Outboard Fuel System Problems! Diagnosing a Rough Running Outboard - Part 1

Find and Fix your Outboard fuel system problems. Fuel system issues can cause causing a rough running outboard. In this video I'll go over some of the fuel system issues you may run into with a rough running outboard motor. I'll cover how to Diagnose fuel and fuel flow related issues that can cause a rough running outboard engine that I have seen or experienced in the past. If you have any suggestions or tips I may have missed, please post them in comments!
There is one area that I missed covering in detail, that is to make sure your hoses haven't collapsed or deteriorated. Fuel lines typically have a lining inside that can deteriorate and fall apart causing small bits to clog the fuel system.
Here are a few affiliate links to items that might be useful to you in troubleshooting fuel related issues:
This is an inexpensive fuel pressure gauge ideally suited for carbureted outboards, it has a low range which is hard to find in the more expensive test kits.
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Attwood Replacement Hose and Bulb: amzn.to/2RfKAIW
Attwood Primer Bulb: amzn.to/2Zmxz4H
Sierra Fuel Filter: amzn.to/3mcjDEf
Complete parts list for hoses, filters used on this Outboard:
extremediy.org/parts-list-vro...
For a collection of the tools and materials we use, Make sure to Visit our Amazon Affiliate Storefront:
www.amazon.com/shop/josesextr...
A Quick disclaimer, I am not an outboard technician. I do however do my homework and consult with experts when necessary before doing much of the work I do on outboards. Last of all, I get a service manual on the outboards I work on and a thoroughly familiarize myself on the area I am going to work on.
Contents:
0:00 Introduction
0:34 Gas Tank Vent and Connector
2:26 Primer Bulb
3:34 Failed Primer Bulb Emergency Hack
4:44 Fuel Pump
7:37 Carburetors
7:54 Quick note on Ethanol
9:00 Syncing the Carburetors
10:13 Choke/Primer
10:38 Fuel Lines
11:00 Summing it all up
#OutboardFuel
#RoughRunningOutboard
#OutboardTroubleshooting

[@erichineman3534]

Great series on the Whaler Reston and outboard maintenance. I’m inspired. Bought a 13’ Whaler with a 25hp Johnson and a 40hp Johnson two weeks ago. I have my winter project all lined up. Thanks Jose!

[@ExtremeDIYGuy]

Sounds great! It's been a fun ride, It's pretty much finished, just need to catch up on the videos!

[@masterblast4069]

Great video, very real world advice. Thanks.

[@ExtremeDIYGuy]

Glad it was helpful! Thanks for watching!

[@MrShadowhunter66]

Wow, best video I’ve seen on the fuel system! Thank you so much

[@ExtremeDIYGuy]

Glad it helped!

[@conk8636]

Hey straight to the point thank you sir.Us old guys appreciate.

[@ExtremeDIYGuy]

From one old guy to another, Your Welcome!

[@safehavenstudio5936]

Thank you so much 3 mechanics later and none of them even told me it might be the fule line or bulb thank you so much

[@ExtremeDIYGuy]

Your welcome! Glad my video could be of help

[@Paul-sh4on]

Excellent video...Thanks

[@ExtremeDIYGuy]

Your welcome Paul

[@FoodPornNetwork]

Great video!

[@ExtremeDIYGuy]

Thanks!

[@jeffperkins6514]

Great video, thanks. 👍

[@ExtremeDIYGuy]

No problem 👍 thanks for watching!

[@truestoryz]

great video. thanks!

[@ExtremeDIYGuy]

Glad you liked it!

[@dduff4013]

Great vid!

[@ExtremeDIYGuy]

Thanks!

[@painter08]

Good Presentation. New sub...I have a vintage 85hp evinrude 1980. Ran great for summer then i noticed a fuel leak. The fuel hose sharp bends were wearing out. I replace a fuel pump also. Just doesn't sound right, reinstalled old pump going for test drive #3. I am feeling like my baby is not get the right amount of fuel...

[@ExtremeDIYGuy]

Did you check the fuel tank and lines from it?

[@bryanhansen9924]

Thank you

[@ExtremeDIYGuy]

No problem thanks for watching

[@lesfaust9634]

Yup I think I have a bad fuel connection from the attwood disconnect..I'll check it in the morning..thank you buddy for the info

[@ExtremeDIYGuy]

No problem 👍!

[@christophersanderlin2223]

When you talk about grounding out the outlet of the plugs, what exactly are you referring to? Pulling your kill switch to interrupt Magento connection or grounding them out as in grounding each plug to the block. Just like you would checking for spark. Great info thank you.

[@ExtremeDIYGuy]

That's to protect the coils, they need a place to discharge when turning the engine over.

[@lmt-adventures620]

The steps are great and we’ll covered, but may I add that they don’t always necessarily have to be in that order. It’s a good idea to look under the cowling while it’s running rough and just do a thorough walkthrough as you might discover, say, sink and link way off, before you change/replace anything else.

