Help with 312-8 No Start

[AndyK149 62]

Hi all - 

I was having some trouble starting my 312-8 this year.  It would start after awhile, and then would barely run on choke for a few minutes, and then it would be good to work.  I decided to pull the carb off and clean it.  It has the Walbro non-adjustable one.  I pulled everything apart and put on new fuel lines as well.  Now I do not get any start at all.  I have tried all positions for the two adjuster screws, including their original positions and nothing.  The spark plug is black but dry and I don't smell any fuel.

 

Last year I replaced the fuel pump after it died.  The fuel pressure seems low to me when I crank with the line off of the carb.  It slowly bubbles out of the hose, but, I'm not sure what is "Normal".  

 

I didn't mess with the carb very much since it was fairly clean.  I have the float/needle with the clip and reinstalled that.  However, whatever I did made it worse.  I could get it running before, now not at all.  Shame!!  As it stands, it will just crank all day with no signs of life.  Any suggestions?

[pfrederi 18,721]

First lets make sure it is a fuel problem.  Spray some carb cleaner into the carb throat then try to start  if it does then give the carb a sharp rap with a soft hammer (free the needle valve which may be stuck)  If nothing then I would take the carb off and clean it again and make sure the float is set correctly 11/64"..  Fuel flow on these is not like a car spurting out bubbling is probably OK.

Edited May 2, 2019 by pfrederi

[AndyK149 62]

Thanks.  I will look at the float again.  I do not think it is adjustable on the Walbros but I could be wrong.  As in, I do not think it has an adjustment tab.  

[pfrederi 18,721]

Float level is adjustable per manual, float drop is not.  i was wrong about 11/64 for Walbros float should be parallel to the carb body when upside down

 

 

[953 nut 60,406]

7 hours ago, AndyK149 said:

The spark plug is black but dry and I don't smell any fuel.

Put a new one in anyway.

 

7 hours ago, AndyK149 said:

when I crank with the line off of the carb.  It slowly bubbles out of the hose, but, I'm not sure what is "Normal". 

Could be some air in the lines, I would put a finger tip over the end of the line and crank it over to see if there is any pressure, don't need much like Paul said.

[AndyK149 62]

I have very good spark, I pulled it out and can see a big bright spark when I crank.  This plug is less than a year old.  Boy I am really reluctant to bend the tab on the carb float, it does NOT look like the other carbs I have seen where there is a bendable tab.  There is a tab that the needle clips to but it is extremely thin and fused to the plastic float and I am afraid to bend it. It looks fragile.

 

I took everything apart again and blew air through it and re cleaned everything.  It is very clean.  The needle does seem to move freely when I move the float, but that is with the bowl off.  

 

I'll get some starting fluid.  It wouldn't fire on brake clean or WD40.  I gave up on it last night.  Have had the carb off about 10 times and need a break - was getting frustrated.  Never had anything like this happen before so I am at a loss.  I really appreciate the suggestions. 

 

 

[clueless 3,272]

Do you use ethanol gas? Get some carb cleaner, not brake cleaner  and try to start it. Taking the carb apart and blowing it out is not necessarily cleaning it. I would try to found a rebuild kit for it, after all your getting good at taking it apart. Hang in there we're going to get this. 

[ohiofarmer 3,380]

Think like a diagnostician. Assume nothing, but proove everything. 

 

First, proove you have a good spark. Next, put a test tank on a stand a foot or higher  above the carb to eliminate the questions about the fuel pump.

If the engine still does not work, put a bit of fuel directly I to the intake.

I would also suggest that a you tube by Mustie1 on the subject ."will it run" could be helpful. Mustie1 is very logical in his work and a joy to watch. He has fons of stuff on small engine repair.

[AndyK149 62]

Thanks all for the suggestions.  I was able to get it running well today.  I'm not sure what I did differently, I guess I just came back with a level head and started over.  Compressed air, brake clean, a little wire through all the orifices and confirmation that the float was at a level position.  I took a lot of cranking, but we are back in business.

 

What is funny, or not funny (depending on your perspective), is that I don't believe I really needed to pull the carb in the first place.  I think a little turn of the low RPM screw on the carb was all it would have needed. Anyway, it was the first time I ever saw inside that carb and it is good to see it was clean.

 

Too rainy to use today, which is a bummer, because the tractor is running well and I just put my new gearing (pulley) on that I am looking forward to trying out.