D Mod/750 Mod Engine

[David_L6]

I don't like dry filler blocks. My C is cooled the way that Brinkman recommended. In fact, he did the work on it. My 44 has O'Brien exhaust. See pictures. If I were building a 44 right now I'd buy a Bayer exhaust from Dudley Malone and water cool the filler block with the welded in water jacket like Brinkman recommended. I've never seen a Parker filler block (Tim Kurcz makes them now) but you may be able to set it up the same way.

I run NGK B8S and B8HS plugs depending on the motor.

I ran Klotz R50 for years but have been running Pennzoil full synthetic the last few years mainly because I can buy it locally instead of ordering it. I run 3 pints oil to 5 gallons gas. I have run more oil than that but I won't run less. You can run automotive gas but you may not pass inspection. I run either VP C12 or av gas. Those cost more but they will pass inspection every time. There is no speed difference that I've noticed.

[Dave M]

Carbs

KC carbs are difficult to master. Be prepared to spend some time on this. I would reccomend you contacting Eric Vanover on KC Carbs. He is a master of these. If you need his contact info, let me know.

When I say spend some time, I mean testing. Not adjusting it in a test tank. You can get it close with a test wheel, but you still need to go run it a lap or two so you can tell what it is doing. Once you get it right make dam sure you don't mess with them, ever. Means don't lift the engine by them, or anything like that.

[Bob Rusnak]

Dave, thanks for the carb information. Since I have one powerhead that seems to run well using the KC carb, .069 fixed jets and a dry exhaust, I will leave that one alone as it is reliable. The other Merc. 500 powerhead would not take fuel using another set of KC carb's. Would you recommend trying a set of KA carb's on that engine? In your oponion what is the advantage of the KC over the KA carbs? You mention the KC's are very difficult to get right. Are they that critical to figure out? The Merc 500 powerhead was apart several times and put back by several different builders and could not find anything wrong inside. When trying to do (test) all this at a race time just runs out. The open exhaust restricts most of the areas for testing so need as much info as possible during the winter months. Thanks again......Bob N-96

[ram95]

Bob, having an interest in building a D-mod for myself, I've been following this discussion and was curious as to your comment it "won't take fuel". Could you elaborate on that a little?

[ram95]

Bob, having an interest in building a D-mod for myself, I've been following this discussion and was curious as to your comment it "won't take fuel". Could you elaborate on that a little?

[Morris85C]

IF you can not test because of open pipes i would try to find some one with a dyno I dyno all my moters before i test saves a lot of time have the intake ports been work on Ihave to be carefull here be caues i dont want to get blasted from you guys BUT i found that if you mess with the intake ports you have to be realy carefull on the intake port timeing you could mess up that block to were it my never run agine the rule if thumb here from my shop is never thouch the intake ports morris85c

[Bob Rusnak]

Woun't take fuel? It all started this year at Melville NJ. The motor was untested and started on the bank. Dave Young took it for a test run when the race was put on a hold for wind, with permisson from the referee. Dave said the engine was surging, of running out of fuel. Changed the fuel pump and went for the first heat where it locked up on comming for the start. Dave rebuilt the engine, had the block bored .015 and put a set of new Mercury pistons in it. Took it to Franklin, Pa and on Friday, went to start the engine for the first time. Did not sound all that good. As soon as you backed off the throttle, the engine quit. Changed furl pump, no difference. Took out fuel tank, not the problem, changed ignition, no change. Took carbs off and complety took them apart. Could not find anything wrong. By this time, Friday's testing was over. I wanted at that time to put the other enging on and run it in Sat. racing but was talked out of it. Went out for the first heat and motor quit after getting on a plane. Not much time between heats so tried the last heat and came right in. That was it for Sat. On Sunday, I put the MK 58 engine on and it ran perfect for two heats. It was not that fast but ran. Tried to change props between heats but a brand new prop would not fit. Shear pin hole was not in alignment so just jacked the engine up a little and it ran a little better. Still have not figured out what is wrong with the other engine. The only thing I did not try was changing the carbs completly. I did not have another set with me and just no time to swap from the other engine. That was the last race we went to with the Mod engine for the season. Had two raced we committed to with the 500 (PRO) runabout which were paid to attend. Skipped all National events this year due to many reasons, (price of fuel) etc, etc. Hope to have a better time with the mod engine next season. ....Bob N-96

[Danny Pigott]

Ports

Lonnie you are right about the intake ports. Have run these engines from 1970 an have tryed it all. Danny

[Dave M]

Carbs and Ports

We have one set of KC carbs that work, and the rest are KA carbs. On my runabout engine I run the 44XS carbs. I really don't like them to well, as the floats have a horrible tendancy to stick, just as they do on a lot of the stock engines. Trick is to make sure they are full of gas before you put it in the trailer for transport.

Lonnie is right on the intakes.. he also learned the lesson the hard way it seems. Most of your top dogs have learned these lessons the hard way.

It sounds like you had carb issues at Franklin, to bad you could not have elminated the question by swapping out a set of known working carbs and seen if that was the issue. I have ran into that trouble myself, and swapping a set of carbs worked. For some unkown reason the carbs simply would not work. Currently my 750CCMR engine has a blubber on top end, probably why I could not catch Lonnie at Whitney Point. (well okay I had no shot at him or Davids there. they were smoking fast on the huge course.) Had there been testing there, the outcome might have been a little better for me.

