Jump to content

Nominations for Tractor of the Month
Garden Tractors and Parts on eBay



Photo
- - - - -

Case 448 -- Can't get to run right... no matter what I try!


  • Please log in to reply
52 replies to this topic

#16 KennyP ONLINE  

KennyP

    FORDoholic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2253
  • 28,482 Thanks
  • 39,716 posts
  • Location: Collinsville, Oklahoma

Posted November 25, 2015 - 05:37 PM

Could be wires as indicated. I'm only familiar with the single cylinder kohler models. Does the twin onan have two coils? If so it could be the coil or condenser (if yours has one) on the failing side. Coils and condensers sometimes only begin acting up once they warm up or are put in higher throttle as they near full failure.

Also...can you elaborate on the air gap? Was the needle not seated properly or did you mean the carb was not mounted tight enough against the motor and was drawing air in that way?

Most Onan's have one coil that fires every revolution so it catches both sides. If it's not firing on one side, I would look at that plug/wire.



#17 gopher OFFLINE  

gopher

    New Member

  • Senior Member
  • Member No: 2755
  • 569 Thanks
  • 631 posts

Posted November 25, 2015 - 06:10 PM

You can switch wires around on coil to see if problem moves to other cylinder. If not you might have a intake valve hanging up causing the backfires through carb. Another reason for bf in carb. is carbon buildup but you did valve job so that's not it. Only other thing for bf through carb is ignition advanced to much at .021 Onans usually run good.  



#18 Case448 OFFLINE  

Case448
  • Member
  • Member No: 68323
  • 13 Thanks
  • 33 posts
  • Location: Michigan, USA

Posted November 27, 2015 - 03:37 PM

The air gap was between the upper carb and lower carb (where the gasket is). I had a high spot on the carb body, so the gasket was not sealing. This gap was at the same level as the high speed jet in the carb throat. So the vacuum in the carb throat was drawing air through the gap and from within the float cavity, which was replenished by the air hole into that cavity at the top of the carb, RATHER THAN drawing gas through the high speed jet as it was supposed to, because air is easier to move than gas (it will move the one with least reistance to being moved.)

 

I noticed this potential problem after taking the carb apart, and noticing the lack of an impression in the gasket at the center, around the throat portion of the carb, while the impression around the outside (at the bowls edge) was pronounced. Sanded top and base of carb on plate of glass with fine sand paper, cleaned up well, problem seems to be solved.

 

Hope that makes sense.

 

Dave


Edited by Case448, November 27, 2015 - 03:47 PM.


#19 Case448 OFFLINE  

Case448
  • Member
  • Member No: 68323
  • 13 Thanks
  • 33 posts
  • Location: Michigan, USA

Posted November 27, 2015 - 03:42 PM

UPDATE TO PROBLEM #2:

 

Motor starting VERY hard. Barely wants to run. Occasional backfiring through carb and exhaust, but not starting. Whatever this "ignition" problem is, it's getting worse by the day.

 

Pulled both plugs and turned over with plugs laying on top of motor, to observe spark (or lack thereof), and type of spark (if any).

 

Spark intermittent and weak both sides. Sometimes comes and goes completely, but if spark is there, it is always weak looking and intermittent.

 

Not sure if coil or plug wires could cause this? They are the only (2) major ignition parts I have not replaced.

 

Also, do these  motors  fire every other revolution when the cylinder actually needs to fire, or does each plug fire on every revolution?


Edited by Case448, November 27, 2015 - 03:49 PM.


#20 gopher OFFLINE  

gopher

    New Member

  • Senior Member
  • Member No: 2755
  • 569 Thanks
  • 631 posts

Posted November 27, 2015 - 05:45 PM

They both fire same time. You can test the coil with ohm meter. You can find that test in the Onan service manual in the manual section here.


Edited by gopher, November 27, 2015 - 05:56 PM.


#21 olcowhand ONLINE  

olcowhand

    Red Tractor Nut & Diesel Addict

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Sponsor
  • Contributor
  • Member No: 20
  • 35,650 Thanks
  • 29,840 posts
  • Location: South Central Kentucky

Posted November 27, 2015 - 05:51 PM

 

Also, do these  motors  fire every other revolution when the cylinder actually needs to fire, or does each plug fire on every revolution?

 

Your engine (points based) fires every other round, both plugs at the same time.  But the later electronic ignition models fire every revolution, so they do have a waste spark.



