Carb Backfire

FIAFRED · #1 (**permalink**) 12-09-2001, 01:01 PM

Gang.

Was returning from an afternoon ride and was accelerating hard through second gear when there was a loud pop through the engine(backfire versus mechanical break). The engine would continue to run, but with popping through the carbuerator. Pulled over and gave a visual on the plug wires, distributor, and wires. Guages read steady in operation. Removed the air cleaner and started the engine. Popping appeared to be backfire through the carb, with spark visual in carb. Jets on one side seem to flow gas in a retarded manner, while the other side seems to mist. Have a Holley 650cfm, on my 351w. Does anyone have an idea if this sounds like carbueration, or am I possibly not firing in one of the cylinders, or something other?

Fred

poorboy · #2 (**permalink**) 12-09-2001, 02:53 PM

Fred;
Sounds like a bent push rod or loose or broken rocker arm. Does it continue to pop whenever the engine is running?

Poorboy

FIAFRED · #3 (**permalink**) 12-09-2001, 03:25 PM

Don,

You sound like you hit the nail on the head!! Iwent up to the auto parts store to replace a insulator cap on a spark plug wire which had melted near a header pipe, and that is exactly what the parts manager said. That a valve spring had lost it's retainer clip, snapped or possibly bent a rod. Yes, the engine continues to pop through the carbuerator when it is running. After rechecking the carb jets, they are fine as they flow. I have not reved the engine much over 5000rpm through any gear, the oil pressure continues to hold 50+ lbs, and the running temp has stayed under 200 since installing the puller fan. Is this something that I have caused? What should I do about getting it fixed. Obviously, I will have to talk with Bill Parham since the engine is still under warranty, unless my oil cooler line mix up has caused this. I have driven the car 500-600 miles of trouble free operation, with the engine runnig strong. So what's next?

Fred

PS Is it time to send you a round trip ticket from Birminham?

Steve Siedlecki · #4 (**permalink**) 12-09-2001, 04:21 PM

Fred The same thing happened to me on a new engine. Do you have roller rockers with poly locks??? They have a set screw in the middle of the nut. Just one of them loosened up and caused the same symptom... The valve wasn't opening..
No harm done just readjusted and off it went...
I hope that it is all that is wrong with yours..

Steve...

FIAFRED · #5 (**permalink**) 12-09-2001, 05:06 PM

Steve,

Yes, I have roller rockers on my new engine. Don't know about the poly locks. Was this something that could be corrected at home or did you have to go out to a shop for the repair?

Fred

poorboy · #6 (**permalink**) 12-09-2001, 06:04 PM

Fred;
Just pull the valve covers, and look, if a rocker arm has loosened up enough to cause trouble it should be obious. If you don't find anything you think is wrong you will need to check the valve adjustment on each one. To check valve clearnce, take off the dist. cap and note at witch plug wire the rotor is pointing at, both push rods on that cyl. should be snug. Turn the engine enough so the rotor points to the next plug wire then check those rockers, do this for all 8 cyls. If you find 1 that is loose tighten the nut in the center if the rocker until you can by takeing the push rod between thum & fore finger and roate it while tightening the adjuster nut until you can feel some drag on the push rod, you will be able to feel if the push rod is bent. If it turns smooth without any wobble is should be stright, tighten it about 3/4-1 turn more. All this is asumeing you have hyd. lifters.

Poorboy

FIAFRED · #7 (**permalink**) 12-09-2001, 06:18 PM

Don,

I'll go out and take a look... will report back. Thanks.

Fred

FIAFRED · #8 (**permalink**) 12-09-2001, 06:30 PM

Don,

Well that took a long time! Pulled off the driver's side valve cover, and there it was plain as day. A bent rod...slid it right out. Do I just head to the parts store and buy another? Does this happen very often, and is it something that I did? Is there anything special to do about putting in the new rod. As always, thanks for your support!!

Fred

poorboy · #9 (**permalink**) 12-09-2001, 08:55 PM

Fred;
Take out next to it so you get the right length. I think your engine just has magnum roller tip rockers. Does your engine just have the standard rocker adjusting nuts? It could have been just a loose rocker, let the push rod get out of place. You will have to turn the engine to bring that cyl up on compresson stroke to set the valves.

Don

FIAFRED · #10 (**permalink**) 12-09-2001, 09:19 PM

Don,

The rocker has a nut over a threaded shaft which holds the rocker in. In visually looking at the nut, and trying to turn the nut by hand, it was not loose, if that means anything. The rod is stamped with 8.750, and bent about 11/2" down from the top, where the rod is narrowed to seat under the retainer plate. Does this give you any more info that will help you direct me on how to go about instaling a new one?

