Carburettor adjustment

[Mickwhitt 4,647]

Hi guys.

 

In the quest to get my little red Fred running smooth I'd like to check the carb is set properly.

 

I know the method of setting the fast and idle jets in theory.

 

Can someone walk me through the process? Mainly how much rotation of the jets is required to take them from rich to.lean. the manual looks like its nothing more than a quarter turn.

 

My fast jet seems to take quite a bit of turning to go from rich to lean. 

 

The tip of the needle is quite worn, bent and corroded, would that have a bearing on the running?

 

 

Exhaust seems sooty to me but that could be because of the rings too I guess.

 

Any help welcome.

 

Mick 

 

 

[stevasaurus 22,769]

That tip does look pretty worn and could be an issue.  As you know, you bottom out those screws and back them out what the book says for your engine and carb.  Adjustment after that...do the side screw first and it should only be like 1/4 turn either way.  Listen for the engine to run smooth.  Next do the top screw and do the same thing.  Make sure your points are set correctly...that can make more of a difference in how that horse runs.  

 

[lynnmor 7,317]

Idle it slow to adjust the idle mixture screw.  Adjust the screw till it idles the fastest and adjust the speed down if necessary.  Now run the screw in and out and you will see the engine begin to falter in each direction, then turn the screw to the mid point between.  The high speed mixture can then be adjusted starting with the specified turns out.  Quickly open the throttle and watch for instant response, if necessary turn the screw about 1/8  turn and retest.  Find the setting that gives the best response.  On either screw err on the rich side, you don't want to go too lean on air cooled engines because of potential valve damage, over heating or pre-ignition.

[jay bee 906]

Am I understanding that you adjust the high speed screw at an idle speed?  Or do you increase the speed to a high RPM and then adjust the high speed screw?  

[Handy Don 12,277]

Set the high speed with the engine at high speed

[Handy Don 12,277]

3 minutes ago, Handy Don said:

Set the high speed with the engine at high speed

TEST each new setting by letting the engine idle and and then quickly opening the throttle. The engine should not falter. If it does, open the high speed jet a small amount and retry. Repeat until success.

[lynnmor 7,317]

10 hours ago, jay bee said:

Am I understanding that you adjust the high speed screw at an idle speed?  Or do you increase the speed to a high RPM and then adjust the high speed screw?  

The words used to name the various components causes much of the misunderstanding.

The "throttle" on the dash is not the throttle, it is the engine speed control that sets the governor.

The throttle plate in the carburetor is the actual throttle.

The "high speed" screw adjusts the mixture at large throttle plate openings regardless of engine speed.

Turning the "high speed" screw while the engine is running fast but not under load will not give good results because the throttle plate is only open a small amount.  Loading the engine by quickly opening the throttle plate will give a brief test of the mixture.

Doing a spark plug reading is probably the best way to follow up a mixture adjustment.  Running the engine hard for some time, such as continuous plowing or snow blowing, followed by quickly shutting down and pulling a plug to check its color.  Color charts such as this are available online.

[Maxwell-8 4,277]

Some great advice, can a rich mixture give you smoke?

 

[lynnmor 7,317]

13 minutes ago, Maxwell-8 said:

Some great advice, can a rich mixture give you smoke?

 

If the smoke is actually from the fuel, it would need to be very rich.  Usually white smoke is oil and gray or black smoke is fuel.

[Maxwell-8 4,277]

3 minutes ago, lynnmor said:

If the smoke is actually from the fuel, it would need to be very rich.  Usually white smoke is oil and gray or black smoke is fuel.

It's pretty white, its a kohler k301, i thought it was rebuild recently, somebody must have done a bad job or not at all.

Edited December 19, 2020 by Maxwell-8

[Mickwhitt 4,647]

I fitted a new plug and tooled up and down the drive for a while. 

The plug looks like this now...

Any thoughts on it?

Looks oIled a little.

adjusting the fast running jet is really difficult, probably because its worn.

I'm trying to source a new jet, but I have seen the bottom adjusting conversion by Brian Miller, anyone know of it and if it is a worthwhile kit to consider.

Mick 

[Maxwell-8 4,277]

For sure rich and oily.

 

You notice any engine oil consumption?

Edited December 20, 2020 by Maxwell-8

[Mickwhitt 4,647]

Its not smoking and I will monitor the oil closely now its running more reliably.

When I rebuilt the engine I didnt replace rings etc. The bore looked fine and measured pretty even which is why I just rebuilt.

Not sure I could find a small engine shop who could take on boring and rebuilding the engine if its needed. But I will tackle that problem if it comes up.

Mick 

[sparkie333 265]

On 12/18/2020 at 3:55 PM, stevasaurus said:

That tip does look pretty worn and could be an issue.

I agree the needle needs replaced that is Number 1 there may be more things to addressed. Good luck.

Edited December 30, 2020 by sparkie333

[Mickwhitt 4,647]

Where can I get hold of a new needle?  Not sure if kohler dealers here will carry them.

Could have a go at making one? Bit of precision machining for me.

Not sure how the threaded part and needle are joined together, must be made separate and pressed together. 

