4 strokes and primer bulb issue?

[th365thli]

So I had time to gather my thoughts, as well as more information. The main confounding factor is that the first run of the day is fine. Any subsequent runs seem okay as long as I don't wait too long between periods of running. It's only after I run, and after a long period of time of no activity, does this issue manifest.

The representative from Bass Cat Boats on another forum is adamant it's a fuel pressure/delivery issue. He claims that boats use fuel lines that are too narrow (1/4 or 5/16). He suggested either adding an inline pump or a larger primer bulb.

I then talked to one of the builders of my bass boat (Falcon). He said that while he has heard of Fuel demand valve issues, they are rare. He only recalls two cases. He also said that they use 3/8 inch fuel hoses. Finally, he explained that they don't use anti siphon valves, just fuel demand valves to prevent fuel flooding the engine.

The last bit of information I got was from another forum as well as the Suzuki outboards Facebook group. Apparently there was a TSB sent out late last year that actually seems to describe my very symptoms. The solution was to have Suzuki install a beefier lift pump. Talking to one member on the Facebook group, the beefy lift pump seems to have fixed his issue, which was vapor lock. Not sure if this applies to my inline 4....

So now I'm in a bit of a bind, trying to figure out if this is a fuel delivery issue, or a vapor lock issue, or both.

So my plan of attack is to inspect the tank and the fuel demand valve. Change the primer bulb to an OEM Yamaha one, and place it vertically. If that doesn't work, then I will have to either install an inline fuel pump or chase this TSB pump down.


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[th365thli]

Hopefully the final update to this frustrating issue.

I had sent the v6 lift pump tsb to my dealer. He contacted me back saying those were only for 6 cylinder motors. He then provided some new input. He had brought up the issue to the Suzuki regional rep. They both agreed this was a very strange issue. DF200As aren't known for vapor locking. But at the same time, a fuel issue doesn't make sense either since it always runs fine first crank/run of the day. We had talked discussed fuel delivery, primer bulbs, fuel demand valves etc. But nothing was adding up. It didn't make sense that any of those components failed. If they failed, I should not be able to be running first thing in the morning. Yes having to prime the bulb might indicate a leak of some sort, but the fact I can run beautifully after priming the bulb doesn't jive with that either.

They came to the conclusion that it could be a fuel issue. The quality of the fuel I'm using could be crappy. They believe that we are still on winter blend gas because of the coronavirus craziness. Winter blend mix has a higher RVP, meaning it's more prone to evaporation at higher temperatures. Lo and behold, I did some googling and the EPA is allowing refineries to sell winter gas until May. Cars are largely unaffected since they run richer than outboards, which tend to run lean. I'm just quoting my mechanic.

I admit I was a little skeptical, but it would be easy to prove. I had the conversation with my mechanic on wednesday when it was hot (85 F). He told me to run it this weekend (today) when it was much cooler (58-65F). If I'm able to run without issue, then it's a vapor lock issue caused by shitty fuel. If I'm still having problems, then we know it's something else. Lo and behold, I ran it today all over the Neuse River, and not a single issue. First crank and run of the day was flawless. FIshed for about 45 minutes, second run was fine. This pattern continued.

Obviously I'll keep monitoring the situation, but for all you USA boaters.....watch your gas.

[redlowrey]

It would take an extremely hot engine for the fuel to boil in the fuel lines and evaporate out of the vst, which is not the problem with your engine. from what you were describing something has happened between the tank and the low pressure pump. Take the boat out again and when you do your long run and stop, remove the fuel cap if you can and listen for the air to rush in or blow out.
I think what happens when you sit for a long time, the tank is not venting and the fuel is being pulled back to the tank that is why your primer is empty. In your first post you said the primer was flat and had no fuel in it, if that was the case, having a vapor lock problem you would still have fuel in the lines to the other side of the low pressure pump.

Mate your engine has an 02 sensor and so does your car, it will run at stoich air fuel ratio 14.7 to 1 the only difference your boat engine will stay in open loop for longer periods when under load.
Put a straw in your mouth and put your finger over the end, what happens, the straw goes flat, same thing with the fuel line, if fuel cant flow out of the tank it creates a vacuum.
What I can't understand with these dealers they have scan tools to look at data, if you in any way had a problem with vapor lock they could look up the data and see the temp gradients and fuel trims
changing as the engine got hotter. If it got to the stage where the fuel was boiling the engine would be running lean and the computer would be changing injector pulse width accordingly.
You had no lights or codes.

[th365thli]

It would take an extremely hot engine for the fuel to boil in the fuel lines and evaporate out of the vst, which is not the problem with your engine. from what you were describing something has happened between the tank and the low pressure pump. Take the boat out again and when you do your long run and stop, remove the fuel cap if you can and listen for the air to rush in or blow out.
I think what happens when you sit for a long time, the tank is not venting and the fuel is being pulled back to the tank that is why your primer is empty. In your first post you said the primer was flat and had no fuel in it, if that was the case, having a vapor lock problem you would still have fuel in the lines to the other side of the low pressure pump.

