View Full Version : FD-67 Just about done

02-16-2008, 06:01 PM
Couldn't wait for the finishing touches - wanted to share a few pictures of the "finished" product. Given that I got it as a rusted-cruddy hulk, I'm just happy to have it together again and in running condition. I replaced the small reed blocks with a new large port set and added a CD-distributor ignition from a Merc650. The best parts about doing the Looper and the Deflector motors are the knowledge I gained and the people I've met and heard about. Thanks for all the help along the way with these fantastic motors!!!

02-17-2008, 12:22 PM
hi roger,

that's a far cry from the mud bee santuary you started out with! can't wait to have you tell us what it sounds like. it's been fun figuring out what goes thru all those holes in the block. sam cullis's diagram helped.

i've got fc52 almost done. putting the lower unit together today. it polished up real nice. i'll give you a call this week about the ingnition. i want to use the tested you made for me.

take care,


02-17-2008, 12:37 PM
Had to post this, as it says it all.

02-17-2008, 12:48 PM
those gen 3's look sweet!!!!


02-17-2008, 04:06 PM
That is sweet looking D. I had the same megaphones on the 44 Flathead I had and it really does sound different between the generations of exhaust. I am also impressed that this one (like others I have seen restored here) is cleaner than when they were delivered. Beautiful job!

02-17-2008, 05:25 PM
Beautiful work Roger

John (Taylor) Gabrowski
02-18-2008, 10:00 PM
That is one nice clean restoration of a Flathead. Very few times seen out there is the use of the smaller ignition coil you normally see used on later models of Merc 2, 4 and 6 banger engines. Question is why did you not use that big mutha hockey puck of a ignition coil seen very commonly put on 4 cylinder and 6 banger flatheads when they started to leave magnetos and automotive point and condenser types behind? What discharge voltage in comparisson between the two or was it just because the system your using is a much more compact and estherically simple looking system?

02-19-2008, 12:00 PM
Hello John,
I started messing around with these ignitions about a year ago, and partnered with Larry McAfee to evaluate them. Larry's son Kevin is actively racing C,D&E Mod in NBRA and did very well running these ignitions last year.
The distributor is universally used across the Merc650 (4-cyl) to Merc850 through the late 70's. They are battery operated but triggered by the distributor. The large coil you spoke about was used on the 650's+ but the 85hp version came out with the smaller coil you see on the Looper. The coils (both) are bullet proof and generally never fail.
Larry built a tester that drives the distributor with a air driven die grinder (in excess of 11,000rpm) and a pressurized chamber with a plexiglass top that houses the spark plugs. With a simple wiring harness and battery the whole system can be bench tested at RPM and under simulated cylinder pressure. The cylinder pressure is critical, as it effects the spark in a big way. We can see no difference in the large vs small coils. Thus the small coil is able to charge/discharge (saturate) as well as the larger version. The switch box and coil can be mounted in the boat or on the motor - your choice. The switch box does draw in excess of 5 amps (less than 7) at higher RPM, so don't skimp on the wire size.
The CDI/Rapair replacement unit is a bit more efficient (uses less power) than the Merc unit. It requires the use of their coil with their switch box. They also make a replacement trigger which is housed in the base of the distributor. Their trigger uses magnetic switching vs the optical switching of the Merc unit. Magnetic is preferred over optical. Thus they provide a steel disc for the trigger. BTW, there is an up/down orientation on the disc that must be followed for correct timing. They are usually labeled.
That's a crash course in the Type IV ignitions. Good question, hope this helps to answer your question. I should warn you that some of the switchboxes have a rev limiter installed. I usually buy the 6cyl version to avoid that - Roger

John (Taylor) Gabrowski
02-19-2008, 02:46 PM
Roger: Thanks very much for the session. I have only one distributor like yours and I got a load of those smaller coils and the system as well as the earlier systems all used that big hockey puck coil. That same system was on pics from a Merc D Mod Fast Fred sold a while back too and its a nice compact setup that is a for sure.

I suppose that using the small coil on a Merc Lightning Energizer/Distributor for Merc 4 cylinder engines would then also work too? Nicer things with some experiments can sure come in small packages. :)

Not long ago (couple years back?) to cut power consumption down on the Merc CDI systems with the hockey puck coil, I went on a weekend binge at an auto wreckyard to look for low drain high output solid state system ignition coils and found one Honda coil that belted out 30KV at 12 volts unpressured and could go up to 60KV when the system called for it. Nice thing was that you can use 2 -7.5 volt RC stick batteries to power the Merc trigger box, the Honda coil and the needs of the magnetic or the LED distributors for half and hour and then use the quick charger attached to your car battery charging system to regain it all in less that 15 minutes per battery stick. That takes out the 12 volt heavy marine utlility battery out of the boat and gor those that liked to use 18 volts out of 2 marine lead accident batteries, the 15 volts out of the 2 RC battery sticks does the trick with the Honda coils. Seeing you guys are now using that small Merc coil not a bad thing to see how long 2 RC batteries would last with that coil plugged in.

