Onan gas generator starting problems

[Beckytek]

Ever since I've owned this boat my generator has given me problems starting. I had the carb off a couple of times to adjust the float and general cleaning, investigating. I must have adjusted the choke 50 times. Every time I think it's fixed, the next time it won't start. Once it starts it runs great with constant speed under heavy and light load.
This morning I started it right up and ran it under load for 1 hour. As I'm getting ready to leave I try it again and no go. Some days it works fine but I can never count on it. I can always get it to start if I remove the top of the carb and move the choke to different positions.
Any suggestions on what could be wrong?

 

[roundIII]

Probably the choke needs replacing. This is an electric choke that is designed to stay "hot" all the time. Hot enough to burn your fingers. If the choke is not hot then this could be the problem. Check the wiring and fuses first before buying the choke.

If everything else is working correctly as you describe give this a try. I think the part is $75 from Onan.

These generators are very susceptable to air leaks in the fuel lines affecting performance. Make sure that all connections are tight to filters and everywhere that you can see. Even if there is no visible leaks or odors there may still be air being sucked thru.

RR

 

[67hat34c]

Lots can be wrong.

MCCK fuel pump gets tired, would replace fuel pump. I got exact replacement from auto parts store, Had to look through the bins but found the pump.

also the fuel line can be no bigger than .25 ID. Pump gets old and a little warn and it can not pull from larger hoze, whats easier sucking water through a .25 straw or a 1" pvc pipe.

Carb float well thats a crap shoot on these things. its high enough when no gas leaks out when its turned off. but if too low then it will hunt.

If i remember the choke is either 3/16 or .25 gap between flat part of the butterfly and the body.

Yes do replace the choke, worth it.

How is the carbon build up on piston head and cylinder head, had them off lately?

One thing to consider is that the engine gets a little hotter when you shut it down, no water flowing so could be something to do with a thermal switch as well. You can isolat them as well.

as always do not look at just one thing or the obvious, check everything, why not change plugs , oil, check or replace the sensors , flush cooling system etc etc. make everthing new thats easy to do then you dont have to fuss with it again for a while.

 

[Maynard Rupp]

When it won't start...Is it getting a spark? Remember both cylinders on these stupid things fire at then same time so don't worry about firing order. Remove a plug and ground it. Turn the engine over and watch the plug for a spark. Someone here mentioned the exhaust overheat sensor. I think if it thinks the exhaust is too hot, or maybe the water going into the exhaust. I am not sure and my manual is on our boat. I am 1200 miles from the boat. That sensor is on top near the exhaust outlet. It has a wire going from it. I am sure that it should have no continuity until it trips from overheat. Just use an ohmmeter and see if it is open. If it has continuity, I am sure it grounds your ignition and the engine won't run. Remember the rule....Fuel and fire. Check for both as an engine that won't even start is lacking one or the other.

 

[Beckytek]

Thanks for all the trouble shooting tips guys. Looks like I have my work cut out for me. Maynard, I don't know if I thanked you before but am doing so now for your direction on how to time the genny. I followed your suggestions and it worked great. Ron

 

[67hat34c]

points points points

open breaker box and while cranking look at points, open and close as they should? is there an unusual glow around them. if there is a glow when firing then they are burnt and condensor is toast. an old timer pointed this out to me when i was turning mine over with breaker box open.

 

[Beckytek]

Worked on the genny this week. Changed antifreeze, changed oil, installed all new water hoses, installed a new spring in choke assembly. Checked the points, and plugs, tightened belt, adjusted choke opening 3/8 " as per manual. The heater element is hot and working. Hit the starter and it started right up and ran for an hour, then I shut it down. After about 3 hours, I tried again and no go. I didn't check the exhaust switch for continuity, I forgot my meter. Next time at the boat I'll check it. Looks like a likely suspect. Ron

 

[67hat34c]

Fuel pump. Take it off and go to auto parts store, they will have the exact same Facet pump but it doesnt say onan and it doesnt have the price. it should be about 35.00

 

[Beckytek]

Took the boat out for a 3 hour cruise today. The genny started right up and ran for most of the day. By the time I got back to the slip the genny wasn't running. I tried but it wouldn't start. Checked the exhaust over heat sensor. It read open on the meter. So now I know the source of my trouble. Thanks all for your expert advice. Ron

 

[67hat34c]

isnt it normaly open? when closed it grounds the coil and kills it.

