5700 RPM now running 4900 RPM WOT

[randyray41]

I have a 1987 Yamaha 175 hp outboard mated to a 1991 Gambler 21 ft. bass boat. I recently bought this rig and it was running around 5700 rpm's but with a skip in the motor. Yesterday, I replaced the fuel line and the skip went away but the RPM's now will not rev higher than 4900 which has cost me about 8-10 mph. The bulb was leaking gas. My question is; is it possible that the leaking bulb was causing a "lean condition" and the motor was running higher RPM's? This motor should run in the 5700 rpm range WOT, but won't do it now. The prop is a 23'" pitch. I even raised the motor 1" up on the jack plate. Have a better hole shot but not really a noticable increase in WOT RPM.

I did a decarb last weekend trying to fix the skip as well as change the plugs after the decarb.

Anyone have any thoughts on what to do now???

 

[Inducted]

Re: 5700 RPM now running 4900 RPM WOT

Assuming that all your fuel lines and fuel filters are clean I would double check your carbs. How about all your linkage and timing adjustments? It seems like you can't get WOT.. Are the throttle plate being restricted?

 

[randyray41]

Re: 5700 RPM now running 4900 RPM WOT

New fuel filter. Carbs are opening fully. Have not checked timing, but it was getting full RPM prior to changing fuel line.

 

[Inducted]

Re: 5700 RPM now running 4900 RPM WOT

I do not think that a leaking fuel primer ball or hose would cause a lean condition that would have caused your engine to run at 5700rpm then fix the leak now the rpms are 4900 . This does not make sense to my small brain. But this does......... Spray a can of de carb into your 24 year old carbs free up some crud and now you have a clogged high speed jet. Just a thought.

 

[randyray41]

Re: 5700 RPM now running 4900 RPM WOT

How would I check the high speed jets? or clean them?

 

[Inducted]

Re: 5700 RPM now running 4900 RPM WOT

Of course the best way is to remove carbs, disassemble and clean all passages with carb cleaner, soaking overnight if necessary.

Since you were getting 5700rpm Shortcut way.. Remove carb drain plugs, try to catch any debris it might show which carb has issue, with drain plugs removed pump in fresh gas let drain. Spray carb cleaner, let drain. put drain plugs back in hope for the best...
Be careful with all this drained gas fire hazard!!!!!!!!!