[darr]

I replace my 350 motor with a 400. I put summit headers 1-5/8 primaries on it. hei ignition also. set timming to 16 degrees btd. plugs gap to 60. I put # 46 heads on it off of my 350. cr should be around 8.5. problem is when i put pedal to floor runs great. burn the rubber off my tires. when i drive normal, car seams sluggish. no get up and go, unless I floor it. Is back pressure a problem, or my timming. 670 street advenger carb is on it. motor is pretty much stock. I need advice. thank you.

[darr]

shaker, spray base of carb with soapy water, no vacum leak there. while I was at it I spray anything I thought might could have a leak. couldn't find a leak at all. I don't have a tac yet, so I can't tell you what rpm range it idle at. thanks

[shaker455]

Also while you have it off make sure all your vacuum ports are either connected or caped.

espically the one in the front for the PCV and the one in back for the brake booster.

There should be four ports in all.

[Malky]

71, I have I agree that the 3.55 gears really add some snap (especially once you fix your tuning problem) but if you do a lot of highway driving, try a simple test before you put them in - drop down a gear and drive with rpm in the 3000-3500 rpm range. This is what you will be doing in the 65-75 mph range. Now imagine doing that for 1/2 hr. (This assumes you have a 1:1 top gear ratio.)

[shaker455]

71:
Rick was talking about your idle mixture screws on the carb and setting them with a vacuum gauge to get the highest vacuum reading at idle, he was not referring to your vacuum advance.

If the car starts okay and doesn't "hot Start" or ping I'd leave the timming for now and focous on the carb as it's most likely to be just the idle circurt out of tune.

Have you ever dialed in the idle mixture screws with a vacuum gauge before?

Jeff

[shaker455]

71,
What's you car idling at for RPM?...do you have a tach?

There's nothing wrong with your throttle blades just your carb is not set up properly but I think I can get you back on track.

Sorry my friend but usally nothing works completely right out of the box!...you have to learn how to fine tune it to you appiclation.

Now your talking about your "idle stop" screw...right?...that controls you throttle blades...

Not your "idle mixture" screws...correct?

Are you telling me your throttle blades are completely closed?...I bet there up too high on the transfer slot and making your car feel like a mutt.

You need to take the carb off and flip it over and look at the transfer slot and reset it so it looks like a little square to the proper position as I described eariler.

Mark one side of the screw head of the "idle stop screw", place it back on the car and keep track of how many turns clockwise it takes to achieve your normal idle and let me know the results.

[RicksGTO]

Could be a lot of things, especially with a new engine. I'd start with the easiest things first and see if it isn't something simple. I'd try and gap the plugs to around .045-.048 for HEI, mine runs much better with the narrower gap with my HEI. Be sure your spark plug wires are all in the right order, look at the firing order again. Check for a vacuum leaks around the carb. base and manifold as well. 16 degrees is a lot of advance, I'd back it down to 10-12 and see how it responds. Try the carb. settings and set your air/fuel mixture with a vacuum guage attached, set it at the mixture that gives you maximum vacuum and see if that helps. Those are a few simple things that you can try in a few minutes for free, so I'd try those first. Also, was the carb. a known good running unit prior to this engine? How were the valves adjusted on this motor as they may be out of adjustment? Good luck on it, Rick.

[shaker455]

One other thing about your carb is the position of the throttle blades.

Once you got the motor running with the new carb did you turn the idle stop screw to pick up the idle?

Your going to notice a higher idle once you got your best vac reading so it's okay to drop your idle back down to where it should be and that will bring the blades into the proper position which is about .020" into the tranfer slot.

If you took the carb off and look at the blades from the underside you'd see a vertical slot in the front of each primary bore and it should appear as a small square .....thats correct position... a long slot is bad as it's drawing off your main system at idle...might be a good idea to take a peek!

w

[PONTIAC DUDE]

Gearing and the rpm your at when you mash the throttle has a lot to do with <span class="ev_code_RED">Feeling</span> sluggish.

All 400 Pontiacs will burn the tires from a dead. But if your trying to move mass at an rpm way below the torque and power range of the cam, with no gear in the car and a stock converter......this is to be expected. To a point.
You can work on the jetting, air flow, timing curve, etc, etc to help. but you need to work on the <span class="ev_code_RED">Whole Package.</span>
This is what makes one car out perform another with the same combo. Which is the basis of NHRA Stock and Super Stock class racing.

[shaker455]

71:
What intake are you using?

If you can't control your idle speed you might have a vacuum leak around the carb base like Rick had mentioned....maybe spray some soapy water at the base gasket blocking the air movement from the fan with a piece of cardboard or something so your stream goes where you aim...

