backfiring thru carb?

This is a 327 (with the camel back heads) motor..Comp cam,not sure of compression ratios ,202 heads ,z28 springs , 2" super sucker plate,demon 650 carb,MSD dist.But im not running a box with it.. I am getting poping back thru the carb when its under a load? When its at a stop and i rev it out it sounds great. I just put this togeather.. I dont know if its fuel related or timing or cam .. I did notice there are some bubbles in the float level site glasses when im on it hard..Just totally frustrated.. Any 1 got any ideas.. I was also thinking maybe my octane might be to low ,even at 91.. Maybe i should mix in a half tank of race fuel ( 106 )?? I didnt mention its in a boat ,but that shouldnt matter..Thanks

Too tight valves, cam lobe worn, broken valve spring, all possibilities. Does it pop once, or continue to pop on what sounds like each cylinder firing sequence, if so that is valve train isssues.

I'm with maxwedge on this one, I like the "too tight valve" theory as the most likely cause, which will wipe out a cam real fast on you. An engine with a tight valve or more will have a shake to it at idle, but no miss will be detected. This is a hard sell for some people, but after you've seen a few its easy to pick up on.

Bob

It s mostly ok till i hit the secondaries on the carb,like when im runnin half throttle its ok till i mash the peddle then it starts poping..sometimes once or twice,sometimes repeatidly. Can you tell me the correct way to set the valves,or how to check for too tight valves? Is this the correct way to set the valve train, 1/4 turn past the time the push rod starts getting pressure? Set in this order? TDC #8 EXH,+45* #2 intake,+90* #4 exh, + 135* #1 intake, BDC #3 Exh, +45* #8 int, +90* #6 Exh, +135* #4 int, TDC #5 exh, +45* #3 int, +90* #7 exh, +135* i think #6 int? BDC #2 exh, +45* i think #5 intake?, + 90* #1 exh, +135* #7 int... Could you tell me where to start or what to start looking for to find out whats wrong? Any help is greatly appres. THANKS.. FRUSTRATED>>>>>

WOW !!! I just pulled the valve covers again and saw the #4 exhaust rocker off slightly to the side of the valve spring? Pulled the rockers off #4 and both push rods are bent slightly? Is that a too tight valve???? Do you think that the cam is flat or will i be able to put new push rods and reset the valves and try again... AAAAHHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!

If you haven't done anything to the rocker arms, and this engine ran fine and is now doing this, then the most likely choices are either a burned valve (somewhat likely) or one or more flattened cam lobes (very likely). When the cam lobes go away, they wear out their lifter as well, causing excessive lash on that valve (the tapping sound if you have it). A big pointer to a cam lobe failure is the presence of metal in the oil - not chunks of it, but small particles (the size of dust particles) that give the oil a sheen, like metallic paint. The layer of hardness on the cam lobes is very thin, so once the lobe starts to wear, it usually grinds off in short order (we're talking single thousands of miles, like 2 or 3 thousand).

NO i wish that was it.. I put this togeather( if that tells you anything!! Trial and error i guess? Or ERROR !!!) Yes it did run good for a little while . Maybe 10 or 15 hours on it when it started to go bad..What i really need is instruction on setting the valves.. Is it the way i discribe it above, or am i totally of base? Maybe also cam replacement? Seems to me i shouldnt need to replace the bearrings in it,being so new. So i should be able to just slide it out and a new one in? Along with new lifters ,and at the least get a couple of years usuge out of it?? What do you think? THANKS... Im off to get a good look at the oil...

Oil looks really good no signs at all of any metal shavings.. Looks like good clean oil...

OK, you said you put the engine together yourself. I am assuming you used a new cam and new lifters - if not, you should have - did you follow the flat tappet cam break in procedure? Generally, you should get the engine started up and run to about 2000 RPM, and keep it there for 20-30 minutes, then shut it down and change your oil and filter - then you would be able to start driving it normally ... if you didn't do this on a new cam, the lobes probably failed fast (as will happen). The reason this is so imperative is because the cam lobes are fairly rough when they're new, and need to be worn in to the lifters. If the cam does not receive proper lubrication during this critical time, the hardness layer will wear through and the lobes will be wiped off. The only lubrication the cam gets in the SBC is from oil that is slung off of the crank, and during cam break in, the cam has to be subject to a liberal amount of oil. At speeds below 2000 RPM, there is simply not enough oil to lube the cam during the break in procedure.

