Engine Stumble Question

[dznucks]

What does it mean when you stomp the throttle and the engine wants to stumble or bog before reving up? the motor runs fine at any other time other than when you hammer the throttle.

Its a 350 with and edelbrock 1406. I am pretty certain the prob is in the carb. i am wandering if my secodnary's are too rich.

[60ratrod]

you might wanna rejet. you might actually have a lean. my 72 with a 1406 would stumble and hesitate at cruising speed when i would give it gas, usually at 1500(in town) and 2500(highway). so you may be running lean. check your plugs and see what they look like.

[dznucks]

It doesn't act up at cruise or part throttle. Its under hard accel. that it will do it.
say your cruising at 45 mph 2200 rpm and then you stomp it almost to the floor it will stumble before it accelerates. during the acceleration the engine feels like it running rough (i feel its too rich), so when you ease back up on the throttle you can feel the motor smooth out and it will actually accelerate faster as you let up on the throttle a bit. i am wondering if i need to let up on the accelerator pump shot and lean out the secondary's.

[dznucks]

plugs look fine, slightly tan.

[60ratrod]

then i would go to the cal chart in the edelbrock book and go one stage richer from where you are sitting currently at WOT. i would look to see which one is just the rod change for WOT.

[mongoose]

does it work better when the choke is closed? if it does means you're to leannn

[dznucks]

It acted different when i held the choke closed and floored it. i wouldn't say better, but it didnt stumble.
i was at the base calibration for a 1406 with the heaviest springs in (from the 1487 calibration kit). I went to calibration point 23, which was a rod only change, and it does act better when i punch it. i will post back tomorrow morning after i drive it to work.

thanks guys.

[cdowns]

i posted in wrong post sorry

[dznucks]

The stumble when i nail the throttle isn't as severe, but the power mode is alot rougher than it was. its like it doesn't want to smooth out until your out of the power mode or secondary's.
should i go richer or am i too rich?
would the accel pump have anything to do with it? i am in the middle hole on the pump shaft.

[60ratrod]

again, check the edelbrock book. you can try to change the accelerator pump stroke. but i would check the book

[dznucks]

i leaned out the secondary's and that seems to help. i have gone from the stock rods to calibration point 24, 23, and then to 19, with the backfire out of the carb getting worse the richer i went.

to address mongoose's question of whether its better when i hold the choke closed, yes its much much better when i hold the choke closed, no backfire at all, ie I am lean. that being said why would the problem get worse by going richer.

my timing is at 12 deg initial and 32 mechanical with 12 added by the vacuum advance. do i need to advance my timing further to 14 or 16?

[dznucks]

I haven't mentioned yet that it is a stock 350 with a mild "towing" cam. Vacuum is steady at 17".

[mongoose]

what are you making richer? the whole primary side? or the the shot... if the stumble gets better with the choke closed.. or your hand over the horn, just richen up the pump shot.

[dznucks]

i was richening up the primarys via the rods. let me try the pump shot.

[etg]

Hope it's okay to revive an old thread. Anyone know how DZNDCKS was able to fix this problem? I have a 350 block with 305 heads and what sounds like a mild rv cam, and en edelbrock 1406 600 cfm electric choke carb. I was just messing with the choke today and got that to work, although it idles faster than it should I think (without a tach I'm just going by ear). BUT It will backfire and pause if I stomp the gas. Stead acceleration is fine, but stomping it makes it pop and I saw fire come out the carb. I keep reading this is a lean problem, either something is not calibrated or the accelerator pump is not working, but the carb is pretty new (2 years on the truck without being used), so I'm guessing it's just not set right. I just downloaded the manual, any hints or tips? I know to check my timing, but I have no clue how to dial it in.

[60ratrod]

Well first off 305 heads are the worst choice for that motor. Next for dialing in the timing just right read the sticky at the top of this section. But i would really check to see where the timing is at. Too far retarded can cause this too. And the idle should increase while the choke is opening as the motor warms up then return to normal which should be around 700-750 rpms
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[dznucks]

I did solve this problem, i was way too lean. i installed a A/F gage and tuned that edelbrock to as good as it could possibly get. My motor is a 350 with RV cam.

I could never get that carb to ever run right and i had a Demon and Holley on the shelf. The holley was better then the edelbrock, but with a lot of i was able to make the demon run like a champ.

i no longer run the carb, so problem solved.

[etg]

thanks dznducks. I think I will read the manual and figure out how to tune the carb to the right settings, That would be the obvious first step, since it's new and so is everything else, I think it will work fine. As far as the engine choice, I'll admit it sounds lackluster. I originally had a 305 and was offered by the shop a 350 block and they would use my heads. They said the compression would be higher but not much else would be different. If anyone can shed some light on this great.

[60ratrod]

Higher compression isn't always a good thing. 305 heads are way too small for a 350 all around. The valves are too small, the intake and exhaust runners won't flow enough for that motor. With the bump in compression that those heads are giving you you are going to run into pinging and detonation unless you run premium and tune the snot out of it. Depending on the style of pistons he used in the short block you are looking at a static compression of at least 10.5:1. Generally where you want to be with a street motor is about 9.5:1. Do you know what kind of pistons he used? Flat top, dish?
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