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Excuse the long post but I am trying to provide as much detail as possible. I have a brand new DF300 repowering my 1998 Pro Line 251 Walkaround. I've lost some faith in the shop that installed the engine after a couple conversations on the issue I'm asking about here as well as a few other bugs from this repower job that were due to a lack of attention to detail so I thought I'd see if anyone here had any other ideas.
I put it in the water last weekend to begin the break in intervals (15 min @ idle speed, 1:45 at 3000 RPM, 1:00 at 4000 RPM). Since I was told I could open the throttle just long enough to plane off then come back down to the target RPM range I figured out right away that the engine struggled when it got up around 5000 RPM. Anywhere between 4800 RPM and 6000 RPM the engine begins to surge, dropping down to 1-2k RPM and then back up and this repeats until you come off the throttle to a level it can maintain. My initial feeling was that it was starving for fuel. I called the shop that did the install while out on the water and all he could tell me to check was the fuel lines which were all fine. He then asked me to send a pic of the fuel line he installed from the new primer bulb to the engine. He could neither tell me what size line he used nor what size line it should be - only that the tech he had do it should have used the same stuff they use on Yamahas. Turns out it was 5/16" line. That was smaller than the line I had there on the previous motor and smaller than the fittings on the bulb he installed so he suspected that might be the problem. He asked me to complete the break in intervals which I did and at 4000 RPM the boat ran flawlessly for 2 hours over the course of the rest of the day but would still struggle at higher RPMs.
When I got home rather than tow the boat 45 min away to his shop where he wouldn't be able to duplicate the issue in his parking lot (which would also leave me without it for another week or longer) I replaced the bulb to engine fuel line myself with 3/8" and while I was at it I ran all new line from the tank pickup to the new bulb. The shop didn't have any other ideas to offer and asked me to let them know if that took care of it. I got it back in the water today hoping I'd fixed it but I had the same issue - get up around 5000 RPM and the motor acts like its struggling because RPM increase from there seems slow and strained and then at some point the RPMs will fall off dramatically as the engine begins to surge. It does this whether or not I go WoT out of the hole or from a cruising speed @ 4000 RPM. Again today the engine ran silky smooth in that 4000 RPM range for several hours - not a single hiccup or hesitation.
As mentioned I replaced the entire run of fuel line with new and after splitting the old lines apart they were fine and the inner liners had not collapsed. I also checked the tank vent and it isn't obstructed.
What's left? Is it possible that its propped wrong? That is, do these engines have a safety feature that knocks down the RPMs if they are at a certain throttle position but don't achieve an expected RPM in a certain amount of time? Even though its acting like outboards I've had in the past do when they aren't getting enough fuel its hard to fixate on that when all filters, lines, etc... are brand new.
Thanks in advance.
I put it in the water last weekend to begin the break in intervals (15 min @ idle speed, 1:45 at 3000 RPM, 1:00 at 4000 RPM). Since I was told I could open the throttle just long enough to plane off then come back down to the target RPM range I figured out right away that the engine struggled when it got up around 5000 RPM. Anywhere between 4800 RPM and 6000 RPM the engine begins to surge, dropping down to 1-2k RPM and then back up and this repeats until you come off the throttle to a level it can maintain. My initial feeling was that it was starving for fuel. I called the shop that did the install while out on the water and all he could tell me to check was the fuel lines which were all fine. He then asked me to send a pic of the fuel line he installed from the new primer bulb to the engine. He could neither tell me what size line he used nor what size line it should be - only that the tech he had do it should have used the same stuff they use on Yamahas. Turns out it was 5/16" line. That was smaller than the line I had there on the previous motor and smaller than the fittings on the bulb he installed so he suspected that might be the problem. He asked me to complete the break in intervals which I did and at 4000 RPM the boat ran flawlessly for 2 hours over the course of the rest of the day but would still struggle at higher RPMs.
When I got home rather than tow the boat 45 min away to his shop where he wouldn't be able to duplicate the issue in his parking lot (which would also leave me without it for another week or longer) I replaced the bulb to engine fuel line myself with 3/8" and while I was at it I ran all new line from the tank pickup to the new bulb. The shop didn't have any other ideas to offer and asked me to let them know if that took care of it. I got it back in the water today hoping I'd fixed it but I had the same issue - get up around 5000 RPM and the motor acts like its struggling because RPM increase from there seems slow and strained and then at some point the RPMs will fall off dramatically as the engine begins to surge. It does this whether or not I go WoT out of the hole or from a cruising speed @ 4000 RPM. Again today the engine ran silky smooth in that 4000 RPM range for several hours - not a single hiccup or hesitation.
As mentioned I replaced the entire run of fuel line with new and after splitting the old lines apart they were fine and the inner liners had not collapsed. I also checked the tank vent and it isn't obstructed.
What's left? Is it possible that its propped wrong? That is, do these engines have a safety feature that knocks down the RPMs if they are at a certain throttle position but don't achieve an expected RPM in a certain amount of time? Even though its acting like outboards I've had in the past do when they aren't getting enough fuel its hard to fixate on that when all filters, lines, etc... are brand new.
Thanks in advance.
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