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K&B 3.5 ???

Old 08-20-2007, 09:13 AM
  #1  
jdoug
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Default K&B 3.5 ???

I just got this engine for trade on some work for a buddy. I don't know how old it is or what model it is. I took it completely apart and checked everything out. Everything is in working order now. I need to know what glow plug to get for it. I also did some reading on the KB 3.5 and appears that there are 3 carbs for it, the gold being the best. Should I go with the gold carb? I will be putting it on a TS2.

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Old 08-20-2007, 09:58 AM
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topfuel4430
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Default RE: K&B 3.5 ???

It, from the outside, appears to be a 8906 model engine. Does the prop shaft screw into the lower unit, or does it clamp in with the two lower unit halves? I would guess it screws in since it has the longer skeg.

It has the thin flywheel, thin single bubble head button, case without the brace web on the mounting lug, and the black carb of course. I could, again, guess and say its an older 12mm crank, but that could have been changed for the newer 13mm font housing and crank, while still using the other older parts. The only way to know exactly what you have it to tear it apart. If it is a 8906, 12mm crank, and that is the original long skeg with the threaded prop shaft, I would say its from the 80's to early 90's. The black carb that is on it will work ok, but a gold will be better. We do a modification to the stock black carbs that will work better than the stock black and gold carbs, but if you are just looking to play the black will do just fine. The gold would be an easy bolt on upgrade.

It depends on how much nitro you intend to run in the motor. An MC-9 or equivilent will work ok for higher nitro (35% and up) or the K&B 1L or MC59 will work better for lower nitro (35% or lower). There are many plug options available, and most of them have appropriate heat ranges to work with most anything you will run. Its hard to say what you should go with, without know your fel intentions.

Hope this helps.~
James
Old 08-20-2007, 11:03 AM
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jdoug
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Default RE: K&B 3.5 ???

topfuel - Thanks for the info. Yes, it has the thread-in prop shaft. Not sure on the crankshaft size. I will be running ODonnel's 30%, so with that said, I think I'll go with the MC59.

What is the mod you do on the black carb? Also, where is a good place to start on the needle? It looks like it only has one needle for tuning and an idle screw.
Old 08-20-2007, 12:02 PM
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Dan S
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Default RE: K&B 3.5 ???

post a pic for the other side of engine, just to get the other view of the carb.

Dan.
Old 08-20-2007, 12:03 PM
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jdoug
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Default RE: K&B 3.5 ???

other side of carb...

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Old 08-20-2007, 12:14 PM
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topfuel4430
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Default RE: K&B 3.5 ???

Jdoug, you will have to set the needle as needed. They say 4.5 turns from the factory, but that is typically too rich. It can be anywhere between 2 - 5 turns out, depending on fresh the motor is. Its just something you will have to play with. Basically, set the needle so that it takes about 2-3 seconds to "clear out" on the bench when throttling the motor up. It will sound rich on the bench, but this should be in the ball park.

The black carb only has the one needle as you stated. No need for a low speed needle. Boats are not generally intended for low speed running, so there is not much need for one. The engine will/should however run fairly slowly if you choose to do so. as for the modification, you will have to check out my site, as I dont think I am allowed to talk about my products or services on here.

Also, if you are just running for sport, you may consider running the MC-9, it is a much tougher plug than the 59. It will last much longer as long as you dont go to lean. The 59 is better suited for the nitro content, but that plug is pretty fragile.

~James
Old 08-20-2007, 12:24 PM
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Default RE: K&B 3.5 ???

This is an early model black carb, the needle on the left side is your HSN (High Speed Needle) adjustment varies from 2 to 4 turns out approx.

there is no LSN screw (Low Speed Needle) it uses a small hole on top of the carb for air to keep the engine idling, not the best but it works.

if you can put your hands on a more recent Black, Red or Gold carb with the newer style HSN and either an LSN with a screw or disc for adjustment.

the throat size are:

Black= .265"
Gold= .312" and
Red= .345

Dan.
Old 08-20-2007, 01:38 PM
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jdoug
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Default RE: K&B 3.5 ???

Thanks all, for all the info.
Old 08-20-2007, 02:54 PM
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topfuel4430
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Default RE: K&B 3.5 ???

