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BF 200 RPM Difference Between Engines...Why?

E

Ep4

Regular Contributor
I have a pair of 2003 BF200's and see a difference of about 300-400 rpms between the port and stbd at WOT. They have the same props on them but the port has a newer gear case. I am not aware of any changes in the ratios from '03 to '12. The gear case was changed before I bought the boat.
Both engines have all new fuel filters, as well as the racors on the boat. I have also replaced the plugs, O2 sensors, cleaned the IAC's,checked the map's and made sure the cables are allowing both engines to open fully.
Both engines seem to be slightly erratic at idle but nothing serious. I never had 4 strokes before so am not sure how steady or smooth they should be. They run perfectly smooth at all other rpms and have no noticeable issues with power or performance. Both props have just been balanced and cupped. The engines have just over 900 hrs on them. Should I be looking into having the injectors checked/cleaned? Could they be causing the rpm issue,idle roughness, and any fuel economy issues? I do notice the port engine does burn more fuel than the stbd at the same rpm. I can never get the port to equal or use less fuel than the stb unless I greatly drop the rpm. The difference is about 1-2gph on average.
 
Yes, the port is the counter. I should also mention the boat is a cat. I have been watching the floscan closely to determine the best cruise rpm and have always seen the port engine burn more fuel. I did try to swap the lower units around and saw a slight increase in overall fuel economy but a little bit slower top speed. I don't recall seeing the fuel usage increase on the stbd when the LU's were swapped. I am tempted to change them back just to verify, but I am pretty sure the issue stayed with the port engine.
I also raised the engines up 2 holes because the cavitation plates were under the surface, now they are right at or just on top. The boat would porpoise some when taking off out of the pass, so I would have to trim the engines way down and/or use the tabs. I don't seem to have that issue now and it rides more level. I don't have the ability to raise the bow up very high now, but I don't see much benefit in that anyway since the ride is much rougher if the bow is too high.
 
I don't think your problem is that unusual due to prop and hull configuration variations. But those types of hydraulic/mechanical issues that are way beyond my level of competence. I would explore any of the websites dealing with your particular make and model of boat.
 
I was going to check the ratios by pulling the lower units, just to be sure. The coils plug right onto the plugs so I am not sure what I would be checking with a gap tester. The linkage is fully advancing on both engines, to the stop or within the tolerance in the procedure I read. Isn't the timing advanced by the ecm? I would like to decarb but what you are suggesting is that I spray the seafoam in, then sit at the dock for 30min, then run at WOT until the smoke stops. Isn't there a way to do it at home? I used to do my 2 stroke at least once a year by spraying deep creep into the carb throats. On my vehicles I have done it through a vacuum line with a small tube and some sea foam. Can it be done this way on my BF200's? Will the decarb hurt the O2 sensors? I just replaced them and they are not cheap. Should I put the old plugs and O2 sensors in for the decarb, then swap them back after?
Any opinion on the injectors being a possible issue? After 900 hours, should I pull them and have them checked/cleaned?
 
I went back and re-read your initial post and all of the replies. The rough idle may be an indicator that you have an engine performance problem rather than an engine mounting issue.

Timing is controlled by the ECM. I would consider swapping the ECM's and see if the problem moves with the ECM over to the other motor. If so, then the problem is with the settings in the ECM. It is not very unusual for the ECM's to have minor variances in performance. I have not heard of any way to reprogram the ECM. If that turns out to be the problem, I would have a conversation with Honda Customer Service in Atlanta. If the problem does not move with the ECM's then you are back to a fuel or spark issue on the slower engine, or a mounting problem.

I agree that a compression test would be helpful in tracking down the problem - Fully charged batteries, kill switch engaged, all plugs removed, throttle wide open, and crank for at least 5 seconds. Also consider doing a cylinder drop test where you disconnect one cylinder at a time while the engine is running to see if performance changes. If a dropped cylinder does not change performance, then that could be the problem area.

Your engines should be idling at 650 rpms +/- 25 or so. The idle should be fairly smooth, like an auto with a performance cam (which is exactly what that engine is.)The plugs cannot be re-gapped, they are iridium and factory set. Use only NGK IZFR6F11 plugs - no substitutes, even though the manual says the Denso's will work, they fail too often on this engine.

A good decarbon treatment using Sea Foam or Yamalube Ring Free (or similar) will clean the injectors also. Those are supposed to not harm the O2 sensor, but I'm a skeptic, so if the old O2 sensors are still good, I would swap them out for decarbonizing. To do this adequately, you need to be either on the water, or use a sizeable test tank. Do not try doing it with muffs - it will overheat and possibly damage the engine.
 
I checked the old plugs and they did not look bad and the gaps were all well within the specified range. I replaced them anyway, with the correct NGK's.
I believe the old o2 sensors were bad. I did try to test them and there was no real response to heat, and one engine showed on the MIL when I checked it jumping the service plug.
The idle sounds about right, but I can double check that. Maybe the engines are idling as they should and I am just not used to the way they idle. I don't run across too many Hondas where I launch so I don't really have anything to compare to. I do run treatment in the fuel and the tanks are always full, to try and combat the ethanol issues. I will try to do the decarb soon to see if that helps anything. Would I be best to try and let a vacuum line suck it in, or use the spray and shoot it into the air intake?
 
