Yesterdays tinkering

John Goddard Thu Jan 26, 2012 9:33 am

Quite day at work yesterday and I wasn't feeling the full shilling so I went home.
After 3 gallons of tea and moaping about the house I thought about the serious business
of running some cox engines and fiddling with some bits Ha.
Most of the afternoon was spent with my Golden Bee and a Cox silencer.
This was my easiest starting engine (some of you are probably way ahead of me here) which
revs nicely and peaks at about 1+2/3's out needle wise. However, stick a silencer on and
it becomes Texaco II, I still haven't got Batts for the tach but it was running MUCH slower
that my Texaco in fact adjusting the needle didn't have much effect other than richening
stopped it and it wouldn't quicken to anything like it's normal 13k.
I realise this must be the spi choaking the engine so I decided to slow it down.
After putting 2 gaskets in and closing the needle to (I kid you not) 1/2 turn it just sat
chugging away, after 15 mins I got bored and I stopped it with half tank of fuel still in it.
Anyway it got me thinking (dangerous I know) the Tarno carb instructions specifically advises the
use of the cox silencer when using their product on a Tee Dee. How can this be? or is this perhaps why
one member on here last week said his was much harder to set up than Bernies and it
didn't have as wide a rev range? Am I right that conventional wisdom is that SPI and silencers
don't work?
J

**RknRusty** Thu Jan 26, 2012 9:49 am

John Goddard wrote:... Am I right that conventional wisdom is that SPI and silencers
don't work?
J

That's what I've always heard, though I have never had a muffler to prove it with. With a muffler, SPI sucks in exhaust gasses instead of fresh air so it's not burning the proper mix it was designed for. That's why some engines like the QZ don't have SPI while their louder counterparts do.

fit90 Thu Jan 26, 2012 9:57 am

There are some engines that have SPI and a muffler and do well. I have a medallion with an exhaust restricting throttle linked to the spray bar and it runs well and it has SPI. I think that as a general rule SPI engines do not care for mufflers but there are some exceptions. What creates these exceptions is way beyond my level of understanding, but I would guess it has a little to do with the timing, glow plug heat range and the amount of SPI. Just a guess though.

Has anyone else had an engine that had SPI, a muffler and ran well? Don't limit it to just Coxes. I have heard that the early VA's had SPI, a Muffler and not only ran well but also throttled well. This is just something I have read.

Bob

John Goddard Thu Jan 26, 2012 9:59 am

The difference is marked to say the least Rusty.
My fastest 049 that I've tacho'ed is a 190/4 Acrocub product engine
(spi) which is a screamer but the muffler killed it dead as well.
Sataurday maybe non spi muffler test day.
J
Wink

John Goddard Thu Jan 26, 2012 10:08 am

fit90 wrote:There are some engines that have SPI and a muffler and do well. I have a medallion with an exhaust restricting throttle linked to the spray bar and it runs well and it has SPI. I think that as a general rule SPI engines do not care for mufflers but there are some exceptions. What creates these exceptions is way beyond my level of understanding, but I would guess it has a little to do with the timing, glow plug heat range and the amount of SPI. Just a guess though.

Has anyone else had an engine that had SPI, a muffler and ran well? Don't limit it to just Coxes. I have heard that the early VA's had SPI, a Muffler and not only ran well but also throttled well. This is just something I have read.

Bob

I guess engine age/use plays a part as well Bob. I've noticed that some engines seem to have more under piston gap and for longer than others but whether that is by design or perhaps worn crank pins/bigends and pistons that need the reset tool who knows?
Huh...

John Goddard Fri Jan 27, 2012 8:49 am

Have just noticed that both Bernie and Matt sell venturi spacers to lift the Carb on a teedee to allow the fitment
of a silencer.
What's is all about Alfie?
Very Happy

**Cribbs74** Fri Jan 27, 2012 9:40 am

John Goddard wrote:Have just noticed that both Bernie and Matt sell venturi spacers to lift the Carb on a teedee to allow the fitment
of a silencer.
What's is all about Alfie?

My .049 tee dee came with that spacer from the get go. If you run the stock cannister muffler you have to flip the NVA for clearance. I tried to run a muffler and it killed my tee dee. I have a throttlw sleeve on it now and it runs well.

fit90 Fri Jan 27, 2012 11:38 am

I have also found that with the starting springs the venturi assembly and spring interfere with eachother if the needle is on the engine's left side. The venturi spacer take care of that.

Bob

Surfer_kris Fri Jan 27, 2012 5:03 pm

fit90 wrote:
Has anyone else had an engine that had SPI, a muffler and ran well? Don't limit it to just Coxes. I have heard that the early VA's had SPI, a Muffler and not only ran well but also throttled well. This is just something I have read.

