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6.5 K&B inboard nitro marine Carb retrofit?

Old 11-11-2012, 06:19 PM
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neverthought
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Default 6.5 K&B inboard nitro marine Carb retrofit?

I have an old 6.5 with a water cooled exhaust throttle, can I convert this to a carb? It's really fast but messy (spits nitro all over) and has no control other than FAST and Stop,
can anyone guide me? Thanks, Pete
Old 11-12-2012, 03:23 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

A standard carb should work on your engine. If you're looking to buy one, here is a link to the MECOA website showing the various carbs:
https://shop.mecoa.com/shopdisplayproducts.asp?id=187
Old 11-12-2012, 07:09 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

You can keep a eye open on Ebay for a carb. K&B is very common. .67 & .65 use the same case I believe.
Old 11-12-2012, 04:50 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

Yup, switching to a carb should be a simple process. Used parts are out there. You just need to figure out which carb you need. And then post a WTB on Intlwaters for sale section.
Old 11-12-2012, 06:11 PM
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neverthought
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

Guy's, Thanks for your input but I'm still a bit confused... on the MECOA site there is a note: "Always refer to these as 7.5's or 6.5's - NOT .45 or .40"[/b]
Why?
Advanced builder you mention .67 and .65? now i'm really confused.
Old 11-13-2012, 02:06 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

Okay, lets clarify things a bit:
6.5cc=.40ci
7.5cc=.45/.46ci
11cc=.65/.67ci

Now that we have that size part cleared up, I'm guessing MECOA would rather stay to one sizing system to prevent confusion on their part. My question at this point is do you have a .65ci or a 6.5cc? From what I'm seeing, the .65 can use an exhaust throttle due to it's front exhaust and rear carb while the 6.5 is a side exhaust that wouldn't use an exhaust throttle per the picture of each engine on the MECOA website
http://www.mecoa.com/kb/marine/marine_inboard.htm
Old 11-13-2012, 03:55 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

I'm pretty sure I have seen a K&B 6.5cc with a front exhaust configuration (over the flywheel). It was a very old model. Saw it at the hobby shop a couple years ago.
Old 11-13-2012, 04:25 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

I definitly have a 6.5 K&B marine with a liquide cooled front throttled exhause over the flywheel. K&B use both nomenclature but for some odd reason on the link below it say not to them as .45 or .40 this is why I asked WHY? i thought it was a bit strange but there must be a reason?
if you go to the link below, it looks like the #9181 but with venturi and exhaust throttle.

http://www.mecoa.com/kb/87/87-parts.htm


Old 11-13-2012, 07:36 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

Could you post a picture or two of it? I've never seen a K&B 6.5 in that configuration
Old 11-13-2012, 08:32 AM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

ORIGINAL: neverthought

Guy's, Thanks for your input but I'm still a bit confused... on the MECOA site there is a note: ''Always refer to these as 7.5's or 6.5's - NOT .45 or .40''[/b]
Why?
Advanced builder you mention .67 and .65? now i'm really confused.
I'm not a K&B expert but the .65 is older version the .67 is the newer of the 2- the .65 liner/piston should fit a .67 case. I think ,If the engine is used ,time for bearings So say replace once a year. If you run hard then twice a year. Depending on how good at clean-up- after a days run. Nitro is very hard on steel bearings. the cable/prop tends to push on the front bearing sideways The one under the flywheel If ones goes the the other need replacing as well. I like http://www.bocabearings.com/
Old 11-13-2012, 12:53 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

it looks like the #9181 but with venturi and exhaust throttle.

http://www.mecoa.com/kb/87/87-parts.htm

Old 11-13-2012, 01:25 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

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Old 11-13-2012, 01:27 PM
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Old 11-13-2012, 01:33 PM
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Old 11-13-2012, 01:43 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

You do have a exhaust header to add once you pull the exhaust throttle. YES Or how will you tie in your pipe? I feel you'll never find one.
Old 11-13-2012, 01:52 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

What RPM do you get at the prop with your gas? What speed do you achieve?
Old 11-13-2012, 02:48 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?


