Hey info, bypass pills and such..

[Blown 472]

How does the bypass system work on your mechanical fuel injection? do you change jets?? does is change flow or psi as the throttle opens?? What does the barrel valve do??

[Infomaniac]

The pump is positive displacement. The more RPM the more flow.
It meters fuel through a bypass jet. Changes how much is returned to the tank.
The barrel valve meters fuel at idle and just off idle. After that it does nothing.
The nozzles flow more as pressure increases. Pressure increases as RPM increases.
It has a high speed bypass also. Spring loaded valve opens at a preset pressure and another jet meters fuel returned to the tank. Takes away fuel at higher RPM's when needed.
Less load on the engine at high speed = less fuel needed.
Clear as mud?
The whole system operates on the principal - the more pressure you put to the fuel (pump RPM), the more it will flow through an orifice (nozzles and bypass jets). It does reach a point when no more will flow regardless of how much pressure is put to it.
The nozzles and bypass jets work on that principal.
[ June 04, 2003, 05:40 PM: Message edited by: Infomaniac ]

[Blown 472]

So the amount of bypass stays the same via the jet and does not increase or decrease the amount bypassed during the increase in rpm?

[Infomaniac]

The amount bypassed increases as much as what the increased pressure will push through the jet.
The same applies to what is pushed through the nozzles.
Plus what the high speed bypasses.

[Blown 472]

I see, the idle/low speed bypass is a fixxed orifice and by the nature of pressure forces more out.
I am kicking around a bypass system for my carbed dealio using carb jets in a log system to meter the fuel out. And just wondering how the injection system works. I know I could buy a bypass reg but I kinda like building my own stuff. Thanks for the info, info.

[Infomaniac]

Gofastracer uses an injection main bypass on carbed deals. Would be cheaper than a diaphram bypass regulator.
Ask him where he gets his stuff.

[Blown 472]

Thanks.

[Infomaniac]

If you are using an electric pump, a jet should maintain a constant pressure. Unless you have marginal delivery and the engine uses a lot of fuel from the lines.
A mechanical pump increases volume as RPM increases. Would need to jet pressure low at idle to get the correct pressure at speed.

[Blown 472]

I have a clay smith mech pump.
I see, I would have to run it at wot and jet for that psi. Thanks agian.

[78Eliminator]

I am just getting into the hilborn injection stuff and have been reading up on it the past few days. This might be a stupid question:
When you do mechanical injeciton, do you still have a fuel pump IN ADDITION to the fuel injection pump (the one that is usually driven off the cam)?