yamaha 150 rebuild carbs again!!?

[jimf232]

Hi, I have twin 1990 yamaha 150's, one that will not idle again (stalling) and at 1500-1700 rpm fuel can be seen pouring into the throats of the carbs. Carbs removed < 50 hrs ago, cleanned and completely rebuilt. New fuel tank, new lines, 10 micron filters (< 20 hrs on them). This is the 3rd time in the last 2 years the carbs have been rebuilt, anyone else having these issues?
No problems at all this year up to this point but the boat had not been run for about 3 weeks, could the ethanol fuel be the issue?(fuel is stabilized w/ startron) causing needle valve rubber tip to break down and not seat properly, or gumming floats etc.

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

Are running your fuel stabilizer? If you are in the habit of running your motor after you get home you might consider pinching the fuel line and choking the carbs dry or you can do this at the dock before you trailer. Harbor Freight or I think even Home Depot have plastic fuel line pliers that are pretty cheap.

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

you can clean the carbs for breakfast,introduce debris n them at lunch and guess whats for dinner?
unless you like buying lift pumps pinching of fuel lines or running with a line unplugged isnt reccomended.
its also why there is a drain screw in each fuel bowl.
you simply CANNOT run all the fuel out of the bowls.
test a fuel sample for E content.
what brand of needle valves are you using? yamaha or aftermarket?

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

you can clean the carbs for breakfast,introduce unless you like buying lift pumps pinching of fuel lines or running with a line unplugged isnt reccomended.
its also why there is a drain screw in each fuel bowl.
you simply CANNOT run all the fuel out of the bowls.
test a fuel sample for E content.
what brand of needle valves are you using? yamaha or aftermarket?

Not likely on a 2 stroke, and no you will not get all of the fuel out of the bowl but you will get the fuel level below the main jet. Coupled with the fact that the outboard will be most likely be tilted up, the remaining fuel will collect in the front of the carb bowl. Since the bowl is vented to the atmosphere most of the remaining fuel will evaporate, any remaining residue (if any) will be broken up the next time fresh gas is introduced into the carb. By the time the customer is out the no wake zone and up on plane the gentle vibration of the motor and the solvent action of the gasoline any small particles left (if any) will pass through the main jet and into the engine. Yeah I guess you could tell the customer to drain (possibly all six) drain screws every time he goes fishing...but I would rather take the butcher's word for it.

 

[99yam40]

Re: yamaha 150 rebuild carbs again!!?

the dried up fuel will usually come loose in chunks or flakes and plug the jets and passages.
It is best to leave full of stabilized fuel and run often or drain with the drain plugs, but then you still have the fuel lines and pump that will have fuel residue that when dried up that will plug them up from time to time.
The stuff I have seen looked like plastic wrap, just real thin piece/sheet laying in bottom of bowl that gets sucked into jet restricting the flow

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

True you should always run your fuel stabilizer and what you are seeing is a completely filled carb bowl. When you choke the fuel down to the main jet there is a clearence of about 1/32th of an inch. This amount (with treated fuel and evaportation) will not varnish enough to cause problems. Now if you have a Merc or an Evinrude/Johnson with an enrichener, then definately you have to use other means to get the fuel out of the carb.

 

[robert graham]

Re: yamaha 150 rebuild carbs again!!?

Using fuel stabilizer all the time, a fuel/water separater and draining the carb float chambers at least a few times a year is pretty darn good insurance against fuel related problems. At least that's my personal experience and my motor is a 1999 and carbs never been cleaned or screwed with, still runs like brand new! Good Luck!