ORIGINAL: advanced builder

You do have a exhaust header to add once you pull the exhaust throttle. YES Or how will you tie in your pipe? I feel you'll never find one. A lot of .67-90 engine are being dumped on Ebay ,Why the cost to run -em that's why we have Zenoha now days. Time to up grade. Sorry Going to gas is a no brainier. Glow plugs $8-10 apiece nitro fuel $40 a gal ,you'll get 4 runs on a gal on a 16 oz tank See were I'm going.
Hi Neil,

His boat is a 6.5cc or .40ci. It is not a .65.
Old 11-13-2012, 02:53 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

ORIGINAL: neverthought

What RPM do you get at the prop with your gas? What speed do you achieve?
Gas boats are BIG and SLOW.

Their RPM's are low, 15,000 at best. They can be fast with a mod motor, but you only save money with cheaper fuel. And your .40 is probably quite fuel efficient. Gas boats are not cheap to build. All the hardware is bigger so more expensive. Same with the hulls....

My gas mono with mod K30 is about the same speed as my .45 nitro mono. Around 50 - 55 mph.




Old 11-13-2012, 06:11 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

The 6.5 (and later 7.5cc) was / is also called SRII or SR2...an evolution of the (aircraft ) Formula 1 Pylon engines, in the mid 70's. The metric nomenclature was supposed to help from being confused with the "standard" K&B .40 model #8011 baffled piston engines, and their versions.

You have the early, disc rotary valve version...the opening in the backplate is .437" so you'll need a carb w/ that size neck. I used to have an airplane version that I converted from an F-1 pylon engine...I had a friend make a carb adapter from Aluminum to accept a Perry pump carb (.375" bore ) and used a Perry V-30 pump. I wouldn't expect too much in the idling dept. but I think you boat guys are kinda used to that? (Boat engines generally idle quite a bit higher than a typical airplane engine I'm guessing )Probably a lot better than an exh. throttle though? (I've never used one of those )
Old 11-13-2012, 06:20 PM
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Default RE: 6.5 K&B inboard nitro marine Carb retrofit?

The case is symetrical, so you can swap the front, crank housing for the backplate, to have your exhaust point whichever way you want.
Old 06-17-2022, 03:45 AM
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Bringing an old post back here. I have recently acquired a Dumas hydro with this engine. Anyone have baseline carb settings?
Old 06-17-2022, 06:25 AM
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A K&B 40(or 6.5cc) is made of "unobtainium" at this point. You might be better off to replace it with a new CMB .46(7.5cc) since parts for that K&B and people that know how to tune them are almost impossible to find
Old 06-21-2022, 07:56 PM
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If you have an engine that is in good mechanical condition and runs, why dump it for something else that would cost heaps more? We aren’t dealing with rocket science here. Heck, I have a FIFE K&B 3.5 with an exhaust throttle. I suppose I’d be better off replacing that too?

That doesn’t strike me as sound advice. Especially when the guy asked for basic carb settings.
Old 06-22-2022, 02:31 AM
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Originally Posted by 1QwkSport2.5r View Post
If you have an engine that is in good mechanical condition and runs, why dump it for something else that would cost heaps more? We arenít dealing with rocket science here. Heck, I have a FIFE K&B 3.5 with an exhaust throttle. I suppose Iíd be better off replacing that too?

That doesnít strike me as sound advice. Especially when the guy asked for basic carb settings.
you know anyone?
Old 06-22-2022, 05:33 AM
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Originally Posted by 1QwkSport2.5r View Post
If you have an engine that is in good mechanical condition and runs, why dump it for something else that would cost heaps more? We arenít dealing with rocket science here. Heck, I have a FIFE K&B 3.5 with an exhaust throttle. I suppose Iíd be better off replacing that too?

That doesnít strike me as sound advice. Especially when the guy asked for basic carb settings.
Do you know the basic carb settings for a K&B 40? The only person I knew that would have known passed on a few months ago. Add to that the fact that MECOA hasn't manufactured or sold one in years, it doesn't lend well to most knowing anything about it.

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