TheSamba.com :: View topic - Carb Preheat (to help eliminate Weber progressive icing?)

Tue Oct 16, 2007 8:27 am

Well... it'll definitely improve vaporization and fuel economy but I don't think it's going to do alot about the icing, that occurs upstream from it in the venturi.

The heated cookie tin around the filter is the better fix for that.

Tue Oct 16, 2007 8:29 am

I actually sold one of those via the classifieds (that actually looks like my pic) a few years ago when I had the Weber progressive.

I got it from a Chevy dealership in Connecticut. I believe it fit a Chevy Vega that was outfitted with the Weber progressive.

$60 if I recall correctly. Never tried using it because I went back to the stock dual carb setup.

Tue Oct 16, 2007 9:04 am

I would think these would help if the wattage is high enough. It should decrease icing as well as improve atomization and fuel distribution. Assuming that there is a pretty large current flow to the heater you should power it through a relay. I would not think there would be any reason to try and circumvent the built in thermostat in the unit, I suspect that it is going to be on most of the time anyway. Used in conjunction with some form of intake air heat the combination should be quite effective.

Thanks for finding this. Let us know how it works.

Tue Oct 16, 2007 10:02 am

type2sam wrote: I actually sold one of those via the classifieds (that actually looks like my pic) a few years ago when I had the Weber progressive.

no doubt it is your photo. i didn't keep track of the ad, and it is long gone, but i got it here for sure, thesamba logo is on the side.

i do think it will help some with the icing problem. steel is a decent thermal conductor and this should heat the top if the manifold quite a bit. you can also use some thermal wire wrapped around the runners.

i agree that in order for this to work at all it probably will draw lots of current.

Tue Oct 16, 2007 10:54 am

I had asked Bob Hoover for his opinion on the matter and IIRC he said much as you have - that the "full" solution required warming the intake runners such that the air/fuel mixture didn't condense on the runner walls or something to that effect. Mentioned that Canadian Tire sold what was essentially a little electric blanket that you could wrap around the runners.

Ultimately I decided to go back to stock as I felt achieving success with this combination would take more experimentation than I was willing to entertain. YMMV.

Fri Oct 19, 2007 10:50 am

The root of the problem stems from the extremely poor quality of the center section casting, in that the heat-riser passage is often blocked or under-size.

The problem of inadequate carb heat is usually exacerbated by the use of an after-market exhaust system that defeats the purpose of the heat-riser, plumbing one exhaust port to another instead of to the tailpipe. The exhaust gas must flow THROUGH the heat-riser to do any good. When the #2 & #4 exhaust ports are connected to each other, there is no through-flow.

Lagging the inlet-side heat-riser pipe is common in cold climates. Unfortunately, it usually leads to rusting.

The electrically heated manifold blanket sold by Canadian Tire (and other FLAPS) was meant for extreme cold wx, where an engine might not even start without pre-heating plus a shot of ether. But it has a found a year-round home on poorly maintained bugs & buses fitted with center-mounted carbs, stock as well as Webers, that suffer from coked-up heat-risers and inappropriate exhaust systems.

-Bob Hoover

Fri Oct 19, 2007 12:06 pm

Thanks Bob :)

My bus has the stock exhaust set-up. And has been well maintained, so I think the only "problem" could be the center carb addition.

Since my bus is a 73 there is a heat riser from the exhaust into the engine bay. I plan on using that to heat the tin box around the airfilter.

This morning I obtained a used EFE heater from a junk yard. The EFE is off a chevette, and it looks like it will fit.

I will try both of these to see what is best.

Since I live in Canada and only drive the bus short distances in the winter, this should be good. Then in the summerwhen these mods are not required I plan to remove them.

Shawn

Fri Oct 19, 2007 3:03 pm

>Since my bus is a 73 there is a heat riser from the exhaust into the engine bay.

------------------------------------------------------

My comments were specific to upright engines.

-Bob Hoover

Fri Oct 19, 2007 5:46 pm

The 73's and other T4 engines with stock carbs drew heated air into the carbs, but did not have heat risers. A heat riser was not needed when the carbs were bolted directly to the heat producing heads. A heat riser and a preheated intake air system are not the same.

Fri Oct 19, 2007 11:20 pm

I have one of those heaters. They will *NOT* fit in a T4 progressive manifold without some machining to the manifold itself. The heating element sits too low to allow a seal. They are not plug and play!

Sat Oct 20, 2007 7:57 am

jasonious wrote: I have one of those heaters. They will *NOT* fit in a T4 progressive manifold without some machining to the manifold itself. The heating element sits too low to allow a seal. They are not plug and play!

