Flathead's Combee TomCat

[Flathead]

I've moved my post to this forum for obvious reasons. V-dub motor = automobile engine. You know what was funny? A couple of days ago I was browsing through a VW engine rebuild book and the author stated "Your VW engine will give years of reliable service provided you remember a Volkswagon is not an automobile, it's a Volkswagon". So, if a Volkswagon is not really an automobile, then is it's engine an automobile engine? Just kidding.

Here area few pics of what I have and what I have done. It appears the boat was in some type of accident before I bought it. The cage was canted to one side and you can see one where the prop tip sheared right through the cage. Kind of scares me a little. Fixed that up with a come-along. Just pulled it back into shape.

The accident mangled the prop tips a little, so I ordered a Ultra prop from competition. Should be here in a few days. In one of the pics you can see a hex shaped extension to elevate the cage about 1.5 inches. That will allow me to run a slightly larger prop diameter safely. I'll be trimming the prop myself, so I hope to end up with a 54-55inch prop. We'll see. I have a variety of pitch blocks coming, so hopefully I can get her dialed in pretty quick. The boat tachometer is off a little. it reads the engine rpm's are about 400-500 faster than what the actually are. I confirmed this with an ancient dwell/tach meter I found at a local snowmobile swap meet.

I'm hoping the new prop will get me onto plane. I'll feel much more comfortable starting the rebuild project this winter knowing I have a good motor/boat/prop combination.

Bruce

[buster]

Flathead,

Looks like you have made some good progress. Mine is still about the same as when you saw it. My problem seems to be a lack of ambition now that the weather has turned cold. I just may wait until we get warmer days.

Keep posting the pictures though, It' lookin' good

Dave

[Papee]

Now you have a taste of it. Using the motor in an airboat application is most likely the hardest on the motor, it's not like a stock application or even a dune buggy. You are asking it to pull 90% of the time it is running. These days when I make changes to my 084 boat it may look like I am trying to find more speed but in reality I am looking to make the boat more efficient so the motor does not have to work as hard. Another MPH in top speed gets you a better cruising speed also allowing you to run the boat at a better cruising speed but not as hard on the engine. Unless of course you are gaining speed by increasing engine rpm.

I look for things I can do the the hull or the way the boat is set up for more performance, total weight or weight distribution. The most important thing in building a mini is spending time on your hull making it work as well as possible. This is kinda what I set out to do when choosing to run a direct drive, I was always the one trying to get the most out of as little as possible while keeping the setup reliable.

I was one of the first, if not the first to get a 12 ft jon boat to plane out with a 8hp motor running direct drive with no motor modifications other than removing the governor. I used a very light hull(thin) which lead to other problems on the rocks here but the boat worked very well until the day I sold it. I sold it to a kid who tried to improve it and also added more weight to make it fancy and it went downhill from there.

Not long ago I saw a very nice looking VW boat at the river. The boat was beautiful! The problem was it wouldn't plane out very well if at all. He spent all his time adding fancy seating, a cool control panel that folded up and out of the way when fishing, as well as junction boxes for his wiring. While making a nice build and very nice looking boat, he also added a lot of weight and the weight that was there was not equally distributed. I always use what my daddy taught me, He was a mechanic at Piper Aircraft, KISS... Keep It Simple Stupid! I just always thought he was calling me stupid until I caught on.

Well enough of my ramble, just remember what ever you do... Keep it fun and have fun while you're doing it.

If the wimmins don't find you handsome, at least have them find you handy!

[buster]

Flathead,

First, I think you made an understatment about the big storm. I believe I heard it was the most snow in one storm of all time. Guess what, winter starts next week

Next, Since your project is lookin so good, I may just wait until it's done, and then steal your ideas. Hope ya don't mind

Dave

[buster]

Flathead,

That's coming together real good. I especially like the diamondplate on the transom. That looks sharp.

Hope it performs as good as it looks

Dave

[Flathead]

Dave,

That diamond plate IS the transom. I left enough of the original fiberglass to maintain some structural integrity, but the diamond plate in the only thing between me and davey jones locker

Bruce

[whobbies]

Bruce, I should of read on, and now noticed that you converted to the Rotax engine. Were you able to get the VW engine to perform the way you wanted? I am now trying to decide what way to go with mine, any advice will be appreciated.
Thanks,
Tony

[Flathead]

Hey Tony,

I will be glad to offer any advice/insights/observations you may find useful.

