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best distributor replacement

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stevewitt1

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I have a 1986 3270 MotorYacht that came with BB225B VolvoPenta's. I repowered with 5.7 4-bolt main long blocks. I stayed with the pre-87 version to use the original intake. My performance and economy have been going downhill the last two years. Had the carbs rebuilt and jetted, they are original Rochesters. I still have problems devoloping rpm's over 3100-3300. I don't run hard, usually around 3070 rpm would show me .80 kmpg. Now shows me only .67 kmpg and noticed continuing to give more throttle movement to achive cruise rpm. My original distributors look rusty and crusted inside but the springs are still visable, though scaly. They have pointless plates in them that I think were a retrofit, though present when I bought the boat.

I am considering replacing and wonder if the sierra 18-5494 or the Mal-9-26306 are both acceptable. The Mallory comes with a kit, new coil, wires and dist. My wires are probably 5-7 years old. Time flys when were having fun.

Any suggestions or advice would be greatly appreciated!

Thank You in Advance
Steve

visit us at: http://www.ocontoyachtclub.info
 
Steve, are you sure that the hull is clean and free from any marine growth?
This will slow a hull down tremendously!

Poor ignition timing may cause similar symptoms.

What I would do before doing anything else, would be to mark off your harmonic balancers up to 30* or 35* BTDC or Clockwise of the original TDC mark.
(assuming that you are running two (2) LH rotation engines and V/P I/B MS 3 or 4 transmissions.)

Try to mark them @ 5*, 10*, 15*, 20*, 25*, 30* and 35*.
There is a decal available IF you know the exact diameter of the balancer.

I'd then strobe each engine with your standard mode timing light, and write down the progressive advance curve up to, and including, 3.1K rpm.
Post this curve on the forum......, and one of us can take a look at it.

Progressive Ignition advance is critical for producing horse power.... especially in the cruising RPM range.
Old advancing systems can become inoperative, and may not offer the correct TA (total advance).

As for an Ignition Distributor selection...
I can only make a personal recommendation!
One of my favorites is the VR (variable reluctor) YLM units.
This would be Mallory's # YLM 624 AV and is a magnetic reluctor/sensor triggering unit.
(if stbd engine is RH, then this becomes a YLM 624 BV)

There is also a YLU..... but this is Photo-Eye triggering.
The VR (YLM) has proven to be a longer lasting, more trouble free unit, IMO.

If you don't mind the Hall Effect triggering, you can go with one of the other brands..... personally, I'd not!
Hall Effect is no where near as accurate!

You can also go with an EST system in an HEI.... but now your advancing is done electronically.... no longer mechanically!
Again, personally, I'd not go this route!
We don't necessarily need HEI, and you cannot trouble shoot this system very easily while on the water.
For this, it's best to carry a complete spare distributor module and control unit on board! Cha Ching $$$$$$! :eek:


Here are your Sierra and Mallory #'s...... 18-5494 or Mal-9-26306
Both of these numbers are suggested as a YLM 624 AV replacement.
NOTE and Use caution:
Many of these new numbers (both Sierra and Mallory) will often refer to; "Replaces YLM 624 AV".... when in fact, it may not be same.
It may replace......., but may not be VR and may very well be photo eye!
If VR Magnetic becomes important to you, then you must specify that is what you want.

There is an e-Bay seller who has been recently selling this unit as "re-manufactured" for under $200.
Word is, that they have had a module change only, and are actually brand new and/or possibly used for a short time only.
I've seen two of them.... they looked brand new to me!
He had them listed as a "YLM 624 AV".


Good luck, and I hope you resolve your problem!
.
 
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Well I’m off to a good start. I decided to replace my original Prestolite distributors. I installed Mallory YLM 624 AVs. I also installed new Mallory coils, Mallory wires and plugs.
I had ceramic resistors on my old system and the Mallory’s called for a resistance. My old distributors had the positive wire to the ignition side of the resistors but Mallory calls for the positive to go to the (+) terminal on the coil which is after the resistor. Does Mallory just do it different?

Question:
Is it alright to use the old ceramic resistors? Is it correct to wire the positive from the distributor to the (+) terminal on the coil which is after the resistor? I haven’t fired either engine up yet as I thought I should wait for an educated opinion on these issues.
Any help is appreciated.
Thank You in Advance
Steve Witt 1986 3270 MotorYacht “Forget-Me-Knot”
 
Steve, basically, there are two functions here that you need to be aware of..... and that can be confusing:

  • One; the Mallory module requires power in order for it to work.
  • Two; the triggering system (part of the VR module) is making and breaking coil continuity constantly.
In your 4 page instruction sheet for the YLM 624 AV, on page 2, Figure 2, it shows a module power connection directly to 12 vdc.
All other figures (1, 3 and 4) show "resisted" voltage here.
NOTE: last page/upper right is this note; Red Wire; If you are using a ballast resistor, connect to 12 volt side of ballast resistor!

So you can see that there is conflicting information here! However, they will work either way.

Note that the "green" triggering wire is coming from a coil that has a resisted power supply!
If you look further, you'll see that ALL Ignition coils that are being shown, use "resisted" power. Apparently this is to reduce corrent on this side of the module!

TA is always the more important of the two, so don't forget to check/set TA before thinking all is OK.
This may involve a BASE advance that is slightly different from OEM specs.


As for the ceramic resistors...... if the voltage is correct, there should be no issues. The resistance is measured in ohms.
 
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