WOT Fuel Burn Difference BF200's

I just did a decarb on my pair of BF200's today. Ran on a concentrated small tank with sea foam, then let sit and finished with a few long runs up to WOT. The engines seemed to run fine before this, but are approaching 1k hrs, so figured it was a good idea to do them. I bought the boat used, so have only run it for one season. The fuel mileage is not great, but they run well. They are 2003 BF 200's on a 2660 Prokat. I am running 14 1/4 x 17 3 blade ss Solas props. At WOT the port engine was burning 21gph at 5500 rpms on my floscan, where the stbd was only burning 16gph at the same. The stbd will turn 6k with the engines trimmed down but the port will only turn 5500. If I trim up I can get the port to 56-5700 max, but the stbd can turn over 6k trimmed up. I have noticed this fuel burn difference since I got the boat. I cruise at 28 mph and burn about 9-10 gph stbd and 10-11 gph port, even if I run the port at say 41-4200 and the stbd at 44-4500 rpm. I have to offset the rpms to try and keep them in a relatively close burn rate. Since I got the boat about a year ago I have replaced the racors, the fuel filters on the engines, drained the vst's, changed the plugs, cleaned the IAC's, decarbed, replaced both O2 sensors, new water pump kits, gear oil,thermostats,manifold zincs, and just removed the injectors on the port engine and had them cleaned and tested. The port runs a little bit rougher at idle on the flusher than the stbd does but they both run strong at anything above idle. I am not sure if the decarb smoothed out the idle on the port or not as I have not run it on the muffs yet. The decarb was done in freshwater, so I just used the flush port when I came back. I put the old plugs and O2 sensors back in to do the decarb, so I plan to swap them back tomorrow. Any ideas what may cause the port to burn so much more fuel than the stbd? The port is a counter rotator and has a new gear case on it. I was not under the impression there were any changes to the ratios, but the new case does look slightly different than the stbd. Other than that, the engines are identical. I do run ethanol but keep the fuel treated and the tanks full at all times. I have seen no sign of water in the racors or the vst's since day one,so I don't believe the fuel quality is an issue.

How many fuel filters did you find? I have the exact same motors, same year as you too. You should be able to see the fuel filter on the starboard side of engine, there is also one in the vst and a strainer under high pressure fuel pump..mine was very dirty...there is another filter in between intake and block. Not sure if this would be the cause of your problems, but FYI.

I changed the high and low pressure filters, my racors and cleaned the bowl with the float in it on the stbd side of each engine. I thought the injectors may have been a possible cause, so I had them flowed and cleaned but the only thing they found wrong was the spray pattern was off a bit. Cleaning corrected that but the engine runs the same and the fuel economy has not changed. I ran the engines to get them warm and they are both running rough at idle now but fine at anything above 1k. I plan to put the new plugs and o2 sensors back in now to see if they improve. I figured the decarb may have fouled the plugs. It did run fine at the dock when we came back from the decarb though.

Compression?

I only checked it cold, but will get some numbers later today when I can check them warm before putting the new plugs back in. There was no great differences between any cylinders on either engine though.

So checked the compression warm today. The engines did not seem to run well when I started them to warm them up prior to pulling the plugs. Did compression test, put new plugs back in, new o2 sensors back in and checked the IAC's again to make sure they were clean. Engines seemed to still run rougher than they did prior to the decarb. They did run a little better once I swapped out the plugs and sensors, but I can't figure out why they would run worse now. The compression seems to be somewhat low, but I did use the gauge the seems to read lower for some reason. I have 2 of them. Figured once I started with one gauge, I would stick with it.
Compression: Port engine, port side top to bottom 186,184,190, stbd bank 180,175,184. stb engine, port bank 190,174,186, stbd bank 190,177,185.
I can check with the other gauge if needed, but if I remember correctly it is around a 10psi difference between the 2 gauges.

Anyone have ideas or suggestions? I can't figure out why the engines would run rough after the decarb process. Would clearing any codes help? The 02 sensors I put back for the decarb were bad, so I am sure there is a code stored now for that.

I'm away from my shop manual for the moment, but there is an air intake sensor (I forget the proper name) that often gets clogged and will affect performance, especially at idle.

