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Discussion Starter #1 (Edited)
I have a 1990 316 with a P218G Onan. I am in the process of replacing the carb. I removed the 3 steel shrouds over the top of the engine and muffler. I bent a wrench that allowed me to back out the two bolts that hold the carb to the manifold. Any suggestions how to get the carb to "release" from the manifold? Do I tap it with a small mallet or pry it? It has never been off and I do not want to break the intake manifold.

Also, any suggestions how I might get the 2 bolts started when I am installing the new carb? I have read that this can be done without removing the manifold. I feel I am getting close to getting her running right again.

Thanks!

Chesapeake Bob
JD316
 

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I remove those carbs with the manifold attached, that way all the bolts you need access to are easy to get to. There's a bit of disassembly to do to get to that point but it's all easy to do, just keep track of what goes where.
 

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Discussion Starter #3
I got the carb off tonight. With the manifold still bolted to the engine, I used a mallet and a block of wood, striking the old carb from each side. After about 5 or 6 hits from each side, it came loose. I also scraped off as much of the old gasket material as possible. I attached the throttle/governor rod and clipped it to the new carb. I am hoping to get her started this weekend. I want to change the fuel filter while it's easy to get to.
 

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The intake manifold on these engines is made of 2 pieces that are held together with some rivet-like protrusions that come from one half, go through holes in the other half and are pressed into a rivet-like fastener. These fasteners don't take well to a lot of shock and the manifold can end up with a leaky joint. If you should end up with this, there are some threads on this site that will explain a couple of leaky manifold repair techniques.

Don't throw away the old carb unless it's totally destroyed, they're usually cleanable/repairable.
 

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Discussion Starter #5
Thank you for your advice Captain Pete! I was hoping not to have to repair the manifold. I did notice last night that the RH side of the manifold was loose where it bolts to the engine. I tightened those bolts as well on the LH side. I am thinking this could have been part of the problem all along, although a mechanic told me the ethanol had probably done a # on my carb. Either way, I am hoping to have her running this weekend. It has not run right in a long time but I feel there is a lot of life left in it if I can just get it to run as it used to.

Chesapeake Bob
JD316
 

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Thank you for your advice Captain Pete! I was hoping not to have to repair the manifold. I did notice last night that the RH side of the manifold was loose where it bolts to the engine. I tightened those bolts as well on the LH side. I am thinking this could have been part of the problem all along, although a mechanic told me the ethanol had probably done a # on my carb. Either way, I am hoping to have her running this weekend. It has not run right in a long time but I feel there is a lot of life left in it if I can just get it to run as it used to.

Chesapeake Bob
JD316
I've found that the manifold bolts have a tendency to vibrate loose over time, so what I end up doing is to either change the manifold-to-block gaskets and tighten the bolts (new gaskets will tend to absorb a bit of the vibration) or to throw away the old gaskets, use RTV and tighten the bolts. A drop of blue locktite will also work in a pinch.

Ethanol will leave a deposit in your carb that restricts the flow/atomization of the gasoline and will eventually cause the engine to constantly run lean, but if that's all that's wrong with the carb, it can be cleaned be taking the whole carb apart, including all the plugs on the sides of the carb (I think there are 2 or 3 of them on this one) and cleaning out all those deposits (I call it varnish only because it looks like it). Usually the jets can be cleaned and re-used and the needle valve should probably also be changed along with all the plugs that were pulled out. Mechanics don't like to do this for a couple of reasons such as lack of an ultra-sonic cleaner and the time it takes makes the cleaning fairly costly to the end-user.

Based on your name I'm making the clever assumption that you're from the Chesapeake area. I had the pleasure of enjoying that area for a couple of years (quite a few years ago) when I was working near the Pax River Naval Base.
 

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Discussion Starter #7
Weekend update and a question.

I successfully removed the carb and replaced it this weekend. At the same time, put new spark plugs in, replaced both fuel filters, and replaced the air filter and pre filter.
The secret to removing the carb without removing the intake manifold is I took a long, 12-point 1/2" box wrench and bent it to almost a 90 degree bend. This I used for the carb bolt on the RH side. The LH required short and medium length open-end wrenches.

She runs 20 times better than before. It will start in less than a second, will now idle, and I have RPM's like the old days.

My question is this: I may take apart take apart the manifold next winter. Does the exhaust and muffler have to be removed to removed to intake manifold?

Thanks!

Chesapeake Bob (along the shore of the Bay)
 

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Discussion Starter #8
That question should read... "does the exhaust and muffler need to be replaced to get to and remove the intake manifold.

Thanks in advance!
 

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For best access to that whole area including the valve covers, I'd recommend stripping off the tin, intake, and exhaust. I'll take a closer look at one of my Onan engines to see what's essential to remove but off-hand, I believe that you would need to remove the exhaust to remove the intake, but to remove the exhaust, I think you'll need to pull off the clutch - if I remember correctly, the exhaust mounting bracket is held down by the top 2 clutch mounting bolts. I'll try to confirm this sometime today and take a couple of pictures.
 

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Here's my update without pictures but if you feel you'll need them, I'll post them. I took a close look at a B43G that I have partially disassembled and see that it may be possible to remove the intake manifold without taking off anything else other than the tin. Facing the front of the tractor, the right hand exhaust pipe goes over top of the intake while the left side is in front of the intake and if you can remove the two bolts on the right side of the intake, you might have enough room to slip it under the exhaust pipe. Otherwise, my recollections are correct, you first need to remove the clutch in order to get to the upper field coil mounting plate bolts, these are allen key style machine screws. The rest of the exhaust fasteners are easy to see and remove.

An alternative that comes to mind but that I haven't tried is to remove the 2 right hand exhaust manifold bolts and disconnect that pipe from the muffler by loosening the U-bolt. You may be able to move or remove that pipe without removing any of the other exhaust fasteners.
 

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Guy's,

You have to lift the intake approximately 2" as there is a flange (one each end of the manifold) that is part of the manifold that extends downward into the engine block. Those flanges hinder moving the manifold in either lateral direction without first lifting it upward so those flanges clear the block. That makes removing the exhaust pipes necessary either in conjunction with the muffler or individually.......................Gary
 

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Many folks recommend you make the holes in the muffler mounting bracket into a "slot" so the next time someone else takes it apart they only have to loosen the bolts that mount the PTO plate.
 
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