Sounds like you need to check everything over real good. Look to see if your intakes were ported and cleaned up. Check to make sure your Reed cages are sealing on the block. Make sure your reeds are not sticking, and also closing all the way with no gaps. End main seal sealing well ? Mag can also be breaking down at certain RPM. We have had mags check okay on the bench for spark, but when on the engine they break at certain RPMs.

One sarcastic tip, don't let off the throttle during the race if it is quitting, keep it nailed !

[PROPDOC]

I Agree!!

I agree with Dave's last post. With the engine that you can't get to run make absolutely sure that it is sealed at all the main areas (i.e. crankshaft seals, carb monting seals, crankcase is sealed, reed cages are sealed, and one that might be overlooked is the labyrinth seals between the cylinders.) With the Merc if there is the slightest crankcase leak it will run pretty well with out a load on it but once you get it in the water it won't run at all. If you are unsure of the condition of your labyrinth seals try replacing your reed cages. The labyrinth seals are the grooves that machined on the inside of the reed cages where they seal onto the crankshaft.(if you didn't know and if you did my apologies for the explanation) Also it could be as simple as changing out the carbs. I hope that some of this is helpful.

[Art K]

Mod d

As Dave said he has one engine with KC carbs that runs good. We have the same situation. One with KC`s one with KA`s. Built both engines originally with KC carbs One ran great with the KC`s the other would run good for a few laps but then would foul a plug. Tryed everything from hotter plugs,float settings ,needles and seats.leaner mixture etc,finally put a set of KA carbs with fixed jets .069, engine runs great now. Only difference between engines is gear ratio one is 14-15 the other 1-1 and there is a slight difference in the way they are ported on the exh. side. And I do work work on the intake side, not sure if it helps a lot. But our engines do win races.
Art K

[nbass]

My two cents worth

We find that the port timing on many of the 500 blocks are all different. I think in all cases the transfer ports are too small and the transfer port timing is too high to account for their small size. This may be in part the problem. Secondly, the reed system is inefficient and depending on the reed block modifications or lack there of, a slightly larger carb does not keep the carb velocities in the right zone. I suggest use what always works.

Can be frustrating, expensive, and down right irritating, Good luck!
Neil

[Bob Rusnak]

Thanks all for the response's to this thread. I now have compiled a great deal of new information. It just may be that the port work on the block is no good. Just hoping it is just a set of carb's will fix the problem. Put together a few sets of KA series carb's. I will have with me an way of comparing if the engine runs. Will also try an adjustabe set of KA-7A carbs which I took off my MK55H. Don't run that engine anymore anyway. One of the problems is the location of the equipment. The race trailer and boats are in Western Pa. and The engines are on Long Island. I have a Krier runabout hear on LI and set up for eather a 250 Pro engine or the 750 Mod. Tried the 500 Konny on it and was out of control. The first test session for all this will be at Franklin, PA on Memorial Day Weekend if the race is on. Wish I had access to a dyno but that is not to be. My thoughts some how keep going back to the reed cages. They are the large brass ones with long stops and fiber reeds. Could be the centers are a little worn but not shure at thie point. Will try one more time before tearing the engine apart. Thanks again..Bob

[Dave M]

Please

Thanks all for the response's to this thread. I now have compiled a great deal of new information. It just may be that the port work on the block is no good. Just hoping it is just a set of carb's will fix the problem. Put together a few sets of KA series carb's. I will have with me an way of comparing if the engine runs. Will also try an adjustabe set of KA-7A carbs which I took off my MK55H. Don't run that engine anymore anyway. One of the problems is the location of the equipment. The race trailer and boats are in Western Pa. and The engines are on Long Island. I have a Krier runabout hear on LI and set up for eather a 250 Pro engine or the 750 Mod. Tried the 500 Konny on it and was out of control. The first test session for all this will be at Franklin, PA on Memorial Day Weekend if the race is on. Wish I had access to a dyno but that is not to be. My thoughts some how keep going back to the reed cages. They are the large brass ones with long stops and fiber reeds. Could be the centers are a little worn but not shure at thie point. Will try one more time before tearing the engine apart. Thanks again..Bob

Just make sure the carbs you have are working on the stocker before you remove them to try on your D mod. I would fire up the stocker and make sure they are working well on that before I simply removed them and placed on a race engine. You need to eliminate one possible problem at a time and not change a bunch of things at once. That never works out to well.

Good luck in your project.

[mercguy]

Oooops.... lest my post be mis-interpreted, What I was trying to imply is that we try our darndest to make a mod-motor deliver more than its 'stock' power. And in the process we fail..... sometimes. Other times, we win!! The mfg isn't alway right. And Elmer Kiekhaefer knew that fact better than anyone, tho he took a great deal of pride in what he produced. Above it all, Elmer was a competitor, not unlike any one trying to make a D-Mod merc run.

Alex
madrussianracing

who's this Elmer cat???? Them **** Tohatsu fumes must be getting ya all crazy and chit!