Horrible Fuel Economy-Causes?

[itsjustme0770]

Ok, I need some help. I have a 1994 Yamaha L250 which was just completely rebuilt. It is pushing a 26' center console. I am getting horrible gas mileage. Approximately 20-25gph with normal use (not traveling at WOT). The floats are not stuck and the choke is not on. Thoughts or help would be greatly appreciated.

 

[rodbolt]

Re: Horrible Fuel Economy-Causes?

how do you know the "Choke" is not on?
at or near WOT that motor will burn about 25 GPH.
its a carbed 250 hp two stroke and its just how they work.
many possible causes, thermosensor giving incorrect signals or the T-stat or stats are stuck open or removed.
low pressure pump diaphram failed.
incorrect TPS setting.
leaking or missing orings at the enrichment solinoids.

many many things can cause additional fuel burn on that engine.
and BTW the reason for asking about the choke is that engine doesnt have a choke.
second question, was it rebuilt for a #6 piston failure ?
lots of things can go wrong,quite a few either technician or customer induced.
mostly that engine was rock solid but there were some stator charge coil issues that would bite.

 

[itsjustme0770]

Re: Horrible Fuel Economy-Causes?

Rodbolt,

You are correct, I should have said choke override. Its on the port side and if left open, the fuel economy goes to s&#t. That's not it though. I do think you may have something with the lower fuel pump diaphram as I have noticed a bit of a slick behind the engine, which as I recall is the tell tale sign of that problem.

Can you suggest the best method for determining which pump it is?

We were running the engine at WOT for only short periods of time, and more often at trolling or low planing speeds.

Thanks a bunch.

 

[rodbolt]

Re: Horrible Fuel Economy-Causes?

its not an overide, trust me this engine has no choke, its an enrichment system that can be manually turned on for emergency rope starting or in the event the enrichment pump should fail.
before ya get jiggy with this engine, search a bit on the carbed 3.1L posts I have done recently.
its a simple monster but has some quirks that most techs never saw.
its a simple 6 carbed engine that has an ign control ECU that can also enrich the fuel electronically to about 20% if nessasary and under certain operating conditions.
a simple leak on an enrichment injector oring can do bad things.

 

[itsjustme0770]

Re: Horrible Fuel Economy-Causes?

Thanks. I spent about 4 hours last night reading your prior postings. Lots of interesting information there. I did not see any discussions of enrichment injector o-rings. What I am trying to troubleshoot is extraordinary fuel consumption coupled with unburnt fuel in the exhaust. The carbs are brand new and should be fine. (I understand should be does not mean are.) From yours (and others) posts, the most likely culprit is a bad low pressure pump, as I have read that one of the symptoms is fuel slicks out of the exhaust as well as excessive fuel usage.

Is there a way you would suggest testing the low pressure pumps or just replace them as they are pretty cheap. Thanks in advance for your informative response.

 

[rodbolt]

Re: Horrible Fuel Economy-Causes?

the test is top secrect.
cant tell ya without national security and Homland getting involved.
oh well they can just arrest me.
a quick simple test?
hold your fuel primer bulb with the arrow straight up. engine off.
pump the bulb till its nice and firm.
then keep pressure on it,
if it goes soft in your hand either your check valves in the primer bulb failed OR fuel is leaking past a diaphram or a carb needle.
if the bulb stays firm without exceptional pressure by hand then odds are high the diaprams are not leaking and the carb needles are sealing.

like I say this stuff aint rocket science, if I can do it most resus monkeys can.

let the engine idle for about 10 min, hold your hand on both heads, if the stbd head stays cold you may be fighting something as simple as a bad Tstat.

if the stbd head,for any reason, goes below 113*F on that motor it opens the enrichment valves cause it thinks its cold.

more fuel, more slick easy to find and the thermosensor cn be tested with a standard ohm meter and some knowledge.

ya gotta remember, totally rebuilt can mean anything from it was repainted to it was actually reconditioned.
if I did not rebuild it ,or a few select techs I know, I have to assume it was patched up and sent out.
trust me its the way it usually works.

so far you really havent given us any data to work with.
without it we cant help.

what I can tell you is if you do a link and sync exactly like the manual says and it idles at anyting other than spec, it freaking broke.
on this ttype engine,just like ALL ECU controled motors and ALL EFI motors there is NO idle speed screw.
it either works as designed or its misajusted or broke.
my time is billed at 85 an hour. I wont rebuild a low pressure pump cause the parts are about 25 dollars and when the time is tossed in you just got a rebuilt pump for about 10 bucks over the cost of a new one.
however its very simple and easy to do.
I actually dont make a nickle off of parts sold and I do try to save my customers cash.
and like I told you, above about 4200 RPM 20+ GPH is rather normal for that engine.

 

[Salty Dog]

Re: Horrible Fuel Economy-Causes?

I have the same motors and fought the same problem as you with one of them.

After months of trying to fix it I found one of the enrichment solenoids was installed with two washers on it.

One was stuck in the carb and the other came off with the solenoid. It's a long shot but take a close look.

 

[itsjustme0770]

Re: Horrible Fuel Economy-Causes?

Thanks a ton salty. This is helpful too.

 

[Salty Dog]

Re: Horrible Fuel Economy-Causes?

Have you used the winky blinky yet?

 

[itsjustme0770]

Re: Horrible Fuel Economy-Causes?

The engine is actually in Honduras. I just ordered a winky blinky and am going to ship it to my guy in Honduras. Any other diagnostic tools you would suggest?

 

[Salty Dog]

Re: Horrible Fuel Economy-Causes?

TPS harness makes things easier.