D Mod/750 Mod Engine

[Bob Rusnak]

Need some technical help on setting up a 44 Merc Mod engine. There seem to be many different opinions to the max. engine timing. Could anyone give me the timing information using eather a Merc 500 or a MK 58 and a Merc maginto? My other question is in using fixed jets, what would be the jet size to be used in a KA of KC carb. I started with .069 jets and need some further advice from some of you experienced Mod racers. Thanks Bob N-96

[Dave M]

Timing

Need some technical help on setting up a 44 Merc Mod engine. There seem to be many different opinions to the max. engine timing. Could anyone give me the timing information using eather a Merc 500 or a MK 58 and a Merc maginto? My other question is in using fixed jets, what would be the jet size to be used in a KA of KC carb. I started with .069 jets and need some further advice from some of you experienced Mod racers. Thanks Bob N-96

I would reccomend 375 for your timing, it is a good place to start. We don't vary to much from that.

For Jets, trial and error. Try what you have and then go rich or lean based on your tests. Without knowing what has been done to the engine it is difficult to make an educated guess on this.

[Morris85C]

Dave is right but let me add a littel note does the mag move or is it lock down it does matter on the jet sizes i would start off fat dont want to burn her up let say 71 or 72s you will have to drill them out with a drill bit this is a good starting point an lean down from there do some testing an you will come up with your own way that works good for you this shoud put you in the ball park

[Sonny]

timing

I recall reading somewere to start arround .320 btdc and go up in incraments of 10% until you get to .370 btdc. At .370 you drop down to 5% incraments until the boat stops going faster at extended throttle and then come back one 5% step and thats it. Thats how it was explained to me but I could be wrong. Hope it helps.

[Bob Rusnak]

Thanks for the replys from you D mod drivers. I am swinging the mag. and the timing was at .280. We are running it on a Luce boat. Locked up a Merc 500 (cooling problem)on three occations but the MK 58 ran well. It was real good on a old Krier 250 boat using a set of carb's with adjustible jets that came off one of George Luce's engines. On the new Luce boat the MK 58 (timing at .280 and .069 jets) ran well but about 3 mph off the lead boats. We wasted a lot of time with the Merc 500 powerhead which hurt our momentum for the season. I had an old MK 58 block that was ported by Dick O'Dea and decided to build one more powerhead. I have a set of Lon Stevens exhaust on it but can put Bayer on if these do not work. I pretty much followed the Brinkman book to build the powerhead. I will be using a Konig 14-15 unit with a DeWald 4 blade prop he made for me. We were hoping to make more races last year but the financial situation did not support it. Hoping to have some what of a good year next season and hope we can get a little more speed from the MK 58 powerhead. Any additional information will be a big help and I know it takes a lot of time and work to be on top. Thanks Bob Rusnak

[David_L6]

I have a Merc 500 block and run timing anywhere between .300 and .320 (I don't get too picky with trying to get it set at exactly .3xx.....) I've never run fixed jets so I have no clue where to start with those.

[Kev43V]

You can put a substantial amount of time and effort in to being last too. But for some reason i do not think it is as satisfying. I will let you know for sure if i am ever on "top". LOL
now for the real reason i am posting. It just gives me a warm fuzzy feeling inside to see people helping others out as much as I see so many boat racers doing.

[Sonny]

All of my time and effort goes into being last...lol.

[crankbearing]

What Carbs?

Hey Bob,

What Carbs are you or will you be running! Here is a list of things before jetting.

Carbs
Mixture and what oil
Porting - How Much
Timing
Plugs

Do not drill out your jets, go to your local Machine Shop supply store and get some proper reamers. I bought a complete set from .050 all the way up to .150 for like 80$. I have a jig for the jets and I open them up in the drill press. Drill bits leave grooves or marks internally on the jest and you never KNOW what actual size your jets are. we used welding tip reamers in a pinch.

You should always start FAT and go down once you reach where you want to be. After that I go up 1 half size and compensate with the low speed adjustment.

