Engine Trouble Please Help!!!

[BLACK AND BLUE 67-72]

This last weekend my friend and I changed his intake and carb, the intake is an Eldebrock Performer RPM and the carb is a 1406. The problem is that the engine sounds like it is misfiring at about 3500 to 4500 RPM'S, It varies because it doesn't do it all the time.Also it feels like the engine is bogging down at a certain RPM. We marked the position of the distributor and placed it back into the same position, placed a timing light on it and the engine is in time, it starts and runs great other than that. The engine has new plugs and wires and a new cap and rotor. Could it be the spark advance or the weights in the distributor, or the pickup coil, or something else? Please Help!! Also a question about the vacume line for the vac advance on the distributor, does it go on the full or timed port ? Mine was hooked to the full and ran fine but a friend of ours said that it is supposed to go to the timed port, so I switched mine and it kinda feels like it has more power, or maybe it's just me.

[slam33]

what does he have for a cam, pistons, and exhast ? If your running an RPM on a fairly stock motor thats probably where your problem is. The RPM needs a larger cam, around a 234/244 duation. I tried a RPM on a stock motor and never got it to run right, swapped in a regular performer plus and runs fine.

[lngbed71]

Maybe the condensor, or points if you do not have HEI, I chased almost the same problem for days, then changed to HEI.

[bigjimzlll]

did you block off the 3/8 vacuum port in the rear of the carb? you can run the advance off either port..some engines like ome more than the other...check the 5+7 plug wires...really sounds like theyre crossed..the rpm will work fine..maybe just not as great down low as the performer..check vacuum leaks..than wires(triple check)..than rotor and cap

[BLACK AND BLUE 67-72]

The 3/8 hole is plugged with the allen plug, The cap and rotor are new Accels and the wires are new super stocks,with new Accel plugs. The vac advance is hooked to the timed port and the modulator is hooked to the full vac side. The intake gaskets are Mr. Gasket, and I did as the instructions said with the front and rear gaskets, got rid of them and used silicone, it runs great from 600RPMS to 3500 RPMS then usually around 3800 to 4500 RPMS while the 4 -Barrel is opened up, it will start misfiring and popping. So I didn't know if it was something to do with the Distributor or something else. The vacume lines are new, new fuel pump, new fuel lines, new filter, new radiator, new hoses, new water pump,etc. . There are no signs of oil leaking anywhere on the intake, and it is set at 8 Degrees BTDC. The cam is stock as with the pistons and rockers. It's really frusturating when you spend almost $700.00, and the Da@# thing Doesn't run right!!!! Any other suggestions???

[BLACK AND BLUE 67-72]

ttt

[lngbed71]

Does it back fire through the carb or exhaust when operating at the higher rpm's?

[Class of 69]

I'm not familiar with your specific carb, but does it have adjustable floats?? It could be running lean at the upper end due to inadaquate fuel supply. Will feel like a bog (starving) and cause a lean mixture popping. It sounds like everything else is new and you've tried all other areas I am thinking of. Maybe a vacuum leak in the secondary side of the carb?

[BLACK AND BLUE 67-72]

It's kinda hard to tell. Maybe through the carb? The exhaust has turndowns and at that RPM the truck is going around 70MPH, with alot of road noise.Not sure on adjustible floats, it's supposed to be ready out of the box. And the bogging was taken care of by adjusting the timing from 6 Degrees to 8 Degrees BTDC.But the popping is still there.

[slam33]

Your running a stock cam, loose the RPM and go with a regular performer to begin with. I know the RPM is really cool but it will not work with your motor, sorry bout that. I've tried it as well as lots of other guys here on the board. It's a no go. Once you get the right manifold on it, things will calm down a bit and then you can get a good tune on it. As it is right now your having to run a lean mix to compensate for the manifold at idle, it gets worse as the revs go up. If you fatten it up then you can't get it to idle right and the tune is all outta wack.

[MOTHERTRUCKERS]

Check the spark plug color for a lean mixture (white or light tan) if lean go up 4 jet sizes at a time, if it pops through the carb the power valve can be the problem also, accel plugs are not that good in a small block, change to autolite 25's in mild small blocks their a lot better plug.

[lukecp]

I think i see the problem. So, it only happens when the 4-barrell is open? I had a similiar problem when i put a new carb gasket underneath my old Q-jet. The holes on the gasket were too small and wouldn't let the butterflys on the carb open all the way. I simply removed the gasket and hogged out the holes with a dremel tool and it worked just fine.

[BLACK AND BLUE 67-72]

Thanks guys! I will try to test your suggestions this weekend or next, and see what happens!