Now that chawk said that, check the air intake solenoid valve as well as the butterfly flap that it controls. Make sure it holds with vacuum and that it's well lubed and not sticking.

Are you referring to the one on the bottom of the intake at the rear or the engine? I just had the port side apart when I had the injectors cleaned and I did clean the butterfly and checked the valve to ensure it held vacuum. Could the butterflies have gotten gummed up from the decarb? I did also spray some deep creep into the intake while the engines were running and I was doing the decarb. The dealer said the compression readings were all ok prior to my purchase, but they could have been lying. It seems they did that about a lot of things. They even wrote the compression readings on the block for each cylinder. All were 205-210. They are not that high now and I have put less than 50hrs on it. Could it be possible the valves were adjusted with the carbon buildup and now without the carbon, they are tight?

Yes, that's the one..mine were sticking. Have you checked engine for codes?

I manually moved the linkage for the butterflies and it was free on both engines. I did not notice a big difference in the running while I was moving them though. I tried to check for codes and now both of the mil lamps are on solid when I turn the ignition on with the shunt in place. I jumped the black and white/green wires on the service plug. Last time I checked them, prior to changing the o2 sensors, one engine would flash the mil lamp and indicated a bad o2 sensor, the other had a solid light. I have no idea why both of them are solid now. I reset them both anyway. I ran both engines again and the stbd still has a roughness to it and a noticeable miss that stays up to at least 2k rpm. It is more like a faint poof throughout the rpm range. The port engine runs a little bit better but is still a little erratic at idle. The only other thing I did since running them last was check/clean the map sensors. I did not see any difference after doing it though. Is it possible the engines had carbon buildup and the valves were adjusted that way, then the decarb removed some of the buildup causing them to be out of adjustment now, potentially causing the engine to run poorly? I definitely don't hear any tapping from the valve train. Just trying to figure out my next move. Should I decarb again, then adjust the valves?

Have you checked ignition timing?

I have not checked the timing, but would it have changed from just doing a decarb? I never ran into that issue before. Are you thinking the timing may be the reason the port engine burns more fuel and turns less rpm @ wot? Or why the idle is not smooth on either of them since the decarb?

I was under the impression the mil should flash to indicate everything is ok. If it stays on solid with no flashes, then there is a problem in the circuit, wiring, dcm, etc. Should the light stay solid? If so, I can't understand why it would not throw at least the o2 sensor codes when I ran it with the bad o2 sensors in there.

Ep4 said:

I have not checked the timing, but would it have changed from just doing a decarb? I never ran into that issue before. Are you thinking the timing may be the reason the port engine burns more fuel and turns less rpm @ wot? Or why the idle is not smooth on either of them since the decarb?

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The "poof" sound was why I was asking about timing.

I checked the timing on both engines and all looks to be right. I adjusted the belts while I was in there. So now where do I look? Should I try and adjust the valves? I am not sure when they were done last. The bottom line is that the engines run worse now after the decarb. I can't figure out why that would be. The sea foam should not have done anything to the filters, so fuel should not be an issue. The port engine burns more fuel than the stbd and turns about 500 less rpm at the same trim level @ wot. This has been the case since I got the boat, so that is not a new problem. 5 gph difference at wot seems to be a pretty big one.
Could a difference in fuel pressure between the engines cause the fuel burn difference and rpm difference? Could the port having a brand new gear case cause the rpm difference? Were there any ratio options or changes from 2003 to 2012-13? The port is the counter rotator, but that should not cause the rpm difference.

Any ideas?

Planning on trying to run the boat tomorrow and may decarb again, then change the oil. Is there any reason I should not decarb again, or do it with the newer plugs and o2 sensors in there?

It shouldn't do any harm, IMO. Would recommend changing the oil after the decarb.

