surging

[mark barton]

2004 90 hp mercury 3 cyl 2 stroke. at full throttle motor is surging, loses rpms and surges back up, doing it pretty bad now. noticed it missing at top end before this started. any ideas. replaced fuel filter so far.

 

[mark barton]

is there a special password I need to use to get an answer???lol

 

[Bob Bourget2]

There are a couple of things that could cause this issue. Fuel deprivation and / or loss of ignition. I would suspect the fuel system. Make sure your fuel hose and primer bulb are updated to the new e-10 resistant stuff, replace the pulse pump if it wasn't done recently and go from there. Oh....and the password is "patience".......

 

[Scott Hammer TOXIC]

:lol::lol::lol:at Bob.....Welcome to the Bob B. Show admittance is free.



TOXIC

 

[mark barton]

thank you very much for the info,

 

[David Willett]

I just purchased a 2004 Nitro NX750DC with a 90 Hp Mercury,and have a similar we took her out today to see how it would run. It started and idled just fine, took off and it sputtered a bit but did not think to much about it and she lined out and ran good for 3-4 minutes until we stopped and fished a bit, gor ready to move , it started right up and took off got up on plane trimed her out and was running about 4500rpm and it started to surge like it was running out of fuel, slowed down and it ran ok. decided we shoud go bck to the boat ramp and could not get the boat to run over 2000 rpm with wot, pushed the choke and it would rev up enough to get on plane, after a few seconds it would start to bog, choke it and it would recover for a few seconds again.

the fellow I bought it from said he dod not use it much and he kept stabill in the tank. I put some fresh gas in it before we left.

Reading an answer from above, what is the pulse pump. the primer bulb feels full, and any other ideas on what might be wrong. Gonna change the filter.

 

[Bob G.]

The pulse pump is a fuel pump. You need to make sure that the fuel line is good from the tank to the motor. If it is the older non-ethanol rated Mercury hose, you need to replace it NOW! The older hose had red lettering, the newer ethanol rated hose has blue lettering. I bought a used boat last year and this is what the fuel hose from the primer bulb to the motor looked like:

 

[Bill McElroy]

The pulsing and surging of the motor "could" also be the ECM.....I have a '97 150EFI 2.5 ltr and it ran exactly like you described. Changed out all the fuel lines, filters, etc and it didn't cure the problem. Luckily for me, I have a mechanic that had seen the exact same problem a few mos. prior and he checked the ECM...sure enough, it wasn't working properly,...he sent it down to a place in AL. and they were able to repair it for $600.00 vs over $1100 for a new one!! I got it back and the motor runs like a scalded dog now. Definitely look for the easy causes first,..BUT...if you've tried everything and it's still doing it.....have the ECM looked at, and DON'T settle for a new one if you can get it repaired. It's not cheap...but it's 1/2 the price of NEW!!



Keep that in mind!!

Mac