I haven't been following this closely, but a comment anyway. On some chain saws I have had apart that don't have a large phenolic carb insulating spacer, they have a small spacer such as you are using. But, this is important, they have insulating sleeves ON THE BOLTS that mount the carb, and fiber washers under the nuts that hold the carb on. This prevents the heat from transferring through the bolts into the carb...

AV8TOR

This ones starts and runs well until it gets hot. The other engine runs very well with the same arrangement and the carb is cold to the touch after running. This carb is also cold to the touch after running, so I don't think it's a heat-in-the-carb problem.

The spring has made zero difference (makes sense since the other engine has no spring and that runs fine). But it's stopping in for now.


I do have a different pickup arrangement on this one and I just noticed it was just on the cusp of being too far away from the magnet. I've altered it - but it's too late to try again tonight.

The plug also has black oily gunk in it - which is hard to clean in such a small item. It's only had 10 mins running, but this engine is brand new. The first one was fully run-in. Plug is next suspect though. Don't have a spare yet.


More tomorrow!

Good luck trouble-shooting. This is an 11mm carb, right? I wonder if that's a tad big for a 30cc. ESPECIALLY given you have a REALLY short air path because the carb is mounted directly to the head intake. Usually there's a pipe going down to the carb, adding some head pressure. These are just some things to think about. I used a 6.5mm carb on a Saito 1.5 and it worked nicely.

I like the idea of the insulating washer under the head of the screw, because in that case there is metal-to-metal contact. A great heat conductor. But for the screws, I still maintain just air is a better insulator than any sleeve put in there. My guess is the sleeve is for centering, not insulation.

Well, the thing is how does one know whether the carb mounting bolts are touching the carb body somewhere or not? With the sleeve on the bolt, you know it can't touch metal to metal. Anyway, that's how it was done on at least one saw I had apart one time. I think it was an older McCulloch saw.

Shrink tubing would probably make a good bolt insulator/sleeve....

I think unless it is really a very hot installation, the only problem encountered with a non insulated carb setup would be vapor lock after having been run. Without cool fuel running through the carb, and cooling air, the fuel boils in the carb and can make hot restarts tough.

AV8TOR

Solved.

It was the ignition pickup being slightly too far away.

Spring in carb definitely not required with pipes from the crankcase breather via carb to manifold as shown


20/64ths without accelerator pump idles very well, but has to be set too rich for a good transition. The other engine WITH accelerator pump (and larger bore) does not suffer this problem.

I'll try a smaller carb, but I am sure it will restrict revs. I have a tacho these days!

WT-38 is the way to go with 180 Four Stroke.

* Accelerator pump.
* 24/64 venturi (9.53mm).
* No governor.


WT-37 is the next size down but does have the governor (may or may not be a problem).

Take it out and plug the hole, make like a small gasket and put it at the end of the hole and screw the govern back in.
That is what I did, If not...it will cut off at WOT.

Adrian

A couple comments: First, the governor is a great thing to do. I'm guessing a lot of readers would appreciate some closeup photos where this is, and how to disable it. Also, (not sure) but I think your pulse tubing routing is a little unique in that it sounds like there are TWO sources, and the exact routing and theory behind it might have been bypassed. I didn't read all 4 pages of this forum, so I could be mistaken. If not, how about a pneumatic chart of this, and the theory behind it, as opposed to simply intake. Thanks!
Rick

Hi Rick,

Here are some close up pictures of WT-37-1 that I think is absolete and hard to come by.
The governor is good but not for us we want to go hi RPM's not to throttle back.
The stuff I made is real hard to see in one of the pictures ...is on my tumb were the governor can be seen.
You screw it out, make a small round piece or you can solder shut the hole the is on the side of the governer
in the grove . But then will be hard to revert back later.

As far as intake...I do not know if you refere to mine or not but mine is simple. Instead of going outside and have a tube and more work....
I just went inside.


And here is a list... PDF of all carbs that MYWIFE !!! Camelia put together for me. All barrel carbs and butterfly WYK and WT from the smallest to 12.2mm venturi.
Where you see no price...is no longer available. On WT series all carbs that have ACC Pump if say no does not have it but my worth to try. On WYK series are all carbs that have both needle LO/HI. So she did this in 2 days. over 1000 carbs that she went trough.

Thank You
Adrian

Thanks for the piccys. I wondered what the governor looked like [8D]

And thank your wife for the carb list!

Adrian,

Thanks for posting the governor pics. Helpful to newbies.

For the pulse tube routing, I was addressing that to Dogshome. Still curious. Probably will have some followup questions once it's posted. :P

Hat tip to Camelia for that carb listAdrian, I think you did much better this time around.

For the intake carb helper spring, such as on the WT456, one wonders, if that spring seems to not be needed, if Walbro actually did any testing before they put it into the design.

Addressing a comment on page one (yes, ancient history) "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.", it may be because a throttle throat for a glow/alcohol based setup won't need quite as large a diameter compared with gasoline. Why? Because methanol has more innate oxygen content than gas. Hence, the term "oxygenated" fuel. In effect, methanol can have a smaller venturi because it carries more of its own oxidizer in the fuel itself. Seems like a glo carb used with gas gets very sensitive because when adjusting with glo fuel, you're only affecting a fraction of the overall oxygen going in. Switch to gas, and any adjustment is affecting a lot more of the air going in.

Here's a teaser. Anyone ever seen a giant "walbro-like" carb such as that shown in this picture, next to the mystery engine, which is my current conversion project.

Hi Guys, here is something out of the topic....but funny in a way of speek.
Look what a mini v12 can do.


[youtube]http://www.youtube.com/watch?v=TKIMH3nBPYs&feature=youtu.be[/youtube]


Rick, I never seen a ...Monster like that...how old that is?

