Hard start when hot, vapor lock?

[Cav Trooper]

I have a problem with my 54 M37 starting after sitting 1/2 hour or so. It appears that the carb floods out. I don't know whether it is perculating. I have an electric fuel pump which I relocated from the engine compartment to near the fuel tank. I installed a marine water/fuel spin on filter before the pump. I tried to start the truck after that and it would not run. I checked the fuel delivery and it seemed I had plenty of fuel being pumped. I ordered a rebuilt carb from Midwest and the engine fired right up. It idles a little high, I need to tweek that. It drives and accelerates and idles fine other than a little high. My big problem is it will not start when hot if let set for more than 15 min. I can smell gas and if I hold the throttle to the floor it will start. The longer I let it sit, the harder it is to start if the engine is still hot. Today, it took me 45 min. of letting it sit and trying to start periodically. When it started it sputtered and blew some black smoke and finally idled ok. I drove it about 1 mile and stopped again for 1/2 hour. It started right away since I held the peddle to the floor. I got stopped at a train crossing for 10 min. at idle. I drove about 4 miles and it stalled at a red light and it took me another hour to get it started, I contribute this to vapor lock since the temp is about 90 deg. The engine does not overheat and the temp gauge rides at about 165 deg. I had another stop for 45 min. and had the same hard start problem, another 10/15 min of cranking and finally firing eradically and finally smoothing out. When I am driving, it runs great. Is there a cure? Can I wrap the fuel line without it looking like some cobbled up mess?

[Cav Trooper]

BTW, the manifolds have been removed and new gaskets and the heat riser has been rebuilt and set to summer.

[M37UK]

Have you checked your carb float and needle valve?
My carb kept flooding until I checked the float and found it was shutting off the fuel far too late.
Dont presume a rebuilt carb is perfectly set up.

Cheers

[Cav Trooper]

So, what you are saying is a rebuilt $300 carb has to be rebuilt before you can use it? This means I have to buy a rebuild kit for the gasket set so I can take the top cover off and set the float.... Not what I want to keep spending money on. Midwest sent the first rebuild and it leaked gas out of one of the bottom cross port plugs. Good thing it didn't catch on fire. John sent me another (this one) that seemed to work ok. Now I get this news.

[cuz]

Usually a gasket can be loosened and re-tightened when it is still very new without any harm.

Generally if the float level is incorrect it will misbehave all the time not just when it's hot.

Can you post a photo showing all your fuel plumbing in the engine compartment?

On another note does your pump installation instructions suggest the filter position be before or after the pump?

[HOODWINCK]

Hi Guys ,

just to add something here,i bought a brand new carb,and put it on assuming it was all set up from new,headed for Belgium from the south coast of England,all was going well then it started to cut out just like you said,just wouldnt start,and where i broke down i didnt have phone reception,i managed to get it fired up eventually having taken the carb apart cleaned all the jets with carb cleaner,took the distributor off too,checked the point gap and spark,it broke down again this time in the garage forecourt of a brand new petrol station,where i decided to change the fuel pump,dripping nice new oil on the forecourt..at this point the breakdown guy turned up he was impressed that i was working on the engine doing him out of a job,anyway he spaced out the needle on the intake,and hey presto worked great,got me to the show and back,once i had come back i decided to have a look at the float level ,and it was way out,i set it up as per the manual,put the top back on,and its been sweeet as since then..and the gaskets not leaked either..

Sorry long story short..

Hope its the same problem sounds like your not having fun,and its all about enjoying your truck after all..

Paul.

[M37UK]

So, what you are saying is a rebuilt $300 carb has to be rebuilt before you can use it? This means I have to buy a rebuild kit for the gasket set so I can take the top cover off and set the float.... Not what I want to keep spending money on. Midwest sent the first rebuild and it leaked gas out of one of the bottom cross port plugs. Good thing it didn't catch on fire. John sent me another (this one) that seemed to work ok. Now I get this news.

No, rebuilt carb doesnt have to be rebuilt, just checked.No need for new gasket either unless you tear yours when taking the top off.
I had exactly the same issue as Paul after I installed a "new" carb. It was only after reading what Charles et al. were discussing about correct float height that I checked mine and discovered it was way off.

[Rich]

Cav Trooper,
On my M-37 I made a new metal fuel line that goes from the mechanical fuel pump to the carb with an inline filter.
I made the line run as far from the exhaust manifold as I could, it runs 1/2 " from the passenger side frame rail, then over the top to thr carb. Also check that there are no leaks in your fuel line fom the tank to the carb.
Rich Szklany

[Cav Trooper]

Ok, I've been working on this problem and I think I have most of it fixed. I installed a pressure regulator in the line and set it at 4psi. I rerouted an new fuel line out as far as I could to help prevent vapor lock. I checked the floats and they were actually low, I readjusted to spec. I found a fuel line coupling leaking and replaced that. I replumbed the fuel filter to be on the pressure side of the fuel pump. I also found a bad electrical connection to the fuel pump. I have since driven the truck about 150 miles and the only thing that still happens is that after stopping and shutting the truck off for a 20 to 30 min. it is hard to start ie; acts like it is flooded. If I start it as if it is flooded/pedal to the floor, it will start right up, if I don't floor it, it will act flooded and not start. I can deal with that as long as I know what to do each time. I drove 48 miles one way up to the Dayton MVPA show this last week and it ran great all the way. I took back roads and it was about 1 1/2 hr. drive at 35 to 50 mph. I had no vapor lock issues and the temp was around 90 deg. I think the problem is solved, at least for now. I also installed a electronic ignition module, don't know if it helps or not but the truck fires right up. I got 9mpg for the whole trip.

[cuz]

Is your heat riser set for summer?

[T. Highway]

Is your heat riser set for summer?

The second post said it has been set for summer.

[Cav Trooper]

Yes. I rebuilt the whole damper assy with new parts and set to summer.