Surging When Cold

[utahseries]

What would cause a 2.25 to surge violently when it's cold? It does it in stop and go and the highway. And, when it's on the highway you have to drop the rpms a ton to get it to stop surging. After it's warmed up it runs fine.. Fairly annoying... so if anyone has an idea of what it could be, I'd love to hear ideas.
Thanks

[parrie]

Diesal or petrol?

[bugeye88]

Sounds like a fuel supply issue. Could be more noticeable when the choke is partially out when cold requiring more fuel. The usual suspects: fuel pump, clogged fuel filter, partially blocked jets, float bowl adjustment. It gets fuel and jumps then looses fuel supply and dies....repeat.

Good Luck,
Rob

[utahseries]

Petrol. It does it for around 15 minutes in the morning and the rest of the day it's perfect.

[bugeye88]

Utah,

Another thing it may be related to is the fact that it only does it when COLD. Given that it has been cold in these parts(i'm in Ut also) maybe your getting some carb icing until it warms up. Are you using a stock intake manifold? The stock ones have exhaust heating of the intake manifold which is better than others in the cold. Still could be icing though. Maybe run some gas line antifreeze through it once (one bottle for 1/2 tank) and see if that helps. (even though I'm not a fan of ethanol in gas, one shot to remove any water build up in the tank couldn't hurt).

Cheers,
Rob
Bugeye88
68 series 2a Bugeye

[CKubinec]

I was wondering, does the choke have any affect on what it does. Also what sort of carburator on it. Also seen small vacuum leaks cause surging when cold.

Chuck

[parrie]

Definately sounds like a fuel supply issue. Is this symptom new to the truck? Does it only occur during cold weather? If so I would agree w/ Bugeye...possibly some icing of the carberator or maybe some condensation trapped else where in the fuel delivery system that is freezing and partially blocking flow until she gets warmed-up. I'd try running some dry-gas through before I started tearing this apart.

[stomper]

I'm thinking there might be a vacuum leak at the carb or intake manifold, that closes up as the metal warms up and expands. These can be tricky to find, but using WD-40 or carb cleaner and spraying it on the joints while the engine is cold may cause the engine to rev, thus indicating where your vacuum leak is coming from.

[utahseries]

It has only started this recently, and the temp has been in the 40's each morning it has done it.. The choke is really only out to get it started, (for as little time as possible). I've also thought about the vacuum leak. We've thoroughly gone over the fuel system and it's as clean as can be. It's running a zenith; the engine is a REME re-manufactured motor with around 2500 miles on it.

[bugeye88]

Utah,
OK so no fuel line freezing. Still sounds like some sort of fuel delivery problem. Do you have a low pressure electric fuel pump on it yet. If not I would consider one as it helps fill the float bowel before starting and can come in handy if other fuel pump problems arise. I have mine after the mechanical pump and controlled by a on/off switch in the cab. Vacuum leaks also good possibility, as mentioned by Stomper. Crud in the fuel line or at the fuel pickup in the tank can also lead to the pump not being able to fully fill the float bowel right off the bat and for the car have intermittent lack of fuel until the pump catches up. All those other Landy's running well? Love a good mystery.

Cheers,

Bugeye88

[LaneRover]

My brother once had a gummed up mechanical fuel pump that would allow him to drive for a bit and then lose power.

Could yours be gummed up in a way that doesn't affect it when warm?

[utahseries]

We've gone through the whole system from the tank to the carb and we can't find anything out of the ordinary, so it's most likely a vacuum leak. And to answer your question Bugeye, they are all running like a dream!

[stomper]

When looking for the vacuum leak, pay particular attention to the joint between the exhaust manifold and the intake manifold. It may be hard to squirt carb cleaner on this joint, but I'm guessing there is where the problem is. The cast iron exhaust manifold and the aluminium intake has a gasket between them that is likely perished.

[cedryck]

You can use a propane tourch to find a vacume leak as well, this works great, just do not light it, use it with the flame OUT obviously.