Adrian.

You spotted this sketch?

Tillotson on my Dolmar 62cc chainsaw engine looked a bit like that. Walbro do more than the small WT you know (I know you know!)

Nice detective work. It is a Tillotson HS-179B. I don't have any specs on the carb, but I do have a rebuild kit for it. Tillotson was a Borg Warner company back then. The engine is a Homelite 54.2cc, quit a monster. The book says it also was fitted with an "equivalent" Walbro SDC62. That has a WHOPPING 14.25mm venturi.

I actually stumbled on the fact the Homelite XL12 chainsaw has both a loyal vintage following, and it also has a cult following. The XL12 stands for a 12lb head, the lightest available in 1964 when it came out. People are inheriting these things for two generations straight with incredible loyalty. They were the first truly lightweight magnesium alloy chainsaw in the world. I know, when doing this conversion I started a small bright fire at the base of my belt sander when a spark lit the debris pile. OK, that's the loyalty part; here's the cult part.

The Homelite XL12 was prominently featured in the movie poster for the Texas Chainsaw Massacre. Here's a copy of it, where it even SAYS XL12!

Dogshome, I now recognize your pneumatic diagram from my long thread "Saito glo to gas conversion". I think your setup works because the intake part of it only happens every other revolution, but you're getting a +/- pair of pulses every revolution on the crankcase part of it. Now, the question is how much pulse pressure is robbed by the intake part when the intake valve is closed, and how much robbed when it's open too? Remember, that line is open all the way from the pump diaphragm cavity all the way out to ambient thru the carb venturi. Yes, it's a long path usually, except on that ASP where the carb is direct-mounted to the head. A precise low pressure gauge would be interesting to use here, as a test. My guess is most of the pulse is from crankcase, with some parasitic happening from the intake part of it. But latency from the small diameter tubing is allowing it all to work. In other words, the dominant pulse comes from the crankcase, and the diaphragm reacts before the pulse can "escape" out the intake. And it's enough to scavenge the oil coming from the crankcase.

Impressive engine! Couple things; why only a 24 inch propeller for a 300 cm³ engine? Also when the engine quit did you notice how quickly the propeller stopped? Could there have been that much internal friction? Regardless very nice work!

IS 200cc and the engine is NEW not broken in .
Camelia is pleased witth your ....comment...This time around...LOL

Adrian<br type="_moz" />

I am glad Cemelia found my comments entertaining.
! 200 or 300 cm³, whatever! I am running a 24 inch propeller on a Zenoah G 62, less than half the size of that the V 12. So I'm still wondering about that. By the way, if this message seems punctuated strangely, it is because I am dictating it to my iPhone's Siri while driving!

I just did something that has been on my list for a long time! I have these Black and Decker electric screwdrivers with nickel metal hydride batteries that are always dead when I go to use the screwdriver. I replaced all the battery packs with home made low self discharge batteries from the hardware store. You can tell because usually the label says precharged. I only mention this because I suspect I am not the only one who is annoyed by these older electric screwdrivers. Yes you can buy new lithium-ion screwdrivers, but why spend the extra money when it's not necessary.

Off topic but in response.... I have a really nice set of battery powered tools in a kit. There's a neat hand held sander, a jig saw, a flashlight, and a good drill in the kit, and the kit came with two batteries. It isn't that old, (3 years or so I think), but both batteries are junk. I priced the batteries to buy new Nimh cells to rebuild these battery packs, and it would cost more than the whole kit cost me from Harbor Freight! Bummer!!

AV8TOR

I know what you mean, Aviator. With tools that contain a lot of batteries, sometimes the cost doesn't "pencil out". These old electric screwdrivers have only either 2, ro 3 pak cells. At $1.50 each for AA size, the 3 cell cost is $4.50 which is quite tolerable. Another point, the LSD (low self discharge) can't deliver quite the current that Nicd, standard NmH, or Lipos can. I did this same LSD replacement with an old Craftsman cordless drill and though it works ok, the rpm is noticeably lower than it used to be. Cost, as Aviator said, was high, about $22. Cheap compared with Lipo, but rpm suffers. BUT, when I use it after storage, IT WORKS!

http://www.menards.com/main/electric...354-c-6309.htm

A little storybefore I did the replacement, I bought a little Lithium Ion screwdriver for $19 thinking I'd get around the NmH self discharging THAT way. But that screwdriver was geared way too high, the RPM was too high to really work well. It was WASTED money!

Now, BACK TO RC! These LSD batteries make GREAT flight and ignition packs! Charge, go to the field and fly, pack it up, and fly the following week WITHOUT TOPPING OFF the batteries!

That's what I reckon Definitely the spring on the pumping diaphragm makes no difference in this configuration. It 'works' either way. So much that just flipping the prop draws from 8" head, a 1/8" per flip unchoked.

In the interests of science I now have a WT37 and a WT38. If the 37 proves too small (I think it will by tacho readings) then I have other plans for it...

As much as I like engines, and engine rebuilding, I've been spending the last six weeks cutting and repairing wood. With a bit of crash investigating mixed in. See this link: http://www.rcuniverse.com/forum/m_10832283/tm.htm

My Rx and Yak54 of 5 years decided to go South a few weeks ago. Glitch, oops!, Big glitch OOOOPS!, Not listening, bang! 20MPH straight down at about 1/3 throttle. 26cc Petrol engine destroyed and wiring looms snapped as the various bits of plane disengaged from their partners. Pretty comprehensive considering it was a soft ploughed field.

I have 1 good servo and a Lipo though!


Wood burner job that one

7600RPM on 16*8 JXF (20:1 synthetic oil)
2300RPM idle.

WT38.