| Author | Message | ||
| gusc Rating: |
There was a recent discussion about Onan carburetors here (I think) but I get nothing on search? My air cooled Onan Model 7.5JB-18R/9269AB gen carb is apparently gummed up with old gasoline. It ran for about an hour after I bought the bus and ran the next day for about 20 min. It backfires and pops, indications of a too lean condition. The fuel smells awful, very stale. I want to remove and clean the carb but have no drawings in the manual to show the carb parts and how it is constructed. I have done this countless times on my antique trucks but have manuals for all them. Does anyone have an exploded view of this carb that you can send to me or parts/maintenance manuals for sale? | ||
| Pete/RTS Daytona (Pete_rtsdaytona)
Rating: |
this should help - most onan carbs are similar http://www.bdub.net/manuals/onanmanual.pdf | ||
| Jay Gerlick
Rating: N/A |
Find a product call "Sea-foam" and doouble the recomended amount for your tank size and run it. Best stuff in the world!!! | ||
| Brian Brown (Blue_velvet)
Rating: N/A |
I had to do the exact same thing on my old Onan genset. There's really not too many parts involved, so the lack of a manual shouldn't be a big deal. Take some digicam pics beforehand if at all worried. After you're done, be sure and dial in the idle and mixture set screws, the points, and then check the governer. | ||
| Jim (Jim_in_california)
Rating: N/A |
Yeah, detail-stripping carbs of this primitive a type is easy. CV carbs are a lot harder as the diaphram on top can get ripped up or just cracks with age. Take the carb apart, soak the bits in more or less any solvent (paint thinner, fresh gasoline) and then my favorite trick is to blow out all the air passages with a can of compressed air as used for cleaning a computer's insides. I had a chance to look at an Onan carb off a gennie like mine: an 1800rpm 4kw model. It looked exactly like a miniature S&S Super "E" as used on Harley-Davidsons  and almost certainly works the same basic way, possibly with one less fuel circuit is all. | ||
| David Hartley (Drdave)
Rating: |
Short answer; Disconnect the fuel line,Drop the bowl, pull the float assembly. Wash them out nicely. Take a can of carb cleaner like gumout with a spout and shoot it up the tubes and jet tubes. Mark the idle and high speed screws, write down how many turns to screw each one all the way in. Back out the screws and remove each one and spray carb cleaner into the holes and then use compressed air to blow out the gunk from the jets and seats. Put the screws (and springs) back in and adjust to where they were approximately. Re-assemble the float assembly to the carb, re-install the bowl. re-attach the fuel line and give it a try. Most of the Onan carbs are japanese made and the ones that aren't are like on a lawnmower. | ||
| gusc Rating: N/A |
Many thanks to all for a very helpful response. This is a 5KW gen and not sure it will power my two ACs and refrig but will give it a try. It has very few hours. I was pretty excited when I noted that the model number started with 7.5 but then found that is only for 3 phase, not a lot of use for 3 phase on buses! Pete, thanks--downloading it now. I appreciate the link. Jay, where do I find Sea Foam and what is it? Brian, I started to do this but the bottom screw which I assume is the power valve was so hard to turn I was afraid I might break it. Jim, what is a CV carb? David, thanks for what is surely a complete step-by-step procedure. I have Berryman's carb cleaner which does a really great job so will use that unless someone thinks I shouldn't, very powerful stuff. It really cleans out everything including all the passages but is death on gaskets. Can I find new gaskets at a reasonable price anywhere? I live in a very small town, no Cummins outlets here. | ||
| David Hartley (Drdave)
Rating: N/A |
Cardboard works. Ace hardware sells sheet gasket material. | ||
| Richard Bowyer (Drivingmisslazy)
Rating: N/A |
Gus, is this a 12 lead alternator that you can re-connect for single phase output? If it is presently connected for 208/120 volt output (low wye) then you could use three separate 120 volt distribution panels for 2.5 Kw per phase. If it is connected for 240 volt (delta) then it is a different story if all 12 leads are not available. Richard | ||
| Jim (Jim_in_california)
Rating: N/A |
"CV" means "Constant Velocity" - it's an advanced type of carb found on motorcycles. Not gensets . They're a pain to work on. | ||
| gusc Rating: N/A |
I got the carb bowl off, full of rust. Cleaned it and reinstalled-runs fine but needs more attention and there is very slight leakage around the bowl to carb gasket. Will tackle that tomorrow. Found one plug lead almost falling out, that didn't help. Condenser also was so rusty I don't think it was contributing anything to the ignition system. Unfortunately the manual from the link is for a totally different carb, doesn't even look as if they came from the same place. The power valve is in the bottom of the bowl just like on my '56 JD tractor! From what I can find on the net this model (JB) was first built in '60 when Onan was owned by Studebaker!! I can't find parts or specs for it listed anywhere, I'm even guessing at the plug gap and carb power jet settings. I'll set that once I get it running well and loaded. It isn't set up for 3 phase, just has the specs listed on the data plate. It is 120v only. I think that 7.5 was just to make a buyer think he was getting more than he really was, it is rated 5KW for 120v. I don't know how many leads it has, I'm not even going to get into the alt section now since my problem is with the engine. All I want is for it to produce! I don't even know for sure if this thing was built as an RV gen? Help, I sure would appreciate any info anyone has on this antique, I hate to throw it away because it appears to have had very little use. | ||
| John Jewett (Jayjay)
Rating: N/A |
If I remember correctly you will have more luck with the Italian made Tillitson carbs for parts. My Onan had one on it. Kinda' like the one on my old Vespa motorscooter. It didn't run worth a s*** either. The float stuck on it and when the RPM went sky high, the voltage did too (165 V)...hence my new fridge, TV, water heater etc. Cheers...JJ | ||
| gusc Rating: N/A |
JJ, I just happen to have a spare Tillitson carb for a '31 Chevy 1 1/2 ton dual wheel truck. I doubt it would work though, the Chevy has a 194ci enging! |