Did not get a chance to run the boat today but did decide to adjust the valves on the stbd engine. Found the intakes were in range .008-.009 but the exhaust were tight at around .009. I adjusted them to .012 now and went ahead and changed the oil. It was dirty from the decarb. I did notice the intake and the tubes were a a little dirty on the port engine when I took it apart to do the injectors. I thought the stbd would be the same way but it looked pretty clean. I am guessing it was from the decarb. I used the spray in the throttle body and the mixed fuel can When I did it.
I noticed a little bit of puddled fluid in the bottom of corners of the intake. I thought it was oil at first, but it smelled like fuel or a solvent. I came to the conclusion it must have been the sea foam combined with any oil and carbon residue mixed in from cleaning the inside of the manifold when I sprayed it in.
I wanted to get the port valves adjusted but ran out of time, so that will have to be another day. I also bought some new timing belt tensioner springs and readjusted the belts. I figured they were only a few bucks and I was already shipping the oil and filters, so why not.

I may not be 100% correct about this, but it is probably worth checking if no one here with more knowledge says otherwise. The new O2 sensors have a reduced number of holes in them when compared to the older ones. This means that there is a SW update that should be loaded with the new sensors unless your new ones are the older type again. Could a mismatch between your new sensors and old SW version cause the issues you are seeing? As I said, I am not 100% on this, but we have been through a number of O2 issues on a pair of BF175's and I know that part of the fix was getting the SW to properly match the sensor version, but I don't remember if this was seriously affecting fuel use etc when they were incorrectly matched.

I bought the old style sensors when I replaced them because I don't have the new ecm to go with the new style. I did find that out on this forum before I purchased, thankfully. The weird thing is that the port burns more fuel but the engines have everything the same except for the cr gear case. I still have to adjust the valves on the port engine, but that is about it. A buddy mentioned fuel pressure possibly being higher on the one burning more fuel. I am not sure how I can check that though.

Ep4 said:

I bought the old style sensors when I replaced them because I don't have the new ecm to go with the new style. I did find that out on this forum before I purchased, thankfully. The weird thing is that the port burns more fuel but the engines have everything the same except for the cr gear case. I still have to adjust the valves on the port engine, but that is about it. A buddy mentioned fuel pressure possibly being higher on the one burning more fuel. I am not sure how I can check that though.

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I think the CR gearcase has an extra gear, so you might get a small amount of extra fuel burn from that, but not the numbers you are seeing. We have done a bunch of O2 sensors on our 175's and your fuel difference looks about what I would expect to see with one faulty O2 Sensor. Only other thought is to check if the props are still a correctly matched pair. It looks like you have pretty much covered everything else other than maybe some vagaries in the water flow under your hull.

Again, three things come to mind. (1) Possibly an incomplete decarb. Could you explain exactly how you did the decarb, e.g. what ratio of SeaFoam and fuel, how long you ran the engine on that mixture, how many iterations you did, etc.

(2) After the decarb, did you pull the VST and HP filter and clean them thoroughly, inspect the needle valve and float in the VST, clear the screen to the HP filter, etc. etc?

(3) Way back in the fogginess of my memory, I recall there are efficiency issues around the direction of the rotation of the prop. This was based on the time that I owned a boat with an old Volvo outdrive where the prop ran counter-clockwise. That is, something about more energy being required run a prop counter to the rotation of the engine as opposed as in the same direction as the engine rotation. The reversal in the torques between the two was not energy efficient. To what extent that effected fuel burn, I have no idea.

Maybe someone with a lot more training in mechanical engineering would jump in on this last item.

chawk_man said:

Again, three things come to mind. (1) Possibly an incomplete decarb. Could you explain exactly how you did the decarb, e.g. what ratio of SeaFoam and fuel, how long you ran the engine on that mixture, how many iterations you did, etc.

(2) After the decarb, did you pull the VST and HP filter and clean them thoroughly, inspect the needle valve and float in the VST, clear the screen to the HP filter, etc. etc?

(3) Way back in the fogginess of my memory, I recall there are efficiency issues around the direction of the rotation of the prop. This was based on the time that I owned a boat with an old Volvo outdrive where the prop ran counter-clockwise. That is, something about more energy being required run a prop counter to the rotation of the engine as opposed as in the same direction as the engine rotation. The reversal in the torques between the two was not energy efficient. To what extent that effected fuel burn, I have no idea.

Maybe someone with a lot more training in mechanical engineering would jump in on this last item.

