1998 dt150 losing rpms

[rfkhunter]

Won't go over 4200 rpm, seems like it starving for fuel. If I run it just around 3/4 throttle it's OK for the most part. Bulb gets soft, won't stay hard and I just replaced the hose, bulb and water separator filter. I checked the fuel screen near the low pressure pumps and it's clean. If the bulb is pumped while moving it seems to increase rpms momentarily. It started several times instantly while out fishing, but then one time had trouble until I opened the throttle a bit. Any ideas?

[Solarman]

How long has this been happening? What have you tried so far other than the filters?

Inspect the low pressure fuel pumps, they supply the needed fuel to the vst. When inspecting the pumps, make sure the two clear discs, in each fuel pump, (check-valves) are not cracked, or fragmented. If fragmented those pieces will lodge on the backside of the needle valve seat, restricting flow of fuel going into vst needed for high pressure pump. They do NOT sell those discs in rebuild kits, only in new replacement pumps.

The diaphrams can be replaced with the kits, the check valves can not. Identify any trash you find in the fuel system, this may tell you if something else is breaking down, that needs attention.

Good luck, post back what you find out when able.

[rfkhunter]

Thanks for the reply. I spoke with Mechanic at Suzuki dealership. He said definitely sounds like fuel issue, but there's many possible causes, of which one I'm praying isn't the expensive HP pump. I will look into what you mentioned myself. I'll probably reach a point beyond my capabilities and have no choice but to have them look at it

[Murray]

Get yourself a genuine Suzuki service manual, it will give you the confidence to dig deeper into the fuel system. They present the material in an easy to understand format with plenty of pictures. I paid for mine just following the maintenance procedures.

[rfkhunter]

Thanks Murray will definitely look into that.

[rfkhunter]

Is this what I need?

[Murray]

I’d try to stick with a Genuine Suzuki manual if at all possible.

[Jose flores]

Same issue with me have u found out a solution

[Solarman]

Jose, we know nothing about your motor in this thread, let's not confuse this issue. Please start your own thread with your motor history.

RFK, this fuel system does get a bit involved, and you could possibly check a few things?

RFK, can you find/borrow a portable fuel tank with a hose to connect at your motor? This could tell you/us if your problem is your fuel & tank. Pumping bulb helps us know it sounds fuel related. It still does not help solve the problem.

Did you inspect the LP pumps? As stated before, the LP pumps supply the VST (vapor separation tank), through a float needle valve assy, the fuel required by the HP pump.

So step one, borrow/try a different tank with fresh fuel (small 2-3 gal tank is all you need for test), if possible.

Step two, remove and inspect diaphrams and check-valves (clear discs) in LP pumps. Identify, any trash, or missing/broken pieces, in LP pumps.

Good luck, post back on what you find.