Home » Public Forums » GMCnet » Onan runs like hell
| Onan runs like hell [message #276416] |
Tue, 21 April 2015 18:08  |
 |
ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
|
Senior Member |
|
|
Well I've installed my Pertronix module (home made bracket - not the fancy kit) and replaced the carburetor, plugs, coil, and wires but the old troll runs awful. Sometimes if I twist the main jet on the carb she smooths right out and then back to running poorly again - the wiggle shuffle. I'm beginning to hope it's just carbon build up - here's why:
When I initially installed the Pertronix I set the timing rather advanced. It ran well, but still stammered and was rough. I moved the sensor down to about 26 degrees. Still ran poorly.
I bought a carb rebuild kit (I don't know why) and once I put it back together she wouldn't start. (I'm certain I gave up too soon on the rebuild...) I bought the rebuilt carb from Nick at Advanced GMC and put it on, but the screw for the main jet was toward the block and not accessible. Still it started and ran okay. I twisted in the idle screw and it ran a little better, not great.
After installing the new Air Conditioner I let the Onan run for about an hour until I heard it clank and rattle and cough. In a panic I ran to the coach and shut off the old beast.
Today I took the carb off, loosened the bowl and positioned the main jet outward, put it all back together and started it up. Running poorly I adjusted the screws to what the manual recommends. No help. Twisted the main jet in all the way - she ran beautifully for 20 seconds and then stammer and shake.
I have never, ever, ever, met a carburetor that liked me, but I don't think it's the issue. It runs, so I have fuel and I have spark. All the twisting and fiddling with the carb makes no substantial improvement.
I'm at a loss. Valve adjustment? Burnt valve from too-lean carb? Decarbonize the cylinder heads?
I had thought to do a compression check but could not find my gauge set. Any suggestions would be appreciated.
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
|
|
|
|
|
|
|
|
|
|
| Re: [GMCnet] Onan runs like hell [message #276426 is a reply to message #276416] |
Tue, 21 April 2015 19:16  |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
|
Senior Member |
|
|
> On Apr 21, 2015, at 7:08 PM, Larry Davick wrote:
>
> Well I've installed my Pertronix module (home made bracket - not the fancy kit) and replaced the carburetor, plugs, coil, and wires but the old troll
> runs awful. Sometimes if I twist the main jet on the carb she smooths right out and then back to running poorly again - the wiggle shuffle. I'm
> beginning to hope it's just carbon build up - here's why: […]
I do not think you should chase a fuel problem until you have ruled out the most recent major change you made - installation of the Pertronix - as being a cause of the misbehavior.
How does it act if you go back to the breaker point system temporarily?
How about setting the pertronix timing to be the recommended factory amount (timing mark in the little window in the blower housing)?
Have you used a spark tester inline with one of the plugs to see if the spark is consistent?
My experience with Pertronixes is that they are _incredibly_ sensitive to a) how close they are to the flywheel magnet and b) the orientation of the face of the pertronix to the magnet. You might very well have a irregular firing signal from the pertronix which would be observable with a spark tester.
My flight instructor always told me that if you make a change and things start going bad - undo the change and then re-evaluate the situation.
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
|
|
|
|
| Re: Onan runs like hell [message #276436 is a reply to message #276416] |
Tue, 21 April 2015 22:51 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
Pull the heads and decarbonize them. Also gently clean the carbon off of the valves and piston tops. It is about a 1/2 to 3/4 hour job. If you have access to a bead blaster, then bead blast the heads. Otherwise, use a brass brush on a Dremmel tool. I went through what you are going through about 10 years ago. Decarbonizing made all the difference in the world.
I'm gong to agree and disagree with Jim Miller. Magnet polarity does make a difference. Gap on the magnet pick up is not critical. I have mine mounted with a very large gap. Something like 1/8 inch (.125") and it starts and runs just fine. I'm not suggesting that you make yours that large. I was doing some testing one time and just left it there after I finished.
What do you have the spark plug gap set to? I hope you realize that the two plugs are wired in series. So a wide gap one one or a single open wire will cause BOTH plugs for fail to fire simultaneously.
I have my timing set to 26 BTDC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: Onan runs like hell [message #276442 is a reply to message #276416] |
Wed, 22 April 2015 01:15 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
|
Senior Member |
|
|
ljdavick wrote on Tue, 21 April 2015 16:08
After installing the new Air Conditioner I let the Onan run for about an hour until I heard it clank and rattle and cough. In a panic I ran to the coach and shut off the old beast.
Decarbonize the cylinder heads?.
I would not bother with decarbonizing. It ran for an hour. It runs ok for short Times. Carbon is not building and going away.
When an engine won't run it is spark or fuel. Other major problems like valves, rings and carbon are not intermittent. It is not the advance because it is intermittent; it is not kicking back during starting. I suppose if it was too retarded it could have gotten too hot after the hour, but I am guessing not. It would get hot way faster than that.
I am thinking it is not the new carb. Is it getting steady fuel from the pump and tanks? Suggestions about returning to points will eliminate the new petronix. I like that suggestion as eliminating recent changes.
Put a timing light in it to see if the spark is steady..
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
|
|
|
|
| Re: [GMCnet] Onan runs like hell [message #276446 is a reply to message #276436] |
Wed, 22 April 2015 04:51 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
|
Senior Member |
|
|
On Apr 21, 2015, at 11:51 PM, Ken Burton wrote:
>
> I'm gong to agree and disagree with Jim Miller. Magnet polarity does make a difference. Gap on the magnet pick up is not critical.
