Frustrated - flames from carb/stalling issue

[awd92gsx]

OK....since installing my cylinder heads/intake/carb/cam a couple of months ago, I can't even get the car to run correctly under a load. In neutral it runs fine, no problems whatsoever...it even idles ok in drive/reverse...I can drive it...but, as soon as I put a load on it I get inversion through the carb and sometimes flames shoot out of the carb as well. After the inversion it will die, or at least try to die on me.

 

Here's the list of parts:

 

350 bored .40 over stock compression

1.6:1 roller rockers

262/272 Summit Racing camshaft (part # SUM-1102)

600cfm holley carb (new)

Weiand Action Plus Intake

Dart Aluminum heads

 

Things I've checked:

 

-Carb (that's the reason the Holley is on there instead of a Qjet)

-Manifold/Vaccum leaks. (I've even gone as far as pulling the manifold and replacing the intake manifold gaskets with some high quality FelPro pieces AND used a sealant on the manifold gaskets to ensure a proper seal. I've sprayed the entire intake/carb area with brake clean/carb cleaner and found no signs of leakage

-Timing - If I run 12-13 degrees of base timing it WILL die as soon as you put it in drive at an idle...but if you bump it up to about 18-19 or so it will idle in drive, but, die under a load. Vaccum advance appears to be working properly....when engine is revved advance jumps up to around 36-40 (depending on where my base timing is already set)

-Camshaft Timing - I pulled the front cover to ensure I wasn't off on my timing marks for some reason, they are dead on.

-Plug Wires - I had found that some of my plug wires were arcing against my headers due to no clearance between the plug boot and the header, but, I replaced the burnt wires and applied some header wrap on my headers...they don't APPEAR to be arcing any more...but, I haven't been able to look while somebody power brakes it for me.

 

The car ran absolutely perfect before installing the new par.

 

Now, it only seems to invert through the carb during initial accelleration. If I power break the car when I first give it more throttle it starts to stumble, but, a few seconds later it will clear itself up...unless I really mash the throttle, then it will shoot a flame through the carb and die (most of the time).

 

I'm open to any and all suggestions (other than dropping an LS2 in there )

 

Help!

 

Frustrated in Phoenix.

[80LS1T]

The thing that jumps out at me is the plug wires. I would get a new set for all 8 plugs and try it again. It doesnt take much to mess up a plug wire with heat from a header. I know because I too melted some wires on my old headers.

 

Also double check your firing order is correct for your wires.

 

Backfiring through the carb usually means wrong timing, lean, or wrong firing order. Thats what I have experieced aleast.

 

 

Guy

[280zwitha383]

If I had to guess I would say firing order. Usually firing out of the intake is a sign of bad timing... I wouldn't think that a bad wire would cause the problems you are desciribing, but stranger things have happened.

[Corzette]

Yep...firing order is my guess, provided your not off a tooth on the cam...

 

Terry

[jbk240z]

I once had a '78 TransAm that had the backfire through the carb thing. The previous owner had installed a new mild cam, headers, intake, carb, etc. Well, I played with timing, changed the distributor, plugs, wires, carb, intake gaskets, etc. To no avail. An old timer I was talking with said, "you got some flat lobes on ur cam boy". No way, I thought the cam is new..........

well I pulled the cam , and sure enough there were two flat lobes. I guess the cam was not broken in properly. Anyway, I'm not saying this is your problem, I just thought I would share the experience with you. Good luck on getting it solved.

[jt1]

Hydraulic cam? If so, check to make sure the rockers are adjusted properly, and that the plungers in the lifters aren't stuck or bottomed out. Also check to make sure the pushrods aren't binding against the heads. One thing that could cause this is the intake valves not closing completely.

 

jt

[Pop N Wood]

Backfiring through the carb usually means wrong timing' date=' lean, or wrong firing order. Thats what I have experieced aleast.

 

Guy[/quote']

 

I will third or fourth that. Bad plug wires can cause cross firing, as can the distributor cap. Check the inside of the distributor cap for carbon tracing...deposits around the inside which are evidence of arcing. Also check for cracks. I had a car do what you describe and it was a bad cap.

[WickedWild]

My vote is on the valves not opening or closeing all the way. Run it with the valve covers off with load on the engine.

[iaconsultants]

It could also be you need to re-stab your distributor, in many cars you can miss by a tooth or two and the car still runs but has a lot less or no power under load. This can also cause backfire issues through the card. Another possibility is check your distributor cap (hoping it is new) and see if you already caused heavy oxidation or some burn marks. You might be running to hot a spark for your distributor, wires, and plugs combination. They can even jump post to post if there is a bad wire and a hot spark. Mixied up wires tends to cause a rough idle. A bad wire causes a dead spot idle that can also be intermittent but will usually idle fine cold and when it gets warm will start acting up and loose a little power but generally does not cause a backfire through the carb but does cause a stumbling effect. Here is a long shot if you are running a power valve in the carb then you could have blown out the power valve with one backfire and then you will keep backfiring like you are. To check the power valve is easy just remove and apply a suction with your mouth on one side and see if it holds. If not you will need to replace it. My bet is that your distributor needs to be removed and then put it back in when the car is at TDC not BDC. I have seen it before and it is an easy miss. God luck.

Robert

[awd92gsx]

OK...

