A forum like this is great, but one irritating thing is that people post questions and describe problems in detail and in long running threads, but then - assuming they solve the problem ? don?t post to say so and to describe the solution. I am taking the opposite tack. I never posted with my problem, but I will share the solution.
In 2005, my 1996 Honda BF90 developed an annoying engine stumble at 1300 to 1500 RPM. It ran great at other speeds, and the stumble did not preclude use of the motor.
Naturally, I looked over all systems closely, but found nothing. I am not a novice, having in my younger days built hot rod versions of Datsun engines and otherwise repaired bad running gas motor.
Going into the 1996 boating season (freshwater, summer use here in New Hampshire), I worked the problem. I studied this forum and other internet postings. A number of posts reported Hondas with engine misfires, rough running, stumbles (call it what you will) at low rpms. For BF 75s and 90s, the suspect for my precise symptoms seemed to be the low speed jets in the four (!) carburetors. A few posts suggested using Seafoam engine cleaner in copious amounts. This I tried, doggedly, throughout 2006. I wanted not to crack open the carbs if I could help it. The problem persisted.
Replacing the Low-Speed Jets.
So, in the Spring of 2007 I decided to replace the low speed jets in the carbs. First, I bought a service manual. I bought a cheap CD on ebay, but could not get it to open. I bought another cheap CD on ebay from a seller that pointed out that his competitors' products often did not work, while his did. This one also would not open, but at least provided an error message saying it needed an older version of Adobe Acrobat. Using an older computer, I managed to get it opened. So, I spent $24 and troubleshooting time just to have a service manual. Being a cheapskate can waste time.
The service manual is a Honda manual,(not an after-market version like a Chilton). However, it does have some mistakes in it (one picture identifies the high speed jets as the slow speed jets, and vice versa, as I recall it).
Next, I bought the gaskets and four new slow speed jets. I had read that the practical way of removing the carbs was to remove the intake manifold. Now, the Honda is a beautiful engine, very high quality manufacturing. But, to make it smaller, the air box that attaches to the four carbs, and the carbs themselves, have bolts that are very hard to access with the manifold still attached. In contrast, the manifold could hardly be easier to get off, which then makes removal of the airbox and carbs easy. (On reassembly, don?t forget to bolt the airbox back on before bolting down the intake manifold.)
So, who really cares if the manifold has to come off? OK, I had to buy a manifold gasket (between manifold and cylinder head), but all together the gaskets and jets were (if I recall) $80 or $90 (memory is fuzzy ? there were 8 little gaskets for between carb and intake manifold and a big gasket for the mating of carbs to airbox, and the intake manifold gasket mentioned above). What?s the catch?
The catch is removal of the old intake manifold gasket. It was caked and baked on to the cylinder head. I probably took four hours of tedious work with a razor blade to get it off. I used a product from Permatex ? a spray on gasket remover bought at an auto parts store ? which was effective but only with careful and repeated use. This stuff takes paint off and damages plastic, so a lot of care is needed in its use.
Apart from the manifold gasket, the removal of the carbs and cracking them open and replacing the slow speed jets was fun and easy. As I said, very high quality manufacturing was evident all around. Some dexterity is required in disconnecting linkages and gas lines (in particular), but nothing to mention compared to the intake manifold gasket.
You do need a torque wrench to do this project, and some of the torque levels are on the low side. Years ago I hunted around and found a good small torque wrench, but I recall that a lot of what was for sale was limited in its range at low torque settings.
By the way, the insides of the carbs were very clean. The jets were not obstructed in any obvious way, although they may have had a bit of varnish in the teeny holes. I did not boil the carbs, although I probably should have having gone that far.
Engine Problem ? Not Gone.
Fully reassembled, inspected and reinspected, the engine started right up. In this I felt lucky, because I do not have a four carb synchronizer and so could not perform that task.
For the first 15 minutes, there was only the teeniest stumble. But then it came back, as bad as before. The only difference is now it seemed to go over a broader RPM range, up to 2000 rpm.
