1972 250C - want to convert to fuel injection

[thorsen]

I have the Weber setup on now and it does not use a fuel return. Maybe I will try my old Zenith's with the fuel return and see if that helps the problem any.

I bought my Petronix from RetroRockets. I picked up the flame-thrower coil too. I am very pleased with the unit.

[cth350]

You might want to try just leaving the hood open a crack. Though not in neighborhood where they'll take your battery for scrap and don't forget to slam it again before you drive off.

You could also bypass the current electric fan controls for an automatic on setup that would keep the engine compartment cooler. Probably not worth the energy for the short time required or the small benefit gained. -CTH

[todds]

Yeah man, I hear ya. My Webers do the same damned thing. I'm so used to flooring it to start it now I don't even think about it. The Zeniths were real good about not boiling even when I had heat riser stuck the wrong way. Make sure yours are stuck the right way! A Weber may not warp but it sure will boil! I've read similar posts in a few other forums and I think that they just tend to be more susceptible to it.

A couple things people have reported improving the situation:
-Swapping metal lines for rubber near the engine
-Electric fuel pump - from the theory that the o.e. pump heats the gas up being attached to the hot engine.
-Make sure the fuel lines attach on the side away from the engine (there are two mounting points on the Webers)
-Make a huge ugly heat sheild out of sheet aluminum that shrouds the entire carb area blocking it from the engine/exhaust.
-Fuel pressure regulator

One idea I had about the manifold setup is to make a small plate to cover the top of the heat risers/exh manifold out of thick metal, then leave an air gap between the exhaust and intake by building up the remaining area with washers or nice machined collars of some kind. I'm sure this would alleviate any kind of summertime boiling and it'd be easy to make a plate with four holes in that size. This is sort of the equivalent of blocking off the little exhaust crossover in the intake of a domestic V8.

[thorsen]

When I rebuilt the exhaust manifolds I neutered the heat risers, so that is not the problem.

I pulled my spare intake/exhaust manifolf from the shelf and looked at a way to block off the top of the exhaust manifold and space it away from the intake manifold. The exhaust is cast iron so it would be very tough to weld, plus I don't think a piece of sheet metal would last long there. It would have to be about 1/8" thick to resist warping, then you are getting close to the bottom of the intake.

The intake looks to be relatively thin, so I don't think there is much to grind off.

[thorsen]

I put the Zenith's back on and they boil just as bad as the Weber's do. I suspect the summer blend gasoline in Chicago is part of the problem.

I bought a TBI unit off eBay, but there is a 280S parts car for sale a few towns over; I could just scrap the fuel injectory off it........

[thorsen]

On the right is the stock exhaust manifold with the provision to heat the intake manifold, and on the left is the air-gapped manifold without the ability to heat the intake manifold. I made a plate out of 1/8" steel to close off the top of the exhaust manifold, and when the intake and exhaust are stacked there is 1/4" gap between the two (previously the bottom of the intake was open to the top of the exhaust).

I need to make a plate for the manifold on the right and pull the manifolds off the car. It will be interesting to see if this prevents the carbs from boiling fuel.

[ja17]

Hello,

The Zeniths are set up with a fuel return line and shut off valve, so that the fuel circulates back to the tank when the car is at idle. This allows fresh cool fuel into the carbs and the circulation also cools the carbs themselves.

Make sure that the brass valve on the front carb is woking properly. I have never noticed any fuel boiling problems with these Zeniths when all is working properly.

After all linkages on the carbs are adjusted properly, you should see a strong stream of gas from the acceleration discharge tube in both carbs as soon as the linkage is moved! IF not, you will have hesitation, or stalling problems during take off.

[thorsen]

The problem is that the fuel boils off after the engine has been shut down. The return line doesn't do anything if the engine is not running.

[thorsen]

And we have a winner. I ground the bottom of the manifold down and removed the ribs that help with the heat transfer. After making the block for the rear manifold I removed the manifolds already on the car, installed the Webers, and took it for a test. The gap between the intake and exhaust manifold ended up being 1/4".

It was 90 today here in Chicagoland, and I made the loop I made 2 weeks ago when I last had the problem. AC on high the whole way, I pull into the garage and there is no boiling. The fuel bowls on the Webers read 110 degrees and gradually climbed to 120 as the heat soak took over, but they never boiled. I was seeing 150 degrees on the Webers when the fuel was boiling. I close the hood and let her sit for 30 minutes and there was still no boil. The car started right up and purred right along.

Now I can get on to more important things, like cruise control and a better stereo.

Added a picture. The tip of the screwdriver is the space between the intake and exhaust manifold.

[mercmad6.3]

Originally Posted by UT_Tech

Your 250C should be able to get 20 MPG without any radical surgery. Try running the coast-down test on our website. If your car measures the equivalent of 15mpg in road horsepower then there's a problem.

It should be doing that and better STOCK. I suspect you have one of the crappy weber conversions which do nothing for the car. The best idea were carbs the car came with and a competent person to do as correct tune up every `12-18 months.
my V8's do 20+ MPG all the time on the highway. (3.5,4.5 6.3 and 6.9 ). It's all about maintenance.
To prevent boiling try making spacer blocks to lift the carbs of the manifold. The best material is WOOD. Plywood makes great spacers and you can get it in various thickness. Try a 1/2" spacer. If heat is still getting through ,go to 3/4" thick.

[thorsen]

Originally Posted by mercmad6.3

I suspect you have one of the crappy weber conversions which do nothing for the car. The best idea were carbs the car came with and a competent person to do as correct tune up every `12-18 months.

Yes, I have a crappy Weber conversion. It does more for the car than the Zenith's do, especially since someone neglected to maintain the heat-riser flaps and warped the Zenith's. Do you know where I can buy a new set of Zenith's?

Originally Posted by mercmad6.3

To prevent boiling try making spacer blocks to lift the carbs of the manifold. The best material is WOOD. Plywood makes great spacers and you can get it in various thickness. Try a 1/2" spacer. If heat is still getting through ,go to 3/4" thick.

I am using phenolic spacers. A 1/2" spacer would put the air cleaner into the bottom of the hood and a 3/4" spacer would put the air cleaner through the hood.

[alabbasi]

Originally Posted by mercmad6.3

my V8's do 20+ MPG all the time on the highway. (3.5,4.5 6.3 and 6.9 ). It's all about maintenance.

Ron, we have smaller gallons here in the US. I've not seen more then 15 mpg from my 6.9 and the 250CE that I drove back in England put me in dept from fuel charges (I was a student at the time and 4 star was damn expensive). I don't think I got more then 15 mpg from that car either.

I do drive with a very heavy foot though.

[todds]

Hey nice job Thorsen! You did it man, I knew the air-gap thing would work! I plan on doing the same thing to my spare manifold set in the garage (less the grinding) I'll keep the original ones bone stock to compare.

It's odd that the fuel return system is so vital for summertime running, in most cars I've owned the fuel return circuit started before the carbs anyway. I understand that all the heat is important for the dead of winter but I've never had a problem with the risers off, with either webers or zeniths, and it gets pretty cold here in Boston for quite awhile. It always started and ran perfectly in the cold. One thing I'm not sure about is if the fuel economy might have suffered as a result, and probably a little more carbon sooting things up. Either way, I'd wager the constant boiling is far more detrimental to both mpg and engine internals than perhaps a little extra choke in the winter.

[todds]

Just curious, how's it been for the past week or so? Has the flooding totally subsided?