Exactly WHY is my car hard to start when warm?

Posted By: RapidRobert

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 05:13 AM

Quote:

How would this happen? Would not the evaporating/boiling fuel simply vent out of the bowl vent tubes?

It'd depend if it was heavier than air or not & it's probably still evaporating when he comes back then it gets sucked in when he cranks it

Posted By: jbc426

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 01:10 PM

I had this problem and was also baffled until I spoke with Doug Dutra, the famous slant six guru. He explained what was happening:

When you shut off a warm engine, the heat from your engine's intake manifold is boiling the fuel in your float bowl and causing it to drip into the intake etc causing an excessively rich condition. This happens because the fuel percolation drops the float and allows more fuel from the still presurized fuel line, between the fuel pump and the needle and seat to flow more fuel into the carb to bring the float level back to normal. This continues until the pressure in the fuel line between the fuel pump and the needle and seat goes to zero. In the mean while, a significant amount of fuel has now percolated out of the carb AND the pressurized fuel line between the fuel pump and the carb (until the presure is released by the process). Quite a bit of gas ends up in the intake every time you shut off a hot motor.

This is how you fix it:

#1 Use two gaskets and a sheet of aluminum to isolate the carb from the intake manifold. This will likely require longer carb studs. Be sure to check for hood clearance. (this helped a lot, but did not eliminate the problem completely)

#2 Install a fuel return line from a 3-nipple fuel filter, which is available from any autoparts store between the fuel pump and the carb, and the fuel tank. The third nipple on the 3-nipple fuel filters has a metered orifice to limit the amount of fuel it flows. I had to install a return line and a 2 fitting fuel sending unit on my 68 slant six car to complete this installation. The car had an original 5/16 fuel line, so I added a 3/8ths line as the main fuel line and used the 5/16ths line as the return. I bought a dual fitting fuel sending unit for less than $50 off ebay, ran the lines, installed the 3-nipple filter. I never had a hot start problem again.

Attached picture 5252917-10-130[1].JPG

Posted By: RapidRobert

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 01:23 PM

that's good stuff, #1 for the heat & #2 to release the psi

Posted By: jbc426

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 01:41 PM

Yah, that Dutra is something else! If you don't want to spend the money on a new dual nipple fuel sending unit, you can drill and add a fitting to your existing sending unit by using those brass hardware store parts, some cheap aluminum return line and the fuel filter. The total cost is around $40 or less.

Posted By: jt1

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 01:41 PM

I understand the fuel boiling and evaporating out the vent tubes, but how does any fuel get into the engine to cause a rich condition? It seems something would have to force the fuel thru the jets and out the boosters.

John

Posted By: Magnumguy

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 02:09 PM

Quote:

Seriously try a heat shield, it deflects most of the engine heat around the carb...In order to clear the linkage I had to trim one corner a little but it works great... Not a pretty as some other spacers but more effective & I care more about function as I like to drive my car... And if your gonna drive it it's gotta start..

Where'd you get the spacer (shield) on the right?

I wonder if you don't have your floats too high. Every Magnum I've owned (and it's been alot) would start pretty much the same hot or cold, except one of my current driver one. It will smoke black some when it starts hot, rolls over OK, but takes 2-3 seconds, but almost instant cold.

Posted By: RATTRAP

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 02:20 PM

Prob not heat as much as your timing is off

Posted By: BossRide

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 02:28 PM

Quote:

Prob not heat as much as your timing is off

That has crossed my mind... maybe I'll double check it... with the Holley and intake, mild cam and headers, should I set it different that the stock specs?
It was set when the engine was installed and I forget exactly what we set it at, it's been almost two years.

Funny thing, the old tired 2bbl 318 did the same thing... start great, spin over and over when hot. It acts like the gas has left the carb, and it will catch slowly, but not be skippy or stumble, just light off slowly.

Posted By: Rug_Trucker

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 02:44 PM

Quote:

I understand the fuel boiling and evaporating out the vent tubes, but how does any fuel get into the engine to cause a rich condition? It seems something would have to force the fuel thru the jets and out the boosters.

John

Slant sixes are the worst. Fuel line is routed like crap! Even before they started adding alcohol to our fuel my 72 had to be held to the floor to start hot. This was on 50* days too!

