Ravivos

Hi all,

I bought a Walbro WT-433 carb for my CRRC GF26i, it suppose to be a 11.1 mm size venturi,
the original carb that came with the engine is a Walbro wt-745 which, according to walbro's website, is a 7.94mm venturi.

when compared the two carbs together, it seems that the WT-745, which suppose to be the smaller one, have a bigger bore that the WT-433.

Take a look at the attached picture, the right carb is the WT-433 and the left one is the WT-745.
it clearly shows that the left carb have a bigger bore.

please advice,

thank you.
Raviv.

JohnF

The venturi size is not the only thing that matters. Be careful what jets are being used.

Ravivos

Hi all,

I went out for some testing today,
bolt the engine (CRRC 26cc) to a test stand and fired it up with the two carbs (original - WT745 and the new WT433)
as i mentiond before, the WT745 (original that came with the engine) suppose to be smaller in diameter (bore size), but in reality - the WT433, 11.11mm carb, is smaller.

test results were very surprising -
there is a difference of approximately 100-200 rpm at top end in favor of the original carb (WT-745).
the thing the shocked me most was the numbers -

Original carb (WT-745):
17X6APC - 9700rpm!!
18X6 W APC (cut down to 17X6W) - 8900rpm

New carb (WT-433)
17X6 APC - 9500rpm
18X6 W APC (Cut down to 17X6W) - 8800rpm

Can someone please explane why the original carb, how suppose to be smaller, has a bigger bore and prforms much better?

video of the engine running with the 17X6APC prop will be posted shortly

Ravivos

Here is a short video.
17X6APC prop with the original carb.

[link]http://www.youtube.com/watch?v=Zy1jVNE66X8&fmt=22[/link]

Super08

My Feedback: (2)

Their should be a number stamped just inside the throat of the venturi. It will tell you what the venturi size is in 64ths of an inch. I.E. a 433 should be stamped with a 28. So 28/64=.4375" which is 11.1125 mm. I have found other carbs on the Walbro site that had incorrect information on them. Also what is the other number on the 745 carb beside where it is stamped 745?

edit: I just looked at your pic above and it almost looks like it is marked 32, but it is hard to tell. If so it is a 12.7mm.

Ravivos

Hi Super8

You are correct, walbro website is wrong.
the WT-745 has the number 34 stamped on it , so its a 13.49mm carb.
I guess this explains way the original carb is stronger than the WT-433.

i just wish i knew it before bought the 433.

it sure turned out to be quite a jem of an engine

Super08

My Feedback: (2)

Wow that is a big carb for a 26cc. How is the idle and transition? I have a SPE26 converted to Rcexl ign that came with a 9.53mm carb. I changed it to a 11.1mm carb and picked up 3 or 4 hundred rpms. My earlier v2 Dl50's came with an 11.1mm carb. The new ones are 13.5mm I believe.

Ravivos

It idles great, 1800rpm without a problem,
when tuned, it will transition without a single hesitation and all in all works really good, very easy to tune.

togatoga

My Feedback: (42)

I think ultimately, the main bore restrictor would be the carb adapter.