7.4 Bravo 3 idle/timing question

[Druff1]

I'm having an issue with my 95 7.4L 454... I just replaced the distributor cap, rotor, pick up module, and the ignition control module(mounted on the back of distrubutor along with the knock sensor), on what i am told is a Thunderbolt V?

My issue is that my idle is at 600-650rpm, and when i want to give it a little more throttle, it sounds like it's choking out a little, then it jumps to 1200rpm. Sits everyone in their seat, if you kow what i mean? It runs excellent after that. Toping out at 4300rpm.

Does this sound like a carb issue or a timing issue?

 

[HT32BSX115]

Re: 7.4 Bravo 3 idle/timing question

Howdy,


If you followed the procedure in the manual for timing a T-5 ignition, then it's not timing.

It sounds like it's a carb issue. A malfunctioning accelerator pump would cause a hesitation similar to what you describe.

Also,

You might be a tad over propped if 4300 is your normal top RPM..... You'll get best performance if you select a propset that gives you 4600 RPM at WOT. (your rev limiter is fixed at 4700)

I would ensure that everything else (including timing) is running correctly before messing with a different propset though.....Also try a different tach. They're FREQUENTLY off at high rpm......

What is your drive ratio, and speed at 4300 RPM? You'll probably have either a 2.00:1 or 2.20:1 drive. there should be a sticker on the drive that indicates ratio unless it's peeled off.......


Let me also add that 4300 is in the Mercruiser recommended RPM range (4200-4600) for WOT.......It's just that most manufacturers suggest propping to the high end when lightly loaded (people, fuel, gear etc) at the pressure altitude (elevation) you'll operate regularly.


Cheers,


Rick