Hard Starting Hot

[Steeveedee]

The heat riser valve would be attached to an exhaust manifold, and the exhaust pipe attaches to it. It has a counterweight on it, which you should be able to move if the valve flap isn't stuck. You can try moving it. I'd recommend doing it cold. The pipe to the air cleaner is for Carburetor Heated Air. There is a valve in the snorkel that is closed cold and opens when the engine warms up. If it failed (or is disconnected) it can cause your carburetor to be hotter than normal under regular driving conditions.

[Rich72C10]

@Steeveee - nope, don't have that at all.

Heat test, after idling up to normal temp, outside is a cool 72.

At Shut Down Temps
Manifold: 150
Lower Carb Bowl: 98

5m Shut Down Temps
Manifold: 180
Lower Carb Bowl: 115

10m Shut Down Temps
Manifold: 176
Lower Carb Bowl: 125

15m Shut Down Temps
Manifold: 166
Lower Carb Bowl: 125

The carb base plate is running 135 or so 5 minutes and greater.

[Rich72C10]

Ran the truck up again for 10 minutes in the garage. This time around after ~15 minutes of being shut off the bottom of Carb bowl got to the same ~125 but the top of the bowl got to 120. Carb Base plate to Manifold still ~135.

Now I did this since after my 1st run I started her up at the end, zero problems. After my 2nd run where the whole bowl was at least 120 I tried again, started right up.

So either I need to drive around normally and not just garage idle but I would think heat is heat (by idling or driving). I also have a ambient temperature of 72 outside but that is not the temp in my garage now after the truck running.

Last bit could be that the STA-BIL 360 has started to help? I filled up and put my measured amount for my tank on Tuesday afternoon. I only driven about 10 miles before my garage test a bit ago (I didn't drive her at all yesterday).

Edit Update after a short ride / keeping hood closed
After about 12 minutes bowl reached 135 throughout the height of it and 150 at base plate. Started a wee bit harder this time but perhaps 1/2 crank more then when cold. Thinking the STA-BIL 360 must be helping.

[72c20customcamper]

Dont think stable has anything to do with it . Sta-bil is to keep the gas and alcohol from seperating or phasing out as it's called in the industry.

[Carl Spangler]

Originally Posted by Rich72C10

Ran the truck up again for 10 minutes in the garage. This time around after ~15 minutes of being shut off the bottom of Carb bowl got to the same ~125 but the top of the bowl got to 120. Carb Base plate to Manifold still ~135.

Now I did this since after my 1st run I started her up at the end, zero problems. After my 2nd run where the whole bowl was at least 120 I tried again, started right up.

So either I need to drive around normally and not just garage idle but I would think heat is heat (by idling or driving). I also have a ambient temperature of 72 outside but that is not the temp in my garage now after the truck running.

Last bit could be that the STA-BIL 360 has started to help? I filled up and put my measured amount for my tank on Tuesday afternoon. I only driven about 10 miles before my garage test a bit ago (I didn't drive her at all yesterday).

Edit Update after a short ride / keeping hood closed
After about 12 minutes bowl reached 135 throughout the height of it and 150 at base plate. Started a wee bit harder this time but perhaps 1/2 crank more then when cold. Thinking the STA-BIL 360 must be helping.

FWIW, I found that 125 (ish) degrees at the bowl is the point where I start noticing hot start issue. At 135+ I can hear percolation which leads to heavy fuel saturation and bad ju-ju. There is a whole science about fuel vapor pressure and additives. It would be great if someone would contact STA-BIL and get their feedback about their products and vapor pressure.

[Rich72C10]

It is also pretty cool outside, that could be helping my starting up or I am not doing enough real hard driving before shutting down. After I reached 135, the hard starting did come into play after I left it set with that temp for a bit over 30 minutes.

Though if temp has anything to do with this, then it seems I am clearly in the range of "high temp" after shutting down, even with cool low 70 temps outside.

It seems to me the riser that is coming in should help if it keeps my carb bowl below 120. Though between the divorced choke and that breather line I am going to have some fun.

[LNP]

Originally Posted by Rich72C10

hmm, okay I looked up exhaust manifold heat riser, which seems I have asked about before when I saw a posting with a strange "pipe" coming off the exhaust to the stock air cleaner. I don't have that "stove pipe" thingy or anything to get stuck

Ok first photo is a heat riser. This is a 1964-78 Chevy heat riser. The second photo is a 72 Chevy air cleaner assembly on the engine. The vlave in the air inlet is the vaccum activated heat diaphram. If the vaccum diaphram is bad the valve in the snorkel will not open. It is normally closed. That diaphram is replacable.

[Rich72C10]

I haven't any of that.

[LNP]

Originally Posted by Rich72C10

I haven't any of that.

The heat riser itself will be on the drivers side in between the exhaust pipe and exhaust manifold. It slides on the exhaust manifold studs ahead of the exhaust pipe flange.

Engine looks real nice

[Accelo]

Could this also be related to percolating / vapor lock / fuel boiling?

These issues are a lot more prevalent at the higher altitudes. I see you are in TX at 425 feet. Lowers the possibility but doesn't remove it.

You had it idling for a long time without issues. One would think it would cause more heat than the sun.

