[Echofive]

I just put my motor in my el camino, started it broke it in etc... It runs strong except when i stand on it. when floored it pops through the carb, and stumbles. somtimes after i start it it pops through the carb also. I have set the timing at 12 initial. the engine is a 350 with edlebrock performer RPM heads and intake, flat top pistons comp cams 270 mag cam. (.470 in/exh 224 dur. 110 sep) flat top pistons, 1 inch spacer. crane XRI elec igntion hooked directly to keyed 12v source with stock coil, gets good spark. idles ok, runs ok. The carb is a 670 street avenger. Do you thing the stock jets are too small for this engine? I was told by an older hotrodder fellow that i should up them 2 sizes and see how it runs. It also pops and dies sometimes when i press the gas after starting when cold.

Couple things im unsure about are total timing, carb idle setup, rocker arm adjustments, accelrator pump shot adj.

How many miles should i put on it b4 i can switch to synthetic. It has about 100 miles on it so far.

Retorque everything after about 500 miles?

 

[TurboS10]

What you are describing does sound like a lean condition, but I would start with the accelerator pump. Make sure that it is set so that it reacts as soon as you hit the throttle. I am not sure if they do, but I think that the avengers have power valves like the holleys. It is possible that the valve is not opening soon enough. It is also possible that the secondaries are opening too soon and need a little stiffer spring(assuming vacuum secondaries). There are alot of things that can cause the carb to go lean when it is in the transition period from cruise to WOT. You just have to eliminate them one by one.

That said, I would try bumping the initial timing up a few degrees before doing anything. The best way to do this is to switch the vacuum advance on the distributor to a manifold source instead of a ported. This is assuming that you are getting 12 initial with the vacuum advance unhooked and it is not on ported now. If you did not set the timing with vacuum advance hooked up, reset it.

Chris

 

[Echofive]

i set the timing at 12 initial with the vaccum adv plugged. ill try a full vac today. I tried putting in a stiffer spring that helped out a little bit. but still popping a little. Should i bump the jet size up a couple? to what happens?

 

[TurboS10]

Bumping the primary jet size will certainly not hurt. I am not real clear on whether the condition clears up after the initial drop of the throttle or if it persist. If it is popping all the time, you definately want to go up a couple jet sizes. If it is just when you drop the throttle, it is only a lean condition caused by the transition from cruise to WOT in which case the main jets have much less to do with. In that case accel pump, squirters, PV, secondary timing(spring) are the big players.

You want to set the timing with the advance unhooked and plugged to around 12. Then when you hook up the advance to manifold vacuum the timing will advance and the engine will speed up. You will likely then have to reset the idle speed. Timing definately has alot to do with how an engine acts on acceleration. If it is too slow the engine will tend to pop back through the carb. Hooking to manifold vacuum will help this alot and make the engine much more responsive.

Chris

 

[Echofive]

OK, I hooked up my advance to full vac. Noticed a nice diffrence. it does seem alot more responsive.. in drive that is. I also adjusted my acc pump and it doesnt bog off of idle anymore. It still pops through carb at WOT. even half throttle seems to stutter/bog not a whole lot but i think there is alot more power potential. Will increseing Jet size Kill my gas mileage more? I'm gettint like 8 mpg right now. I dont give it more than 1/4 throttle very often. So I think something is out of adjustment. Could rockers being to tight make it pop like that?

 

[NovaSS350]

Yes having the intake valves lashed to tight could cause this same problem. How tight did you set them? I usually do it with the engine running and tighten until they stop clattering then another 1/4-1/2 turn. Are you using regular nuts or poly locks.

 

[camaroman7d]

If you are only getting 8mpg with that setup, you definetly have some tuning issues. If you hold the accelerator at a steady speed (lets say 50mph) does the car surge/stutter as you are driving? If so you are too lean on the jets, if you mash on it from that speed what happens?