Rerouting the fuel line worked excellent! No return line needed. My 74 slant Dart has the same problem.

Fuel injection hose with the fuel injection clamps routed over the valve cover with enough slack to pull the cover to set your valves works. It is in a sticky on www.slantsix.org in the engine section.

I have watched hot steamy gasoline boil and dribble into my hot intake many times.

Posted By: cataclysm80

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 03:07 PM

Quote:

This might make you feel better.

Mine has gotten to the point that it won't even start when warm. Nearly had it towed last week when I shut it down to fill up with gas. By the time the tow truck arrived it started and I was able to drive home. Fires up great cold, runs great, but if I turn it off and try to restart hot I can just crank away till the battery is nearly dead.

My original 1938 ford flathead does that same thing. I've been told it's caused by a bad coil that fails when it gets hot.

Check your spark next time it happens.

Tav

Posted By: 68Bullit

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 03:25 PM

With all the talk about percolation and fuel boiling, makes you wonder why more fires aren't getting started! If that's even possible?

Here's one though, for those with more than one carb. Right now, I'm using a Holley 750DP, but I also have a nice TQ. What few times that I've used the TQ, it didn't seem to hot start any. Would this be because of the phenolic design? In other words, would an extra 20 degrees cooler, which the TQ's are said to run on average, make the necessary difference to keep the fuel boiling at bay?

Posted By: moper

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 03:32 PM

What does the engine have for cylinder pressure? As bad as the gas is, I have yet to have an issue like this on any of mine or customers'. We have the 10% ethanol fuel, have for 4 years now at least. My truck has run at 220� before when working, and 45 minutes after parking, it turns over 2-3 times and it's fine. I find most of the issues with starting are a result of tuning or lack of cylinder pressure due to wear, or camshaft choice, or camshaft timing. Much more so than percolation issues. JMO.

Posted By: 1_WILD_RT

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 03:51 PM

Quote:

Where'd you get the spacer (shield) on the right?

http://store.summitracing.com/egnsearch....p;x=39&y=10

Posted By: 68Bullit

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 05:20 PM

How thick is that shield? (How much vertical space will it take up, gaskets included) for those with hood clearance concerns?

Posted By: 1_WILD_RT

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 05:44 PM

Less than 1/4"... Most of the heat rises around the plate rather than through the carb body...

Posted By: 71383beep

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 06:56 PM

I too experience this problem. We also have the mandatory 10% ethanol blends and have come to the conclusion that a a vapor separator is probably needed.

It sucks though. Go for a cruise. Car starts and runs just fine. park for a half hour and she won't start. Pedal to floor crank and eventually she'll fire. Very frustrating.

I got a separator from the last swap/show. Now I just need to cut my nice new steel braided carb supply line...

and install a return line.

Posted By: rss

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 11:10 PM

Quote:

I find most of the issues with starting are a result of tuning or lack of cylinder pressure due to wear, or camshaft choice, or camshaft timing. Much more so than percolation issues. JMO.

If you are correct, then why would the car fire up instantly when cold but not start hot? Do poorly tuned cars run well cold???

Posted By: MNobody

Re: Exactly WHY is my car hard to start when warm? - 05/26/09 11:32 PM

"I have watched hot steamy gasoline boil and dribble into my hot intake many times."

I had the same problem with my 750 Holley on my 318, the bowl's were getting so hot you couldn't touch them up by the carb base. The whole problem was solved with a 1/2" plywood spacer under the carb, the bowl's are almost cool to the touch now and it doesn't sound like coffee brewing in the carb anymore, i do still get a little smoke out of the primaries but no fuel dripping above the throttle plates.

Posted By: BossRide

Re: Exactly WHY is my car hard to start when warm? - 05/28/09 11:46 PM

Quote:

I

I got a separator from the last swap/show. Now I just need to cut my nice new steel braided carb supply line... and install a return line.

Is this separator to vent gas or fumes back to the tank?

My car had the charcoal canister and some vent tubes that run into a box-thing at the top of the tank. Can I run a separator to that?

How does that work?

