Gas tank swap?

[TexasDave]

Is this why we have a vacuum line to the CDI?  Dave

[racerrad8]

Is this why we have a vacuum line to the CDI?  Dave

No

Randy - RPM

[ribbert]

This is the most important in case of a crash where the engine is no longer running but the ignition is still on to prevent fuel from being just pump through the carbs as the bike lays on its side.

So, if you want to convert a gravity bike to fuel pump the only other option would be to use a low oil pressure switch to shut the pump off when the bike is not running. There will need to be a bypass switch to prime the carbs when they are empty or if the bike has been sitting and the fuel could have evaporated.

The only problem we found with a low oil pressure switch is the FJ idle at around 3-5 lbs when warm. We tried to use them on the cars but with the engine warm & idling the oil pressure was not enough to keep the switch energized and the car would run out of fuel.

Randy - RPM

If you wish to retain that feature there are other options. Mercury switches, rollover switches, vacuum switches, you can even get inertia switches, they're all cheap and easy to incorporate. You could even run the ignition through it so the engine doesn't have one almighty rev as it slides down the road with no oil pressure. If you wanted to retain the ability to prime the carbs, a simple spring loaded switch bypassing the safety feature would do. Just depress it for the duration of the prime, no chance of leaving it on.

Personally, I wouldn't worry about any of it but if you do, it's easy and simple to overcome without any real complication or expense and the FP would be a nice upgrade.
You could even find a suitable mercury switch at the wreckers. They were popular for bonnet and boot (hood and trunk) lid light switches.

Noel

[andyb]

These switches are required for racing.

They're called tether switches.

[Pat Conlon]

At my last low side accident, a mercury switch would have save my engine from oil starvation issues as it lay on it side idling, while I'm on my back 20 (long) feet away.
FJ engines do not like that....

[ribbert]

At my last low side accident, a mercury switch would have save my engine from oil starvation issues as it lay on it side idling, while I'm on my back 20 (long) feet away.
FJ engines do not like that....

Not so common these days with more robust engines but I have seen a number of bikes that have run big ends from lying on their side with the engine running and no oil pressure, it doesn't take long.

BTW, your LAST low side?, just how many have you had? You refer to it so casually.

Noel

[Pat Conlon]

Low side? Only one on my FJ....
In the '60's, one on a dirt bike (knobby tires on the street, uuuuggh) and don't forget mini bikes....

[Flynt]

At my last low side accident, a mercury switch would have save my engine from oil starvation issues as it lay on it side idling...

Practice kill switch actuation as the bike slides away...   

Frank

[Paul1965]

Okay FJ gurus, I need some help. I got a chance to let the bike run for a few minutes today (10 minutes), and it runs way richer than I was anticipating. I swapped out the tank, installed the electric fuel pump and UNI pods but have left my carbs completely stock. What is the most cost effective and quickest way to lean it out? Or is that too stupid of a question to even ask lol! I thought about maybe just restricting the flow of gas after the pump, but I'm afraid that might just jack up the pressure even more and make things worse. The last time I had a Mikuni apart was about 20 years ago and that was on my SkiDoo Mach 1, so I'm not sure what my comfort level is pulling the FJ's apart.

[racerrad8]

What is the most cost effective and quickest way to lean it out?

You have to change the needle & sets in the carbs to the smaller diameter seat.

Needle & Seat Assy (1.5)(F/Pump)

Randy - RPM

[FJmonkey]

left my carbs completely stock.

The needle seats are larger on the stock (Gravity feed) carbs. This means the fuel has a larger surface area (like having more leverage) to push against the needles and floats. The needles and floats may not be closing at the correct level due to the pressure created by the fuel pump. Changing the seats out and resetting float heights might be a good start. Get new O-rings with the new seats. Might as well get new needles while you have the carbs open. And up your idle jets to #40 is also a good mod, the stock jets are too lean on the idle.

Randy beat me to the punch....

[Paul1965]

What is the most cost effective and quickest way to lean it out?

You have to change the needle & sets in the carbs to the smaller diameter seat.

Needle & Seat Assy (1.5)(F/Pump)

Randy - RPM

Thanks Randy/FJMonkey for the speedy replies.

Randy, I was just at your site looking at carbs forgetting how much they went up lol. Would you be kind enough to put together a list of everything I would need for the swap so I can check to see what it will cost? Or is that info posted somewhere already? I would also consider sending them to you for a rebuild depending on the cost and turnaround time.

[craigslist1340]

If you afford it, let Randy do the carbs. I got my back and he fixed a whole bunch of stuff wrong with them that I didn't know about. He sent me photos of the insides, man they were nasty. They have never looked so good, and the bike runs great with the newly rebuilt carbs and Uni filters.
John

[Paul1965]

New reman carbs arrived today (er, sorry Randy found someone closer to me).

[Paul1965]

Carbs are installed and so far seems good. I couldn't drive it, but it sure started, idled and revved very nicely. The carbs are from a 1200 and were rejetted and tuned, and are modified for a single inlet fuel system.