MFI Pump - Open Heart Surgery

[356RS]

Originally Posted by Flieger

So it puts the stylus on a different cam profile, similar to opening the throttle?

No. Making changes to the thermostat or the baro cell will not change the position of the stylus on the space cam. It changes the position of the balance bar lever mechanize um which then changes the position of the main rack.

[Flieger]

Originally Posted by 356RS

No. Making changes to the thermostat or the baro cell will not change the position of the stylus on the space cam. It changes the position of the balance bar lever mechanize um which then changes the position of the main rack.

OK, so looking on the diagram a few pages back, the thermostat and barometric cell operate on the balance bar which acts like a multiplier for the input from the space cam? (Say 75% to 125% of what the cam says is what is delivered, depending on the balance bar orientation?)

[356RS]

To simplify this, the profile of the space cam is not changed, the stylus position never moved, only the main fuel rack is, and only because of an altitude change or a cold/hot temperature condition.

[jeffc280sl]

Flieger,

I don't know about the percentages you have listed but I do agree that fuel volume as determined by the stylus and space cam can be increased or decreased based on the the affect of the thermostat and baro cell on the balance bar and in turn the control rack. Generally speaking a downward movement on these devices will lessen fuel volume. An upward movement will increase fuel volume.

Fuel volume as set by the space cam will be minimized with a fully warmed engine operating at high altitude (downward movement of the balace bar) and maximized in a cold sea level environment. (upward movement of the balance bar).

[Eddyvdw]

Just a quick question. Please look at the pictures I posted a few days ago of a cold and warm thermostat. Looking at the warm thermostat, is this the maximum extension of the thermostat rod when warm?
Ed

[jeffc280sl]

Ed,

I read the pin extends about 4.75mm when fully warm. You want to make sure the pin inside the pump is on its stop. You can look at this by removing the cover plate and then manually push on the thermostat lever. If it is on its stop you should not be able to push thermosts lever any farther.

[304065]

Here are some measurements I took of the mechanism, sorry for the dark photos.

MFI thermostat data. . . and distaster!

[Eddyvdw]

Thanks, I'll give it a try this weekend.
If you look at the picture, do you think it's close to the stop?
Ed

[al lkosmal]

Originally Posted by 356RS

Why just put a bolt in and set it when you can use a lever assembly. With a lever, like in the photo below, you can control the main rack for "cold starts" then adjust till warmed up, or just richen up the AFR when needed by simply moving a knob on the dash.

Mark,
So you are using this arrangement as a "cold start" mechanism? Are you using a lamda sensor and AFR gauge to monitor and adjust, as required, after starting...or?

The adjustable, on demand, Supertek version makes sense to me, but I don't quite get the purpose of the adjustable, but then locked down/fixed version. I'm learning a lot from these posts, but I'm still an MFI newbie.

I'm not crazy about the stock cold start system on my 71E........It seems to work well, but it looks like a fire waiting to happen. I keep a fire extinguisher in the car, but I really don't want to use it.

Regards,

Al

[911st]

Fire risk is significant on these MFI cars. Renewing the tubing to the primers is a great idea.

On my 72/2 stacks I wrapped zip ties around the primers to ensure they would not pop out and spray fuel on the hot motor.

Bought a perfectly rust free 72T for $2300 that had such a fire. Just had to clean things up, get a used left stack for $20 back then, and a used air cleaner and I had a great little car.

[356RS]

Al,
Yes, this is my cold start mechanism. I do not use the OEM raw fuel jets system. The lever set-up in that photo has a great advantage over the stock thermostat. What happens in the cold start position the lever opens, swings back away from the pump housing allowing the thermostat rod & lever inside the pump to release the spring pressure of the balance bar causing the main rack to move much feather forward into a very rich fuel condition, way more than a normal cold thermostat can, and that extra fuel is now your cold start fuel. After the engine starts I just pull the lever back a little at a time during idle while she warms up. Once the engine is warm and the lever is pulled back toward the pump with pressure now being applied to the thermostat side of the balance bar, the pump is in the normal warmed up condition. No need to have AFR meter with this set-up because all your really doing is manually substituting the OEM thermostat with a rod & lever. The bonus is that you can obtain more fuel at start up, then adjust the rod/lever back into the pump when warm and the balance bar will be back to the stock position in the pump just like the OEM thermostat would do when fully warmed.

[al lkosmal]

Mark,
That's what I thought and it makes sense to me. I'm going to go that way. What purpose does the adjustable, yet locked in place, version have. Are these being used to lock the thermostat mechanism into the full warmed up position? Is this configuration typically used along with the factory cold-start or modded pushbutton cold-start?

thanks,

al

PS: Don & Flieger ...can you provide me with your experience in using your version(s) of the thermostat replacement? What are you using for cold start?

[356RS]

The adjustable/lock nut version is a simple way to just set the pump into a warmed up, normal operation condition as long as the adjustable blot is set so to push the original thermostat lever on top of the pump all the way in, fully warmed up. The general reason to use this set up is because those engines are using headers, no heater box's so no warm air channeled up to the thermostat. For the track car this is not an issue in most cases. The street car with this set up most likely still has the OEM cold start solenoid system working for them or something similar like the push button method you mentioned.

[jeffc280sl]

Mark,

I imagine this setup could be used in the fully warmed up position for fuel economy driving and then richened up some for performance or the track.

[Flieger]

I am using headers. I have the stock cold-start squirters from the solenoid into the plastic stacks. I once had a fuel line come off and saw the gush of fuel to confirm. The car is a little reluctant to start. Usually takes three tries, even in California weather. Once it fires, idle is rough for the first 30seconds or so. I can then drive off but try to keep the idle up a little using the hand or foot throttle at stop signs.

Once, I disconnected the electrics to the solenoid to see what effect the cold-start had. I could not get it to start. Ever. I plugged the solenoid back in and it started right up.

The car is "cold-blooded" but works great once it is warmed up!

2.7RS spec

I am intrigued by Mark's cold-start/thermostat substitute- are they for sale as a "kit" my mechanic could instal?

[911st]

Cockpit adjustable AFR's. Cool!

I could start my 2.8 w/o a thermostat by holding the throttle to the floor.

[356RS]

Originally Posted by Flieger

are they for sale as a "kit" my mechanic could instal?

I believe Henry "Supertec" has them for sale, not 100% sure. I have made my own and I'm in the process of designing one with other modifications to make it easier to control.

[911st]

I am sure his system works great.

However I have wondered if a pull cable is effective at keeping the pump at its warm position. My concern it it might migrate to a richer position unintentionally.

Seems a spring loaded system that holds the full warm position to ensure full engagement, and that can then be pulled against for cold start, might be more positive.

[356RS]

You are exactly right. The normal movement & vibrations of the engine will alter the tension on the cable and that in turn changes the position of the lever/rod setting. This is one of reasons I'm working on a better designed unit.

[al lkosmal]

Mark,
Let me know when you have one ready. I am interested.

Regards,

Al