dogshome

I have a couple of the SC/ASP 180 four strokes. I'd really like to convert one of them to gas with spark ignition

Walbro carb with 11mm bore - check!
Adaptor plate to fit carb to head - no problemo, got some 8mm ally sheet waiting.

My first question is, where to connect the pulse line for the carb pump? The crankcase breather is normally connected to the inlet manifold via a short length of tube. I intend to keep this arrangement. So the pulse line could be connected to the crankcase (drill and tap another nipple) or to the inlet ahead of the carb.

Next question is oil content with the plain bearing rod. 20:1?

I read about gas/glow, but it's the very low idle of spark ignition that I'm after - not just the cleaner running [sm=cool.gif]

w8ye

My Feedback: (16)

20: 1 on the oil and use a mineral oil like shell outdoor air cooled two stroke or equivalent

Pulse line: Tee into the vent line and run externally to the pump on the carb

dogshome

OK, sounds good! I've put a nipple on the inlet and will fit one to the carb cover. Then I can tune the T piece to get the best pulsing [sm=thumbup.gif]

w8ye

My Feedback: (16)

I have a ASP 120 since 2002. After running it several times, I decided it was down in power compared with my other brand 120's.

I checked the cam timing and the dot was straight down at top dead center. The valve overlap period was complete before top dead center.

I moved the cam timing dot to be in line with the lifters. (1 tooth retarded from factory setting) It now has all the power anyone would have ever expected from a 120.

The timing position was moved to be like that on a OS 120. Now the valve overlap sequence is more or less centered about TDC

w8ye

My Feedback: (16)

It also might work better for your carb regulator atmospheric vent hole to be toward s the rear instead of towards the front. You should be able to unscrew and turn it around?

dogshome

Power has never been a problem with this engine. On an 18*8 Graupner it takes my 70" Yak vertical as much as you like, as fast as you like The other one in my 90 size Edge is waay tooo much It's got significantly more poke than the SPE 26 I have. It's been a while since I stripped either of them, but I suspect that the tiimg is as per your photo (from memory).

Fuel consumption is reasonable and oilymessiness is too.

But. I'd like a very slow idle and no messing with a glow plug or oiling to stop corrosion afterwards.



Got the pressure reference line sorted now thanks - soldered a tube to the hatch for a bit of silicon hose into the fuz [sm=thumbup.gif]


Waiting for a glow-sized spark plug to come.

I'll let you know how it runs!

w8ye

My Feedback: (16)

Be sure and give us a report on how this works out for you

It is looking like you are doing a sanitary job.

tkg

My Feedback: (1)

When pumping form the crankcase with a converted 4c sometimes there is a problem with oil in the pump line. One drop will stop the pump.
The WT 456 Walbro is designed to pump from the intake manifold pulse, you might try one if you have the oil in the pump line problem

dogshome

That's interesting. I have the option of drilling a second tapping on the carb pump cover. That way the flow can go through it on it's way to the manifold. I have it on a T branch which could conceivably block as you suggest. I might just tap it and plug it anyhow, then can swop around if there is a problem.

dogshome

[8D]

dogshome

Nearly ready.

dogshome

[youtube]http://www.youtube.com/watch?v=NnvX2p30HcQ[/youtube]

RichieN

My Feedback: (5)

Can you tell us what prop you are using and RPMs for this setup?

Thanks,

w8ye

My Feedback: (16)

Sounds like the rotors on a Huey Helicopter in the video. The engine sound is echoing in the garage. Does hit a good idle.

Get us a longer video outside?

dogshome

Will-do a better vid!

Same 18*8 Graupner as on glow, which may be a bit much for it. I'll have to borrow a tacho on Sunday.

Since fitted a velocity stack as a LOT of fuel was being sprayed out and blown away. Tweaked needles in accordingly

dogshome

6500~6800 on 18*8 Graupner Sonic. Did not go any faster on full throttle than half. So prop is too big! Subjectively it feels and sound like it did on glow. But.....
Cylinder never went above ~70C at most, but it is about 5C here now.

Will try a 16*8 Master tomorrow.

I need quite a rich idle to get a good pickup. The idle needle needs to be set quite a bit richer than the most efficient setting (fastest idle). This may all change with the prop tomorrow. A question for you though:- The original glow throttle is 10.4mm diameter, the Walbro is 11.1mm. I guess the overall area is about the same taking into account the spindle on the Walbro. I note that my SPE 26cc carb is quite a bit smaller.

How is the choke sized? 2 stroke, 4 stroke RPM, CC etc. Does anyone have a chart/estimator?

[youtube]http://www.youtube.com/watch?v=lJzKIN9vTSc&feature=channel[/youtube]

[youtube]http://www.youtube.com/watch?v=5Kd-U9yJk6I&feature=channel[/youtube]

av8tor1977

My Feedback: (6)

Theoretically at least, it should do fine on the 11.1 mm carb because that is a good size for this size engine, and also because it is pumped and doesn't rely just on vacuum drop (so to speak) for fuel draw.

I recently converted a Honda 31 four stroke gasoline engine for model use. I used a "run of the mill" WT series Walbro carb, and I ran the pump off of the intake pulse in the carb manifold. I did this because of problems reported with oil in the crankcase pulse lines causing problems in four strokes running a WT type carb, as stated above. I used a spring from a four stroke carb against the pump diaphram in the carb. I was worried that the intake pulse in the four stroke manifold would be too weak to operate the pump in the carb, but it works fine, even at full throttle. The Honda GX31 I did turns an APC 18 x 6 prop at about 7600 rpms with this setup, and the fuel flow is consistent.

AV8TOR

w8ye

My Feedback: (16)

Hope you get it balanced out soon

togatoga

My Feedback: (42)

I'd go 9mm for the carb for better transitions and less loading up on larger props.The RPMs would favour that size bore. I did a gas conversion for my asp180, using 16:1 mix and used the original carb as I did not have an adapter for a walbro.The carb was sensitive and the motor ran hot.In fact it quit because of overheating. I am wondering if you added any shims to lower the compression. I'd like to have another go at it with a walbro.Any chance you'd be able to show the adapter you've made for the walbro? it looks really well made.

foresterxt

My Feedback: (35)

Better yet, why don't you knock out a few of those carb adapters I'd be in for one!

dogshome

Thanks for the interest [sm=regular_smile.gif]

I have an SPE 26 which I could swap the carb with - that's 9.5mm. Maybe the 11mm one I have might pep up that low-powered engine []


The adaptor is cut with a drill, junior hacksaw and dremel from some ally and some PTFE sheet I have laying around. I'll get a pic when I change the carb. Took around an hour of steady cutting and filing and would be easy to copy

P.S. There is a queue for adaptors forming at my local club having run it at the field yesterday [sm=spinnyeyes.gif]

dogshome

7700 on 16*8 Master fully lean. Detuned to 7500 which it seems very happy on. I still need a very rich low end to get a reasonable transition though. I think the choke is too big or it needs the accelerator pumped version?

At full bore it is fine, tickover is like a clock even when rich. Just that big bit in the middle I'm not happy with!

dogshome

This is an adaptor I made to fit a Super Tigre exhaust to an ASP engine. Similar idea for the carb here.

dogshome

Well a 9.5mm with accelerator pump and check valve gives 'electric' style performance on a 16*8. Very good idle and transition. So will fit it to my 60 size Edge (that has this engines glow brother in it) and see what happens [&:]

w8ye

My Feedback: (16)

what is the model number of that Walbro?