Tecumseh, Dellorto, slide carbs, Black Widow

cfh

Well-Known Member
#1
I recently bought a messed up 1971 Rupp black widow. Unfortunately it was painted and did not have the original motor (or original Dellorto carb.) I guess that's understandable as the bike shipped with no governor and no air filter. So i can't imagine those engines lasted that long.

This particular Black Widow had a snow blower 5hp motor. The carb was a messed, and not angled either. So i installed an angled intake manifold and a standard tecumseh/china $10 carb on the bike. It rode and ran really well. The guy put a nice motor on this bike, it was responsive and fast.





For fun i searched for an original Dell'orto ua19s carb. Someone here was selling one for a decent price, so i bought it. Then off the blackwidowmotorsport.com and got the required throttle cable ($50!!) and the intake manifold ($40). Got it all installed and ran the bike. There is definitely an improvement. Not like night and day, but a lot more RPM potential and more responsiveness from the Tecumseh. It is an improvement, but for the price, frankly it's probably not worth it.



It got me thinking... instead of spending all that money, was there another way to get the same results? Now mind you, i can't match the look of the euro Dellorto, but perhaps there's a way to get that slide carb performance, without spending hundreds of dollars.
 
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cfh

Well-Known Member
#2
A few days ago i'm looking at ebay and there's a slide carb for sale, with air filter, for like $22. It's advertised to work with a Briggs Animal motor. Why wouldn't this work for a Tecumseh? Maybe it would so i bought one.

https://www.ebay.com/itm/Carburetor...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

From my experience with the Dellorto, i know the stock throttle on most minibikes would not work. So i bought one of these $11 throttles from Amazon.

https://www.amazon.com/gp/product/B01MPX353V/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1
 
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cfh

Well-Known Member
#3
After getting the throttle and the carb, i wanted to see if it would work on a stock Tecumseh 5hp HS50 motor. I made a change to the carb... The intake portion was threaded, but in metric. So i ran my 1/4-28 tap through the two holes to make it american SAE threads. The intake portion of the carb has a rubber O ring in place, so there was no need for a special gasket. The carb lined up really nice (not perfect but damn close) to the stock Tecumseh intake manifold. I bolted it to the motor. The stock fuel line for the tecumseh set up was a bit short. So i used the carb drain line as a transition to the new carb (which has a smaller fuel intake nipple.) It lined up all very nice.

On this motor i did not remove the governor (mistake). I left all the governor exterior parts in place, because frankly did not know if this set up would work. And i wanted the option of going back to the original carb set up without too much work.



 
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cfh

Well-Known Member
#4
I fired the motor up outside and i was pretty shocked! it worked great. Just some adjustments to the idle speed and i was really surprised at how well it ran this Tecumseh HS50. Though it wasn't installed in a bike, i could tell it wanted to go and go fast. It definitely reminded me of the Dellorto, but at like 1/10th the price!

The only big downside is the throttle cable is awful close to the exhaust. I really need to make an intake manifold extension piece to move the carb away from the exhaust. Also if you're running a fancy exhaust (unlike seen in the pictures above), the throttle cable may be in a bad position. Really need to think about these things and see if i can come up with an easy solution. Comments appreciated...
 
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#5
Hello. Please post pictures of the gov arm and linkage. Looks like in the picture posted it is still hooked up. Rupp disconnected all that when the UA19S was installed. Also.. the muffler is not black widow and as noted nor the engine. Did you get the BWMS correct HS50 intake?
 

cfh

Well-Known Member
#6
Yea i know the exhaust on the Black Widow is probably from a Roadster2. And as stated, the motor was not original. I think someone blew up the original motor and just discarded the entire motor/exhaust. I was told the bike was on the curb, waiting for the garbage man, and someone rescued it. They probably put the HS50 on and got a Roadster exhaust.

I bought all the parts that didn't come with the Dellorto carb from BlackWidowmotorsport.com. As stated that included the intake manifold and the throttle cable.

The governor is still there on both motors. When i rebuild that silver HS50 all that stuff will get sorted out and removed. But for right now i left them in place, not know how the Dellorto or the other slide carb would ultimately work.
 
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#7
Hello,
Leaving the links and governor in place, you won't see the potential of the UA19S carb. As you stated you run the risk of engine failure for sure. Same as 1971. Also,, the gas tank indication of black widow is not correct.
 

delray

Well-Known Member
#8
I know your just playing around with the two different carbs and all. looking to see how it improves the performance. like you said early there was a small improvement,but that was it. you will never see much more either unless you do the whole package deal. better cam,advance timing,gearing,good header on the bike....etc.....that snowblower intake is terrible. can't get anymore restricted then that. mm carbs are made to go and there is nothing really there to help it go....:scooter:
main thing your having fun with it and it's aways fun to play around on this stuff......:thumbsup:
 

cfh

Well-Known Member
#9
yea but is there a better intake manifold than used on the snowblower? i had not noticed that minibike-ready tecumseh intake manifolds as being any different.

i don't really want to go nuts on the motors. but if there's some easy and inexpensive way to get a bit more out of the motor, i'm all for that.
 