[@ExtremeDIYGuy]

That's good advice! Hit the areas you can without replacing anything first. You are correct, they don't have to be in that order, as long as you cover all the bases.

[@skipjohnking-montaguwhaler4929]

Thank you for these tips. My old Honda 10 fuel line connector is leaking at the engine, causing fuel starvation. I can’t find a new replacement female connector that matches the male on the engine. Should I try replacing both male and female connectors for a newer design, or do you advise another solution?

[@ExtremeDIYGuy]

Hard to say without seeing it but that's probably what I would do, Good luck!

[@ZackofAllTrades87]

Thanks for the video. Where would you look if you're bulb goes soft after running the motor for a bit. I have to reprime every time I want to restart when out on the water.

[@ExtremeDIYGuy]

Is it just soft (normal) or collapsed? If it is collapsed the vent on the tank is probably not working. If it is soft and you have to re-prime, I would look at the fuel pump or some of the fuel lines may be deteriorating and clogging the lines.

[@ZackofAllTrades87]

@@ExtremeDIYGuy thanks! Just goes soft after a few minutes and I need to reprime to start. Replaced the main fuel line after I found black rubber in the carb bowls. I will probably do the small ones and the fuel pump too. I appreciate it.

[@ExtremeDIYGuy]

Good deal, sounds like the lines are deteriorating! Good luck and hope you get them replaced easily!

[@saliminthehouse]

Great video man! Im still running into an issue with my 40HP 2 stroke mercury outboard though. Will start first time and run fine at low throttle but as soon as i try give it 80%+ it bogs right down. If i press the bulb a little bit it powers right up to full power though. Ive bought a new fuel tank and line with fresh fuel and spent 1000$ on a mechanic to serivice the engine/clean the carb and its still doing the same. Any ideas? Cheers!

[@ExtremeDIYGuy]

I would check the output pressure of the fuel pump. Sounds like it's not getting enough fuel when you throttle it up.

[@bucket2675]

@@ExtremeDIYGuy I’m having the same issue with a 40hp Johnson motor, unsure on year but it’s a 2 cylinder, am new to outboard motors and this is my first boat, I have watched your videos and it already has a fuel pump installed, motor starts and idles fine, but once up towards full throttle it dies down, once you use the fuel bulb and pump the fuel pressure back up it goes how it should, how would I check the fuel output pressure on the fuel pump, thankyou for any help

[@lmt-adventures620]

Definitely fuel pump related esp. if it starts easy when you squeeze bulb and then start at first but then bogs under load unless you feed it more fuel. Good start by swapping line and tank, but the mechanic might have cost you for something you could have fixed on a weekend. Let us know how you fixed it.

[@jamesgrant9580]

I got a older mariner 150 2 stroke. It cranks an runs good in start choke. If you put it in gear it looses its prime. Its not sucking/ pumping gas into the carbs to keep running. But now while in gear you can keep choking it an it'll run just goes in an out.. Even if you put an electric fuel pump on it it does the same thing

[@ExtremeDIYGuy]

Sounds like you need to clean your carbs sounds like your having a fuel issue. The fact that it runs when choked means its not getting enough fuel. More likely than not I think a cleaning or a rebuild of the carbs would help. Hope this helps

[@fishingwithfilitsa]

Your video is good

[@ExtremeDIYGuy]

Thank you!

[@larrysims2549]

I have a 88 70hp johnson that someone removed the oil injection system but left the original pump. My pump has bit the dust and I'm trying to figure out what the alternative for fuel pump would be without buying the factory pump as it is costly and no need for the original at this point.

[@ExtremeDIYGuy]

I explain how to replace a VRO fuel pump with a standard one in this video kzbin.info/www/bejne/fnvUmquvq6ulaq8 Good luck!

[@CountryFeral84]

G’day Jose, I just swapped fuel pumps from the VRO unit to a standard pump, new lines, new manifold (no thanks to my own fault) now she starts but doesn’t idle unless pressing the key to engage the fuel primer solenoid, smokes a lot and backfires every now and again.. Any thoughts?

[@ExtremeDIYGuy]

first thing that comes to mind is making sure the idle jets are correctly adjusted, I would also look at a possible vacuume leak somewhere in the system, maybe the new manifold?

[@khrisshultz2532]

I have the same engine, having a issue where I'm not getting fuel to the top cylinder. Had a friend rebuild the carbs and idk if he didn't do something right or if it's the reed valves. Could you give some insight? Bottom cylinder is wet and top is dry to the bone. 120psi on bottom cylinder and around 75-80 on the top for compression

[@ExtremeDIYGuy]

I hate to say this but if those compression numbers are correct that engine is shot and probably needs a rebuild. However, I would pull the carb and take it completely apart to make sure everything is correct. you may also want to check the reeds.

[@bigworm6635]

I have an 81 johnson that runs great on the hose, and wont hardly run in the water. Carbs are spotless, vent was open, bulb tight etc. Anything else to check ? Thinking it could be linkage etc.

