sluggish series scenario

[bhoult]

My friend has a 69 lla 88. It's a nice little stock truck with a pretty healthy 2.25 running a zenith carb and a Pertronix distributor (it's pointless....really - I'm here all week :).

It runs super for the most part but looses power when it's warmed up and trying to climb hills. My friend seems reticent to dive into messing with it, so I'm ready to just start tinkering. I ran a Weber on my series truck with a pertronix and never encountered the same problem - which to me seems like a fuel delivery issue. I almost feel like we should swap out the carb to see if we get a change in performance - if not then look at the routing on the fuel line for vapor lock issues. I have a few low psi electric pumps lying about as well I could try just to see if I strike it rich with a part swap.

Any similar experiences out there?

Thanks -.b

[ANDYD]

I had a similar problem on my series truck and someone noticed the heat shield that should be between the carb and the exhaust manifiold was missing. (the manifold heat when the engine got hot on hill climbs was causing vapour lock issues).

Another thing worth checking is the breather on the fuel cap, sometimes they get blocked which creates a vacuum in the fuel tank. Ive seen the metal sides of a fuel tank sucked inwards from vacuum due to the breather being blocked!
He could try running the same hill with the fuel cap loose to see if it makes a difference ...

[red90]

Why not start with checking the fuel pump. Remove the lead from the coil to the distributor so it won't run, disconnect the hose into the carb, stick in a bucket and crank to see what kind of flow you get.

[bhoult]

Thanks for the quick replies! I will incorporate these suggestions as we work through the variables. The thing I find interesting is the apparent impact the change in engine temperature has. Sometimes, in cases like these, there's a sympathetic wave form of another issue - i.e. it takes time to get warm and it also takes time for the true cause to manifest itself - like the fuel tank sucking itself into an hourglass.

We'll start with the simple things first - pull off the fuel cap and then check the fuel pressure. I have an inline pressure gauge and a steep driveway, so I can simulate/test a lot of variables. We also have a killer hill few hundred feet from where we live, so good testing ground.

I really appreciate the brainstorming, so I'll get some results in the feedback loop asap.

-.b

[swamijake]

It doesn't sound like a warped carb body, but if the other ideas don't pan out, the zenith is known to warp over time. Here is a solution.

http://www.lrfaq.org/Series/FAQ.S.carb.zenith.fix.html

[island dormy]

Hello

I ran into the same issue with my 1962 Dormobile and a webber, the stock land rover mechanical fuel pump just runs out of omph when it gets hot out side or a big demand is made on it ( Running a long uphill) I added a flow through Facett electric pump and this cured the problem. High altitude also makes the problem worse. a good friend with a rochester carb ran into this in Colorado.
In one of the Rover landers Mags I did a very good write up on this exact problem.

First off though check for a clogged fuel filter.

Victor 1962 Dormobile

[Gromit Dog]

Ditto fuel supply.

I'm on my first Land Rover series, but I have had a LOT od old British Cars.. they all ended up with electric fuel pumps :) Fawcet brand, cheap and quieter than the Carter type.

B

[bhoult]

So we sourced a "good" Zenith carb to borrow for testing and it gives the same performance as the currently installed Zenith - eg poor.

The fuel pump and flow are now in the target zone that most comments have pointed us to, so we've ordered a 2.5 psi pump, relay and cut-off switch. I was curious if anyone has ever tried to put the electric and mechanical pumps in series like they do in aviation with an electric "boost" pump. The advantage I see is that the mechanical pump will be there as a "get home" measure should the electric crap out. Of course a leaky mechanical diaphragm would be a problem.

Thanks -.b

[island dormy]

Hello

To answer your last question yes you can run both if you buy the correct flow through electric pump. By flow through I mean that the original manual pump can easily suck fuel through the new electric pump with no restriction from the electric pump. There are electric pumps that have built in back flow valves and also will not let fuel through unless they are running.
Mount the pump low down near the tank with a fuel filter in front of it and it also does not hurt to have another filter in front of the webber.
I normally just use the original pump but in hot weather especially after shuting off the engine for 10 minutes or so I flip on the electric and the rover runs great. No more stalling 20 feet from your last parking spot as the carb is empty and the fuel pump is vapour locked and no more bucking on the road when you need full power.

I guess you should also check for a kinked or blocked fuel line or plugged pick up sock in the tank.

Victor

[bhoult]

So, after trying a different carb and replacing the fuel pump, the real problem turned out to be the pertronix coil (purchased along with distributor a just a few thousand miles ago). We swapped out the coil with old spare and problem solved. I would have never expected such a thing as it acted just like fuel starvation - so that's where we started. At any rate, thanks for all the help.

[ANDYD]

Glad you were able to fix it and thanks for posting how it was resolved. All good to go for the summer now!