hard start when hot.

[DutchEdwin]

I tried to adjust the carburetor today. I encountered two problems.

The one in this tread....hard starting when hot.

The carburetor is a 4 barrol, with automatic choke. The choke operates fine, Carb has been cleaned a week ago and has new valve needles etc. complete overhaul set installed.

I have a good cranking engine, have enough fuel, have a good spark (at least I can see one when I took the spark plug out) when I cranked the hot engine.

I tested to start the hot engine after 1 minute, no problem. After 15 minutes or so, won't start. I didn't touch the gas pedal. After that I pumped in some gas.....no start etc.

Stopped for dinner. After 1.5 hours started up right away.

Let the engine get hot again. Stopped for 15 minutes and tried to start with the gas pedal 1/3 pushed in. Was hard to start but did after a few cranks. Stopped again for 5 minutes, again the gas pedal 1/3 in. No result. couldn't start it again.

Did some search and came up when a tread where Greg g and grey beard mention float adjustment needed

http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=4931&highlight=hard+starting+warm+engine

Has anyone ever tried or solved this problem by adjusting the float, or do I just have to follow the advise.....learn to start a hot engine by slowly pushing down the gas pedal and letting evaporate the gas that has flooded the engine. (what is the down side when I adjust the float?).

Thanks. Edwin.

[JBNeal]

That's what I've always had to do, floor the throttle on a hot engine without pumping it. I figger that opening up the throttle causes the carb to purge fuel & vapor in the float chamber, allowing a higher pressure differential from the fuel pump to the carburetor float.

[Young Ed]

Edwin are you touching the gas when you start it hot? You could try it without touching the gas at all.

[DutchEdwin]

I tried starting with and without touching the gas. No result in starting.

But when I touched the pedal, it did give fuel as I didn't do it slowly.

Going for an other try today, keep you posted for the result.

[greg g]

Check to see if you have still wet fuel aroud the base of the carb. Especially after it has been sitting after a run. If so then I would suspect you still have a problem with your needle and seat and or float level. Also did you check your float for the possibility that it is leaking??? Remove it and shake it to assure there is no fuel in it. If they have a pin hole, fuel will get inside and keep it from floating up enough to close the needle, which will aloow the float bowl to over fill.

When hot slowly floor the gaspedal and crank with wide open throttle. Have somebody watch the tail pipe. If it blows black smoke when it starts that would back up the point that is it flooding after engine shut down.

[DutchEdwin]

To solve the hard starting problem when hot I took the carburetor off and adjusted the float level. I set it 0.7mm (0.027 inch) deeper at the primary float and 0.5mm (0,02 inch) at the secondary.

I checked the floats, for leaks, they were ok.

Started the engine and set timing (6 degrees advance looks best) and mixture. After the engine had run for 1 hour stationary I shut it off. The temp showed the engine was very warm (2/3 of temp Needle range).

Tried to start after 10 minutes with pushing the pedal very slowly to the floor before starting so vapour could get out. Started for about 1.5 minutes....no starting.

Went to the carburetor and opened the butterflies. Inside the butterflies were dry. Carburetor base dry on the outside. Inside the intake the metal was wet, but when I operate the gas handle there is some fuel injected, no matter how slow you do it.

Should I lower the floats more?

Float setting specification: prim: 1/8", secondary 3/16". Drop primary 5/8", sec.: 11/16" . I did not readjust the drop after adjusting the level.

Edwin.

[1955 plymouth]

I would try to not touch the gas pedal when starting the car unless it has been sitting for a while.

[Frank Elder]

Hows the saying go...if you think it is a fuel problem, it's probably electrical....if you think there is an electrical problem it's probably fuel:eek:

Maybe a overheated coil?

[DutchEdwin]

I did some research on the hotrodders.com site.

They came up with some idea's for problem.

The problem could be electrical or fuel. Probably both.

Electrical. A week coil will produce less spark when hot. Thus easy to start when cold. Hard to diagnose. Easy to solve, $30 for a new coil.

Also corroded connections, bad wiring, wrong plug could be the problem.

There are some fuel related problems.,

1) leaking float needles. Will lead to overflow of the float chambers as the pump pressure will bleed into the chamber.

2) overheating carburetor. Will lead to expanding or boiling of the fuel in the float chamber. Both lead to flooding the intake with fuel. (Greg g’s post from 2007).

The diagnose is simple. When the hot engine is shut down. Look into the carb. with all butterflies open and see if fuel drips into the intake.

There are some measures you can take to correct this.

1) Ignore the problem. Start with the pedal to the floor and keep it there until it starts. This can cause two problems. Short term, leaving you on the spot with an empty battery. Long term, when the fuel leaks into the cylinders it will wash away the oil lubricating the pistons.