As before, the engine was still working well enough to use. Putt-putting around at low speeds was annoying, mainly to me, with the stumbling almost constant but never stalling.
I was frustrated, to be sure, but inwardly happy that having done as much as I had, the engine still worked. Not every carb rebuild I have done (back in the day) went that well.
A New Diagnosis.
I take my boat to the Adirondacks, deep in the woods. A good friend of mine living in Stillwater on the Beaver River Flow is the local fix everything guy, and in the Adirondacks that means fixing outboards. Over a beer, I discussed my rough running problems.
He asked me quite early if I drained the gas every fall. I was a bit evasive in my answer, and he was polite and did not press it. I decided a moment later to be honest. So I told the truth. ?Bob, for 40 years my Dad and I never bothered to drain gas or use Stabil or any of that for our outboards, and never had a problem. So, in truth, I never drained the gas or did anything.?
Bob told me that he is now doing a land office business in outboard motor repairs, with gas problems being a constant problem and great for his business. He claimed that since 2005, gas formulations have included chemicals that absorb water, and that that is the problem. Marine fuel systems, unlike cars, do not have sealed gas tanks, so air comes and goes all winter. So, he said, you should just drain your gas completely in the fall and start fresh in the spring.
He went on to describe all the service calls he gets in May and June, where jet skis and motors are started, run five minutes, then quit. He drains all gas from everything, which in some cases is enough to fix things. In other cases, a symptom he described as ?gas snot? is present in carbs and fuel systems, requiring a much more complete tear down. He said Stabil and other gas preservatives do not prevent this problem or help in any meaningful way. To his knowledge, the problem essentially started around 2004 or 2005.
Well, I came back and researched the issue on the internet. I cannot confirm some of what he told me. For instance, there is a lot of information about E10 ethanol blends, with ethanol being hygroscopic (absorbing water). Bob insisted that other chemicals in gas formulations are also a culprit if not a bigger problem (cause some gas is not an ethanol blend), but I can find nothing on that.
Regarding E10, there are rumors (I see) that some blends exceed the 10% ethanol limit. Maybe, or maybe not, but it is clear that E10 absorbs water, to a point, then the water can separate out. And, it absorbs tremendously in marine fuel systems that are vented (unlike cars). There are also suggestions about that mixing E10 with MBTE gas blends (now being or perhaps already phased out) produces gas snot. Anyway, gas can be a problem, although I could not find others describing it as the pervasive problem Bob was describing. (My local Honda mechanic indicated gas was not increasingly a problem in his experience.)
I followed Bob?s advice, and siphoned gas from my tank. The gas was a darker color than usual, but with no visible water separation. Well, there was a little bit of water in one carb bowl (which I also drained). I replaced the two gas filters too.
I tried an experiment with the gas that had a little water at the bottom, separated out. I added some gas dryer (isopropyl) to see if it absorbed the water. The water remained separated., suggesting my gas is nearly saturated.
I tried a second experiment. I dumped some of the gas in my rotary lawn mower (vintage 1986). It then seemed to have an intermittent misfire, although it was functional enough. Not conclusive, but I thought it was running worse.
Problem Gone.
I took my boat back to the water yesterday. I needed some fresh gas for it, having drained the tank, but the stations in my town have E10 gas. Next to the lake, I have crossed a county line, and the gas there is not E10, so that is what went into the boat.
We drove it all afternoon, and it ran as smoothly as back in 1997. The fresh gas made all the difference. Bob had the diagnosis right. Get rid of the old gas and start with fresh.
My tentative conclusions. -- Gas quality may be a much bigger problem now than before 2005.
-- Buy gas for the boat that is not E10, if at all possible (pretty easy for me to do where I am).
-- Drain the tank at the end of the season and burn the gas elsewhere. Drain the carbs and the gas filters too.
-- Tape off the air vent in the fuel system in the winter.
