I recently built a 400 sbc. I bought the shortblock assembled from a machine shop, and put on vortec heads and all the other goodies. But the problem i have is its smoking at idle pretty good, i think its a whitish blue color smoke. It wasnt really smoking much when i first started it and drove it about 30 miles but now after its been sitting about 6 mos its smoking and fouling all 8 plugs. I installed new plugs and it ran better than its ever ran before but after about 20 min of idling it after installing new exhaust its missing really bad again and i know its the plugs fouled up again. It did smoke alittle bit when i first ran the engine and it fouled the first set of plugs but i thought it was the carb or tuning and didnt think nothing of it. But the vortec heads were low mile and have fresh valve jobs and i installed umbrella valve seals to allow for more lift on my cam. I dont know where to start, i dont know if its the valve seals, guids, or piston rings. I know the cylinders had a fresh hone job and looked good when i put on the heads and i had new pistons and rings so im hoping all thats good. Does the motor just need to be ran down the road for awhile to seat everything up good. Ive drove it about 30 miles but havent hit the road with it since because the car isnt legal. but any help is appreciated. thanks

 

Id also like to add that more specs on the motor can be found in my sig. And the plugs are definately black. And the motor doesnt have a pcv system, i just have breathers in the valve covers as thats the way ive always done it. If you need anymore info just let me know as id like to get this thing on the road.

 

How many miles on the 400 cid? If you haven't seated the rings, then you'll need to run the ***** off it (heavy load), and get those seated. You might have polished the bores and are getting massive blowby.

Try stepping up to hotter plugs (2-3 steps) and see if they stay clean. Watch the heat line on the plugs to see if they are too hot or not.
Watch out the tailpipe to see how much black smoke you're getting. If it's at idle, or if it's under load, etc etc. That can help you tell where you're getting the oil you're burning.

Side note - You drilled the vortec heads for the steam holes, and used 400cid head gaskets right? Just figured I should ask to be sure...

Keep in mind, with a big cam like that, and the high compression, you will have a tendency to load up at idle, since you're probably running it quite rich to get it to idle. One way to help that is to increase your timing at idle. I hope you don't have it super rich and running 10* of advance or something eh? You should probably have 32* all around (no curve), and less throttle blade angle at idle.

 

Thanks for the response. Yes, i had the heads drilled for steam holes and used 400 heads gaskets. The motor only has the 30 miles that i drove to park it where its at now. I got on it a few time but didnt drive it hard by any means. The only time ive saw black smoke is when i punch it from a stop, which ive only done a few times. The smoke i notice is bluish(kinda hard to tell which color for sure) It seemed when i drove it down to park it that it wasnt smoking at all, especially when driving. But as ive stared it here and there to idle it, it has got alot worse. To the point that now it fouls the plugs in 20 minutes. And the exhaust is completely black inside and it has only been on 20 minutes worth of run time. I guess when i get back in ill install my msd ignition system and set the timing( right now i do it by ear) and install hotter plugs(does anyone have a part number for hotter plugs specifically for vortec heads that i could get from autozone?) And if you have anymore ideas i appreciate it.

 

Your definately pig rich at idle.I'd venture a guess that an 850 carb is a bit much for your combo,a 750-800cfm unit would likely improve your problem,as well as give better throttle response.

 

I need to update my sig, the motor now has a Holley hp 750 DP Street on it. I thought the 850 was a bit much myself, i thought the carb might of been the reason it was cutting out but found out is was fouled plugs.

 

The carb size won't effect it's idle quality.

Set your timing and idle mixture right and you should be fine. Check the heat line on your plugs and change accordingly.

 

this is a horribly stupid question i'm sure ,but what is the heat line your referring to sonix?

also blue smoke means burning oil ,but if your not sure that it's blue it may very well just be overly rich. personally i'd probably do a dry then wet compression test and see if the rings are sealing good.

Also a pcv in 1 of them covers is far from a bad idea... a little negative crank pressure does promote sealing. for the 3 dollars one costs i'd run it and see if it helps any.

 

http://www.angelfire.com/fl4/pontiac...Readplugs.html

Your plugs can (and are supposed to) self clean. You just need to get them hot enough to do it. But if you get them too hot they will promote detonation, hence, read the heat line.

And yes, having no PCV will help push oil past the rings alright. I'd run a PCV, it's better for oil life.

 

wow sonix i really really feel ignorant for asking that ,but i do appreciate that post up.... I actually never knew of the heat line aspect about plugs........ thats a good tuning device. for us to poor to afford a Wb.

i've also found a infared thermometer is great for tuning especially in a carb'd application when you have wet fuel distribution to worry about. Personally i'd rather run a cylinder or two a little rich then have any single running too lean so egt's are quite helpful in determining this.

anyways thanks again for the link, as i'm still working on brushing up with all the tricks to tuning (need all the help i can get since i failed my ase cert for engine performance lolz).

 

I finally got home and had some time to work on the engine. I replaced the plugs with champion rs13yc they didnt have hotter plugs for me. But it runs great again, i drove it around for about 5 minutes(no plates) only let it idle for at most 7 seconds, then i checked the plugs and they are already completely covered with black soot. There is no way to check the plug heat range or even jetting simply becuase the whole end of the plug is covered black sooty. I did notice that the engine dosent smoke when driving or reving, only when i let it idle does it smoke after a few seconds. I also checked my oil and it smells like gas? I think its time to check my carb jetting, i think someone might have been into it before me. And i didnt have a chance to check my timing because my timing light broke on me, but i advanced it as much as i could to still have the engine crank itself withought being sluggish. The smoke at idle really dosent look black, it looks for blue or white mix. I think its definately a tuning issue with the carb and not the rings or valves like i thought. I was just wanting to update incase there were anymore ideas. thanks

 

I wonder if it is so rich that the gas is washing the cylinders wall of oil...that would be bad
Fouling the plugs and the smell of gas in oil.
Causing blow by without oil to seal the rings.

any news?

