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Honda 75 surging

J

JackB1

Member
I was not having any luck on other forums with this problem so someone directed me here.
My Honda 75 carb model is only on its second outing this year. Both times the following issue was present. At about 1200 rpm I will get surges of as much as 400rpm. Not continual but intermittent. However when opened up it runs fine topping out at its normal 5400 rpm. Occassionaly when running at the 1200rpm I also seem to hear a little pfft noise from the engine. It did stall once at idle but not again after several hours on the water.
After the first outing I pulled the 10 micron filter, poured the gas into a glass jar to check for water. None at all and very clean. The fuel also appeared fine. I had put a full tank of 89 octane in for the winter and it was stabilized.
I am thinking it still acts like water but would appreciate any suggestions. It may just run itself out and so far I have used 1/2 tank [13 gallons] of the fuel. I was going to put in some E-Zorb for ethanol on the next trip to see if that helps and I will be able to add regular [non-ethanol] gas on the next trip out as our Marina just began carrying it.
 
From what you describe, it sounds like there may be some water in your fuel. I'm not familiar with the 75, but if it has a vacuum separator tank, drain it. Drain and check any on-board filters.

To minimize fuel problems over the long term install a Racor 10 micron fuel/water filter on the tank line, before the pump-up bulb.
 
Thanks for the reply. As mentioned above I do have a 10 micron filter just before the pump bulb that I pulled and drained into a glass jar and found no trace of water. I know there is a small plastic filter on the engine but how would any water get past that main 10 micron filter? The onboard filter is so small I would think that any small amount of water that may have condensed into it would burn off. Weather has kept the boat in but I plan to be out tomorrow again. I am tempted to put in some E-Zorb which would handle any water in that onboard filter but concerns about the product have me a little wary.
 
Can't comment on the E-Zorb. Never used it.

How much surging are we talking about in terms of minimum/maximum rpms?

Since that is a carb model, you may have some of the carborator passages getting restricted. I would run some Sea Foam or similar fuel cleaner/decarbonizer through the system.

Another possibility is a restriction on your fuel tank breather. When the surging happens again, open up the fuel tank filler cap and see if it goes away.
 
If the motor is "sneezing", it is running lean. As Chawk_man suggested, try some Sea Foam. Also, run as much of the old fuel out as you can, then refill with fresh. Even with stabilizer, fuel goes bad pretty quick.

The 75 has idle, intermediate and main jets. There are several transition passages in the upper part of the carburators. If any of those are even partially plugged up, it can the transition from idle, intermediate, etc somewhat erratic.

Also, check you spark plugs to be sure that they are clean. If you question their quality replace them with NGK DR7EA. Only use the NGK brand.

Drain your bottom carburator into a glass jar to check for any water that may have gotten by the filter. The most likely place for water to accumulate would be in the bottom carburator.

I am thinking fresh gas and Sea Foam may do the trick.

Mike
 
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