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Discussion Starter #1
Hello Guys, My SS 18 is giving me FITS!! I had some problems with it a while back and you Guys were a huge help and I thought I had it fixed, but the problem is back again. The engine will only run with the choke partially out. It did this before and with the help of Small Fry, and several others I thought I had the problem whipped! Not the case. In the beginning I found that the intake seam was leaking. I drilled out the factory rivets, used Permetex #2 fuel resistant gasget sealer (as suggested) to repair the leak and re-assembelled the intake with small allen head bolts,lockwashers, and nuts, but since the end gasgets looked good I did not replace them. Re assembelled everything and it ran fine until about a week ago. Then the same thing again. It wouldnt run unless the choke was 1/4-1/2 out. I checked the end gasgets using carb cleaner and as I suspected they were leaking. I ordered new gasgets from Garys place and installed them yesterday and no change. Using carb cleaner I looked for leaks and can find nothing. In the first round with this thing I discovered that the condition of the factory fuel pump was questionable so rather than order the 90.00 repair kit I installed an in-line Mikuni pump and it works fine. I also disassembeled the carb, checked the float level ( and set at the recomended 1/8") cleaned all air/fuel passages, etc. And it ran fine until a week or so ago. Now the problem is back. What is the best way to check for leaks around the intake manifold, and carb? I have been using carb cleaner but have heard that an un-lit propane torch is better. I really need some help with this. I'm starting to invent new cuss words again!! Thanks in advance, Litz
 

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Cranky Motorsports
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I have been having the same issues with my two onan 16's. I know "new gas" has been cause for discussion before, however i am beginning to think it may be causing problems... Especially with the steel tanks, the gas seems to cause buildup in the carbs. In Mass we have 10% ethanol gasoline, in Cali it may be worse cause your pollution laws.. I notice lately in my SS16 with a steel tank that the gas seems to react to the steel tank (there are some pits inside so the metal is fully exposed to the gas..) and it had a crusty yellowish buildup inside the carb, and the gas was yellowy (only like 2 week old gas)
Just sunday I had to pull apart both carbs on my 16's and give them a thorough cleaning. Luckily, it can be done with the carbs on the tractors.

I found nothing inside the carbs as far as bad gaskets, or torn diaphragms, however, after cleaning the passages with brake clean and blowing air through everything, they both run fine again.
One issue I did have in my steel tank ss16 was i think i put the needle on the wrong side of the float last time, which did not allow the needle to open- the float would stay shut most of the time. Made sure it was right this time and no issues so far... I also ordered a new diaphragm as a backup.
The 16/6 had a bad plastic float in it- the plastic separated from the steel so i think the float was not working at all. Luckily i had a brass float lying around as a spare.

Funny thing is, my GT18 with the B48M has no issues with fuel ever (since i rebuilt the carb)- i even have a "big" clear fuel filter on there with no issues.
 

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Discussion Starter #3
I dont think that the gas, or fuel tank are the problem. My SS 18 has a plastic tank which I removed, and cleaned during my first round of these problems. I also replaced the fuel line, and filter so I dont think that is the problem. Also cleaned the carb, checked and adjusted the float, etc. then it ran fine until the end gasgets on the intake started leaking. I replaced them yesterday and the problem continues. I checked for leaks again and so far cant seem to find any. I am going to try using an un-lit propane torch and see if I can tetect any leaks that way. Thanks for the reply, Litz
 

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I had a bad float also where the the plastic/foam separated from the steel. You could hardly notice in less you looked real good.

Is that new pump elec ? Doesn't seem like it would run lean with a elec pump in less maybe the float is not letting enough gas threw ?
 

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Cranky Motorsports
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I had a bad float also where the the plastic/foam separated from the steel. You could hardly notice in less you looked real good.

Is that new pump elec ? Doesn't seem like it would run lean with a elec pump in less maybe the float is not letting enough gas threw ?
My 16/6 had the same issue with the float- mine was really bad though...
 

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Discussion Starter #6
Hey Small Fry, thx for the reply. The fuel pump is the pulse type, much like the original except it's an in-line pump. It's the same pump that I use on the modified Honda clone engines that I build for my race karts. I checked the pump last night and it's putting out tons of fuel so I dont think fuel delivery is the problem. I'm going out in a few minutes and check again for vacume leaks using an un-lit propane torch. I don't think I have ever had this much trouble diagnosing a problem. Thanks, Litz
 

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Any leaks found yet ? I'm wondering if a leak is even the problem. Even though the intake gaskets were leaking, after new gaskets you still have the same problem. That would make one think the leaking intakes were not really the problem., not good but not the problem ?
 

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Discussion Starter #8
Here's the latest on my problem. I checked for leaks again using both carb cleaner, and an un-lit propane torch and found nothing. I removed the top from the carb and like before I cleaned all the passages, etc. with carb cleaner. I checked the float and it looks fine and is set at factory specs. (1/8") The float is the fiber type, but it looks fine, and floats fine in a bowl of gas. I also checked for any signs of it rubbing on the sides of the float bowl and couldn't see any signs of that. I'm totally lost on this thing. It absolutely won't run without the choke at least 1/2 way out. I may be wrong, but wouldn't it have to be either a leak in the intake system, or a bad float? I'm certain that the carb is absolutely clean . I'm thinking that I should probably order a brass float even if that isnt the problem. What do the rest of You Guys think?
 

