So I'm thinking of microsquirting my '71 CB750, using GSX-R throttle bodies. I've already put Megasquirt and GSX-R throttle bodies on my '77 rabbit, so this shouldn't be too hard. My big question is about the fuel supply. I'd rather not mess with my tank, so to you think the stock petcock will flow enough volume to an inline high pressure fuel pump? My petcock does have two 1/4" hoses coming off of it, so I could T them to a larger hose to be able to get a little more volume. Would that be adequate?
You could always add a swirl/ surge tank to the system. I would think that two 1/4 inch hoses could flow more than the engine can drink though. I approve this project! Keep us updated.
I 'squirted Dr.Linda's Sportster. I was still waiting on a Microsquirt, which was due out "any second now" and after hearing that for a couple years, I built my own. Anyway, I ran it: Petcock to T, T to a metal can type EFI fuel filter of about a cup capacity, to the fuel pump to the fuel rail to the regulator to the T.
She says it's like riding with an automatic transmission: Just put it in a gear and go. Smooth. Also, factory EFI systems have problems with fuel supply when low on fuel, Dr.Linda has never had that problem. The 1 cup-ish fuel filter can acts as a mini tank/surge tank.
Biggest problem was getting enough amps to run the whole thing. That and making it all fit was like putting 5 lbs of E36 M3 in a 3 lb bag.
16vCorey wrote:
So I'm thinking of microsquirting my '71 CB750, using GSX-R throttle bodies. I've already put Megasquirt and GSX-R throttle bodies on my '77 rabbit, so this shouldn't be too hard. My big question is about the fuel supply. I'd rather not mess with my tank, so to you think the stock petcock will flow enough volume to an inline high pressure fuel pump? My petcock does have two 1/4" hoses coming off of it, so I could T them to a larger hose to be able to get a little more volume. Would that be adequate?
It's not going to need very much more volume (although you will have some recirculating back to the tank), and it's not being pushed through the petcock as much as pulled by a pump downstream. I wouldn't expect any problems.
Excellent. This will likely be a winter project if I can manage to get all the other crap I need to finish done. I'll keep you all posted on it's progress!
I don't know why this didn't occur to me until now, but since my petcock has two nipples, is there any reason that I couldn't use one for the supply and one for the return?
The fuel would be heated up more than if it were returned to the tank, as you'd keep recirculating the same fuel.
I'd want to hide as much as possible. I'd probably go with the petcock nipples as send and return, and use an in-tank pump of some sort.
Matt, it hasn't been a problem on the Sportster, including some high temp runs across I90 in the summer. I have the pump mounted on the left down tube.
DILYSI Dave wrote:
I'd want to hide as much as possible. I'd probably go with the petcock nipples as send and return, and use an in-tank pump of some sort.
The more I think about it the more I like this idea. The way the petcock mounts, it would be really easy to make a simple flange with two nipples to replace it all together. I even have an extra tank I can cut up to figure out how to mount an in-tank pump. The only problem I can foresee is making the pump serviceable. It seems like it would be really freakin hard to get it in and out of there. I could cut the tank, mount the pump, and weld the tank back together, but if it ever went out I'd be screwed.
Dr. Hess wrote:
Matt, it hasn't been a problem on the Sportster, including some high temp runs across I90 in the summer. I have the pump mounted on the left down tube.
Good to know. What kind of pump are you running?
I'm imagining a petcock on each side, is that correct?
pres589
SuperDork
10/9/13 2:49 p.m.
What about a tank swap to something that already has FI? Solves a pile of issues.
There's also the electrical question of supporting the added draw of the pump and the 'squirt.
The pump is from a Victory. I think it's a Walbro. I bought it on ebay and of course it didn't work so I replaced it with one from the Victory dealer. I thought the Victory sourced one would draw less current, being from a bike and all, but it's really just a typical Walbro automotive EFI pump. If you have the amps, go through the catalogs and pick the smallest flow high pressure pump you can find and go with that. If I recall, this one draws about 3.5 amps. I would not mount it inside the tank, and pay attention to what I said about going lean in a turn. A carb has a float bowl to supply you with fuel during those conditions. You really need to think about that on a bike when you're converting to EFI. Going around a corner and having the bike die from no fuel is not a good thing. EFI systems have no tolerance for sucking air, unlike a carb.
DILYSI Dave wrote:
I'm imagining a petcock on each side, is that correct?
Nope. It's like this one:
