quadrajet
 

ok guys lets check out your knowledge.i've just re built my1991 twin 350 mags that were rated at 270hp with the new roller cam head work and pistons.i need to have the carb updated for the new motors.does anyone know a good carb rebulider to rejet and etc? and roughly the cost.

Jones carburation (JET) used to work on them. Sorry, I don't have a number. The Carb Shop was also familiar with them. As I recall they were in Ontario California.

I have had good luck with carbs from The Carb Shop.
1461 E. Philadelphia, Ontario, CA 91761
Phone: (909) 947-3575 Fax: (909) 947-7495

If you want to do it yourself, it's pretty easy. The 350Mag Q-jet was set up with a pretty rich primary circuit (0.069jet/0.036rod) compared to the 454Mag (0.068jet/0.041rod), so it'll probably be ok for you. You may only need to tweak the idle circuit and the secondaries.

First, check to see if the idle mixture screws have enough range for the new cam's duration. You need to be able to make the engine run rich by backing out the screws. If it won't run rich, you'll need to enlarge the idle mixture ports. There are probably at 0.08" now, and you can go up to 0.095" max (or largest screw dia minus 0.03").

After you set best idle with a vacuum gauge (best vacuum), check the primary circuit. Disconnect the accelerator pump linkage (and shift linkage). Rev the engine from idle. Without the pump activated, you should get a slight hesitation. If no hesitation, primaries are too rich. If a real stumble, too lean. I'll bet you'll be ok at stock.

Unless your cam is a pretty aggressive (less than 10" vacuum at idle), the stock primary spring should be ok

For the secondaries, your stock CH rod will be a little anemic. Pick up a CK (CP?) from Edelbrock (#1952). Also try to find an AU and/or DA from Chevy.

Adjust the air valve to 1/2 turn from zero; discard the stock inline fuel filter for a larger aftermarket one, use the FelPro insulating gasket and have fun.

If you are rebuilding the carbs, compare the accelerator pumps in the carbs to the ones in the kit. If noticeably different, use the Edelbrock marine pump (#1982).

Good luck

Call Bob Campbell at Q-Jet Specialists. He is in Milford, Michigan 248-685-7345. He retired from the GM Proving Grounds in Milford and worked on fuel systems for years. Q-Jets is all he does now. He has done good work for me and several of my friends.

Great info given so far by these guys Sonic. One other item if you decided to rebuild yourself is the needle and seat. The set that comes in many rebuild kits are too small, .124 I think. You should have at least .134 needle/seat and set float appropriately. I made the mistake of using the supplied needle/seat one time and the fuel bowl would run empty at WOT. Bad thing. BTW I have two qjets for sale that I rebuilt over the winter and tuned for 454s. Many tuning parts included like assorted metering rods, jets, hangers etc. Will sell cheap.

Dave

you guys are ok thanks dave.what type of money you looking at.
paul

Something like $50ea plus shipping. I probably have that much in parts in them.

Let me know if you are interested.

Dave

For that money, I will take one, or both if I have to, if any of the guys posting before me dont want them, or if somebody only wants one!!!!!! Just want to make sure anyone posting before me gets first dibs, dont wanna step on any toes, but I could use one.

hi dave ill take both you can call me 603-436-7950 or personal email [email protected]
thank you paul

Sonic

Let me know how the new stuff comes out. ive got twin 350 mags too...looking for some more performance.

Sonic, I emailed you. Rchevelle, if Sonic changes his mind I will let you know.

Dave

Thanks, if not, are ya intersted in re-working mine???

I can fix big CHIT, and I build brain surgery equipment for a living, but somehow I always seem to screw up a carb??????? Something about all those small parts, and tweaking them just right, Give Me a BFH, and I'll fix it!!!!!!

I would be happy to. What is yours doing now that you want changed, or are you just trying to get more power output?

Dave

Well, it started with that annoying, stumble when the secondaries opened, I adjusted the air valve spring, but it still has a little, only if you jam it real quick, if you advance the throttle slow it is fine. I have a feeling the secondaries are not rich enough, it is just a stock 350, but I added thru-hulls, and a Mallory electronic ignition, I am afraid I might be running a little lean at WOT, and dont want to burn anything up.

Likely Q-jet issues are: 1)sticking air valve (guess you've already eliminated that); 2) accelerator pump and adjustment of same; 3) low fuel level in bowl; 3) fuel pump pressure and volume (6-7psi); 4) dirty circuits (e.g. sticking discharge ball, sticking power piston).

Not having enough tension on the air valve spring can cause a bog as well; a 1/2 turn should work fine for a 350. Also, check your initial timing and advance curve.

You should be running at least CH secondary rods. A lot of Merc 350s came with CLs, which are too lean IMHO.