NEW 489 BACKFIRING

[Shovelrick]

I put new M&H Race Master DR's 275/50r17" on my car since I had horrible traction issues with the old 454 that was around 400 hp and had older MT ET Street 295/55r15" on a set of Weld Draglites, it has 17" TTII's all around, so the 1st time I really get on the gas is from a rolling start around 15-20 mph to see if it will get traction and stay straight for 2-3 seconds and it did but now when I start the car I have a loud backfire till it warms up then it turns to more of a mis and the engine doesn't sound the same as before, after it was built, short block by a well respected race engine builder, I did the top end and had him check over my work then he broke it in on his new dyno then 5-6 dyno pulls 589 hp @ 5,700 rpm 600 tq 4,200-4,400 rpm So what's the 1st thing to take a look at when hoping to Not have to set up the mag base dial indicator on all the rocker arms, I'm checking plugs, wires & timing after work today, TIA Rick

 

[kmakar]

Sounds like a timing issue to me....

 

[Shovelrick]

That's what I'm hoping for, dist moved some when I jumped on it so I'm keeping my fingers crossed LOL

 

[kmakar]

That's what I'm hoping for, dist moved some when I jumped on it so I'm keeping my fingers crossed LOL

Hopefully you didn't lose any teeth on the distributor gear.....

 

[Shovelrick]

It's a Nitrided gear from Straub Tech so hope it didn't get wrecked

 

[kmakar]

Just thought about it, has your choke been adjusted at all, or is it disconnected?

Maybe after it's warmed up enough the butterfly is opened enough so it doesn't backfire anymore?

 

[Shovelrick]

The AED 1,000 carb doesnt have a choke but I had a little down time between jobs so I got 1 bank of plugs pulled, checked gap @ .035 cleaned and re-gapped to .045 and got 3 back in but had to go back to work, I have an hour or 2 before I take Kathy to a Dr appt in Tampa tomorrow so going to try to finish then

 

[Shovelrick]

Woops again LOL I'll get the hang of it

 

[kmakar]

Woops again LOL I'll get the hang of it

We allow you to delete your own posts too....

 

[Shovelrick]

Pulled, cleaned and regaped to .045 the rest of the plugs, hooked the timing light up, removed the air clnr and fired it up, 1 loud backfire and 2 small pops and back to normal, it was only idling at 600ish rpm so I turned the speed screw up to 750ish and timing was 18°-19° btdc with vac hooked it was 37°-39° @ 700-800 rpm, it all bounces a little bit and I didn't think to put my Mighty Vac on but will either when we get back from Tampa or tomorrow but it sounds a lot better, still burn your eyes, pig rich though but my Big worry was I screwed the valve train up but looks like its OK

 

[kmakar]

Pulled, cleaned and regaped to .045 the rest of the plugs, hooked the timing light up, removed the air clnr and fired it up, 1 loud backfire and 2 small pops and back to normal, it was only idling at 600ish rpm so I turned the speed screw up to 750ish and timing was 18°-19° btdc with vac hooked it was 37°-39° @ 700-800 rpm, it all bounces a little bit and I didn't think to put my Mighty Vac on but will either when we get back from Tampa or tomorrow but it sounds a lot better, still burn your eyes, pig rich though but my Big worry was I screwed the valve train up but looks like its OK

Maybe you'll need to adjust your mixture... if it's that rich that could be fuel left over to burn causing the backfire and pops.

 

[Shovelrick]

I used an infrared Tmeter and #7 was 80-90° colder than the rest on drv side was #3 130° rest were 175 & 178 pass side were all around 200° and Mityvac was bouncing from 5 to 10 so I have an issue on the drv side valve train darn it

 

[Shovelrick]

Compression test next then pull VC, might pull VC 1st to see whats up

 

[Shovelrick]

Compression test next then pull VC, might pull VC 1st to see whats up

No thats messy ill ck comp 1st

 

[Shovelrick]

Well comp test showed 170+ to 180+ on 1,3,5,7 but #7 was wet when I pulled it, I pulled the VC off and nothing obvious and now Im thinking #1 Bad plug, #2 bad lifter, #3 Bent PR, #4 Cam went South hoping just a fuel fouled plug and all will be fine in my 489 Universe

 

[Shovelrick]

While I have the VC off I might as well check lift with a dial indicator, I meant when I pulled #7 spark plug it was wet, and I only posted a couple pics of comp but they all were within 10 psi or less I should have put #7 plug in another cyl to see if it changed temp on the header Duh

 

[kmakar]

If the compressions was good in all cylinders, maybe the # 7 plug or plug wire?

 

[Nashville Cat]

If the compressions was good in all cylinders, maybe the # 7 plug or plug wire?

Agree. If compression is good, valves are working ok.
Is your timing steady or jumping around ? 18-20 degrees is a lot of vacuum advance ; might be safer to restrict it to 12-14.
But that's probably not causing your backfire. #7 plug is too wet like Kevin guessed ?

 

[Shovelrick]

Yes #7 wasn't firing, if I'd been thinking I should've started out swapping #7 plug to another hole then checked that header tube temp, too many irons in the fire I guess, anyway I'm this far so might as well check lift at top spring retainer with the dial indicator for lift just to be sure the cam & lifters are doing their job, I'll be replacing the plugs too, I have many many spares LOL

 

[Shovelrick]

l put knew NGK BKR5E plugs gapped at .045 in today and the BF's gone, I couldn't get the mag base to stick anywhere since it's an alum top end so tried the steering shaft but it still moved but the rockers looked like they were moving same as others, the vac guage is still bouncing so next is the cigar test then Im going to try leaning out the carb, still running very rich