Post by: Stein on July 20, 2014, 06:16:10 PM
It idles extremely rough and bogs down a bit until it gets up in rpms and then seems to run great. I ran the carb screw all the way in to all the way out and it doesn't seem to make any difference (did this out of gear in the driveway as well as under power in the boat at the lake). It does much better since the carb clean and fresh gas, but it still isn't running that well.
I also took the fuel pump out and put it back together and checked it by pulling the starter cord. I also placed the fuel tank high above the motor and it doesn't make any difference - I think the problem isn't there.
I can run the boat ok at 3 mph or greater but anything under that is not so great. The guy I bought my boat from bought it new and said it never ran that well. He has receipts for several tune ups but they didn't fix whatever is wrong.
Any ideas, my very limited knowledge has been used up?
Post by: TheHunt on July 20, 2014, 08:09:54 PM
Post by: lokidog on July 20, 2014, 08:15:16 PM
The only thing I can think of is the fuel lines. I would also wait to see what the experts say on this site.
I would try new fuel lines as well, they tend to deteriorate from the inside when gas sits in them, especially with the ethanol. I have had a dark sort of varnishy stuff in there as well as bits of rubber. :twocents:
Good luck.
Post by: Fishnclifff on July 20, 2014, 08:29:59 PM
The new ones have a chitty element that melts and clogs up.
I change mine at least twice a year.
Post by: Bmcox86 on July 20, 2014, 08:39:18 PM
Post by: BigGoonTuna on July 21, 2014, 06:09:36 AM
Post by: Stein on July 21, 2014, 07:00:45 AM
you might want to find someone who has an ultrasonic cleaner and run the (fully disassembled) carb through it, then do a full rebuild. your issue sounds like a partially blocked idle circuit to me, something might be lodged in there. it doesn't sound like a fuel filter, if that was an issue the problem would get worse as you throttled up.
Thanks. What parts are replaced during a rebuild, the seals and gaskets? There aren't many parts in a 4 hp carb.
Post by: L-ofalab on July 21, 2014, 08:14:12 PM
you might want to find someone who has an ultrasonic cleaner and run the (fully disassembled) carb through it, then do a full rebuild. your issue sounds like a partially blocked idle circuit to me, something might be lodged in there. it doesn't sound like a fuel filter, if that was an issue the problem would get worse as you throttled up.
I agree with low speed circuit. I thought someone was recommending adding a fuel filter instead of it being dirty, either would be good to add or clean but because it runs OK at higher RPM that would probably not be the problem. I used to work on lots of motors of all kinds and there used to be 2 carb needles, HI & LO. Many motors have gotten away from that design and frequently there are only pre set jets where there is no adjustment. Many carbs are sealed with plugs that are tough to remove without ruining the carb but your plugged LO speed passage could be where it is not cleanable and only a new carb would help.
Post by: Stein on July 22, 2014, 01:10:30 PM
Post by: L-ofalab on July 22, 2014, 08:33:38 PM
Post by: Stein on July 23, 2014, 06:02:06 PM
Post by: Kc_Kracker on July 24, 2014, 10:28:23 AM
Post by: pilebuck on July 24, 2014, 10:49:12 AM
Post by: Kc_Kracker on July 24, 2014, 10:52:13 AM
Post by: Gobble Doc on July 24, 2014, 10:59:26 AM
I've got a 40 HP Yamaha and I too am intimidated to tear the carbs apart. I took mine to BaySide and it was indeed expensive. I think there are 3 carbs. Are there timing adjustments to make when you reassemble? Or is it really as easy as taking it all apart and cleaning and then just reassembling?
Post by: Kc_Kracker on July 24, 2014, 11:56:35 AM
Post by: deltaops on July 24, 2014, 12:01:33 PM
Mine is now doing the same thing and I am about ready to pull the carbs off and clean them. pretty easy and saves on the wallet.
Post by: Kc_Kracker on July 24, 2014, 12:14:38 PM
Post by: quadrafire on July 24, 2014, 12:16:51 PM
Post by: Kc_Kracker on July 24, 2014, 12:32:36 PM
Post by: Gobble Doc on July 24, 2014, 02:14:11 PM
Post by: JackOfAllTrades on July 24, 2014, 02:32:42 PM
-Steve
Post by: deltaops on July 24, 2014, 02:56:44 PM
If the fuel mix adjustment does nothing... Idle circuit venturi or the jet is likely gummed up. Could still be a vaccume leak but it would probably idle high and stumble as you increased throttle. Butterfly adjustment? I don't know why people are intimidated by carburetors. Note your steps to taking it apart. Right down to how many turns a screw takes to get out. Use your smart phone to take photos as you disassemble. Take it apart on a clean bench with a bath towel spread out. Don't lose any parts!
