Outboard Motor Fuel Line Question

Anyone happen to know the maximum length 5/16's ID fuel line can be for the primer bulb to operate correctly? Got the boat out in the driveway today to check out a 6hp Yamaha and had trouble getting fuel flow through the line. The primer bulb wouldn't get firm. Replaced the bulb and all fittings without much success. Finally got the motor going, but I think the fuel flow through the line was more due to the fuel pump on the motor. I put this fuel line together, and it's a couple feet longer than the one's Yamaha sells (with the primer bulbs included.) Do you think that 2 extra feet would cause this problem?

fuel line

does the fuel line exit the tank thru it's own pick-up? if so is there a check valve at the tank? if you come off the water seperating fuel filter, when is the last time you changed it? does it have a shut off vavle? and did you check for a pincned or kinked hose? those are a few of the possibilities.

5/16" is huge for that size motor. Since you had just hooked it up, getting it primed might have been a large part of your struggle. Make sure all your clamps are super tight so that there is no air leak to lose vacuum. But back to the line size, we can take a little pole but my main motor is on the 5/16" and my kicker uses 1/4".

SuperD said:

5/16" is huge for that size motor. Since you had just hooked it up, getting it primed might have been a large part of your struggle. Make sure all your clamps are super tight so that there is no air leak to lose vacuum. But back to the line size, we can take a little pole but my main motor is on the 5/16" and my kicker uses 1/4".

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Dave, aren't all the Yamaha fuel fittings made for a 5/16 ID hose? According to our dealer 5/16's is the correct size for up to a 90 hp (this dealer has been known to be wrong though.) I'll check it again...might just have needed to be primed like you mentioned. I'm also thinking the added distance of hose between the tank and the bulb might be the culprit. I'll look into your suggestion lowe164mt and will post what we find out...Thanks

Well it's working good now! Got the bulb 2 1/2 feer closer to the tank and it seemed to get the gas flowing alot better. Between that and getting it primed I think were good to go now...signfishin Thanks again for your suggestions.

Since I just replaced the fuel line on my father's yamaha I have some experience with this. It sounds as though you've got it working but I thought I'd post a thought or two on it. My first thought when reading your post was to ask if you made sure the air vent was open on the tank before you tried to pump up the bulb. I had some trouble with the bulb on our motor because it didn't want to fill back up right away after I squeezed it but it worked anyway. I don't remember if I had the vent open before I tried to pump it or not but I know I never had any trouble with it after the first time. And also, we are running a 1/4" fuel line for his 15hp 2 stroke yamaha so I am pretty sure that 5/16" would be a little overkill for a 6hp motor.

After my Dad talked with Yamaha today it appears the 5/16's ID line is what they recommend.
We noticed a strange thing we've never seen before when trying to figure this out on the 2nd day.... the plastic fuel tank was collapsed on the sides from running the motor the day before. The Yamaha Rep said it indicated a problem with the valve on top of the tank. We had it open but it might be clogged up or defective.