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Discussion Starter · #1 ·
New here, Hi to everyone.

I have a B+S Engine 31C707-0175-E1 17.5 HP on my Murray Select rider. The mower had sat outside for one winter. I've replaced the battery, fuel, oil and completely cleaned the magneto, all connections and the carb. Nikki carb, solenoid activated, non setting jets, no fuel pump.

Nikki Carburetor Model# 28XX00-31XX00 Part# 498888N

Wouldn't start initially so I gave it a blast of ether. Ran until ether was exhausted.

Currently the carb is getting fuel as evidenced by removing the solenoid and watching the fuel drain from the bowl.

The problem.

The engine turns freely but will not start. I believe the engine is being flooded. White smoke and sometimes fuel comes from the exhaust as it tries to start, it also comes back to the carb from the breather.

Any thoughts? Much appreciated. I'm sure there's things I've done not mentioned. If you ask I'll answer, been at it for a couple of days. Thanks, Steve
 

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Check your oil level. It may be contaminated with old fuel. If the level is over full, drain and refill with new oil to proper level. Since the engine will run from a prime, then it's likely that the main jet in the carburetor is plugged or restricted. You will need to take the float bowl off and clean out the bowl and main jet at the very least.

Best of Luck... :thumbsup:
 

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Discussion Starter · #3 ·
Thanks for responding. As of right now the mower won't start. I'm suspecting the needle isn't operating correctly and flooding it out. I don't think the head gasket is bad. I have ordered a new carburetor, the rebuild is $35.00 and the new carb is $69.00 with the solenoid included. I'll be draining the oil and fuel before I put the new carb on.

I'm curious about the workings of the solenoid though. It seems to me it fuctions as follows (or so I think)

When the key is off the arm should be extended (up), keeping the float up and the needle firmly pressed into it's slot. When the key is on, the arm should retract letting the float drop thereby dropping the needle to let fuel fill the bowl -- sound correct?

I get confused at this point, if the float drops, how could SO much fuel flow that it would flood the engine? It seems only so much fuel would be able to flow through.

I'm wondering if the new carb will come all prepared for a simple bolt in place and run?
 

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The solenoid does not operate the float. It's actually an after fire solenoid, it's sole purpose is to close off the main jet of the carburetor when the key is switched off, to help prevent an after fire (big bang) than can occur in a hot muffler when an engine is stopped. It will not prevent a carburetor from flooding or fuel from leaking out into the engine and eventually the crankcase.
 

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Discussion Starter · #5 · (Edited)
Thanks for explaining that. In order for the carb to flood wouldn't the fuel have to continue to flow from the needle valve into the bowl? But if the key is off and the main jet is closed off, how would the fuel continue to get to the engine?

Or, Is it a matter of if the engine is not firing and not burning off the fuel, then the fuel will continue to over fill and end up in the crankcase?

In which case, how would I know if it's really flooding due to the carb, but it may be a spark issue?
 

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Thanks for explaining that. In order for the carb to flood wouldn't the fuel have to continue to flow from the needle valve into the bowl? But if the key is off and the main jet is closed off, how would the fuel continue to get to the engine?

Or, Is it a matter of if the engine is not firing and not burning off the fuel, then the fuel will continue to over fill and end up in the crankcase?

In which case, how would I know if it's really flooding due to the carb, but it may be a spark issue?
When a carburetor floods for whatever reason, the fuel will continue to flow into the carburetor and eventually overflow. The solenoid restricts flow into the main jet, but does not eliminate flow. If the carburetor is flooding the fuel will eventually work it's way past the solenoid valve up and out of the carburetor. There is only 2 ways for fuel to make it into your crankcase. A flooding carburetor is one way, another would be a faulty fuel pump, if your engine is equipped with one.

The spark has nothing to do with the carburetor and whether it's flooding or not. If gas continues to flow when the float bowl is full, then it's going to leak, it may not be at a rate fast enough to cause it not to run, or affect the way it runs (when running), but it will continue to flow when the engine is not running. Your ignition spark is not the issue.
 

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Discussion Starter · #7 ·
Thanks again. I was under the impression that once the plunger on the solenoid closed off the main jet there was no way for fuel to make it past the bowl, once the bowl was full. I must be wrong. I would imagine if the engine is filled with extra fuel the spark plug would foul and not be able to ignite it. Another concern is if the fuel mixes with the oil and gums up the whole works. Before I install the new carb would it be wise to remove the old one as well as the spark plug, and crank the engine over a few times?
 

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It would be wise to drain the oil and refill with new motor oil, but other then that, the new carburetor should take care of it.
 

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hey 30year, quick question, do you know if briggs fixed the walbro carbs from doing this crap?

cause I just ordered a new walbro for a customer cause thats what he wanted, and i told him I couldn't gaurentee that it would really fix it

do you know if they have had a design change or anything?

/thread de-rail
 

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I have not seen or heard of any changes in the Walbro carburetors. I have not run across any that a new needle and or needle and seat did not take care of. I usually add an inline cut off when I do one, I tell my customers that if they get in the habit of turning the fuel off, they will never have this problem again. I thinks it's more of an issue with the fuel and how it causes the tip of the needle to deteriorate faster, then a design flaw.
 

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Thanks for explaining that. In order for the carb to flood wouldn't the fuel have to continue to flow from the needle valve into the bowl? But if the key is off and the main jet is closed off, how would the fuel continue to get to the engine?
I'm thinking you answered your own question. If the needle isnt seated in the seat, fuel will continue to flow if the motor is on or off. I would look into that area and make sure its not being held open from debris. Could just back blow where the fuel comes into the carb and see if anything comes out, reassemble and see if it quits doing it.
 

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Discussion Starter · #12 · (Edited)
Should I install a shutoff for the fuel line? If so, what would be the best materials to use for one? Brand name? Question on the fuel filter, Does the fuel filter play a major part in flowrate? or, Is it primarily only for debri removal?

Well the carb didn't arrive today. They checked and it will be there tomorrow 9-10am.

I drained the oil just now and it was filthy, I was surprised seeing how I'd changed it already. I drained all the fuel out, removed the breather and pulled the spark plug to air it out.

It's covered with a tarp until tomorrow morning.
 

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I use these type of inline cut off valves:

http://www.m-and-d.com/RO-5841.html

The fuel filter is there primarily to prevent contaminates from getting into the carburetor. You can have problems if you use a fuel filter designed for a system with a fuel pump versus gravity feed type set up. Be sure you use the correct one for your setup, or you may have issues.
 

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Discussion Starter · #14 ·
Thanks. My set up is gravity fed. I'll get that shutoff valve, Another question. If the carb doesn't come with the gaskets, (just thought of it) Is there anything in a way of a sealer I can use? I've noticed on the breather side of the carb there's no gasket at all and on the opposite side there's a gasket.
 

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On the side the air filter attaches to, there should be an O-Ring seal, but no gasket. In a pinch I might use a gasket sealant on the old gasket, but would prefer to use a new one.
 

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Discussion Starter · #16 ·
On the side where the breather attaches to the plastic piece that attaches to the carburetor itself (intake elbow to carb) I can see where some type of red gasket sealer was used where the plastic meets the metal on the carb, according to the B+S exploded view there should be a gasket there, I bought this rider new and since this is the 1st time I've taken these components apart there is and never was a gasket there, on the outgoing side of the carb where the carb meets the intake going to the engine there is a gasket between the carb and the plastic piece, The exploded view also shows another gasket from the plastic to the engine which has never been there since the 1st time I took it apart as well. I think 1 of 2 things has happened here. Either the factory skimped on the gaskets OR the rider I got at Home Depot was returned and it was sold as being new when in fact perhaps it wasn't.

It figures, on a day when I really want to get on this project, it's raining!
 

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Discussion Starter · #17 · (Edited)
Called the guy yesterday for my carb. Said he was waiting for UPS. called again and told him to call me either way to let me know if it does or doesn't arrive. He never called. I don't think he ordered the carb at all. Going there tomorrow morning to ask to see the UPS tracking number.

I put the carb on, same symptoms. White smoke at exhaust and breather. Keeps cranking over but no start. Also have oil coming from exhaust and the breather tube.

?????? Thanks.
 

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Discussion Starter · #18 ·
Quick question.

I spoke with a mower tech yesterday and relayed the info of my problem. He said to pull the spark plug and crank the engine to clear it of excess fuel and it should start. I didn't ask if I should disconnect the fuel source when doing this.

Should I disconnect the fuel source prior to cranking over the engine to clear it?

Thanks.
 

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No, but if your carburetor is still flooding, it may continue to do this. If the carburetor is flooding then you might want to cut off the fuel supply in order to get it to start after you clear out the excess fuel.
 

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Discussion Starter · #20 ·
Thanks for responding and your help.

Last night I pulled the plug and cleared it. Hooked everything back up and cranked it. I have oil coming out of the breather tube but the oil that was coming from the exhaust is pretty much gone. Still getting white smoke while cranking. Took off the breather tube when cranking (oil still shoots out) and it's to the point where it wants to start but just isn't catching.

Thoughts? Thanks, relying on this board to cure what ills it has.

I've also been looking for the rebuild for this engine, can't seem to find the specific kit, I wouldn't mind doing a rebuild if that's what it needs.
 
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