infinityron
Contributing Member
Ok, at the great risk of exposing myself to sarcasm and ridicule, I am hoping hoping hoping for a really simple, layman explanation of timing procedure on a Thunderbolt IV, 7.4 carbed engine (1990)
I am a fairly good diyer and owned more boats than I can count of all types for 50 years. I've kept them running, replaced major parts and even pulled engines and drives for rebuilds and reinstalled and started up. But I confess that all the gobbledegook timing theories and explanations still baffle me. I've managed to install distributors and time well enough but I've never fully understood all the math that gets disbursed in timing discussions. Still trying to get it.
Issue...so I want to fine tune the timing on my 1990 mercruiser 7.4 MIE with Hurth trans and Thunderbolt IV distributors. Rochester carbs.
Here is my current process from scratch....with distributor cap off, I bump the engine until timing mark on balancer is at or close to 0 while simultaneously the rotor is pointed at or very close to #1 plug position. (the rotor only goes once around between same cylinder ignition, so to me that is at or near top dead center).
I replace the cap and start engine. Using a dial back timing light on 0, and engine idling 650ish I verify that timing mark is landing at or very close to 8 degrees BTDC. Lock down distributor.
I then push rpms to anywhere over 2500 and using the dial back light, confirm that the timing is advancing and that it is about 30 (?) degrees. If no backfiring or other loud noises and smooth operation, I pat myself on the back and look for something else to do.
Since timing advance is built into the module, its either advancing properly or its not. You can not physically manipulate distributor total advance without also completely changing the idle timing. Correct?
I have seen numerous other threads and posts on the subject that become way too complex or some that are even more naively basic as my procedure. A few people suggested you lock down idle timing at either 8 degrees or 10 degrees BTDC and put the tools away and go home.
Anyone?
I am a fairly good diyer and owned more boats than I can count of all types for 50 years. I've kept them running, replaced major parts and even pulled engines and drives for rebuilds and reinstalled and started up. But I confess that all the gobbledegook timing theories and explanations still baffle me. I've managed to install distributors and time well enough but I've never fully understood all the math that gets disbursed in timing discussions. Still trying to get it.
Issue...so I want to fine tune the timing on my 1990 mercruiser 7.4 MIE with Hurth trans and Thunderbolt IV distributors. Rochester carbs.
Here is my current process from scratch....with distributor cap off, I bump the engine until timing mark on balancer is at or close to 0 while simultaneously the rotor is pointed at or very close to #1 plug position. (the rotor only goes once around between same cylinder ignition, so to me that is at or near top dead center).
I replace the cap and start engine. Using a dial back timing light on 0, and engine idling 650ish I verify that timing mark is landing at or very close to 8 degrees BTDC. Lock down distributor.
I then push rpms to anywhere over 2500 and using the dial back light, confirm that the timing is advancing and that it is about 30 (?) degrees. If no backfiring or other loud noises and smooth operation, I pat myself on the back and look for something else to do.
Since timing advance is built into the module, its either advancing properly or its not. You can not physically manipulate distributor total advance without also completely changing the idle timing. Correct?
I have seen numerous other threads and posts on the subject that become way too complex or some that are even more naively basic as my procedure. A few people suggested you lock down idle timing at either 8 degrees or 10 degrees BTDC and put the tools away and go home.
Anyone?
