RedGut86

Hey guys, so I bit the bullet and put on the 1095 AFRs (65cc). My Ported Darts (65cc) flowed about what the Elimnator Street heads flowed but at a 200cc ported head, I figured I should pick up some good power with the Comp AFRs.

Long story short, got them on and it has a miss and is backfiring out of the exhaust...and it is getting worse it seems.

I've backed off all the rockers (loud as hell now) so I don't think I am hanging a valve. Things that could cause this?

- Burned exhaust valve
- Bad head gasket
- Piston kissed a valve
- Anything else?

The two things I want to additionally mention and see if anyone knows about here are:

1) My intake barely seals the gaskets (1206). I think I am going to need to add some material to it. I did use a thin film of RTV to make sure it grabbed the gasket on the top side...but I don't think even if it was leaking this would cause that issue right?

2) When I set the driver's side head down on the block it would only go on one of the two dowel pins at once and wouldn't sit flush. Pulled it and double cleaned around the dowel pins (no change) and then kept trying to slowly set it down and it looked like it finally dropped evenly. I'm wondering if this could still be problem and causing the headgasket to leak slightly?

Compression test came back all w/in 20% and I tried the harbor freight leakdown tester but it was a piece of junk and wouldn't seal between its fittings so I don't have a leak down test.

Sorry for posting this here, but this is the only board I frequent here and I'm looking to you guys (Joe) for some help, not sure where else would be appropriate. Self taught on how to build motors and pulling my hair out here.

Thanks in advance!

EDIT: See third post below, Spark seems to be good (wires/plugs/cap/rotor etc). Also, I can hold a piece of paper to the tailpipe and it will intermittently (only for a very short interval) suck the paper flush. It is more of a flutter since all 8 cylinders are coming through all the tailpipes but it would appear that it does have some suction which makes me think exhaust valve or maybe gasket?...

//<86TA>\\

iTrader: (14)

forgive the question, but its free and i've seen experienced people mess up before. are the sparkplug wires on right?

RedGut86

No, thanks for the reply. I wish so badly it was that. Heck, the first time I fired the motor many years ago I had a spark plug wire off (5 and 7 switched) and I thought I had screwed up something on my new motor for a second!

Sadly, checked, double and triple checked. Even had somebody else check them too. No dice, they are on right.

Also, all the plugs are getting spark. Car has a brand new cap and rotor as well. Plugs are new and not fouled.

Good question and I wish it was the cause. Thanks.

1989GTATransAm

iTrader: (3)

Are you getting a good seal at the header gasket? Any leaks may cause the O2 sensor to read wrong and cause a rich condition with the resultant backfire.

RedGut86

I'll go check again, I think it was good. I haven't seen anything that looks like a leak in terms of blackness etc around the gasket.

Would that cause a miss though? Or suction at the tailpipe?

It definitely could be a combination of things so I'll report back on the gasket as it could be contributing a separate problem, but you can definitely feel the miss especially when you are holding any rpm steady in gear.

It also feels like you have to give it a lot more throttle to get the motor to rev, I would say it feels like a clogged cat but I can guarantee that is not currently an issue.

Thanks for the suggestions Allen!

(As an aside, I still haven't ported the manifold but man it needs a good hogging out once I get this problem squared away. The 1206 gasket makes those ports look little!)

RedGut86

I'll also add in terms of piston to valve clearance (I'm thinking if it is a kissed valve, it had to be crappy valve adjustment hanging one open big time) because both heads are 65cc combustion chambers, the cam remained the same (LPE 219 with 0.560" lift), quench is 0.039" (0.026" gasket with 0.013" deck). The only change was from a 2.02 to a 2.08" intake valve, I used a 0.002" thinner head gasket and of course the CC shape change.

TMFK

[QUOTE=RedGut86;4598740]

Would that cause a miss though? Or suction at the tailpipe?

Do a compression test. If you find a weak/dead cylinder, do a leak down test. You could unplug the coil and spin the engine over to see if it sounds even first. Hope this helps.

RedGut86

I did run a compression test. (It was a cold one though...)

Driver's side: (#1,3,5,7) : 100, 110, 110, 110
Pass side: (#2,4,6,8) : 122, 115, 110, 115

Also, vacuum is fairly steady at idle, does bounce ~0.5-1 mmHg.

Orr89RocZ

iTrader: (20)

Just thinking of the obvious. Timing is set right, distributor is in right? Correct length spark plugs for the heads? Whats the plug gap?

I dont think the valve would hit the piston, you'd probably hear something like that at idle. You should have plenty of PTV with that cam anyway.

Do verify the intake manifold is sealing right against the heads. That certainly wouldnt help the situation

RedGut86

I thought I should be good on PTV too.

I'll verify the intake seal, starter fluid?

Plugs are AR3933, pre-gapped and cut-back by autolite. Cold, but they appear to be burning ok and recommended by an engine builder who knows his stuff.

Thanks for the input.

Orr89RocZ

iTrader: (20)

ignition module in the dizzy still ok? Cant really think of anything else that would cause this.

Pushrods are straight and not bent?

RedGut86

Ignition module... could it be that? I do have an MSD 8366 distributor, I'll have to look around for another module.

Could a bum ignition module cause a popping/backfire in the exhaust though?

I sure wish my big cap HEI dizzy still fit, I'd just drop it in to check but unfortunately it is too big now.

Orr89RocZ

iTrader: (20)

Bad module probably could cause missing and failed ignition resulting in fuel being lit in the exhaust. I know these things can go bad, but not sure how to test for it other than to visually inspect it for burn marks/corrossion/etc.

Popping like that sounds like timing problem which could be from bad dizzy or failed ignition firing. Its worth inspecting if you havent already done so. Inspect everything from cap/rotor/module/wires just to double check.

RedGut86

Hmm, I will.

Plugs- new
Cap/Rotor - new
Wires- ohmed out on the high side, but I would think they are ok as long as they are carrying spark, no?

Dizzy... well the reluctor did look rusty/corroded when I pulled it out but...
Also, the dizzy was in a box that got knocked off the shelf when the heads were being swapped, it chipped the rotor which is why I replaced the cap/rotor but I wonder if something else got messed up in the fall...

How do I test the module besides replacing it?

Thanks

Duts87ss

iTrader: (10)

It's been my experience that ignition modules don't create any issues; they either work or they don't. I have, on the other hand, had a pickup coil go bad and keep any timing advance from making it to the plugs. A drop could have very well damaged the pickup coil.

GS89IROC

Today i called a eprom burner to have chip burned for me. One of his final questions was do you have an msd distributor? cuz several people have complained of a missfire....turns out that the msd distriburors have had bad pick up coils....just thought i would share that.......

RedGut86

Thanks guys I am going to check ohms on the pickup coil and also the gap between it and the reluctor as well. An intermittent miss at idle definitely fits the description. Man, I want to romp on this new setup so bad... I hope this solves the problem.

Though if it does, I'm not sure I want to pay the bill!

Thanks! I'll update with results.

88BlackZ-51

iTrader: (2)

comp ports? i thought u for the street ports? kool!

RedGut86

No, comp ports. The street ports would not be an upgrade from my Dart heads. (Same flow but with Ti retainers etc...)
https://www.thirdgen.org/forums/engi...ro1-200cc.html


I did get to ohm out the pickup coild 590ohms. So that looks good, also looks like clearance to the reluctor ring isn't bad. The ring is definitely rusty looking though....