Jeep Strokers

Last post on this was in 2014. Part of the severe lean out problem was surge in the stock Rambler fuel tank. Even with 10 gallons in a 20 gallon tank it would pull so hard that the fuel would move away from the pick up. Fixed that with baffles and pick ups. No more dropping fuel pressure under heavy acceleration. However it still leans out to about 25:1 at 3500 rpm, starting as it gets on the cam. I am thinking about trashing the FI system and sticking a good old 650 CFM 4bbl on it. However before I do that I want take another stab at diagnosing the problem.

Intake and exhaust manifolds are off right now. Ordering a set of headers, probably Clifford dual outlets since I know they will fit the Rambler chassis. Once I get the exhaust hooked back up and the 99 intake back on I want to do some testing.

My first thought is that is that the 52mm throttle body may be choking the engine. Roughly the same build (258 based motor) used a triple two barrel Weber set up (3-45 DCOE's) with 42mm ventuiris (one per cylinder) and ran great.

Could I just be starving the motor for air and fuel?

Vehicle: 66 Rambler American Convertible
Engine Specifications
OBDI electronics
Cylinder head is ported (see nosigma collected work sticky)
Harland Sharp rockers.
21CC dished RPM machine pistons
.040 overbore
63.8-64.5 CC chambers
.041 gasket
.005 off deck
SCR 9.33-9.24
DCR 8.01-7.93
Quench .048
Cam is Comp Cams 68-232-4
99 Intake & Stock 99 Throttle body
Injectors are 020-155-715 28psi @ 43lbs
Adjustable MAP sensor,
Adjustable fuel pressure regulator
I have run fuel pressure from 28 to 50 lbs with no change, though that was before the tank baffling.

compression following cam break in.
1 200lbs
2 200lbs
3 194lbs
4 200lbs
5 195lbs
6 196lbs
Innovate Motorsports AFR meter

Which fuel pump are you running? Have you checked if it's putting out enough fuel?
Also check the fuel filter if it isn't new.
You could machine away the 56mm narrowing at the bottom of the stock 60mm TB to improve the response.

25:1 = Yikes
52mm TB is very small for that engine.

Cheromaniac,

The fuel filter is new. It was replaced along with the pump when the new, blasted, baffled and coated fuel tank went in.

I dont remember what fuel pump was installed. I took a look underneath but cant read anything on it without removing it. I did spend some time looking at fuel flow and pressure charts to make sure it was way more than sufficient for delivering over 50psi at the flow required for over 350hp which is well beyond where this motor should be. The fuel pressure is stable at all RPM levels (at least as far as I am willing to run it at WOT) at 43-45lbs. The hood is off and I had the pressure gauge mounted to the fuel rail with the dial aimed back a the driver so I could read it while driving.

John

I agree that 52mm is small, very small. I ran some TB calculators and saw that for this build 52mm is limited to about 2800rpm. 70mm would get me to 5500 rpm which is about right.

Is there a Jeep OBDI TBI that is any where near 70mm? The Jeep 4.7 is 68mm but its an OBDII. Paying $400 for an OBDI compatible TB is a bit more than I want to do as an experiment. If I could find a salvage yard OBDI throttle body bigger than 52mm which gave me more rpm's before it leaned out that would indicate the problem is throttle body size and make it worth taking the risk on an aftermarket high dollar TB.

Suggestions on a larger OBD1 TB to test with?

John

What are the specs on your injectors again? Your symptoms sound like the injectors could be potentially too small.
Is the part# 280-155-715?