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Discussion Starter #1
I just picked up a 1977 446 with a Onan engine in it. I am new to the Onan engines and I need a few questions answered. The engine cranks for about 10-15 seconds before it turns over. it also backfires when put under a heavy load. I also noticed today that the oil is very watered down and it smells like gas. The engine does not smoke at all and I will be going a compression test on it this weekend if I get a few minutes to myself in this crazy house.

The previos owner pulled the OEM Onan engine and replaced it with this Onan performer engine from a wheelhorse 516 H. The engine runs very smooth and quite otherwise. Would a stuck float cause fuel to seep into the crankcase or could it get in there form a stuck float AND attempting to crank the engine for over 10 seconds?
 

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Do you mean backfire as in it comes back through the air filter or backfire as in there is raw fuel going into the exhaust and burning off there. And raw fuel seeping past the rings into your crankcase?

Pull the top of the carb off to see if there is any junk in the bowl. The needle and seat may be damaged allowing all that gas to get in there
 

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I would suggest that you remove the top of the carb and check to see if you have a brass float or the composite float. If you have the latter, then it needs to be replaced because they are affected by the alcohol content in the fuel. If you have the brass float, then check it for a leak. If a small amount of fuel manages to get inside the float, then it won't work properly and flooding can take place.

Floats can also get bent and then rub the side of the float bowl. Needle and seat can stick and that will cause flooding.
 

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Discussion Starter #4
Thanks guys. I will check that carb out this weekend. I may replace a few things for good measure anyway but i will the carb apart and see which one I have. I did not use it this morning to push some overnight snow. I didnt want to ruin the bearings since the oil is so watered down
 

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An Onan Performer will be a P series Onan. It will have an ethanol resistant float in the carb and there is no brass float available.
Clean the carb, change the oil and run it.
Bob MacGregor in CT
 

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Discussion Starter #6
Thanks Bob. That is my plan as of now. Im waiting on Boomer to get back to me on suggested parts I may need to freshen the carb up.
 

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Depending on the production year of your Onan, the carb may have an accelerator pump. If the engine had been surging previously at every surge the accelerator pump squirts in extra fuel and this can contribute the fuel dilution in the lube oil. The fuel pump is located on the outside of the blower housing and it could also be another source of fuel dilution in the lube oil if the diaphram has a hole.
The reason for the accelerator pump is that to comply with stiffer emissions regs, the mixture was leaned out more and the accelerator pump was added to prevent the RPM drop which happens when the throttle is increased. All carburetored vehicles have an accelerator pump and it adds a momentary squirt of fuel to carry thru during an increase in throttle.
If you have a Nikki carb it will come apart fairly easily and you don't have to remove the accelerator pump to clean the carb. I remove the intake manifold when removing the carb and replace the intake gaskets when I reassemble. Removing the intake makes removing the carb much easier.
Bob MacGregor in CT :letitsnow:
 

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Brad.

congratulations on the Big wheel you been looking for :thumbsup: Hope you get the carb figured out. When do we get to see some pictures? :winterrules: :letitsnow: :446:
 

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brad
ditto to what bob said about the float.
brass not ava, (nikki carb, not needed)
as stated pull the top off and have a look see.
within the last two months i have had two local customers that had problems
with their nikki carbs.
in both cases someone was in there before, and had dropped the top of the carb and broken the brass tube.
keep us posted.
thank you. boomer
 

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Discussion Starter #11
I found it on CL in the RI section. I called the guy and told him I was leaving in 5 minutes to go look at it. It was a 40 minute drive. I will take a few pics of it tomorrow when its nice out.


Stay tuned for pics and more info on what I find.
 

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Discussion Starter #12
Here is a very small update and some pics. I went into the cold gagrage to get some numbers off the carb and take a closer look at this new toy. I pulled the air filter housing off and noticed that one of the plug wires wasnt on too tight. I dont know if it was misfiring because of this. I then pulled the plug wire off the other plug and the inside of it was all rusted. I will not be getting some tune up parts for this engine before I make another attempt at firing it up. I also took some numbers off the Nikki carb as well as the serial number to the engine. As soon as the wife gets home I will head outside for a better more detail look at things.

Serial number on the engine is 873287055

I/10538B
Nikki carb. numbers on it are
6100
146 0412
27-11 770











 

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Looks very similar to the Onan in mine. The fuel pump setup is a little odd.

Looks like it's in pretty good shape and even with a set of AG's on the rear.



I like how you put all the parts you took off in your seat. I do the exact same thing. :sidelaugh: :sidelaugh: :sidelaugh:
 

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Discussion Starter #14
I dont usually work on my tractor in the garage but I dont want to move it around to the backyard to get to the shed.
I have nice big shed that has all sorts of bench space so that I dont have to make one big pile of parts.
 

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I have a huge bench but it's cluttered with tools, scrap metal, rags, radio, toolbox, bench vice etc etc etc.... :lol: :lol: :lol:
 

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Looks good Brad...you are going to love those Ag's :thumbsup:

Looks like you will be going through the electrical wiring as well.. :chopwood: :letitsnow:
 

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Discussion Starter #17
The electrical issues will be dressed up in the summer time. I will also be painting it and putting the cab on it. Engine will also be decarbonized.
 

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Hi Brad,
I see by the pics that the PO didn't remove the air deflector that is a Case part but installs on the engine. You may want to find one as the cooling air flow will be directly toward you and the steering tower. This part would have been on the B43 Onan that came out and with some minor modification would have fit onto the P series engine. The exhaust heat shields which are Case parts are not there and that make for problems with the other engine parts that are close by like the fuel hose for example. The fuel pump is located in the normal spot for a P series Onan. There is a hose that connects behind the pump that is also connected to the crankcase behind the blower housing. As the engine runs, the crankcase internal pressure varies which provides the pulses to operate the fuel pump. Nice looking Goodyear Ags probably two ply, I had a pair on my Economy 1614 that I had years ago and wish I still had.
Bob MacGregor in CT :headscratcher: :mrgreen:
 

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Discussion Starter #19
I do get a lot of air blowing on my legs while operating it. I was thinking that this air may supply some sort of warm air into the cab and keep me above freezing. I may have to put a carbon monoxide detector in there though :crazy:
 

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CASE 220/4 said:
I do get a lot of air blowing on my legs while operating it. I was thinking that this air may supply some sort of warm air into the cab and keep me above freezing. I may have to put a carbon monoxide detector in there though :crazy:
For sure it can get unbearable particularly in the summer. When I repowered my 448 from a B48 to a P218 and with the P series engines running leaner mixtures I noticed the increase in the cooling air temps and exhaust pipe temps with an infrared temp sensor. Much higher temps than the B48 cooling air was and I added several deflectors and vents in the hood and a vent in the steering tower access panel. Tom Goldencove now has my 448. Tom calls it Mad Mackies Special Edition 448 as I did lots of mods to it. I also mowed commercially with it, my 4018 and my Scag Tiger Cub all three with collection systems installed. The HydraBagger went on the 448 to Tom.
Bob MacGregor in CT :winterrules:
 
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