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Cranky Motorsports
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you try fattening the fuel mixture up?
 

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Could the needle and seat be sticking ? Dirty or wrong fuel filter some how maybe ? Old fuel pump not letting enough gas threw ? Did you gut the old pump ?

The new float is a good idea if you can't find any other reason for the problem.
 

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Discussion Starter #12
The needle and seat appear to be working fine and I replaced the fuel filter when I replaced the fuel line a month or 2 ago so I don't think those are the problem. I also gutted the fuel pump when I installed the Mikuni pump. Just this afternoon I disconnected the fuel line from the carb. and started the engine and it's pumping tons of fuel so I've eliminated that from my list. Like I said earlier the float looks good, and I'm sure that it is set correctly at 1/8" and as far as I can tell it doesnt seem to be touching the floatbowl anywhere. I'm going to order a brass float in the morning anyway. From what I hear most of the guys with Onans say the fiber ones are junk. I ordered the intake gasgets from Gary's and the quality was very good. I'm pretty sure that he also sells Onan floats. I'll keep you Guys posted on any progress. I'm still open to suggestions. You Guys have NO idea how much help you have been and I truly appreciate it. Thank You, Litz
 

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A long shot could be the intake valve guides are loose enough to allow air to sneak by them and lean the fuel mixture enough to cause your trouble too--an "internal" vacuum leak...usually you'll get some oil smoke or consumption if they are that loose though...
 

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Discussion Starter #14
Don't think that is the problem, the engine is in good shape. No smoke, and good comp. Thanks for the input though,Litz
 

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You've eliminated a lot of possible fuel issues. IIRC you mentioned a plastic tank. Check it again for water. I've had water problems on a weekly basis with plastic tanks and the right weather. You may have fixed the leak and you seem to be fixated on that problem when it's something else. Don't neglect heat, current gas is really prone to vaporlock. Make sure you don't have excess heat getting the fuel pump or filter hotter than it should be.

To be completely different, I've had small engines that had the similar symptoms as yours and the problem wasn't fuel. If your plugs are worn/partially fouled, wires bad(even slightly wet under the boots, or dirty), it can imitate lean mixture and the engine will like a little choke to run best.

You'll get it, and you'll wonder how you missed something so obvious after you find it, it's always obvious after you find it. :banghead3
 

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Just because the "factory" float looks good with no sign of rubbing the sides---don't make it good.Buy a brass one and let us know.I chased that rabbit for a week before I thought,I can't see what's going on with top of carb.installed --so maybe it is the foam float.Turns out once I replaced it w/brass one--Done-fixed it!!Good luck with your rabbit running!
 

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Discussion Starter #17
Back again. Here's what I have done since my last post. 1. Replaced the fiber float with a brass float. 2. Re-built carb, and fuel pump. (The fuel pump was gutted when I bought the tractor and it had a mikuni in-line pump) 3. Replaced the intake manifold (end) gasgets. A few weeks ago I drilled out the factory rivets sealed it with Permatex#2 gas resistant sealer. (Small Fry's suggestion) I then used small allen head screws, lockwashers, and nuts to replace the rivets. I have checked the seam for leaks no less than 5 times with carb cleaner and can not detect ANY change in engine rpm when spraying around the seam, and end gasgets. When I repaired the intake seam I also removed the fuel tank and thoroughly cleand it, rinsed it with fresh gas 2 times and replaced the fuel line and filter. I replaced the fuel filter again today with the small type recommended for Onan engines on Gary's website. It still won't run unless I use the choke to keep it running. (a little less than 1/3 choke) I used it for a while tonight moving some dirt with my gannon and now and then it would backfire through the exhaust. I'm goin NUTS trying to figure this out. When I installed the brass float the float setting was just a tiny, tiny bit over 1/8". I don't think that would be enough to cause this problem? Where do I go from here? I'm 99.9% sure that the fuel pump went together as it is supposed to. If I assembelled something wrong I don't think it would work at all? Like I said before the fuel pump was gutted when I bought the tractor. I pulled the plugs after I ran it tonight and they don't look the best, but I've seen worse. Maybe I should replace them like Buffboy suggested. I'm kinda gettin tired of spending money on this thing and not getting any good results. (I would sure like to see a good exploded diagram of the fuel pump) Any suggestions would sure be appreciated. Thanks for the interest Guys, Litz
 

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Cranky Motorsports
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Here are exploded views of the carb with a separate pump, the pump, and the carb with integrated pump. Dumb question... Did you verify that you have an 18hp pump instead of a 16hp pump?
Carb tech 1.JPG

Carb tech 2.JPG

Carb tech 3.JPG
 

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Discussion Starter #19
GT 80, Thanks a bunch for the reply, and especially for the fuel pump diagram. When I got the tractor the fuel pump had been gutted so I wasnt sure how it went together and I installed pump spring plate, and the pump spring on the valve side of the diaphram! It looked to me like the plastic valve was made to accept the spring. Anyway I dis-assembeled the pump and moved the spring plate, and spring to the other side of the diaphram. I havent had a chance to see if it cured the problem yet. (It's early here and I don't want to wake the neighbors up.) But I will let you know the outcome. Thanks again for the diagram, Litz
 

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Cranky Motorsports
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You're most welcome!!
 
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