Say hallo to my leetle frand!

[Frank Acampora]

I have always maintained that a simple carb change will not increase horsepower to a noticeable degree. Well, now we shall see. Notice the black manifold? That's a TC carb attached to it. The venturi is 1 5/8 (2.07 square inches) diameter versus the 1 5/16 (1.35 square inches) diameter on the WB carb I removed. Total time for swapping carbs was about 20 minutes. --Easy job!

So: Next time I run this boat, I shall see if there is increased performance, no increase, or damage caused by lean running (because the carb will have less air moving through it than it was designed to handle.)

The manifold and carb were taken off a late model Force 50 with the 3.375 bore and 50 cubic inch displacement. The engine they are now mounted on is a 3.187 bore for 44.6 cubic inches.

 

[TrikeFreak]

Re: Say hallo to my leetle frand!

I'm just learning about boat motors (the hard way). But, I can tell you from experience with 3 wheeler 2-strokes, you get more top end with a bigger carb, but you MUST get it more fuel too, or you're running too lean. We always go up in jet sizes when going with a bigger carb. Some folks claim you lose low end going to a bigger carb, but you gain top end. But, maybe this came off the same sized motor, and it was jetted okay for your application. Just sharing my experience with other 2-strokes, and sure wish there were more choices for carbs on these motors.

 

[foodfisher]

Re: Say hallo to my leetle frand!

Physically speaking, I can only inhale so much air. Wouldn't i need bigger lungs to inhale more? Just having more air available doesn't increase my ability to suck it in.

 

[Frank Acampora]

Re: Say hallo to my leetle frand!

Precisely my reason for the experiment. I believe that port timing is the defining factor in horsepower production. This will put the argument to bed, just as when I switched from a 2 piece lower unit to a one piece and proved that the one piece WAS about 2-3 MPH faster.

Trikefreak: You will find with these Tillotsen carbs that as engine size, horsepower and carb size increases, so does the high speed jet size, thus allowing more fuel at wide open throttle. For example, The WB carb I removed most likely had a jet size of around .066. The TC carb I installed will have a jet of around .096

 

[redstrat]

Re: Say hallo to my leetle frand!

"Say hello to my leetle frand" I'm glad you weren't just posting a selfy here Frank. Good luck with the experiment.

 

[Frank Acampora]

Re: Say hallo to my leetle frand!

Nope! That was a quote from "Tony Montana" Al Pacino in Scarface, who used the Queen Mother of dirty words more times in that film than any other previous film.

 

[tater76]

Re: Say hallo to my leetle frand!

I put a set of carbs, intake, and reeds from an 89 85hp on my 73 75hp block, and they work fine. Not sure if there is any size difference in those models or years, (I didn't bother to look) but I have not seen any gains or losses, and have A LOT of hours on the combo.

 

[Frank Acampora]

Re: Say hallo to my leetle frand!

Well, I finally was able to test the 50 with the larger TC carb. Results were about what I expected--- nothing much to get excited about.

The larger carb was difficult to get idle correctly on, mixture screw needed to be set very rich. When I finally did get the engine to run reliably, hole shot was slower because low RPM power was less and the boat actually lost about 200 RPM top end.

Since changing the carb is only a 15 minute job. and since I took the old carb and manifold with me, I changed back to the WB carb originally on the engine. Lost RPM and top speed were regained as was the hole shot.

SO: As I always maintained, a simple carb change will NOT give a power increase. So, without other changes, don't bother to switch carb in a quest for more horsepower.

 

[foodfisher]

Re: Say hallo to my leetle frand!

Max out the bore?

 

[MickLovin]

Re: Say hallo to my leetle frand!

Well, I finally was able to test the 50 with the larger TC carb. Results were about what I expected--- nothing much to get excited about.

The larger carb was difficult to get idle correctly on, mixture screw needed to be set very rich. When I finally did get the engine to run reliably, hole shot was slower because low RPM power was less and the boat actually lost about 200 RPM top end.

Since changing the carb is only a 15 minute job. and since I took the old carb and manifold with me, I changed back to the WB carb originally on the engine. Lost RPM and top speed were regained as was the hole shot.

SO: As I always maintained, a simple carb change will NOT give a power increase. So, without other changes, don't bother to switch carb in a quest for more horsepower.

Will this be the same for me, mine is idling fine, just can't get out there to water test it, also I couldn't seem to see the Jet size on the TC5D carbs, I know I had .080 on the WB's.

 

[Frank Acampora]

Re: Say hallo to my leetle frand!



No, Mick! I should have clarified in the post: I always maintain that a simple carb change will not boost a 9.9 to a 15 or a 15 to a 25. This is not exactly true with larger engines.

In the case of this engine, the bore is only 3.187 for about 44 cubic inches. Later model Force 40 and 50 were 3.375 bore for about 50 cubic inches. These engines were able to utilize the big TC carb and in fact did come from the factory that way.

Your engine is 3.3125 bore with a total displacement of about 99 cubic inches, meaning each carb is servicing about 50 cubic inches. I have done this swap at least three times and there will be no adverse effects on your engine. The engine in my avatar is a 105 with the same displacement as your engine and TC carbs. With your engine it will be more like installing a 4 barrel on a Plymouth 318--It won't make it a world beater at the track without changing heads and cam etc. but it will pep it up some and make it honest.

I am hoping that when you finally do run it you will see 1-2 MPH more and not just equal performance. Oh, yeah, I forgot to mention: With the big carbs you can open up the reed stop plated about another 2 MM each side. This allows the reeds to open more and (hopefully) delivers more air. One of the differences between Chrysler engines with WB carbs and TC carbs IS the opening of the reed stop plates.

You can also cut these stop plates in half to eliminate or reduce any possible reed sticking (to the plate thus increasing blowback) Or you can drill the stop plates like the later Force models. Actually changing to the later square tipped Force reeds will not increase performance over the round tipped reeds on the Chrysler 4 Cylinder engines. I proved that a couple of years ago on my 140.

TC 5 carbs will have a jet size of around .092 to .096 depending upon model.