Engine only running on choke

[Steve2018 3]

I have a mower with a 8hp briggs and stratton engine but it only seems to run on choke and when running the revs rise and fall like it goes RReerrrrRRerrrRRerrrRRerrrr

 

So far I have tried new air filter,  new fuel,  new oil breather tube and new plug gapped correctly. 

 

I fitted a clear fuel filter from eurocarparts as well to make sure fuel going in was clean but there only seems to be a dribble of fuel in it,  hardly any at all.... 

 

Any help would be great

 

Thanks

[Stormin 4,458]

Have you had a look in the tank? May be debris in the bottom blocking the outlet. Is the fuel line clear and not kinked or trapped some where? Try blowing back up the fuel line to the tank and see what happens.

 

[Wristpin 400]

What you describe is typical of hunting caused by fuel starvation, usually by an internal blockage in the carburettor.  This is often caused by the ingress of dirt or these days a fuel quality issue leading to obstruction by gumming. The solution is a careful strip and clean of the carburettor using an aerosol can of carb cleaner to blow through all jets and orifices, or, if you know anyone with an ultrasonic cleaning tank, a good hot wash in that.

 

[Steve2018 3]

Thanks i will check the tank,  i thought maybe rust but the tank is plastic but you never know what's got in there over the years

 

Yea stripping the carb was suggested by the previous owner.  He said it stood outside over the winter then started doing it when he went to use it again. Will check the carb after the tank. Thanks

 

Just noticed in the manual it lists 2 fuel filters.  One type for engines with a fuel pump and one for engines without a pump...  I think i have fitted a filter designed for engines with fuel pumps by using an automotive filter... 

[nigel 1,876]

As whristpin says sounds like blocked main jet in carb also check carb bowl is clean

[Steve2018 3]

Is it ok to use brake cleaner or is carb cleaner needed? 

[Stormin 4,458]

 

21 hours ago, Steve2018 said:

I fitted a clear fuel filter from eurocarparts as well to make sure fuel going in was clean but there only seems to be a dribble of fuel in it,  hardly any at all.... 

 

That's why I suggested checking the tank and fuel line, to make sure fuel is getting to the carb before pulling the carb to bits.

[Steve2018 3]

32 minutes ago, Stormin said:

 

 

That's why I suggested checking the tank and fuel line, to make sure fuel is getting to the carb before pulling the carb to bits.

Yea thats first on the todo list before anything else just need to get time to look at it again. I thought even if the fuel filter was for a car then it still would have filled with fuel when left sitting for a few days.... But nothing, its fully empty now the filter after running it when I checked before going to work

 

Thanks

[Wristpin 400]

You need to bear in mind that a filter sold  for car use is designed to be used for a pumped fuel system and not a gravity fed one  as used on many mower engine installation. An example of this is that  Briggs and Stratton market three grades of filter, each with a different micron rating, one for gravity fed systems ,usually red, and another for single cylinder pumped systems, usually white and a clear one usually found on twin cylinder set ups.

For the filter to fill up under gravity it is necessary for the air in the system to find its way out. If it can’t , such as when the carb float valve is closed, the filter will just sit there empty.

Any one who has worked on many Vanguard and Intek installations will recognise the strange phenomenon of a happily running engine yet with a filer that appears to be empty. 

 

[Steve2018 3]

Checked the flow this morning,  pulled the fuel pipe off the carb and the fuel came running into the filter and out. 

 

Was going to blow down it but didnt want the taste of petrol before work lol.... 

 

 

Yea I think I will remove the filter and run without one until I get it running then fit the red briggs and stratton filter

 

Thanks 

[Stormin 4,458]

I would say, if fuel is running out of the filter ok, then up to there is ok. Try it without the filter and see what happens. If  no result the problem is not the filter. So it will be carb next.

[nigel 1,876]

I still think it will be the main jet

[Sammoore13bolens1053 11]

8 hours ago, Steve2018 said:

Checked the flow this morning,  pulled the fuel pipe off the carb and the fuel came running into the filter and out. 

 

Was going to blow down it but didnt want the taste of petrol before work lol.... 

 

 

Yea I think I will remove the filter and run without one until I get it running then fit the red briggs and stratton filter

 

Thanks 

 

I believe it’s going to be the jets, like Nigel said. Take it apart and clean them, so you can see daylight through them. My John Deere 68 has one of these engines, I like them. The main jet is the one in neck, that you will have to remove the carb and then the carb bowl, float etc, don’t lost the needle or seat. It’s a bronze jet, and can strip quite easily, be careful.

