11 replies to this topic

[Sask_Mini]

74 with stock pre-A+ engine.  Car seemed to be running fine, but was doing an oil change and decided to check the plugs at the same time just to see how they looked.  They were covered in dry black carbon, which surprised me because I had actually leaned out the mixture a couple months earlier because the exhaust smelled rich.  Note, even with the carbon fouling I didn't notice any misfiring or loss of power

 

NGK BP5ES are the plugs I had in it, went looking for a new set but could not find any of the non-resistor type plugs locally.  So I decided to just go with the NGK BPR5ES thinking that they must be better than the fouled ones that I had.  I know the answer to carbon fouled plugs is likely a carb mixture issue,  so I leaned the mixture again by turning the adjuster counter-clockwise when viewed looking down from the top of the carb.  Using the lifting pin and listening for rpm changes I set it as lean as I think I could safely go and then took the car for a drive.  No issues at idle but applying anymore than quarter throttle would cause the engine to stutter and had a lack of power.  I pulled the choke out slightly to see if that improved things and it did.  So I assumed that that I had the mixture set to lean.  I pulled over and quickly adjusted the carb to richen the mixture and then test drove again, doing this in multiple small adjustment until the stuttering went away.  It's not a daily driver so over the course of the week I put about another 50km on the car and then pulled the plugs to check them again.  They were just as fouled as the prior set. 

 

The car went into storage for the winter shortly after this, but its getting close to the time of year when I can bring it out again and I'm just wondering what I should try next.  I was thinking of the following:

 

1.  Do a quick compression test

2.  Check the base timing  (There is no mark on my crank pulley, so I've done this in the past with a mirror through the flywheel inspection port.  Is that the correct way to do it?)

 

Am I going through things in a logical manner?  Or am I missing something?

 

I can get pictures of the spark plugs if you guys want to see, but just imagine the electrode and strap being covered in dry black soot.  

 

Any help is appreciated.  

[alpder]

If this is something new that's occurring, then maybe add a carb check and/or service to your list. (Which already looks like logical stuff to be checking.)  If it's an SU carb then checking that the choke mech isn't leaking fuel, that the needle-valve works, that the float hasn't sunk, and that the piston is free would be the most important items. Fixing my leaking choke reduced fuel consumption 30%. And my black plugs are now starting to fade to grey.

[Sask_Mini]

It is an SU carb, I never even knew a leaking choke could be a potential issue.  I'll do some research on how to check for that.  The car does seem to use a lot more fuel than I think it should, but I always just associated that with the tiny fuel tank.  

 

I've rebuilt small engine carbs before, but never one for a car.  I do have the rebuild kit though, so it might be time to give it a try.

[Lplus]

It is an SU carb, I never even knew a leaking choke could be a potential issue.  I'll do some research on how to check for that.  The car does seem to use a lot more fuel than I think it should, but I always just associated that with the tiny fuel tank.  

 

I've rebuilt small engine carbs before, but never one for a car.  I do have the rebuild kit though, so it might be time to give it a try.

If the carb is the orginal for a 74 it will be an HS carb and have a moveable jet so the choke operation will be by pushing the jet down, so there isn't a "mechanism" and it can't leak fuel the same way as an HIF carb enrichment mechanism can.

 

A misfire under acceleration can be caused by lack of dashpot oil.

 

I'm assuming the needle is standard and hasn't been replaced recently.

 

I've long ago given up with the piston lift method of idle tuning. I set the idle and weaken the mixture until the engine starts to misfire then richen until it runs evenly. Richening until max idle speed is attained will give the richest setting you should ever use but I tend to go for the weakest it will run evenly then richen another flat.

[ACDodd]

Ummm this just needs a proper tune up the, needle is not the correct profile for the engine.
The mixture nut is not how you set the mixture to make it drive correctly. That is why you are having fouled plugs. Continuing to drive it like this will wash out your rings.

Ac

Edited by ACDodd, Yesterday, 08:07 PM.

[Sask_Mini]

You are correct, original HS carb and the needle has never been changed under my ownership.  The only mods I can see are an upgraded exhaust manifold and a minispares intake.  Newish cap, wires and coil on the car as well.  

 

 

I check the dashpot oil pretty regularly and try to keep it a few mm's above the plunger (kind of at the level where there is a little flat spot on the rod).  But, that being said, the previous owner used ATF instead of dashpot oil in it.  But the engine ran pretty good so I never bothered to change it out for the correct stuff.  Also, I live in Canada so local parts are far and few between for me and any part I need is typically 2 weeks away minimum and comes from the UK.  

[Sask_Mini]

Ummm this just needs a proper tune up the, needle is not the correct profile for the engine.
The mixture nut is not how you set the mixture to make it drive correctly. That is why you are having fouled plugs. Continuing to drive it like this will wash out your rings.

Ac

 

I can give the needle replacement and re-centering procedure a try.  How would I go about choosing the correct needle for my engine?

[ACDodd]

Watch all 4 parts;

https://youtu.be/i52...oTX2O4NiJQkyqiG


Ac

[ACDodd]

And then watch all for 4 parts of this demo I did at a car show in the uk;

https://youtu.be/Y6N...feR9bjkPJtjBrI8

Ac

[ACDodd]

And also watch this one for the 12 most common faults
I find when tuning customers cars;

https://youtu.be/mF1...AlxbYp0aJqW1vw3

Ac

[Sask_Mini]

Thanks Ac! This is some great info and thanks for making video content for rookies like me to learn from.  

[ACDodd]

No problem, and that’s why I do it, as there is very little actually good info out there.

Ac