The cam lobes and lifters also wear into eachother, so if you used an old cam with old lifters - UNLESS the cam was in good shape and you ensured the lifters were put back onto their respective cam lobes, the lobes on the cam will wear off. Likewise, if you put new lifters onto and old cam, you'll wipe the cam. The bottom of the lifters have a slight convex - this is what spins the lifters in their bores and keeps the cam back in the engine (prevents the cam from "walking forward" in the block). Also the cam lobes are not entirely flat, either. They have a slope to them, a little lower in the front than in the back, and this works with the convex on the bottom of the lifter to spin it (minimizing wear on the cam lobe and lifter surface), and keep the cam back in the block.

Old lifters won't have the proper amount of convex to them (and may even be slightly concave), and an old cam won't have a consistent slope to their lobes. You can see how one would cause damage to the other if they were mixed.

It had Brand new everything...Ive done everything you say exept change the oil again... Its in a boat so its not the easyest thing to do..What about setting the valves.. Can you give me the correct way to set them.. Im going to put some new push rods in and see if i cant get some more time out of it ,at least the rest of the summer,and ill start another rebuild over with another block and try again...

It had Brand new everything...Ive done everything you say exept change the oil again... Its in a boat so its not the easyest thing to do..What about setting the valves.. Can you give me the correct way to set them.. Im going to put some new push rods in and see if i cant get some more time out of it ,at least the rest of the summer,and ill start another rebuild over with another block and try again...

Dude, summer's over. :)

Anyways, yes if you have #1 at TDC, remove your valve covers. Loosen up all of your rocker arms. Now, one by one, start adjusting them by spinning the pushrod with the fingers on one hand while tightening the rocker down with the other hand. You want to slowly tighten the nut until the pushrod stops spinning, then 1/2 turn more. Ignore the valves that are at any degree of being opened by the cam, for now. Rotate the engine over one complete revolution - #1 TDC again, and perform the same adjustment to the valves that were being lifted before. Verify now that all rockers have been adjusted, put your valve covers back on and you should be good to go.

All this assumes, of course, you have hydraulic lifters. If you have solid lifters, then follow the lash adjustment specified for that engine.

It had Brand new everything...Ive done everything you say exept change the oil again... Its in a boat so its not the easyest thing to do..What about setting the valves.. Can you give me the correct way to set them.. Im going to put some new push rods in and see if i cant get some more time out of it ,at least the rest of the summer,and ill start another rebuild over with another block and try again...
Cut open your oil filter and look at what is trapped in there, then you will know if cam failed, or get a dial indicator on each rocker and measure the lift and compare it to the others for significant wear differences. Great advice from "silicon" btw.

DUDE >>> SUMMERS NEVER OVER HERE IN LOST WAGES ,, NEVADA... HA HA.Thanks you guys!!!! You have helped a great deal ....I will check the filter and replace the push rods ,reset the valves and see if i cant get some more use out of this thing...

While I never owned a 327 I have worked on a lot of 350 which are similar. When ever I had a rocker turn sideways I sent the head to a machine shop for a valve job. As some guides could be knurled the ones moving needed new guides and maybe a seat for the guide. With you luck I would get all new seats.I would think you need to take the heads to a machine shop and purchase a new cam and pushrods. Buy a tool so you can turn the oil pump with a drill motor. This will give you about 20 to 40 psi on the system before starting. Have somebody who is good on engines show you how to properly the valves. I would do a new timing chain when you replace the cam.

Silicon212, maxwedge& bobss393 >>> Hey just wanted to thank you guys again for all the advise... You guys were right on i did everything you guys said to do and check ,and ill tell you this things never ran better!!!! At least i can get somemore use out of it and i will have to keep an eye on the bad hole.. But for now were back on the water baby!!!!! Who loves ya????
THANKS, Bob

Silicon212, maxwedge& bobss393 >>> Hey just wanted to thank you guys again for all the advise... You guys were right on i did everything you guys said to do and check ,and ill tell you this things never ran better!!!! At least i can get somemore use out of it and i will have to keep an eye on the bad hole.. But for now were back on the water baby!!!!! Who loves ya????
THANKS, Bob

Awesome, glad to be of service. Now, about your boat - is it an inboard prop or is it a jet?

Is it just me, or does a 327 in a boat sound like a mismatch? Unless you're running a high RPM surface drive and foil, the torque band would tend to be out of the useful RPM for a conventional screw.

Sorry about the responce time.. Its a 17' jet drive.. And the 327 is what was in it when i got it so i rebuilt it and put it back in? It launches like a bat out of hell and the high reving rpm is what a jet drives speed is all about.. The more RPM the faster you can go , right..

So, what is the prognosis? Pulling an engine from a hold is no fun chore.

So the prognosis is its runnin pretty good now. ! I think im gunna leave this one alone for now,now that its runnin and put a cam in the 21' 454 i have now . thanks again..
Bob

I have had a 388 backfire through the carb (holly four) when the power valve was blow. Replaced the power valve and back firing quit