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Old 05-15-2008, 11:32 AM
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HELP!!! Bad bog and 50 degrees total timing?

OK Let me start by telling you what I have. I have a zz430 replica (350 zz4 sbc short block, gm fast burn heads, air gap manifold, holley 4150hp 750 double pumper, gm hot cam 218/228 .525/.525 lift 1.6 rockers, th 350 trans with 2800 stall converter, 4.11 posi, 28" mt et streets) in a 68 camaro. It has a bad off idle bog...almost stalls. It runs very rich! The carb had 70's up front and 83's in rear, 27 and 35 squirters, all other adjustment are good. When I set total timing at 36, it had no power and very bad bog. To get the car to run clos to good, I hav total timing set at 50 degrees. I am not sure what is wrong. Should I pull apart the front and check the timing between cam and crank? Also, If I am taking apart the front, would anyone recomend a different cam. I would like something more tougher sounding with more power and with using these heads. I read before about a gm cam part #12370847 234@.539 intake and 242@558 exhaust with 1.5 rockers. I appreciate any input on my bog problem and any suggestions on the cam. This car is a sunday street rod. Thanks

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Old 05-15-2008, 12:50 PM
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Quote:
Originally Posted by Eagle1
OK Let me start by telling you what I have. I have a zz430 replica (350 zz4 sbc short block, gm fast burn heads, air gap manifold, holley 4150hp 750 double pumper, gm hot cam 218/228 .525/.525 lift 1.6 rockers, th 350 trans with 2800 stall converter, 4.11 posi, 28" mt et streets) in a 68 camaro. It has a bad off idle bog...almost stalls. It runs very rich! The carb had 70's up front and 83's in rear, 27 and 35 squirters, all other adjustment are good. When I set total timing at 36, it had no power and very bad bog. To get the car to run clos to good, I hav total timing set at 50 degrees. I am not sure what is wrong. Should I pull apart the front and check the timing between cam and crank? Also, If I am taking apart the front, would anyone recomend a different cam. I would like something more tougher sounding with more power and with using these heads. I read before about a gm cam part #12370847 234@.539 intake and 242@558 exhaust with 1.5 rockers. I appreciate any input on my bog problem and any suggestions on the cam. This car is a sunday street rod. Thanks
Wow I hate these kind of problems as they can be timing or ignition or both.
Putting a different cam in while this problem is unsettled, will just add to theconfusion.

My knee jerk reaction is to look at the cam timing to the crank. 50 degrees of ignition lead would make one consider the cam is out of time and that usually leads to the timing chain and gears either showing wear or not having been set up accurately to start with. How many miles are on it and how you dive it would influence the former. How it got set up would influence the latter.

Then I read your carb set which on the surface looks good, but rich running has a number of influences, one of the big ones you didn't mention is the power valve. A couple things, Holley power valves have a tip in point based upon engine vacuum, this is stamped on the valve. Rumpety rump cams tend to kill manifold vacuum which is what's holding the power valve closed. If the idle vacuum is lower than the valve's opening point, it will start adding un -needed fuel. Another issue with the Holley is back fires blowing out the valve, then it leaks fuel all the time. The other thing is general set up, if the throttle plates are open too far on idle such that they expose the idle to main transition slots these will add richness to the idle and cause a bog as the the throttle is advanced toward more opening. This of course assumes that float levels are set properly and nothing else is leaking from a crack in the metering plate and stuff like that. In a trimming sense, it might like a different air correction jet, but save those thoughts till the rest of this stuff is looked at. There are also power valve jets that need to be sized but this again is tuning after everything else is working. The power system is controlled for on and off by the power valve but the jets in the power system determine the amount of fuel, they are located in the metering block behind the valve, but I'm giving you enough information to be dangerous to yourself. Don't mess with power system jets or air correction jets, till everything else has been exhausted. There is a power valve saver kit that protects it from backfire damage, if one isn't in the carb you should install it.

I think your converter stall is a bit high for the cam, but that won't contribute to your rich running or bog, it's just an opinion. I think the stall will go better with the bigger cam, but I'm not too keen on the bigger cam without first solving the current problem.

