Reed valve with extended intake

[Fabian]

Does the Walbro not come with the hollow M4 stud?

The Walbro style diaphragm carburettor does "not" come with a hollow M4 stud, but if you want to be sneaky and are not worried about having a lip on the M4 screw for the hose to bite into (which was never a problem on the screw without a lip) then you can use a hollow M4 adjuster screw from a rear derailleur.
My preference was to have a 0.3mm lip as extra insurance, hence the reason why i used an M4 button head capscrew with the lip ground down on a disk sander.

Is the fuel overheating problem a rare problem?

Without a thermal isolation spacer the fuel overheating problem becomes a large problem; it simply won't allow the carburettor to operate properly once the cylinder head temperature gets past 160 degrees Celsius and excessive thermal transfer being passed into the carburettor will boil the fuel completely once the cylinder head temperature gets past 180 degrees Celsius, thereby stopping the engine from operating.

For this reason the thermal isolation spacer is a "critical" component in the carburettor assembly stack. It is also the reason why every chainsaw or small engine using a Walbro style diaphragm carburettor is fitted with a thermal isolation spacer.

What are the inner diameters of the Walbro carbs (without detracting for the space the butterfly valve occupies?

The non venturi bore diameter is either 14 or 15mm from memory.
With a standard exhaust that's been slightly modified, the Walbro carburettor makes "no" extra power over a correctly jetted NT carburettor (which uses a 14mm non venturi bore diameter.
Rock Solid Engines does sell a larger diameter diaphragm carburettor, but the limitation in the system is the 14mm intake tube diameter.

As i have mentioned before, the big advantage of the diaphragm carburettor is stable carburation, as well as being virtually leak proof, as well as having external high and low jetting adjustment; giving you the ability to quickly adjust air/fuel requirements as atmospheric conditions change.

 

[seb1008]

Fabian thank you for explaining the need for the thermal spacer, I was not clear on the exact reason for it's use.
Could you tell me what brand of silicon hose would be the best for use on the exhaust? I see you use some on your exhaust.
I think you wrote that you use a 2mm drill to drill the 4 mm button head screw, is this correct?
The 3mm drill is the correct size to drill into the cylinder before I tap it for the 4mm screw right?

 

[Fabian]

I think you wrote that you use a 2mm drill to drill the 4 mm button head screw, is this correct?

I drilled a 2.5mm hole through the 4mm button head capscrew with a full cobalt 2.5mm drill bit. You can drill the hole in one go using a 2.5mm drill bit but i found it to be more precise using a 2mm drill bit, then enlarging the hole with a 2.5mm drill bit.

It must be said that you will need a good drill press with minimal slop in the chuck and spindle bearings, otherwise the drill bit will not run perfectly straight down the centre line of the button head capscrew.
If you've never done any precision drilling work before, there is a good chance you will f*&k it up the first time, and maybe even the second time. For that reason, it's a good idea to purchase three or four 20mm button head capscrew bolts.

The 3mm drill is the correct size to drill into the cylinder before I tap it for the 4mm screw right?

Yes, that is correct

Could you tell me what brand of silicon hose would be the best for use on the exhaust? I see you use some on your exhaust.

The silicone hose is only attached to the exhaust as a method of noise suppression; being surprisingly effective.
I can't tell you what brand of silicone hose to purchase, because i walked into my local hose and tubing specialist and asked for silicone hose that would be suitable for my application. I purchased 2.5 feet of 13mm internal diameter, high temperature, chemical resistant silicone hose, rated to 260 degrees Celsius.
So far that hose has been on my bike for a year and although it has discoloured from "clear" to light brown, it is still soft and supple, and continues to do the job at suppressing noise.

The length of 2.5 feet works out perfectly; any less than that and the bends becoming too tight; with the hose trying to collapse in on itself.

In this case, both performance improvement and noise suppression go hand in hand, because you will have to cut off the internal baffle pipe attached to the inside of the muffler cap.
Cut the pipe off; approximately 2 inches from the inside base of the muffler cap, so as the pipe is just long enough to slide into the last baffle at the end of the muffler.
Now take the pipe you've cut from the muffler cap and cut it up into two identical lengths. These two pieces of metal pipe will slide inside the silicone tubing so as to allow you to fasten zip ties around the bike frame and silicone tubing; without crushing the tubing when zip ties are securely fixed in place.

