Topic: Solved: Vapor Lock or Seafoam After-effect? (Nope)

[Kaze]

EDITED: In short, I caused the problem by routing my fuel line under the carbs... don't do that...

At the start of the week I warmed up the bike a few minutes, then added Seafoam High Mileage Engine Treatment to my tank, in the prescribed amount. Idle immediately dropped and the bike acted like it was about to die, so I had to hold the throttle open a bit for about a minute or 2. (It never does that otherwise)

This is my first time adding any sort of fuel additive to any motorcycle, but it came recommended.

Friday I went out for a ride. I was on the freeway going 60mph or so, and 20 miles into my trip, the bike started sounding and acting like it was out of gas. The trip meter read that I'd only traveled 75miles since last fill up, but I switched to reserve anyway. For a moment it was better, but then a minute or so later, it was sputtering and choking like a fish out of water. I was only 1/4 mile from the exit, so I limped it off the highway, holding that throttle open but barely able to go 50. Got to gas station...bike died at the pump.

It took just 2.2 gallons in to fill the tank, so the odometer hadn't lied. Checked my float bowls, plenty of gas. Bike ran awesome after the fill up, so I rode another 30miles and then came home.

The carbs are spic and span, new fuel lines, new fuel filter as of 100 miles ago. When I got home, I removed the gas and checked my fuel tap. The mesh "sack" filter on the tubes is clean. No tears. I used a telescoping magnet to pull any bits of rust from all over the inside. I collected a bit of rust (fingerprint size), but nothing near the fuel tap. I blasted some compressed air through the tap where it connects to my fuel line with it turned to "On" and "Reserve". Everything is normal. Nothing in there suggests that the fuel tap was clogged when the bike was choking.

100+ miles or so ago I changed the gas cap seal. It seals quite well. I wondered if what I've experienced is something akin to vapor lock. I checked the breather hole at the bottom of the cap, and it is free and clear of muck. I blasted some compressed air through and felt air around the rim of the seal.

I found a discussion about vapor lock from 2015. http://forums.sohc4.net/index.php?topic=144611.0
Katman said, "...on my 75 750k...would be going along and would act like it was running out of gas. Lines, filters everything good. I could open the gas cap for a few seconds and close it and it would start and run like normal. Suspected the vent so I replaced the cap, and no more problems."

Sounded like my problem, but I'd rather not replace something I can fix. So I searched up how to disassemble the gas cap and found this: http://forums.sohc4.net/index.php/topic,35056.0.html Indeed, I did have a bit of a problem there, but I don't know if it would have affected my ventilation or not. And I won't know until next time I get to half a tank of gas...

Question: Do any of you know, if adding a chemical like Seafoam would alter the air in the tank in such a way that my little stock breather hole wouldn't be enough? It sounds odd to me, but I'm not a chemical engineer or even a good mechanic.

[Kelly E]

With the new gas cap seal working well a partially plugged vent in the cap could cause intermittent fuel starvation issues.

[Kaze]

...I feel like there are more bikes in your sig since last time I looked...

About the gas cap breather, I'm perplexed. The vent hole lets air through...  If I were a little bit quicker on the draw, I would have taken that rubber off and stuck the rest in the Berryman's Chem-Dip for a few hours. Shoot... now I'm feeling like maybe I should go back out there, take the cap apart again and do just that...

[Kelly E]

...I feel like there are more bikes in your sig since last time I looked...

About the gas cap breather, I'm perplexed. The vent hole lets air through...  If I were a little bit quicker on the draw, I would have taken that rubber off and stuck the rest in the Berryman's Chem-Dip for a few hours. Shoot... now I'm feeling like maybe I should go back out there, take the cap apart again and do just that...

I swear we didn't buy any more bikes today. We are selling a couple more at some point. We recently sold the 79' CB 750F.

[scottly]

EDITED.

At the start of the week I warmed up the bike a few minutes, then added Seafoam High Mileage Engine Treatment to my tank, in the prescribed amount. Idle immediately dropped and the bike acted like it was about to die, so I had to hold the throttle open a bit for about a minute or 2. (It never does that otherwise)

This is my first time adding any sort of fuel additive to any motorcycle, but it came recommended.

Exactly how much of this additive did you add to how much gas?

[PeWe]

I had an aftermarket fuel cap seal that blocked the vent hole.