I heard that there were rev limiters on some of the 4 cylinder trigger boxes, any way of telling those apart from those that don't have the limiters other than going to a 6 cylinder box?

That is all one nice compact system! :)

02-19-2008, 03:27 PM
Roger, I've had enough trouble with 6 cylinder boxes that fire but get weak after about half a lap. I've given up on them and use all CDI boxes. They fire my 6's off easier and let me use less choke. Like you said, they use a lot less power. I think it is 1 amp vs 6 amps.

02-19-2008, 04:02 PM
Concerning the Sw.boxes, I really don't know how to tell which ones have the limiter. I think it is safe to assume the boxes marked 6-cyl do not (at least when used on a 4-cyl.) and these were used on the 454 I/O's too - all the same part number. I agree with Sam that the CDI is an overall better unit and its packaging is better (Sw.Box & coil on same plate). Their power output is better, that's the key. Pretty good price and I think they give APBA members a discount.
Question to Sam: Are you using CDI's trigger or a Merc trigger in the distributor? The job of the Sw. box is to fully charge the coil before it needs to discharge to fire a cylinder. If the RPM's get too high the coil may not get fully charged and the spark falls off. Also, if the optical trigger fades (with age or grime) it will actually change the dwell time as it triggers the switchbox late. I don't think that is why you're seeing certain Merc boxes fade away. Don't know why.
I wouldn't mix and match coils with switchboxes. The switchbox and coil are engineered to work together. CDI has the advantage of a newer electrical design and better magnetics for use in the coil. The CD units fire hot a 0 RPM and thus help starting a lot. I personally like the Oddesy batteries as they pack a punch given their weight / size and hold a charge while not in use. Worth the money!!!
BTW these are a Type III not IV system, my mistake.

02-19-2008, 04:21 PM
Roger a 6 cylinder switch box will not work correctly on a V-8 ... it will have the wrong tach signal

I haven't had any trigger failures other than bad insulation on wires so I'm still using Merc triggers

It is rumored that some of the 6 switch boxes were limited, but some people who should know say none were limited

The big difference in the original Merc switch boxes is the tach output signal

I agree, I would not take the little OMC coil off of a CDI box either ... it works fine. The Merc coil that works with the Thunderbolt distributor is actually a medium sized one. The small 50 hp ADI coils will not work with the Thunderbolt distributor for more than a few minutes before they burn up. The slightly larger Merc coil and the tiny OMC coils will work

I like the Oddesy batteries too. About 20 - 25 starts of my padded 6's on a charge

John (Taylor) Gabrowski
02-19-2008, 04:28 PM
When I quite trying to develop a dirct charged Merc & Mariner 3 cylinder 2 carb 3 Holer I just set aside their ignitions when I got rid of the blocks. I never gave their ignitions a second thought until I started looking at a second Crescent. If a 6 cylinder Merc trigger box will work on a 4 banger Merc sans the tach circuit would not the 3 cylinder trigger boxes work on a Merc 3 cylinder too sans its tach output?

02-19-2008, 04:30 PM
yes yes

02-19-2008, 05:05 PM
I agree that the tach ckt. is different in the 4-6 boxes and the I/O box, but the I/O box will work fine (sans Tach). Basically, that's why Larry and I run all of our Sw.Boxes at speed to verify they aren't limited. I haven't found anyone who knows how to tell unless you knew what year motor it came off.

Careful on the 3-cyl boxes. Remember that the switch box is triggered by either the distributor or flywheel magnets/coils. I think that all of the 3-cyl were flywheel triggered - not sure. In this case (Type IV I think) the switch box generates its own power from the stator and is triggered by another set of magnets / trigger coils under the flywheel. The 6's just use two of these Sw.Boxes (and a different F'wheel trigger.
I haven't had the best of luck with my 6-cyl. motors (stock) and this ignition. The Sw. boxes are EXPENSIVE and I was told that you shouldn't mix different revision code boxes on the same motor (2X expensive!!!) I always thought their low speed spark was weak. Does anyone have a good replacement - setup - suggestion for the 6's???

Maybe we ought to move this to a technical thread?

02-19-2008, 05:51 PM
If you are going to speed test them, I'd recommend you do a 10 minute minimum run at speed

I've never heard anything about a mismatching problem with switching switch boxes on distributors and have had no problems that seem to relate to a mis-application. I don't know if that makes me brave or stupid. CDI only makes one replacement box for all the 4 & 6 boxes.

When the Merc boxes were new their low speed spark was impressive ... maybe SCARY is a better word. If you've had some with weak spark at any speed there was something wrong with them.

I use Merc triggers and CDI boxes on my 6's (all padded, one has 275psi cranking compression). They fire instantly and need little choking even on the chilliest days. This was not the case with old Merc boxes. I would not even trust a NOS Merc box ... they haven't been made in many years and could go bad just sitting on the shelf in my opinion.

I have a bunch of used Merc boxes that I would be happy to get $30 each for if anyone wants them.

The technical portion of this thread continues here: http://www.boatracingfacts.com/forums/showthread.php?t=6242