-- The slow speed jets are sensitive on BF 90s, perhaps to dirt but certainly to water molecules in suspension in gas.
In 2005, my 1996 Honda BF90 developed an annoying engine stumble at 1300 to 1500 RPM. It ran great at other speeds, and the stumble did not preclude use of the motor.
Naturally, I looked over all systems closely, but found nothing. I am not a novice, having in my younger days built hot rod versions of Datsun engines and otherwise repaired bad running gas motor.
Going into the 1996 boating season (freshwater, summer use here in New Hampshire), I worked the problem. I studied this forum and other internet postings. A number of posts reported Hondas with engine misfires, rough running, stumbles (call it what you will) at low rpms. For BF 75s and 90s, the suspect for my precise symptoms seemed to be the low speed jets in the four (!) carburetors. A few posts suggested using Seafoam engine cleaner in copious amounts. This I tried, doggedly, throughout 2006. I wanted not to crack open the carbs if I could help it. The problem persisted.
Replacing the Low-Speed Jets.
So, in the Spring of 2007 I decided to replace the low speed jets in the carbs. First, I bought a service manual. I bought a cheap CD on ebay, but could not get it to open. I bought another cheap CD on ebay from a seller that pointed out that his competitors' products often did not work, while his did. This one also would not open, but at least provided an error message saying it needed an older version of Adobe Acrobat. Using an older computer, I managed to get it opened. So, I spent $24 and troubleshooting time just to have a service manual. Being a cheapskate can waste time.
The service manual is a Honda manual,(not an after-market version like a Chilton). However, it does have some mistakes in it (one picture identifies the high speed jets as the slow speed jets, and vice versa, as I recall it).
Next, I bought the gaskets and four new slow speed jets. I had read that the practical way of removing the carbs was to remove the intake manifold. Now, the Honda is a beautiful engine, very high quality manufacturing. But, to make it smaller, the air box that attaches to the four carbs, and the carbs themselves, have bolts that are very hard to access with the manifold still attached. In contrast, the manifold could hardly be easier to get off, which then makes removal of the airbox and carbs easy. (On reassembly, don?t forget to bolt the airbox back on before bolting down the intake manifold.)
So, who really cares if the manifold has to come off? OK, I had to buy a manifold gasket (between manifold and cylinder head), but all together the gaskets and jets were (if I recall) $80 or $90 (memory is fuzzy ? there were 8 little gaskets for between carb and intake manifold and a big gasket for the mating of carbs to airbox, and the intake manifold gasket mentioned above). What?s the catch?
The catch is removal of the old intake manifold gasket. It was caked and baked on to the cylinder head. I probably took four hours of tedious work with a razor blade to get it off. I used a product from Permatex ? a spray on gasket remover bought at an auto parts store ? which was effective but only with careful and repeated use. This stuff takes paint off and damages plastic, so a lot of care is needed in its use.
Apart from the manifold gasket, the removal of the carbs and cracking them open and replacing the slow speed jets was fun and easy. As I said, very high quality manufacturing was evident all around. Some dexterity is required in disconnecting linkages and gas lines (in particular), but nothing to mention compared to the intake manifold gasket.
You do need a torque wrench to do this project, and some of the torque levels are on the low side. Years ago I hunted around and found a good small torque wrench, but I recall that a lot of what was for sale was limited in its range at low torque settings.
By the way, the insides of the carbs were very clean. The jets were not obstructed in any obvious way, although they may have had a bit of varnish in the teeny holes. I did not boil the carbs, although I probably should have having gone that far.
Engine Problem ? Not Gone.
Fully reassembled, inspected and reinspected, the engine started right up. In this I felt lucky, because I do not have a four carb synchronizer and so could not perform that task.
For the first 15 minutes, there was only the teeniest stumble. But then it came back, as bad as before. The only difference is now it seemed to go over a broader RPM range, up to 2000 rpm.
