Very Frustrating

With warmer weather rolling into our area, I took several hours to make needed improvements to my motorbike.

Over the past few weeks I have:

Removed the engine and improved the motor mounts. That went about as well as possible.

Improved my homemade beer can air filter. I found a perfect thin piece of styrofoam filter material that works perfectly. I mixed my pieces, cutting them more precisely to maximize airflow.

I've spent hours trying to perfect my fuel line, using all types of fuel hose material.

So, today. it was strangely warm and I took a trip to the market. The bike jumped very quickly when I goosed the throttle and I had a great ride to the store until the engine died just as I stopped.

On the return, I could not get a good engine run. Oh, it wants to run but it just won't pop and go. I can pedal and it will purr but not enough giddyup to take the stress from my legs. I played with the choke a little and I got a pop out of the motor and shortened my pedalling distance, but not enough. I look down and - guess what? - a little fuel spewing out, thankfully away from the engine (which isn't very hot now anyway). I pedalled home the final quarter mile.

Very quickly I cut a new piece of leak free fuel line and took a test ride. No change; the engine will run but no energy. No gas kicking out of the exhaust. Choking seems to make it worse. I was very frustrating. I have spent a lot of hours on this thing in the past week! It is always something.

I have the feeling that the thing is running too rich...either too much fuel or not enough air. I checked my filter. the thing was running great just minutes earlier. It's very frustrating.

I've got a sneaking feeling, Timbone, that what you've got is a spark problem.

BGW, this got my attention. I m a pretty bright guy but electronics is my weak spot.

Got home from work and opened up the magneto box. It is still pristine in there! Checked all my connections. Everything looks good. Took a few runs to try and start the engine, even with the fuel valve closed. Same purring; no pop.

The problem was the fuel line- a bit too much bend. I removed the whole thing, drained the fuel, and cut new pieces and tightened everything down. Went out and the engine popped immediately. However, new problem: clutch is slipping. Sigh.

I'll make that adjustment tomorrow. Will take 10-15 minutes.

I've never gotten a perfect, bomb-proof fuel line. I found some very cool 3/16" stainless tubing, but it is too small to fit into any compression fittings I can find. I'd really like to find something like that and wrap it in some good latex tubing. One of the big problems is that the inlet tube on the carb is set so freaking close to the body of the carb. It really limits what you can attach there. :-/

=Timbone=

strange...i just ordered a roll of 3/16 stainless.. after somehow ordering 5/16 which is ever so slightly too large for what i want it for...a flash boiler. not the cheapest, as it comes from the US... pay more for shipping! but still 2/3rds what id pay over here, if i could find it, which i cant, because we dont have salt on our roads, so plain mild steel does the job...

they dont use compression fittings on stainless steel, they use single flare tapers, AN3 or something...37.5 degrees or so. change that brass fitting on the carb and youll need to replace it with something that has a seat...as its the seat for the needle valve. remove it and it will flood, permanently.


flaring it is hard, bending it is harder still... stainless is horrible to work with it doesnt even braze/tin very nicely due to the layer of chromium oxide without some seriously nasty flux and some scraping while hot...


a hard line also requires a u bend or a loop for some degree of flexibility... if i went that way, id use brass/copper lines.

why the fuel line problems? bit of 6mm vinyl has never failed me yet... even after three years of use and aussie sunlight, by which point theyve gone hard, brittle and yellow... at a few dollars for a 20 metre roll, i dont really care about the occasional replacements...

I have all kinds of fuel line material I have amassed. Why the problems?

This is my first and only kit engine. On my first build, the kit fuel line (a springy, latex like tubing) was perfect. The barb from the petcock to the fuel filter and the fuel filter to the carb inlet made for perfect fits. These fittings are all for 1/4" ID. All that tubing was eroded over time.

With my new build, my exit is a 1/8" MIP thread, which I have jumped to a 1/4" barb fitting that is slightly different from the stock kit fitting. From the tank to my inline fuel valve, I use a heavy duty fuel line that is made for lawnmowers. It works great! But it is a bit too wide to fit into the very small space offered by the carb fuel inlet.

I have tried 1/4" ID polyvinyl line that fits great on the fuel valve barb, but it will not quite seal on the carb inlet. It leaks! And there is not enough room to attach a tiny hose clamp to seal the deal.

What really worked great was some 1/4" OD polyvinyl tubing that I really had to work onto the carb inlet. It fit very tightly and lasted a while, but over time it would split.

I came up with the really great idea to use the thin stainless tubing, cut to perfect length, and wrap it inside some 1/4" latex tubing. That is not going to work well because the weight of the stainless strains the connection of the latest tubing at the carb inlet. As of now, I am running some spongy and grabby 1/4" ID laatex tubing as my lower run. It seals well but it is borderline on strength.

It's so cold now it doesn't matter but I may just come up with a whole new line. I'd like to just hardwire in a slim copper line the carb but I am unsure how to get a perfect fit at the carb fuel inlet.

=Timbone=

I think I have resolved my fuel line problems:

Here is my basic scheme:

The frame enclosed fuel tank has a 1/8 FIP opening. I used a Watts LFA-41 angled needle valve and use a good polyvinyl 1/4" tubing to fit in there. From Dax, I ordered a one foot piece of fuel line that fits very snugly on my carburetor fuel inlet valve. To connect those two different tubes, I use a Watts 3/16 double barb fitting. The two different pieces of fuel line grab snuggly and there are no leaks.

I think this will serve me well.

=Timbone=