Moparts
472 hemi problems
Posted By: Crocker
472 hemi problems - 09/03/08 06:52 PM
I bought a 472 hemi last fall (not a crate- built by a reputable machine shop). Just got it in the car and fired it up last week to break in the cam. Right away It didn't run right and ran hot. Here's what happening with it.
- Low vacuum
-Running Hot
-Kicking back even at 0 deg advance
-Runs on when shut off
-Wont idle unless curb idle screw is jacked up
-Backfiring up through the manifold when under any load
My memory is not that great but I was sure I checked the timing chain before installation.
1.Are these pretty much the symptoms of late valve timing?
2. What's the best way to test plug wires? Resistance? Continuity?
I'd really appreciate some feedback.Thanks
FYI - 472 alum head hemi- 10.3:1 comp, 292 duration cam, 870 street avenger carb. carter hi vol fuel pump. 91 octane fuel
Posted By: lewtot184
Re: 472 hemi problems - 09/03/08 09:36 PM
sounds like the symptons of late ignition timing or a very slow advance curve for that cam. thats what i'd look at first.
Posted By: Crocker
Re: 472 hemi problems - 09/03/08 10:28 PM
Yes,The ignition timing is late or retarded. I am presently running about 2 deg btdc (vac adv unhooked)at idle because if I try to set the Timing where it's supposed to be which is a total (mech and dist with vac unhooked) at higher rpm, Or even 5 or 6 deg btdc at idle, The engine seriously kicks back while cranking and runs on.
The distributor is a M/P unit with a short advance curve.
Posted By: Spike
Re: 472 hemi problems - 09/03/08 10:32 PM
Make sure your timing mark is lined up with the actual TDC. If the balancer or cover was replaced the timing mark may be way off.
Posted By: DLP4
Re: 472 hemi problems - 09/04/08 12:04 AM
My hemi has similar specs and I had a problem with run-on when I shut it down. I have the MP distributor and I found that hooking the vacume to the metered port of the carb solved the problem for me. That port has no vacume at idle and apparently with the lopey cam and the advance the engine was getting confused. No more run-on
Posted By: Crocker
Re: 472 hemi problems - 09/04/08 12:45 AM
I have the vacuum advance hooked to the correct port. Their is no vacuum at idle.
The other problems I am having is run on, extremely hot intake manifold/ engine, low manifold vacuum and backfiring up through the carb with any load
Posted By: Crocker
Re: 472 hemi problems - 09/04/08 12:48 AM
Spike, I will definitely check the damper. I should have thought of that one
Posted By: Crocker
Re: 472 hemi problems - 09/04/08 11:22 AM
checked the timing mark by pulling no 1 spark plug. Looks to be OK.
Sounds lean to me. 870 carb on a 472 HEMI. Really too small.
Posted By: Crocker
Re: 472 hemi problems - 09/04/08 01:46 PM
What size of carb would you suggest? The carb i have is sized for 500 to 600 hp and up to 500 cubic inches. I have a mild street engine. The engine has no vacuum at idle, diesels on even with retarded ign timing, back fires up through the carb anywhere above idle
Has anybody had experience with late valve timing or installing a timing chain wrong?
Vacuum is so low the power valve is functioning at idle and will sting your eyes out. Carb is brand new and pump squirters are working fine, but even with this rich condition at idle, it will still backfire up through the carb when i attempt to rev it above idle
Posted By: Anonymous
Re: 472 hemi problems - 09/04/08 02:23 PM
a small carb wont cause those problems. theres a vacuum leak of the cam isnt degreed in correctly
Quote:
- Low vacuum
-Running Hot
-Kicking back even at 0 deg advance
-Runs on when shut off
-Wont idle unless curb idle screw is jacked up
-Backfiring up through the manifold when under any load
check the distributor timing and make sure its reasonable- not overly advanced or retarded. Check the and set the idle speed to something reasonable like 1000 rpm. mess with the mixture screws to get the best vacuum.
report back what vacuum you can get at idle.
check the plugs. they could be all black and not firing by now. might want to put in a new set.
stupid i know but CHECK THE FIRING ORDER AGAIN.
what size cam is it? was it degreed in? and if so, by whom?
Posted By: Anonymous
Re: 472 hemi problems - 09/04/08 02:48 PM
I have a 472 Hemi with real 10.5 compression, aluminum heads and a 292 degree cam. I run 20 degrees initial advance with 35 degrees total in at 2000rpm.
You may have multiple tune up problems. First of all I would recurve the distributor so you can run more initial advance, then check fuel pressure and look for vacuum leaks. If that doesn't solve your problem you will have to degree the cam.
I run 94 octane in mine and it never runs on or pings.
Your 870CFM carb is fine, it may limit top end power but it is easier to tune for the street than a more exotic setup.
Sheldon
Posted By: Crocker
Re: 472 hemi problems - 09/04/08 09:49 PM
Update:
There was 5" of vacuum on the vac adv port so for now, I have it plugged...until I solve this problem.
The car is running a little better, no backfiring up through the carb
I tighten the intake manifold which was a little loose...Now, The idle mixture screws will slowly cause the engine to stall when closed, so I am pretty sure there is no vacuum leak.
Right now I am running about 6 deg btdc. Anymore and there's run on and kick back. I am not going to attempt total timing yet.