[Steve2018 3]

Thanks going to have a look on saturday when i have all day to mess around with it without rushing around

 

Should I order any new carb gaskets / seals or just have a go cleaning and refitting it all first? 

 

Thanks

[nigel 1,876]

No just take carb bowl off carefully take main jet out, should just unscrew clean jet the screw that holds the bowl on might be a jet so check that as well

[Wristpin 400]

When removing the float bowl it sometimes helps to gently rotate it a couple of degrees to break the seal between it and the O ring gasket. Then gently tip the bowl left and right in the hope that the O ring remains with the carb body. The objective is to try and avoid stretching the O ring as once stretched they can be a B**** to get back unless left to shrink for a couple of days or more.

[4x4forks 258]

Check carb main jet and also emulsion tube. They will block with crystals from stale fuel . Long brass tube with lots of holes in the sides. You may have to push the tube out . 

[Wristpin 400]

Before going any further with specific instructions for stripping/cleaning the carb on an 8HP Briggs it will be a good idea to pin down what 8ph Briggs you have and what carburettor - there have been a few over the years. So, Model, Type and Code numbers as stamped into the cowling, please   - often just above the spark plug. 

[Fix'em all 49]

Sometimes when cleaning the jets in the carb, there are hardened deposits  that carb cleaner alone does not shift. I find a wire from a wooden handle wire brush is perfect for poking out blocked jets without damaging the jet

 

[Steve2018 3]

191707 6030-01 is the code

 

I had a look today at it,  looked at my eurocarparts clear filter and its already got dirt floating in it so decided to blow down the pipe,  there was some resistance then no resistance so put the pipe back to the carb and the filter filled right up which looked like a highly improved flow started it and again revs hunting up and down :-(

 

Next step I removed the carb and found - 

 

1 - No gasket between the carb and head so just metal on metal.. 

 

2 - big hole in the exhaust silencer (but guessing this would be just a noise issue and why its so loud rather  than causing a running problem..)

 

3 -  Probably the main cause of the complete problem,  the High speed needle valve on the bottom of the carb was fully in!! 

 

Took it apart anyway while it was off and cleaned it out,  some  dirt but less than I thought

 

Put it back together,  set needle to 1.5 turns and idle needle to 1 turn and started it and it now runs without the choke,  increased the revs but then it started bogging down and firing black smoke out (guessing too rich)  so turned high speed needle in 1/4 turn and now revs to full revs but some blueish looking  smoke starts to appear at full revs

 

It says to set the idle RPM to 1750 rpm,  how do you know when its at 1750rpm? Do you need a special  tool for that? 

 

Thanks again

Just waiting for the carb gasket to arrive as well.. 

[Anglo Traction 1,016]

53 minutes ago, Steve2018 said:

It says to set the idle RPM to 1750 rpm,  how do you know when its at 1750rpm? Do you need a special  tool for that?  

Best way is to get yourself a Laser Tacho, they are not expensive and mine gets much use around the workshop checking lathe spindle speeds etc.

Checking/setting the Idle speed on a Kohler 12hp -

  

[Steve2018 3]

Thanks found this one on Amazon

 

https://www.amazon.co.uk/Digital-Tachometer-Small-Engine-Non-contact/dp/B00HWLTW90/ref=sr_1_1?rps=1&ie=UTF8&qid=1527962133&sr=8-1&keywords=Laser+tachometer&refinements=p_76%3A419158031

 

Set it to a idle RPM that sounds like my push lawnmower for now.  Only thing ive noticed is at full throttle it sort of sputters and puffs smoke out the exhaust,  but knock the throttle back a notch or two its fine. 

 

But Maybe the missing carb gasket could be the problem for that... 

[Stormin 4,458]

If the smoke is black, it's a tad rich at full revs.

[Steve2018 3]

The smoke at max revs is more grey / blueish looking but back it off a notch and theres no smoke 

 

Just noticed The govenor link spring that goes over the throttle arm has snapped :-( 

 

Is the spring an import part? 

[Stormin 4,458]

Grey/blue smoke is a sign of burning oil. Maybe over reving. Replace that spring.