Surging, when cold

#1
Hello

Fresh from achieving smoother running victory installing a new coil and thermostat (88degrees if I recall) on my Federal 2000TC, I now have the next thing on the list to solve - putting to one side for a moment that I neglected to set the handbrake adjustment when installing rear calipers recently - is that the engine rhythmically surges and slows. This is very bad at cold (high choke) but maybe is present a tad even under lower fuel flow conditions. Maybe the order of a few seconds per surge. I rebuilt the carbs a while back. Is this anything to do with the float level? Any suggestions about how to fix it?

Thanks!!
 

Demetris

Well-Known Member
#2
From your description it sounds as if you let the choke out for too long. Full choke is needed just to start; imediatelly afterwards half or even less (depending on the temperature) should be enough, and in about a minute the engine should be able to run smoothly just on fast idle. That is if everything is set up correctly.
 
#3
Hello

Fresh from achieving smoother running victory installing a new coil and thermostat (88degrees if I recall) on my Federal 2000TC, I now have the next thing on the list to solve - putting to one side for a moment that I neglected to set the handbrake adjustment when installing rear calipers recently - is that the engine rhythmically surges and slows. This is very bad at cold (high choke) but maybe is present a tad even under lower fuel flow conditions. Maybe the order of a few seconds per surge. I rebuilt the carbs a while back. Is this anything to do with the float level? Any suggestions about how to fix it?

Thanks!!
88 degrees seems to be rather hot. You may get overrun on a hot day. You might want to try 82. They were 77 from the factory but these thermostats are hard to find!
 
#4
My car is the opposite of the daily driver so running slightly warm just a tad past vertical is not really a concern. Actually when warmed up it's running OK. The car used to be able to quickly have the choke pressed back but nowadays (post overhaul) it will just stall on the dip in the cycle so the choke is needed for a lot longer.
 
#5
have you set the carburetors? they might be slightly unbalanced or slightly weak. Apart from following the workshop manual , i rechecked my work using a Gunson colortune which showed I was slightly out on mixture. For balance either use a piece of tubing listening to the hiss or a balancer . Is the ignition ok? any looseness in the distributor?
 
#7
Hi

It’s almost certainly not the balance as they are exactly matched. I use a decibel meter in the inlet which results in pretty much exactly the same airflow - especially compared to the ill fitting Gunson thing. It’s such a huge surge that’s why I was thinking fuel. I have had dodgy tuning (in fact that’s probably the default condition to some extent) and it’s not done this before.

Of course with carbs I don’t want to start tweaking the set screws of doom and really make it worse!

Thanks
 

Tom W

Active Member
#8
A simple check that both carbs are set to the same mixture strength would be to remove the dashpots and pistons, and to measure the depth of each jet compared to the bridge with a vernier caliper or similar. Of course, this assumes both jets and needles are equally worn.

You should also fit the correct temp thermostat. How often, or little, a car is used doesn’t make any difference to its operating temperature. If it’s running too hot, then things will be outside their optimum operating parameters. Before I replaced my radiator, my car got hotter then normal if I sat in traffic for ages, and definitely ran rougher whilst it was hot.

To explain the surging though, I’d first be looking for something in the system that could generate a feedback loop. I.e. something on the engine which, when changed, causes the revs to raise, but then changes back as a result of increased revs.

What oil are you running in the dashpots? Too thick an oil, or a sticky dashpot, could cause a delay in the pistons reaching the correct height though they should eventually reach equilibrium. Do both pistons fall at the same rate, and are both springs the same? You could have one carb fighting the other.

The other place I’d look for a potential feedback loop is the ignition system. A change in timing at idle will cause a change in RPM. Is there any backlash in the distributor drive? Maybe play in the lower timing chain, that causes the timing to wander at lower revs, then stabilises out as the revs pick up?
 
#9
Hello. Thanks for the great comments!!!

Re: Thermostat. I now concur with this and earlier comments. The bugger is now officially too hot! So another thermostat is in the offing. Although it’s a lot better than with none at all. Maybe I was reading the Alaska winter motoring configuration notes before I got this one.

I replaced the dist rotor and that improved things; it was missing a bit. Did points too. Now running like a champ when hot (literally). Put more ATF in the dashpots.

Let’s see what happens when I start up from cold next time.....

But the tach just packed up so the fun never ends.....
 

sdibbers

Well-Known Member
#10
Don’t run with no thermostat. Ironically enough that can cause overheating due to the coolant flowing through the rad too quickly. If you’re based in the states Rockauto.com sell both 160°f (71°c) and 180°f (82°c) thermostats that might work out for you.
 
#11
Hi.

Oh, it had a thermostat alright 1969 vintage but it was stuck open! So I swapped one problem (rough starting until hot) with the mirror image issue (OK till hot). Actually better, but still not where it should be. Fortunately it still is in the green, but pretty darn toasty. So will be swapped out for one you mention. At least the shipping is cheap.......
 
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