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Re: What makes a gas engine run rich

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03-02-2001 18:58:59

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If you would give a bit more information on what you've tried so far that hasn't worked, your chances of getting useful feedback would go up considerably.

What plugs are you using now, and which have you tried in the past? Have you removed a plug and looked at the spark to see if it's weak?

Have you tried to operate it without the air cleaner hose attached? Is the choke plate operating properly; especially, is it opening all the way? Does the air intake to the carb. look wet. If so, under what conditions? Does the tractor appear to operate differently with the air cleaner connected (if so, it may be partially plugged - not a bad idea to pull it off, fill it with kerosene or diesel to clean its screen, and drain it good before reinstalling it in any case - supposed to be done periodically, but probably hasn't been since the tractor was new).

How far off their respective seats are your adjustment screws on the carb. set? Have you REALLY tried to move these as close to closed as the tractor will tolerate and still run? These control the fuel/air ratio, and are the most "obvious" source of too rich a mixture.

Have you looked for leakage around the intake manifold? Unlikely, but a leak here could necessitate overly rich adjustment at the carb. and result in fouling at the plugs.

Have you checked the timing and the valve lash lately?

Might be most anything on this list, which hopefully is helpful - let us know how you make out.

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03-02-2001 21:52:45

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 Re: Re: What makes a gas engine run rich in reply to dick, 03-02-2001 18:58:59  
I certainly appreciate the feedback. Your list of possibilities sparked a few new ideas. Here is a list of what I have done so far.
-Had carb overhauled and flow tested twice.
-Checked the float level in carb with external hose while tractor was running. Found to be OK.
-Changed out the fuel pump and checked fuel pressure.
-Put in hotter plugs. Running D21's currently.
-Replaced the coil, condenser, points, distributor cap, plug wires, and coil wire.
-Set the timing and checked centrifugal advance.
-Ran carb without air intake hooked up and also checked air intake and filter replaced.
-Went from unleaded regular fuel to super premium unleaded fuel.
-Cleaned fuel line, filter and bowl.
-Disconnected and blew out fuel line with compressed air.
-Checked compression on engine. Found to average about 160 + or - about 8 lbs.
-Put in a lead additive to a tank of fuel and tried that.
May have forgotten some items. If it is of any help, the tractor runs richest at slow idle, and will almost choke you with fumes from unburned gas. When the tractor is run hard with a load, it seems to do better. Has plenty power and doesn't miss. But, when plugs start to foul out, the miss returns. Solution, pull the plugs, sandblast them or replace them, and problem goes away for a little while. But, I haven't really checked to see how "strong" the spark is, and the intake manifold could be a problem I guess. I have sprayed around the manifold with WD-40 to see if I could detect any change in engine sound, but nothing happened. Again, thanks for the list you provided me. Any thoughts are appreciated.

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03-04-2001 21:39:42

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 Re: Re: Re: What makes a gas engine run rich in reply to Gene, 03-02-2001 21:52:45  
Gene, I have had a simular problen, tried everything. After reading the RE's: to your question, I checked the choke butterfly, and found it only partially opened. The stop on the choke would not let it open to the full open position. The plate behind the choke arm that the stop is on, has several positions that can be changed by removing one screw. I removed the screw and rotated the stop so the butterfly is in the full open position. Time will tell, but I think I have helped things considerbly. I have eliminated the black smoke completely, and the engine runs smoother.

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03-04-2001 21:51:57

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 Re: Re: Re: Re: What makes a gas engine run rich in reply to ed, 03-04-2001 21:39:42  
just wanted to be on the two week follow up messages, in regards to Genes rich running engine problems.

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03-03-2001 10:41:34

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 Re: Re: Re: What makes a gas engine run rich in reply to Gene, 03-02-2001 21:52:45  
Sounds as if you've done about everything but whatever it is that's required to fix the problem.

In your comments below, you indicate that your carb. doesn't seem to have a main fuel adjustment, just an anti-dieseling solenoid. Too much fuel flow has got to be your prime suspect since you're getting black smoke, strong gas smell, etc. There has to be some sort of restriction on the incoming fuel other than the solenoid valve. Most IH carburetors have a main screw - do you have an operator's manual for this tractor? If so, it should have a section about adjusting the carb. If not, buying a manual would surely seem like a low-cost option to all of the other things that you've done. Chances are about 99 percent plus that your problem is in your fuel supply control somewhere.

