And why?)



There are a couple adjustments to be made (acc. pump and float position); 'close' is probably good enough for these - 'exact' is likely overkill.

 

[TowPro]

Pretty easy. I would recommend trying to rebuild it before replacing it with a rebuilt, that way you know you got the correct jets.



My only advice is to take your time, watch for stuff falling out, have a good diagram, and replace the float. They are known to have float issues, the plastic float fills up with gas.

 

[TORQUE THIS]

Scott, thanks, I'll keep it in mind. ToolMan is going to help, so I might need some help... :-laf


Looking at the carb where the fuel line connects, there are 2 adjustment screws, where should these be set?

 

[TowPro]

Scott, thanks, I'll keep it in mind. ToolMan is going to help, so I might need some help... :-laf





Looking at the carb where the fuel line connects, there are 2 adjustment screws, where should these be set?

If this is in the front, down at the bottom they are the idle mixture screwes. Look up "lean drop methoid". I think you turn them out until you just hit max RPM, then turn them in until the rpm starts to drop. I think there is an RPM drop number but I can't remember what it is.



don't forget to use a wrench made for fuel lines when you loosen the fuel line (5/8" If I recall) and you will need a 1" wrench for the filter (that is the 1" fitting right behind where the fuel line attaches, at least on cars its there). Loosen the filter (1" wrench) before pulling the carp, its a PITA to loosen after the carb is already off.



Tip for the future. when replacing a fuel filter in the carb, run the carb low first by cranking the throttle several times with the engine off and accelerator pumps will dump fuel into the engine. Then replace filter. This allows the fresh fuel to flow into the carb and washes out any dirt that may have come free when you changed the filter.



The next time I see someone replace the filter and a piece of dirt gets loose and sticks in the fuel needle wouln't be the first!

 

[mcoleman]

I always replace the plastic float with a brass one. The mixture screws can also be adjusted using a vacuum guage. Adjust until you see the highest vacuum on the guage and call it good. There is also a couple of adjustments on the secondary air valves. You can adjust how far they open and lift the metering rods out by opening them and seeing if the stop is allowing full open on the top flaps. If not file it until it opens all the way up. The speed they open with or ease of opening is adjusted on the side by using an allen wrench and a small screw driver. Just don't release the adjusting screw once you back the set screw off they are spring loaded. Quadrajets are great carbs if you know how to tune them. We have always removed the carb mounted filter and replaced it with a less restrictive but high quality inline filter.

 

[Straight6Jeff]

Also, in beteween the body and throttle plate, there is a foam "sponge"... ditch that. Get some JB weld and epoxy the bottom plugs on the body where the foam sponge would sit. The foam is there to catch leaky fuel from the plugs. Also make sure there is not any slop in the throttle arms.

 

[mcoleman]

OOps forgot about the well seals. It's very important to seal those. That's why so many Q-jets have to be pumped and pumped to start.

 

[TORQUE THIS]

Well, the marine carb is much different than an auto carb. There is nothing to tinker with or adjust.

Rebuilt the carb, only parts in the kit were gaskets, float needle and a few clips for the linkage.

Idles really good and dosen't run rich anymore. However, from 2500 rpm it hesitates and then smoothes out, does this all the way up to WOT.

Any ideas??

 

[TORQUE THIS]

Well I played with the idle mixture screws and it makes no difference...

Any ideas???