4 HP Kohler exhaust pipe

[eibbed 63]

I've got a good starting, non smoking 4 HP Kohler that I want to put on my Suburban 400. It idles real nice, but when give it more gas, it immediately runs rough and doesn't smooth back out until it is back at idle. Any thoughts on how to get her running smooth at all speeds?

Also, is there a way to attach and run black pipe from the exhaust port opening and eliminate the oval can muffler? Here's what she looks like now.

Thanks,

Dave

[Coadster32 793]

You should be able to use a pipe tap on the exhaust port. Use grease on the tap to hang onto the chips. Also bring the piston to TDC and then blow out really good when done. As far as the engine, it could be a few things. If your carb is/was cleaned, and fuel supply isn't clogged, then I'd start by letting out the choke a bit, and see if it responds better. This should tell you if you're too rich or lean. Adjust accordingly. Good luck. :omg:

[wallfish 17,156]

I have 2 K91s that need to be tapped for threads. I was also thinking about using a 1/2

[rickv1957 72]

Appears to be running rich by photo looking at exhaust port,Rick

[854WH 0]

maybe it needs a muffler because there might be to much stuff goin out then coming in. try running it without the air cleaner to level out the intake and outgoing. see if thats the problem. :omg:

[VinsRJ 723]

I agree with Rick, looks to be running rich. Look to the carb, a good cleaning is a start.

As for the exhaust port you will need to sourse a 3/4" pipe tap. I personaly like to use ATF tranny fluid as cutting oil and chip collector.

[eibbed 63]

My next door neighbor gave me a 3/4" pipe tap to use, but it was too big to get it started in the port. The tapered end measured roughly 7/8" diameter. My exhaust port appears to be somewhat oval. The opening is roughly 3/4" tall and a little less than that in width. Looks like a plan B may be in order, but I'm not sure what that is.

If I go with the 1/2" floor flange will I be reducing the exhaust flow too much?

Thanks,

Dave

[DMK855 15]

Dave, the hole is not big enough for a 3/4" as you now know!! I personally think you would be fine to tap it with a 1/2" NPT tap and use 1/2" pipe!! That is what I plan on doing with mine. I know in the manual, the K91 uses 3/4" pipe and the Clinton uses 1/2" pipe! That being said, I think 1/2" would be ok!! :omg:

[wallfish 17,156]

The floor flange won't work either. I bought one today to check it out and discovered that there is a bevel in the hole on the flat side that makes it to big to get a seal. 1/2" NPT tap is the way to go I guess. My Clintons and K90 use 1/2" pipe. I also have a K91 that has a cast iron exhaust manifold on it and that is the size of 1/2" NPT pipe also. Another option would be to make a flange out of 1/4" steel and weld a nipple to that. I too noticed that the ports are egg shaped and should probably be drilled first.

[algrc120man 0]

wallfish is on the right track with the exhaust this is the way used to make my pipe flanges on my 5 hp briggs go cart engines if tou cant find a good gasket the orange high temp silicone will take the heat this is what i use when people bring me a vehicle with cheap headers on it. as far as the running rough problem i would check the points and point gap to make sure they have not slipped i have had this happen a few times and the engine would run good at an idle but not on high side :omg:

[eibbed 63]

Hey guys,

I finally got back around to working on the exhaust port again. I drilled out the hole to 3/4" to make it round, then tapped it with my new 1/2" pipe tap. Actually I did this on two of my 4 HP Kohler engines.

The 1/2" black pipe is hard to get started and with ample coaxing will screw only one complete turn into the exhaust port. It's the same on both motors. When I back it out, the threads look like they have been rounded off a little. I was hoping to get more turns, but for now I guess I should be satisfied with one, if it will do the job. Maybe there is some type of sealer I can apply when I screw the pipe in. Once again, any suggestions or comments will be greatly appreciated.

Thanks,

Dave

[rickv1957 72]

Dave,you should be able to screw tap in deeper to increase thead diameter a bit as tap is tapered,Rick

[buckrancher 2,694]

I opened the hole size up and tapped with a 3/4 npt on the k91

I'm rebuilding not sure if I remenber the drill size 59/64 I think

I pluged the two 1/4-20 holes and had to shift off center but it fit

problem is you can't do it by hand you need a bridgeport mill to

change the hole center line and clean the dia. up with a endmill

before you can drill it up to size and tap

[jimbotelho 1]

did you run the tap all the way in until it bottomed out?? thats the only way that you will get the taper enough to get a few turns :omg:

[eibbed 63]

Rick I ran the tap in a little more as you suggested and Jim yes I think it did bottom out. I can now screw the pipe in on both engines approximately 2 1/2 complete turns which is about four threads.

Buckrancher thanks for the advice, but my intentions are to come out of the exhaust with a 1/2" nipple and screw on a 1/2" to 3/4" 90 and continue on with 3/4" black pipe to accomodate the heat shield clamps and muffler.

I'm going to clean the carb and check the points in the next couple of days.

Thanks again to all of you who responded to my post.

Dave :D