heat soaked engine gets idle surge on restart. (1 Viewer)

[hey you]

Sand it. Use a very flat surface and figure 8 the each side of the carb on a very fine grit paper. Go slow, don't over sand.

 

[destin]

yeah my only leery bit about the high heat metal tape, is what the vacuum leak had enough power to suck it into the intake? that would be... BAD lol

i could be just being a wuss too.
meh

if anyone has a pristine single barrel for sale let me know ha!

 

[destin]

lol

so a vacuum leak at the air horn back, would this cause weirdness with the choke on? ( ie when you limit air, it will try to suck more air through that leak yes? )

keep your eye out for a good single barrel carb for me everyone...

 

[IDave]

That leak would ONLY affect you if you need full choke, unless it's leaking on the inside around the float chamber too.

It looks like you have the standard metering rod from what I can tell. Here's the selection of rods for the SD50 as posted a few years ago by Mark A. (Mark, I apologize if you didn't want this shared.) As you can see, there's a few variations and I think some might work better than others for your truck and might affect your hesitation. And, the height is adjustable, and specified, so maybe that's what needs tweaking.

 

[destin]

So you saying that big gap in no way effects the way he carb runs, nor would it ever cause a lean condition?

I pulled the choke in a bit and it caused some weird pulsing, I imagine from the leak...
Looks like I have the top / second metering rod.

 

[IDave]

Well, unless it's completely closed off by the choke valve, there's a lot of air coming down that giant hole in the top of the carburetor and that little sliver of air isn't going to amount to much.

 

[destin]

Well, unless it's closed off by the choke valve, there's a lot of air coming down that big hole in the top of the carburetor.

Lol true

 

[IDave]

I won't say that that gasket isn't working poorly elsewhere and causing trouble in one of the passages or another internally, but I don't think that gap is your issue.

The magic number for the step up rod is 28.5 mm.

 

[desertpat]

I had symptoms of a hard to start a hot engine shortly after shutting it down on a OEM rebuilt engine and a new OEM engine.
I'm saying a new short block, fuel pump, carb, intake and exhaust manifolds and a worked over head. Etc.
That was a 1984 and I wasn't shy to spend $ here where OEM parts are good and plenty and cheap.
When cold, even on a hot day, I can start it with a hand crank - 1/4 turn fires it up.
On hot days with engine hot after shut down, it took a lot a lot a lot of cranking with the starter.

I had the same experience with both cruisers restored here - the first one was a 1983 and I replaced everything for new on the restoration. Bla Bla.

Both were a bitch to start with hot engine on hot days after shut down. Bottom line.

I simply insulated the fuel line from the fuel pump to the carb with layers of insulation and the outside wrap was a foil for reflection.

The problem was drastically reduced.
Both of my cruisers are in Canada now but I have noticed a bit of the same sympton there on the one cruiser I drove there for the last 3 years while on summer vaca.

In my opinion, you are vaporizing gas in the line that supplies fuel to the carb, especially where the line passes over the head and manifolds.
You said it yourself - bubbles going back to the tank.
The bubbles are being generated inside the hot fuel line that has a shut off valve on the carb end in the float assy.


If you search the web, you will find that insulating the fuel line is a fix, not a band-aid for vapor lock.

Why not try for the easy solution - just get a long strip of foam insulation and spiral wrap the line to see if it helps.
Make sure it is heat resistant so you don't have a fire or melt down.
The cooling fan is the second easiest fix. Obviously, Toyota recognized that high heat from the engine / exhaust manifold is causing grief and thus they developed a fan that shuts off.
A well designed heat shield at the carb base might help also??

Middle East spec cruisers do not have the carb fan option and it gets to over 120 deg F here typically from June to Sept.
And it's a lot hotter on blacktop roads or in the sand.

........ KISS.

 

[destin]

Def i think shielding and insulation make a lot of sense man.

I had a few other issues to sort out before that that came to light throughout this thread.
ie the vacuum leak on the air horn and the weak AP circuit.

DesertPat, I am curious, what kind of spacer Are you running between your carb and your manifold?
I have aluminum, and i think if i switched to a synthetic it might help quite a bit too.
But yes you are right, most of the heat is coming off the head and the manifolds. radient heat!

did a cold start today and it seemed alright. cannot use the choke though, carb freaks out under choke, I think because of the vacuum leak on the horn. Gonna go wheeling today maybe out in tillimook or mount hood, slow and mellow. Sometimes you need to get out and drive em instead of constantly fixing them.

Posted up a WTB ad in the classifieds for a good single barrel carb with no problems ( or I might get a double barrel intake and pop on a trollhole carb and be done with it )

I keep ya guys posted In the end i need a carb with a working choke and no leaks
this one seems to leak gas into the intake when it sits too, not ideal.

Thanks for the help so far fellas, if you guys have any other input I am always glad to hear it!

Cheers

Destin

 

[desertpat]

I run the composite carb spacer.
I must say that this thread got my attention right off the bat when you said bubbles were going back to the tank - something we wouldn't see unless there is a clear hose.
Gasoline does readily vaporize - more that I ever thought even contained in a metal line, by your report.

With a heat source like that over the head / manifold creating vaporized bubbles that run back to the tank due to expansion, the issue is worse than I ever imagined.
Vapor lock (as it is called) was a huge issue for me here where the ambient temp was so high.

Thanks for sharing this observation.

 

[destin]

I run the composite carb spacer.
I must say that this thread got my attention right off the bat when you said bubbles were going back to the tank - something we wouldn't see unless there is a clear hose.
Gasoline does readily vaporize - more that I ever thought even contained in a metal line, by your report.

With a heat source like that over the head / manifold creating vaporized bubbles that run back to the tank due to expansion, the issue is worse than I ever imagined.
Vapor lock (as it is called) was a huge issue for me here where the ambient temp was so high.

Thanks for sharing this observation.

Thanks for your help man, I appreciate it.

From what i understand the composite risers help considerably.
Consensus is that it can keep the carb drastically cooler than the aluminum spacer. Which is quiet a lot in this context.

info from one site i researched:

--- On the other hand, pure phenolic spacers are constructed from an advanced composite material (similar to plastic), which can reduce heat conductivity 10 times greater than aluminum for a much denser air/fuel charge. Obviously, aluminum spacers are still widely available. The advantage in aluminum is that it can be easily modified for a given application. The disadvantage is that in some cases, an aluminum casting can be porous. Because of this, several manufacturers now offer billet aluminum spacers CNC-machined from 6061-T6 material.

----

 

[fireflyr]

Six into one header cured it for me. Just getting the intake manifold and carb off the exhaust manifold was huge. I swear I could hear the fuel boiling in the carb on shutdown on hot days.