K&B 3.5 IB (#8912)

[JonWid]

I picked up a K&B 3.5 IB on ebay. I think it is #8912. It has never been run and is in very good shape. I reversed the crankcase configuration to put the muffler on the back side in order to allow the venturi to be rotated up instead of on its side. (See picture.) Will the engine run in this configuration? Is it possible to rotate the exhaust pipes?

Also, I have a question about the venturi needle. This is my first venturi/exhaust throttle motor. The needle doesn't seem to screw in very far on the post, maybe 1.5 turns. When it stops going in, the jet is not fully closed off. I noticed that the needle length extends out of the other side of the set screw by about an inch. Should the needle go in further and close off the jet completely? Is it possible to move the needle down the set screw in order to lengthen it? Any idea why the set screw would stop after 1.5 turns on the post? Is that normal operation?

Last question: Any suggestions on a beginner boat to put this in?

Thanks,

Jon

 

[dannyual767]

Sorry Jon, I don't have any info on your engine and I'm just in here hijacking with a couple of questions since I'm very interested in one of these K&B 3.5s as well h34r: . In fact, I think that I was watching that one on ebay.

1. Does anyone know the hp rating of this engine? Jon, did you get the instructions and if you did does it state the hp rating?

2. Would I be better off looking at the OS .21RG instead for just sporting around at a decent speed? I'm not looking at racing and just want a decently powered 3.5 that is reliable and not totally finicky!

Once again Jon, I apologize for jumping in here and if you want, I'll delete this post.

Danny

 

[Ray Sametz]

Jon, I think you have an airplane motor that someone put a fly wheel on, the wrong way too. Just a guess. All you K&b guru's help this newbee out. Ray

 

[PondSkimmer]

If my thinking is right No it will not run in that configuration you will need to change the crank. By rotating the venturi to the 12oclock position you also either increased or retarded (depending on what way you turned it from) the intake timing by 90*

 

[JonWid]

Danny, I didn't get the instructions and I didn't see the specs on K&B website. I don't think they are making this model anymore, looks like they will bring back the rear drum induction model. As for HP, you could probably assume it would be similar to the 3.5SS o/b because they have pretty much the same setup except for the exhaust throttle. Jon

If my thinking is right No it will not run in that configuration you will need to change the crank. By rotating the venturi to the 12oclock position you also either increased or retarded (depending on what way you turned it from) the intake timing by 90*

Point well taken about the timing change. I will return it to the original configuation.

Back to my question about the venturi needle--can anyone say whether the needle should be able to screw in further than 1.5 turns and be able to shut off the jet completely?

Also, still looking for any recommendations for a good basic beginner boat to put it in.

Jon

 

[piper_chuck]

I've got 4 similar engines at home, 2 aero and 2 outboards. One of the aeros came with a venturi. If nobody else posts, I'll try to remember to go out to the garage tonight and give it a good blow! Power should be in the 1HP range, that's about what the outboard with the similar powerhead produces. I may even have a K&B model sheet showing a pic of one of these. A good beginner boat would be a .20 size mono. You could go with one of the many fiberglass choices out there, or if you like to build, go to RCBM and order a set of plans for John Finch's Wild Thing. One other boat that could work ok is the Aeromarine Mean Machine Catamaran hull. You can find them at Fun R/C Boats http://www.funrcboats.com/ .

 

[Geraghty]

I picked up a K&B 3.5 IB on ebay. I think it is #8912. It has never been run and is in very good shape. I reversed the crankcase configuration to put the muffler on the back side in order to allow the venturi to be rotated up instead of on its side. (See picture.) Will the engine run in this configuration? Is it possible to rotate the exhaust pipes?

Also, I have a question about the venturi needle. This is my first venturi/exhaust throttle motor. The needle doesn't seem to screw in very far on the post, maybe 1.5 turns. When it stops going in, the jet is not fully closed off. I noticed that the needle length extends out of the other side of the set screw by about an inch. Should the needle go in further and close off the jet completely? Is it possible to move the needle down the set screw in order to lengthen it? Any idea why the set screw would stop after 1.5 turns on the post? Is that normal operation?

Last question: Any suggestions on a beginner boat to put this in?

Thanks,

JonView attachment 4803

1.No,the motor will not run with the front end rotated.The intake timing is now out of sequence.

You could put in a K&B 3.5 airplane or car crank and then the motor would run with the venturi pointing up.

[i probably have a crank here somewhere if you decide to do this.]

2.You can switch the exhaust end caps around any way you want them for exhaust outlet orientation.

3.Have you blown thru the needle valve to see if it is shutting off all the way??

If you take the needle valve out/spraybar assembly out of the front housing, remember the hole in the spraybar needs to be positioned correctly when you re-assemble the needle vale assembly in the front housing.If it isn't the motor will not draw fuel.

 

[JonWid]

I picked up a K&B 3.5 IB on ebay. I think it is #8912. It has never been run and is in very good shape. I reversed the crankcase configuration to put the muffler on the back side in order to allow the venturi to be rotated up instead of on its side. (See picture.) Will the engine run in this configuration? Is it possible to rotate the exhaust pipes?

Also, I have a question about the venturi needle. This is my first venturi/exhaust throttle motor. The needle doesn't seem to screw in very far on the post, maybe 1.5 turns. When it stops going in, the jet is not fully closed off. I noticed that the needle length extends out of the other side of the set screw by about an inch. Should the needle go in further and close off the jet completely? Is it possible to move the needle down the set screw in order to lengthen it? Any idea why the set screw would stop after 1.5 turns on the post? Is that normal operation?

Last question: Any suggestions on a beginner boat to put this in?

Thanks,

JonView attachment 4803

1.No,the motor will not run with the front end rotated.The intake timing is now out of sequence.