Rupp 72

Active Member
#10
I believe Delray was taking about the intake port, not the intake manifold. So doing something like porting the intake and exhaust and adding a header pipe will give you much better air flow and make better use of the Dellorto carb.
 
#11
The price of a Dellorto UA-19S is high because few are available and for someone restoring a Rupp Black Widow or other that needs one to be original the price is what it is. Slide valve carburetors perform better on the top end and still work at low speeds unlike a throttle plate carburetor that need a smaller venturi to work at low speeds but gives up flow on the top end. I have seen posts here for performance built engines with what looks like Mikuni multi diaphragm type carburetors, one advantage the Del or slide valve carburetor would have over diaphragm carbs is less issues with ethanol blended fuels damaging the diaphragms of older carbs.

Tony
 
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#12


This was my cheaper version than going with the original Dellorto carb. Pz20mm carb. Tecumseh HS50 ported, compression release ground of cam. Made my own intake manifold. After getting main jet sized right. It runs very good. Still running strong for 5 years now.
 

delray

Well-Known Member
#13
Patrick, is that the bike you took to windber about 4 or 5yrs ago. if so that little guy was so fast for a flathead.
I have to say that is the first flathead that really impressed me. remember that bike well on the trails.
rooster tailing dirt all day.....:scooter:
also randy had a mild little rupp that I like too. I believe mike has the bike now?


clear you mail box buddy. I got stuff to send to you soon.....
 
#14
I recently bought a messed up 1971 Rupp black widow. Unfortunately it was painted and did not have the original motor (or original Dellorto carb.) I guess that's understandable as the bike shipped with no governor and no air filter. So i can't imagine those engines lasted that long.

This particular Black Widow had a snow blower 5hp motor. The carb was a messed, and not angled either. So i installed an angled intake manifold and a standard tecumseh/china $10 carb on the bike. It rode and ran really well. The guy put a nice motor on this bike, it was responsive and fast.





For fun i searched for an original Dell'orto ua19s carb. Someone here was selling one for a decent price, so i bought it. Then off the blackwidowmotorsport.com and got the required throttle cable ($50!!) and the intake manifold ($40). Got it all installed and ran the bike. There is definitely an improvement. Not like night and day, but a lot more RPM potential and more responsiveness from the Tecumseh. It is an improvement, but for the price, frankly it's probably not worth it.



It got me thinking... instead of spending all that money, was there another way to get the same results? Now mind you, i can't match the look of the euro Dellorto, but perhaps there's a way to get that slide carb performance, without spending hundreds of dollars.
Something to check out when searching for more power, The screw in Rupp exhaust manifold has a 30 percent smaller inside diameter than the bolt on BlackWidow exhaust manifold. The B/W straight pipe offers another 20 to 30 percent improvement over the baffled Roadster/2 pipe. Performance improvements to intake and exhaust need to be matched or balanced to each other.
I think the Mikuni type slide carbs offer a great and cheap performance upgrade.
 

cfh

Well-Known Member
#15
The exhaust on my "black widow" (jury still out if it's a real BW!) is a bolt on. But i suspect there is a baffle. i haven't taken it off (yet) to check. i'm just happy it's running, and running well with the Dellorto!

are you saying having a straight pipe gives a 20% increase in performance over a baffled pipe? i find that pretty hard to believe there would be that much difference...
 
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cfh

Well-Known Member
#16
to get the slide $22 carb to work better on the stock Tecumseh, i fabricated an aluminum spacer block. This will move the carb away from the engine about an inch, which should help keep the cable away from the exhaust. I will take a picture later with this block mounted.

 
#17
What about the angled intake manifold? Doesn’t that space out about an inch as is?
I bought one recently from BWMS, it needed some serious porting to match the gaskets.


 

cfh

Well-Known Member
#18
The problem with the black widow motorsport angled intake manifolds is they are made for 4hp Tecumseh. The intake manifold is a big different on a 5hp Tecumseh, and they don't really work as well. They do work just it could be better.
 
#20
It needs some epoxy in the corner, not too tough. Mine is on Hs50 as well.
Doesn’t seem any harder than machining an aluminum spacer block, to me.

To each his own though

The block looks really good and it achieved your goal, so huge win nice job
 
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