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New motor running rough-BBC

Posted By: 440challenger

New motor running rough-BBC - 09/26/10 12:39 AM

Ok dont shoot me, im a die hard mopar guy, and i almost converted my die hard chevy old man to 100% mopar. BUT We finnaly got his BB CHEVY in his chevelle and running which we've been building together for years. Its a 13-1 comp 720 roller cam dart head 496 stroker.

Compression on all cylinders is 175-180

Plugs are NOT hitting the pistons closing the gaps

Ignition is a msd6al we just got back from msd (reconditioned)

Firing order is correct and timing is at 36 total.

1050 dom .. it had 88 squared jetting with 5 power valve front and rear.Fuel pressure 7psi. I blocked the rear and went to 84 fronts and it made no difference.
Its running like it has a bad miss-revs up very rough...Im not sure where to go from here.

I told him lets try putting an hei diz in to eliminate the msd and see if it makes a diff.

Running no alt(havent hooked one up yet,just batt volatge with a charger on it).

Any pointers on where to start? Thanks guys!
Posted By: CompWedgeEngines

Re: New motor running rough-BBC - 09/26/10 12:43 AM

1) Have you mechanically confirmed TDC?

2) Have you looked at the rocker gear and valve adjustment since starting it?

3) Double checked plug wires and swapped and/or changed spark plugs?
Posted By: 440challenger

Re: New motor running rough-BBC - 09/26/10 12:49 AM

yes, TDC is confirmed.

Did not pull the valve covers but that is next on the list.

triple checked plug wires and plugs look clean.

I was going to run it tommrow and take the temp on each cyl and see if any are cold...
Posted By: topside

Re: New motor running rough-BBC - 09/26/10 01:02 AM

Odd to pull power valves and then jet down; usual ballpark is to go up about 8 jet sizes when deleting PV. That assumes same carb on same motor & running fine with the 88s & PVs.
Check the fuel delivery, just went through that on the racecar. Trash in the filter blocked 1/3 of its area (flat screen), and at 2 jet sizes too fat, it was dead lean and accelerated roughly, with only 5PSI fuel pressure. I've heard that the BBC can wipe cam lobes pretty quickly - a buddy's motor did that during break-in, though there may have been contributing factors. I'd expect the motor even at idle would sound like it had a dead hole, if it's a wiped lobe. Pulling the valve covers and looking at te valvetrain action as you bump the motor over should identify the flat lobes.
Posted By: 440challenger

Re: New motor running rough-BBC - 09/26/10 01:21 AM

Carb is one from holley a reconditioned unit. just thought it was really fat, only took a few mins to try.

Excuse my lack of knowledge but can you whipe out a roller camshaft?
Posted By: Cudahlr

Re: New motor running rough-BBC - 09/26/10 01:30 AM

Make sure the power valve is good and the gasket is correctly seated. Both can cause it to run very poor and rich.
Posted By: moparfan

Re: New motor running rough-BBC - 09/26/10 01:31 AM

Are you sure the cam isn't a 4/7 swap.
Posted By: topside

Re: New motor running rough-BBC - 09/26/10 02:29 AM

Sorry, I blew right past where you mentioned roller cam; I was just listing what I could think of.
Posted By: Eric

Re: New motor running rough-BBC - 09/26/10 02:29 PM

Pull the plugs and look for a crack in the porcaline(sp).....I chased a high end miss for weeks...brand new plugs.
Posted By: supercomp

Re: New motor running rough-BBC - 09/26/10 03:01 PM

I would switch msd box. They are notorious for ruining your day. New or not.
Posted By: 440challenger

Re: New motor running rough-BBC - 09/27/10 12:12 AM

Well did a lot of diagnosing today and still have the problem.

Timing was deffiently right. Checked many many times. All plugs are good,not cracked etc.

Pulled the valve covers,all is well. Was hoping for tight valves but everything was dead on. The cam is not a 4-7 swap.

ELIMATED the MSD box, coil and distributor by running a factory Gm hei.

I have to think its in the carb? I dont have any more 1050s so i was going to see if they make an adapter to go to a 4150 .
Posted By: 440challenger

Re: New motor running rough-BBC - 09/27/10 03:14 AM

Seems like the 8896-1 that we put on the car is pretty well known for running like crap.This car will be on the street a lot. Is there a way to make this carb more street friendly? Its a 3 circuit.
Posted By: Defbob

Re: New motor running rough-BBC - 09/27/10 01:22 PM

Could the cam have been degree'd incorrectly?
Posted By: Oyvind Mopar

Re: New motor running rough-BBC - 09/27/10 07:44 PM

Check that your carb is not leaking fuel internally past the needle/seat. Could be faulty O-ring around the needle/seat assembly, or dirt on the needle/seat, or a stck float not closing properly. Would typically make the engine run rough and smokey. If you have an electric fuel pump; try to shut it off while running the engine and listen to the engine if it smoothens out; this is simpler than dismantling. Or, you can look into the carb and see if gas is coming out of the maincircuits during idle (flooding)
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