The motor in question is a 4cyl Suzuki Motorcycle Engine. Has been in storage a while. The symptoms seem familiar, but my brain is fried from other projects.
Choke open, starts and idles fine. If you close the choke, even after warmup, it dies. If you rev above 3500 RPM, starts to cut out and run rough. Air filter and airbox are fine, no obstructions. New plugs and wires. No kinks in fuel line, new fuel filter, fresh gas.
What am I missing?
Carbs clean?
Clean the carbs. I bet the only jet that isnt clogged is the enrichment jet.
Use a lot of marine stabil next time.
when you say "choke open" you actually mean "choke closed", right?
Not much on bikes, but dying on a closed choke sounds like a clogged air bleed. Agree with cleaning the carb.
Very common problem on motorcycles with gummed up carburetors.
Fueled by Caffeine wrote: Carbs clean?
The answer of course is "no".
novaderrik wrote: when you say "choke open" you actually mean "choke closed", right?
No, it's choke open. On nearly all motorcycle carbs the "choke" is actually an enrichment circuit that dumps a lot of extra fuel behind the throttle valve. Opening the choke opens that circuit allowing the extra fuel to flow. I don't know of any even remotely modern m/c carbs that have a n air restricting choke valve.
And yeh, it sounds like clogged jets to me.
Like everyone said ... clean the carbs.
Modern ethanol-enriched fuels. The shelf life of gas these days can be measured in days. I work at Home Depot repair. Guaranteed bad fuel or stuck float.
Pull the bowls. Drain the old fuel. Take a single strand of copper wire and run it up through the jets. Clean the bowls and reinstall. Ride with a smile.
The ethanol does two things: it absorbs water, and it likes to react with something be it the metals or the plastics. It makes a white crusty stuff that clogs jets. You have no idea how many times I resurrected an old lawnmower, snowblower, or tractor by just taking 10 minutes doing the above. After the first snow this last winter we had a line out the door with snowblowers that wouldn't start. Every one of them (bar none) was bad fuel and it was fixed with the above procedure. In the interest of customer service I just did it and didn't charge. This February I got smart and put a sign up that said "lawnmower tune-ups $50." It includes an oil change, a spark plug, air filter, carb cleaning, and blade sharpening. We've made a killing on what amounts to $7 in parts and a half hour labor.
If you took yours to a 'zuki dealer I'm sure it would cost you $300 for the same service.
What happens is the ethanol attracts water, water corrodes the aluminum/mag body and the oxide just clogs the whole thing up. This is why I recommend a marine grade fuel stabilizer. I also like to add 2 stroke oil to the fuel, heavily, at least 24:1, this seems to prevent any varnish proper from forming, just a thick sticky tar that fresh fuel will wash away. It cant hurt the war on corrosion either. I have a really beat rider mower that gets stored that way and never refuses to start. When I winter the Yugo I fill the carb though the vent with 2 stroke oil, because it cant hurt and I hate dealing with that bastardized Weber if I can avoid it.
I let a two stroke snow blower sit for a coupla years w/o attention. In prep when I needed it I pulled the fuel bowl... nice, nothing but oil left after the fuel evaporated and no corrosion.
Plus one for the oil like Kenny said
In reply to Kenny_McCormic:
If that's what you like to do, get your hands on some opti 2. The recommended mix ratio is 100-1, and there is a fuel stabilizer already in it.
FYI, it has nothing to do with ethanol. This has been a problem long before ethanol was ever put in the gas.
My snow blower and lawn mower sit for months with gas laced with ethanol.
When I put then away, I run them for a while with Stabil.
Never had a problem. I did have to clean the low speed jet on the blower this year.
The snow blower is 17 yrs. old and the mower is 25.
Echo synth oil available at Home Depot is quite good 2 smoke oil. Cheap and readily avaable.
The 2 stroke oil thing for storing a 4 stroke doesn't really matter with regards to what oil, just that there's plenty of it, you could use ATF or any low ash oil for that matter. It just needs to be there to keep any dried up fuel soft and to coat the inside of everything to help keep it from corroding. Thats my theory anyways, I've never rebuilt any 2 stroke carb other than to fix leaks and bad diaphragms, just get it running, hold it WFO, and if it hasnt got a intake restricting choke, use your hand to choke it out, the vacuum spikes pull all the gunk through.
I'll take "What does my lawn mower do?" for $200, Alex.
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