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-   -   Spring tension on throttle (https://www.rcuniverse.com/forum/engine-conversions-92/8101534-spring-tension-throttle.html)

the mother of invention 10-31-2008 09:08 AM
Spring tension on throttle
 
I have a 34cc Briggs & Stratton Fource 4 cylcle motor converted for aircraft. I made a spacer for the carb and cut the spring tension back on the throttle. It will run at idle or with the choke almost closed. I thought it may be sucking air. Checked the gaskets and they are not leaking. I think when I trimmed the spring for less tension that without the tension it leaks in air around the barrel. Any thoughts on changing the carb or fixing this problem.

I don't want that spring tension on the servo all the time so would like to find a more RC friendly carb with less tension and easy movement.

Thanks,
Eric

av8tor1977 10-31-2008 09:50 AM
RE: Spring tension on throttle
 
It may not have a leak, it may just be too lean. When you run a more open exhaust and without an air cleaner, that leans out the carburetion, which is too lean to begin with anyway. You need another, adjustable carb.

AV8TOR

the mother of invention 10-31-2008 10:18 AM
RE: Spring tension on throttle
 
That makes sense. It has a WYL-451 carb. 9.0 venturi, 12.0 choke bore, 9.0 throttle bore. 31mm on centerbolt pattern.

Any suggestions for a replacement?

The Raven 10-31-2008 07:37 PM
RE: Spring tension on throttle
 

ORIGINAL: the mother of invention

I have a 34cc Briggs & Stratton Fource 4 cylcle motor converted for aircraft. I made a spacer for the carb and cut the spring tension back on the throttle. It will run at idle or with the choke almost closed. I thought it may be sucking air. Checked the gaskets and they are not leaking. I think when I trimmed the spring for less tension that without the tension it leaks in air around the barrel. Any thoughts on changing the carb or fixing this problem.

I don't want that spring tension on the servo all the time so would like to find a more RC friendly carb with less tension and easy movement.

Thanks,
Eric
I have yet to convert my engine but I intend to try a different carb. While the one provided will get you to around 5500rpm (tested on a friends 'stock' conversion) I think some more rpm is required and probably more tunability. My intention is to try a Walbro taken off a Ryobi 31cc (I have several from conversions), if that carb can flow enough for a 31cc 2 stroke at 7000rpm it should flow plenty for a 34cc 4stroke at approx 6000-6500rpm. The nice thing with the Ryobi Walbros (at least the ones I have) is they have both a high and low needle and are not compromised by being an EPA model.

jtisch 11-08-2008 02:11 PM
RE: Spring tension on throttle
 
You can also drill out the main jet on the WYL, I did that on my 40cc Briggs.

J

Thomas46 11-10-2008 03:37 AM
RE: Spring tension on throttle
 
In my converted GX35 I installed WYK-194 sold at www.davesmotors.com
2 needle carburator, diameter 10.5mm.

Works very well, maybe it also fits to B&S engine

Regards

Thomas

captinjohn 11-10-2008 10:11 AM
RE: Spring tension on throttle
 
Is this the page http://www.davesmotors.com/s.nl/c.88...egory.27872/.f Capt,n

Thomas46 11-11-2008 02:11 AM
RE: Spring tension on throttle
 
Yes, it is, if you scroll down you find the carb in the middle.

It is the same design as the original from Honda, but full adjustable, no main jet but H-needle

Regards
Thomas


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