 

Let's start wth the basics, back at square one rather than throw darts are a board and see which ones stick.

List all the specs and clearances on the short block build and the cylinder heads. Machine work done, piston to wall clearance, pistons installed, rings, ring end gaps, etc. Youhoujld be able to get than information from the shop that did the work.

What power valve is installed in the carb and what's the vacuum reading? Ignition timimg, camshaft, lifter preload setting, on and on.

Because your condition can be caused by anot number of different things, we need lots of details to try to pin point the cause. Otherwise all you'll get are unsupported guesses.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2020!!!

 

wait this is a carb that someone could have set up on thier own

check into your jetting

 

Unforunately im an over the road truck driver so i have limited time to work on the motor, but before i left i ran it another 20 min or so and didnt let it idle at all. It smokes dark grey smoke and black when i punch it, but the smoke is dark and definately not white. It still runs great which tells me the plugs arent fouled up yet... after about 40 minutes total run time but like i said they are completely black and sooty. I have no idea on the shortblock measurments, the machine i got it from its 600 miles away and for all i know out of business. I set the valve lash 1/2 turn past when resistance is felt while spinning the pushrod. The heads have been milled alittle bit, not much and they are standard vortec heads off a 98, they were a factory pull of because the engine smoked they were on, turns out they didnt have valve seals installed so i had them milled, valve job and put on springs and umbrella style valve seals to allow more lift for my cam. I traded my 850 demon carb for this one which is a like new hp 750 street version. He said it was on his high horse motor and wasnt enough so im afraid he might of jetted it up really rich for his motor and its not working on mine(ill check it when i get back in). Its got a crane 294 cam(i dont have the part number right now but its somewhere in the 488 lift, 236,244 dur range). Its got the stock crank turned .010,.010, gm 5.7 rods, and keith black standard forged pistons. Ive almost decided to get a scat forged rotating assy and get the block bored .030 and put it together again all new with a bottom end to handle whatever i want to throw at it, plus have it be internally balanced, but while im at it ill get some dart pro1 heads( i need standard ports, which afr dosent seem to offer) and just go all out on it. Id prefer to run the motor like it is for a year or so and maybe blow it up first before i do a full rebuild on it(as long as i dont throw a rod out the block) but if it dosent stop giving me probs ive got no other choice but to redo it myself to make sure its right. But it just huffs alot of smoke and it didnt use to(come to think of it, it didnt when i had my 850 demon on it, atleast not nearly as bad) I havent checked the carb out yet, so i dont the any jets or accelerator pumps. I wont be able to check out the carb for a few weeks, i just like to gather as much info as i can so when i get home ive got a list of what to check out. And if you actually read this far, thanks in advance.

 

You said "air gap intake". Is it a Vortec style intake, or a "regular" SBC intake?

Did this happen with either carb, or only the 750 on there now?

 

The intake is designed for vortec heads, its just not a name brand intake, but it looks like a air gap intake from edelbrock, i thinks its proform or something like that. With my original carb, the plugs slightly fouled which could have been when i blew my original head gasket and never changed the plugs. The motor had a hesitation and slight cut out when revving it so i thought it was a carb problem and replaced with current carb. Since i installed the current carb the original set of plugs fouled to the point where it wouldnt start, second set fouled in 20 min or less and the third set is on now and has 45 min or so and still going just no idling. The 850 demon never fouled them up that bad and may not have fouled them at all it may have been from other means that they originally went bad( coolant in the cylinder from head gasket) and i never noticed much smoke to speak of with the demon, i also let the motor idle long periods of time and drove it about 35 miles or so with the demon and they never went bad it always started up fine, just had alittle hesitation and cut out from where the plugs werent in the greatest shape(i didnt know it was the plugs causing the prob at the time) now its smoking like a bitch(dark colored) and completely coating the plugs. I really think im gonna get like a small 600 or 650 to just bolt on it and see if it fixes the smoking and plug fouling, im kinda curious now it it is just a carb problem.

 

that 400 prob needs more than a 600 edl

there is a prob with the carb

how good are you at taking things apart and putting them back together

dont know much about holleys- never rebuilt one just edl and quadrajets

if you buy a edl try a 700 for that 400

 

the 600 carb is only to put on and run it to see if it still smokes and fouls plugs, since a 600 wont be too much i know it shouldnt be rich with one shouldnt have the smoking and plug fouling. Its only a trial and error, temporary use only. Rebuilding a carb is no problem as ive rebuilt several atv and motorcycle carbs it shouldnt be an issue, i just want to try a smaller one for trial and error to see if it solves the problem, if so ive got a carb problem, if not then look elsewhere.

 

Yep, carb first. Float level, power valve rating (if it runs one/them), fuel pressure, leaking boosters at idle, idle mixture screw adjustments, metering block idle circuit too rich, etc.

With your cam and idle speed, the vacuum level could be so low that the carb's idle circuit is being screwed up.

Other thoughts: Not enough ignition timing, vacuum leak.

BE SURE TO FREQUENTLY CHANGE THE OIL AND FILTER TO KEEP FROM KILLING YOUR BEARINGS.

Jake