Posted By: Anonymous

Re: Exactly WHY is my car hard to start when warm? - 08/30/09 04:46 PM

Bump...
My '74 Fury 400 was a hot start and flooding nightmare when I went to a Thermoquad and Edelbrock intake. I swapped out the steel line for an insulated stainless mesh covered fuel line from the mechanical pump to the carb. Of course the composite body on the Thermoquad was designed to eliminate heat soak transfer to the fuel bowls but even with that, the big block generated so much heat that the only cure was to keep the fuel line cool. You not only cook the fuel in the bowls but the fuel gets cooked in the line from the pump to the carb. My only problem now is COLD starting! Always has been a bear... crank for 20 -30 seconds and then runs like cr*p for 4 minutes... IF it even starts.

Posted By: hooziewhatsit

Re: Exactly WHY is my car hard to start when warm? - 08/30/09 04:59 PM

Quote:

Bump...
My '74 Fury 400 was a hot start and flooding nightmare when I went to a Thermoquad and Edelbrock intake. I swapped out the steel line for an insulated stainless mesh covered fuel line from the mechanical pump to the carb. Of course the composite body on the Thermoquad was designed to eliminate heat soak transfer to the fuel bowls but even with that, the big block generated so much heat that the only cure was to keep the fuel line cool. You not only cook the fuel in the bowls but the fuel gets cooked in the line from the pump to the carb. My only problem now is COLD starting! Always has been a bear... crank for 20 -30 seconds and then runs like cr*p for 4 minutes... IF it even starts.

how is your choke set up? On my 318, unless the choke is firmly shut, it'll just crank

Posted By: MoparforLife

Re: Exactly WHY is my car hard to start when warm? - 08/30/09 05:06 PM

Another very easy thing to do to ease starting is to hold the gas pedal all the way to the floor when you atart the warm/hot engine. This helps clear teh engine of unburnt fuel just like unloading a flooded sitiation. Granted it isn't a cure but in all reality short of spending a lot of money there is none.

We went through alot of so called cures and fixes and in the end accomplished very little except spend money. The above helps, learn to live with it, we did.

Posted By: BossRide

Re: Exactly WHY is my car hard to start when warm? - 08/30/09 05:14 PM

I have since cured my problem...

I suspect it was a combination of things. I replaced the original coil with a new one, added a heat shield, reset the timing and then fine-tuned the Holley with a vacuum gauge, and my starter had slowly been dying, getting slower and slower when cranking. I put a new one on and it spins over like crazy and fires right off.

I also had a charging issue after the motor mount broke and the alternator's positive post hit the inner fender. The regulator wouldn't allow more than 12 volts, so I replaced both of them.

Thanks to all who offered advice.

Posted By: aarcuda

Re: Exactly WHY is my car hard to start when warm? - 08/30/09 05:44 PM

mine does this too. but only if its hot out and it sits for 30 minutes or so. Then its hard to start and idles like crap until it clears up. theres gas on top of my center card and on the bottom of the aircleaner lid when this happens.

its definitely heat related. my carbs are boiling hot. so is the manifold and I have the heat crossover blocked and a valley tray. its heat soaking from the heads (aluminum conducts heat pretty well.

I cant use an insulator as my carbs seal to the hood (340 sixpack) so im interested in ways to fix this too. i can hear the gas gurgling in the bowls

Posted By: moparcanuk

Re: Exactly WHY is my car hard to start when warm? - 08/31/09 02:04 AM

Quote:

Mine lights off instantly... I think the new fuel boils off due to engine heat.. In a modern fuel injected car where the fuel is injected & the fuel is always pressurized it's a non-issue but a carburator where the fuel sits on a hot engine....I've blocked the crossover & added a heat shield...

http://images.google.com/imgres?imgurl=h...sa%3DN%26um%3D1

This solved my buddy's starting problems so I tried one on my 440 air grabber. Had to remove it as there is not enough clearance.

I'm going to try blocking off the heat risers and add a thin aluminum spacer with 2 gaskets.

Posted By: Daveo383fury

Re: Exactly WHY is my car hard to start when warm? - 04/30/13 05:43 AM

I know these posts are a little old but it came up when I googled it. After reading the posts I went out and checked my 383 fury with edelbrock manifold and holley 4bbl. Started it up and let it run. Carb never got hot-maybe a little warm but not bad. Noticed immediately that the secondaries were leaking gas...drip drip drip. Gonna pull off the carb and check the body gaskets by the butterflies and change em out. Fortunately with holley you can adjust the floats from outside the carb. Turned the secondaries all the way down ran it again and no leak. Seems to have nothing to do with getting hot just a leaky carb.