Bob

There are the Norvel .049, .061 and .074 for instance, all screamers and good throttling with SPI and mufflers too...

John Goddard Fri Jan 27, 2012 5:25 pm

I think the Norvel is a different kettle of beans Kris.
It has Schneurle Porting like most 2 stroke bikes had which I think was completely absent from
our Favs.
Very Happy

Jaspur_x Fri Jan 27, 2012 9:05 pm

The G-mark engines (both the 03r/c and 061r/c) have both spi and mufflers,and do throttle quite nicely.

It is not normally a good thing to have both spi and a muffler,it cuts back on power scavenging etc. but it does seem to not be a huge concern to most engine manufacturers over the years.

I often considered tinkering with removing the spi from my G-mark 03r/c just to see if it incerased performance at all,but removing the spi requires a compromise of the original design so I have not.

microflitedude Fri Jan 27, 2012 9:58 pm

Jaspur, how would one go about "removing" SPI?

**Cribbs74** Fri Jan 27, 2012 10:15 pm

microflitedude wrote:Jaspur, how would one go about "removing" SPI?

Good question, I suppose you could shim the cylinder, assuming G-marks are fundamentally the same as cox engines. Unless the g-marks have a cutout in the skirt.

Jaspur_x Fri Jan 27, 2012 10:40 pm

Yes, the G-mark cylinders are internally basically the same as a COX, 2 bypass ports,no boost ports.

1 way to eliminate spi is to shim up the cylinder,I dislike this because it obviously lowers compression via increased cylinder (squish)volume as well as effects port timing etc.

Other ways are a bit more work,a longer piston skirt,raising the low edge of the exhaust port,a shorter con rod, all have their own challenges too.

I havn`t done any efforts to eliminate spi with any of my engines yet, but a cox 049 would be the simplest as you can simply buy a p/c set that has no spi.
All the ways you can eliminate spi are too much tinkering around for me at this point lol!

**Cribbs74** Sat Jan 28, 2012 6:51 am

John Goddard wrote:Have just noticed that both Bernie and Matt sell venturi spacers to lift the Carb on a teedee to allow the fitment
of a silencer.
What's is all about Alfie?

John,

Now that I think about it, that spacer may or may not have come on my TD. I remember buying that exhaust cannister so I wonder if I bought that spacer too. That purchase was over 20 yrs ago so I may be mistaken. My New .051 does not have a spacer and from what I can tell neither do the .051's that we are dealing with.

I see TD's with the clamp style exhaust and the trombone style throttle a lot, I wonder if that is a better setup? Cox must have intended for people to use mufflers if they sold a spacer to clear them.

I guess the simple answer is to run 'em loud and wide open! If folks can't appreciate a TD on full song then forget them!!! lol!

nitroairplane Sat Jan 28, 2012 7:26 am

cribbs74 wrote:
John Goddard wrote:Have just noticed that both Bernie and Matt sell venturi spacers to lift the Carb on a teedee to allow the fitment
of a silencer.
What's is all about Alfie?

John,

Now that I think about it, that spacer may or may not have come on my TD. I remember buying that exhaust cannister so I wonder if I bought that spacer too. That purchase was over 20 yrs ago so I may be mistaken. My New .051 does not have a spacer and from what I can tell neither do the .051's that we are dealing with.

I see TD's with the clamp style exhaust and the trombone style throttle a lot, I wonder if that is a better setup? Cox must have intended for people to use mufflers if they sold a spacer to clear them.

I guess the simple answer is to run 'em loud and wide open! If folks can't appreciate a TD on full song then forget them!!!

Easier said than done.
Unfortunately not all 10 million people hear like the sound of a tee dee.

**Cribbs74** Sat Jan 28, 2012 8:26 am

Yeah, I know. Wishful thinking. You should see the look on my wife's face when I fire one off! Kids run for cover and the neighbors dog starts howling.

John Goddard Sat Jan 28, 2012 10:28 am

Once I get me sticky Mitts on it all Ron
I think I'll go stay at Juniors for a weekend.
He's out in the sticks so I can conduct some
Hexperimentation in a completely non scientific
Way. Not too worried about the neighbours but
The curly person has said that Furryface (her
Little girl) don't like 'that racket'.
lol!

PV Pilot Sat Jan 28, 2012 10:45 am

cribbs74 wrote: Kids run for cover and the neighbors dog starts howling.

Amazing how universal that is,,. The neighbor has 6 Redbone Bloodhounds. They hate me.
https://www.youtube.com/watch?NR=1&feature=fvwp&v=DgfMMFmLaTE

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