88 Evinrude VRO 120 hp surging at high RPM like it's starving for fuel

[Staticride]

e120tlcca vro (Oil tank removed, sensor unplugged and port on pump closed off)

My 88 VRO will get up to plane just under 4K RPMs and then back off down to 3K RPMs all by itself. If I leave it at WOT it starts surging, like its getting a burst of extra fuel and wants to go, then chokes down and looses power, then repeats. If I squeeze the fuel bulb repeatedly I can run at 5K RPMs smoothly.
Here is what I have done so far:
Checked compression good
Swapped power pacs (thinking SLOW mode was kicking in)
Checked that I am getting spark from all coil pacs and cleaned grounds
Put in new Carb kits
Put in new Champion plugs gapped properly
Checked for overheating
Made sure fuel take is vented properly
Changed out fuel, new oil and used sea foam
Installed Racor fuel/water separator
Replaced fuel line from tank
Replaced inline filter at fuel pump
Replaced squeeze bulb
Took apart the VRO pump and checked the fuel side diaphragm for holes/ tears

Non of the above has helped
Please HELP!

 

[ondarvr]

You either have an air leak or the fuel pump is failing.

 

[Staticride]

I did not check the air side of the VRO fuel pump, I just saw that this side also has a diaphragm, but if it was bad, wouldn't the engine starve for fuel at low RPMs as well?

 

[ondarvr]

A fuel pump can begin to fail at either high or low speed first, and maybe altogether at once.

Fixing the problem by squeezing the bulb rules out just about every cause other than an air leak or fuel pump.

 

[oldboat1]

I also think it's a fuel pump issue. Think I might put on a standard fuel pump from one of the earlier models (maybe $80 for OEM).

(There is likely an inline filter on your pump, and that could be clogged -- worth checking.)

 

[racerone]

No filter on a VRO pump assembly.-----Run with a seperate / different portable tank as a test.

 

[oldboat1]

^^interesting. Parts diagram for the '88 pump shows a filter, but only for the oil side. On second reading, also notice the OP says a filter was replaced -- so I wonder if the oil assembly was correctly removed and plugged. Guessing, but think the oil line with the inline filter would go away when converting to a premix system(?) Maybe the conversion needs to be revisited when setting up that portable tank.

 

[lmuss53]

Pump it up hard with the engine not running and look for a leak somewhere in the lines. If you don't find a leak I would change the fuel pump. If you don't want to pay for the kit or a new pump on the VRO look to swap it out for a non VRO pump. If the vro is unhooked I would look to replace the pump with a non vro 3 line pump from a similar motor, like an 88SPL from the same year.

Read this post and look at how Rickdb1 replaced the VRO pump on his 70, the pictures are worth a thousand words. Look at the Sierra 18-7353 for the replacement pump. the line diameters might not be exactly right but the pump will work with a little massaging. There are 3 or so part numbers shown in the thread, look at all of them and pick out the one that best suits your motor. Read Ricks text, he explains thing well.

http://forums.iboats.com/forum/engin...dard-fuel-pump

 

[racerone]

The filter would be for the oil.----That is out of the picture when pump is used for fuel only !---There are those that say the crossflow V-4 fuel pumps will not pump enuff fuel for the big V-4 loopers.

 

[Faztbullet]

If you can find someone that's carries EMP parts they make a VRO replacement(pre-mix only)pump part number is 4-7359 and very reasonable. EMP has a 2 year parts and labor warranty and I just started using their impellers last year..

 

[Staticride]

Thank you for all the advice, but now I have some questions. I've been checking for air and leaks like suggested. I squeeze the fuel bulb really hard and see no leaks but I am able to squeeze it all the down (not easily). I do have two fuel filters, one at fuel tank is a fuel/water separator and one at the motor is an OMC inline just before the VRO (just like in the diagram for this model) I noticed that there is quite a large air pocket in the inline. Is this normal if its been sitting for a few hours? I rechecked all my fittings, tightened everything down again, ran the motor and squeezed the fuel bulb until all the air was out of the inline filter. Could this have been my issue or will the air in the inline return after sitting a while?

