Fuel Delivery Issue

[Jasonw22]

1973 FJ55, F engine, stock carb (rebuilt 6 months ago)

Problem: Seems to be fuel starved under heavy load ie. going up a hill etc. Idles great.

Check List: New fuel filter, cleaned tank and lines, mech. pump is working fine, no blockage at all. Good spark, good Vac. 19.5 Hg., timing fine, valves adjusted properly, fuel in middle of sight glass at idle, fuel tank venting fine, yada yada yada.

Curve Ball: A couple weeks ago I stripped the banjo bolt fitting on top of the carb. I drilled and tapped it to 12mm 1.5 and used a non Toyota specific fuel banjo bolt. The new banjo bolt has a larger opening and no adjustment like the original bolt.

Question: Is the new banjo bolt allowing too much fuel to bypass the carb due to lack of back pressure?

Thanks for any info,

Jason

 

[Pin_Head]

It depends. If you also drilled out the restrictor port that allows fuel to bleed into the return line, then you will be starved for fuel since the fuel pressure at the needle valve will be too low. The restrictor is in the top casting and not in the banjo bolt.

 

[Jasonw22]

I only drilled out the top end of casting and used a bottom tap. I didn' run it all the way through the casting. Basically I replaced the original 11mm threads with 12mm. I didnt see any ports where I tapped for the new fitting.

 

[Pin_Head]

I was confused. The restrictor is in the base of the banjo bolt, so if your new bolt doesn't have the same size restrictor (looks like about .2 mm), then you won't have sufficient fuel pressure.

You may need to reuse your old bolt and put in an 11 mm helicoil or you could just get a new top cover.

 

[FJ40Jim]

The 73 banjo bolt contains an adjustable return restrictor, which is different from the fixed restrictor bolt on 75-later carbs.

Using a straight banjo bolt will result in fuel starvation under load.

For now, the banjo can be replaced with an oil pan plug & cardboard gasket.

 

[Jasonw22]

Thanks gentlemen. I suspected that was the problem. I am going to machine a 12mm bolt to accomodate the original restrictor. For the time being I will use a plug. The odd thing is that when I first put the new bolt in it worked great. That was with a full tank of fuel. Is it possible the full tank supplied enough back pressure to simulate the restrictor? Great info here on Mud.

Thanks again,

Jason