Posted By: 63stabamatic

Re: Exactly WHY is my car hard to start when warm? - 04/30/13 12:33 PM

My hot starting problems were solved by going to non-ethanol fuel which is becoming more available here in the Rochester NY area. It started at marinas as the ethanol was killing marine fuel systems and engines. I now use it in everything. Here is website:

http://pure-gas.org/

Posted By: MoparforLife

Re: Exactly WHY is my car hard to start when warm? - 04/30/13 01:01 PM

Quote:

My hot starting problems were solved by going to non-ethanol fuel which is becoming more available here in the Rochester NY area. It started at marinas as the ethanol was killing marine fuel systems and engines. I now use it in everything. Here is website:

http://pure-gas.org/

Reason is that alcohol blends tent to have a much lower boiling point and will not take as much heat soak and will spill over the needle and seat causing a flooded condition. Starting warm/hot engines using blended fuels as you would a flooded engine by holding the pedal to the floor opening the throttle blades to allow more air to help clear the condition should help. Along with using a non blended fuel if possible.

Posted By: RoadRunnerLuva

Re: Exactly WHY is my car hard to start when warm? - 04/30/13 11:12 PM

After reading the entire thread here...I admit
to having the same problem. My setup is just a
stock 360 engine with a Weiand dual plane manifold. A 3 year old Edelbrock #1406 600 cfm carb (junk IMO) and ceramic 1-5/8 headers. The car starts fine when cold....has NO spacer or shield on it....
when just warm, it very hard to re-start. This is
even in 50-60 degree weather as others posted.

I ordered (just about 2 hours before reading this thread) a 1/2" wood spacer and an aluminum heat shield kit from Jegs. I hope this helps out...and if not, I'll try the return line trick I read on here too.

Posted By: GTX MATT

Re: Exactly WHY is my car hard to start when warm? - 05/01/13 12:11 AM

I read through this thread yesterday but didn't respond because the issue at hand was an old post, but here's my opinion.

While fuel percolation is an issue sometimes (and I have noticed with E-brocks in particular that I can hear the fuel boiling when I turn a hot car off, so listen for this) I think the majority of issues are cars with incorrectly set up chokes and incorrect timing.

How often do guys adjust their electric chokes?

In your case, with no spacer, I would start there. You don't need a half inch spacer or anything if you don't want one, but you can buy a thick carb flange gasket (like the factory ones) or stack a few of the thinner ones. However, if by warm you mean the car is 140 degrees you really shouldn't be having percolation issues, but a 195 degree engine with no spacer is going to have issues when turned off.

If it will re-fire within 2 minutes of being shut off but not after 10, then percolation is probably not your issue.

Posted By: sogtx

Re: Exactly WHY is my car hard to start when warm? - 05/03/13 03:05 AM

I like this idea ... Or you have a bad needle seat.
Or misadjusted float levels..

Quote:

I had this problem and was also baffled until I spoke with Doug Dutra, the famous slant six guru. He explained what was happening:

When you shut off a warm engine, the heat from your engine's intake manifold is boiling the fuel in your float bowl and causing it to drip into the intake etc causing an excessively rich condition. This happens because the fuel percolation drops the float and allows more fuel from the still presurized fuel line, between the fuel pump and the needle and seat to flow more fuel into the carb to bring the float level back to normal. This continues until the pressure in the fuel line between the fuel pump and the needle and seat goes to zero. In the mean while, a significant amount of fuel has now percolated out of the carb AND the pressurized fuel line between the fuel pump and the carb (until the presure is released by the process). Quite a bit of gas ends up in the intake every time you shut off a hot motor.