Fred

Leo · #11 (**permalink**) 12-09-2001, 09:55 PM

You're getting great information (and I'm taking notes guys, thanks!) but if you want to pursue a repair under warranty I wouldn't disassemble any further. Push rods don't bend for no reason and many other things would fail before a pushrod failed because of oil starvation. Seems that there is either a geometry, clearence or assembly issue...all things the warranty provider will want to identify. As I am building a 351W based engine I am watching this thread closely...please keep us updated!!

FIAFRED · #12 (**permalink**) 12-09-2001, 10:06 PM

Leo,

Poorboy/aka Don, has been around Uniques cars for over 15 years. He has been building and racing engines for more than that. Don also delivered my car from Unique and helped with some of the build. This is why I am asking him these questions. Bill Parham, the owner of Southern Automotive will stand behind my engine, however, he is outside Atlanta, and I am in central Florida. I will not go into anything further without bringing Bill into the loop. Especially if the valve adjustment requires expertise that I do not have, or can obtain. I know that Don could do this repair with no problem. I'm just trying to narrow the scope of the task before me so that when I talk to Bill Parham, and he starts asking me questions, I can stay on the same page with following his lead. Thanks for weighing in.

Fred

Leo · #13 (**permalink**) 12-09-2001, 11:03 PM

You can't always tell if this is a cowboy's first rodeo and who the good players are. I'm always amazed at the depth of talent here! Clearly you're amongst friends and experts and I hope that you will consider my suggestion as nothing other than neighborly. I'll sit back and watch as this story unfolds...having gone through a Trick Flow Specialties head/valvetrain warranty issue (of which they honored well after the warranty expired, thank you!) I really want to see what the root cause was. Thanks for letting me tag along

FIAFRED · #14 (**permalink**) 12-10-2001, 06:05 AM

Leo,

I absolutely took your comments as being neighborly. Truth be known, it is MY first rodeo...that's why I try to surround myself with the most experienced cowboys. I'll post the progress, and hope to also find the root cause.

Fred

poorboy · #15 (**permalink**) 12-10-2001, 08:58 AM

Fred;
Ware the push rod narrows down, is it ware the push rod goes though the guide plate? If it is you may have a bad set of push rods. The push rods should be the same dia. the whole lenght except maybe right at each end. Did you ever get a digital camera? A picture of the head and push rod would help.

Don

FIAFRED · #16 (**permalink**) 12-10-2001, 11:18 AM

Don,

Yes it bent where the rod narrows for the guide plate. In speaking with a local speed shop owner, he noticed that the end of the rod that goes down to the lifter had worn or polished rather badly, and suggested that the lifter might be damaged and in need of replacement. I spoke with Lewis at Southern Automotive this morning and he is going to send me a new rod. He didn't think that there would be any damage to the lifter, but that the rocker has loosened, as you suggested, and the wear on the rod from the sloppy adjustment before it bent probably caused the uneven wear on the rod tip. I shined a flash light down the rod shaft opening and believe that the lifter may have some scarring where it contacts the rod tip. Do you think that I should be on the safe side and look into replacing the lifter, even though Lewis thought that it was probably not damaged? Having looked at the rod tip, the speed shop owner locally, felt that it would be a good idea. He said I could take a gamble and put the new rod in, and that if the lifter pumped oil it might be OK. I want to do the right thing as long as I have to replace the rod anyway.

Fred

poorboy · #17 (**permalink**) 12-10-2001, 12:14 PM

Fred;
The push rod is not suppose to get narrow at any point, if it has that points to not haveing hardened push rods. I don't think you would have done any damage to the lifter, no harder than you have turned it. I would look at all the other push rods, if they show any signs of wearing at the guide plates, replace them all.

Don

FIAFRED · #18 (**permalink**) 12-10-2001, 04:58 PM

Don,

Thank you for your reply. I spoke with Bill Parham this afternoon and he really feels that the lifter is OK. I sent him the bent rod so he could get a first hand look. Southern Automotive and Bill Parham, did not waver one bit about supporting my engine 100% under warranty. Although it's rare to have this happen, and is quite often the result of driver over revving or missing a gear, he did not care about "who done it", but was only interested in making me happy and getting my ride back up. I mention this, not so much for you Don, but just in case there are any non-believers out there who do not realize what fine engine builders Southern Automotive are, and how nice these folks really are. Anyway, I do have hardened rods (MANLEY), and your right again(go figure), after looking at the other rods the guide plate must have shaved the notch when it loosened in the sleeve and was allowed to rub against the plate. Once Bill has a chance to look at the bent rod that I sent him, I will report back.

Thanks as always, for your experience and help in teaching!!

Fred