Gary Anderson

What are the initial and total timing, and at what rpm, for an HP Tbolt IV module?

jpclear

Mercury used seven different spark adv. modules with the T-Bolt IV. (more than that actually, if you count all three design types used) I suggest you refer to Dennis Moore's BB Chevy Marine Performance book; pages 186 thru 189 for the complete rundown. Otherwise give us the pt.# of the module in question and we can supply the specs. --- Jer

z.zuperboat

It Should Have The Advance On The Module

Gary Anderson

Been trying to diagnose the problem over the phone. It's the triangle style module. Owner says no number for advance on the module, just an "HP" mark. It's also an aftermarket motor. He didn't write down the SN.
Anyway, I need to replace the module, coil, & trigger this weekend and set the timing. I'm guessing 32-34 total by 4000rpm should be fine but wanted to know the modules characteristics. I didn't know if there was more than 1 "HP" module.
Gary

220BR

The V8-HP module is the only one that doesn't tell you the total advance in the designation (e.g., V8-22). The HP module has 20* of advance, which is all in by 3000 rpm. More specifically, 3.5*at1750, 13.5*at2500, 20*at3000.

Merc issued a Service Bulletin that has a TB-IV trouble shoot guide.

powerguy

Gary - The HP module was 20 deg. advance all in by 3000 rpm.The only differences in the HP modules is where it is mounted- on metal plate or on distributor.

powerguy

The serial numbers for the HP module are 390-9571A1 or 17316A1.

If you can't find the hp module I have a spare V8-24 module from a 454 mag -24 degree advance all in by 3750 rpm.

jpclear

That would be the second design, V8HP unit. It starts to advance between 1500 and 1750 rpm and increases uniformly to 20 degs. at 3000 rpm. where it's full in. That is the one I use. Gives me a good 12 to 14 deg. advance at idle with 32 to 34 deg. above 3000 to wot. --- Jer

Gary Anderson

220BR, powerguy
YES! that's the info I need. Thanks!
BTW, I went through the Merc troubleshooting scematic over the phone with the guy. THAT WAS INTERESTING! Turned out to be the module, but he said the "little comma looking thing" in the distributor was corroded too.Gary

220BR

FYI, I have picked up one V8-24 and two HP modules off of ebay over the last year. Around $50 to $75. All have worked fine