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Need The Onan Boys Help..


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#1 Texas Deere and Horse OFFLINE  

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Posted October 28, 2012 - 08:33 PM

I have finished installing another B43 into one of our 318's and I can't get it to run without using 80% choke. I have rebuilt the carb and the mixture screw seems to have no effect. I have 2 other carbs. off of other B43's. One of them is the same as the carb I have mounted.

I have pictures of the 2 different carbs., they even have different bores. Can anyone tell me what the differences are? You can see the needle screws are different also

2012-10-28_16-32-26_855.jpg

2012-10-28_16-36-11_162.jpg

2012-10-28_16-32-42_664.jpg 2012-10-28_16-33-20_784.jpg

2012-10-28_16-32-48_931.jpg 2012-10-28_16-33-31_253.jpg

#2 ol' stonebreaker ONLINE  

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Posted October 28, 2012 - 09:32 PM

If it's surging w/o the choke, check to see if it's spitting gas out the carb throat while the engine is accelerating.If so try checking valve lash on the intakes. The spitting means one or both intakes aren't quite closing all the way.
Mike
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#3 Texas Deere and Horse OFFLINE  

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Posted October 28, 2012 - 09:38 PM

Thanks Mike, I will.. :thumbs:

#4 ol' stonebreaker ONLINE  

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Posted October 28, 2012 - 10:15 PM

I solved the same problem on a B&S 8 HP by feeding it lots of Marvel oil at WOTdirectly in the carb throat. The intake must have been sticking slightly because in less than a minute it smoothed out. My SIL's onan was doing the same thing and Marvel didn't fix it and I was in the middle of getting ready to move so didn't have time for it. I told her to tell the shop she took it to my diagnosis. I guess he didn't buy it. Went thru the carb and it still did it. I haven't heard any more about it. You could try the Marvel first to see if it helps. My theory is the valve and seat wears enough to lose the valve lash. Since the Onan's have adjustable tappets it could be an easy fix. I could be wrong.
Mike
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#5 Texas Deere and Horse OFFLINE  

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Posted October 28, 2012 - 10:21 PM

You could very well be right, I had a few back fires every once in a while as I was running it. The engine had set for over a year with out it being run.

#6 Farmlife OFFLINE  

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Posted October 29, 2012 - 03:50 AM

I hear alot about Marvel. I know its been around forever. The only thing I use when I must use something is the Lucas line. Ive used everything from their oil, tranny stabalizer, steering stabalizer, fuel additive.....it all actually does exactly what the product label claims and thats a very rare thing these days. I would like to learn more about Marvel tho and I don't wanna hear from the company i'd rather hear from guys that actually use it.
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#7 olcowhand ONLINE  

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Posted October 29, 2012 - 08:44 AM

I agree to check valve clearances Brian, especially since going through possible carb issues so many times already. Have you sprayed WD40 around all the intake & where it bolts up? I say use WD instead of carb cleaner because of possible fire issues with the cleaner. You could just have a vacuum leak.
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#8 ol' stonebreaker ONLINE  

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Posted October 29, 2012 - 08:50 AM

I add 20% to the oil in my vehicle engines as recommended by Marvel. I'm reluctant to add 20% to my small engines. Maybe 10% to keep from thinning the oil too much. I've only been using it for a couple of yrs, heard of it from several mechanic friends. I've also heard lots of good about Lucas products.
Mike
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#9 ducky OFFLINE  

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Posted October 29, 2012 - 08:55 AM

Also check that manifold for leaks. I have seen them separate where the two have are sealed and riveted together.
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#10 ducky OFFLINE  

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Posted October 29, 2012 - 09:07 AM

Brian here is the cross on the 149-0388 carb. Looks loke it came off of a JD 318.
http://onanparts.com...products_id=310

Can not find the other part #.
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#11 jms180 ONLINE  

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Posted October 29, 2012 - 03:35 PM

Found these Onan carbs made by NIKKI.

Attached Thumbnails

  • Untitled 3.png
  • Untitled4.png

Edited by jms180, October 29, 2012 - 03:55 PM.

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#12 olcowhand ONLINE  

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Posted October 29, 2012 - 04:28 PM

The 20hp & up had Nikki carbs.
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#13 Rock farmer OFFLINE  

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Posted October 29, 2012 - 05:13 PM

I agree to check valve clearances Brian, especially since going through possible carb issues so many times already. Have you sprayed WD40 around all the intake & where it bolts up? I say use WD instead of carb cleaner because of possible fire issues with the cleaner. You could just have a vacuum leak.

Good idea - I'd do that!

80 percent choke means your getting too much air and not enough fuel.
Could be air leaks around the carb or manifold.
Could be not enough gas getting through the carb or could be a lack of vacuum sucking the mixture through the carb. (Valves)
Or it could also be a weak spark.

The larger the displacement of the engine, the more air it pumps.
Hence the larger the carberator throttle body diameter will need to be.
Are you using the larger bore carberator? I would try the smaller one.

I hope this helps!

Joe
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#14 KennyP ONLINE  

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Posted October 29, 2012 - 05:31 PM

These Onans a notorious for leaking manifolds along the split. That would explain the need for some choke. I've been lucky so far.
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#15 Texas Deere and Horse OFFLINE  

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Posted October 29, 2012 - 10:46 PM

Found these Onan carbs made by NIKKI.


Both these are from JD's, one from a 318 and the other a 316. All 3 engines including the engine just installed are B43 engines. I have read that Onan used different carbs for different HP out of the same bore and stroke engines.

I agree to check valve clearances Brian, especially since going through possible carb issues so many times already. Have you sprayed WD40 around all the intake & where it bolts up? I say use WD instead of carb cleaner because of possible fire issues with the cleaner. You could just have a vacuum leak.


Thanks Daniel, I was worried about the flash issue when I was spraying around the carb/intake
.

Good idea - I'd do that!

80 percent choke means your getting too much air and not enough fuel.
Could be air leaks around the carb or manifold.
Could be not enough gas getting through the carb or could be a lack of vacuum sucking the mixture through the carb. (Valves)
Or it could also be a weak spark.

The larger the displacement of the engine, the more air it pumps.
Hence the larger the carberator throttle body diameter will need to be.
Are you using the larger bore carberator? I would try the smaller one.

I hope this helps!

Joe


When we where racing Karts, the bigger bore helped the engine breath and produced more HP.




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