 

[Staticride]

Also if I do replace the fuel filter with a non VRO, I looked at the ones you all have suggested and they seem to be a single pump, Master tech recommends a dual pump for a Looper, Isn't that what I have? sounds silly but I'm not sure of the difference between a V4 and a V4 Looper.. Here is the website http://www.maxrules.com/fixomcvro.html

 

[James R]

The fact that the bulb squeezing helps the motor to run correctly certainly indicates a bad VRO. I apologize to those that like the VRO but I dont trust them with the oiling and if the fuel pump side fails all the more reason to convert to a standard pump and 50:1 mix. I have three motors currently in my shop, one of which is a 120, and I have removed the VROs and replaced with standard pumps this past week.The OEM pump suitable for your 120 is 0438559. I mounted the pump on the VRO bracket. I use the same pump type, 2 in tandem, for 150s.Hope this helps.

 

[lmuss53]

I have seen old V6 motors with 2 of those pumps on them. The pumps were plumbed to a T that went on the end of the pulse hose out of the block.

I don't think the single VRO pump puts out more volume than the non VRO pump. If you're concerned one won't put out enough fuel maybe put on 2 plumbed that way and run one to each carb bank.

The 1983 140 is the last year I can find without VRO and it uses one of the block mounted pumps.

I have drilled and tapped the housing on one of the block mounted pumps to put a nipple in for running that off a hose before. I tapped the hole that goes up against the block and plugged it with a lock tight coated set screw on that pump. You could do that with one of the pumps from an older pre VRO 140. If you look at where the vacuum port goes into the 3 line pumps as opposed to the block mounted ones you'll see it is the same casting just drilled in a different place.

I'm going to be talking to my friend with the repair shop tomorrow, I'll ask him if he knows which pump will work as a direct replacement for the VRO pump on this120.

Not to throw rocks at the maxrules guys but they seem to have the same pumps as Sierra and Amazon, just for a LOT more money.

Edit, There you go James R provided the answer while I was typing. I'd still look for the Sierra equivalent and buy it on Amazon.

 

[Staticride]

Awesome advice guys, Thank you. James, do I only need 1 for my 120? Just want to make sure. and it looks like the pump has 5/16 fittings, what do you recommend to hook it up to the 3/8 hoses? Thanks again!

 

[Staticride]

From the pictures it looks like the OMC 0438559 has the correct size hose fittings, but the Sierra 18-7353 fittings are smaller.

 

[Staticride]

is that the reason for the price difference?

 

[lmuss53]

I think you could buy the Sierra and go to your hardware store and buy the correct barbed fitting to replace that small one and be just fine. You are paying for the BRP and OMC names with the OMC pump. There is a third one on Amazon an Itaco 438559, looks like the right fittings, priced between OMC/BRP and Sierra.

 

[oldboat1]

The '82/'83 OMC pump (115 and 140hp) is 0438556. You can get them through iBoats, about $95 -- think they are sourced through Crowleys. Equivalent Sierra pump 18-7352 is available here for about $50. Your call -- will get all kinds of opinions on oem vs. aftermarket. James R an Imuss53 have hands on experience -- 0438558 was mentioned; might look at 0438559 as well -- prices vary). Can just plug in the numbers in parts and accessories, above, and get cross-references/applications for J and E models.

 

[lmuss53]

Thanks oldboat, about once a year the question comes up about which pump is the best one for this application and we chase numbers around for a couple days. The OMC 0438556 and the Sierra 18-7352 are block mounted pumps, so they won't work for the VRO replacement, the OP will need a 3 port pump for that. I'm going to rethink what I said above, since there is some question about the output on the Sierra and the difference in the hose sizes, to get one that is mostly plug and play I would go with the OMC 0438559 or the Itaco, probably the OMC pump since the Itaco is mostly an unknown .

The iboats prices are close enough that I would probably just go to the top of the page and buy it from our forum hosts.