Certified Yamaha Tech is stumped

[DWarner]

Have a 200hp vmax 1998 (carbs 2, cycle) saltwater series with fuel flow problems. At 4600 rpm the motor surges. If you squeeze the primer the surge goes away for a few seconds. This also occurs when a seperate (known good) fuel system is connected to the engine. Replaced fuel pumps, fuel filter, water separator and new primer bulb. The tech has taken off cleaned and reconnected the carbs three times as far as I know, per the Yamaha factory peoples suggestion with no difference. He says it's not spark and I don't know if he has the equipment to test vacuum or fuel pressure.The engine has under 300 hours.
Rodbolt, I don't want to insult the man but is there something obvious that's being missed.
Thanks for your help

 

[Ray Neudecker]

Re: Certified Yamaha Tech is stumped

You and he have hit the basics pretty well. Fuel restrictions can be mean. Did he completly rebuild carbs with new bowl gaskets and needles? Did he flow test them?
Not sure why but I have had some real struggles with those model carbs. The flow test should help if he has replaced the needles and bowl gaskets.

 

[JB]

Re: Certified Yamaha Tech is stumped

Yes. He has not tested the cylinder crankcase that drives the fuel pump for vacuum/pressure.

A leak in the crankcase or bypass area can cause even a brand new fuel pump to be weak in fuel delivery.

Not familiar with your engine, but most have the fuel pump driven by crankcase vacuum/pressure pulses. Many have a cover bolted over the bypass area and all have seals on the crank and gaskets on the reed manifold. Failure or weakness in any of those will make the fuel delivery from the fuel pump weak.

Your symptoms are classic for weak fuel delivery.

 

[rodbolt]

Re: Certified Yamaha Tech is stumped

you really need to post a model number, all the Vmax 200's in 98 that I can find are EFI motors.the Vmax was actually made in a 3.1 and a 2.l litre version from 98 to 02, but all were EFI from 98-02.
post your complete model number.
the P,s and L 200 were 2.6 motors, how many low pressure fuel pumps does your engine have? and a vacum/low pressure gauge is less than 20 dollars at walmart.
also look between the engine fuel filter and the lower lift pump for an inline check valve, if its there remove it.
for a 200 fuel system vacum at the lower pump inlet should be between about 1"Hg and no more than 4"Hg. less usually indicates an air leak and more a fuel restriction. but first I really really need to figgure out exactly what motor we are discussing as the fuel and ign systems are vastly different.

 

[DWarner]

Re: Certified Yamaha Tech is stumped

Model is S200TRW, 2 fuel pumps, 3 carbs. IS crankcase leakage common for a 300 hour Yamaha?
Thanks for all the input.

 

[rodbolt]

Re: Certified Yamaha Tech is stumped

the S is not a Vmax, its a 2.6L saltwater series carbed 200.
you need to perform the fuel system vacum test as outlined in several marine tech guides since 01.
they beat it into ya how to to the test at every seminar and class. as far as weak sealing.
I guess it could happen but I have never seen it on a yamaha.
you can also use a squirt can filled with premix and the test wheel part # YB1626 and spin it up at the dock to full power,5300-5500 and squirt fuel into each carb throat and note the difference, can also be done with a known,trusted helmsman thats not on your life insurance policy.
but I agree, if pumping the primer makes it go away its a pump/delivery issue. somehow one or more fuel bowls are not staying full.
the Vmax 200 in 98 was a totaly different animal.

 

[DWarner]

Re: Certified Yamaha Tech is stumped

Thanks for all your input gentlemen.. The carbs were the problem. Apparently there was some restriction around the needle and seat that was causing problems on one of the carbs. Not exactly sure though but after the third cleaning the boat runs just fine. My mistake on the VMax didn't have the boat in front of me.
Keep up the good work, it is appreciated.