Clogged Jets???

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
Hey Guys,
I have a boat that I bought last year. It has a 2001 70HP Johnson, model # J70PLSIS, and it is on a Lowe 17' Aluminium boat. It has ran great until recently. It ran fine and then when i stopped to fish for a while, when I cranked back up, it will not get above 2000 rpm...unless im by myself in the boat for a long time at WOT....then it will ever so slowly creep upwards and can eventually get to around 3500 rpm and about 20mph. there basically is no hole shot at all.
I thought my shift/throttle cable had gone bad or gotten loose, so i pulled the cover and adjusted the thumb screw (probably not its official name). The problem went away temporarily after fiddling with the shift cable adjuster thing, but the problem came back, and it no longer helps at all. It probably was a coincidence on the first time.

Clearly this seems like its starving for fuel - and i did try pushing in on the choke but it does not help.

Idles just fine and purrs like a kitten. Fires right up.
Does this sound like a high speed jet issue? Maybe clogged??

Thanks!
SM
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
With the engine running, using insulated pliers, remove the spark plug wire from the s/plugs one by one. The drop response should be the same on all cylinders. Is it?... Explain.

Remove the spark plugs and keep track of which one came from which cylinder. Describe their appearance.

Check the compression (all plugs removed). What is the individual psi reading of each cylinder?

Spark plugs still removed... At cranking speed, the spark should jump a 7/16" air gap with a strong blue lightning flame... a real SNAP!... Does it?.... Explain.
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,598
Are the throttles fully opening? Check without engine running, but in gear.
 
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