The popping through the carb when cold is to be expected, if you are not using a choke.

If you fixed your off idle stumble (which was acc. pump related), now you just have to figure out the rest of the tune-up. How did you set your air mixture screws?

I don't think jet sizes are going to hurt your mileage, you have some other tuning to do as well. You have to take it one step at a time. I would suggest starting with the idle circuit and then work on the main circuit. If you try to do too much at once you are going to get lost and not know what helps or hurts. If when you mash on it it pops or "bogs" you probably need a larger acc pump cam and/or squirter.

Before I started messing with that I would like to know how much vacuum you have and would suggest setting your idle mixture screws by either vacuum or highest RPM (should be the same). Once that's done reset your idle. Go for a ride and see how it runs. If it bog/pops off idle then move to your squirter/acc pump and get that sorted out. Then worry about jetting once you get you idle/part throttle smoothed out.

Royce

 

[NovaSS350]

Couldn't that off idle bog also be a timing issue?

 

[camaroman7d]

NovaSS350,
Yes it could be timing related.

He said he had 12* initial but, never mentioned total or at what RPM the timing is all in by. This is why I said there are a lot of tuning issues to work out. It's just not as easy as bolting in the engine and going. This would also explain his poor fuel mileage. It is just a matter of tuning one thing at a time until it runs decent and then tuning it again for best performance.

Royce

 

[Echofive]

I drove it home from work, warmed it up b4 i took off, it did pop thru carb a few times, (i dont have a choke) i was going about 55 down the road and gave it some gas to a lil more than 3/4 throttle it accelerated but kinda didnt sound right, it like sounds like garbage. kinda hard to explain. doesnt sound smooth like it used to. floored it and it sputters for awhile then catches eventually. doesnt pull smoothley

I'm going to adjust the idle mixture with a vacuum gauge this weekend, and readjust all my rockers whiles its running. One guy i tells me 1/4 turn and one guy says Half.. what would you do Royce?

It's getting there, just taken time. Thank you guys for all your help!

 

[TurboS10]

Royce is giving you good advise. You must tune these things one at a time and it will get there eventually. On the rockers, 1/4 or 1/2 does not really matter. I always use 1/2.

Chris

 

[Echofive]

I was trying to do the rocker thing, and its hard to tell when they start clicking, cuz my exhaust is soo loud. but i will try again once i get an old vavle cover cut in half.

I got on it again and it seems to really pop at about ~4500 (I dont have a tach) it quits pulling and pops alot. and it doenst seem to be really any faster than it was with the stock 350. and I added Heads, cam, pistons... I'm gonna keep playen with it let you all know when i get it runnen better.

 

[NovaSS350]

What kind of ignition are you running. Some say that the stock HEI is only good till about 4500 RPM....

 

[engineman302]

imp: is it a new carb or old ,what about fuel psi, float level for secondarys?

 

[Echofive]

The ignition is a Crane cams XR-i (elec ign) under a stock distributer the rev limiter is set at about 5500 and the with a stock coil. the fuel pump is a new stock unit. i dont know about fuel pressure, whatever a stock one will pump i suppose.

I've tried 2 springs in the vaccum sec. float levels are how holley said to set them just below the bottom of the cleat sight plug.
The carb is about 18 months old it prob only has about 2,500 miles on it as the car wasnt driven very much and it sat for about 9 months.

 

[engineman302]

:smash: if the carb set around for any length of time, i would check for dirt dobber plugs in it, here at my place if anything sets for a month they seem to find the smallest holes to build in. i would go ahead and take it apart and check the metering blocks for blockadge.but first i would borrow a carb from a friend on a running engine to eliminate other problems.i had a 72 chevy one ton with a 350 and it ran fine until i called on it then it poped and spit i put a new fuel pump on it and it done the same thing ,i knew the carb was good so i checked the fuel flow and found it less than it should be,i took a air blower and blew a rock out of the line from the tank to the pump.