Using the spray in the intake will probably work okay. But below is how I've done a thorough decarboning in the past...

My method for decarbonizing. There are other ways to skin this cat.

Disclaimer: I’ve never had to do this on my Honda 225 (1510 hours) yet, but may need to do so soon. We are fortunate in this area to have access to non-ethanol gasoline. However, I’ve done it many times on old two strokes and inboards. Many marine sites and experienced tech’s say that this procedure works equally well on four strokes.

This procedure must be done on the water or in a large tank. DO NOT ATTEMPT WITH MUFFS.

Rig up a separate small fuel tank. It’s best if you can find a 4 gallon or 6 gallon outboard fuel tank with a pump-up bulb in line. But you can use any container that you can safely run a fuel line out of. The Honda fuel pumps will pull the fuel in with no problem.

Set up this auxiliary tank so you can switch from regular fuel to doctored fuel rather quickly – see below.

Mix gasoline to Sea Foam at a ratio of 8:1. That is, for each gallon of gasoline (128 oz.), add one 16oz can of Sea Foam.

Start the engine, let it warm up. Turn it off. Switch the fuel line over to the doctored fuel container. Restart engine. It will take a few minutes to burn through the fuel in the VST and fuel lines before the Sea Foam gets into the injectors. You will see it start to smoke and cough when it does. You may have to increase the idle to keep it running once the engine gets loaded with the Sea Foam.

Run the engine 15 minutes at no more than 2000 rpm. Then shut it down and let it sit for 15 minutes.

Switch over to regular fuel and restart the engine, the smoke and black soot you see is the carbon burning off.

Repeat the process a second time. If the engine smokes after the second time do it again. I’ve never had to do this more than twice on any engine.
 
Go to top of this page. Click on "Honda Outboard Forum" and to the left you will see a blue box that says something to the effect "Post new thread"
 
chawk_man said:
Using the spray in the intake will probably work okay. But below is how I've done a thorough decarboning in the past...

My method for decarbonizing. There are other ways to skin this cat.

Disclaimer: I’ve never had to do this on my Honda 225 (1510 hours) yet, but may need to do so soon. We are fortunate in this area to have access to non-ethanol gasoline. However, I’ve done it many times on old two strokes and inboards. Many marine sites and experienced tech’s say that this procedure works equally well on four strokes.

This procedure must be done on the water or in a large tank. DO NOT ATTEMPT WITH MUFFS.

Rig up a separate small fuel tank. It’s best if you can find a 4 gallon or 6 gallon outboard fuel tank with a pump-up bulb in line. But you can use any container that you can safely run a fuel line out of. The Honda fuel pumps will pull the fuel in with no problem.

Set up this auxiliary tank so you can switch from regular fuel to doctored fuel rather quickly – see below.

Mix gasoline to Sea Foam at a ratio of 8:1. That is, for each gallon of gasoline (128 oz.), add one 16oz can of Sea Foam.

Start the engine, let it warm up. Turn it off. Switch the fuel line over to the doctored fuel container. Restart engine. It will take a few minutes to burn through the fuel in the VST and fuel lines before the Sea Foam gets into the injectors. You will see it start to smoke and cough when it does. You may have to increase the idle to keep it running once the engine gets loaded with the Sea Foam.

Run the engine 15 minutes at no more than 2000 rpm. Then shut it down and let it sit for 15 minutes.

Switch over to regular fuel and restart the engine, the smoke and black soot you see is the carbon burning off.

Repeat the process a second time. If the engine smokes after the second time do it again. I’ve never had to do this more than twice on any engine.
Click to expand...

How would you go about disconnecting the fuel lines? Keep in mind I will have to do this 2x per engine. My fuel lines come from a barb on the floscan sensor, then go to the primer bulb and out to the engine. Should I see if I can find a tee of some sort, or a quick connect that I could maybe leave inline after I am done? I am guessing I will need at least a gallon of mixed fuel for each engine to be able to do this a couple of times each.
Once I have let it sit for 15 min, can I run at cruise or do I really need to run at WOT? Should I also spray some air intake cleaner or seafoam into the air intake, just to make sure the intake is clean?
 
There are many different fuel line setups, so you will just need a logical place to do the disconnect. I usually try to do it at the output side of the pump up bulb. Make sure you have a plug or clamp for the open end while the fuel line is connected to the test tank. If necessary, simply cut the fuel line at a convenient place. You can get a barbed fuel line connector and screw clamps at most NAPA stores. I would not try using a T connector. I would safe side myself and mix at least two gallons for each test. Any excess can be dumped back into the boat's tank. You're probably okay to run at cruise, but when I was doing this with old outboards, I would run them up to WOT just to make sure I blow everything possible out of the exhaust. If you are going to do the decarb, I don't see any reason to spray Sea Foam into the air intake also.
 
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