Mighty Mac B8- Onan runs smooth- cuts out?

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1816case

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Feb 13, 2015
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I replaced the fuel line and filter. I 'think' I cleaned carb last fall..But will do so again to be sure. Can the points make it run smooth then start cutting out to the point of almost killing then straightens out? I know I never touched them. Just seems to me if was points it would run poorly all the time not surge in and out from smooth to cutting out. I also was wondering if maybe the original vacuum operated fuel pump might be going bad? I do have a electric one if needed.
 

foton

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I would suggest a total tune up,but starving for fuel is what you describing ,which could be a fuel pump or maybe the governor,and carb ,. I do not know which onan you have but from what I remember when sourcing parts for mine( 2 cylinder opposed flat 14 hp. I think a ck series?) those mechanical pump diaphrams are NLA. so electric might be the way to go just make sure you get a low pressure one, i think 3 psi is all you need, much more and you will over pressure the needle and seat and flood the engine.
 
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1816case

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Feb 13, 2015
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I would suggest a total tune up,but starving for fuel is what you describing ,which could be a fuel pump or maybe the governor,and carb ,. I do not know which onan you have but from what I remember when sourcing parts for mine( 2 cylinder opposed flat 14 hp. I think a ck series?) those mechanical pump diaphrams are NLA. so electric might be the way to go just make sure you get a low pressure one, i think 3 psi is all you need, much more and you will over pressure the needle and seat and flood the engine.
Thanks- as luck would have it..found my problem and was just going to update. it was a real loose and old fuel line from pump to carb. loose as clamp was slid down on hose and hose was all cracked. thank goodness it didn't spray fuel all over engine and start fire- i obviously didn't clean carb as I would have replaced that hose. runs and purrs smooth now. well did. shut off now nothing when turn key. new battery. I should be able to trace that. starter has been clunking so maybe..
 

haymaker

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Mar 14, 2023
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I had that happen on my Bobcat 542B yesterday.
Several taps with a hammer on the starter and it cranked again.
I think I have a bad spot on the starter. Time to get it off and take a look to see if I need to replace it.
Maybe you could try the old hammer trick on yours.
GL
 

2bobcats

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Jan 27, 2018
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I have done the hammer trick I would get the starter off soon as the more you tap on it the more damage is done internally so repair would not be possible.
 
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1816case

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I will get to it when can. I had also bought a new 'smaller' battery due to the tight space. it has just 520 cca.. where as the bigger one had like 800cca. If I jump the new battery- it cranks over and starts.. But nothing if I don't jump other than a 'click'. Its only a 20 something hp onan- even a small car battery should crank it over shouldn't it? They can crank over a 4 or 6 cylinder car engine? Maybe my starter since does knock sometimes is having lot more draw than normal?
 

foton

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I would think a 500 amp battery will do the trick if all else is in good shape,but it is very possible that your starter is on its way out drawing more amps than it normally should.
 

mrbb

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Jul 19, 2016
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have you ruled out vapor lock,( I am assuming this is a gas motor machine??, could be wrong though) for the running issue?
warmer weather now, and it can happen!, machines working in dusty environments, vents can get plugged up over time, or even seen spiders build webs in caps blocking vents!, never hurts to check simple things and rule them out!
when issue acts up, just pull fuel cap off and see if it changes anything!


as for the battery size,
have you checked voltage readings at starter
as over time wires get corroded , grounds go bad, and that can alter voltage flow to things and cause, both your clicking and starter issue's

,so might be worth checking voltage at starter to see if your actually getting good power to it! as well as inspecting , connections, grounds and wires themselves! making sure all are good, clean and corrosion free!
 

foton

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well is they are nla from onan if you can find one anything just about (after market) is better than nothing. I know that starter and alternator repair shops are getting harder to find in my area, people just buy new which screws people who have old stuff that is no longer made and has to be fixed. If you have acess to a battery load tester use it at the starter, it will tell you if you have a corrosion wiring isssue. (resistance fault).
 

mrbb

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555
you might also have a starter relay/or solenoid in /near your fuse box that could be bad, or again corrosion issue, causing your problem with starter, many times this goes before the actual starter itself!
 

haymaker

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Mar 14, 2023
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I have had to change out my starter relay on my 542B twice in 30 years.
Most frequently in a situation where I get nothing or just a click it is a bad ground or corroded connection.
Good luck.
 
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1816case

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Feb 13, 2015
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update: was a bad battery clamp. it had a crack in it and no matter how tight the bolt was it would get loose. poor connection. fixed that.. and that bad fuel line from fuel pump to carb replaced... runs amazing smooth now. starts immediately touch little guy. Used it yesterday to pull a fairly large fallen tree rest of the way over so I could get at it with saw. still need more experiece to get use to 'T' control... wish it was the 2 hand levers like bob cat.
 

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