First, any and all help/knowledge is greatly appreciated. I am a novice so please take it easy on me ray: Background: 70 455 Motor. I do some poking around cause the car seemed to be struggling when i jump on it (jumping on it to me is taking it from 45 to 65 quickly). First stop was my carburetor. Looked kind of old, beat up from the years. What I found was that I had a Yellow dot 4MV 7040244 Q-Jet. So I decided to purchase a rebuilt Purple dot 4MV 7040240 Q-Jet. I swap the carbs, it starts up, a little rough, slight adjustment to the idle screw seems fine. I take it around the block. Starts out good, slight tap on the gas and tires gettin loose :3gears: I think i am in Schaeffer City, make a turn at the light no traffic in front of me i gun it.....bogs down and sputters like Chitty Chitty Bang Bang o No: so i read Section D - ROCHESTER 4MV Carburetor, a lot of info, but just not sinking in at the moment. the one thing that jumped out at me during the swap was an "extra" vacuum line located bottom front right of the new carb that was not present on the old??? sorry for the :rant: but any insight would be great. Thanks. Steve
Where did you get the rebuild carb from? Can you post a picture of current set up? Need more specifics. When you "gun" it, does that mean floored? If so, it is probably the secondary bog and need some tuning to minimize that. First thing I would do, is set the timing correctly like Larry's power timing thread points out. Then, if still some bog, you will probably need to adjust the secondary flap a little tighter. If your secondary release is old and not holding vacuum, that needs to be replaced.
gun it = floored. I am working on the timing now and will post some pics also. What I "feel" is like it is only running off of 2 barrels??? I will have some pics in a few.
X-2 Start with the basics, a good tune up, set the timing, adjust the carburetor idle mixture and speed screws and go from there.
Sounds like the secondary air valve might not be set tight enough. You can look around here in the carburetor section for the setting, since it varies with displacement, cams, etc. It makes a big difference to have the secondary air valve adjusted right, when there is such a large volume flowing there.
7040244 is a 350 carburetor. You can't expect it to run correctly on a 70 455, especially if the 455 isn't stock. It can be modified to work. Stock jetting on that carburetor was .069/.045 with BS secondary rods.
Larry - thanks for the timing post. Certainly required some adjusting. So I believe to have the timing correct now. Still have the issue when I jump on it that it boggs , sputters and never really kicks in. What I feel is that the engine is running off of only 2 barrels ....
As Larry said, that carb is for a Buick 350 and GM built these carbs specifically for each year and engine size. Just think about the air required to make a 455 run at idle compared to a 350, much different idle air passages are required. You will not get the Buick 350 car to work well on your 455 unless you buy the book about Q jets by Cliff Ruggles and spend about 40-100 hours modifying and experimenting with the carb modifications internally. Your best bet is to order a Buick 455 carb from Everyday Performance, or from "carmantx"... Or find another reputable carb re-builder and make sure they use a 455 this time.
one thing i notice from the pic of the passenger side of the carb is that the choke flap is almost all the way open and the secondary lockout lever is still engaged holding the secondaries closed. The lockout should engage when the choke is closed, and disengage when the choke is fully open. I mention it because you said it felt like you were running on two barrels. check the choke linkages and verify free movement and correct adjustment. edit: looking again at the pics it looks like the choke flap is not opening to a full 90 degrees. it should.
Ken - How much play should there be in secondary lockout? Seems to me as if it is very loose... for now my weekend warrior project will go on hold. thanks again for the comments/suggestions. Steve
it is able to swing way forward by hand when disengaged, but thats not important. What is important is that when you hold the Choke Cam all the way down in front with one hand, you should not be able to push the lockout back with the other hand far enough to engage the secondary shaft pin. Thats how the system works. When the choke is full open and the cam all the way down, it prevents the lockout from engaging. Otherwise it just hangs loosely. I would just take the thing off there, personally. I never use one.
