So i just finished a 72 360 block and fired it yesterday. I primed it really good put the oil drive gear back in and set the distributor pointing at #1 cylinder while the motor was at TDC. It fired up fine, but i had to keep the throttle on pretty hard to keep it going. I had a couple back fires while i was trying to move the distributor for timingbut nothing crazy. after i got it to run for a while i called it a day. This morning the thing wants to backfire like crazy out of the carb. I even got a little flame in the carb for about 5 secs. until i got it out. I've built tons of cars and blah blah blah but never had a campfire in a carb. My questions are 1 do you think the carb is cooked and could that make the car explode!? and 2 if it's backfiring out of the carb that means it's too advanced right?? not retarded. I tried retarding it quite a bit and it still didn't want to run. I usually have a buddy around when i'm doing this kind of stuff but i'm solo on this one and don't really wanna light my face on fire. any suggestions?
72 360 first start question
- Thread starter Mophile
- Start date
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TrailBeast
AKA Mopars4us on Youtube
Lean conditions, ignition timing and valves not closing or at the right times/or at all can cause backfires out the carb.
Advanced or retarded either one can also.
I'd verify the firing order and ignition timing first, then on to fuel and valve timing.
It's also very easy to accidentally swap the cylinder number 5 with 7 wires, and that will also cause poping.
Short fires are not a big deal usually if put out soon, and the car won't explode.
If left on fire it will boil the carb over and make a bigger fire though.
Keep a wet towel handy if it makes you feel better, and that way you can throw it over the carb if the fires don't go out by themselves within a few seconds.
Advanced or retarded either one can also.
I'd verify the firing order and ignition timing first, then on to fuel and valve timing.
It's also very easy to accidentally swap the cylinder number 5 with 7 wires, and that will also cause poping.
Short fires are not a big deal usually if put out soon, and the car won't explode.
If left on fire it will boil the carb over and make a bigger fire though.
Keep a wet towel handy if it makes you feel better, and that way you can throw it over the carb if the fires don't go out by themselves within a few seconds.
good advice, thats what i started doing actually. I was just worried that it could ignite through the line back to the tank somehow. firing order is definitely correct, would too lean or too rich cause a backfire. this carb had been running great on a 318 about a month ago so I don't think the lien mix could be that far off?? i have the vaccum port on the distrubutor roughly facing the #4/#6 spark plug as a starting place but I can't seem to get it to idle worth a crap either by advancing or retarding. after priming i installed the oil drive gear facing #1 and then the distrubutor as well. I'm sure i was at TDC. so I'm a little stumped. could it be valve lash? I just had the heads rebuilt. I know you can't ever assume the machine shop did a good job but i wouldn't think i'd have a dead valve.
If it were me, I would pull the cap off the dizzy, bring number 1 up to TDC compression stroke. Once you do that, look at where the rotor is pointing, it should be pointing at the driver side front intake bolt.
It's quite possible when you dropped in the distributor drive that it's off a tooth or two.
It's quite possible when you dropped in the distributor drive that it's off a tooth or two.
Rapid Robert
Well-Known Member
massive vac leak. & set the timing marks at 15BTDC. turn dist housing slightly till the magnet is dead even with the tooth. (the rotor will be at either #1 or #6). find the leak first tho, intake gasket shifted/mismatch/open (uncapped) nipple/bad carb base gasket/leaking vac line/hose. EDIT one tooth off on the t chain will shift phasing 15.6 deg on the crank, not sure it'd even run like that unless the chain set/cam was mismarked which it does happen. You might get rockover on #1 or #6 & see if the dampener slit is within a degree or two of TDC. pull the plugs for easy turning. get the slit on TDC & using a 1&1/4" socket/breaker bar move the crank back & forth a bit from TDC & note which (#1 or #6) pushrods both are moving, the cyl that they are moving then move the crank back & forth & hit the spot where both pushrods are moving and are at the SAME height & at that point (rockover) the TDC slit should be within that 1 deg (2 maybe) of TDC & this is with a tight/no slop chain. if so your phasing is OK & the prob is elsewhere & you dont have to open up the t cover & mess with the chain. keep us updated on how it goes. MORE EDIT for dist phasing, with the slit at 15 BTDC and the magnet dead even with the tooth, the rotor should be pointing (with springs retracted which they should be at rest) somewhat close to the cap terminal and the can will shift it CCW (on a SB) from that at rest position when it starts and you are above ported. SHORT VERSION: Confirm cam and dist phasing (dist phasing first cuz its easier) & if one of them ain't it then start searching for a vac leak
SSG_Karg
Enhanced member
What type fuel pump, mechanical or electric? I just went through this with my brother-in-law's car. It was doing exactly what you described. After basically rebuilding the entire engine, we tracked it down to a bad fuel pressure regulator. He is running a Holley electric pump and the reg. **** the bed and was giving it too much fuel and it would backfire the carb and cause carb fires. Just a thought if you're running an electric pump. Good luck..
that's a lot of info! so the way I've always found TDC is to manually turn the engine over until #1 piston comes to it's highest point mark it on the balancer and then turn the engine reverse direction until it happens again, mark it. true TDC is halfway between those two marks. That's how pop's showed me and it's always seemed to work. If i am at TDC and i pull the dist./oil drive gear and drop them back in again pointing at #1 plug I should be good as far as a starting point correct? Vac. leaks are definitely a possibility. it'll run if i keep the throttle on but the second i let off the juice it croaks. thanks.
