hooch getting a new fuel source

[AApple]

Good to hear it's gettin there, Joe!! :clapping: :clapping:
You say the carb is not jetted properly "out of the box", but....one size does NOT fit all, especially in your case, with the Frankensteined Hooch-mobile. Seems like everyone that has done this single carb swap has had to mess with the jetting on them, and I doubt that any one particular set-up is gunna be right for everyone else's. I bet once ya'll all get your particular set-up dialed in, it will at least be a great starting point for others that follow in yer footsteps. I'm sure glad youse guys are doin all the leg work on these things, tho....PROPS to all of ya. :clapping: :clapping: :clapping:
CGW guys ROCK! :yahoo: :salute:

 

[dan filipi]

Yep, we're finding it overwhelmingy obvious that different size runners, different plenums, and heated plenum or not heated, has different jetting needs.
Tom's weber may be jetted fine for most needs but to get the full capabilities from idle to sustained high rpm load, jetting is mandatory.

 

[Ansimp]

I am wondering if your varying idle is related to poor atomisation due to possible icing of the plenum Joe

 

[joedrum]

could be tony I just barely got ride in be fore down pour ... I didn't give the idle much thought ...because of icing ....seems when you get things really close idle is the only place where icing was issue ...if that was it ....

it seems all issues from here will be small ones including icing ...im or the fence about adding to much heat ...and prefer something passive heat from motor trans fer but don't really know yet ..me and dan talk quite a bit on things ...no telling where it might go....

but as for running its never ran so good

 

[AApple]

So...I keep seeing these posts about heated/unheated plenums and such. Makes no sense to me. Usually, the object of the game is to get the fuel/air mixture to the combustion chamber as cold as possible. A cold mixture = denser mixture. Icing? Perhaps...if ya live in Minysota, or Alasky. :smilie_happy:
Joe...if you want to find out if a heated plenum would help your idle, get a heat gun(or hair dryer), and heat the plenum up for a few minutes before starting it. If a heated plenum is goin to solve the idle issue, that will tell you.
Now...I can remember, back in the days of carbs on car engines, Ford, and some GM cars had a small, electrical grid under the carb, to help with cold starts(and supposedly to improve fuel mileage, but Idano aboot that). Since these carbs youse guys are using ar really close to the same carb Ford had on the smaller engines, you could try to put one of the heater grids under yer carb, wire it in to a relay, and maybe into the temp sensor, and there ya have it. A heat source for the fuel mixture going into the combustion chamber when the engine is cold. Once the engine gets to operating temp the grid turns off.
Just an idea.... :headscratch: :builder:

carbheat

• AApple
• Nov 6, 2013

 

[dan filipi]

As I understand it, a cold dense charge is best (as in cold air intake) but the fuel liquid needs to be vaporized to turn it into a gaseous state. Fuel vapor and air mix is needed for combustion, any fuel liquid (droplets) that make it past the intake valve is unburned or not burned as efficiently as fuel vapor.

As you lower the pressure on a liquid, you also lower the boiling point so at a given temperature the liquid fuel will vaporize faster at a higher rpm/higher manifold vacuum.
At idle vacuum is lower so it stands to reason the boiling point temp is raised.

Heating the manifold with a heat gun while hooch is running would be a good test to watch what the idle does.
Just as a liquid will dry off a frying pan faster when it's heated (vaporized) than when it's cold, gasoline will do the same in a heated plenum.

I learned this stuff by studying refrigeration principles.
The liquid freon inside the lines is constantly vaporizing (under a lowered pressure as it's sprayed into the evaporator line to absorb heat) then pressurized to bring it back to a liquid and remove it's heat.
It fascinates me how it works.

 

[AApple]

the fuel liquid needs to be vaporized to turn it into a gaseous state

True dat...it's the carb's job to accomplish this, tho, as air passes over the venturi, and the fuel is introduced into the air flow. That's where the fuel is supposed to be broken up into tiny particles/vapor. In a perfect world, it would work, but...some raw fuel will always be ingested into the combustion chamber. :mrgreen:

At idle vacuum is lower

:headscratch: Huh?
I guess that would depend on where you take a vacuum reading....above, or below the throttle blade(s). Manifold vacuum(below throttle blades is high at idle. Vacuum above the blade(s)[ported] is almost non-existent with the throttle closed.
However....once the throttle is opened, and the fuel/air mixture passes the throttle blade, it IS under little to no pressure, so I suppose the boiling point would be lowered... :yes:
It's just strange that this single carb deal apparently needs some sort of heated manifold/plenum to work properly. Automobiles have been around for a long time, and I've never heard of any of them having icing issues with the fuel in the manifold, once it leaves the venturi. Airplanes are not really comparable, since they normally(hopefully) operate at much higher altitudes, where the air is much colder to start with.
Just trying to get a grip on the whole concept of needing heated plenums.... :read: I doubt I'll ever go the single carb route, but it's definitely interesting what ya'll are doing, and getting worked out! :good:

 

[dan filipi]

Well I think needing heat to the plenum here is needed because most cars have a heated air intake source which I'm sure comes into play here.
We have not tried heated air yet. That could be better.

My son's car, we just added a custom cold air intake which does away with any heated air.
There is a definite difference in how well it runs when cold.
It's a stick shift so any tiny skips in fire are felt especially on take off in first gear.

 

[AApple]

custom cold air intake which does away with any heated air.
There is a definite difference in how well it runs when cold.