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

my patience with an MMI grad and one year of hands on is rapidly wearing thin.
on the 1990 150 carbs you simply cannot choke, cajole or even get a voodoo doll to get the fuel out of the bowl low enough to prevent nasties.
would it be to simple to simply unscrew the bowl DRAIN plug and DRAIN them?
there are 6, one DRIAN for each bowl.
1/32 of an inch is 031"
.
aint gonna happen, the pilot fuel jet is probably 3/8" from the bottom, not to mention the drain channel is at least .125" deep.


what drives the fuel pump diaphram on a two stoke?

what dampens the pulse on a two stoke fuel pump?


what happens if the diaphram is asked to pull more than it can? fuel line dissconected or pinched off?


what happens with a lean sneeze.

.

explain to us nut heads what you think a lean sneeze is and why it affects a fuel pump diaphram on a two stroke.
bet MMI did not go over that one.

wow I self edited, most before DonS could bust me, again .

but jeff.
post how the fuel pump works and why on a two stroke yamaha.
we are all waiting.
also post what the diaphram does when no fuel is present on the intake side.
also post what happens to the pulse side when it lean sneezes.
but I am waiting for your explanation of a lean sneeze.

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

Well if you have ever suspected piston skirt damage on a cylinder that the fuel pump is tied to and tested it, you will find that in a good operational (skirt) piston the max psi that the primary compression/transfer event piston movement towards BDC is only about 4-6 psi at idle or just above. This pressure is never compounded because of the intake port opening for the transfer/scavenge event. It's just like when you hook up a vacuum gauge checking for fuel restictions. If you kink the line before the gauge you will find that the max vaccum you will draw is about 6" of mercury. Well their is also a mechanical fuel pressure spec to follow in the manual that require you move the gauge to the positive pressure side of the fuel pumps. Why do that? If your pulling 6"hg, then your pressure is good (what goes in has to come out). Given the fact that to achieve this test has no effect on the full/current level of the carburetor float bowl the restriction has no adverse effects on the combustion chamber. Now I would say that the cam driven mechanical fuel pump on a 4 stroke might have different consequenses for prolonged use, but that fact that you can choke a carb out in less than a minute, no harm is going to come to that spring operated diaphram that ethenol is not doing currently. The fact that you are constantly choking before stalling, and means that your lean sneeze will be kept to a minimum if at all and because the exhaust port opens before the intake, a lean sneeze is not that detrimental, and being their is not a fuel pump on every cylinder I like my chances . But feel free to try it at least once, choke it the way I am describing and if you let your motor sit for say a week, pull the drain screw and check for fuel content with or without fuel stablizer just mark it on your calandar, because if I know boat owners a week is a lot shorter than 7 days. -Fin

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

you have just proven my point, I did not even have to call you an idiot.
you did it all by yourself.
the mods cant bust me.

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

theboatorme
you proved my point.
you can clean carbs all day long, but until you solve the debris issue your simply gonna do it again.
yes this nasty stuff can and will form on the fuel lines, clean the carbs and a week later that yellowish nasty stuff from the line inner walls is in the bowl clogging the jets.

jefferson, quit while your ahead, or behind, just quit.
put the shovel down.

its quite a bit more than 6 psi, and you still can only regurgitate what your MMI instructor told you.\

a lean sneeze is a sudden explosion in the crankcase due to a lean air/fuel mix in the crankcase.

it is VERY detrimental to not only the fuel pump diaphram but also it can break crank snouts and shear flywheel keys.

as that piston went up the vacum behind it draws in the next air/fuel mix,except DFI 2 stroke, as that piston fires and is heading back down from TDC the lean A/F mix explodes, the reeds are closed and this uncontroled crankcase explosion tries to force the piston back up. actually trying to change the rotation of the crankshaft.

and that is why lean sneeze is very bad and can pop fuel pumps.

theboatorme can quit laughing at me, or simply crack another cool refreshing beverage.

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

Agree to disagree I guess, just stating the facts that I have encountered working on boats and never had a problem with it. But hey you have to agree this is better than dock scuttlebutt.

