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Pipe for K&B .84 marine engine

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Pipe for K&B .84 marine engine

Old 06-17-2010, 03:26 PM
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pakeppler
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Default Pipe for K&B .84 marine engine

Hi, I recently purchased a .84 (13cc) K&B engine (7/8” OD pipe outlet) for a 42” shovel-nose step-hull hydo that I am building and I’m looking for exhaust pipe recommendations.
I have had complaints about noise in the past with my deep V boat powered with a 23cc gas engine with a pipe, so I would like something that is as quiet as possible. I will not be racing this boat, this is for recreational use only, so highest performance is not an issue.
K&B recommends either the Prather rmodel 9040 for 11-15cc engines or a MACS 1290, I can’t find a 1290 but I did find a MACS model 1389 (21&rdquo “muffled pipe” and a model 1382 (20.75&rdquo “super-quite pipe” for 13cc engines. However, the 1382is expensive at $193.
Prather also has a tuned pipe muffler for 11-15cc engines model 9065 that I would need to use with their standard pipe. I could not find data (length or pipe width for the Prather pipe).
Also, I’ve only run gas engines with water-cooled pipes. Are there any heat issues that occur when using a dry pipe in an mostly enclosed cowl? I have not found any wet pipes for this engine.

Also, I will need to add a pressure fitting to runa line to the fuel tank. Where on the pipe should this be mounted?
Thanks for any advice you can give me!Pete
Old 06-17-2010, 09:43 PM
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Default RE: Pipe for K&B .84 marine engine

I can't say on the pipe, but that engine may be too much for the hull. A 42" round nose is more suited for a 67 than a 84
Old 07-20-2020, 04:58 PM
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I have a new in pack Prather 9040 for sale if interested,
Old 07-20-2020, 05:24 PM
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Something I missed in your initial post was the question about a pressure fitting. A pressure fitting needs to go at the widest point on the pipe. In the case of the 9040, it's where the two cones are welded together. One thing to be aware of is that the pipe is very thin, meaning you may only have two or three threads to screw your fitting in to. Another option would be to get a flanged fitting with threads on the outside that uses a nut to secure the fitting. This will require a hole large enough to get the threads through but that's not an issue. What is an issue is getting the fitting through the hole. Most use a stiff, bendable wire stuffed through the hole and out the wide end of the pipe. That said, you use the wire to pull the fitting through the pipe and into the hole, feed the nut over the wire and tighten. Make sure you use a good threadlocker or you will have the nut back off while running
Old 07-24-2020, 11:38 AM
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Another quick way of mounting the pressure fitting is to TIG weld a small blob on the pipe where the fitting goes and drill it there. The extra thickness gives you a solid mount.

Scott
Old 07-24-2020, 05:19 PM
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Originally Posted by Pylonracr View Post
Another quick way of mounting the pressure fitting is to TIG weld a small blob on the pipe where the fitting goes and drill it there. The extra thickness gives you a solid mount.

Scott
Your "blob" still needs to be at the widest part of the pipe. If it's not, the pressure through the fitting will be uneven and the needle will never be correct, a primary reason for an improperly running engine.
Old 07-25-2020, 03:15 PM
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Originally Posted by Hydro Junkie View Post
Your "blob" still needs to be at the widest part of the pipe. If it's not, the pressure through the fitting will be uneven and the needle will never be correct, a primary reason for an improperly running engine.

Correct. I kind of thought that would be fairly self explanatory since I said that you weld a small blob where the fitting goes. Apparently I was not concise enough??

You weld a small blob where the fitting goes, file the top of it flat, drill and tap it. A drop of red loctite keeps the fitting from coming out.

Scott
Old 07-25-2020, 04:23 PM
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Originally Posted by Pylonracr View Post
Correct. I kind of thought that would be fairly self explanatory since I said that you weld a small blob where the fitting goes. Apparently I was not concise enough??

You weld a small blob where the fitting goes, file the top of it flat, drill and tap it. A drop of red loctite keeps the fitting from coming out.

Scott
Scott, if it was just me you were communicating with, your post would have been fine. The issue is when people that have never worked on our "toys" are involved. My post was mostly for them so, if it elicited confusion, you have my apologies.

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