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Carb help on B & S twin cylinder 21 hp intec


will1528's Avatar
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04-26-15, 07:22 PM   #1  
Carb help on B & S twin cylinder 21 hp intec

Have traced reason it wont start to a fuel problem .

will start when you put a little fuel in the carb but immediately quits after thats burned up . So that eliminates compression or spark as the reason
* fuel pump is pumping strong
* gas is getting to the float bowl
*have taken the carb. off twice & removed the only part that is removable on this carb ( the float bowl) carb cleaner sprayed everywhere i could get spray in ,
* choke plate & throttle working as it should
* blew air in it
*replaced --still wont crank --new carbs for this thing are 160.00
* I was told by a shop person that I need a new one .I just cant see what else other than cleaning it good would make it run again .
* would the solenoid on the bottom of the bowl have any bearing on this problem --seems to reason that as long as there is gas getting in thye bowl ,nothing is wrong with the solenoid --Right?
Thx for any help on this

 
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cheese's Avatar
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04-27-15, 12:35 AM   #2  
The solenoid could definitely cause the problem. It doesn't have anything to do with gas getting into the bowl. It closes off the main jet. If the solenoid is stuck shut, it will not allow the engine to pull any fuel through the carb.


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04-27-15, 05:11 AM   #3  
The solenoid is there to help prevent a backfire/afterfire when the engine is turned off. When you turn off the engine it kills the spark but the engine is still rotating and air and fuel is still being sucked through the carburetor as the engine coasts down. That air fuel mix can explode/ignite when it hits the still hot exhaust causing an annoying backfire. So, the put a electric solenoid on the carburetor. When you turn off the key the ignition is killed and so is power to this solenoid which allows it's plunger to pop up and block the flow of fuel to the main jet, instantly cutting off the flow of fuel. If the solenoid is not getting power or if the plunger can't retract then fuel is blocked from part of the carburetor. The solenoid does not affect fuel getting into the carburetor. I just prevents it (fuel) from getting to the main jet.

The solenoid is pretty easy to test and it's also pretty easy to defeat if you don't want to use it. Some people snip off the plunger so it can't block the fuel and just live with the backfiring at shutdown. But, it's pretty cheap and simple so I like to keep it working.

Inspecting the anti-afterfire solenoid

 
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04-27-15, 09:41 AM   #4  
Thank you ,will try the solenoid test

 
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05-03-15, 04:21 PM   #5  
follow up to fuel solenoid previous post

My twin cylinder intec B&S engine did finally start but only after I took the little cap off of the end of the solenoid plunger that when it gets stuck in the extended position will not allow gas to go up in the main jet . But now it runs very rough & smokes which it never did before I took the carb off & cleaned , replace fuel filter & lines ,adjusted valves & magneto (coil) etc. new plugs etc. Question is this , do I have to do more than take the cap off the plunger to allow gas to flow freely where it suppose to go up into the carb . Could the stem of the plunger still not allow enough gas to go thru the inlet .If so , .How do you remove the stem inside the bowl ,Trying to avoid buying a 60.00 solenoid.


Last edited by PJmax; 05-03-15 at 04:34 PM. Reason: combined post w/original thread
 
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05-03-15, 10:09 PM   #6  
What color smoke?

Take the solenoid out and clean it... free up the plunger and work it back and forth with carb cleaner until it works on it's own. Usually that's all that is required.


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05-04-15, 01:09 PM   #7  
darkish gray --plugs turn black very quickly .

have cleaned the plunger at least twice --it works freely

Since I took the little black cap off the end of the plunger ,it cranks the best it ever has , & actually idles pretty smooth sometimes. But once you start opening up the throttle its gets really rough & cant get up any rpms .. Do I just need to get another carb ? think the smoke & plug fouling is from a too rich problem ,so if my theory of not getting enough gas into the main jet would not stand up , Correct? Or is there just enough gas getting through to start & idle but not enough when I give it throttle ??

 
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05-04-15, 04:27 PM   #8  
It's flooding. Is the choke opening? Are your main jets in place in the carb? Some carbs have jets that come out easily and sometimes fall out without being noticed, causing a very rich condition.


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05-04-15, 06:30 PM   #9  
* choke is working like it should

* only removable part I saw when I took the bowl with the solenoid on it ,then lifted up the float assembly was 1 little brass jet that just set in the hole in carb base . There were other holes there .Did there supposed to be more than 1 jet. Cif so ,could have definitely fell out when Ifirsst took apart. This carb has no low or high speed adjustment needles . And yes I agree ,about it flooding out .

 
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05-05-15, 10:13 AM   #10  
Is it in a hole next to another hole just like it? If so, I'd say the other jet fell out. There were several different variations of carbs used on these, so I can't say if your had one or two, but I don't recall any just having only one.


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05-05-15, 07:45 PM   #11  
ok Thx .I will look for a parts list for this carb & see if there is 1 or 2. or a rebuild kit for it

 
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