Rapid Robert
Well-Known Member
will it stay running with a steady throttle above idle? yes reversing/going halfway is correct to find/confirm TDC with carefull measureing. I'd set it at 15, line up the magnet, see if the rotor is fairly close to the cap terminal & give that a shot but the more I think the more I think vac leak but we might get lucky. do ya feel lucky, well do ya!
i always feel lucky i drive a mopar. It'll run all day if i keep the throttle pegged. it sounds great but if i let of the throttle even with the idle all the way up its takes a crap. What do you mean set it at 15? When i drop the dist. into the oil gear the rotor is locked. it's one way or 180 the other way. do you mean set the gear facing #1 when the balancer mark is 15 degrees advanced vs. TDC? basically skipping a couple teeth to the advance side?
thanks
thanks
Rapid Robert
Well-Known Member
set the dampener timing slit at 15 BTDC on the timing tab then turn the the dist housing slightly till the magnet is dead even with the tooth. at that point the rotor will be pointing to or pretty close to either the #1 or #6 plug wire. fire it up & see what happens. "I" feel lucky! (on this deal)
nm9stheham
Well-Known Member
With all the backfires, it seems like the spark is ending up in the wrong cylinders; a lot of what people are saying is to get the rotor lined pointing right at the correct spark tower. The OP's procedure sounds a bit too inaccurate for being sure of doing that.
Also, check the rotor and cap to make sure that they are clean and not hitting anywhere inside the cap.
Not much worry for the fire to go back through the fuel line.... you need fuel AND air to have a fire. You don't have air in the fuel line. But have a CO2 fire extinguisher around; you DON'T want to use a dry chemical extinguisher on your new engine and get any of the 'stuff' inside.
Also, check the rotor and cap to make sure that they are clean and not hitting anywhere inside the cap.
Not much worry for the fire to go back through the fuel line.... you need fuel AND air to have a fire. You don't have air in the fuel line. But have a CO2 fire extinguisher around; you DON'T want to use a dry chemical extinguisher on your new engine and get any of the 'stuff' inside.
"nm9stheham" that was my first instinct. i just sharted a little when i saw a fire in the carb. somehow never had that over the years. i had a fire extingusher but definitely didn't want to spray that crap into my engine. we towel does the trick. I think I'm a tooth off even though it erally looks lie i'm pointing at #1 when at TDC. Im gonna try moving it both tomorrow. keep you all posted. thanks
I'm stumped. I was sure i must be a tooth off but no. I'm 100% sure i'm at TDC and i moved the oil gear a tooth each way and it barely ran on either of those. I set it back to the correct TDC rotor pointing at #1 and it'll run, if i keep the throttle pegged. I opened up the lean to air mix but no difference. I have mey vaccum advance on th edist. running to the port on my carb right above the lean air mix screw, which is the same on my other cars. I've been through the wiring again and everything seems correct. If it ran like crap with the throttle pegged I would think ok somethihng's seriously wrong somewhere but it sounds perfcet until i let off and it croaks. I've set the timing every which way and there's only one setting that will run and not ignite a fire in the carb. When I put a timing light on it though it's not even close. I tried runnning it 180 but no dice. I'm confused. any thoughts?
when number 1 piston is at TDC firing...numbe 1 on the cap needs to line up with the rotor...
set your damper to TDC take the cap off and see where the rotor is point....
moving the oil gear also known as the intermediate shaft does nothing for your timing...lining up the rotor and number 1 on the cap is the key.....
set your damper to TDC take the cap off and see where the rotor is point....
moving the oil gear also known as the intermediate shaft does nothing for your timing...lining up the rotor and number 1 on the cap is the key.....
Bulldozer
free ice cream sandwiches
exactly...
the rotor can point to Syria as long as its firing the #1 cylinder at tdc. all this rotor pointing to the #1 bolt hole really confuses a lot of people. that's way they left the factory but is not critical in any way to make the car run right
Rapid Robert
Well-Known Member
(1) do "rockover" to see if the cam is phased correct to the crank (2) set (turn) dampener to 15 BTDC (3) line up magnet (4) see if rotor is under the #1 plug wire cap terminal (#6 plug wire if you are checking rockover (pushrod movement/even height) on the the #1 cyls' pushrods) EDIT in fact I am going to ASSuME that you were good dot to dot & no gross errors in timing gears keyway/dots and cam when mfr'd & I'd forget rockover for now & just take care of the dist
"70aarcuda" - I get that moiving the oil gear doesn't change timing it just relocates the rotor, but if I'm at TDC and I set the oil gear pinting at #1 and the rotor follows suit, i should be in the ballpark no?? My #1 on the cap is also pointing at the #1 cylinder. Like i said I've moved the dist left right ( a tooth) to no avail as well as sweeping the timing left/right with no results.??
Yes im saying timing marks on timing sprockets were not lined up properly. I dont know how to check without looking at marks, there might be a way. I know I put in cam wrong one time, pain to fix for me. It is possible. :burnout:MT
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