This is kinda long... motor is a 588" all aluminum with orginal B1 heads. Hogans sheet metal intake with two Pro Systems dominators on top. Bought motor from a guy that had it in a dragster running in the 6's with a small shot of nitrous. The motor and carbs were set up for alcohol and I opted to switch them back to gas(C23) for various reasons. Sent the carbs to Pro Systems to have them switched to gas. Finally got the motor in and started up. It runs fine at idle and up to 3,500 or so but anything above that the motor acts like it has a load on it and won't hardly rev up at all. It really labors just to rev up to 7K and won't go any higher than that. Checked and double checked timing and valves and everything is correct there. Checked plugs and all were black and sooty except number 3 and number 8 and they looked almost like they hadn't been fired! Put fresh plugs in and same thing. Tonight I tried to see if car would get up on converter and it won't. Set two step at 4K and car stalled at 3,800. Set two step at 5K and car still stalled at 3,800. Converter is a 6,300. I don't have any experience with dual carbs or sheet metal intakes or a motor this big and powerful for that matter. I'm lost on what to look for here and what direction to go. Does anyone have any ideas on where to start. I'm happy to post up more info if needed, just trying to not be too long winded. Any ideas????

Just a couple of ideas. Check your grounds. Try another ignition box. Make sure that Pro Systems didn't accidentally put Alky jets back in it. As a wild guess, I would think 88 jets would get you fire up and running decent enough to see if it makes a difference.

I really never thought about checking grounds and making sure it wasn't electrical. The stat sheet I got back on the carbs shows that it has 88 jets squared on both carbs. But I haven't taken a bowl off to verify, I guess that would be a good idea. But you would think they would flow the carbs after they changed them and make sure they fit the specs right?? I don't have another ignition box to try without pulling one out of another car or changing some wiring around but it may come down to that. Keep the ideas coming....

Wow, good guess . I've seen bad grounds and bad 7531/30T boxes make a motor act like you described. When I wire in an MSD box, I try to always use Weather packs so they can be switched out easily enough.

Sounds like a bad ignition box.

not that i know anything but i would try a single carb barrowed from some1 to see if it reved past 3,800 if you can.

The box is a digital 7 but not the programmable one. P/N 7520 brand new just installed. I used all the weather pack connections but I don't have another box like this one to try. The box in my other car is a 7531 and I don't think it has the exact same connections because of all the extra wires but it may, I'll check.

So you guys think I may have an ignition problem causing the motor to not want to revv. I hadn't thouht of this.

Try switching the pick up wires around..

Common mistake.


Chris..

Is it a crank trigger?

You can switch them at the box right?

The motor will usually run both ways. However if they are wrong the motor usually acts as you described.



Chris..

I agree with Chris make sure the pick up wires are correct. If I remember correctly the timing will retard when you rev up the engine if they are backwards. I have also seen if the cam is a 7-4 swap and you do not have the wires in the proper firing order it will behave the same.

I third that answer about the pick-up wires possibly being incorrect. Check them even if the plug only goes on one way...they could still be wrong.

Double check the crank trigger wiring and the firing order. Do you know if it is a std cam, 4/7 or a 4/7 2/3 swap cam. Yo may also want to check to ensure the throttle blades ar not open to far allowing fuel from the boosters to get in the mix. Also might make sure the two cylinders with the clean plugs that appeear to not be firing are in fact firing....

I don't about the cam. The two cylinders that are running clean are firing tho. I hope its as simple as the trigger wires being crossed, that would be great. I'm hoping to have time to go out to the shop some time today and check that out.

Yep to what Chris said, very common mistake. And like Al said double check firing order to all cylinders, etc. I have heard of some problems with the 7520 box as well. You may also need to try a new coil.

Ok....went out to the shop and made a pigtail up to switch pickup wires around and car wouldn't start that way. Wouldn't even try to hit so I guess that is not the issue. Firing order is correct. Also tried one more thing with the carb and it didn't work either. I pulled all the 3 circuit air bleeds out of the top of the carb. Someone told me to try that so I did and it didn't help either. I'm really starting to lean towards a bad ignition box now. My grounds are fine. The box is grounded directly to the battery....

Did you check with the cam card to make sure you don't have an altered firing order? I'd be surprised if the carbs are the issue. Try another box and see what happens there. Did you put a timing light on it while trying to rev it? Could be that the box is pulling a ton of timing out too.

I would try to verify if the cam is a swap set up or a standard firing order cam. Although that would not really account for the plugs, but I am also a bit curious with two that seem to be ok...Does not make sense to me. I would think if it were a carb issue all the plugs would look the same, so I would imagine it is safe to say that is not the issue.