I was going to try and get hold of a bottom adjusting kit but that looks a remote possibility. 

Mick

[rjg854 11,392]

Could you possibly some used carbs and get the needle from one of those? 

[formariz 11,988]

5 hours ago, Mickwhitt said:

Where can I get hold of a new needle?  Not sure if kohler dealers here will carry them.

Could have a go at making one? Bit of precision machining for me.

Not sure how the threaded part and needle are joined together, must be made separate and pressed together. 

I was going to try and get hold of a bottom adjusting kit but that looks a remote possibility. 

Mick

Those are readily available here. I am not sure vendors will ship them there. One of us could certainly do that for you in last resort. Many different needles fit same carburetor. Difference is on number and location of holes. They are designed with different engines in mind. You need to check dimensions on throttle and venturi bores to determine correct one for your carburetor. Same number carburetor will have different dimensions on those two areas hence the different needles.

Look here in the link below. I follow this site religiously and I have solved many issues that seemed unsolvable for ages. Just don't buy anything from him. I have without any issues but it seems that there are few exceptions to that. The correct needle with the correct carburetor is the solution to many problems fuel related. I have even followed his advice on modifying the needles bottom hole and the difference starting the engines in low throttle is like night and day.

http://gardentractorpullingtips.com/carbfuel.htm

Edited December 31, 2020 by formariz

[Mickwhitt 4,647]

Well I managed to find a number 30 carb off as K321 i believe. 

It was pretty much scrap as it had been in a river, but the inside of the carb was fine.

The high speed needle is similar to the one on my carb but the cross holes are different.  The tip of this needle is in way way better shape than mine so i want to use it. Im going to measure and drill the holes to exactly match my needle.

That way I should get the same thing only better.

With luck this newer needle will allow me to adjust the high speed mixture a little better, we will see.

Mick 

[wallfish 17,023]

I would just try it first before modifying the holes. maybe just a small adjustment will be enough to equal the different hole sizes. 

A little too late for the suggestion and never tried it, but what about using lapping compound to mate the surfaces of the needle and seat? Would that brass be too soft to work? Or maybe the compound would leave too deep of scratches? 

[Mickwhitt 4,647]

The needle part number on mine is correct for the model of carb so the hole number and positions should be correct. That is confirmed by reading up on the pulling tractor site. So drilling a few 1/32 holes will be easy. 

I was going to try it before I modify it but that seems unnecessary as too small a hole means it woukd not idle. 

Mick

 

[lynnmor 7,317]

1 hour ago, Mickwhitt said:

The needle part number on mine is correct for the model of carb so the hole number and positions should be correct. That is confirmed by reading up on the pulling tractor site. So drilling a few 1/32 holes will be easy. 

I was going to try it before I modify it but that seems unnecessary as too small a hole means it woukd not idle. 

Mick

 

Don't you have a idle mixture screw to adjust?  The idle circuit is not affected greatly by the high speed screw.

 

My concern would be the condition of the hole where the point of the high speed screw meters the flow.  With the finish being knackered on the point might not be a big problem since you adjust the flow anyway.  Often folks jam the screws in and damage the mating surface. I really think you have more going on than the condition of the high speed screw end.

[Mickwhitt 4,647]

Well I fitted the needle without drilling it.

The engine runs fine and it is so obvious that I can now adjust the fast running mixture accurately compared to the previous worn and damage needle. 

Obviously I have not run it under load so that may well expose any problems with this new needle. 

If im reading it right, fuel is allowed out of the float chamber via the emulsion tube through the gap made by the tapered needle. The fuel then enters the small hole at the bottom of the needle and up to the top where it goes to the slow running jet, entering the air inlet after the throttle butterfly.

 At higher throttle speeds the fuel is pulled out of the central holes in the needle and straight into the venturi. 

Mick

[sparkie333 265]

OK I'm pulling for you sound like you are on your way to getting it fixed.

[Handy Don 12,277]

4 hours ago, Mickwhitt said:

Well I fitted the needle without drilling it.

The engine runs fine and it is so obvious that I can now adjust the fast running mixture accurately compared to the previous worn and damage needle. 

Obviously I have not run it under load so that may well expose any problems with this new needle. 

If im reading it right, fuel is allowed out of the float chamber via the emulsion tube through the gap made by the tapered needle. The fuel then enters the small hole at the bottom of the needle and up to the top where it goes to the slow running jet, entering the air inlet after the throttle butterfly.

 At higher throttle speeds the fuel is pulled out of the central holes in the needle and straight into the venturi. 

Mick

Very cool bit of business you've done there, sir!

[Mickwhitt 4,647]

I tried Fred this morning and he ran a bit lumpy at high speed, so obviously not enough fuel due to there being only two holes in the needle.

So I drilled two new holes 25 thou diameter and opened up the lower hole to 1/32nd as advised on pulling tractor site.

Immediately the difference was clear. Ticking over smoothly and instant response to opening the throttle.

I can adjust the fast jet too as I said so it seems I've made a big step forward. 

Next job is to make a new tapered tip from brass for the damaged needle and graft it on to see if I can rescue it.