As you read through the thread you will get a pretty good idea of how the Fatcat performed with the VW engine. It sounds like your goals and mine, as far as performance are concerned, are similar. I wanted the Factcat to be able to get on plane hauling two people and a modest amount of 'gear' in deep water. Frankly, it never did. Just too heavy and not enough hp.

I would bet you will end up with a similar result if you go with the same 1600cc dp engine I was using.

I was left with the option of spending a great deal of money for a reduction unit to try to get better performance, using a larger VW motor, or scrapping the whole VW motor idea and going with something else. My choice was obvious, and so far I've been very pleased with how it's turning out.

Having said that, I'm the first to admit my experience with VW motors before the Factcat was exactly ZERO. To this day I'm not sure I ever had it tuned to give it's rated hp. Plus, using a direct drive, the prop speed is limited to 3000-3200 rpm's or so therefore that's all the rpms you can run the motor at. Those Tomcats were originally built using VW motors(at least some were) so I would tend to think mine may have been a little weak.....

Anyway, if you have any question just ask or send me a pm.

Good luck

Bruce

[Duane Scarborough]

Buster,

That's looking nice ! It was especially thoughtful of you to put down all of that white stuff on the ground. Makes the pictures stand out pretty well.

Thanks,

Duane

[Flathead]

What do you do in Minnesota in the winter when there is no snow? Work on the airboat! I finally got all the sleds out of the shop and the Fatcat in. I installed the new exhaust and Presto, the flat spot went away! It all appears to be working perfectly I'm sure glad that new exhaust solved the proble. I'm not sure what I would have done if it had not....... I'll post a pic soon. Gee, it's been a while since we heard anything about Buster's build..... or any other for that matter.

Flathead

[buster]

Wow, a boat that jumps out of the water, that's a problem some guys would spend lots of money to have!

The Fatcat is lookin' real good with the new upholstry etc.

Dave

[Bryan61]

I had a vw dual port I think it was a1973 rebuilt with a 52'' two blade I think the pitch was 28 { it was stamped on the prop] but I could only turn it 2700 rpm and the people a arrowprop told me about 3200rpm But unfortunetly it flipped over when i was turning without any prop speed and the river was very high.

[Bryan61]

that a nice looking yellow combee tomcat, I'm trying to find a small airboat hull so I can get away from my plywood hull but in Iowa there just arent many around and a new 10' lund jon boat is about 480 dollors

[Flathead]

So, after some research, I've decided my motor is not 'peaky', rather it has a flat or dead spot around 4500rpms where it does just not respond to changes in throttle settings. Might be carbs, might be exhaust tuning. details, always details.........

Bruce

[buster]

I have heard that those 2 cycle engines are real fussy about exhaust backpressure etc. Do you have the stock exhaust-muffler, or a homebrew setup?

Dave

[Bryan61]

I have heard that those 2 cycle engines are real fussy about exhaust backpressure etc. Do you have the stock exhaust-muffler, or a homebrew setup?

Dave

No its got a small supertrapp muffler

[Flathead]

It's a stock exhaust. However I did have to change the angle of the bend in it to get it to fit. I changed the angle of the bend by cutting out a pie shaped wedge and then welding it back up. I would guess I shortened the expansion chamber by about 1" give or take. That's why I think I will look at the exhaust tuning first. fortunately I have another stock, non-modified pipe to try, if I can get it installed, even temporarily, without modification......

Bruce

[Flathead]

Well, that made no difference. Had the same flat spot at the same rpm's. Next I will look at my carb jetting. I did change it from the original snowmobile setting to run in warmer temps. Maybe I'm a bit too rich ( or maybe too lean...) details, always details.

Flathead

[Flathead]

OK, I'm not too lean. Changes jets to make it richer and it got worse. So I ordered some smaller jets and we'll see what happens. Basically what the problem is if I set the prop pitch too high, them the motor can't get past 4500rpm's. If I back off on the pitch, then the motor gets past 4500 rpm's but rev's past my 6500 engine rpm max.(way past) There is no happy medium. The color of my plugs are telling me to lean it out, but I'm already using considerably smaller jets that what it recommended. What the heck, it's only a motor. They'll make more.......

I'll get er'

Bruce

[buster]

Hey Bruce,

Sounds like you got yourself what we used to refer as a "Problem Child". I never been too good at diaganosis, but I know a guy, maybe you heard of him, goes by the name of Duane. He generally can come up with reams of info about most any problem a guy might have.

If he does, be prepared to to a lot of reading. He will most likely have the answer, but it may take you a while to sort it out. He's a good guy to know when you need to find tech info about something!

Dave