 

The firing order is correct. It runs perfectly fine while not under a load (IE...in neutral) unless you really stomp on the throttle, then it might hiccup a tad bit, but, otherwise do ok. The problem is when it's put under a load.

 

Now, one thing I did forget to mention is that under normal timing conditions (anything around 12) my #3 & #5 cylnder header tubes would actually glow...advance the timing to around 20 and they'd stop glowing. Hmm...wonder if my valves might be a little tight on those cylinders?

 

I've been told I might have to run more advance, but, exactly how much advance should be needed?

 

I had experienced the two flat lobes (actually, that's the reason I had put in the new cam), but, it would also have problems in neutral, rather than only under a load.

 

Supposedly the new holley's come with the anti-blow out valve for the powervalve already installed, but, I haven't ruled that out either.

[iaconsultants]

interesting so one cylinder bank has two glowing header tubes. Could you do a compression check on all your cylinders and see if those two cylinders are different from the rest. I am just wondering and this could tell somethings. Also when you run the car see if you get puffing from the valve cover (crank case pushing air up known as blow by). You probably know where I am heading but I hope I am wrong.

Robert

[Mikelly]

It still sounds like you're out of time somewhere... Maybe the cam gear is off a bit?

 

Mike

[peej410]

my Z had all sorts of problems when i first started it up, first problem was that i was off a tooth on the dizzy (distributor) second was a valve was way too tight, (bent a valve) third was the distributor. my car did the exact same thing the first time i drove it, huge explosion through the carb and very little power, there was no hood on it and it was running open headers, it really lit up the night sky!!! check compression, re-time it, check double and triple check your firing order, make sure you dont have any tight or loose valves. check all your plug wires, use wire seperators, only let the wires intersect perpendicular to one another. look for manifold leaks on the cylinders that are running really hot. check to make sure that all the needles in the carb are clean. make sure your accelerator pumps are squirting evenly (visual check) make sure also that nothing crawled up your exhaust (happens to us all the time) and clogged your mufflers with dog food or insulation. when trouble shooting a problem like this eliminate EVERY possible variable and youll find the solution in no time.

[PeterZ]

Good ideas from everyone above. I would also recommend verifying the cam is what you ordered. I helped install a kit for a truck and the cam was way wrong and did what you describe but it had 8" Hg at idle. Summit sent the wrong cam in the right box. Summit was OK with replacing the cam but we had to pay shipping and for all the gaskets. We didn't check while the engine was on a stand. Also, my Z8 cam runs like $#!+ without about 25 degrees advance at idle. (It has the performer kit with alum. heads) I had to get creative in changing the advance curves so I didn't have 60 degrees at 4500RPM but it is much happier now. I could see how a lean condition and/or "retarted" timing could make a few cylinders run hot, I have no idea how effecient your intake is at idle. Good luck.

[MONGO510]

have a flat cam. Remove rocker covers, watch each rocker arm. the lobe that is flat will have a noticable difference in lift and a noticable difference in its acceleration. Good luck.

[Michael]

I'd have to agree with the folks who have mentioned the wiped cam lobes - especially if this is a hydraulic flat-tappet cam from Comp. I had the exact same symptoms on my big-block, after installing a mild hydraulic flat-tappet cam from a Comp "K-kit". Unfortunately this won't be revealed by a cranking compression test - you'll have to pull the cam.

[awd92gsx]

Well, the reason I changed the cam is because I had a couple of lobes go flat on me, but, when that happened, I could definitely tell I had a miss, even in neutral...

 

Would a flat cam lobe cause issues only during a load, though?

 

If it is a flat lobe again, I'm gonna have a V8Z with lots of goodies for sale...cheap.

[Michael]

In my case 4 lobes were wiped - one was wiped right down to the base circle! Idle quality was quite good, with the only exception being an occasional popping noise every few minutes. The popping noise increased in frequency and volume with increasing rpm. There was no discernable loss in performance except at the bitter end, when one pushrod actually broke in half and another buckled and was on its way to breakage. However, this was my first V8 and I had no benchmark for comparison of how much power to expect.

 

Another thing to check, if this is a hydraulic cam, is the valve lash. If you adjusted the lash by the usual method (tighen the rocker nut until the respective pushrod no longer spins by hand, then tighten another 3/4 turn) on every valve, and then notice that for some reason one or more valves seem to have picked up some lash, chances are high that the respective lobe is toast. Of course, it's also possible that somehow the rocker adjustment nut isn't holding tightly on the rocker stud - that would be good news, as it were.

[strotter]

Another thing to check: did you replace the little bracket with the timing marks on it? This one got me, turns out there are a couple of version with 12° (I believe) difference between them - early and late styles. 12° off on your timing may cause those symptoms.

[awd92gsx]

Michael,

 

I remember that happening on my old camshaft...but, I've not heard any lash noise since installing the new camshaft. I'll try to go out in the garage and watch for the valves going up and down tonight...

 

Strotter,

 

I thought about that, too, when I put my cam in and checked to see if both lifters were all the way down when it indicated TDC on my timing marks...they appeared to be down..

 

the puzzling thing is that I can advance the timing and get rid of 90% of my issues...Now, I remember when my cam lobes had worn I couldn't get it to run right no matter where the timing was set...it would still miss. NOT to say that a worn cam lobe couldn't or wouldn't cause my symptoms, but, I wouldn't think a mechanical issue would be so affected by timing...but, I may not be completely understanding what causes the symptoms either.