Thank you that is great to know, my first step will be th tin box for sure now

Shawn

Sat Oct 20, 2007 10:57 am

Since you are the only one to chime in who has tried one, how well does it work? How hot is you manifold after say 10 minutes of steady driving? I think that there would be a large number of people interested in your results.

jasonious wrote: I have one of those heaters. They will *NOT* fit in a T4 progressive manifold without some machining to the manifold itself. The heating element sits too low to allow a seal. They are not plug and play!

Sat Oct 20, 2007 4:26 pm

Wildthings wrote: Since you are the only one to chime in who has tried one, how well does it work? How hot is you manifold after say 10 minutes of steady driving? I think that there would be a large number of people interested in your results.

jasonious wrote: I have one of those heaters. They will *NOT* fit in a T4 progressive manifold without some machining to the manifold itself. The heating element sits too low to allow a seal. They are not plug and play!

I never used it :lol: When I found out that machining would be required, I went with a dual Dell setup (which is as sweet as can be).

All have all the parts, minus the machining. If anyone is interested being a guinea pig, PM me!

Sat Oct 20, 2007 4:34 pm

davis911s wrote:
Since my bus is a 73 there is a heat riser from the exhaust into the engine bay. I plan on using that to heat the tin box around the airfilter.

That is no heat riser. That is the EGR pipe. Do not plumb it. You do not want to be drawing indiscriminate exhaust/heat into the engine room.
Colin

Sat Oct 20, 2007 4:53 pm

Colin

I am talking about this "hole" I guess heat riser is not the right term, sorry :oops:

It takes heat from the 1-2 cylinder bank .
I am going to route a tube from that into the tin box around the air filter housing for warm air

You can also see the insulation wrap that I have put around the runners to attempt and hold in heat.

Shawn

Sat Oct 20, 2007 7:33 pm

davis911s wrote: I am talking about this

It takes heat from the 1-2 cylinder bank .

Yes, that would be the "preheater inlet" that brings up freshly warmed cooling air from around cylinder #1's fins.
Now the factory had all of that sealed up properly with a flapper that ensured the supply of cylinder cooling air was thoroughly shut off as soon as the thermostatic valve cut off the vacuum to the actuator. Your issue is this: How do you shut off this supply of warm air once the engine is warm? If that air were allowed to dump into the engine compartment 24/7 you'd be diminishing the cooling ability of the engine, much like missing heater hoses or the little flaps inside the blower outlets allow the cooling fan to dump hideous quantities of hot air right off the exchangers into the engine compartment.
Colin

Sat Oct 20, 2007 8:54 pm

Actually I don't believe you would get "hideous" amounts of hot air coming up through this system. The pressure underneath the cylinders is very close to atmospheric while the engine compartment is only just a little below atmospheric. In the original VW intake air system, air was sucked much more than blown up through the preheat ducting.

Just dumping the air in an open box around the air cleaner would cause little heated air to flow up through the ducting. To get sufficient air flow one would need to seal the ducting to the carb as was done on most intake air systems using carbs during the 70's and 80's. The first system I build for my '74 used the stock preheat system and a sealed air cleaner for maximum flow. This system worked enough to prevent icing after warmup but it didn't raise the temperature as much or as quickly as I would have liked.

My next improvement was to draw air not off the bottom of the cylinders, but to tap into the heat exchangers themselves. This provides warm air much more quickly and eventually the air gets much warmer. Even though I used a Datsun air cleaner I stuck with a VW thermo/vacuum valve. The VW valve is the best out there, it is two stage and its temperature settings are adjustable. Even with very hot air off the heat exchanger I have never had issues with the carb getting too hot, the valve works. My valve is set about 20-30°F above the stock.

Many have probably seen this photo by now, but here it is again. Note how the hose feeding the flapper valve on the air cleaner is connected to the outlet of the right heat exchanger.

My air cleaner and hot air duct system was actually very easy to build. If I were to build another one it could easily be done in an evening after work.

Sun Oct 21, 2007 10:35 am

World wide, the most common engine for the 'loaf was the upright 1600. VOA chose not to offer that configuration causing most Americans to think '73 & later Transporters only came with the 'Type IV' engine. But later model 'loafs with the upright engine were imported by VW of Canada and a few more slipped into the States as direct imports by returning Army personnel.

Other than the tin-ware and rear cross-member, installing a husky upright in a later model breadloaf chassis is a trivial chore. When properly done the result is a lighter, more powerful vehicle that is much less expensive to maintain.

-Bob Hoover

Sun Oct 21, 2007 11:02 am

Bob Hoover wrote: When properly done the result is a lighter, more powerful vehicle that is much less expensive to maintain.

-Bob Hoover

That's gonna get some feedback! :lol: