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Need help with B&S 3.5 Won't start/cuts off


CHARLIENLAURA's Avatar
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05-02-08, 09:26 AM   #1  
Need help with B&S 3.5 Won't start/cuts off

Okay so I'm at my ropes end.
Model #95902
So had this guy running fine last year yada yada yada...
I have changed the diaphragm, cleaned the carb,changed gas,oil , cleaned the air filter, checked for spark , currently have the muffler and exaust hole soaking in carb cleaner, disassembled,reassembled 500 times pulled cord 6 trillion times ,and it primes fine. I have only been able to get it to start a handful of times and none of those have lasted more than10-15 secs. I do have black deposits on the spark plug ground and have some black gunk (oil,gas?) in the muffler.
Any ideas would be so welcome it isn't even funny

 
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Airman's Avatar
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05-02-08, 09:37 AM   #2  
Post the type and code number in addition to the model number.

In the meantime, loosen the gas cap and see if it will start and run. If it does run, the vent is blocked. Replace cap or clean vent.

 
CHARLIENLAURA's Avatar
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05-02-08, 09:43 AM   #3  
95902 3105 01
I have cleaned the cap and actually tried to start with the vent both in and out.I did try to start with gas cap off but it was before I did most of these other steps. I can't try it right now as the muffler and exaust are soaking still.
Thanks ,Charlie

 
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05-02-08, 11:35 AM   #4  
The issue seems to be gas.

So this has been the problem from the very begining of my ordeal. I have spent much hours and made many improvements and adjustments. After all this I can get it to crank every time now.The problem remains I am not moving gas. I filled the carb with gas from the tank, fired it up and it ran long enough to burn that off then it cut. Clean carb ,new diaphragm,gas cap check. So what am I missing? Cheese you seem to be the expert around here, any clues?


Last edited by CHARLIENLAURA; 05-02-08 at 11:37 AM. Reason: n/a
 
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05-02-08, 03:56 PM   #5  
Does your engine have adequate compression? Without adequate compression enough air is not sucked through the carburetor to make the fuel pump diaphragm work.

Are the screens on the carburetor pickup tubes clean? The long tube picks up gas from the tank and deposits it in a well where the small tube, actually the main jet, sucks it into the carburetor venturi. The small tube has a screen that slides over it. Remove the screen and you will see a small hole in the center of the tube. Run a piece of copper wire through the hole to ensure it is open. You should be able to look down the carburetor venturi and see the wire come out the other end of the jet.

Is the carburetor sealed against the fuel tank mounting flange? An air leak here can cause your problem.

Is the seal installed in the throat of the hole on the carburetor that mates to the manifold on the engine?

Beyond this I am out of ideas.

Good luck

 
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05-02-08, 04:18 PM   #6  
1) You did not mention repacing spark plug .30 gap

2) Do you have the rubber O-ring and plastic retainer in place. Many times when carb is removed those remain on intake pipe.

3) After intalling new diaphram did you use "fresh fuel from the pump"?

4) As already stated, check compression

 
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05-02-08, 10:55 PM   #7  
All good ideas above. I'll strongly support checking the O-ring, or lack thereof, and the retainer clip that holds it in place. Also, check the plastic intake tube to be sure it isn't loose or cracked.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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05-03-08, 06:03 AM   #8  
Hi guys, thanks for the responses.
I have a new,properly gapped plug in, the o-ring and clip are good. I don't know how to check compression.
Let me elaborate a tad more on what i am getting here.It is starting , and it is running very strong for the few seconds that it does run.It seems to me it is getting plenty enough air for the engine to combust properly,it just is not moving gas. Looking at the carb it really does'nt seem theres much that could go wrong, so is it possible for these simple little things to somehow actually be bad? I appreciate you guys' help. Charlie

 
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05-03-08, 06:26 AM   #9  
I understand your frustration. A crude way to test compression is to hold a finger over the spark plug hole and pull the starter cord. A decent level of compression will blow your finger off the hole.

Remove the carburetor and look in the hole where the short pickup with the removable screen goes. If there is no fuel in the well, fuel is not being lifted by the long pickup tube. Fuel has to be in this well for the carburetor to suck it in the engine. One of my previous items will most likely be the cause.

 
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05-03-08, 10:20 AM   #10  
Cool well thanks alot Airman ,
The elbow is installed, Will test compression (Crudely ), and I have not noticed the flange at the carburetor but will pay more attention when I stick the wire through there. You definitly nailed it on the head as the pickup is not filling the well and is the root of all my probs here. I,m thinking maybe some heat rated RTV sealant around the elbow,breather tube joint and the base of the carb outta do the trick,along with a new air filter. Could a muffler cause the air restriction preventing the carb from functioning? Thanks again ,Charlie

 
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05-03-08, 11:34 AM   #11  
I think your problem will be an air leak between the carburetor and fuel tank mounting flange or where the carburetor that mates to the manifold, round tube, on the engine? In situations where I cannot correct an air leak I like to use nonhardening permatex to seal it off, messy but works.

I personally have never seen a 4-cycle engine with a muffler than was carboned up to the point to restrict exhaust. Common on 2-cycles, I have never experienced it on a 4-cycle.

 
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05-03-08, 04:55 PM   #12  
During all this cleaning the carb did you pry out the main jet from the stem under the thimble looking screen, manufacturing can leave small particles of plastic hanging that come loose and create a big PITA. Have a good one. Geo

 
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05-03-08, 09:01 PM   #13  
You did install a brand new Diaphragm, correct? If you have a need for sealant, there is something wrong that needs to be addressed. The elbow at the breather pipe has no effect on the problem you're having.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
smallengineguy's Avatar
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05-04-08, 04:13 AM   #14  
Posted By: geogrubb During all this cleaning the carb did you pry out the main jet from the stem under the thimble looking screen, manufacturing can leave small particles of plastic hanging that come loose and create a big PITA. Have a good one. Geo
There is also an o-ring on the tube that may need to replaced, although usually you get hunting/surging when this fails not --no start--. When you installed new diaphram did you install diaphram onto tank, then gasket, then carb? A new carb is only $25 and is PN# 494775 it may be a viable option before the gas gets too high

 
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