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Discussion Starter · #1 ·
'92 420 with Onan P220, if after 2+ days I haven't started it, the Carb must be primed with fuel for it to start. Starting/Stopping on same day is fine/works well.
-Been happening for 6+ months
-Fuel filter has been replaced twice (it is good). However it is always empty. Even after it is running, don't see fuel in it.
-Have not ever replaced fuel pump or carb - they are original (owned it for 8 years.. this is a relatively new problem)

Just this past month, noticing the engine (remanuf 2 years ago - top grade remanuf) that when it runs it seems to be "holding back", like it doesn't purr smoothly anymore. It is still running, but does kind of a sputter (higher rpm), then quickly drops back. Could this be fuel starvation? I don't notice any power problems, mower, tiller all work well.

So - advice please, how to troubleshoot? Most likely parts needing replaced? (don't mind spending $ to replace, but would like to no most probable failures)

thank you
 

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Don't know what type pump you have, but if it is a common diaphragm-type there may be damage to or contamination on one of the "flapper" check valves in the pump, permitting drain-back. Make sure there is no fuel in the crankcase, to. If the pump will come apart easily, I'd check the diaphragm and valves in it. If it has the pulse-type pump operating from crankcase pulses, they are fairly cheap on eBay. I've already replaced the one on my wife's Kawasaki Mule, and have a spare since I expect it to go again.
 

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Fuel pump, fuel selector, cracks in lines, missing check valve in tank can cause it

I gave up and spent less than 10 dollars on a priming bulb like they use on boats, few squeezes and it starts right up
 

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1. You need to ensure your fuel supply and return lines at the fuel tank are intact. This will make the fuel supply sporadic or non-existent. If their are rubber or plastic fuel hoses here, they do decay over time.
John
 

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1. You need to ensure your fuel supply and return lines at the fuel tank are intact. This will make the fuel supply sporadic or non-existent. If their are rubber or plastic fuel hoses here, they do decay over time.
John
It might have been a typo, but there is no return line, just primary and reserve pick up lines.
 

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It might have been a typo, but there is no return line, just primary and reserve pick up lines.
KB is correct the parts are referred to as fuel pickup lines, If either line is not intact they will allow bleed off of fuel in the lines. Thanks KB,
John
 

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Discussion Starter · #7 ·
Thank you - right on the mark advise - appreciate sharing your learnings. Since I'm inspecting anyway, I'll replace the tubing from tank to carb, and replace the fuel pickup fittings in the tank. Additionally inspect and/or replace the fuel filter.
 

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Parts for the onan fuel pump are NLA, so if the fuel pump internal check valves are bad (usually are after 25 - 30 years) replacing the fuel pump is what you will have to do (3rd party - Chinese made, Non serviceable). Or get a bulb primer. (cheap but effective, I looked for external check valves but they are NA for the hose size and are very large in size (I'm still looking for something anyway). Finally electrical pump (usually has check valves inside).
 

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Discussion Starter · #9 ·
6/11 Update: All parts in, so I replaced every fuel line, the filters & fuel pump tip-to-toe all new. Primed the line, and it started up.
1) Slowly increased the throttle, and RPM followed until it got to 30% below the RPM I usually mow at, and it died (like it couldn't keep the right air/fuel mixture).
2) Pulled the fuel line to the carb, and fuel came squirting out - so nothing wrong with fuel availability.
3) Repeated 1) and same exact thing. Did it a few more times, same thing.
4) Checked the springs, rods, etc connecting to the throttle linkage, and carb, everything looks correct.
5) Watched the rod going to the carb, and when it is about to die, it is oscillating back & forth(1/2 sec forward, 1/2sec back, repeat),
like it is trying to compensate for some issue, and after 3-5 forward-back motions - the engine dies. (but if I stay below this RPM, it can runs indefinitely (minutes)

Anyone see 5) before? What is going on?
A. I'm happy to replace the whole carb (is that $199 "new" on that bidding site the way to go?, Just get the $59.99 carb rebuild kit?)
B. Little afraid to do either of those, until I have some help from this forum, to know root-cause /how to troubleshoot to root cause since it is an external rod system that is vacillating.
C. Should I shoot a video & can I post a link to youtube video - would that help?
 

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Brian,

That rod links the governor to the carburetor (the engine speed lever on the dash is not directly connected, but actuates through the governor.) With the governor "hunting" at higher RPM as you observed, it may be blockages in the high speed jet -- so in a sense it is fuel starvation inside the carburetor. If you have been using fuel with ethanol in it there may be jelly-like blobs blocking something (these are water/alcohol emulsions as the ethanol attracts and holds water...) Once you get the carburetor cleaned up, try to run gas with no ethanol in it and you will have much less maintenance. Buy the carburetor gasket kit and it is a relatively easy rebuild...the aftermarket carburetors are generally much lower quality than the one that came with your tractor. The carburetor rebuild procedure is in section 50 of the attached document:

View attachment CTM2 - small file.pdf

Chuck
 

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Here is a simple check: I'd check that your float level is not too low (adjusted on most by gentle bending of the tab that presses the float valve closed). Most need it set so it just closes when the float is level. Also make sure that when the float drops, it pulls the valve open.
 

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You replaced all the fuel lines, but did you replace the pulse line from the crankcase to the fuel pump? Many people forget about it.
 

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remove 90 at carb and you might find it clogged up with gunk
 

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Discussion Starter · #14 ·
Thank you for the suggestions, his the answers:
i) Switched to non-Ethanol exclusively 4 years ago, so there might be old build-up, but not recent on the needles, etc Checking Carb Jets great idea
ii) Did change the pulse line, when I put in remanuf engine.

1) Brought over my expert Carb friend, and we tore down & inspected the Carb. Everything was clean, and working as expected. We could still start the engine, but now with the air cleaner off - noticed the air-fuel mixture blowing up from the top of the carb, not sucking down. We were both expecting valve seat issue to be the culprit.
2) Compression on the Right Side good (80), compression on the Left Side = 0.

Boy - I wish there a way to repair a valve seat, without yanking the engine, and sending it back to the remanuf. Last time I inquired on this forum about that, being a solid aluminum head - everyone saying even if it can "kinda-be-done" it results in an unreliable seat, and probably also causes too much stress on the piston, etc.
>>If someone has had success doing a valve seat on an Onan P220, without removing the engine from the tractor - love to hear about it.

Otherwise, I'll be mowing with an LT190 I just bought (as this(318/420) era of Deere L&G's are hard to come by out west - and I needed to mow for a few months while this gets turned around).
 

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need to bore out the seat for an over sized one which requires removing the engine
 
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