1999 Suzuki DT25C surging, fuel issues.

[Old Fart]

My 25 HP Suzuki is giving me a fit. It was running good when I bought it used 2 years ago, and then it got to a point where it would idle for about 20-30 seconds and then spit and die. Above idle, it would run fine but I had to rapidly punch it into gear and take off or it would die out.
I pulled and rebuilt the carbs, making sure every passage and jet were clean and all floats were adjusted correctly. It ran like a swiss watch on the flush cuff and idled great, but when I put it in the water same problem. Then it got to where it wouldn't rev properly and top speed was under 2000 rpms.
I redid carbs again and I know they are flawless. I also installed a new fuel filter, and rebuilt the fuel pump. The diaphragm on the fuel pump appeared good, but was a stiffer clear plastic one and the new kit I got had a thin rubberized one that also included a spring and spring cover. There was no spring on the original plastic diaphragm. I installed the new kit and spring, and the motor seemed to idle way better and not shut off, and rev up good. However at WOT it would stumble and bluster. It would run up to 3/4 throttle just fine.
I checked all the fuel lines, and replaced the line to the fuel filter inlet and fuel pump outlet with clear lines. Also redid another fuel tank with new hoses, bulb, and fittings to make sure they were all good and am running non ethanol gas in this tank.
Noticed line from motor fuel fitting to fuel filter stays full of gas with no air pockets or bubbles, but line coming from fuel pump outlet to carbs is only semi full. Disconnected line and it does pump a steady stream of gas but is not real powerful, maybe enough to fill a 1 cup container in less than a minute (guessing) at idle. Motor is now surging at all speeds and running very crappy.
Compression is 108-110 on all 3 cylinders, new inlet cover gasket and rubber piece between top 2 carbs, reed valves all perfect, new spark plugs (good spark on all), and I'm pretty certain this is not carb related. Seems to be more of a lack of fuel pressure from fuel pump, but not an expert there.
As I said earlier, new diaphragm is thin rubberized cloth and has spring pieces. Old diaphragm was stiffer plastic with no spring.
Any thoughts gentlemen? Sorry this posting is so long, but I tried to include all I have done. Seems like the more I try and work on this thing, the worse it gets. Thanks for any and all help.

[boats.net]

Get a timing light and check to see if misfiring at high speed.

[Old Fart]

Get a timing light and check to see if misfiring at high speed.

Boats.net, thanks for your reply. I recently purchased many items from Boats.net for this motor. Purchased new fuel pump diaphragm kit, fuel filter, intake gasket, impeller kit, flywheel key, and ignition coil. I have subbed the new coil in on all 3 cylinders and does not change anything. However I will try to take a timing light next time and check spark continuity while running on water. At idle, have very good blue sparks using tester.

[boats.net]

Check timing as well.

[Old Fart]

Thanks again Boats.net, will try to check timing also when I get a chance.
Had some time this morning so I used a vaccum/ fuel pump tester gauge on the motor while running on a flush cuff at idle. Fuel pump output pressure was 2 PSI (low) and input vacuum measured at fuel filter inlet was 5 HG after I squeezed the hose with pliers to cut off fuel flow.
I have read that vacuum should be 4-5 HG on fuel pump inlet side, so this appears normal, but output PSI should be 5-7 PSI. Sounds like a weak fuel pump output to me. Can you advise what normal pressures should be, and am I measuring them properly or should I measure in different places?
Also noticed input line going to fuel filter is solid gas with no air, but output from fuel pump has air and some bubbles in line. Should this be solid gas only, or is it normal to have some air in line feeding to carbs?

[Old Fart]

UPDATE :

Pulled fuel pump last night and disassembled. Re-installed original plastic diaphragm and put back together. Also left in spring assembly that I got with diaphragm kit that was originally missing from the pump.
Re-installed fuel pump on motor, and cranked up on flush cuff. Immediately noticed it seemed to idle more rock solid, and now there is no air in the line feeding the carbs. All fuel lines are solid fuel now.
Connected pressure gauge to fuel pump output and now reads 4.5 PSI and not 2 PSI like it was. Seems to climb a bit when I revved motor up some.
Will be 1-2 weeks before I have time to take out on water and try, but with any luck this will cure the problem.
Replacement rubber diaphragm from kit seemed OK except for what appeared to be a thin spot where you could see what appeared to be a tad of light through it. No pinholes or splits noted. Maybe just not enough rubber in that one spot to seal it. It is a Genuine Suzuki diaphragm and not an aftermarket one.

[Catfish Charlie]

I know this is a Old Post but I'm having the same issues as Old Fart...Did the fuel pump solve your issue?

[Solarman]

Charlie, Well this is a very old post, however O-F did go through all his carbs exactly as he should by blowing out every fuel and air passage, and making sure all carbs were thoroughly cleaned, fuel pump was rebuilt, and all fuel lines were tight, before going back to his fuel pump again. He did add clear fuel lines, which showed him his pump was not providing proper fuel flow to the carbs.

Charlie, you should start your first post off exactly as he did. First, identify your motor, and what happened, or what led up to it running poorly, and as specifically as you can, what it's running like now. Then "anything" you have done/noticed to try and correct the issue? Tagging another post distracts most of us to that previous motors problems, even though it may seem to be just like yours, it could be very different?

Yes, you can use previous posts as a guide, but many problems can be different, but sound similar. Your problem is the one that counts.

Start your own post, and answer the questions above, then we can work from there.

Good luck, post back on what you have.