PHP Warning: Use of undefined constant VBA_SCRIPT - assumed 'VBA_SCRIPT' (this will throw an Error in a future version of PHP) in ..../includes/functions_navigation.php(802) : eval()'d code on line 1 Surging Power - Fuel Pump??
Looking for some advice from you experienced boaties.
I have just fitted a 1996 Yamaha 175 V6 to my CC Reef Ranger 18 wich I have restored. On the first test run to check prop pitch selection everything worked fine apart from power surging from 4500-5500rpm.
The boat was fully loaded ie 4 adults + about 60ltr fuel + about 80kgs ballast to simulate full fuel. Running a 15 pitch prop it got to about 5700rpm @ 34.6 knots GPS
Running a 17 pitch prop it got to about 5500rpm @ 38.6 knots GPS
WOT operating range for this motor it 4500-5500rpm according to Yamaha so I chose the 17 pitch prop.
On both trials the boat started to surge above 4500rpm. Pumpng the fuel bulb when underway solved the problem.
According to the manual this motor guzzles 75ltrs/hr at WOT (scary $100/hr) so needles to say I will aim to cruise at around 3500rpm @ 22 knots.
Fuel lines are new 5/16 size or 8mm (Just checked actually 3/8 or 10mm)
Fuel bulb is new
CAV filter assembly is new
Petrol conversion element is fitted
Breather to fuel tank is new and clear of debris
So what is my fuel starvation problem?????
I am thinking either CAV filter restriction as these are rated to flow 45ltr/hr of diesel. Does anyone run big V6's using a CAV filter.
OR do I need to renew the fuel pump diaphrams?
Any other thoughts would be much appreciated. A new ETEC would be nice and solve the problem, but a bit expensive and beyond my budget.
first step try a complete remote fuel tank and hose etc to isolate the problem area first, no use pulling things to bits and buying parts till you know where to start! is the 8mm line the correct size, I seem to think they should be 10mm but I could be wrong as it is quite a while since I replaced any fuel line.
Yes I run a 225 four stroke Yammy with a CAV filter, and have no fuel problem.
When my motor was fitted they connected a vacuum guage in the line to check fuel flow and I recall them having to upsize the fittings that were in the CAV filter, have you done this?
Sounds like it is either starving for fuel or sucking in air along the line somewhere.
I would check again that all fuel line connections are sound, the hose clamps can permit a vacuum leak if they are not the right size and tightened up correctly.
Just checked fuel line again - it is 3/8 or 10mm not 8mm as I stated earlier.
Both fuel delivery and breather are approximately 3m long and 3/8 10mm lines.
I havn't got a vacuum gauge to hook up to the fuel line to test whether I have a restriction or not.
I have pressuried the line with the fuel bulb and appear to have no leaks. ie I pump the bulb up to very hard while my offsider checks for leaks. The bulb stays hard (indicating I think no slow leaks) and no visible leaks.
I reckon Noelm's got the best idea, had same symptoms on my old boat though the motor was only 40hp turned out to be a small split in the fuel hose at one of the connections. I cut off the split section and rejoined the hose and never had the same problem again, I think it must have affected the prime just enough at high rpm to not provide quite enough fuel. Give Noelms idea a go and you will pretty much eliminate half your possible causes straight away.
Is the fuel pre-mixed with two stroke oil? If so, perhaps the filter cartridge is not coping with the oil. Some cartridges are more suitable for certain applications
I did a basic check on both of the fuel pumps last night. According to this site http://www.iboats.com/bbboard/bbBoard.cgi which has a heap of information for all brand names, you can test the fuel pumps (one at a time) by removing the two bolts which secure them to the crank case and gently squeeze the fuel bulb - no dripping of fuel should occur.
On my upper one fuel dripped out fairly easily. On the lower one smilar results. This indicates that the fuel pump diaphrams need replacement as they are porous and should not be.
I removed both fuel pumps and stripped them for inspection. The fuel pumps are a service item anyway and not knowing the full history of my engine I decided to rebuild them anyway.
The upper pump was visually newer and held together with loctite. Inspection revealed a clean housing with oneway valves operating correctly. Diaphram was intact with no visible pinholes but not very pliable and nearly failing ie worn through around the perimeter where it seals.
The lower pump was loose (I undid it with my fingers) from the crank case. It was not held together with loctite and the phillips head screws were loose too. The metal/gasket sealing surfaces have been gouged clean with a screwdriver (arrrgg) >. Diaphram spring slight corrosion and diaphram in similar condition to the upper pump.
It looks as though I have made the right call to service both pumps even if it is not the cause of the fuel starvation problem.
My parts should arrive in a few days an maybe a test run next weekend.
I have been unable yet to water test, but scruitenizing (sp) the fuel delivery line I found a few things to mention.
The CAV filter fittings are 10mm but the ID was only 5.5mm. Thinking that this may be a restriction I honed them out to 7.5mm see pic. This surprised me somewhat, as I had a CAV 5/16 fitting on the shelf and it too was 5.5mm ID. You would think that a larger OD would result in a larger ID..... Not so with CAV fittings.
Also on recomendations from iboats head guru, I connected the fuel line directly from the CAV filter to to the fuel screen under the cowl. Effectively bypassing the inline joiner which was also a 5.5mm ID restriction.
Fuel pumps were rebuild with new diaphrams and gaskets. Very easy job. Just a matter of dissasembling the units giving them a good clean and reassembling them with new parts. What I did do, which might be a bit over the top, is finish the alluminium end caps to a true flat condition. This is done by rubbing them in a figure of eight on a piece of 400grit wet and dry sandpaper mounted on a peice of glass (ie truely flat surface). This removes any rough machining marks or screwdriver scratches in my case and alows a good sealing surface for the gaskets.
FYI $55 per pump for genuine gaskets and diaphrams from Yamaha. Was quoted $120 for a new pump assembly. Seems very dear to me compared with US prices.
Will hopefully get a water test this weekend to see I there is any change in the surging at high RPM.
75ltrs/hr at WOT (scary $100/hr) so needles to say I will aim to cruise at around 3500rpm @ 22 knots.
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