Honda 75 surging

[JackCB]

I have a 1996 75 hp carbed Honda. It is well maintained. 10 micron filter and have run about 4 tanks of ethanol before I was able to convert to regular gas now carried by our marina. I use PRI-G stabilizer full time.
What happened beginning this year is I am getting a surge at 1100 rpm that usually is about 2-400 rpm but on occassion it surges to 2000rpm. Very annoying when docking. Twice it has stalled but I was able to get it restarted and needed to give it some juice to get it rolling again. Most of the time it idles ok. It is at the 1100 rpm mark that surges begin. It can run wide open at 5400 rpm all day.
I emptied the 10 micron fuel filter into a jar and it was clear. I drained each carb into a baby jar and fuel was clear. THEN.. I decided to use some power foam which is a carb cleaner that foams up. I rigged up a small 2" section of carb drain hose to the plastic straw and was able to fill the carbs via the drain tubes. I let them sit for an hour then drained them again while also squeezing the primer bulb to flush them out good. I drained each into a baby jar to see what I would get. The top 3 carbs started draining a cloudy type gas which I assume was from the power foam then cleared up. The bottom carb however ended up with what appears to be a blackish substance that settled to the bottom of the jar. At first I thought that was good as I had obviously cleaned something out. I flushed the carbs several more times but unfortunately the surge still exists. Idles Ok but push it sightly above that 1100rpm and it surges again. I am wondering if it could be the fuel line between the filter and engine? Would appreciate any advice before hauling it to a mechanic.

 

[JackCB]

Re: Honda 75 surging

Was hoping for more of a reply but here is an update from my mechanic.
I just spoke to the mechanic today. Carbs are cleaned but the reason for the stuff in the bottle mentioned above is still a mystery. Remember I had previously run checks on my 10 micron filter by pouring contents in glass jar. Perfectly clesn. The mechanic said the small on engine fuel filter was also clean. That leads us to believe that this crud is somehow coming between that filter and the carbs. The only thing we can think of are the fuel pumps, They do have black fuel lines between the pumps and the carbs but they should handle ethanol ok??? Could it be fuel pump diaphram? He was also wondering if it might be oil and is currently pondering the situation. What would be the most likely culprit to produce this debris between the on engine fuel filter and the carbs?

 

[cp]

Re: Honda 75 surging

JackCB - While I have no real idea as to why your motor is surging, it occurs to me that you and your mechanic might be barking up the wrong tree in focusing on debris or a fuel restriction as the cause. Think about it:

Does it not seem illogical that debris blocking a carburetor jet, for example, would result in a surge (or increase) in RPM as you are seeing?

Would debris not instead result in a bogging (or loss) of RPM, since a restriction would reduce fuel flow and result in a drop in RPM, not increase fuel (or spark rate) to give the surge or gain in RPM such as you report?

Just food for thought, didn't want you to lose sight of the forest by being too close to the tree. Good luck.

 

[JackCB]

Re: Honda 75 surging

That is a good point but what also may be happening possibly should not have been described as a surge [which is certainly what it feels like when driving] which is my fault. Is it possible that the boat should really be running at 1400rpm when it is running at 1100rpm and then when the carb clears or kicks in it increases rpm? in other words the surge could be described as bogging depending on how one looks at the rpm change. Remember the boat runs great at wide open throttle 5400rpm.
Cleaning the carbs, by the way, did eliminate the problem. We just are not sure where the black sandy substance found in the bottom carb originated.The mechanic for a while thought it might have been an oily substance and attempted to duplicate it by pouring some oil in a bottle of fuel. That was inconclusive. I plan to have the boat out early next week to give it a run and see how it goes. I figure, if am really lucky, that ethanol somehow cleaned out something in the lines between the on engine filter and the carbs and now that I am back to non ethanol fuel will not see a repeat. I am usually not "really lucky".

 

[cp]

Re: Honda 75 surging

Great to see that you eliminated the problem by cleaning the carbs. Thanks for closing the loop on this thread. Safe and happy boating to you. Aloha.

 

[JackCB]

Re: Honda 75 surging

I sure wish that the thread could be closed out. Unfortunately the story continues. I picked up boat after carbs were cleaned and put in at local ramp. Started up fine and left ramp area at about 1100 rpm with NO surging. Feeling good at that point. Got to the river and opened up to about 3800rpm heading for local restaurant. After about 1/2 mile the rpms went suddenly down to zero and engine stalled. I could start it easy with choke but could not get it into gear without stalling. Removed cowl just to see if there was something obvious that mechanic might have missed like leaving carb drain open etc. All looked fine. After 8 or 9 times of restarting it finally was able to be put in gear and I started back to the ramp slowly. I decided to try and open it up as I was getting braver the closer to home I got and for a short distance was able to run it up to 5100 rpm which is 300rpm short of full speed. I then was near the ramp and went back in at 100 rpm...still no surging. Seemed like a completely differn't problem. Boat was taken back to mechanic where I am waiting for latest diagnostic. I am thinking, from the conversation, that they will be looking at fuel pick up and related area as opposed to on engine. Very frustrating. Any ideas?

 

[hondon]

Re: Honda 75 surging

I'dd want to know what those fuel pressure vaccume numbers are at the point of failure.Sounds like you have a delivery problem to me.

 

[JackCB]

Re: Honda 75 surging

Well, here is a surprise. I received a call from the mechanic today who said that my filter was loaded with water. Remember, I am the one who pours the contents of thier filter into a glass jar occassionally to check for just that problem. It has always been crystal clear. They will be siphoning the water from the tank and we will rely on the filter to remove the rest. I am contemplating how this happened. One possibility is that I had put my first tank of regular fuel in which became available at our local Yacht Club marina this year. Prior to that had always filled up at gas stations. The only other possibility was water intrusion when the boat sat through a heavy rainstorm while sitting at the mechanics. All other times it is covered with tarp. My fuel vent is in the cap and the only other possibility is the access port at tank top. I have a hard time believing it was either of those two places. I am going to check with the marina to see if any other boats had problems. A mystery so far but at least this time we know what caused the problem.