Bogie
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Old 05-15-2008, 01:08 PM
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As much as I want the bigger cam, I was thinking the same thing and didn't want to add confusion to the matter! The power valve is a 6.5 and my vac is around 14. The hot cam, 1.6 rockers, and heads were bought used. I bought them from a friend, so I know they weren't used much. The shortblock was brand new. Timing chain, cover and gears were bought new. I'm thinking it wasn't set up right from the beginning being that I didn't put it together. Does it make sense to take the timing cover off to take a look at the way it was put together? Or can this be done without taking it apart?
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Old 05-15-2008, 01:26 PM
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You rod bearings won't last long at 50 timming.....
36 to 38 is the max
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Old 05-15-2008, 03:40 PM
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Is 50* equal to one tooth on the cam gear?
Is the timing tab on the cover the right one?
Has the timing mark on the balancer slipped, or is it the right balancer.
Have you tried to time the engine with the vaccum disconnected at the distributor and the gauge on manifold vaccum. Turn dist. until the highest vaccum is rerached at idle (below 600 RPM's), then check with a timing light and see where the tab and balancer are reading?
Ran across the same problem with a NEW 250HP crate (GM) last week, the only way we could get it to have any power was to time it with a vaccum guage and when we checked it was at 45* inital timing with the light (turn Back).
Keep us posted!!!.
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Old 05-15-2008, 05:02 PM
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I wonder if the timing mark on the balancer is correctly matched to the timing mark on the cover. check with a piston stop.

then I would do a compression check. this would help determine if the cam timing is correct.

double pumpers should have about equal jetting around the carb. why 70 and 83's ? that is a vacuum secondary setup.

yes, the cam is small for the gear and stall, but I would get the engine running properly before swapping cams.
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Old 05-15-2008, 07:24 PM
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Ok this is what I came up with. First, the jetting is higher in the back because it does not have a rear power valve. When I time the engine with a vac gauge, I got the most power out of it and a lot of the bog went away. It was there only when I launch the car but not as much. I set cyl #1 on TDC, harmonic bal dead on the mark and the distributer seemed to be off a tooth. I removed the distibutor and put it on one. But now, I can't adjust it because the square part of the hei distributor hits the firewall. Does this make sense that if the distributor was off a tooth, it will show 50 degree timing but its really not. Do I bang the firewall or leave it the way it is? I appreciate any help. I'm learning a lot as I go along!!! Thanks
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Old 05-15-2008, 08:29 PM
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Just remove the Distr. and turn it to where you will have room to adjust the timing. Then relocate the plug wires to the rotors #1 terminal.
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Old 05-16-2008, 08:05 AM
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Quote:
Originally Posted by 454C10
I wonder if the timing mark on the balancer is correctly matched to the timing mark on the cover. check with a piston stop.

then I would do a compression check. this would help determine if the cam timing is correct.

double pumpers should have about equal jetting around the carb. why 70 and 83's ? that is a vacuum secondary setup.

yes, the cam is small for the gear and stall, but I would get the engine running properly before swapping cams.
How do I check the cam timing thru a compression test? Will this determine if the cam and crank are lined up properly?
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Old 05-16-2008, 08:35 AM
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Your distributor is installed incorrect.
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Old 05-16-2008, 11:27 AM
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It could be that the timing is fine and the balancer ring has turned. Remove # 1 plug find TDC and verify thet the timing marks are correct. A wrong timing cover or balancer will cause a lot of timing problems.
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Old 05-16-2008, 02:06 PM
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I am almost sure it has a lot to do with timing. Either way, I am pulling it apart because I want a different cam.
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Old 05-16-2008, 03:46 PM
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Any opinions on comp cam mutha thumper series part #08-601-8. With my 1.6 rockers, it will give me 556 I and 542 E lift and duration is 235I/249E.
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Old 05-16-2008, 06:58 PM
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Before you take off the timing chain line up the dots and tell us if it is on the money or if it is off!!
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Old 05-16-2008, 07:09 PM
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Quote:
Originally Posted by solidaxel
Before you take off the timing chain line up the dots and tell us if it is on the money or if it is off!!
This is vital information for us to help you fix your problem.
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