#22 KennyP ONLINE  

KennyP

    FORDoholic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2253
  • 28,482 Thanks
  • 39,716 posts
  • Location: Collinsville, Oklahoma

Posted November 27, 2015 - 06:12 PM

Your engine (points based) fires every other round, both plugs at the same time.  But the later electronic ignition models fire every revolution, so they do have a waste spark.

An Onan fires every revolution, Daniel! That's why there is only one coil!



#23 Case448 OFFLINE  

Case448
  • Member
  • Member No: 68323
  • 13 Thanks
  • 33 posts
  • Location: Michigan, USA

Posted November 27, 2015 - 06:16 PM

RESTATING ---

UPDATE TO PROBLEM #2:

 

Motor starting VERY hard. Barely wants to run. Occasional backfiring through carb and exhaust, but not starting. Whatever this "ignition" problem is, it's getting worse by the day.

 

Pulled both plugs and turned over with plugs laying on top of motor, to observe spark (or lack thereof), and type of spark (if any).

 

Spark intermittent and weak both sides. Sometimes comes and goes completely, but if spark is there, it is always weak looking and intermittent.

 

Could coil or plug wires could cause this? They are the only (2) major ignition parts I have not replaced.

Or, any other ideas?



#24 KennyP ONLINE  

KennyP

    FORDoholic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2253
  • 28,482 Thanks
  • 39,716 posts
  • Location: Collinsville, Oklahoma

Posted November 27, 2015 - 06:37 PM

You have new points and condenser? Which Onan is this?



#25 olcowhand ONLINE  

olcowhand

    Red Tractor Nut & Diesel Addict

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Sponsor
  • Contributor
  • Member No: 20
  • 35,650 Thanks
  • 29,840 posts
  • Location: South Central Kentucky

Posted November 27, 2015 - 06:48 PM

An Onan fires every revolution, Daniel! That's why there is only one coil!

No, both pistons fire at the same, both on compression stroke at the same time.  Only one points lobe on the camshaft, so spark only every other revolution.  Now the electronic versions trigger off the crank, so they do have a spark every revolution, one being waste spark.

  As to your issue Case448, to me it sounds like the coil itself is dying.  My Onan I'm putting into my Caddigger did the same as yours a few years back.  I tried everything including new spark plug wires, but ended up getting a new coil & it ended my problem.  My spark was also very weak and intermittent.


  • KennyP said thank you

#26 Case448 OFFLINE  

Case448
  • Member
  • Member No: 68323
  • 13 Thanks
  • 33 posts
  • Location: Michigan, USA

Posted November 27, 2015 - 07:03 PM

You have new points and condenser? Which Onan is this?

 

Yes, new points and new condenser about two weeks ago.

 

Onan B48M


  • KennyP said thank you

#27 propane1 ONLINE  

propane1
  • Senior Member
  • Member No: 54307
  • 6,111 Thanks
  • 3,205 posts
  • Location: Charlottetown, Prince Edward Island, Canada

Posted November 27, 2015 - 07:30 PM

Could the coil be wired backwards, I mean the plus and minus wires going to the coil. Noel

#28 tater195 OFFLINE  

tater195

    I dont deny your history..... dont deny mine

  • Senior Member
  • Member No: 62468
  • 1,317 Thanks
  • 937 posts

Posted November 27, 2015 - 08:26 PM

I did some speed reading from post #10 -23, so this is my $.02, sorry if it was already covered and I missed it, go back to the basics.. backfire through the carb is: 1. early spark 2. carb flooding 3. intake valve not closing or 4. exhaust valve not opening.

 

A timing light would rule out #1, low fuel level would rule out #2. #3 could be related to the valve job, #4 would be the cam or bent valve stem



#29 KennyP ONLINE  

KennyP

    FORDoholic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2253
  • 28,482 Thanks
  • 39,716 posts
  • Location: Collinsville, Oklahoma

Posted November 28, 2015 - 06:30 AM

Yes, new points and new condenser about two weeks ago.

 

Onan B48M

The B48M Service Manual has an ohm meter test for the coil. It's on page 23.



#30 olcowhand ONLINE  

olcowhand

    Red Tractor Nut & Diesel Addict

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Sponsor
  • Contributor
  • Member No: 20
  • 35,650 Thanks
  • 29,840 posts
  • Location: South Central Kentucky

Posted November 28, 2015 - 08:05 AM

My apologies everyone, as I must have had my worst ever brain fart yesterday regarding the Onan.  Yes, it both points & pointless models spark every round, with one piston on compression one round, the other the next.  In my defense, I had to take a pain pill yesterday for my neck, so I guess it affected my thinking, plus it's been years since being into an Onan.  I'll go hide in my corner now.






Top