-Steve
:yeah:
I am not intimidated as I have taken quite a few a part myself. From cars to small engines, they are pretty easy to do. Just remember how you took them out and a part and reverse the order when putting them back together.
If you are unsure, take lots of pictures during the process. :tup:
Post by: pilebuck on July 24, 2014, 03:13:07 PM
Post by: Stein on July 24, 2014, 05:26:36 PM
Post by: L-ofalab on August 02, 2014, 05:47:18 AM
Post by: Stein on August 02, 2014, 12:39:43 PM
There were a few pieces of junk that floated out for sure. All parts look like new. Assemble and it fired right up. At the lake, it ran great except the mixture screw has a tendency to back out, so the o-ring is probably worn and I need to replace that.
The only problem I had was when I tried to get it to idle crazy slow for sockeye.
I also ran several other things through the cleaner. I think it isn't the most powerful, but for the price it seems to work well.
Post by: Kc_Kracker on August 03, 2014, 06:20:43 PM
Post by: bloodhound on August 07, 2014, 07:21:27 PM
for all those out there that recommended changing the fuel filter.......
FUEL FILTERS DON'T FIX ENGINES!!!!! IN ALL MY YEARS AS A MECHANIC AND I AM A OUTBOARD MECHANIC, NEVER EVER, EVER,EVER,EVER ECT HAVE I SEEN CHANGING A FUEL FILTER FIX A MOTOR ISSUE.
except.... on an optimax where the filter has a sensor in it and when the filter has to much water in it it will sound an alarm, changing the filter will shut off the alarm.
Post by: Stein on August 11, 2014, 10:18:40 AM
if it womnt idle crazy slow then its either that AFM o-ring leaking air, or you missed a plugged port in the carb, or adjustment, those are the only 2 things that really affect low idle, oh and good plugs
By "crazy low" I mean like 300 rpm. I could see the blades in the prop spinning. I was trying to get down to .5 mph with a slight wind. It runs great at a more normal idle.
Post by: Stein on August 11, 2014, 10:22:04 AM
keep in mind if you do the carbs on your big motor youll have to buy a vacuum mate to set them up. its easy to do but the tool isnt too cheap.
Is that only needed on multi-carb setups (I hope)? My 40 Merc has a single carb that is now sitting in pieces on my bench waiting for the rebuild kit to arrive. I'm also rebuilding the fuel pump, checking the reed valves, replacing the fuel filter, fuel lines, fuel bulb and thermostat as well as new plugs. It's a 2004, so rather than chase things for the next few years I figured I would go through most of what can be replaced easily and for just a few bucks. I think I only spent about $100 for everything.
Post by: bloodhound on August 19, 2014, 04:30:23 PM
Post by: BigGoonTuna on August 20, 2014, 04:50:13 AM
FUEL FILTERS DON'T FIX ENGINES!!!!! IN ALL MY YEARS AS A MECHANIC AND I AM A OUTBOARD MECHANIC, NEVER EVER, EVER,EVER,EVER ECT HAVE I SEEN CHANGING A FUEL FILTER FIX A MOTOR ISSUE.my favorite quote by customers when i worked in the chainsaw repair business, "i think it just needs a tune up" :bash: i always said there's two kinds of tune ups i'd do, the ones where someone says "give it a tune up"(meaning nothing was wrong and i was just gonna take their money to put a spark plug in) and "i think it needs a tune up" which meant it probably didn't run and could be anything from a fuel line to ignition coil or even a top end.
except.... on an optimax where the filter has a sensor in it and when the filter has to much water in it it will sound an alarm, changing the filter will shut off the alarm.
Post by: Stein on August 20, 2014, 01:29:59 PM
I check the manual and ended up finding a problem with the top CDM, so I ordered a replacement that should be in Friday. It actually makes sense because i was getting much worse fouling in the top cylinder at idle which would correspond to a bad CDM.
I don't know enough about CDMs but apparently there can be failure that only affects low rpm operation.