I heard a strange bubbling sound from carbs when parked after a ride.

Opened the fuel cap made it clear that vent was not fully functional.

Replaced rubber seal with a Honda stock model.

I think one side has a wider lip and must be flipped right. Good idea to see that the vent hole us free from gasket

I do not remember all details years after.

[newday777]

I've only used the regular Seafoam in goldwings, I've not heard of the Seafoam High Mileage Engine Treatment, and definitely won't use it after reading your account. It must be a different formula.
I wonder if you have surface rust in your tank that was released from the use of the high mileage formula and got in your carbs. I just worked on a friend's K4 that had slight surface rust in the tank and found rust in the bowls. I did clean the tank using electrolysis followed up with full tank of Evaporust to make it super clean and then ultrasonic cleaned the carbs. It runs much better now for him.

I haven't put regular Seafoam in the gas of the 750s. I prefer to do a proper ultrasonic cleaning especially with carbs that have set unused for years.

[Tracksnblades1]

Plugged up gas tank vents tend to show up more when the tank is filled to the rim with little or no room for air.

In this full condition there is no air in the tank to offset a vacuum or pressure condition caused by fuel usage or fuel expansion.

[Kaze]

Morning all. Sorry if this turns out to be a book. There are a lot of valid points, so I'll try to answer them one by one:

1. Product is "Sea Foam High Mileage Motor Treatment". (Warning: Not to be used by men over 50 who don't ride often)

2. Quantity was 2oz. The can said "Just add 1oz. per gallon" and then went on about adding more if your bike was running rough, etc. I had a tad more than half a tank by my estimation (odometer said 55 miles or there about.) I measured out 2oz. with a measuring cup. I didn't pre-mix, because the bottle said “Just add”.

3. The gas cap is almost definitely Honda. I guess this by the use of rivets, there are no screws like after-market, and the obvious age of the thing. About a month ago, I cleaned off several years of  crud on the metal inside surface with Scotchbrite discs on my (fake) Dremel. That day I replaced the rubber seal too.

I did not happen to see whether the seal had a longer lip on one side. I don't think mine did. (I bought it from Vintage CB750, and can't recall if it came in a Honda packet, or if it was after-market)

At the time, I didn't clear out the vent. I only shot air through it after this incident. So perhaps me shooting compressed air through it cleared a passage that I couldn't discern visually -- in other words I didn't see any obvious "plug" come shooting out, but maybe I cleared it?

4. I failed to get both internal metal discs under my seal (didn't know about that) which I fixed AFTER this incident (As shown in my photo).

5. Carburetor vs. rust bits: I wondered this too. However, the mesh cover on the petcock tubes are in good condition, and the inline fuel filter is new too. If something did get past those defenses...wow it would be small, but could be?
My carbs were soaked in Berryman's Chemdip last month and working well before this (especially after I remembered to vac-sync.)

What I personally find telling is that the bike reacted very poorly immediately after adding this stuff, like it was going to die, and then acted like this again at half tank. It immediately got better after filling the tank. I don't think I like this product...

Heck, maybe I should put some in my lawn mower and see if it acts all psycho too.

Sounds like I need to go out and ride until the tank is low again, and see what happens. 

[Don R]

 Sometimes I sound like a broken record on the use of inline filters but again yesterday I was draining a recently resurrected F tank through an inline filter into a gas can and it had nearly stopped flowing. I wiped the gas off the end, blew through the hose into the tank and then the flow easily tripled. I admit the petcock screen may have been loaded with rust particles but it may be the gel that I suspect forms in these filters.
 All that said, I have a favorite old tank that I haven't de-rusted or flushed yet and run a bigger size inline filter to protect my Mikunis. 
 The scary part is if I get a low flow situation that may lean out my fuel mix and burn a piston. 

[Scootch]

When you have the "vapor lock" condition have he ever popped the gas cap lid?

[Kaze]

Noob mistake. The fuel line I bought from the auto parts store was too fat to go through the carburetor wall, so I routed it UNDER the carbs. FAIL.
The fact that I had just replaced the gas cap seal and added Seafoam before the bike started acting like it was out of gas, in spite of having 1/2 a tank left, threw me off track. Kelly E noticed the issue yesterday and I felt like an idiot. It's fixed now.