If looking at the photo of my bike with the silicone tubing, you can just see the metal pipe inside the silicone tube where the zip ties fasten it to the bike frame.
The best way of inserting the pieces of pipe are to lubricate the inside of the tubing with 2-stroke oil, then to carefully grind away any sharp edges so the metal pipe can slide inside the silicone tubing without cutting up the internal diameter.
I found that the easiest method of forcing the metal pipe inside of the silicone tubing was to use a large flat blade screwdriver, to push it back and forth, so as to line up with the part of the bicycle frame where it will be attached to with zip ties.

 

[seb1008]

Will a 4mm x 20 mm socket head screw work instead of the button head screw. OK if it is stainless? And I see adds for screws 4mm x .7 x 20mm. It seems like the .7 is the pitch. Should I wait till my tap and die set arrives and see what the threading is like on it before I order the screw.
I bought extra drill bits so hopefully it will work ok.
The new walbro carb, jaguars cdi, pull start, centrifugal clutch arrived today. Still waiting on the thermal spacer from Australia, and drill bits and tap and die to arrive.

 

[FurryOnTheInside]

Will a 4mm x 20 mm socket head screw work instead of the button head screw. OK if it is stainless? And I see adds for screws 4mm x .7 x 20mm. It seems like the .7 is the pitch. Should I wait till my tap and die set arrives and see what the threading is like on it before I order the screw.
I bought extra drill bits so hopefully it will work ok.
The new walbro carb, jaguars cdi, pull start, centrifugal clutch arrived today. Still waiting on the thermal spacer from Australia, and drill bits and tap and die to arrive.

What's wrong with a threaded hose connector like this? You're basically making the same thing from bolt, only difference I can see is these are brass rather than stainless steel; but is there anything wrong with brass?
http://www.ebay.co.uk/itm/Barbed-Th...1-0-Barbed-Hose-Connector-Brass-/231062347508

 

[Fabian]

What's wrong with a threaded hose connector like this?

http://www.ebay.co.uk/itm/Barbed-Th...1-0-Barbed-Hose-Connector-Brass-/231062347508

There is nothing wrong with using that option. The only real difference is that you are drilling and tapping a 6mm hole in the transfer tunnel instead of a 4mm hole.

 

[Fabian]

OK if it is stainless?

From what i understand, you can't use stainless steel in aluminium because it creates a galvanic reaction; corroding away aluminium.

Should I wait till my tap and die set arrives and see what the threading is like on it before I order the screw.

That would be the sensible option.

I bought extra drill bits so hopefully it will work ok.

If you are careful and don't rush the process, you will have total success.

The new walbro carb, jaguars cdi, pull start, centrifugal clutch arrived today. Still waiting on the thermal spacer from Australia, and drill bits and tap and die to arrive.

I feel massively envious.
I remember when that kind of stuff arrived on my doorstep. My girlfriend at the time was relegated to being a casual novelty that only served a purpose to decorate the house, even when she took her clothes off to try and compete with all the new and shiny motorized bicycle products. Much to her frustration she couldn't out-compete all of the accessory items that captured my attention.
It was most annoying to have a naked woman deliberately walking in front of you whilst you were studiously trying to read installation instructions.

 

[FurryOnTheInside]

From what i understand, you can't use stainless steel in aluminium because it creates a galvanic reaction; corroding away aluminium...

That's interesting, I hadn't heard of this before. This link provides a little more detail:
http://www.bssa.org.uk/topics.php?article=89

 

[seb1008]

Furry on the inside, thanks for the idea about the brass fittings.
I found this on eBay " 4M thread to 4mm ID hose fitting brass. The only trouble it is $20.00 for 5.
I will probably use the button head screw
Thanks for the tip on stainless and aluminum.
I do not have to worry about girlfriends. I enjoy being single and going where I want, when I want.

 

[Fabian]

I do not have to worry about girlfriends. I enjoy being single and going where I want, when I want.

I agree.

Women are truly delightful,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, when they are sleeping.
It's the part of the day, (in between) when they wake up, and go to sleep that can be problematic and the greater their beauty, the greater their self created; oversized (and sometime hyper inflated) problems become a mans monstrously large problem; requiring an inordinate level of patience, otherwise known as total servitude.

I really like women when they are sleeping and when their mouth isn't moving.