I run .067 in all my mods, my own and the one's I have built but the formula is always the same, timing, plugs, carbs etc... On some days those are a little rich and on some days they are a little lean, you can always adjust the low speed a little to compensate.

rgds,

[Dave M]

Swinging Mag

Thanks for the replys from you D mod drivers. I am swinging the mag. and the timing was at .280. We are running it on a Luce boat. Locked up a Merc 500 (cooling problem)on three occations but the MK 58 ran well. It was real good on a old Krier 250 boat using a set of carb's with adjustible jets that came off one of George Luce's engines. On the new Luce boat the MK 58 (timing at .280 and .069 jets) ran well but about 3 mph off the lead boats. We wasted a lot of time with the Merc 500 powerhead which hurt our momentum for the season. I had an old MK 58 block that was ported by Dick O'Dea and decided to build one more powerhead. I have a set of Lon Stevens exhaust on it but can put Bayer on if these do not work. I pretty much followed the Brinkman book to build the powerhead. I will be using a Konig 14-15 unit with a DeWald 4 blade prop he made for me. We were hoping to make more races last year but the financial situation did not support it. Hoping to have some what of a good year next season and hope we can get a little more speed from the MK 58 powerhead. Any additional information will be a big help and I know it takes a lot of time and work to be on top. Thanks Bob Rusnak

Bob,

I would set your timing at 375 after reading this post. It sounds like you are well on your way, good choice on the gearbox and what not. One piece of advice I can give you, do not try so hard on the engine. Get it reliable and get the seat time, and work with props. This will benefit you far more than any amount of engine work you can do. A really built up MK 58 will still compete with the 500 blocks, but I am not so sure they would beat the best in the country. I wish you luck, and hope you can get it. Remember, if you followed Harry's book, you should have zero error and the engine will run fine.

[Bob Rusnak]

Plenty of information on the D mod, thanks guys. I will put all this information together and will at least jack the timing up from .280 I had last year and up the jet size. I have a set of KA carbs with adjustable jets and can start with them. I want to use the KC carbs but need to get the engine running and reliable first. I was asked questions like porting. I can not tell anyone as the porting was done by George Luce on two blocks and the other way back by Dick O'Dea so I do nor know any specifactions. Gas and oil? OMC of Quicksilver oil 40/1 and 87 octain gas from any local station. The other thing is all engines have dry filler blocks with no cooling water going through them. Plugs, J4C in the MK 58 and QL77JC4 in the Merc 500. Again thanks for all the help and looking foward to trying all this out at Franklin, PA next season. ....Bob N-96

[mercguy]

Plenty of information on the D mod, thanks guys. I will put all this information together and will at least jack the timing up from .280 I had last year and up the jet size. I have a set of KA carbs with adjustable jets and can start with them. I want to use the KC carbs but need to get the engine running and reliable first. I was asked questions like porting. I can not tell anyone as the porting was done by George Luce on two blocks and the other way back by Dick O'Dea so I do nor know any specifactions. Gas and oil? OMC of Quicksilver oil 40/1 and 87 octain gas from any local station. The other thing is all engines have dry filler blocks with no cooling water going through them. Plugs, J4C in the MK 58 and QL77JC4 in the Merc 500. Again thanks for all the help and looking foward to trying all this out at Franklin, PA next season. ....Bob N-96

40:1? Mercs like LOTS of oil!

[Bob Rusnak]

Oil?

40:1? Mercs like LOTS of oil!

Tried all different ratio's and saw no difference, even with the crank and bearings. Use to use qt./5 gal, plugs were always black. What do you recommend. ....Bob

[oldracer]

Merc Buildup

Hi Bob- Why don't you switch to synthetic oils. All equipment, automotive boats, outboard and I/O engines ran better with synthetics. Got better power and fuel milage.
My $0.02 worth.
Ye Olde Desert Geezer Al Lang

[Bob Rusnak]

Hi Al, I have tried synthetic oils also. I am just use to running alcohol burning engines at 20/1 ratio using caster and noy Powermist oil. Ran qt/5 gal in all my old stock gas engines and now having some fun with the 44 Mod engines. Just there are so many different oponions and needed some starting points. Got one Merc 500 that will not run. I origionally built it and then Dave Young built it again. Will not run!. Will not take fuel!. Changed everything from mag's, fuel pump, fuel tank and had the carbs apart several times and found nothing wrong. This spring I will try a set of KA7A"s with adjustable jets. The MK 58 runs good and swapped most of the parts from this one to see if we could get the 500 to run, still did not. It has been interesting though. We ran the 500 Runabout at the Worlds last Oct. That was some event. EORC awards banquet is comming up next month. That is usually fun.......Bob N-96