hi there everyone. i am in the process of building an rc air boat and i am using a ryobi 31cc. i bought the prop hub and welded my own engine stand. i just bought a wt-324 thinking it would bolt right up... well no. the throtle goes the wrong way and the screw is in the way of my mount. BUT... if i can get a carb spacer it would fit. is there anything wrong with a spacer? please help me here. i only need about half an inch to make it work. i just want to know if the space will hurt the performance of the carb/timing of fuel into the engine. thakns, Bruce

It might even help.

If possible make the holes for the Car. and maniflod match.

Either by tapering the manifold or by making the the manifold the same size all the way through
using the smallest hole as the common size.
You can make the Carb. end just large enough for the Carb. to fully open and be okay if the engine side is smaller than the butterfly in the Carb.

thanks ralph. i know someone who might be able to machine one for me. the carb is the same size as the manifold which is an 11.11mm opening. should i juct make it long enough for me to clear the items that are in the way or is there at too long manifold?

Yes and if you need to rotate the Carb. now would be a good time.

If the manifold doesn't flow smooth it causes turbalance and pooling of fuel.

You should be good to go.

You may concider an external pulse for the fuel pump in the Carb.

I second that. The hole for the pulse is very close to the edge of the adapter (manifold) opening on the Ryobis, and if your adapter isn't perfectly made and lined up you could end up with a leak. Better and easier to just add external pulse.

AV8TOR

if i was to add an evternal pressuer line where would it go? is there a link on here that would show me?

One goes on top of the Carb. and the other can go to the manifold or crankcase.

On top of the Carb. is a raised round spot with a dimple in it. Drill and tap there.
I use the large Super Tigre pressure taps for the exhaust.
They sell them with a drill and tap in a set.

In the picture the fat yellow line is the gas line.
The smaller line is the pulse line and the blue line goes from the other diaphram into the Fuse. for better regulation of the fuel.

Sometimes when the Carb. is in direct wind the way it regulates the fuel changes. The blue line takes care of that.

Here's another pic. This one is of a Homelite with an added external pulse line. I did an external pulse line on a Ryobi the other day, but I don't have a pic of it and the airplane isn't here.

If you add an external pulse line, plug the original pulse hole in the carb with some JB Weld or drill and tap it for a tiny set screw to close it off.

AV8TOR

that small blue line, does that get tapped into the small hole on the diaphramm cover? the raised circle one?

No the small yellow line goes there.
The other end is going to the manifold, or it could go to the crankcase.

The blue line goes to the other diaphram on the oppisite side of the Carb.

Ralph, Can you tell me who you bought the Super Tiger taps from please? I need to do an external pulse on my 40cc, B&S, 4-stroke. If you have any other words of wisdom they will be appreciated. Thanks.

what is the size of the tap cause i have a set and a couple fittings off some old glow carbs. if they are a standard tap i wont need to buy the set.

They are the Du-bro cat number 539, and are 8-32.

The drill looks to be a 1/8, but I can hardly see it
Even using a magnifying glass.

JohnF: I've been working on a Honda GX 31 lately, and several guys said they had problems running a pulse line because it would eventually get oil in it and cause problems. What I did was tap into the intake manifold adapter itself. Of course this will only give a negative pulse instead of an alternating pulse like the crankcase, so you have to put a small spring in the fuel pump of the carb. Be sure that you put the spring on the right side of the fuel pump diaphragm. The "pulse" will suck on the diaphragm, and you want the spring to push it back, ready for the next suction pulse. It works fine this way on my Honda four stroke.

AV8TOR

thats good thinking. what size spring? but if you just take that hose off every couple hours and clean it with something you should be fine.

so i found a peice of aluminum stock about half inch thick and drilled out the 11.11mm bore and the 2 screw holes. i also dared to drill the little hole for the pulse. i can always block that latter if it does not work for me. but its nice to know that i can get around that if need be. so all i have to do tomorrow is loat a truck load of wood from near work to the girlfriends house for the fire pit tomorrow and than get a chance to play with it. ill let you know and maybe if you want to see picts i can post some.

ok well the results are in... and the carb spacer works!!! the small pulse hole lined up and the throtle lever cleared the plate. i ran it today after i installed it and wow what a difference. a stock engine with an 11.11 carb. that was the key. great transition and idled ok. i just have to tune it down some i think. but thanks for the ideas everyone.

AV8TOR, What Walbro carb are you using on your Honda 4-stroke? I would like to use a WT instead of the WYJ on my B&S, 40cc, 4-stroke. The intake hole is oval on the engine. Would it hurt anything if I made it round to match the carb? My thinking is it should be better to match the hole in the carb to the intake hole in the head but I am wondering why they used a oval hole in the first place? I will use a stock Zenoah G-38 spacer which bolts right up and make an external pulse line as you have described. Not sure if I'm going to convert this to glow yet but I am leaning that way. I would really like to be able to start this engine by flipping the prop. Thanks for your help.

It is actually a Zama that is on it at the moment, but I am probably going to put a Walbro of around 9 or 10mm venturi on it, as I want to try the engine on Gas/Glow fuel, and I have had problems with Zama carbs in that application.

I would say make the adapter manifold match the carb and the engine. Blend it all so there are no steps to interrupt flow.

I used the spring out of the original rotary carb in my fuel pump. It is a bit stronger than one would think is necessary, but it works. Be sure to put it on the correct side of the diaphragm. It needs to be on the same side as the vacuum pulse, so that after the vacuum pulse pulls the diaphragm down, the spring flexes it back up.

AV8TOR

BTW, I don't know about the Briggs, but my Honda won't even think about hand starting, even though it is setup with electronic ignition. The compression ratio is so low, it is almost hard to determine which is the compression stroke. I've tried to hand start it but no go... But the very second you touch an electric starter to it, it is running. It starts so quickly that it is running almost before you can pull the starter away. I'm going to look in at the cam assembly sometime soon to see if there is some kind of a compression release. It is suspicious to me that it seems to have much more compression when turned over in reverse than in the normal running direction. That's why I think maybe there is a compression release designed to allow easy rope pull starting.

The engine runs well, turning an 18 x 8 prop at just shy of 7000. It will be interesting to see if it gains much on Gas/Glow fuel when I get around to trying that.

Good luck,
AV8TOR

Thanks AV8TOR, I have a WT498A from Stihl. It only has a H/L needle. Are you familiar with this carb and if so do you see any problem with using it? It has a 34 stamped inside the choke and 127 stamped under WT498A. It is a pretty big bore I think.

That's a 13.5mm venturi. You can try it, but I feel it might be too big for a 40cc four stroke.

AV8TOR

Thanks AV8TOR, I have a Poulan 40cc, 2stroke, chainsaw I am going to pull the engine out of. Have any idea what carb is on it? It's brand new in the box. If it's a smaller carb. I'll just swap them. I'll figure this out yet!

I think some of the Poulans in that size range came with 11mm carbs, and some with larger. You'll have to check. That number cast into the carb throat is the venturi size in 64's of an inch. 34 = 34/64"

Good luck,
AV8TOR

Okay, thanks for sharing your considerable knowledge. I have done a 31cc Ryobi 2-stroke so I should be able to handle this. I'll let you know.