I am having some trouble with my k&b 3.5 inboard. It has great compression and the bearings are good, but it doesnt seem to be able to get any fuel! The carb is set fine as far as the needle valve goes but no fuel is getting into the compression cylinder. When I hold my finger over the carb opening fuel gets in and it runs like a champ for about 5-10 seconds then burns that fuel out and quits. my pressure fitting seems to be ok and all the lines are hooked up well. It acutally lets fuel out the front of the carb instead of taking it into the engine. I have tried two different style carbs on this engine and both had the same result. The first in the front of the engine on the side of the crank, for the second one I changed the front piece of the engine to a solid peice off another k&b 3.5 (same motor type) and used a K&B rear rotor carb of the same diameter with a remote needle valve. This one works a little better but still poors out some fuel.

Anyone have ANY ideas for me?? I am stumped! I can take pics or vids if that will help anyone! (engine is being belt started btw and the glow plug is good)

is it a rear intake engine!? if not if its a frount intake engine the carb needs to be to the right side if your looking at it fron the frount

is it a disk rotor motor? if so, is it 180º out maybe?

originally it was a front intake engine with the carb just as you described. That didnt fit very well in my boat, and I had another K&B 3.5 with the exact same crank case but with a rear rotor carb. Well I took the front assembly off the front carb engine and switched it with the rear carb engine's front assembly. I then took out the front carb engines back plate and replaced that with the rear rotor carb. I can tell the carb is spinning and it is sucking in air when it is turned over. Like I was saying, when I cover the carb it sucks in fuel and runs until that fuel is used up. It just doesn't seem to be able to pull in the fuel by itself. I had this problem with the front carb and now the rear carb too. The rear carb seems a bit better but still no go! All the fuel line is new, just for an FYI

It touches the end of the crank so that it can spin... is this what you are talking about? I made sure to put it in just like the other one was, and I saw that it was spinning freely. you think it is spinning opposite of the intake stroke is that what you mean? I am still learning on this stuff so bare with me!

It could be a fuel pressure problem, a blocked pressure fitting or something. Try pulling off the pressure line from the tank and see if you can blow through it to see if it's clogged at the pipe. If that isn't it, pull off the fuel line and blow through the pressure line to see if it's pushing fuel to the carb.
If the boat has sat for a while, things can get clogged up with varnish.

The crank case is a little different between the crank induction (early) inboard, and the later drum rotor inboard... For the drum rotor, the case is cut away in the area of the rotor, allowing flow up to the boost ports. While it probably wouldn't perform as it should with the early case not being machined for the drum rotor, it should still run... I also suspect that you may have something plugged up at the needle or tank pickup, or maybe your pressure fitting in the pipe could be plugged...(?) I'd also check to see that you don't have any pressure/vacuum leaks around the carb or case gaskets...

My fuel lines are all working correctly, I took the pressure line off the exhaust and blew into it and it blew freely and pushed fuel through the fuel line up to the carb. Is there something I could use to clean the needle up? I am going to try my Mac pipe on it to see if it is the pipe that is the problem. It is a wierd prather silenced pipe and I drilled out the "predrilled" hole to fit a tad bit larger pressure fitting. I will give a pipe switch a try tomarrow and see if that helps.

I never had good luck with the Gold carb. It just doesnt have vacuum it seems. I had to raise my fuel tank real high even with pressure from the exhaust. I think they just pull too much air from around its assembly.

My guess is you have the rotor timing 180 degrees out of phase. The port in the rotor should be starting to open as the piston goes up towards the compression stroke. That results in a low pressure in the crankcase causing the air fuel charge to rush into the crankcase through the carb. If it's 180 out, the rotor port will close as the piston goes up and opens when the piston comes down. As the piston comes down it pressurizes the crankcase and blows the fuel charge out of the carb.

indeed...thats why i asked if he had a disk rotor motor. I know i put my backplate on with the disk 180º out and it would start, but only run for a few seconds, and very poorly at that.

So when should it be fully open? Top dead center?

Most should be open at BDC. I've learned to hate rear intake engines as they can be difficult to get everything lined up correctly.

Yeah I am getting there

should be fully open a little before the piston reaches TDC. With the piston at TDC its about 1/2 closed (on my motor at least).

Alright, I will have to give that a try before I give up!

You won't need to check that the rotor is 180º out on the K&B 3.5; the drum rotor has only one notch for the crank pin to drive it. You can't put it in the wrong spot! The disc rotor K&Bs are another story.

There is no notch, it just presses against the crank, so it must be a disc rotor

There has to be a slot or a hole in the perimeter of the disc or drum. Otherwise the pin on the crankshaft doesn't have anyplace to engage so it can turn the rotor. Oldlug is correct, at least my 3.5 has a drum rotor with a single slot in the perimeter. The crankshaft pin engages that slot and turns the drum rotor.

Your comments about changing carbs is confusing. Typically the front intake port should be above the crankshaft, not on the side. That will definately mess up the front rotor timing. My 3.5 is a rear rotor so I'm not that familiar with the front rotor engine. I don't recall ever seeing the carb on the side. If you simply put a rear rotor front case on the engine and didn't change the crankshaft then you have no drive pin to drive the rear drum valve. Pictures would be nice. It is not a carburetor problem. Some how you have screwed up the intake timing with your mixing of incompatible parts.

K&B has/had a front intake engine where the venturi was laid down on the side but it was an exhaust throttle engine. The flywheel looked odd on it as it looked like it was on backwards to clear the venturi. I still see them on eBay once in a while.

I've got a bunch of each style K&B 3.5 inboard, as well as a bit of aftermarket parts for the early ones. If you put in the wrong crank, or install the bearing housing in the wrong spot, the timing will be way off on the early crank induction engine. On the later drum rotor engine, as long as the drum housing is installed with the intake facing up towards the piston (inside of case), then you can't miss on the timing.

Since Drmeff is saying that there's no notch, and the crank just presses against the rotor, I think that's where the problem is!
While it's possible that K&B has made a disc rotor version of the 3.5, I've never heard of one... Still with any intake rotor style, it must somehow be indexed to the crank!!

hmmm, well when I get a bit more ambition I will take it back apart and take some pics for ya

yeah ok, I am an idiot, there is most certainly a place for the pin to connect to

I still haven't tried running it, i will try tomarrow sometime. While looking at these two K&B 3.5's side by side and my empty tc31 hull I had me a cool little idea

Would it, or would it not be totally sweet to put these two engines (If I can get them running!) side by side in the tc31 with two props etc They fit in there so nice! That would be just awesome looking! I have no idea if that would be impossible to do or not, I would obviously need another set of running gear, and remove the stock one, fill the hole and make a dual setup. For twin engines, do you have to have counter rotating props, or can they both just run clockwise? But a dual fuel tank, dual .21 powered tc31 would be sick if it can be done. I have the whole snowy crappy wisconsin winter to do it, so do you guys think it would be possible???