Distributor in good shape? Do you have another you can try? Just worked on one where the lower bushing had failed.

[Rich72C10]

No, not the Distributor. It's new along with the wires and coil. It did this before changing out the Distributor. So I am 95% this is not the problem.

I am thinking it is perlcolating / vapor lock / fuel boiling. Once I get my riser on, I should be able to tell a difference (or not). I'll be taking reading with my laser thingy - so I know what to look for now. Not sure why I didn't think of measuring temps on the carb bowl before.

[Rich72C10]

I got my riser in today. Though I just realize a 3rd problem, I doubt my hard line will make it to the carb.... but I'll see how far I can get tomorrow morning - if it is not raining still.

[Carl Spangler]

Originally Posted by Rich72C10

I got my riser in today. Though I just realize a 3rd problem, I doubt my hard line will make it to the carb.... but I'll see how far I can get tomorrow morning - if it is not raining still.

Can you post a pic of the thermal insulator you just got? Most are 3/8-1/2” thick which shouldn’t be an issue for the fuel line.

[Rich72C10]

Mr. Gasket Carburetor Spacers - Carburetor Spacer, Phenolic, 1 in. Thick, 4-Hole, Spread Bore.

Photo upload is getting hung at "please wait"....

[Carl Spangler]

Originally Posted by Rich72C10

Mr. Gasket Carburetor Spacers - Carburetor Spacer, Phenolic, 1 in. Thick, 4-Hole, Spread Bore.

Photo upload is getting hung at "please wait"....

Wow, that's a really thick spacer! Should lower the carb temp a LOT.

[BigBird05]

According to the show Engine Masters that 4 hole spacer will hurt your HP a little. It is better to have an open spacer with no individual holes.

[Rich72C10]

Well, I didn't realize that perhaps I should be getting a smaller one - I just read that people have had great luck with this one. I suppose I could also get a 3/8 and 1/2 inch - then see how they all perform. It's not like these things cost a ton of $$.

I have a ton of bits coming in to test and adjust my fuel pressure too, which will allow me to remove my hard line and use a temp rubber line. So, I'll likely need to wait for that to get this 1 inch fellow to work.

[Rich72C10]

Originally Posted by BigBird05

According to the show Engine Masters that 4 hole spacer will hurt your HP a little. It is better to have an open spacer with no individual holes.

hmm.. yet more options and things to worry about LOL

But being pretty much a stock engine, it's not like I am burning my tires at the stop light ;-)

[BigBird05]

That was just for your information. Not a judgement on my part about which spacer is best for you.

[lil hoodlum]

I'm in the Dallas-Fort Worth area. With my previous motor, 1974 350 stock block and heads, I had an aluminum Edelbrock intake manifold and carburaretor. I had hard starts too after driving and shutting off motor, say like running into a store or gassing up. I had to crank it, crank it, and crank it to start the motor. I installed a 1/2 inch plastic spacer and no more hard starts after driving.

With my current motor, 1968 327 with stock intake and quadrajet carburetor, I don't have any issues with hard starting hot issues. My stock intake manifold does have the oil splash pan thingy under the intake manifold though.

[Rich72C10]

my intake has a very similar shield under it too - though where the carb sits, the pattern is different. Seems that one is where you need some kind of a heat shield between the intake and carb? They call yours a hot slot or something like that?

[Rich72C10]

Originally Posted by BigBird05

That was just for your information. Not a judgement on my part about which spacer is best for you.

I didn't see it has judgement at all - all these different bits are driving me to be a little cuckoo

[Rich72C10]

Well, now I see why I needed open hole and not the 4 hole one. Luckily I can get one today (if they get off their butts to get it in to the store) that is the Mr. Gasket open style.

I did install this 4 hole one and give it a test. Running temp it does keep the bowl about ~10 deg lower. But after I parked her and let her set for ~45 minutes I am not really seeing any lower temps when I shoot my laser on the bowl. That was a little depressing to say the least.

The hard fuel line and passenger vent hose just fits! Though my new Electric choke will have to be replaced with the stock divorced choke. There doesn't seem to be a way to replace the linkage on the Electric choke - it's like made into the unit (but I still need to try and pull it apart. Perhaps I can come up with a riser to it at some point...

[Carl Spangler]

Was your 45 minute heat soak with the hood shut? That big V8 has a LOT of thermal energy and with a closed hood it has nowhere to go............. except into the carb. Regardless, I guarantee you the carb would get way hotter without that thermal spacer.

FWIW, when I park my hot truck (with carb insulator) outside, there's always enough breeze to keep the carb on my L6 from perc'ing the fuel in the bowl. When I park my truck in the garage I always open the hood and sometimes even put a small fan blowing at the carb. The worst is 'winter blend' fuel that has a relatively high vapor pressure.

[Rich72C10]

yep, hood closed and in the garage - figured that would be worst case. Though it was a nice ~70 degs outside and misting, so not even close to Texas summer hot.

I suppose it should help more when the engine is actually running and on the move... Now if O'Riley's would get that open whole spacer in I can get it installed and tested.

Heck, I even found that I can open up this Electric Choke and change out the linkage rod. I'll design the linkage with a bit of coat hanger, then find something a bit thicker in diameter. Where, not sure but I'll be on the lookout for something stiffer and will take push nuts.