Little update, I changed over to a throttle body and engine is good. Doesn't struggle anymore when you shake the plane at taxi speed. 80mm is too big for N/A and P-port, I would go smaller next time. My idle RPM/MAP isn't as good as the slide throttle though, because now you have to take care of all the leaks in the fiberglass airbox to metal intake runners. Some ultra black helped.

On 2019-05-16 8:05:31 AM, William Jepson wrjjrs@gmail.com <flyrotary@lancaironline.net> wrote:

Lynn, 

I've used smooth bore carburetors, and factory slide throttles. I've never seen one without bearings, or a inlet ramp for small throttle openings. Paul did one that relies on a Teflon ® slide. Everyone forgets how much pressure is on that plate of plastic. 

Bill Jepson

 

On Thu, May 16, 2019, 10:39 AM lehanover lehanover@aol.com <flyrotary@lancaironline.net> wrote:

The slide throttle is used where the rules allow for only a small intake runner. No choke area is used so it only works with fuel injection. Also there is no loss of diameter caused by a throttle shaft.  So, the allowed runner diameter can be used all through the runner.

 

Lucas slide valves are expensive but work perfectly.  Throttle bodies are cheap and work well. If you get to maximum RPM before you have full throttle, after playing with timing and FA ratio then your Throttle body may be too large.  A home made slide throttle is just added complexity nobody needs, In my opinion.

 

Lynn E. Hanover

 

In a message dated 5/15/2019 7:25:39 PM Eastern Standard Time, flyrotary@lancaironline.net writes:

 

Matt,

                  Oh dear, you also have a slide throttle???  I also put one on the first attempt linked to a vernier throttle cable.  It worked well if you were content to "wind" the throttle open and shut with the vernier.  However on my teat flight my pilot went to push the throttle open and he nearly ended up in the back seat pushing and could not get the throttle to budge.  Sadly he failed my aircraft, with good cause for the "what if" was the need for an immediate Go around. just would not be very instant!!.  IN a temper I had to totally redo my throttle assembly.  I ended sending the assembly back to Paul and asked what was wrong that it refused to "slide":  I am still awaiting a reply on the topic.   I ended replacing it with a dual throttle body that sadly did jnot match the holes exactly, so much work went into adapting.  It ended up being brilliant -- will attach a photo if I can find one--- but as always very expensive.  Had the injectors and all self contained.

ON another engine I put a large throttle body which was too big for I got to full noise at 80% opening.  The ideal size for a dingle throttle body seems to be 70 to 75mm dia.  I suggest others chime in here as I am going from memory which with me is a bad move!!!

Matt, as sad as it is I really suggest you replace the slide throttle as a proper slide throttle as lots of seals and bearings to take the suction, which again makes them very dear.  

 Another option which may not suit is to put dual Rotek  carbies on.  They are OZ and cost approx $500 USD each  --- again my memory!!  I am told they are great value, but you will have to alter fuel pressure to start with  9% psi).

Neil.

On 5/14/2019 3:27 PM, Matt Boiteau mattboiteau@gmail.com wrote:

I have a good one for you guys. I've been trying to get a slide throttle to work. Lots of fixing to make it usable, mainly at lower RPM when the suction is at it's highest. Lapped the outer plates flat, machined down the thickness of the inside slide, doubled up all the bolts to seal fuel from leaking, and stiffened up the throttle cable every few inches. BUT now that I am taxing around, this issue is coming up and I think it has to do with having the injectors before the slide throttle. I think...

 

When I taxi (under 1100rpm prop) and start to step on the brakes, the engine drops a few hundred RPM and struggles. If I pull power to idle to slow down before tuning (600rpm prop), the engine will die. Unless I catch it in time, and stab the throttle. The right brake is more pronounced then the left. Even though the wideband is showing a quick lean condition, I've tried riching up / leaning out the mixture at those lower rpm's to no results. Once I get past 1200rpm prop and the engine is starting to breath, no issues at higher powers.

So we tried an experiment while idling and shook the plane left/right, it reproduces the engine dieing. I did see a quick puff of black out the tailpipe. That make me think at low idle, with the slide opening moves right to left, the fuel is pooling at the bottom of the opening. The shaking is causing raw fuel to make it's way in pass the opening. Drilled a few small holes at the bottom of the slide to hopefully suck in any raw fuel that tries to pool. It's helped a tiny bit, but if I shake the intake, the engine still isn't happy at idle.

I don't have a video of the engine running (will get it tomorrow), but here's a video of the intake setup.

https://youtu.be/tuwBkDuKh9Q

I'm tempted to remove the slide throttle and put in a standard 3" throttle body on my intake box (ie, before injectors). Just want to get your guy's thoughts if I'm on the right track. And if anybody is running a slide throttle.?

 

- Matt Boiteau

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