Its the fuel pump, and i bet you have fuel line larger than .25 id

These little facett pumps get weak and when hot they quit pulling fuel.

 

[Beckytek]

The manual says it is in series with the head temp sensor which is closed. I believe if either one opens it kills the spark. Next time I'm on the boat I'll make sure of this. It was too hot to full with at the time so I just checked the switch and left. When this happens again I'll jumper the switch and see what happens.
My fuel lines are the original ones that came with the boat. I can't imagine them not being the correct size. I did replace all the blue flexible fuel hoses when I bought the boat as they were all original. I probably will change the fuel pump as you suggest since it is reasonable and is good preventive maintenance. They are asking 42.50 for that little exhaust switch.
I appreciate all your good advice. I'll keep you posted. Ron

 

[67hat34c]

prior owner installed aeroquip hoses on mine and they were larger than .25id. Talked to old timer when I was having similar issues and he said that the fuel pump and hoses were my problem. he was right.

make sure fuel system is clean from pick up to the carburator. weak pump can not pull it.

got you on the swith , i assumed it simply grounded the coil and kills the engine.

I no longer have the boat and sold all my spare parts and manuals to another forum member.

 

[Beckytek]

Just an update on my saga with the genny. I removed the exhaust heat switch and checked it. It opened at 200 degrees. I thought that was ok. Checked the water pump and changed the impeller. After replacing the impeller I got no water flow. I then rebuilt the pump ($400) , and now water is flowing. Bought a new fuel pump ($144) and installed same. Changed fuel filter. Started right up and ran great for 1 hour. I returned to the boat 3 days later, started right up but was hunting like crazy. I slowly added a load and it settled down and ran correctly. After about 20 minutes i t got erratic by varying speed and slowing down. I removed the load and it slowed and eventually died. I removed the carb and cleaned everything and checked the float then installed again. It started right up and after making the fuel adjustments it runs great again. So all is well for the moment but I'm still not convinced it will stay that way. Wish me luck!

 

[sdowney717]

I have a mcck 6500 onan with the control-o-matic, spec C.
It never had the exhaust overheat sensor.

I uploaded my manuals here
http://www.docstoc.com/docs/34443851/Onan-Operators-Manual-and-Parts-Catalog?
http://www.docstoc.com/docs/34444824/Onan-Installation-Manual-Marine-Generator?

I have a small HPGC1 fram cartridge fuel filter and I use 5/16 inch line with a mechanical pump.
That line runs back to a 3/8 sized fuel manifold and the tanks have anti-siphon valves.
It works 99% of the time very reliable generator. I added an external cartridge fuel filter.
http://www.smokstak.com/forum/showthread.php?t=103456

smokstak is a very good site to get tech help for the onan.

 

[Beckytek]

I have the manuals for my genny. Some of the adjustments and components are slightly different than your model. I hope everything will work well now that I cleaned the carb. There was some gummy buildup on some of the parts. What I don't understand about this genny is how it works perfectly one day and terribly the next.
I have a spin on filter that came with the boat. It is the same size as the mains.
The saga continues.

 

[Tiara33Open]

I have the 4.5 KW Ensign and it is always having some problem. It has just over a 100 hours in 22 years so I hate to junk it. It sounds like you have a sensor issue, could be the board too. I can say every time I have an issue, I throw $100 or more at the problem. There have been lots of problems, now it is my circuit breaker. Good luck, I know what you are going through because I do not trust mine either

 

[67hat34c]

Hunting can be warn governor spring, carburator float too low etc. also you may want to re adjust the governor with full load. Then do carb low speed and high speed jet adjustments.

Governor sensitivity can be an issue and its a little tricky to get it just right. Too sensative and it hunts, not enough and there is too much pause between load changes etc. If i remember right more sensative when spring is slid closer to the governor shaft.

 

[krush]

Never worked on one of these specificially. With that said, check the simple stuff like vacuum leaks. Make sure the carb mounting gasket is sealing properly. Make sure the carb doesn't have any worn bushing or stuff that could be leaking vacuum. I've had some weird problems on smaller motors in the past due to vacuum leaks and stuff like that.

The nature of your problem doesn't sound like it is ignition related.