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Convert Honda 75 to 90hp

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bastropdan

New member
I posted last summer about a 75hp Honda (2008 or 9 model) having rough idle problems. mycama suggested having the injectors redone. I did that with no positive results; same problems. The Honda reps from Texas, Georgia and Japan all said it was old fuel (wrong), EPA regs (possible) or something else. They had all sorts of excuses. Bottom line is that the engine still runs rough on start up cold and after fishing for a while. I think it may have to do with a fuel problem with the 75 vs 90. They 75 uses too little fuel and it causes a starvation. My question is: What would it take to convert the 75 to a 90 hp? I see where it would take a new camshaft and ECU. I don't care about the warranty, as it is doing me no good as it is. Getting a new engine is out, as I am retired and don't want to spend a fortune for something I will use infrequently. Plus, who wants to buy an engine that does not run good. Thank you for your reply.
 
Rough running has to do with something on the motor.------" too little fuel causes starvation " I am not sure what you mean by that.--------Time to diagnose the motor that you have as I believe there is something wrong.-------Did you buy the motor new ?--Is there a thermostat installed and is it working properly ?
 
racerone said:
Rough running has to do with something on the motor.------" too little fuel causes starvation " I am not sure what you mean by that.--------Time to diagnose the motor that you have as I believe there is something wrong.-------Did you buy the motor new ?--Is there a thermostat installed and is it working properly ?
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I bought the engine new in Jul 12. It has spit and sputtered ever since. I have taken it to 3 mechanics and they all say the same thing after the Honda rep inspects the engine to confirm the problem. One mechanic mentioned a thermostat, but after conferring with Joe Koury the Honda rep, he said everything was fine and it was bad gas. I have heard that excuse 3 times from the same guy. He happens to be the rep for central Texas. I wrote letters to Georgia and Japan, and the rep from Georgia listened intently to what I was saying, but wound up shrugging his shoulders and blamed the EPA for strict standards and pretty much said "Too Bad". When I mentioned fuel starvation, I was thinking they took a 90 and starved it down to a 75. I am at wit's end and am sick of jacking with these people. According to the honda rep, I would have to flush the system and pump new gas into the motor every time I took it out. Makes no sense to me, but Honda is on my list from now on. I may look into the thermostat and put one on myself. Thank you for the reply.
 
From what you said:
It runs (idles) rough when its cold.
It runs (idles) rough after you have been fishing a while. (presumably then engine has been off for a while)

Is the fuel usage OK or a bit higher than you expect? (though if the engine has been like this from new you may not notice)

Does it idle OK just after a long run out to the fishing ground (when the engine is hot) ? If this is the case, does it idle OK for a few minutes and then get rough. This indicates the fault is there when its cold. The ECM should flag this anyway and report a code to the dealer.

If its when its cold its either a tuning problem (ECM) or something obscure like a tiny air leak in the manifold that seals itself when its hot. Are the plugs correct heat range and have they been changed by the mechanic when you first reported the problem?

There may be a very small leak in the fuel line (connector) and when the engine is hot it is a little better at pumping (sucking) fuel.

Also look for water in the fuel. Putting in more fresh fuel wont get rid of the water, but using fuel with some ethanol/methanol (alcohol) will but the engine may run rough till all this fuel flushes through.

If you have a water trap look for tiny bubbles when idling (or even running) which indicates an air leak before the filter.

Diagnosing problems when an ECM is involved is a little hard because the ECM itself tries to correct the problem so the symptoms may not be all that indicative of the real fault. A faulty thermostat for instance may mean the engine never gets to the right temperature so it runs too rich and at idle this will cause rough running. When the engine is hotter (just been on a run), the rich mixture may not matter and the engine copes until the cylinders themselves cool down.

Even if you manage to convert it to a 90hp you may still have the same fault.
 
Hey, Berniek. The engine runs rough when cold. It runs rough after sitting for a while and cooling off. Fuel consumption? No idea. The repairman says the computer/ECM reads that all is OK. I understand about using fresh fuel. I cannot detect the smell of fuel anytime after lifting the cowling. I have 2 fuel filters installed between the tank and engine. The last repairman says he changed the plugs. I have used several different tanks and fuel connector combinations. I have tried so many things. The common thread running through all of this is a guy named Joe Koury, the honda rep. I need to take it to a dealer out of his jurisdiction or go ahead, bite the bullet, and get a Yamaha. That is what everyone told me to do but I figured honda was the best. Then, Murphy came along and got me a lemon. Thank you for all the replies, gentlemen.
 
I need to get my $.02-worth in here.

I have been working on Honda engines since 1970, and Honda Marine engines since 1974. Feel free to ask any one of my dealers (MO, AR, OK, LA, TX) if I am capable of diagnosing engine problems.

I have checked this engine on 2 different occasions and found the same problem both times. I really feel bad for the customer here; he is simply the victim of today's short-shelf-life-gasoline. This particular engine family is a little more sensitive to heavy fuel.

Each time I have serviced this engine, I have found the fuel specific gravity to be between .732 and .738. Good fuel will test between .701 and .721. The gasoline available today has a very short shelf life and can go bad in as little as 2 weeks depending on the conditions. The fix for Dan's rough idle and poor running is straightforward, and works every time. Last week I had a dealer call me about a BF90D down in Louisiana with identical symptoms. I told him what to do. He was very skeptical and said the fuel looked and smelled fine. He called me the next day and told me the fix worked, but he never would've believed it if he hadn't seen it with his own eyes. I connect a fresh (specific gravity checked with my BG Fuel Test Kit) fuel supply and drain the entire system on the engine (filters, pumps, fuel rail, vapor separator, all fuel lines). I prime the system, turn the key on and let the high-pressure fuel pump run for 3 seconds, start the engine, and it runs just fine.

