engine bogging out at 3200

i just rebuilt my 78 350. the problem i'm having is it keeps bogging down on me at 3200rpms. Ive found the sweet spot on my timming and it starts and runs good until i get passed 3200rpms. i have a supposely new quadrajet on it and seems not to have any vacuum leaks? can anybody help me with the problem? when i hit full throttle it boggs completely down. help please ive spent to much money on my engine for it to be doing this.

Jeff Kostis wrote: Sounds like the 4barrel metering rods are not adjusted corectly. You can bend them with a pair of pliers where the curve is. Our quadrajet was the opposite-it would flood out when you went to take off hard. Dont rule out an inadequate fuel problem either. Check fuel pressure/flow to carb. Usually though, a plugged filter/bad pump, etc, would cause it to bogg/die a bit after the 4 barrels open when it uses what fuel is available up.

Number one don't bend any rods on a Q-jet. The problem you are having is a lag when the secondaries open. The most common cause is improper ignition timing. There is no "sweet spot in the timing". Adjust the timing with a timing light to 8btdc as a base line. take her out & see what happens. If the problem still exists but is better or worse advance the timing 2 degrees & retest. Do not exceed 12btdc. Also check the total advance @3000 rpm(can be in neutral at the dock), If you are not achieving 32-34 degrees total advance the secondary operation of the carb is effective. This is all because the secondaries on a OEM Holley, or Q- jet, or Carter are controlled by vacuum drop on acceleration. Any change in the timing effects the vacuum to the secondaries at any given point. Too much advance not enough vacuum drop and too little advance to much drop. There are so other minor things with the initial carb adjustments but this is the most commom problem for that 2800-3200 rpm lag.

Set the timing then re-adjust the idle mixture screws located on the front of the carb's base plate. Screw them in slowly one at a time until the idle drops then back it off a quarter of a turn, do the other side then redo both sides again until it is dialed in. Also make sure the choke stat is set correct. There is a notch/boss on the plastic choke stat and a series of raised bumps on the metal housing it is mounted to, the middle bump will be taller than the others that's zero, set it so that it is two notches rich. Also don't worry about bending any rod on a q-jet you have to bend them to get the choke pull off, accel pump, and secondary metering rods set correctly.

Now there has already been some bad advice given regarding your plroblem and adjusting a Q-jet properly. Bending the arm for the secondary metering rods will only open them up sooner and all Q-jet carbs have mechanical secondaries and are not controled by vaccum, open up the throttle fully and you will see the secondaries open up even if the engine is off and there is no vaccum. Also you can adjust the pivot point for the accel pump and effect how much and how soon it operates.

I suggest you reset the timing to 8-10 btdc and verify that your total advance @ 3000 rpm is not over 32 degrees first, then re-adjust the idle mixture screw and idle as described above. Next I would check all fuel filters including the one in the carb, you'll need a 5/8 line wrench and 1" open end to do this. and Check fuel pressure as well. Once all of that is done if it doesn't fix the problem you will have to make additional adjustments to the carb and I can help you with it. It sounds like maybe the accel pump is a little agressive and the secondaries could be opening to quickly which is an easy fix.

Where are You Located? Decatur, In? or is it in another state?

I can say from day 1 with our omc 225 chevy 307 it never ran 100%. It would not take off like a holley did. After taking it to everyone, they said thats normal, put on a Holley. Im no Rochester fan, but after several days of taking it apart and playing around, I finally figured it ran awesome until 4 barrel time. Thats when I got out the pliers and adjusted (re-bent) the secondary metering rods down a bit and kept tweaking them, taking off hard, soft, and using a radar gun for max speed. Ill tell ya, it runs better than my holley on the other boat! The problem was that fuel can leak by the metering rods when the thottle plates are open, but the pull-off is still closed. The 4 barrels are so much smoother sounding no matter what. That baby will do 49 mph fully loaded! I was amazed at the difference. Everyone says not to touch them as they are pre-set, but as awesome as I got this to run, you bet I will do it with others!! I am actually impressed on how good a Rochester can run!

i had to set my timming 15 btdc. i could not do 8 to 12 because it would either not start or flood out. 15 seems to start and run ok except when i hit 3200. i looked at my x-tra carb and it seem like the secondarys will open only at the bottom. when i went to my boat and open up the throttle the sendondary didnt not open at all. it was kind of dark so i have nt done anything except timming. i will try again tommorrow to see if the secondarys are opening. and that would be decatur illinois 79. thanks for the and ill try what you said to do.

