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Old 11-14-2010, 11:16 PM
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no power/backfire through carb/timing? 355 build

Hello everyone, im new to the foum here and i hope someone can throw some ideas at me, ive been working on a friends 73 nova for a couple weeks in our spare time, and we are having quite a few issues with it, now i figure since im kinda a ford guy that this is the reason for this car giving us so much trouble, karma maybe? haha, anywho below are the specs of the motor and then details of the problem, sorry for it being a lengthy read,

current motor and car specs
350/ 30 over
coyes double roller timing chain, crank gear advanced 4*/not check with degree wheel.
lunati 10001lk barebones cam and lifter kit .443/.465 lift, 214/224 duration @.050, replacing 10000lk
summit racing double hump head copies
2.02/1.60 valves/ springs rated up to .550 lift/
1.5 roller tip rockers
pro products air gap intake
edelbrock 1406 carb
long tube headers into flowmaster copies
stock mechanical fuel pump/ no fuel pressure gauge/unknown fuel pressure
unknown age HEI dizzy
stock th-350
4.10 gears out back

now, im pretty green when it comes to carb motors, and hei distributors, especially of the bowtie sorts, i'm more aquainted with Ford EFI motors, mainly because of my love of the Foxbody Stang haha. But im getting pretty aquainted with the different technology.

so heres the issue with a little back story. He had this motor put together about 6 or 8 months ago, and it wouldnt get out of its own way, idled fine, sounded ok, but driving down the road it was complete trash, so we went to trouble shooting, he was almost positive that the installed the crank gear 4* retarded, not advanced, so we figured ok we would change that and install it straight up to see what happened. while in there we decided to change the cam to the 10001lk, because the original 10000lk was pretty wimpy, we figured that didnt help things. also changed from edelbrock performer intake, non rpm, to the pro products air gap.

so while we disected the motor, and got to the crank gear, low and behold it was actually advanced 4*. so we left it the way it was and installed the new parts and buttoned it back up. the old cam looked fine, no worn/wiped lobes or odd scarring and the lifters looked fine, pushrods and such check out as well. we broke in the new cam, and tried to dial in the timing the best we could, idles fine, sounds decent, but starts hard, kinda hangs a bit like the starter is dragging or it was a very high compression motor, crank over twice or so then pause and then fire up, so i figured timing is messed up. at first it was shooting compression out of the carb occassionally on a failed start, but no fireball, so we figured that maybe we had on of the rockers too tight, so we went back over them again but nothing was out of the ordinary. we have also watched to make sure all of the rockers are moving the same distance as the others to help rule out a flat lobe on this cam, but they all seem match the others, the wieghts in the dizzy were all rusted up and such so we got a new weight and spring kit from mr gasket and installed the lightest springs and no vacuum advance. under the advice of an old racer friend. now i understand some, if not a ton of people think the mr gasket kit is junk, but it was what i could get in a pinch. so we took it out for a test drive, it ran worse than before until we tuned on it a bit with timing and such, seriously this thing should be running circles around my little 5.0 stang, but its not.

now on the road it is really down on power, to compare it ran like the 2.0 cavalier i have, and if you stomped it to the floor it would cut out and pop through the carb, sometimes a fireball. havent had any backfire throught the exhaust. so back to more tuning, ran a compression test and all cylinders where pretty equal around 170, vacuum test show a kinda low vacuum around 15 hg at around 800 rpm idle. currently initial timing is around 17* and total around 30, without vacuum advance. with vacuum advance hooked up its close to 50 at idle. check for vacuum leaks around everything and havent found anything. all vac ports that arent used are capped even replaced the hoses that went to the tranny modulator valve just to make sure, it had a kink in it. vacuum is still at around 15hg at idle. with it set this way we were able to get a little bit of horse powder back out of it, but you had to baby the throttle to do so, slowly increasing the throttle would get it going and you could actually pull in the secondarys for a little boost, kinda caught me by surprise. but still its almost like riding a 5hp go kart, a really big one haha, although at this point that would be more fun. also it smokes from the drivers side tail pipe a very little bit after you are hard on the throttle at in park, kinda grayish in color, not white like water. but its pretty faint, but only from the drivers side exhaust, true dual exhaust.
so we are kinda at a stand still at what to check, firing order has ben checked and check a million times and plug wires are on the correct post of the dist.

the age of the dizzy is a factor and the edelbrock carb was use when he got it, age unknown as well,

would the crank being advanced cause these issues?
do you have to time the spark differently when the crank/cam is advanced/retarded?
bad accelerator pump in the carb?
failing coil or ignition control module in the HEI dizzy?
Bad distributor period?
bad fuel pump?

any ideas would be appreciated, our lack of experience has us learning some things by trial and error but we are at witts end and its tying up space in my garage.

also the cam was installed dot to dot, crank timing mark at noon and came at 6, and a timing tape has been installed on the balancer/damper.

again any help or ideas will be greatly appreciated, thanks

matt.

