Mercury Mark 40-H

[F-12]

Looks like one of you (or both) know how to use a heli-arc torch. I have seen so many projects come through with minimal or no penitration and know someone will be apologizing for a crap job. The intrusion is perfect, beads are consistant and neat. Good job. Also can't wait to see the finished product.

[Aeroliner]

Thanks for the kind words. My brother and I are not the welder but Doug Kay who dose all our 4 cylinder work has a great welder working with him. We will keep everyone posted on this as it progress. With a bit of luck it will be on the water next season. We will be posting some internal block shots when we get there. As it looks now we will have to line bore the assembly even though the unit was preheated before welding. Tonight we should have the mag hanger moved aft on the crankcase.

Alan

[John (Taylor) Gabrowski]

This kind of approach to adding wedge reed valve systems to the front of the Merc 4 crankcase forming 4 sided towers / columns of moving air/fuel exposes more surface area to get more cooling air farther away from heat generating sources without significantly altering crankcase volume CCs. That is a lot of good looking welding. Your approach in using 4 pumpless Tillotson HR carbs is going to be interesting. The farthest I got in terms of using any HR carbs was to put a pair of pumper versions with velocity stacks (for show) on a D-Mod 44 Merc using existing carb crankcase ports with phenolic spacers separating carbs from the crankcase. They worked good once I turned them throttle butterfly verticle. Tunning them was a breeze as well with all ajustment needles verticle and compression spring and gland loaded. But 4 of them???? I am getting 4 Tillotson HL232 carbs switching them between 4 Tillotson AJ47 as starting points, moving toward KA, then KC carbs and then even 4 - OMC 3 Holer carbs before getting to the HRs your going to first. I see that your using squared reed petals and corresponding reed ports they are covering. Motives to your madness on setting up the 4 Tillotson HRs. Setting up for high speed big time air/fuel transfer right off. Because of what I learned about the Ray Nydahl front case casting route I am proceeding on the conservative side as they overcarbed using 2 Tillotson HD carbs (could equate to 4 Tillotson HRs?) slowing down transfer velocities spoiling engine performance. It shows there are a lot of considerations to look at before one even gets to fire and test them.

Nice work, for sure! Your effort is inspiring too!

[Mark75H]

slowing down transfer velocities spoiling engine performance. It shows there are a lot of considerations to look at

Consider that McCulloch used 2 HR's on a single 100cc (7ci) powerhead. I don't think there is anything to worry about

[John (Taylor) Gabrowski]

There was a logging competition on TV based on some town in British Columbia and on that show I saw a McCulloch chainsaw with twin Tillotson HL carbs parked on a reed valve manifold on the 100cc saw. There were other chainsaws with expansion chambers what cut huge log slices off big logs in about 5 seconds too. Since that show I saw the same McCulloch HL carb set and dual carb manifold for sale for a couple hundred bucks on a Kart site that did not wait around before ZAP they were gone. Just a dual carb reed manifold auctioned off on Ebay real quick a few months back. Jim Hallum used the same HL carbs Alky converted and reed manifolds on multi-carb Anzanis to set those speed records. If some Tillotson HL or alternatively HR carbs setups with reed manifold ever existed and knowing the needs of the logging industry probably did have them too I would sure like to have me some!

[Mark75H]

I've never seen the HL's used ... the HR's were std from the factory on the later Mac kart motor. The dual manifold/reed assembly for karts is a common item on eBay, like 20H parts for outboard collectors, always goes for big money.

[Aeroliner]

When I started looking for carbs's I had a goal to see if the the old Mercury twister look could carry over to a 4 cylinder engine. Doug Kay who is doing the work convinced me to make it look like it came from the factory. I had one HR series carb with pump and found from the Tillotson tech data that they made it without a pump. Doug Kay convinced me that we should start at this point because we could always go smaller. If we look at the specs for the HR we find it is rated for 150 to 300 CC engines with a 44 having about 180 cc per cylinder. I have the folks in Ireland looking into my selection and hope to get a recommendation from them. We expect to run the engine in the high 8,000 rpm range. Another thing with the HR that is interesting is the boost venturi feature that should help throttle response on a small race course. We are also going to see if spark advance verses throttle opening can offer some advantage if applied in a time fashion. Most likely we will build a couple versions to see what works best. It is becoming clear that maybe I will need a dyno to really develop the modification to see what works best. Having dyno data that will show RPM, HP, spark advance and throttle opening might prove some theory. One day it would be nice to test the 444 together. Might be a lot of fun for all.

Alan

[John (Taylor) Gabrowski]

There is little doubt from the posted and known data that the Tillotson HRs do fit the crankcase volume aspects of making a good carb for the engine with wide enough a variation to work. The approach of going smaller sounds the better if you don't have the carbs on hand to get the velocities up. I have everything but the HLs in quantity.

Once I got into Modifieds I started locked - fixed the ignitions in a singular advanced position. Only the throttle shafts/butterflys moved with the throttle only simplifying things. Minnesota D-Mod racer Mike Franck has a nice magneto locking system that locked up on an arm and pin setup where you started the engine in a retarded magneto position state to make starting easier and so backfiring would not try to rip the starting cord T-handle through your poor fingers making you scream out in pain and terror! He would then swivel the mag into a locked fixed advanced ignition position that stayed there for racing until you came in and reset it for start for the next heat of racing.

Some how I want to keep things simple and uncluttered so less can go wrong at any time.

[leehall91]

Here is a new carb from tillotson to look at
http://www.tillotson-racing.com/inde...mart&Itemid=27

[Aeroliner]

Thanks for the feedback on a Tillotson carb. Here is what I got back from them.
"Hello Alan,

Sounds like a very interesting project you have taken on. With regards to the HR carburetor I would recommend using the larger of the HR series carburetors which is the HR-199A carburetor. This has a venture diameter of 1 9/32” and a throttle bore diameter of 1.355”. It is fully adjustable both on the idle and high speed system, and can be used in any position as it is a diaphragm carburetor. It is complete with it own built in fuel pump which is operated via the pulses from the crankcase. If you were to remove the pump section and use external fuel pumps then you would have to make sure the pressure of the pumps would not overcome the fuel inlet needle which is held closed by a spring, otherwise you would have flooding problems. This carburetor is not fitted with a choking system.

The price per carburetor is $249.31 + whatever means of transport i.e. courier or post.

Delivery will be made immediately after receipt of payment.

Please also look at our new sight the address is www.tillotson-racing.com

We have released 3 new carburetors last year specially designed for Kart racing. The largest of these 3 carbs might interest you it is the HW-12A carburetor. Please have a look and let me have your comments."