You could put in a K&B 3.5 airplane or car crank and then the motor would run with the venturi pointing up.

[i probably have a crank here somewhere if you decide to do this.]

2.You can switch the exhaust end caps around any way you want them for exhaust outlet orientation.

3.Have you blown thru the needle valve to see if it is shutting off all the way??

If you take the needle valve out/spraybar assembly out of the front housing, remember the hole in the spraybar needs to be positioned correctly when you re-assemble the needle vale assembly in the front housing.If it isn't the motor will not draw fuel.

I've looked and blown thru the venturi. Doesn't appear to be any obstructions in there. When I close the needle as far as it goes (1.5 turns) I can still blow into the jet fairly easy. I have taken it apart, the jet hole was pointing directly down the center of the venturi barrel, so I put it back that way.

Thanks for the boat suggestions, I'll check them out.

Jon

 

[SayMikey]

I picked up a K&B 3.5 IB on ebay. I think it is #8912. It has never been run and is in very good shape. I reversed the crankcase configuration to put the muffler on the back side in order to allow the venturi to be rotated up instead of on its side. (See picture.) Will the engine run in this configuration? Is it possible to rotate the exhaust pipes?

Also, I have a question about the venturi needle. This is my first venturi/exhaust throttle motor. The needle doesn't seem to screw in very far on the post, maybe 1.5 turns. When it stops going in, the jet is not fully closed off. I noticed that the needle length extends out of the other side of the set screw by about an inch. Should the needle go in further and close off the jet completely? Is it possible to move the needle down the set screw in order to lengthen it? Any idea why the set screw would stop after 1.5 turns on the post? Is that normal operation?

Last question: Any suggestions on a beginner boat to put this in?

Thanks,

JonView attachment 4803

1.No,the motor will not run with the front end rotated.The intake timing is now out of sequence.

You could put in a K&B 3.5 airplane or car crank and then the motor would run with the venturi pointing up.

[i probably have a crank here somewhere if you decide to do this.]

2.You can switch the exhaust end caps around any way you want them for exhaust outlet orientation.

3.Have you blown thru the needle valve to see if it is shutting off all the way??

If you take the needle valve out/spraybar assembly out of the front housing, remember the hole in the spraybar needs to be positioned correctly when you re-assemble the needle vale assembly in the front housing.If it isn't the motor will not draw fuel.

I've looked and blown thru the venturi. Doesn't appear to be any obstructions in there. When I close the needle as far as it goes (1.5 turns) I can still blow into the jet fairly easy. I have taken it apart, the jet hole was pointing directly down the center of the venturi barrel, so I put it back that way.

Thanks for the boat suggestions, I'll check them out.

Jon

I think the pin sticks out of the needle valve,if you tap on the center you can make the needle stick in farther. Your engine looks like the old ones we used to run. Broke cranks all the time. Maybe someone has a McCoy crank lurking around in there old stuff for you.....Mike

 

[Scott Schneider]

Damm !! not seen one of those for MANY years.

As stated ... HAS TOO be run with venturi on its left side (viewed from flywheel end) ... BUT WILL run with crankcase either way

Crank in those was a 12mm with a pressed in crank pin, short reach glow plug head as well.

The butterfly exhaust throttle set up is crap !!, find an old prather unit IMHO.

When I first got back into playing with boats in the mid 80's started out with the EXACT engine in a DUMAS little raskal .10 size rigger with widened sponsons. O' what fun that was !!

Others are right though ... a real crank breaker if run hard.

Unless you find some used parts ... a VERY obsolete K&B

Scott

 

[JonWid]

Damm !! not seen one of those for MANY years.

As stated ... HAS TOO be run with venturi on its left side (viewed from flywheel end) ... BUT WILL run with crankcase either way

Crank in those was a 12mm with a pressed in crank pin, short reach glow plug head as well.

The butterfly exhaust throttle set up is crap !!, find an old prather unit IMHO.

When I first got back into playing with boats in the mid 80's started out with the EXACT engine in a DUMAS little raskal .10 size rigger with widened sponsons. O' what fun that was !!

Others are right though ... a real crank breaker if run hard.

Unless you find some used parts ... a VERY obsolete K&B

Scott

Thanks. I returned the venturi to the left-hand side. Do you know if the venturi needle is supposed to shut all the way and turn more than 1.5 turns on the stem?

Jon

 

[dannyual767]

Jon, I think you have an airplane motor that someone put a fly wheel on, the wrong way too. Just a guess. All you K&b guru's help this newbee out. Ray

No, this is a marine engine and I believe the flywheel is on the correct way. I'm always looking at these engines on ebay. Jon has moved some things around but this is the K&B 3.5 inboard engine and not an airplane engine. Besides, you can see the watercooled head.

Power should be in the 1HP range, that's about what the outboard with the similar powerhead produces.

Doesn't really sound like anything to write home about. The OS .21 is rated at 1.7hp. This along with the crank durability issues is making me lean toward the OS.

posted by Scott,

When I first got back into playing with boats in the mid 80's started out with the EXACT engine in a DUMAS little raskal .10 size rigger with widened sponsons. O' what fun that was !!

I'm slooooooowly finishing up a Lil Rascal that I'm going to power with a piped Dynamite .15 engine. I hope it scoots pretty decent.

 

[Geraghty]

Jon, I think you have an airplane motor that someone put a fly wheel on, the wrong way too. Just a guess. All you K&b guru's help this newbee out. Ray

This is the marine flywheel and it is installed correctly.

The flywheel will only go on one way because of the collet on the crankshaft and the recess in the flywheel to accept the collet.

 

[Ray Sametz]

Rod, My mistake, but I think my K&B 21 had spanner wrench holes behind belt groove. Thats why I called for guru's to help. Ray