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Old 11-14-2010, 11:18 PM
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oh yea, plenty of oil pressure and also runs at a normal temp, around 185 give or take.
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Old 11-15-2010, 07:36 AM
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Quote:
and if you stomped it to the floor it would cut out and pop through the carb, sometimes a fireball. havent had any backfire throught the exhaust.
Ayuh,... Sounds like it could be as simple as it's going Lean....

What's the condition of the fuel Filter,..??
How old is the gas in the tank,..??

Lean runnin' motors pop thru the carb...
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Old 11-15-2010, 08:53 AM
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lean or retarded ignition timing.
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Old 11-15-2010, 10:21 AM
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bondo, i was thinking about that, the fuel filter is the usual silver on, not glass so unsure if its all clogged up, maybe moving to a glass unit would be a good idea to see how the fuel actually looks, the filter itself is fairly new, with the engine rebuild. the fuel in the tank is recent only been keeping about a quarter or a little over in the tank at a time, althought the tank itself is original and i dont think its ever been hot tanked or cleaned so sediment may be playing a factor in the fuel issue.
to help with the lean issue i did inspect the plugs when we did the compression test and the tips and arms are black, and kinda sooty, kinda on the wet looking side, not a dry looking soot. so i was thinking either gas soaked, or oil from maybe the rings not being seated all the way yet? also i thought if it was running real lean all the time the plugs would be whitish in color, although i have read that they can be black as well, maybe confusion between people giving advice?

454c10, ive been pondering the timing issue, we have a summit timing tape on the balancer, but its an aftermarket metal bolt on timing tab on the timing cover, in about the same location as the old welded on tab, i made sure to find that tdc was even with the 0 on the tab and the notch in the balancer, since the balancer wasnt number, and it was pretty dead on, given that you can only be so accurate witht the ole screw driver in the plug hole trick. when i stabbed the dist in the engine i lined up the 0 on the tab with the 0 on the timing tape, and have verified it a couple times witht the screw driver method and making sure with the valve cover off that we are on the compression stroke of the number one cyl.

so im leaning towards tearing the carb down and seeing if theres trash in there, and adjusting the floats to 7/16" per edelbrocks suggestions, and im still wondering whether the dizzy is on its way out?
is there any way to definitavely check for a leaned out fuel mixture, without using a a/f ratio guage?

thanks for you guys help, its much appreciated, more ideas and suggestions will definately be appreciated.

thanks
matt
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Old 11-15-2010, 01:53 PM
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You need an adjustable vacuum advance canister. summit sells them for the hei.

I would set the total mechanical timing to 38 degrees which in your case would be 25 at idle. Then set the adjustable vacuum advance to add another 10. (48 total).

I would use a piston stop to check tdc. You can make a stop with an old spark plug and a short extension welded to the end of the plug (instead of the electrode).

pull all the plugs and rotate the engine slowly until the #1 piston hits the stop. mark the balancer at the pointer and reverse the engine rotation until the piston hits the stop again. The center point between the 2 stopping positions is TDC.

Last edited by 454C10; 11-15-2010 at 02:04 PM.
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Old 11-15-2010, 05:24 PM
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thanks 454, we will have to give that a go, it seems the more i crank the initial up at idel w/ vac advance unhooked, the better it sounds but it idles up more and more, normal i guess. 48 total isnt too much? i was just going off of word of mouth and stuff i read that said to try and stay around 34 -36 total timing, but im up for anything at this point. it will be a few days before we can actually try some of this stuff but ill keep you posted, i did pull the carb off today and took the top cover off and looked in it, there was some junk in the bowls from dirty fuel, and the accelerator pump looked ok, the end of it was kinda cocked to one side but you could straighten it out, i guess its on a sort of a pivot, but other than that to the untrained eye, nothing looked out of order, the floats were even as well right around 7/16. so the carb doesnt seem to be the issue, unless its too small of jetting or something

anywho, as always i appreciate your help, and if anyone else has anything to add feel free to help.

thanks again

matt.
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Old 11-15-2010, 06:02 PM
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Sounds to me also retarted ignition, and a lean condition. Also what cc's are the cylinder heads or the casting numbers. If they are an large combustion chamber with flat top piston of an low number value, the engine can act sluggish.
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Old 11-15-2010, 07:40 PM
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yea the heads have a 72cc combustion chamber wich is fairly large, would have rather have seen somewhere around 64 or even 58cc or so but i wasnt part of the original planning of the motor, heres the link for the heads

http://www.summitracing.com/parts/SUM-152123/

but really its his first build and its a learning situation i suppose, for the both of us. as for the pistons i remember seeing them but didnt make a note of what they were, hes pretty sure they are flat top pistons with the valve reliefs, but as for numbers for the pistons he doesnt know, they were in the motor when he originaly bought it, just refreshed the bottom end, new rings and such and installed a new crank. so im pretty sure compression is down, but really its way more than just a low compression issue, at one time during this whole deal it actually put me back in the seat, i wasnt ready for it, i was use to driving Mrs Daisy around, but it hasnt happened since, i mean this thing is like the flintstone mobile, complete with the holes in the floor boards for your feet as well! now just need a big rack of brontosaurus ribs hanging off the door and all will be well.
so thats why i was leaning toward the timing issue since it kinda has intermittent power but definately far and few between, but could be fuel related....too many variables i suppose and not enough time with work and the holidays coming up to get it all sorted out in a timely manner.
maybe start cranking the timing to the moon and listen for pinging and just back it up or retrace our steps and check tdc and stuff again and go back to square one.....also any idea of symptoms of a bad ignition controll module in the dizzy or one thats going bad, or are they like the TFI module in the fords and dont really start to go bad, they either work or they dont?

