Honda gxh50 / under-mount fuel tank?

[GreenMantis]

OK, you are starting with something that had a real Walbro carb, I was starting with the ever cheap, Chinese engine called a 44-5, and it's clone of the Walbro carb. Here are some pix of what I was working with, the manifold in this case is unaltered. The side with the wide port goes towards the engine, the round port matches up to the carb. This won't go on straight, as the holes on the manifold are at the corners, so you end up with the rectangular hole on the manifold trying to match up to the square shaped port on the head, and it looks wierd, and at one point on either side, it barely overlapped enough to make a seal, but it did it ok, and worked. There is a "pulse" port on the manifold, which is supposed to pump the internal fuel pump in the carb, but it is not needed, and doesnt have to be connected or anything. All I did is widen those holes, the ones you can see through, to the edge of the thick plastic they are through. in fact, you can reuse the gasket from the original carb on the 4 stroke engine, and that will work, too.

These Chinese Walbro clones are under $20, and the plastic manifods can be had for about $10, but I did what you are doing: I used what I had available at the time.

 

[GreenMantis]

I would also like to pat myself on the back, when I did this the first couple of times (it took me a little while to figure out that it was starvng for fuel because it needed the needle valve adjusted a bit), I used 12 pack boxes to make my gaskets up.

 

[GreenMantis]

So just starting out down this trail & I'm curious if there is an EXTREME MAKEOVER needed to Under-mount a Fuel Tank if I use this gravity fuel delivery engine?... I've at least seen this application used on a Site where they sell Motorized Bikes but when I called my local Honda Small Engine Expert he said that it may be more trouble then it's worth??? adding that a Fuel Pump is needed which is no BIG thing but then you would need to tap into the Crank with a PULSE LINE...:-/

This is where he lost me... Can anyone expound with your vast wisdom & experience?

And just in case I didn't imply it strongly enough, your Honda small engine "expert" doesn't know anything about Honda small engines. They come with the tap in the case on all of these engines, even the clones have it, and they have fuel pumps ready made to run on that pulse, "more trouble than it's worth" is just a matter of buying the $20 fuel pump Honda makes and sells for these engines as an option for mounting the tank elsewhere. That doesn't sond like any trouble at all, and would be more than worth it, if we didn't already have everything we need to convert it over to a diaphram carb sitting in front of us.

 

[GreenMantis]

That metal manifold you have there looks like it should work exactly the same as my plastic one did. In fact, it looks like it will seal better.
Here is some benefiet from my experience: the engine should not run, in fact, it should not even so much as sputter, while the choke is on. Turning the choke on while the engine is running should kill the engine in very short order. When mine is running perfectly, it will never start on the first pull. The first pull is done with the choke on, and should not so much as sputter. The second pull is done with the choke off, and it starts every time. If you don't pull it once with the choke on, however, it wont start no matter how many times you try. If the engine so much as sputters while that choke is on, you have an air leak, you have to take the manifold back off, and seal the gasket better.

 

[breaksalltherules]

I guess I needed to learn how to adjust the needle valve anyway.

Mine might be a little too long, I checked a month or so ago but I'm going to start back up on this and pull my other carb back off.

I might track down a 3d printer that I could send the thatsdax adapter with the 12mm bore to so they can fabricate the same thing but with a 15mm bore.

Thanks for the info

 

[GreenMantis]

I know that the bolt spacing on the 12mm and 15mm carbs is the same, you could just drill out the 12mm adapter.
Or like I said, you can keep your original carb, Honda makes a fuel pump and the pcv vent hose provides the "pulse" to drive it. Whoever told you that it was too much trouble had their head stuck someplace stinky, it's a $20 part, and 10 minutes worth of installation time. If you don't have everything you need to make the diaphram conversion possible right there in front of you, like I did, it is probably better to go with the Honda fuel pump, instead. I converted mine because I was done in an hour, I didn't have to buy anything to do it.

Adjusting the metering valve was just a matter of bending the lever on the needle valve that contacts with the diaphram. The setting was just fine when that carb was on the 2 stroke motor, but that motor provided a pulse for the internal fuel pump in the diaphram carb. This engine just needs a different setting that allows as much fuel to flow as possible to run right.

 

[GreenMantis]

According to AGK, the stock carb bore on these is .425". Their overbored carb is bored out to .478". Now according to my math, 12mm - .472", and 15mm = .59". This is probably why Dax doesn't bother with 15mm conversion kits, it's kinda overkill. It works great for me, though.

 

[breaksalltherules]

I'm actually running the Walbro fuel pump right now. It's really strong but I want my Walbro carb because it's fully adjustable high and low speed and my Super Titan carb only has a single adjustment screw for the fuel (not the idle adjustment connected to the swing arm)

I was going to get a 3d printer to fab one of the adapters with a 15mm bore instead of 12mm so I could keep the 12mm in case I wanted to go back but if the 15mm carb is working fine for you, I will just drill it out myself and not go through the hassle.

Do you think the the oversize carb negatively impacts fuel efficiency? If there is an increase power trade off, I'd be fine with that.

 

[GreenMantis]

I can't really say about the fuel economy, I had to convert mine to ride it, I had no place else to put the fuel tank, so I can't compare it to before. But it gets great economy, I can't complain, and it runs great. I did have to tweak the metering lever just a bit, but that was all it wanted. My Walbro clone only has one screw to adjust, but it will do the range from too rich to too lean, and it's very happy in the middle of the two. I routed the hose from the crankcase back to the airbox, I just drilled a hole and put a fitting on it.

 

[breaksalltherules]

Right on, thanks for the knowledge.

How did you impregnate your gaskets with silicone? Did you use something like this gasket silicone?

http://i.walmartimages.com/i/p/00/68/62/26/75/0068622675180_500X500.jpg

I bored out the adapter, no problemeo. Going to roughen the intake manifold for better fuel atomization while I have the carb off as well. Eventually I'll end up with a Tourquer v stack with a high flow filter and a rain cover but I'm going to stick with the stock box for right now.