75 HP Honda Rough Idle

[Bill and Brenda Russell]

On our Erie Canal / New York Adventure our 75 HP Honda #3 cylinder was missing at slow speed under 3,000 RPM. We replaced all spark plugs before entering the Hudson River.

No improvement?

As we motored out into the Hudson the motor ran rough as before however above 3,000 RPM it would run normal. Traveling down the Hudson at 4,500 RPM or more everything was normal all the way for 57.9 miles. When we entered the marina in New York and idled back to 1,000 RPM the problem had disappeared.

Everything was normal on the return cruise to Newburg, NY.

Could have been the low speed carburetor jet?

Bill and Brenda Russell

[gljjr]

This sounds like a fuel delivery problem. If this is carbureted, I would bet that you have a plugged up idle jet on one of your carbs. If this is the case, you will need to rebuild the carbs to solve the problem.

[BrentB]

Would running some SeaFoam help?

[Chester]

Techron fuel additive just cured a similiar problem for our boat. IMO some additive is worth a shot.

[bmacpiper]

I have similar symptoms on my 90hp Honda, and have gotten many opinions that the low speed jets are clogged. I have run multiple cans of sea foam and just about every other additive possible through them, and am rebuilding/cleaning this week. Will let you know how it goes.

Since the problem disappears at high rpms, I doubt it's something simple like a clogged fuel filter or failing fuel pump. Might not hurt to check timing and fuel lines, i.e. for small vacuum leaks.

bmc

[BrentB]

Other items to check in the fuel system are
primer bulb
fuel lines
clogged anti siphon valve
clogged fuel pickup
fuel tank vent and vent hose

I would check the primer bulb, ASV and fuel pickup first.
Bulbs go bad and other items are easily clogged with debris
If the vent is an issue, run the boat and stop and open the fuel cap. If air rushes into the tank, check the vent exterior housing for blockage first.

[Connie]

I had the same issues with my Yamaha 75. Ethanol is a real issue for marine engines...I did two things...first, I installed a Racor water separator and filter and was amazed at how much water I take out of my two tanks. I now put an additive into the tanks prior to filling up...one that deals with ethanol...this seems to have fixed the problem. Not all C-Dory's have water separator's installed, so it is well worth the effort to get one...it runs about $85.00 for the Racor and $10.00 for clamps, etc. If you can do it yourself, you will save about $100 to $150 in labor.
My Yamaha is a 2006 and I run about 8 to 12 hours a week on it, but Ethanol fouls up lines and plugs. Not all marine gas is Ethanol free.
Hope this helps.
Connie Irvin, The Guardian

[bmacpiper]

[BrentB]

Posted: Tue Nov 10, 2009 2:17 pm Post subject:

--------------------------------------------------------------------------------

Brent wrote:
Other items to check in the fuel system are
primer bulb
fuel lines
clogged anti siphon valve
clogged fuel pickup
fuel tank vent and vent hose

I would check the primer bulb, ASV and fuel pickup first.
Bulbs go bad and other items are easily clogged with debris
If the vent is an issue, run the boat and stop and open the fuel cap. If air rushes into the tank, check the vent exterior housing for blockage first.


Hey Brent,
On the primer bulb, are you just looking for cracking/leaks? Where is the anti-siphon valve located?

Yes
and age and clamps

ASV will atached to the fuel tank using a connector (elbow, straight, brass or AL on the fuel tank). The fuel connector is threaded into the fuel tank and fuel pick up tube may have a metal screen at the tube's end inside the tank.
This can be clogged and sometimes break or disconnected from the fuel elbow
see
http://www.iboats.com/Moeller_Fuel_Pick_Ups/dm/cart_id.748791066--session_id.025724569--view_id.484762

for an image

[bmacpiper]

Got it, thanks.
bmc

[BrentB]

Be careful removing the fuel tank elbow.
You can use 2 wrenches which are 180 degrees opposite of each other to apply even pressure
(similar to a tap and die T-handle)
or another person suggested using a plumbing basin wrench

[gljjr]

[bmacpiper]

In my experience... By the time the jet gets clogged, fuel additives won't USUALLY help as they don't get a chance to get near the plugged jet. At that point the only thing that will help is to pull the carbs apart and unplug the jet with a tool (IE: small wire or welding tip cleaner depending on how small the jet is). Where the fuel additives help is preventing the issue in the first place![/quote]

Fully agreed. But had to at least try! I'm running stabil ethanol and sea foam regularly now, I just keep a bottle in each storage pocket by each tank, and add them at the gas station.

bmc

[BrentB]

It also could be fuel filter inside the engine
Have you replaced the #3 cylinder spark plug and checked for spark?

[bmacpiper]