just brought a new 600 cfm holley 4barrel carb, having problems with it backfiring out the carb at about mid range starts up fine, idles ok revs up ok but as soon as i take it down the road it pops, backfires out the carb at high revs its fine, timing is ok, new leads plugs no vac leaks anyone struck this before! Cheers Phil
demons,
Apr 23, 3:23am
im guessing jet and power valves sizes. or have float levels been set corretly. my hq has done the same thing changed power valve to smaller one and is better
quickstitch,
Apr 23, 3:23am
did it run fine before the carb change!Might want to do a compression test, check for burnt valves. You may need to change the power valve in the carb after backfiring it. Have you set float levels, mixture set-up !
marcos1,
Apr 23, 3:30am
Camshaft.
quickstitch,
Apr 23, 3:53am
well i guess we will never know. OP, a bit of feedback would help narrow it down.
goose13,
Apr 23, 4:07am
worn lobes on cam!
alvin20,
Apr 23, 5:25am
Backfiring thru' the carb indicates the mixture is too lean!
pdc1,
Apr 23, 4:23pm
so it ran fine on the old carb! If so the mixture is too lean. Check as per post 2. It idles ok because you adjust it by the idle mixture jets, which doesn't effect the high speed jets. I guess it's too late to send back and get a Edelbrock!
quickstitch,
Apr 23, 4:32pm
#9, my choice of carbs too, i am selling a near new holley performance series carb and getting another edelbrock carb, dont think i will ever use a holley again.
pdc1,
Apr 23, 5:17pm
Yeah, a holley is a bit like a toilet mounted on top of an engine, and pushing the flush button. I would guess that a 600 series edelbrock would go pretty good straight out of the box without changing jets. You can get them in both a performer series (slightly rich jets) and the economy series (jetted for economy).
I've seen a couple of issues with new holley 2 barrels. They have had holes that have been blocked that need opening. One was blocked by a gasket. It might pay to pull it apart and have a close look at everything, but try the simple stuff first, float level, power valve and jets
sfw4,
Apr 24, 3:57am
Holley very bad design and always flooding. Rochester& Elderbrok put them to shame
candy1213,
Apr 24, 5:48am
yes too lean! or air leak!
extrayda,
Apr 24, 3:55pm
As said above, was it running fine before the carb change or not! When you did leads etc, did you ckeck dizzy cap / rotor / connections. Are all of the leads seated right! How new is the coil! Does it only miss etc while under load (e.g. getting up to revs while accellerating!), or are you static revving it!I've always run Holleys, and never had many issues with them.
xacoon,
Apr 24, 10:32pm
I concur. I have a pile of holleys that will never see the light of day as long as theyre in my shed, all the local carb gurus 'round this way seem to be making the move to edelbrock after being holley boys for years too
xacoon,
Apr 24, 10:33pm
no I never had many issues with holleys either, but then I hadnt tried edelbrock at that stage either.
johnf_456,
Apr 24, 10:52pm
Holleys are not what they use to be
extrayda,
Apr 24, 11:29pm
Yes, to be fair, I never tried an Edelbrock, so maybe don't know any better :-) I don't have a hobby car at the moment though, and wont for a long time yet, so may never get to know! I wonder if the OP is ever going to return.
mp3539,
Apr 25, 2:36am
the dizzys at the wrong end of the engine mate
quickstitch,
Apr 25, 3:19am
i hope you have the pleasure of setting points on a early chev truck. I like a dizzy where it can be reached. Seen my mate get his t-shirt shredded doing the timing on a chev commodore with an unshrouded flexi-fan. nearly pissed myself.
extrayda,
Apr 25, 3:35am
yup, I always liked the tidier look of the chev dizzy at the rear when I had fords, but setting timing on the ford was much easier :-)However, fitting a supercharger to a chev would be easier.Sadly never got to fit a supercharger to anything though! Unshrouded flexi fans on anything are a menace.
sifty,
Dec 9, 1:00pm
Yep been down this path, Don't rule out an electrical problem causing a problem under load. That's what I had and learned a bit about tuning Holeys as a result.
New Holleys don't blow power valves on backfire like they used to, 600 power valve/jets etc should be ok from the box unless you have some serious cam action. With timing right and no vacuum leaks there shouldn't be too much wrong, possibly a leak under load!If you don't have one buy a cheap vacuum gauge and tune with that hooked up to manifold vacuum port. usually around 1.5 - 2 turns out each side to set idle mixture (tune to get max vacuum, prob around 18 - 20 inches Hg) with vac advance disconnected and plugged. Or as suggested recheck float levels.
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