Ken, when I put the Pertronix on my personal Onan I found the spacing to be very touchy. I had already tested the magnet orientation by swiping it in front of the pertronix while watching the spark. I had to set the spacing at about .040” in order to get reliable ignition; anything wider would result in either flaky ignition or no spark whatsoever. Frankly I was rather uncomfortable with how close it had to run to the flywheel and I ended up building a beefy aluminum bracket to eliminate the chance of it crashing during operation.
I think the original poster should rule out ignition problems first and fuel problems second..and only then move on to more involved activities. By installing the Pertronix he made a drastic change to a critical engine system and that change must be ruled out as the source of the problem before moving on in the troubleshooting procedure.
73 N8ECI
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
|
|
|
|
| Re: [GMCnet] Onan runs like hell [message #276466 is a reply to message #276446] |
Wed, 22 April 2015 12:19 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
I had one crash into the flywheel because the bolts loosened up over time. So when I installed the new one, I played with it to see how wide it would go and still work. I got it up to about .150" before it failed. I already had some holes drilled at about the .120" point so I just pop riveted it in place at that point.
That was my experience. What can I say.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: [GMCnet] Onan runs like hell [message #276468 is a reply to message #276466] |
Wed, 22 April 2015 12:38 |
|
ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
|
Senior Member |
|
|
The timing light is remarkably steady with the Pertronix and not so steady with the points. Keep in mind that this is off of one plug wire. I did change the plugs and even though I “think” I checked the gap these are the remarkably expensive plugs from Applied GMC and had a tip made from an alloy of gold, platinum, titanium, and unobtainium, I think. If the gap were different then the rough running could be to blame.
Also when I put the new wires in they were slightly thicker than the old ones and I really had to force one wire onto the hold down clip. I took a chance and touched that clip while it was running to see if I felt a spark indicating that I had pierced the wire, and did not.
A question - isn’t it true that a spark will jump a gap in the presence of fuel much more readily than it will in the presence of hot exhaust gas?
I am certain to regret these words soon, but, I’m inclined to pull the head and decarbonize them. What could go wrong?
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
|
|
|
|
|
|
|
|
| Re: Onan runs like hell [message #276478 is a reply to message #276416] |
Wed, 22 April 2015 15:11 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
|
Senior Member |
|
|
""I have never, ever, ever, met a carburetor that liked me, but I don't think it's the issue. It runs, so I have fuel and I have spark. All the twisting and fiddling with the carb makes no substantial improvement.
I'm at a loss. Valve adjustment? Burnt valve from too-lean carb? Decarbonize the cylinder heads?
I had thought to do a compression check but could not find my gauge set. Any suggestions would be appreciated.
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca ""
I'd be suspicious of the low oil pressure switch and or wiring. Worst case could be low oil pressure.
Bob de Kruyff
78 Eleganza
Chandler, AZ
|
|
|
|
|
|
|
|
| Re: Onan runs like hell [message #276492 is a reply to message #276416] |
Wed, 22 April 2015 18:12 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
Karma: 3
|
Senior Member |
|
|
Hey, Larry,
Of course I am an "expert" on the Onan just because I found a cracked fuel line and got it to stop leaking by replacing it. PO had neglected this piece of line, I think it was an R5 and just about split in two. Your Onan is running better than mine. I can crank it only, but it does crank fast! Other fish to fry.
But, I am just wondering if you don't have a situation where it is either starting to suck air through a bad rubber fuel line, or, and I have been lazy for not making sure of your coach's particulars, do you have a GM coach and have the famous 1/4 tank sucking air situation, where the intake is 3/4 of the way down the tank so you could drive to the gas station to refill, and you have used the gas running the Onan down to that level?
I think that they should run "sweet" after the Pertronix installation. Usually after just a few minutes of running some flatheads will stop running due to improperly torqued head bolts, but an hour is too long for that to come about. They get hot and leak.
Is that automatic choke working correctly, it might be closing down on you, hence the better running with the main jet all the way closed.
Note all this advice comes from someone who has not succeeded in making his run properly!
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
|
|
|
|
|
|
|
|
|
|
| Re: [GMCnet] Onan runs like hell [message #276514 is a reply to message #276508] |
Thu, 23 April 2015 08:40 |
 |
thesmith
Messages: 589
Registered: February 2015
Location: Cary, NC
Karma: 6
|
Senior Member |
|
|
Am I correct in thinking that they do not make the honda generators for RV anymore.....if so does anyone make a modern version of the Onan that would fit a 26" coach?
Could one rebuild one of Honda standard generators to fit? (take fuel tank off, add exhaust extention etc)
Pete
jhb1 wrote on Thu, 23 April 2015 03:12ljdavick wrote on Wed, 22 April 2015 16:42Quitter! I won't even think of replacing the troll until I've spent far too much money and aggravation on it. Beating my head onto brick walls seems to salve the pain of stupid persistence.
Larry Davick
> On Apr 22, 2015, at 11:53 AM, jhb1 wrote:
>
> Had the same problem gave up on the Troll installed an EV 4010 Honda. Problems solved 
> --
> John H. Bell
> 77 Royale
> Montreal Qc.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
I went thru all the same stuff over a 8 year period new carb de carbon petronix JimB looking at among others best I ever got out of it was 2 hours running without dying from something. So I figured my head was flat enuff from banging it on the wall, out with the troll best upgrade I have done.. And I have Mannys one ton JimBs quad bag and Fuel injection and the Honda is my best upgrade
Cary, NC
1978 Center Kitchen Royale.
|
|
|
|
Goto Forum:
Current Time: Thu Sep 19 17:41:54 CDT 2024
Total time taken to generate the page: 0.04181 seconds
|
GMCforum
Search
Help
Register
Login
Home