Once you shoot it you'll notice a an RPM drop from the engine sucking it up...if thats the case

[Chris C]

Don't know if this was already mentioned but since the carb isn't stock, maybe the trans kick down cable isn't allowing the trans to downshift.

[shaker455]

71:
Yes I will explain, please borrow or buy a vacuum gauge....there about $30. at autozone.


Plug in into a spare "full vacuum" source in the "baseplate" of the carb...this is a port that you can hear drawing air wile running.

Don't disconnect anything like the vacuum advance...

Make sure your choke is staying fully open even when throttling.

Start at one turn out on both screws like your at now and keep youe eye on the vac gauge and slowly turn the screws out 1/8 turn at time and look for a vac increase.

If not found then turn in to max vac but stop when it starts to fall...same with turning out screws and go back about 1/8 turn and that should be good.

your vac should be somewhere from 17-21" hg

[BVR421]

Assuming you optimise your tuneup, sounds like you are close, the change to 3.55 gears will amaze you. A little annoying on the highway with small tires but really effective for accelleration!
First thing to do is to close the plug gap to 045, even the factory did this shortly after introducing the hei. They found it just was to many problems at 060 gap.
double check the internals on the hei if its a used one, not unusual for them to be rusted or dried grease preventing any centrifical advance movement at all. Often a good cleaning and relubing inside with minor disassembly required and they will work like new.
One way to check overall timing and advance function, if you havent already done so, is to observe the movement of the timing marks with the light while slowly speeding up the motor by hand.
Its not unusual to pickup 5-20 honest HP by getting the timing curve right for your car.

[darr]

shaker, I will look for that carb. info. I don't know what the jet size is off hand. when I first put carb on engine, I tried to reduce idle.went out as far as I could on idle screw. That seams odd to me. I can't loose any more idle speed. does that indicate a problem with my throttle blades? in other word, idle screw all the way out. I've notice black soot all over rear bumber and lights. I had both problems when carb was on my 350 motor. same problem is still there. THe carb was suppose to be a bolt on out of the box. thank you for your time and help. I live in chevy country. I need this injun to show them who is chief around here

[darr]

thank-you all for responding. in answer to rick question, my carb is new. just bought it 2 month ago. My valves are not adjustable.pressed in studs. I have however bought mr. gasket ajustable nuts to put on it. didn't know if it would make a difference, so I haven't put them on yet. Geoff, the cam is a stock 4 barrel cam. The gearing is a stock lemans 350 gears. I'm guessing around a 292 ratio. I have bought a 355 gear axle to put under it. I haven't got it yet, but it's on the way. the 350 that was in the car didn't have the power the 400 has, but it was enjoyable to drive. I want to get this 400 to that point. thanks for anything else you made add. oh yell, I set the timeing and plugs acording to the manual on a 76 electronic ign. car. since my didn't come out with hei I didn't know what else to do.

[darr]

thank-you yacker. I am in the processed of changing my plugs gap to 45.timing question here. was told to advance timming till it sparks knock, and then back off to where it quits and that's where I should leave it. Does this sound right to anyone? I'm going to retard it back to 12 degree btd, as rick suggested and give that a try. I will check my vacum advance again. The dude made be right on this. gearing just not there right now. thanks to all.

[darr]

shaker, I was talking about my idle stop screw. my throttle blades are completely closed, but my idle is still a little bit fast. I bet you are right about my throttle blade needing to be reset. how exactly do you reset it. you describe what to look for, but I'm not sure what to do to get it where it needs to be? I've got a edelbrock performer intake on the car.it will be tomorrow morning before I can take a look at throttle blade. I've got to work 12 hours today. I will let you know what I've found. I will check for vacum leak around base of carb today.thank you for walking me through this. yacker, I drive about 1/2 hour to work, so your right about taking a closer look at gear ratio. thanks to all.

[buwalda]

You didn't give any info on your cam. If you have a large cam, it will have reduced low end torque compared to a milder cam. If the engine needs 16 degrees of initial timing to run best, then it could have a large cam in it, along with a not-so-smooth idle. If this is the case, Rhoads lifters should help low end response with no loss elsewhere in the rpm range.

[darr]

I replace my 350 motor with a 400. I put summit headers 1-5/8 primaries on it. hei ignition also. set timming to 16 degrees btd. plugs gap to 60. I put # 46 heads on it off of my 350. cr should be around 8.5. problem is when i put pedal to floor runs great. burn the rubber off my tires. when i drive normal, car seams sluggish. no get up and go, unless I floor it. Is back pressure a problem, or my timming. 670 street advenger carb is on it. motor is pretty much stock. I need advice. thank you.

[shaker455]

I tried to look your Holley street avenger 670 # 0-80670 model 4150 up and I could not find the listing for the jet sizes and powervalve....do you have that info?