85 BRAT, Hitachi, ok at 2k rpm, balks at 2,500 rpm, what is my problem? 49 State

[mkoch]

,85 BRAT, Hitachi, 49 state, new fuel filters, old loud fuel pump, new front and rear fuel filters.

The car will hesitate and lurch under certain conditions.

If I let the car just idle still for a while, and then accelerate, there is not problem accelerating, until about 20 seconds into it, then the balking begins.  The normal acceleration indicates to me that both carb barrels are working.

 

I just drove this car up a 1/10 mile 7% incline several times.  I let this car idle, still, at the bottom of the hill every time before I did the test.

 2nd gear, 2,000 rpm, the car makes it up the hill just fine.

2nd gear, 2,500rpm, the car starts balking halfway up the hill.

I am guessing the problem is the fuel pump, or the valve which fills the float bowl.  

Am I missing something?

 

 

 

 

Edited May 20, 2021 by mkoch
typo

[88SubGL]

It does sound like it’s not getting enough fuel. It could be a restriction in the line but more likely, based on what you’ve replaced so far, it’s the fuel pump giving up.

[moosens]

Have you ever taken the carb off and soaked it , refreshed it with a kit ? Float needle could be an issue here. My opinion. 

as you mention , the valve that fills the float bowl. 

 

[moosens]

And you don’t need to do the full deal to just clean and adjust the float. Not sure how deep you’ve gone before but it’s easily manageable with the usual patience required.

[mkoch]

1 hour ago, moosens said:

Have you ever taken the carb off and soaked it , refreshed it with a kit ? Float needle could be an issue here. My opinion. 

as you mention , the valve that fills the float bowl. 

 

Where are such kits available?

 

[el_freddo]

Before it baulks does it sound or feel like it’s running out of power? 

If so, it’s probably fuel starvation of some description. It could be the fuel pump as previously stated. They shouldn’t be too noisy. You should hear it prime then die before starting the engine. After start up you shouldn’t her the pump over the noise of the EA81!

Cheers 

Bennie

[mkoch]

On 5/21/2021 at 7:47 AM, el_freddo said:

Before it baulks does it sound or feel like it’s running out of power? 

If so, it’s probably fuel starvation of some description. It could be the fuel pump as previously stated. They shouldn’t be too noisy. You should hear it prime then die before starting the engine. After start up you shouldn’t her the pump over the noise of the EA81!

Cheers 

Bennie

I did not notice a loss in power before the balking.  I tried to recreate the problem today, and I was unable to make it balk.

I did some before and after measurements.

Old fuel pump, 2psi (13.8 kPa) at carb, 594 cc/ minute unrestricted flow.

 

New fuel pump 5psi (34.5 kPa)at carb, 983cc/minute unrestricted flow.

The unrestricted flow was from the forward fuel filter, so there must have been some loss to the vapor return line.

 

Is 2psi fuel.pressure a problem with a Hitachi?

[mkoch]

Following up on this.

The new 5psi fuel pump solved the problem.

I could cruise at highway speeds all day!