87 120 V4 Runs Rough

[keithb40]

I am a newbie but have been searching the forum for a similar problem with no luck. My problem is that the engine shakes my boat like crazy between 1200 and 2500 rpm. It idles great, starts easy, and runs smooth as silk above 2500 rpm. The plugs are new, carbs rebuilt within the last 18 months, no air leaks in the fuel lines and I have spark on all 4 cylinders. I have tried fuel treatment and premium gas with little improvement. We bought the boat 11 months ago and it has had the problem since the day we purchased it. Any ideas?

 

[Gary H NC]

Re: 87 120 V4 Runs Rough

Welcome to Iboats! Is the prop in good shape? Does it sound like its running smooth other than the vibration?
I would pull the prop off and check that the shaft is not bent.If you have a different prop give it a try also.

 

[coolguy147]

Re: 87 120 V4 Runs Rough

have u ever floored the motor?

if u have does it like hesitate? cause u might need to adjust ur carbs if thats the case

 

[keithb40]

Re: 87 120 V4 Runs Rough

The prop looks fine but I do have a spare. I'll give it a try. It stll feels as though it is coming from the motor though. I did use a very expensive gas treatment once, $10 a bottle, and it ran great for that one tank of gas. I can't recall the brand but I do not want to spend an extra $10 a tank if I can help it.

 

[keithb40]

Re: 87 120 V4 Runs Rough

I have floored the motor on several occasions and no hesitation to speak of, just vibration until it reaches 2500+ rpm.

Thanks all for your input, keep it coming!

 

[Gary H NC]

Re: 87 120 V4 Runs Rough

You may want to give this a read...
http://forums.iboats.com/showthread.php?t=158076

 

[keithb40]

Re: 87 120 V4 Runs Rough

Thanks Gary, I'll be de-carbing and re-proping this weekend.

I will update on Monday with results.

 

[keithb40]

Re: 87 120 V4 Runs Rough

Well back from the boat and it seems to be the prop. I put on the spare which is a cheap aftermarket prop that has work done to it, and the problem got worse. I de-carbed the engine and after much smoke, no improvement. I put the old prop back on until I can buy a new one.

Thanks all for your help.