Roadrunner 300 full throttle power loss: Fixed!! By new2scootn (Read 1,056 times)

[new2scootn]

So my trike's been either stalling out or drastically losing power on prolonged near full throttle and it's been buggin' the hell out of me. I have known it's a fuel issue and figured it was one of three things: an improperly adjusted float in the carburetor, a vacuum fuel pump that wasn't quite up to the task, or a bad fuel pick-up inside the fuel tank. With a completely full tank it seemed to be symptom free and things got progressively worse as the tank emptied. So the pick-up in the tank seemed like the most likely culprit. I borrowed a video scope and looked inside the fuel tank. I found that there's a copper tube inside the tank that goes from the outlet nipple, down along the seam to the back of the tank, then turns in and down and ends mid-tank about a half inch above the bottom. No filter or pick-up per se just an open ended copper tube-but nothing wrong with that. I followed along this tube and found a spot where it's soldered to what appears to be another tube attached to the side of the tank. This is to secure the tube in the rear of the tank. It was hard to get the right angle for a clear view but it looked like there was a pinhole in the tube at this point. And this was just above the seam of the tank so it made sense that when the tank was full this pinhole would be submerged under gas and as it got to below half a tank it would start to suck air. So how to test this theory... After a lot of thought I figured the easiest thing to try would be to disconnect the fuel line from the fuel pump and blow air into it and suck gas back out(trying not to get a mouthfull in the process-yuck!) while watching with the scope. This proved to be easier said than done but after a few small tastes of gas I got the proper method down and scope positioned. By the way, I had just enough fuel in the tank to have the end of the pick-up tube in about an inch of gas(about a gallon in the tank). So the point where I thought there was a pinhole was above the gas and I was hoping to see some gas seep or spurt out of the hole in between gags. Well I got nothing conclusive but it seemed like some gas was trickling down from above when I was blowing air into the tank. So I followed the tube back up towards the front of the tank and could see more and more fuel splashes. Finally made it back to where the copper tube is soldered on the inside of the tank to the nipple where the fuel line attaches on the outside of the tank. And thats where my problem is... when I would suck a little fuel into the fuel line then blow it back in, it would spray out all around this soldered area. Which means it's suckin' air from inside the tank when the fuel level is below absolute full. So I need a new fuel tank-will be callin' Carl from Hotrodpocketbikes tomorrow to start the process. Next will be trying to trace the loose connection(?) to my fuel gauge--keeps readin' empty(sheesh, if it aint' one thing it's another!) Good thing I don't mind tinkerin'-not sure how crazy the wife is about it though...

[Alleyoop]

What I would do is have a piece of 1/4 in pipe welded to the lowest point in the tank as it sits mounted on the scoot and plug up the top suction type system.
Alleyoop

[jct842]

Any one ever figure odds on some thing like that happening?

I kind of like the idea of a low spot in the tank having a hose barb fixed in to it. There are fittings that might be able to be fished into place after a hole drilled in the low spot too,...with gaskets in place and a nut on the very bottom over the hose barb. I watched a guy put a bolt into the frame of my car from 2 feet away pulling in place with a thin wire when he installed a trailer hitch. Same process could be used to install a hose barb in bottom of your gas tank.

[new2scootn]

Thanks for the advice Alleyoop and jct842. I took your suggestions and came up with a fix that has really worked well. I liked the idea of the fuel line connecting at the lowest point of the tank but wasn't willing to go through the hassle of removing it, prepping it, and having a fitting welded to it. Sooo... if you recall I mentioned previously that there was a drain on the bottom of the tank. Turns out it's in the perfect location for the fuel line. Metric threads though and I couldn't find a fitting that would just thread in so I had to improvise. Found a concrete strike anchor at the hardware store that has proven to be the ticket.

It's got 5/16 inch threads which are real close to the metric threads of the drain plug. I pulled the nail out and you're left with a hollow tube threaded on one end. I cut the excess length of the non threaded end off and ground a groove into the middle to better grab the fuel line. The hole through it was kinda small so I drilled it out to 11/64 inch. Bought a 5/16 tap to match the threads, tapped the drain nut on the bottom of the tank and my makeshift fitting screwed right in. And just by luck the threaded end is the perfect length so when it's screwed in all the way it sticks up from the bottom of the tank about a half inch so it won't be sucking up any garbage laying on the bottom. I used thread sealer on the threads that I had purchased for some natural gas line and propane fittings a while back and absolutely no leaks!

This pic shows the top of the tank with the arrow pointing to the old fuel line nipple which now has a white plug sealing it.

Here's the view from above showing the much neater fuel line routing--no more line laying on top of the tank.

And here's what she looks like from underneath with the new fitting.

And just a close up of the fitting. The more I got to thinking about whether or not to fix this tank the more I figured so what if the new tank is no better(or worse) than this one? So thanks again guys for the suggestions that kinda pushed me into this fix. Oh yeah, almost forgot. This totally fixed my loss of power/bogging down issue on prolonged full throttle. She's runnin' like a raped ape even up hill full throttle. Had her up to 77 mph tonight(ok it was a slight downgrade) but now I'm wonderin' if she might catch 80(no I'm not plannin' on ridin' her over a cliff). Now if I can just get this pesky fuel gauge to work she'll be close to perfect.

[daddue11]

ALLLLRIGHT, Congrats new2scootin , heck, now your even going faster than my Liberty. Keep up the good work brother.

[justincrediblem]

Nice fix new2scootn!

[new2scootn]

Thanks everyone! ;D

[Alleyoop]

FANTASTIC!! Now no more half tank sputtering crap. I still cannot believe why they put a suction type fuel outlet on the tanks makes no sense. Good job my man and thank you for the info on how-to so others that run into the same problem can benefit.

AS THEY SAY "WHERE THERE IS A WILL THERE IS A WAY"
Alleyoop