The 3.5 size carbs, Silver, Black, Gold, Purple and Red do not have a low speed needle, regardless of age. The older 7.5 carbs had a low speed needle, and the newer 7.5 carbs have discs for low speed, but never have had that option on the 3.5cc. Its just not needed. As Dan said, the hole located in the bottom of the newer carbs is for idle, also on the older carb the barrel opening had an indentation cut into the ID of the barrel, that alowed a small amount of air to come through, even when the "barrel" was closed. They later switched to the hole in the bottom of the body of the carb.

I thnk the K&B's came with a Perry carb at some point over the years, and they MAY have had a low speed adjustment, but I am not sure.

The purple carbs are very rare, and are slightly smaller than the Red carb ID. The silver carbs are very old, pre black carb days.

Probably more informaion than you wanted to know....but??

~James
Old 08-20-2007, 09:34 PM
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Dan S
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Default RE: K&B 3.5 ???

James is correct on the old, new and newer carb. K&B have made so many changes that they tend to be hard to follow at times.

I did however asked their technical support a few questions.

They said that the purple and red carb have the same bore, the purple carb were the first one to come out but they had a problem with the dye and the rest came out red, so they stayed with red.

The Purple carb (K&B) are very rare.
Old 08-21-2007, 08:18 AM
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jdoug
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Default RE: K&B 3.5 ???

What prop should I start with this 3.5 pushing a TopSpeed2? Is the prop shaft 3/16? It looks like it is but I haven't officially checked it yet. I do have a Grim 40/52 3 blader that is a 3/16 bore but the drive dog on the engine looks too small, like there will be a lot of slop between the prop and drive dog. Is this normal?
Old 08-21-2007, 09:40 AM
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Default RE: K&B 3.5 ???

Prather 215
Octura 440/2
440/3
Old 08-27-2007, 03:46 PM
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jdoug
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Default RE: K&B 3.5 ???

I rechecked some things over the weekend. My engine does have the 12mm crankshaft. It has the "L" stamped on it, but I also measured it to be certain. It also has the 0.765 OD sleeve which is good and it has pretty compression. I'm going to replace all the bearings and go from a 12mm crank to a 13mm. Doing this requires a few extra parts but not much.

Question for the guys who know this engine. There are 2 different piston/sleeve combos available for this engine. They both cost the same. One is standard timing and the other is piped timing. To start, I'm going to run it stock. I may mod the lower to accept a pipe down the road. How will the pipe timed engine run with the stock exhaust setup?
Old 08-28-2007, 02:36 AM
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topfuel4430
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Default RE: K&B 3.5 ???

Get the piped timing sleeve. ~James
Old 09-07-2007, 05:45 PM
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Default RE: K&B 3.5 ???

ORIGINAL: topfuel4430

The 3.5 size carbs, Silver, Black, Gold, Purple and Red do not have a low speed needle, regardless of age. The older 7.5 carbs had a low speed needle, and the newer 7.5 carbs have discs for low speed, but never have had that option on the 3.5cc. Its just not needed. As Dan said, the hole located in the bottom of the newer carbs is for idle, also on the older carb the barrel opening had an indentation cut into the ID of the barrel, that alowed a small amount of air to come through, even when the "barrel" was closed. They later switched to the hole in the bottom of the body of the carb.

I thnk the K&B's came with a Perry carb at some point over the years, and they MAY have had a low speed adjustment, but I am not sure.

The purple carbs are very rare, and are slightly smaller than the Red carb ID. The silver carbs are very old, pre black carb days.

Probably more informaion than you wanted to know....but??

~James
yes, james the perry carbs did come on 12 mm k&b's (between ex. throttle and black k&b carb), & do have a low speed adjustment. it's the brass disc around the needle. i've ended up with 2 of the TINY little things. great carb, just too small.
Old 01-01-2008, 01:03 PM
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Default RE: K&B 3.5 ???

The red carb worked out really good for me. Exaust throttle was even better. Alot more fun...and had to replace parts alot more!
Old 01-01-2008, 02:07 PM
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Default RE: K&B 3.5 ???

I got a Gold carb if ya ever would consider trading for your black carb. Please PM me if you are intrested.


Paul
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Old 01-04-2008, 05:17 PM
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Default RE: K&B 3.5 ???

By the way...that outboard with the 12mm crank will need a SHORT K&B plug, if you are using K&B plugs. I believe that you can also use a LONG plug if you double up on the glow plug washers. I have both 12mm and 13mm crank motors. I kind of like my old 12mm one and would not change it to a 13. Just my opinion though.


-Don't tase me bro'!)

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