2) Readjust the floats. (assuming they are set to factory specifications). It is suggested they should be lowered by 1.5mm (0.06”). This could differ from the type of carb. When lowered to much the car will hesitate when accelerating at higher speeds.

3) Check the heater valve in the exhaust. When this is open all the time the intake will be heated to much. On engines with aluminium intakes the passage is blocked off with a piece of sheet metal.

4) Place an insulator between the intake and the carburetor. It is suggested that wood will insulate best. I prefer nylon as it is heat resistant (120C) and self extinguishing when at fire and fuel resistant.

I’ll make one my self from a plate 4.5mm thick add 1.5mm for the gasket, makes it 6 mm is almost ¼” insulating material.

5) Place a nylon washer on the carb. studs between the carb. base and the nut.

6) Let a fan blow to the carburetor cooling it for 15 minutes. Actually this was done by Volvo on one of there cars to solve this problem.

I’ll let you know the result.

B.t.w. Feel free to correct me on things I’ve written. These are Ideas I read from car enthusiasts on the hotrodders forum dealing with the same problems on old, modern and modified cars.

[41/53dodges]

did you ever consider vapor lock? when an engine gets hot, and the fuel line gets hot with it, it will get hot enough to boil the fuel out of the lines and carburators, but when it is running, there is fuel flow so that it keeps these components cool enough to operate. what motor are you running and what/where is the fuel pump? mechanicals are plagued with the problem of not being able to pull right when they are vapor locked, as are some electricals.

[DutchEdwin]

Yes, I considered vapor lock.

My fuel line runs from the front of the engine high above the block to the carburetor. I have a glass bowl at the highest point. As I get fuel (checked with the nozzles) no valor lock. This would mostly stall your engine when running at low speed. Had this one on a mountain with my first car an Opel Kadett type E, trying to reach the top (Edelweissspitze on the Grossglockner in Austria). Luckily I just reached the top as the road is busy and 15% steep, if I recall that number right, with sharp curves. Cool mountain weather helped cooling down the engine temp, Good for laughs when your down and safe.

[Troganin]

I had a hot start problem and went through the usual suspects as stated previous. The solution ended up being a new (possibly larger gage) ground wire. Starts every time now.

[1955 plymouth]

the last post makes me think of this problem I have on my Chevelle. I have replaced the starter recently due to broken end cap for pinion gear housing, now the car is hard to start when hot. I asked an older hot rodder and he said the Chevs had a couple different starters that would fit and I should try to find the higher rated starter. Good point, You might very well have a wire contact issue or a weak starter armature.?

[DutchEdwin]

I did some work on it.

I saw some white smoke from the tail pipe (wasn't there the day before).Torqued the head bolts again, now there is only very little smoke coming from 1 tailpipe for 5 minutes at idle or 2 km when I drive it. Then it goes away and stays away. Did check the for head gasket leaks by putting a hose from the radiator vent pipe into a water bucket (with radiator cap removed and sealed it with tape). No air bubbles at idle or high rpm's.

Checked if fuel leaks into the carb when hot....no it isn't. That rules out flooding the engine.

Also measured the temp at the carb on each side at the point where the floats are placed; Temp starts at 38C (100 F) and goes up to 43C (109F). That isn't hot to me.

Checked the nozzles by blowing a little air in with an airgun. All 4 nozzles gave fuel. The car (being hot and not starting just before I tried this) started up right away after that.

Took the car for an 8 km drive. After stop and sitting for 5 minutes it didn't start. Pushing the gas pedal 10 times, it almost started. pushing 5 more...it started. After that waited for 5 minutes, it started right away with the pedal pushed in for 1/3.

Looks to me the engine is not drawing enough fuel from the carb when hot. After getting fuel from the carb it is giving enough fuel. .

I'm going to test new things this weekend, see it the previous owner did mix up the primairy and secundairy main and idle jets. Can someone tell me how I can tell which one is primairy and which is secundairy? They look the same. Must have something to do with the jet diameter.

[Joe Flanagan]

Edwin,

Are you still running the stock carburetor? My manual has a good diagram that shows all the jets, ports, and various parts of the carburetor. Maybe someone can post such a thing here for you.

[DutchEdwin]

Jo, Thanks for the suggestion but I do have a shop manual that describes the carburetor, although the pictures in the book I have are sometimes not very clear in detail but they will do. Just have to learn by doing. Those carburetors have a life of there own. All individuals and female. I wonder why the car manufacturers changed to injection. Takes the fun out of it.

[Joe Flanagan]

I don't know. Sometimes I think it might be interesting to tinker with fuel injection but if it involves electronic stuff and computers and all that crap, THAT takes the fun out of it.

[41/53dodges]

pull the fuel line off the carb(s) and crank the engine, see what comes out, if anything.