No doubt. So....is the whole idea/concept/need for the heated plenum ONLY to help with cold starts, or is there a theory about fuel icing while running down the road? I guess that's where my cornfushun is coming from....
If these things are really just having cold start issues, why the heck not hook up the choke on the carby? A cold engine needs more fuel to run properly....which is the purpose of the choke. Fuel injected engines use the fuel management maps in the ECM to control it, but a carbytater needs a choke to both raise the idle, and cut off some of the incoming air, which enriches the fuel/air mixture.


Or.......am I just overthinkin this?\
btw...I ain't tryin to be a d :sensored: k....I'm just curious as heck! :yes:

 

[dan filipi]

Well like I said, heat helps vaporize.
That's where I'm going with it.

 

[joedrum]

hmmmm there seems to ideal temp for air in atomization....that's the bottom line here ...

 

[dan filipi]

joedrum » Thu Nov 07, 2013 10:46 am[/url]":1f1ytszy]
hmmmm there seems to ideal temp for air in atomization....that's the bottom line here ...

Well the heated air intake IS thermostatically controlled. At least they we're in cars I've owned.

 

[dan filipi]

Heated air would also be dryer air wouldn't it?

Just as water, or paint dries faster in dry warm weather than cold humid or wet weather, meaning it turns into a gaseous state faster, would a heated air intake not help here with gasoline?

Where I'm going with the heated plenum is the frying pan effect on the raw gas though a thermostatically controlled warm air intake could be better. I haven't gone there yet.

I'm trying to keep this simple and so far I think the simplest most effective approach is to heat the plenum with coolant because coolant warms up quickly and it's heat transfer is much faster directly to the plenum than passive heat would be if the plenum was attached to the motor top by brackets or such like Joe and I have been discussing.
West tried a bracket from the engine but I'm not sure how effective that was.

Anyway, bottom line here in Joe's thread is we're trying to figure out his unstable idle.
I've experienced the difference heat makes in the idle so I say he needs to heat it to smooth it out and make it more manageable.
That is IF the size runners are not what's causing the problem.
I saw similar problems in mine with larger runners.

 

[dan filipi]

AApple » Thu Nov 07, 2013 10:27 am[/url]":1wvmplb7]

custom cold air intake which does away with any heated air.
There is a definite difference in how well it runs when cold.

No doubt. So....is the whole idea/concept/need for the heated plenum ONLY to help with cold starts, or is there a theory about fuel icing while running down the road? I guess that's where my cornfushun is coming from....
If these things are really just having cold start issues, why the heck not hook up the choke on the carby? A cold engine needs more fuel to run properly....which is the purpose of the choke. Fuel injected engines use the fuel management maps in the ECM to control it, but a carbytater needs a choke to both raise the idle, and cut off some of the incoming air, which enriches the fuel/air mixture.


Or.......am I just overthinkin this?\
btw...I ain't tryin to be a d :sensored: k....I'm just curious as heck! :yes:

Yes Joel, your being a PITA :mrgreen: JK.

No, cold starts aren't the issue here. They start pretty good with a few twists of the throttle to pump raw gas in then hold it at a fast idle for a couple minutes. A pull choke would be nice though to hold that fast idle.

The real issue as I see it is a very cold plenum and inefficient atomization especially when cold and most noticeable at idle.
The same problems my buddy had with his sandrail running the same plenum.
Out in the breeze there's very little if ANY heat to the plenum.

There may also be venturi or throttle plate icing issues popping up under the right conditions.
I had a strange problem on mine once after a cold start running to the store. It usually will idle below 1000 rpm and drop quickly to idle after a throttle twist.
This one time idle was sluggish and stuck at 1500 rpm. I looked at the linkage and saw it was rotating back slower to idle and "hanging" off the idle stop screw just a hair.
After I stopped in the garage and let it sit a minute with the engine off, the slow return went away. Started it up and revved good and right back to idle like it always does.
I had checked for cable/linkage bind carefully so the only thing I can think was causing it was ice on the throttle plate holding it open.

This happened only once so I'm not sure but undenyably mine runs better at idle and revs better if I start it, let it warm up for a couple minutes, shut it off for a couple minutes, then restart it.
The only difference I can see is the plenum is VERY cold during the first start up then heat transfers to the plenum from the runners while it sits.

 

[Dusterdude]

Sort of on topic?let me ask this.Im going to try a carb on the stock plenum,should i or should i not leave the meshy things in the plenum?

 

[dan filipi]

Dusterdude » Thu Nov 07, 2013 12:54 pm[/url]":2tysk6xe]
Sort of on topic?let me ask this.Im going to try a carb on the stock plenum,should i or should i not leave the meshy things in the plenum?

I would think leave them on since I'd expect the mesh to help break up droplets.

Your build will be interesting. Post pics!

 

[Dusterdude]

Thanks dan and im leaning that way and btw,when i get started im gonna bug the piss outa you,im bidding on a weber 34 dgec on ebay and it looks like i may win it.ill be needing some jetting advice

 

[dan filipi]

Dusterdude » Thu Nov 07, 2013 1:22 pm[/url]":2ch0jzez]
Thanks dan and im leaning that way and btw,when i get started im gonna bug the piss outa you,im bidding on a weber 34 dgec on ebay and it looks like i may win it.ill be needing some jetting advice

Cool.

 

[ekvh]

They might break them up, but they might also make them form. When cold, I would expect them to cause condensing on them.

 

[Dusterdude]

Hmmmm,good point