When these engines try to burn this heavy (non-volatile) fuel, in a cold combustion chamber, the fuel will not vaporize. If it doesn't vaporize, it will not burn and causes the engine to run rough and smoke. As the engine temperature rises, the heavy fuel begins to vaporize better, and the symptom begins to diminish. This is somewhat aggravated by the fuel management system which reads fuel mixture (O2 sensor) and tries to make corrections.

I wish I had a better answer for the customer, but his concern should be with the quality of gasoline, and not the engine, or my competence as a tech rep. Using top-tier fuel, fuel stabilizers and avoiding long periods of storage are my best recommendations.

QUOTE=bastropdan;455558]Hey, Berniek. The engine runs rough when cold. It runs rough after sitting for a while and cooling off. Fuel consumption? No idea. The repairman says the computer/ECM reads that all is OK. I understand about using fresh fuel. I cannot detect the smell of fuel anytime after lifting the cowling. I have 2 fuel filters installed between the tank and engine. The last repairman says he changed the plugs. I have used several different tanks and fuel connector combinations. I have tried so many things. The common thread running through all of this is a guy named Joe Koury, the honda rep. I need to take it to a dealer out of his jurisdiction or go ahead, bite the bullet, and get a Yamaha. That is what everyone told me to do but I figured honda was the best. Then, Murphy came along and got me a lemon. Thank you for all the replies, gentlemen.[/QUOTE]
 
Hey, Joe K. I appreciate your post, as it supports the answers I have been getting from all the mechanics that have examined the engine. The answer is always the fuel. It is maddening to buy a top quality engine that behaves like this, but that seems to be my luck. And Honda of all people. I was hoping there was a quick fix, but I will have to learn the procedure you describe above, put up with all the sputtering, or sell it and buy a different brand. One more question. Is it OK to let the engine run until all the fuel is consumed? I used to do that with my old Evinrude; let it idle until it stopped. One guy told me not to do that as it affects the fuel pumps. It is kind of heartening to know that the BF90D does the same thing. Again, thank you for the reply. Good fishing to you if spring time ever gets here.
 
I waited a few days to make sure any heat in the discussion dissipated:)

Joes Explanation may be spot on BUT.......

You buy a motor with specifications and expectations. Most engine manufacturers know or should know that there will be some variability in fuel quality in most markets they sell into.
Surely if this engine behaves in this manner on less than optimal fuel, then its a design fault? From a consumer point of view, I would expect there would be a warning if an engine required the fuel have special attention or need additives.
After all, other Honda engines do not behave like this.
Its fine to say that is the reason but in my opinion its not fine to say "....well here is why it does it so stiff cheese, you get to live with it"

Perhaps Honda should be putting some time into developing a cure ( like different heat range plugs? ) or even offering to change over the motor. If this engine family is susceptible to this problem, doesn't it point squarely to a design problem?

I guess its a problem of degrees. How old should fuel be before an engines performance deteriorates? A year? 6 Months? 1 month? 2 weeks? 1 week? 1 day? As a consumer, I would have thought in the case of a marine engine 3 months would be reasonable, provided the fuel was in excellent condition at the start. Its been windy for 3 weeks, do I now need to ditch the fuel (250litres or 66 Us Gallons) or add some dubious fuel conditioner? The car is a diesel but I can use the fuel in my lawnmower. (well I would have to mow the lawn twice a day for a couple of years to use that much fuel :( )
 
Hey, Berniek. I appreciate your reply and I understand everything you say. I have talked my tail off to dealers, reps, regional reps, honda america in Georgia, and written to the Big Nippon island and have not received any information or signs that they are willing to make some repairs, install new software, or anything. It has been the most frustrating 1.5 years trying to get somebody to do something. Hiring a lawyer is out (I dislike lawyers more than I dislike outboard dealers) and talking my caboose off to honda in Georgia has gotten me nothing but a shrug and a sigh. They have definitely sh*t in their mess kit on this one and my mission in life is to bad-mouth honda with all of my might. I have already taken 2 potential sales away from them and I hope I can do more. I hate being vindictive like this, but they strung me out so I will string them out. A new Yamaha is in my future because I want to enjoy my retirement toy and not have to worry about getting stuck in the middle of a lake or bay with a crapped-out engine. I have lost all faith in honda and I will never again buy anything with their name on it. Man, I hate being this way. My wife said get another engine and forget about this, but it is hard to get porked and have people just be so indifferent. Thanks again for the reply. Peace and God bless.

Berniek said:
I waited a few days to make sure any heat in the discussion dissipated:)

Joes Explanation may be spot on BUT.......

You buy a motor with specifications and expectations. Most engine manufacturers know or should know that there will be some variability in fuel quality in most markets they sell into.
Surely if this engine behaves in this manner on less than optimal fuel, then its a design fault? From a consumer point of view, I would expect there would be a warning if an engine required the fuel have special attention or need additives.
After all, other Honda engines do not behave like this.
Its fine to say that is the reason but in my opinion its not fine to say "....well here is why it does it so stiff cheese, you get to live with it"

Perhaps Honda should be putting some time into developing a cure ( like different heat range plugs? ) or even offering to change over the motor. If this engine family is susceptible to this problem, doesn't it point squarely to a design problem?

I guess its a problem of degrees. How old should fuel be before an engines performance deteriorates? A year? 6 Months? 1 month? 2 weeks? 1 week? 1 day? As a consumer, I would have thought in the case of a marine engine 3 months would be reasonable, provided the fuel was in excellent condition at the start. Its been windy for 3 weeks, do I now need to ditch the fuel (250litres or 66 Us Gallons) or add some dubious fuel conditioner? The car is a diesel but I can use the fuel in my lawnmower. (well I would have to mow the lawn twice a day for a couple of years to use that much fuel :( )
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