At around 900 rpm there's about 8" of vacuum on the manifold and I need a little curb idle or it will stall.
All I know about the cam is Intake 534 exh 517 and duration is 292.
Do this sound familiar to anyone? If i knew when the intake valve started opening BTDC, I would pull the valve cover, crank it by hand and find out if the timing chain is off a tooth...
Posted By: Anonymous
Re: 472 hemi problems - 09/04/08 10:02 PM
Quote:
Update:
There was 5" of vacuum on the vac adv port so for now, I have it plugged...until I solve this problem.
The car is running a little better, no backfiring up through the carb
I tighten the intake manifold which was a little loose...Now, The idle mixture screws will slowly cause the engine to stall when closed, so I am pretty sure there is no vacuum leak.
Right now I am running about 6 deg btdc. Anymore and there's run on and kick back. I am not going to attempt total timing yet.
At around 900 rpm there's about 8" of vacuum on the manifold and I need a little curb idle or it will stall.
All I know about the cam is Intake 534 exh 517 and duration is 292.
Do this sound familiar to anyone? If i knew when the intake valve started opening BTDC, I would pull the valve cover, crank it by hand and find out if the timing chain is off a tooth...
I would venture to guess that your idle screws are open far enough to expose the transfer slots- thats why you have vacuum at your ported vacuum slot.
have you pulled the plugs and looked at them/ or better yet, replaced them. by now they are most likely a sooty black misfiring mess
Posted By: RUNCHARGER
Re: 472 hemi problems - 09/04/08 11:52 PM
My last two Hemi's (with this great new fuel we run) have responded well to 16-20 degrees initial advance with 35 degrees total. To achieve this you must limit total advance. I couldn't get them to idle properly (especially in gear) without doing this.
From 3000 miles away my suggestion is to first setup the advance curve. Then see what your vacuum is at idle, adjust your enrichment circuit (power valve) to suit your vacuum at idle. Then I would jet it up if it needs it (backfiring usually indicates leanness). I doubt it is a valve timing issue.
Sheldon
Quote:
a small carb wont cause those problems. theres a vacuum leak of the cam isnt degreed in correctly Quote:
- Low vacuum
-Running Hot
-Kicking back even at 0 deg advance
-Runs on when shut off
-Wont idle unless curb idle screw is jacked up
-Backfiring up through the manifold when under any load
check the distributor timing and make sure its reasonable- not overly advanced or retarded. Check the and set the idle speed to something reasonable like 1000 rpm. mess with the mixture screws to get the best vacuum.
report back what vacuum you can get at idle.
check the plugs. they could be all black and not firing by now. might want to put in a new set.
stupid i know but CHECK THE FIRING ORDER AGAIN.
what size cam is it? was it degreed in? and if so, by whom?
ALL signs of a lean condition
Posted By: Crocker
Re: 472 hemi problems - 09/05/08 06:23 PM
I have a jet assortment . Will up the primarys and secondaries by 2 sizes over the weekend. It sucks that I can't get any better than 91 octane...[Edited by Moparts - Keep it clean]
Posted By: torkrules
Re: 472 hemi problems - 09/05/08 08:51 PM
Quote:
I bought a 472 hemi last fall (not a crate- built by a reputable machine shop). Just got it in the car and fired it up last week to break in the cam. Right away It didn't run right and ran hot. Here's what happening with it.
- Low vacuum
-Running Hot
-Kicking back even at 0 deg advance
-Runs on when shut off
-Wont idle unless curb idle screw is jacked up
-Backfiring up through the manifold when under any load
My memory is not that great but I was sure I checked the timing chain before installation.
1.Are these pretty much the symptoms of late valve timing?
2. What's the best way to test plug wires? Resistance? Continuity?
I'd really appreciate some feedback.Thanks
FYI - 472 alum head hemi- 10.3:1 comp, 292 duration cam, 870 street avenger carb. carter hi vol fuel pump. 91 octane fuel
Make sure the intake is installed correctly, in that it is properly sealed. I've been humbled by my 472. I've been working on almost every mopar engine that walked or crawled on this good earth, and the Hemi has put some humility into me.
The intake bolts are very small and the way they go into the head makes torking them critical. Do not over tighten them as you could damage the head. I found that if you use the foam gaskets at the front and back of the block, it could prevent the intake from pulling down all the way (due to the loser bolts) causing a huge vacuum leak (and oil sucking).
I have aluminum heads and 9.5 compression. On the dyno, it made the best power at 31 degrees total timing and 18 degrees initial. It also likes a slower curve (all in by 3000rpm). The cam is an Engle hydraulic that has .592 lift and 248 at 50 and runs on 91 octane. I had a little run on, so I backed the idle down a bit and that solved it.
As for carb size, I'm using a 750 speed demon and runs excellent. The dyno showed the air flow at 6200 rpm to be 749 CFM. An 850 should be fine. I had an 870 street Avenger on this engine at first, but I had tons of problems with it. I'm pretty savy with carbs, and I couldn't get it to work for me.
After this it's time to check all the small stuff (damper mark at actual TDC, plugs, cap, rotor, wires, etc.) If your running an electronic ignition, make sure the phasing is correct of the pick up. If you hook it up back works it causes all kinds of problems.
I check plug wires with an ohm meter. I bend the wires around while checking to see if anything changes.
Good luck and let us know how you make out.