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How does the decarb affect the vst and filter before engine? I didn't think that out would matter as far as creating debris? Maybe I don't understand the proper way

If you do a decarb the way I do - from an auxiliary fuel tank straight into the LP fuel filter fitting, then the Sea Foam can dissolve junk from the various fittings, connectors, valves, and lines and dump those into the VST tank. Thus, it's necessary to drain the VST as a minimum. But in this case, I would remove it and clean it and make sure the float valve is working properly and the needle and needle seat is spotless. While doing that I would also clean or replace the HP filter.

I did not take out the hp filter after the decarb. It was replaced not too long before the decarb though. The fuel burn issues were there before and after the decarb. The only difference I have seen is that both engines run rougher at idle after the decarb. They both seem to have good power and run fine in the water from what I can tell, but on the flusher, they are rougher running and jump around a little. If I rev the port engine up some and let off the throttle fast, then it may stall. I ran offshore yesterday and the stbd engine still burns less fuel than the port, but it was rough so I could not really watch the floscan closely.
As far as the decarb, I ran a can of sea foam to a gallon of fuel, then added a little more, so the ratio was a little more than a can to a gallon. I ran it on the flusher for 10-15 min like that, and also sprayed in the deep creep into the throttle body while it was running. I let it sit for about 15min, then ran them for another 15 minutes or so and varied rpms. My flusher provides plenty of water with the dual feed so I had no temp issues. A day or so later I took the boat to a local lake and ran each engine again on the sea foam mix for 10-15 minutes, then let them sit for 15min, and ran the boat for a good 20 minutes afterward. I ran at cruise and for stretches at wot to make sure the carbon burned off.
The engines always seemed to run rich to me since I got the boat. I replaced the o2 sensors and they seemed to run a little bit better but they always smelled rich and the fuel burn difference has been the same between the engines. I just got an o2 sensor engine light on the stbd engine yesterday, so I don't know what to do now. Why didn't the o2 sensors help when I changed them? Do I need to go to the new sensors now? And change the computers to go with them?

Ep4 said:

I did not take out the hp filter after the decarb. It was replaced not too long before the decarb though. The fuel burn issues were there before and after the decarb. The only difference I have seen is that both engines run rougher at idle after the decarb. They both seem to have good power and run fine in the water from what I can tell, but on the flusher, they are rougher running and jump around a little. If I rev the port engine up some and let off the throttle fast, then it may stall. I ran offshore yesterday and the stbd engine still burns less fuel than the port, but it was rough so I could not really watch the floscan closely.
As far as the decarb, I ran a can of sea foam to a gallon of fuel, then added a little more, so the ratio was a little more than a can to a gallon. I ran it on the flusher for 10-15 min like that, and also sprayed in the deep creep into the throttle body while it was running. I let it sit for about 15min, then ran them for another 15 minutes or so and varied rpms. My flusher provides plenty of water with the dual feed so I had no temp issues. A day or so later I took the boat to a local lake and ran each engine again on the sea foam mix for 10-15 minutes, then let them sit for 15min, and ran the boat for a good 20 minutes afterward. I ran at cruise and for stretches at wot to make sure the carbon burned off.
The engines always seemed to run rich to me since I got the boat. I replaced the o2 sensors and they seemed to run a little bit better but they always smelled rich and the fuel burn difference has been the same between the engines. I just got an o2 sensor engine light on the stbd engine yesterday, so I don't know what to do now. Why didn't the o2 sensors help when I changed them? Do I need to go to the new sensors now? And change the computers to go with them?

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Our BF175's are mounted on a Cat and the exhaust ports are just above the min recommended height off the water. Theoretically all OK, but once you get a few guys fishing at the back etc the engines are really a little low. Since drift fishing with the engines idling is something that the boat is often used for, we believe this is why we are having repetitive O2 sensor issues, and that it may even affect the sensors even before they throw an alarm. Sometimes we detect the sensor failure by the different fuel burns prior to seeing an engine alarm. One of our winter projects this year is to look at building up the transom height so that we can lift the engines and run longer legs on them. I love our Hondas, but they have two important weaknesses that need to be dealt with. One is the O2 sensors, and the other is that they need to be carefully/regularly flushed than some of our other engines to avoid block corrosion issues.