Throttle/Carb Issues

[TEXAN]

I need some help solving my carb issue. After hours searches and trying what is recommended on the forums I continue to get the same results. The boat is loading up around 2-3K and sputters like crazy at 4500rpm in the water. It doesn't make it past 4500 rpms. Prior to carb rebuild, boat ran great on the water. Full throttle was a smooth 6k or so. Although it would ping the rpms during fresh water flushes.

1. Rebuilt carb two weeks ago do to for the new season using Mikuni OEM parts from SBT.
2. Tested Pop off, 28 psi, which is where it was set originally. (used previous springs)
3. Low screw is set to 1 turn out, high to 0. Attempted 1 1/4-1 1/2 on the low screw, same results.
4. Checked for air leaks, even taped holes for my Primer Kit as I didn't trust the O-rings to keep the block off plates in place on the water.
5. After rebuilt, starts on the first try, no hard cranking, idles at 1200 rpm in the water.
6. Throttle linkage is good, and both carb are perfect regarding the butterflies.
7. Occurs with fuel On and RES selected.
8. Took them apart for the 3rd time this weekend to triple check my work, and everything appears to be good. Yet same results.
9. Testing with just the restor plate no plastic black air baffle.

My concern now, is that the carbs may have been jetted at some point. And if this is the case, is there anyway to tell? Aside for that, I'm officially lost. Any ideas?

-TEX

 

[Waterluvr]

Make sure your running 67.5 pilot jets, if both mains are still 142.5's change the pto jet to a 145 and don't be afraid to crack the H adjuster open 1/16 of a turn on the pto carb. With 1.5mm N/S seats you want to try and raise your pop off to 35 psi tested from the filter inlet only and your L adjusters should be right in the ballpark at 1 1/2 turns out.

Take the Rave valves and housings out, inspect and clean everything and measure the housing bore for wear anything over .400 and the housing needs to be replaced and likely everything else will be cooked, the o-ring can't seal gas from the housing when it runs over tolerance and your exhaust timing will be way off.

Aside from that, make sure your adjusted to get full range of operation on the throttle cable and if the boat is new to you double check the pitch on the impeller for size the 17/22 factory prop that was standard on the 97's really runs that boat nicely.

 

[TEXAN]

I'll be pulling them off tomorrow and will try your recommendations. Thanks.

 

[Waterluvr]

I'll be pulling them off tomorrow and will try your recommendations. Thanks.

This is what we talked about with the check valves Tex, sounds like you got everything else squared away on your carbs up to this point the curve isn't nearly as defined as the picture shows but you'll get the idea the mark always goes up when they have a blue or green ink line on them.

 

[Coastiejoe]

Chances are it is in the carbs as that is the last thing you touched. But,, I would recommend unplugging the Voltage Regulator as your description is exactly what happens when a regulator is failing.

 

[TEXAN]

****Update****

First off, I've got to give a huge "Thanks" to [MENTION=71806]Waterluvr[/MENTION] for helping me out with this issue. He was there anytime I had a question, and his level of expertise help me learn tons of information about my boat. If you ever need a guy to point in the correct direction and be there to help you out, he's your guy!

The boat is running like a champ now and throttle response is amazing! Here's a run down of our troubleshooting methods.

1. Pulled to the carbs to verify pop off pressure. Checked out good at 28psi.
2. Verified Fuel flow. Using the inlet fuel supply hose leading to the carb, detached it at the fuel filter, removed the reserve fuel line at the tank pick up baffle, attached the carb fuel supply line directly to the reserve output from the tank. This completely bypassed the fuel on/reserve switch and lines. Disconnected fuel return lines during attempt to start to verify fuel flow. Same results in the original post.
3. Took carbs off again. Torn them completely down again, only this time with pointers from WaterLuvr. Turns out my low side on both carbs were a bit clogged. When spraying Carb cleaner through the low speed screw inlet and small jetting, my flow was minimal coming out of the 3 pin holes supplying fuel inside of the carb. Using copious amounts of carb cleaner, a small needle, and lint free paper towels, I was able to get them flowing like 100lb injectors. The same practice was used for the high side.*** Side Note*** Do yourself a favor and located a fuel flow diagram for the carb and understand where the fuel entry and exit points are. Helped me a great deal. Also, if you use a straw with the carb cleaner us can mimic how the low/high speed screw works. Insert the straw in the hole, spray carb cleaner, and slow pull the straw outward. Viewing the 3 pin holes, you will see how the velocity in flow out of these holes increase as the straw (screw) is pulled (screwed) outward. Pretty cool to see.
4. Fuel check valves could have be upside down. Not sure if this occurred or not, but I had 2 extras and decided to go ahead and replace them. Making sure the marked surface was the top surface, important as the fuel check valves are concaved in shape.
5. Plastic Diaphragm and gasket were backwards. On the fuel pump side I ended up swapping the plastic clear diaphragm and gasket. Not sure how much of a difference it made but it was layered wrong. Locating a parts schematic on Google is what saved me on that one. Do yourself a favor, have one available during reassembly.
6. With those corrections, she starts on first try after a few squirts of the primer.

I'm looking forward to hitting the water this weekend, and on the next project, adding the Bimini Top. Hopefully my experience will help shed light on someone's similar issue in the future, and help resolve their problem just as quickly. Thanks!

-Tex

 

[Waterluvr]

Good work Tex, quite a difference before and after huh? ~Tex is an active duty US service member and I spend a little extra time trying to help those guys out when possible, small token of appreciation from my family to you and your's.

Thank you for your service! Enjoy that boat for the season and when it's time to put it away for storage send me up that MPEM and I'll make you an extra key and get your owner information updated in it and I'll email you screenshots of the timing and ignition curve settings for your records.