 

[jeffersondodson561]

Re: yamaha 150 rebuild carbs again!!?

as that piston went up the vacum behind it draws in the next air/fuel mix,except DFI 2 stroke, as that piston fires and is heading back down from TDC the lean A/F mix explodes, the reeds are closed and this uncontroled crankcase explosion tries to force the piston back up. actually trying to change the rotation of the crankshaft.

Yeah I am going to go ahead and call B*llsh*t on this statement, their is no way that primary compression can combust anything. Ever found a broken,unattached reed valve with your finger in front of the carb, it is not more than 6 psi, much easier to detect but not overwhelming. But Nicholas Gauge's word for it. Next time you got a yamaha fuel pump repair, take the center carb off, close off the fuel line and put your vacuum gauge at the pulse hole at idle and check it yourself. The only way you can combust anything is on secondary compression.

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

Yeah I am going to go ahead and call B*llsh*t on this statement, their is no way that primary compression can combust anything. Ever found a broken,unattached reed valve with your finger in front of the carb, it is not more than 6 psi, much easier to detect but not overwhelming. But Nicholas Gauge's word for it. Next time you got a yamaha fuel pump repair, take the center carb off, close off the fuel line and put your vacuum gauge at the pulse hole at idle and check it yourself. The only way you can combust anything is on secondary compression

ok
now its official. your an untrained idiot spouting the same untrained idiot MMI instructors.


that lean sneeze IS a backfire in the crankcase, nothing more nothing less.
it can generate 100 PSI+ pressures under the piston, wristpin side.
yes it can blow reeds back though the cage, yes it can blow reed and intake gaskets out, yes it can try to slow the pistons downward motion enough that the flywheel simply shears the key.
flywheel is simply gonna try to maintain its speed regaurdless of what the piston,rod and crank is now trying to do.
thats what a flywheel does and why most engines have them.

on a 4 stroke its called a backfire cause without reeds the flame in the intake manifold simply erupts out of the carb.
however most 2 stroke outboards have reed valves that will prevent the combustion and flames from exiting the crankcase, hence the term lean sneeze.

kid ya dont wanna go off on me nor some of the rest here.

but in most 2 stroke efi or carbed outboards, lean sneeze is an uncontroled burn in the crankcase that results in the fuel turns to gas, just as it does in the combustion chamber, pressure in the crankcase spikes way above design limits and it tries to reverse the rotation of that downward bound piston .
the reeds will try to seal off the intake so it is a combustion chamber.

kid, there are a lot of books out on how and why 2 and 4 strokes work.
what these books usually fail to say is how they react when something is wrong.

 

[erniefish]

Re: yamaha 150 rebuild carbs again!!?

wow, i know the rut is on where i live, but this is good, and i always appreciate the knowledge i get from this forum

 

[rodbolt]

Re: yamaha 150 rebuild carbs again!!?

laugh all you wish.
lean sneeze is lean sneeze and I really dont care if its EFI or carbed.
its an uncrontrolled ignition/explosion of the lean A/F mix in the crankcase intake manifold area.
in your car or your 3.0L mercruiser it would be a post about flames shooting out.
in the two stroke world the reeds seal off any passasge back out of the carbs so the ENTIRE explosion is contained between the reeds and the wristpin side of the piston that is coming down and compressing the A/F mix in the crankcase.
and that leads to bad things.

 

[erniefish]

Re: yamaha 150 rebuild carbs again!!?

bad idle, great top end, mech said it might piston skirt, ha ha, on a 2004 150 txrc, less thn 250 hrs , how about a bunch of bad re-circ valves, 4 in all, who would of thought that many? never rule out any thing when it comes to a o/b and btw, i found the solution here

 

[99yam40]

Re: yamaha 150 rebuild carbs again!!?

Ernie you do realize that this is not THE HULL TRUTH right?

 

[erniefish]

Re: yamaha 150 rebuild carbs again!!?

99yam40, i do apologize, to much web surfing, and a few beers= mistake,again i thank everyone on this forum for their wealth knowledge