[@ExtremeDIYGuy]

Timing is a good place to start. idle is easy since you can do that on a hose, high speed can be challenge as it needs to be checked under load in a tub (or on the lake, not advisable)

[@40yeartrucker25]

Are we going to look at filter/screen on fuel pump ?

[@ExtremeDIYGuy]

That would be a possible item to look at. Thanks for bringing it up.

[@edenyork3629]

I’m having trouble with my engine, it starts up fine and idles fine but when I go to put it in gear and accelerate it bogs and shuts off until I work it out then it runs good until I turn it back off and start it and take off again. Johnson 150 2stroke

[@ExtremeDIYGuy]

I recently worked on a friends boat that was doing the exact same thing. It turned out that the gasket on #2 carb had disintegrated, a piece of it was blocking off the high speed jet. Apparently it would idle fine but when throttled up, the debris would clog the jet and the engine would bog down. Might want to check the carbs.

[@thomasjohnson1664]

I'm in a stratos 285 pro xl with a Johnson 175 and when I go to get on plane and hit wide open throttle for 10 seconds it just won't plane, could fuel cause this issue? The engine doesn't really skip or run rough

[@ExtremeDIYGuy]

If it's not getting up on the RPM's enough to plane, a fuel issue is definitely a possibility. It may be starved for gas at higher rpms.

[@thomasjohnson1664]

@@ExtremeDIYGuy thanks for the reply, I took the cowling off and ran it on muffs today. I realized I have a couple carburetors leaking. Plan to rebuild them soon

[@randy1ization]

started a 65 hp evinrude that has sat for 15 years. rebuilt carbs, set idle mixture to 1 1/2 turns out. started motor and it revved up almost to redline. I shut it off. I check to make sure throttle was not wide open and throttle plates were not stuck open. disconnected fuel line from motor and it ran gradually at lower rpms., it wouldnt idle well and carb idle screws seem to have no effect.. when first starting fuel was burping out of the top carburetor. when I pump ball up firm, it stays firm and gas does not flood out of carbs, so I dont thing my carb float is leaking by. I dont understand how the engine ran to redline with the carb throttle plates set in the idle position. and allowed the motor to evv so high .I do not have throttle linkage hooked up to it, it is on a stand. when it happened I didnt notice if the linkage pulled back on its own, due to engine vacuum or whatever. I was in a panic because the key switch was wired wrong and the key would not shut it down. so I pulled the ckoke linkage shut until the motor gradually idled don and died. I had one of these 1972 65 hp motors before and it was fantastic. always started, idled great, and had plenty of power. I put a set of 75 hp carbs on it and it increased the power by ALOT. I thing they choked the power down on thse engines to 65 hp to meet manufacturing specs for whatever reason. When I took the carbs off and saw how big the reed plate holes were, compared to the carb holes I was shocked. I think the only difference in a 65 hp and a 75 hp is the carburetors. I have the electric shift version. I think the electric shift got a bad rep because people used the wrong lube in the lower units. The previous electric shift I had worked flawlessly for several years before I traded the boat for a larger one. At this point I suspect the diaphram in my fuel pump is brittle or has ruptured. am I on the right track here? thanks !

[@liv2fish21]

Have a 94 Johnson 88 with the same issue, replacing fuel pump had no effect, thinking intake manifold gasket is leaking, started slowly idled at 1200 rpms at first now it's up to 2800 rpms, gonna try and replace intake gasket.

[@ExtremeDIYGuy]

I'm think that there might be a vacuum leak somewhere. I would check all the gaskets, and any hoses connecting to the carbs. If the fuel pump or VRO is sucking in air that might cause it as well. If you still have a VRO on it, check the impulse line to make sure it's not disconnected, same for the gasket holding the fuel pump (depending on whether you have a fuel pump or a VRO). Hope this helps.

[@randy1ization]

@@ExtremeDIYGuy THANKS I will check everything I have a regular fuel pump. The thing that makes me think it may be the fuel pump, is when I disconnect the fuel supply, it eventually came down to a decent idle. when I rebuilt the carbs, I was very meticulous,, and pretty sure I got it right, I may check the bolts holding the carbs on to make sure they are tight. will let u know what I find.

[@ExtremeDIYGuy]

@@randy1ization definitely keep us up to date on what you find! Good to share for other folks that may be having the same problem. I've got a pump rebuild video you might find helpful as well. kzbin.info/www/bejne/eoGQopePociiqcU

[@randy1ization]

@@ExtremeDIYGuy I will check it out. just took the pump apart and the diaphram was not torn, but very stiff. im going to rebuild it with the updated ethanol resistant kit, cant wait to get this old motor purring,

[@fishingwithhonor2520]

Nice video, Jose and thank you for sharing. I'm trying to find out what's the problem with my tank... it get sucked in and looks like I'm having fuel restriction.🐟🪝🎣

[@ExtremeDIYGuy]

Sounds like a venting issue. May be try loosening the gas cap and see if it still happens.