This is how you fix it:

#1 Use two gaskets and a sheet of aluminum to isolate the carb from the intake manifold. This will likely require longer carb studs. Be sure to check for hood clearance. (this helped a lot, but did not eliminate the problem completely)

#2 Install a fuel return line from a 3-nipple fuel filter, which is available from any autoparts store between the fuel pump and the carb, and the fuel tank. The third nipple on the 3-nipple fuel filters has a metered orifice to limit the amount of fuel it flows. I had to install a return line and a 2 fitting fuel sending unit on my 68 slant six car to complete this installation. The car had an original 5/16 fuel line, so I added a 3/8ths line as the main fuel line and used the 5/16ths line as the return. I bought a dual fitting fuel sending unit for less than $50 off ebay, ran the lines, installed the 3-nipple filter. I never had a hot start problem again.

Posted By: VL21

Re: Exactly WHY is my car hard to start when warm? - 05/03/13 03:19 AM

Quote:

#2 Install a fuel return line from a 3-nipple fuel filter, which is available from any autoparts store between the fuel pump and the carb, and the fuel tank. The third nipple on the 3-nipple fuel filters has a metered orifice to limit the amount of fuel it flows. I had to install a return line and a 2 fitting fuel sending unit on my 68 slant six car to complete this installation. The car had an original 5/16 fuel line, so I added a 3/8ths line as the main fuel line and used the 5/16ths line as the return. I bought a dual fitting fuel sending unit for less than $50 off ebay, ran the lines, installed the 3-nipple filter. I never had a hot start problem again.

Back in the early '90s I had a '66 Valiant, I had installed the super6 2bb intake setup on.
I did something similar, only not running a return line, I just T'd the hose from the 3rd nipple into the fuel line BEFORE the fuel pump.
My reasoning was that there was no pressure there, so anything bled off at the filter was just bled off.

So, was it just my imagination that made me think it solved my heat soak problem?

Posted By: RoadRunnerLuva

Re: Exactly WHY is my car hard to start when warm? - 05/03/13 10:16 PM

bump

Posted By: Mr T2U

Re: Exactly WHY is my car hard to start when warm? - 05/03/13 11:34 PM

Quote:

Quote:

This might make you feel better.

Mine has gotten to the point that it won't even start when warm. Nearly had it towed last week when I shut it down to fill up with gas. By the time the tow truck arrived it started and I was able to drive home. Fires up great cold, runs great, but if I turn it off and try to restart hot I can just crank away till the battery is nearly dead.

My original 1938 ford flathead does that same thing. I've been told it's caused by a bad coil that fails when it gets hot.

Check your spark next time it happens.

Tav

i had the same problem with my hemi. i have a electric fuel pump with a MSD ignition system. it used to start instantly hot or cold. then i started to have hot start problems that got worse over time. i replaced the coil without any improvement. i changed the distributor and the problems went away. a friend did some voltage test to the pick up coil and found that the pick up coil changed resistance when i warmed up.

Posted By: 451Mopar

Re: Exactly WHY is my car hard to start when warm? - 05/04/13 06:09 PM

The problems could be electrical of fuel related.
Electrical - make sure you have good battery cables and the negative is connected to the block and the body with clean connections. If using a stock ECU ignition box, run a ground wire from the ignition box to the engine (prevents ground loop issues in sensing the magnitic pickup pulse.)
Fuel - The real issue here is the fuel sold today vaporizes much easier than fuel sold in the 1970's. Blocking off the intake manifold heat crossover, and running a vapor return line helps prevent vapor lock and boiling the fuel in the carb.

Posted By: SattyNoCar

Re: Exactly WHY is my car hard to start when warm? - 05/04/13 10:22 PM

In my wagon I hooked up the three nipple filter and ran a line back to the tank. Starts faster than a late model when hot....

old video, but, still starts the same.......

Posted By: ph23vo

Re: Exactly WHY is my car hard to start when warm? - 05/04/13 10:36 PM

Quote:

My hot starting problems were solved by going to non-ethanol fuel which is becoming more available here in the Rochester NY area. It started at marinas as the ethanol was killing marine fuel systems and engines. I now use it in everything. Here is website:

http://pure-gas.org/

yep mine went away just by doing the non eth fuel.. we have a few stations around here that sell it..headed there in a few minutes actually!

Posted By: MY340

Re: Exactly WHY is my car hard to start when warm? - 05/04/13 11:04 PM

Hot starts after 15 minute or longer I always had best result with gas pedal partial or to the floor. Today's crappy gas is so wonderful!!

Exactly WHY is my car hard to start when warm?