As before, the engine was still working well enough to use. Putt-putting around at low speeds was annoying, mainly to me, with the stumbling almost constant but never stalling.
I was frustrated, to be sure, but inwardly happy that having done as much as I had, the engine still worked. Not every carb rebuild I have done (back in the day) went that well.
A New Diagnosis.
I take my boat to the Adirondacks, deep in the woods. A good friend of mine living in Stillwater on the Beaver River Flow is the local fix everything guy, and in the Adirondacks that means fixing outboards. Over a beer, I discussed my rough running problems.
He asked me quite early if I drained the gas every fall. I was a bit evasive in my answer, and he was polite and did not press it. I decided a moment later to be honest. So I told the truth. ?Bob, for 40 years my Dad and I never bothered to drain gas or use Stabil or any of that for our outboards, and never had a problem. So, in truth, I never drained the gas or did anything.?
Bob told me that he is now doing a land office business in outboard motor repairs, with gas problems being a constant problem and great for his business. He claimed that since 2005, gas formulations have included chemicals that absorb water, and that that is the problem. Marine fuel systems, unlike cars, do not have sealed gas tanks, so air comes and goes all winter. So, he said, you should just drain your gas completely in the fall and start fresh in the spring.
He went on to describe all the service calls he gets in May and June, where jet skis and motors are started, run five minutes, then quit. He drains all gas from everything, which in some cases is enough to fix things. In other cases, a symptom he described as ?gas snot? is present in carbs and fuel systems, requiring a much more complete tear down. He said Stabil and other gas preservatives do not prevent this problem or help in any meaningful way. To his knowledge, the problem essentially started around 2004 or 2005.
Well, I came back and researched the issue on the internet. I cannot confirm some of what he told me. For instance, there is a lot of information about E10 ethanol blends, with ethanol being hygroscopic (absorbing water). Bob insisted that other chemicals in gas formulations are also a culprit if not a bigger problem (cause some gas is not an ethanol blend), but I can find nothing on that.
Regarding E10, there are rumors (I see) that some blends exceed the 10% ethanol limit. Maybe, or maybe not, but it is clear that E10 absorbs water, to a point, then the water can separate out. And, it absorbs tremendously in marine fuel systems that are vented (unlike cars). There are also suggestions about that mixing E10 with MBTE gas blends (now being or perhaps already phased out) produces gas snot. Anyway, gas can be a problem, although I could not find others describing it as the pervasive problem Bob was describing. (My local Honda mechanic indicated gas was not increasingly a problem in his experience.)
I followed Bob?s advice, and siphoned gas from my tank. The gas was a darker color than usual, but with no visible water separation. Well, there was a little bit of water in one carb bowl (which I also drained). I replaced the two gas filters too.
I tried an experiment with the gas that had a little water at the bottom, separated out. I added some gas dryer (isopropyl) to see if it absorbed the water. The water remained separated., suggesting my gas is nearly saturated.
I tried a second experiment. I dumped some of the gas in my rotary lawn mower (vintage 1986). It then seemed to have an intermittent misfire, although it was functional enough. Not conclusive, but I thought it was running worse.
Problem Gone.
I took my boat back to the water yesterday. I needed some fresh gas for it, having drained the tank, but the stations in my town have E10 gas. Next to the lake, I have crossed a county line, and the gas there is not E10, so that is what went into the boat.
We drove it all afternoon, and it ran as smoothly as back in 1997. The fresh gas made all the difference. Bob had the diagnosis right. Get rid of the old gas and start with fresh.
My tentative conclusions. -- Gas quality may be a much bigger problem now than before 2005.
-- Buy gas for the boat that is not E10, if at all possible (pretty easy for me to do where I am).
-- Drain the tank at the end of the season and burn the gas elsewhere. Drain the carbs and the gas filters too.
-- Tape off the air vent in the fuel system in the winter.
-- The slow speed jets are sensitive on BF 90s, perhaps to dirt but certainly to water molecules in suspension in gas.
