Carbureted Car suddenly hard to start, won't idle

Lowtechprime

Lowtechprime

Retro Grouch
Hey all!
My carbureted (34 DMTR) 1500 is suddenly hard to start, and doesn't want to idle. It runs fine at speed though.. Thoughts?
 
I will check those things, but I've only been driving it for 3500 miles so it seems unlikely, but if it runs well at speed, what else could it be?
 
Pull the spark plugs and make sure they're clean, pull the primary idle jet and make sure that's clear, check the function of the idle fuel solenoid.

While the plugs are out, do a compression test. (or better still a leak down test)

take the cambox cover off and have a look at the (regrind) cam to make sure it hasn't destroyed a lobe. and while you're there check the valve lash (3500 miles / 5000km after a rebuild is a good time to check it)

SteveC
 
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My vote is for dirt in the idle jet. Also, if you have an idle solenoid, you can disable it by merely pulling out the plunger and reinstalling the housing...obviously no wire needed.
 
What/where does the idle solenoid do/is it? I have the anti run on solenoid at the back of the carb, is that what you're talking about?
 
yeah it's sometimes called an anti dieseling solenoid, as it prevents engine run on.

The plunger gets pulled into the magnet end when supplied with 12v, turn the key off the plunger pops out and closes off the idle fuel passage.

SteveC
 
That solenoid is on the side of the carb but the actual idle jet is easily accessed from the top of the carb.

It's not a soulless future, it's a...cough cough.....smoky future.
 
Well so far, no obvious signs of an issue... Everything is pretty clean for a daily driven car I think.. Idle jets were still shiny brass and clear. Spark plugs look almost new.. no deposits at all... Idle/anti-dieseling solenoid working fine, spade connector tight, no corrosion.. You can feel and hear it click when key is turned.. Air filter also still looks new...
Gonna check leak down/ compression next..
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Lowtechprime said:
Well so far, no obvious signs of an issue... Everything is pretty clean for a daily driven car I think.. Idle jets were still shiny brass and clear. Spark plugs look almost new.. no deposits at all... Idle/anti-dieseling solenoid working fine, spade connector tight, no corrosion.. You can feel and hear it click when key is turned.. Air filter also still looks new...
Gonna check leak down/ compression next..
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What does the fuel inlet filter look like? ( Where the fuel hose goes into the carburetor.)
 
I didn't check, but Everything overall is very clean so I doubt it's an issue.. I have however just discovered what is likely the issue.:eek:
Crankcase Vent Vid
Expansion Tank vid
That looks to me like a blown Head gasket..... 🤬 I'm not sure where I went wrong during assembly, but I'm very proud. My first Fiat build lasted a whopping 3500 miles... No oil in the water, or water in the oil. No steam out of the tailpipe, not down on power..... But what else could That be?
It's a shame, I was really enjoying the car.. Now it's gonna just sit in the Backyard. I don't have the time to spend pulling it apart, plus I don't honestly know what I'd do differently....
 
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A leak down test will confirm it, but that bubbling in the expansion bottle certainly isn't a good sign.

If you have one of those testing kits that detects combustion gasses in the cooling system that would also confirm your suspicions.

On the plus side, sounds like you caught it early, and it's unlikely there is any consequential damage.

Oil/water passages are a long way from each other, so when the head gasket loses seal, oil and water don't often mix, it's more usual for some compression to find its way into the cooling system and some coolant to get into the cylinder when turned off. So the early symptoms will be harder to start, fires up on three and then clears to run on all four (once the water dries off from the heat of combustion) and constant fine bubbling in the expansion tank.

Once you've confirmed the head gasket issue and if you're not going to be working on it for a while, get it hot, turn it off, and drain the cooling system straight away. Pull the plugs and give the cylinders a good dose of WD40 and oil to prevent any water damage to the bore and rings.

Reasons for the head gasket failing can be many and varied. Most common is not retorquing after the gasket "settles" from heat cycling. When you do come to removing the head, all the head bolts should loosen with an audible "crack" if they are still tight. If they don't it means the gasket has settled and the bolt has lost some clamping force.

Don't see it as a setback, see it as a learning experience in engine diagnostics.

SteveC
 
Thanks Steve!

"So the early symptoms will be harder to start, fires up on three and then clears to run on all four (once the water dries off from the heat of combustion) and constant fine bubbling in the expansion tank."

That is spot on exactly the behavior it's displaying. Excellent suggestion too on the clearing/wd40 to protect the bores.
I had trouble early on, I outsmarted myself using ARP hardware on the head that when it came time to re-torque after run in my tool wouldn't fit. I finally got an aircraft wrench that worked and I did retorque at the appropriate time, but we'll see what's up. I just realized though that I can't do a leak down test as I'm right in the middle of rebuilding my compressor so I have no air at the moment!:confused: I've almost got it set up, today was supposed to be the day but I did the 128 exploratory instead... Hopefully tomorrow it will be ready to go..
Just a side note, I did some rough calculations for the Stroker motor to see if I would need different pistons. I had to estimate the volume of the piston dish, but used other similar known pistons as guesstimates. It actually worked out to exactly 10.5:1, assuming a zero deck(which I have not measured yet) but they definitely seem to be in the ballpark...
 
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Try a simple compression test. If one or two cylinders are down from the others then that would also suggest a head gasket issue.
 
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