sorry to be long winded but i just want to give the most info that i can about what we have going on, thanks for the help thus far.

matt
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Old 11-16-2010, 06:54 AM
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read this


http://www.corvette-restoration.com/.../Timing101.pdf
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Old 11-17-2010, 09:07 AM
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thanks 454 thats a good read, i printed it out and kept it for reference, im going to try and work on this thing today at some point, its windy as crap here today so its not going to be fun, ill let you know how it turns out, do you have any recomendations for plug wires for an hei system? also have you used short plugs to avoid spark plug boot burning on long tube headers?


thanks again

matt
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Old 11-17-2010, 10:14 AM
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you sound like what I am going through. However mine has a few other issues that I have taken care of with the same results. i replaced my intake gaskets since they were rotted. i have a distinct misfire on my #6 cylinder. it backfire and pops through the carb. I put a brand new carb on and a Accel HEI Dizzy. i took the intake off adn found the intake vavle on #6 doesnt close all the way and allowing everything to come through the intake. A compression tast was run on it a few years back and it was steady with the others at 120. The #8 was about 90. So it is trickling through the head it seems. So I am in the same boat you and your friend are in right now.
As for plugs. i am running Accel shorty plugs on my 350. part #8199. they run about $30 for all 8. U-grooved. I have gone through a ton of plugs only to have them either foul out or the wires burn up from the headers. I also run accel 8mm HEI wires. I buy the custom set so you can run them how you want. You get great spark if you run them together. Hopefully that helps a little
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Old 11-17-2010, 02:16 PM
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heck yea man thanks for the advice, your stuff sounds like a bummer man, especially since you have started throwing parts at it, although the intake gaskets sounds like a good fix , the low compression #8 cylinder on your motor, my buddies, old time chebby heads, said when you do a compression test and one cylinder or adjacent cylinders come up lower than the others to squirt some oil into the plug hole and then see if it comes back up to pressure, if it does its ok, if it doesnt then theres something else the matter, i dunno if i remembered that right but you might give that a shot, but you can only trust shade tree stuff to a certain degree haha, i take it you did check the #8 intake valve to see if it was hanging too, i know a PIA to check but maybe you have an exhaust valve not closing all the way on the #8 but i suppose you would have to pull of the headers or manifold and contort yourself to look in the exhaust port with the ole maglite to see about that one, this crap is enough to drive you crazy.
, i put a glass fuel filter on it this after noon to see what the fuel is like and its pretty clear and is filling the tube, didnt break down for a fuel pressure guage yet though, however i was playing the the linkage to the accelerator pump, and had it in the last hole towards the bottom on the arm towards the engine block, and it made things way worse, backfiring through the carb at the slightist throttle play and ran even worse, so i moved it all the way to the first hole closest to the carb and it ran alot better, actually was able to break a tire loose a little bit, but you still cant use the throttle more than about 1/8 or 1/4 or it starts to choke out, so either to much or little fuel, or its still the ignition, wich he ordered a new dizzy so we are going to put that in in the morning, and replace this wonder plug wires that are on it currently, they are in sad shape, especially the number 5 wire, anyways, i appreiate your input, and hopefully we both can fix our issues and we can swap stories about makingn the pavement scream!
take it easy,

matt
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Old 11-17-2010, 05:46 PM
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A few things to check,
Have you looked at the exhaust to be sure there are no restrictions. This
can kill power.

Check the fuel pressure with a gauge

You say the vacuum advance brought it from 17* to 50* at idle, this is not
right.

I would expect to see more vacuum at idle with that setup, a leak or a
plugged exhaust or late timing will cause low vacuum readings.

Check the voltage at the HEI, it should be battery voltage. That car
originally had a resistor wire feeding the coil and the running voltage would
only be 9-10 volts. This will reak havoc on an HEI.
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Old 11-17-2010, 08:50 PM
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thanks tbucket, we checked the battery wire to the dist, it seemed to stay at a constant 12.3?? something volts all the time, and i dont belive the exhaust is plugged with anything, but i suppose its possible, no cats just long tubes into chambered mufflers, but i suppose something could have climbed in and died haha, and i have no idea why when i plug up the vac advance it climbs so high in advance, but the good thing is, hopefully, we have a new hei distributor to put in, in the morning...and i should have bought the cheapy mister gasket fuel pressure guage adapter today at advance but didnt do it, we will probably have to go there in the morning anyways so may have to pick it up, but i appreciate the help and ill let you know how the new distributor works out, it needs one anyways.

thanks,

matt

Last edited by Muttstang89; 11-17-2010 at 08:57 PM.
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