I bet the whole problem is happening just because I am GAY!

nates78ski
dude you are so full of crap
I have never seen a Q-jet that has vaccum secondaries they are mechanical. The choke pull off is for the choke not secondaries. please not confuss the guy with incorrect information.

Jeff screw in the idle mixture screws all of the way using light pressure and stop when they stop do not torque on the screws otherwise you'll damage them. Once they are fully closed back them off 1.5 turns and then reset the timing. An easy way to see if the harmonic balancer is slipped is to bring the #1 cylinder up to top dead center then look to see that the zero mark on the balancer matches the zero mark on the timing ear mounted to the block. If it doesn't then you need to replace the harmonic balancer. I'll look and see how far Decatur is from here and if it's not to far and you buy the beer I'll get you fixed up in no time. Q-jets are a little harder to adjust correctly but once they are they stay that way for a long time, holley's are easier but you have to re-adjust them regularly

well im going to check a few things. i think everything is good on my timming.? i still think its my secondaries not opening i'll know for sure tomorrow because ill be able to go down to the dock during the day
what kind of beer do you want?

Do you have a wedge plate? Everything revolves around wedge plates. My .02 worth....
From all my Q-jet experience, (and Holley) I'd rip the thing off your intake and throw it out on the dirt driveway. They are a constant headache. Put on an Edelbrock marine. They are simple to adjust and easy to rebuild when it comes time. Or better yet, convert to throttle body fuel injection. The money will be well spent.

30 years of repairing ignorant wanabee mechanics screw ups have allowed me to earn good living. If you own a Qj, holley or an Edelbrock they have all a have to set up properly. All carbs do wear out with use. I suggest you take this carb to a reputable mechanic to check it on a bench. You may have to drop $300.00 on a new unit and if you do buy the Edelbrock. Easy to adjust & very turn key.Where you located in indiana.

looked at motor a little more today and i believe it is my secondaries not opening. they would not open even when i had full throttle. oh well ill probally get when i get my next day off work

Debates are good for learning. I will watch this one and see what I learn!

One thing I want to throw out there for debate...Vacuum secondaries or manual??? I am hearing two versions...I don't know the Qjet carb well at all,however I did look at Jeff's(who started the post) and it certainly looks to be a manual pull on the secondaries.

Nates78ski...agree..what ever goes on(holley, qjet or edelbrock)will usually require adustment...the carb on the boat is new and he has a spare rebuilt carb in the garage...I don't think he needs to spend more cash,but just wants to understand the carb and learn how to make the adjustments!

Hopefully you guy's that have knowledge of the Qjet get get on the same page and and help solve that poor pathetic bast--ds issue!I can call him that...he's a friend

located in illinois 78

There a series of steps to set up a Q-j properly. These include choke pull, choke thermostat, chock unloader, accelerator pump, choke holdoff or lock, primary metering rod, secondary metering rods, secondary air or vacuum vane windup spring & of course float height and float drop. Some of these require special tools to measure properly. Most of the time you get lucky and they don't need adjustment. If you do not have a history of the boat or do you know if the carb & spare are the proper match to the engine that presents another problem. I think the right path you are on is to make sure that the choke opens all the way enabling the lock out to come off. While the engine is first started cold make sure the choke pull is opening enough. Give me the carb number or look in the rebuild instuctions for this info. When these carbs wear with age & use these adjustment are you baseline. When starting cold if the engine runs rich adjust the choke pull off just enough to get rid of that condition. Now back the lock out lever the choke will take 5-8 mins to warmup @1200-1500 rpm. If it fails to open check that it is recieving warm air from the manifold tube or if it has an electric choke the proper voltage is there. If that is OK then the tension on the secondary windup spring may be wrong. Once again look in the rebuild spec for the proper turns to tension the spring. When you find that loosen the set screw underneath the air horn @the right side of the secondary air vane and hold the adjustment screw with a small screwdriver to adjust. This all sounds a little complicated but it really is not if you understand what to adjust in which order. Check the choke stat for opening & the pull off and let use know what you find before we mess with that air vane windup spring. Good luck!!1