Mate your engine has an 02 sensor and so does your car, it will run at stoich air fuel ratio 14.7 to 1 the only difference your boat engine will stay in open loop for longer periods when under load.
Put a straw in your mouth and put your finger over the end, what happens, the straw goes flat, same thing with the fuel line, if fuel cant flow out of the tank it creates a vacuum.
What I can't understand with these dealers they have scan tools to look at data, if you in any way had a problem with vapor lock they could look up the data and see the temp gradients and fuel trims
changing as the engine got hotter. If it got to the stage where the fuel was boiling the engine would be running lean and the computer would be changing injector pulse width accordingly.
You had no lights or codes.

I sort of understand what you're saying but this is what the dealer told me. Yes, if fuel was boiling as the engine was on, it would throw some kind of signal indicating something was wrong. But let's say I run for a while, then I stop and suddenly quickly cut off the engine. No more water being pumped through cooling the engine, so the engine temperature skyrockets. Let's say I cut off the engine. Then immediately turn it on so the gauges turn on but don't crank it. I'll see temperatures be really hot. It's only after I crank the engine on again will the temperatures gradually come back down since cooling water is being pumped through again.

This is why a lot of suggestions to fix vapor lock include idling for a while after a WOT run, to cool down the engine. Yeah, my temp monitor says 120-124, but that's because of the cooling water. If I idle it longer, when I cut off the engine temps won't skyrocket as much. It also explains why in hot weather vapor lock is more common. Obviously the air temp itself isn't gonna boil gas, but coupled with a hot engine it might.

Also, your theory about the fuel being pulled back to the tank doesn't make sense to me. If that were the case, how am I able to start the motor for the first time every trip? This was verified 3 times. Put the boat in, crank her up for the first time that day, run to my first spot, no issues. You would think sitting in my storage unit every night the fuel would drain back down.

Also, as I clarified, the primer bulb was never FLAT. It seemed EMPTY. The second time I was out I double checked to see if it was FLAT and it wasn't. All I know is that today in much cooler temperatures it ran great. All I can do is to run out this tank of gas, get new gas or non-ethanol, and keep monitoring this situation. I'm not discounting ANY of the input I received here, you guys have been really helpful. I'm just juggling many different possible scenarios, including my Suzuki dealer who I do happen to trust.

[th365thli]

I lifted this from an answer in another forum, note 1, 2, 7. and 8

Things affecting vapor lock:
1.type of fuel, formulation, and RVP(reid vapor pressure)
2. engine cowl temp and ventalation system
3. temp and vacuum on the fuel line that is being delivered to motor.
4. location of fuel tank
5. boats fuel supply. (ID) of fuel line and fitiings, fuel line length, routing bends and kinks and th clamps the secure it. extra fuel filters, fuel manifolds,ASV, shut-off valves, tank selector valves and the # of 90 degree fittings used( every turn causes turbulance)
6. engine coolant temp
7. How quickly the the engine is shut off after running at cruising or higher rpms and how long the engine and engine compartment are allowed to cool off after use.
8. the outside air temp on the day the boat is being used

[redlowrey]

The reason the engine starts ok first up is because the vst is full of fuel, the fuel cant drain from the vst overnight, your not on the same page, I am talking about a long period of operating the engine then stopping and turning off. Your gauges are running at 124 deg and you think your got vapor lock,

[th365thli]

The reason the engine starts ok first up is because the vst is full of fuel, the fuel cant drain from the vst overnight, your not on the same page, I am talking about a long period of operating the engine then stopping and turning off. Your gauges are running at 124 deg and you think your got vapor lock,

You're right, we're not on the same page. And while I respect your knowledge and the attempt to help, you're coming off as kind of a dick. Obviously 124 degrees isn't causing vapor lock, did you even read any of my explanation on what happens after the engine shuts off?

If the fuel is draining leaving only fuel in my vst, how come my first run of the day I can run it as hard and fast as I want? And then the second run after a long period of waiting I can barely get 200 yards?

You presented an argument and I addressed each of your points along with opinions from my dealer because it still didnt make sense to me. Sorry if me trying to understand offended you.

[Murray]

“2. engine cowl temp and ventalation system”

Have you tried running the engine with the cowl off? That would confirm/eliminate your point #2 in post #20

[th365thli]

“2. engine cowl temp and ventalation system”

Have you tried running the engine with the cowl off? That would confirm/eliminate your point #2 in post #20

No I haven't, but I can certainly try. It would have to be in calm water and low speeds for sure. Would love to keep running it to get a clearer picture, but our southern states weather is crazy and this week is thunderstorms and high winds.

[catacom225]

All this and you just have a crappy primer bulb, I've lost count on how many I have changed