At this point, I'd suggest you again try operating for a while without the air cleaner hooked up to the carb. - too little air flow through it is about the only thing other than fuel supply control which would cause the severity of the problems which you describe. If the problems don't magically go away without the air cleaner hooked up, the problem is almost certainly in the fuel supply control.

Good luck, and let us know how you progress.

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03-03-2001 13:23:58

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 Re: Re: Re: Re: What makes a gas engine run rich in reply to dick, 03-03-2001 10:41:34  
Hi Gene, If it's a new tractor to you, check to see what size the main jet is. Someone may have chaged orfice size to larger one than needed.

The float needs to be cut down on fuel. Reclean the carb and readjust the float to a smaller than factory spec. When you reclean the air passages, use Berryman B-12, use a small copper wire to run into the passages. A strand from multi-strand copper wire works well. If any improvement then keep tearing down the carb until clean. I did mine three times and each time I swore it was clean the time before.


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03-03-2001 14:41:18

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 Re: Re: Re: Re: Re: What makes a gas engine run rich in reply to T_Bone, 03-03-2001 13:23:58  
t bone and dick:

Thanks for the help and ideas. I have a manual for that tractor (just operators manual), and it states how to adjust the idle adjusting screw. But, the fuel shut off solenoid "permits full fuel flow through the main jet when energized". The "full fuel flow is stopped when the solenoid is de-energized". And that is it as far as adjustments to the carb is concerned. Now, the main jet, that is part of the solenoid does have two different size orifices listed in the parts manual. And you are right in that it may be the wrong size orifice. I will order the one that is supposed to work for this carb on Monday and see if it is the same size. I bought this tractor when it was hardly used at all, and it ran fine for the first few years. It is possible that someone could have changed jets on the solenoid when I had the carb worked on years ago. I will change the float level to allow less fuel in the reservoir as you suggested. There is one peculiarity that I haven't mentioned. This tractor does have a fuel pump. (I changed it too!). When the tractor is shut down after using it, everything is fine. When I go back several hours later, there is a tiny bit of fuel seeping from the air intake side of the carb. This continues to seep when the tractor is not being used. When I start the tractor up and start using it, this fuel seep dries up after a few minutes of operation. Not sure what thatt indicates, but thought I would mention it. I thought that the housing might be cracked on the carb, but if it is, it is invisible to the naked eye. Anyway, if persistence pays, I should find it someday. Thanks for your help !!!!

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03-04-2001 07:53:01

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 Re: Re: Re: Re: Re: Re: What makes a gas engine run rich in reply to Gene, 03-03-2001 14:41:18  
A fuel leak into the air inlet when the tractor isn't running usually indicates the float level is set too high. Since the float isn't shutting off the fuel intake to the carb. properly, you tend to get too much gas into the engine.

This may be a good bit of your problem. Try setting the float so the level in the bowl is lower.

Good luck, and let us know how you progress. If you still have the strong gas smell, be careful what you're doing so you don't end up with a fire.

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03-04-2001 15:07:33

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 Re: Re: Re: Re: Re: Re: Re: What makes a gas engine run rich in reply to dick, 03-04-2001 07:53:01  
Thanks for the feedback again. Will try to lower float level and will order (reorder) the orifice for that main fuel jet. Will let you all know what the problem was when it is solved. Thanks again.

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Paul Vance

03-03-2001 19:19:24

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 Re: Re: Re: Re: Re: Re: What makes a gas engine run rich in reply to Gene, 03-03-2001 14:41:18  
Gene, on monday, order the proper main jet. On sunday, check your fuel pressure!! If you have WAY! too much pressure gas will leak from the carb while the tractor is running(poorly). If you have just a little too much pressure, fuel will be pushed passed your needle valve and fill up your bowl, the extra gas will be sucked into your intake, causing a slight rich condition(tractor still runs decent). Did you check float level with tractor running? Even if you did, check pressure.
Also, what is your altitude? I live at 7000ft atmosphere psi is avg. 11.6 roughly 20% less o2 than at sea level. Any carboureted engine that is brought here from sea level will run exactly as you describe yours running until you decrease mainjet size by one quarter. This may not apply to you but I see it very often here. (Santa fe NM.) Let us know your results> Paul Vance

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