Rodbolt 17 please help!!

[rodbolt17]

one day Ill have to get you to show me how to do that with the parts thing.
this computer is so old and slow I don't think it would do it and the puter at work is even older, like about 9 years old.

[dorado42]

OK Rodbolt17 I definitely have a better understanding of "vapor lock" now. I understand what you meant about 6HG making fuel boil at 70 degrees. I am thinking this may be the problem also. I am going to check fuel system for restriction (causing excessive vacum). Is about 3 HG correct for the fuel system. One HG for anti-siphon valve, one HG for FMM and one HG for racors. THANKS AGAIN!!!!

[dorado42]

Rodbolt17 also I was thinking IF it was vapor lock why would it take 10+ years for the motors to develop this problem....would the previous owner(s) have had the same problem. Is it possible the OCTANE rating of fuel can be a factor....will increased octane rating change anything related to this problem (I am currently running 87 octane)

[rodbolt17]

87 octane is fine.
however if this problem is recent it may be the fuel brand.
have you simply tried watching the fuel level in the filter cup cycle up and down as the lift pump cycles?

if the lift pump check valve is leaking you will see it after about 10 cycles.

have you had the engines on the laptop to insure all sensors are in the correct range.
beware of in-range failures.

I have seen a few MAP sensors that sent bogus info to the ECU as well as air temp sensors.

did both engines start with this issue at the same time or one at a time?

[dorado42]

I have watched the small element filter empty/refill and it does so....have not watched for 10 cycles though. I have NOT had the motors on a laptop program. The motors started doing it at the same time. Port engine just died one day when leaving the dock (three miles away) was cruising about 3500 RPM and the motor simply lost power down to about 1500 RPM. I checked the fuel filter and all was fine. Idled back to boat ramp and changed filter. Thinking I may be out of gas...idled to fuel dock then starboard died (cruising around 1500 RPM). Added 15 gallons to each tank....could not get port engine to idle and stay running....put boat on trailer went home...few days later could not get ball to get hard on port motor so started by checking anti-siphon valve and pick up tubes....p/U tubes looked clean but anti-siphon valves was believed to be bad....so I replaced it and I believe what you do to one motor you do to the other, so I replaced both of them. Then went offshore and this is when acceleration problems started????

[Bilge Rat]

Fuel is common to both motors.
Could be a weak batch of fuel coupled with high vacuum pressure pulling fuel. This may cause warm fuel to vaporize. A few octane points low could do it but over a few the motor would knock, diesel, lack power.

Ask other boaters that get fuel from same supply if they have had any issues.

Did you replace fuel line all the way back to the tanks?

[dorado42]

Ok I have a vacum gauge and wondered can i test the check valve (that is suspected to be leaking) by placing the vacum gauge on the INLET side of the check valve and see if it holds 5-7 mm/mg. Also I am planning on checking components of fuel system prior to the engine. I am thinking I can check each section (fuel pickup, racor filters, primer ball, etc) with the boat on the trailer, before going to the water...does that sound right...then if nothing stands out, take boat to the water

[rodbolt17]

we had this arugement in class.
we even tried to make an F225 vapor lock in the test tank.
it was impossible.

why Yamaha mentioned vapor lock? most likely a translator error compounded by most folks haven't a clue what is VAPOR LOCK and why they call it a VAPOR SEPERATOR.

fuel under a vacuum will boil at a lower ambient temperature than fuel under pressure.

boiling fuel will cause air bubbles and vapor.

that's why the lift pump places fuel in a VAPOR SEPERATOR.
from there the high pressure pump has a supply of clean bubble/VAPOR free fuel to PRESSURIZE.
fuel under pressure takes WAY more temp to boil.
and the return fuel is run through a fuel cooler.


folks, its the same stupidly simple speed density EFI setup that GM has used for about 20 years.
biggest difference is GM used the gas tank as a fuel cooler/vapor separator and returned fuel to the gas tank.
Yamaha uses a VST tank(mini gas tank) due to the fact Yamaha doesn't make hulls and returning the fuel to the hull tank is a waste of hose.

look very very closely at the so called vapor lock kit.
its not on the suction side its on the VENT side.

yes there were some issues way way back were fuel vapors would collect in the intake causing a hot restart issue.

this can be readily identified by simply cracking the throttle on hot restart to add AIR.

quit beating the restriction or vapor lock horse .
its not your problem.

[dorado42]

Ok...going to water with boat...have external fuel tank and vacum gauge....hopefully will get some answers. I am thinking of starting with vacum gauge at primer ball to see what my baseline reading is when I typically do noy have problems (first thing in my trip) and then keep an eye on it as system warms up.....will also check vacum on inlet side of one way valve to see if it is good..anything else to test Rodbolt17....

[dorado42]

Ok..on the water...so far rodbolt17 is correct wo fuel restriction....fuel rail is 40 psi...question is when the motor is turned off the pressure drops to 0 on gauge....when key is turned to on....the gauge goes to 40 and then drops back to 0 if I do not start motor...please reply

[rodbolt17]

rail pressure should not drop to )psi instantly.
it should hold about 25 PSI for a few minutes anyway.
either the HP pump is failing.the pressure regulator is failing or an injector is leaking.

what happens if fuel vapors perculate and the VST vent check valve leaks it will allow vapors in the air box.
however the ECU has no clue its already excessively rich at the time it gets the crank signal.
at engine crank ign timing,fuel and ISC are all FIXED.
it cannot compensate for that EXTRA fuel vapor already in the intake air stream.

that's why slightly cracking the shutters will alleviate this condition,if it exists.

its also why later engines had a charcoal/carbon canister to retain vapors and slowly reintroduce them at the next run cycle.
and later engines actually use a vapor shutoff valve between the canister and the intake that opens slowly via ECU commands AFTER engine start to burn trapped vapors.

EPA says we can no longer vent vapors directly to the atmosphere.

[dorado42]

Well the problem finally showed itself...the engine ran fine with no problems from an external gas can....when hooked up to motor problem still occurs...ran fuel line straight to outboard and problem returns...so i am guessing fuel line is bad...only part that could not be replaced runs under the floor and can not be removed....so I am just gonna run totally new fuel lines...hopefully it fixs the problem...

[dorado42]

The motors start and idle the problem is when i accelerate...it will take off and then fall back down and then not idle....the ball will not get hard even after pumping 40+ pumps....i had a clear gas line going to primer ball and the line seem to have lots of air bubble..after switching to portable tank seem to be clear fuel only (no bubbles in line).....at no point was there any vacum over 2 mm/hg (even WOT)....the HP gauge was 40 psi....when key turned off pressure would drop to nothing...would jump back to 40 psi as soon as key switched on

[rodbolt17]

if it were a restriction your vacuum gauge would have read higher.

you may have an air leak between your gauge attaching point and the liquid level in the tank.

if it runs fine on a remote tank the problem will be between wherever you attatched the remote and the liquid level in the tank.

this will include any fittings,antisiphon valves and the draw tube.

[99yam40]

I have replaced primer balls, anti-siphon valves, racor filters, fuel lines, low pressure pumps. Both motors act the same, and have their own fuel tank, fuel lines, racor filters etc.

Seems you did not tell the truth on this post if you did not replace all of the fuel lines.

Are you sure the motors are plumbed up on separate tanks or are they on valves that you can switch them around to the different tanks?

Seems there is a common place that both motors share like a valve maybe if both show signs of air bubbles and I would not think twin motors could not be run on the same tank when needed

And I do not think sucking air would cause the 40 to drop to 0 immediately when key is turned off, so maybe more that one problem