MFI Pump adjustment and idle problems

['71 911E Coupe]

Originally Posted by David E. Clark

I'm not sure. I finally found a pair of protractors (the larger one with pointer and one of the two identical smaller ones with one pointer) and was able to set correlation one side at a time. It was a pain in the a$$ and I'm not certain it is any better than getting the measurement perfect and making sure all the linkages move in unison off idle. Of course that was my first time and I was going by what I read in CMA, the factory workshop manual and the advice given here. I'm sure it would have been better if I had someone who knew what he was doing showing me the way.



I agree that hissing must be air - no fluid or mechanical piece would cause a hissing sound in my opinion. It's either air sucking or expelling. I would clean the air passages with a pipe cleaner and a product like B-12 chemtool as suggested in MFI Check Measure Adjust # 4532.21, page 23 and then synchronize the stacks again with the synchrometer. When you are adjusting the air passages, make sure that none are substantially more open or closed that the others and that none are open more than 8 turns.



Any chance that any of the seating gaskets from the throttle bodies or stacks are cracked or broken and letting air suck in through a small opening? That would cause a hissing-like sound - not to mention rough idle and running!

Well I figured I would never find a set of protractors in time, and doing it this way makes more sence (to me), and seems much easier, like you said.

I hope you know what hissing sound I mean. It's like a hissss...hissss..and sometimes it goes hisss...hisss bop...thatbop isn't a backfire just like how some people can many that poping noise with their lips. I really don't know how to describe it as you can see. Mabye I can take a video and that will help...I'll try that tomorrow and try to get it on here. Any-who I actually did buy a can of that B-12 Chemtool at the store last time, So I can give everything a quick spary with that.

So even though they say the screws are suspossed to be turned out 5 turns, you have to balance them all out to the average number, correct???

I read how you have to do this in CMA. Maybe those few cylinders need to be turned in a little more and are getting too much air. I guess I'll have to play around with them and see what it does while the engine is running.

And also, like I wrote above, I did have this whole intake system apart a few months ago... and I replaced EVERY gasket and sprayed most of them with that red gasket sealer spray. So I don't believe I have any leaks...that was a huge problem before I took it all apart though.


Thanks again!

['71 911E Coupe]

Hey guys,

I ran the car tonight. I did not do any work on it, but thats what the whole day tomorrow is for.

Here are two videos of the car running, (I hope they work), and you can here the HISSING sound in them too. Sorry the video quality isn't that good, but if you over the camera sound, you can hear the engine.

Let me know what you think! Thanks!



http://www.youtube.com/watch?v=sDit7ZbNa7o


http://www.youtube.com/watch?v=3ef8-5mqZJ0

[Zeke]

I know what the "hiss--popping" sound is. Your shafts are worn and that's where the air is coming from. I had a loose shaft and the inversion of the intake runner bounces the butterfly. to prove or disprove this, hold the shaft closed against the stop with your hand.

['71 911E Coupe]

Originally Posted by milt

I know what the "hiss--popping" sound is. Your shafts are worn and that's where the air is coming from. I had a loose shaft and the inversion of the intake runner bounces the butterfly. to prove or disprove this, hold the shaft closed against the stop with your hand.

Thanks for replying!

I am goign to get these throttle bodies rebuilt in the future, but for now, is this a major problem???

What should I do to fix this for now if I can?

Will I damage anything with these like this???? It only does it very intermitingly at idle and then more ofter between 1100-1400 RPM.

[Zeke]

The throttle bodies can get worn to the point that the butterflies don't seat well no matter what you do. Mine were like that and my air by-pass screws were screwed all the way in, yet enough air got past the butterflies that the car idled. Not well, mind you. It's impossible to tune the system properly when this condition exists, if it does.

Over time, the ridge formed by the hammering of the butterfly from the intake reversion (I used the wrong term in my previous post) can be fatal to the stacks. The only way to repair them is to bore them larger.

[chan1408]

Hi Anthony,

I'm also a 71E owner (9111200687) w/ the MFI. Some points to agree/disagree with above.

First - oil dilution: If you've read the MFI early car posts for long, either here or at the Early 911S forum, you've heard from some knowledgable folks about oil dilution, and even breaking rods from it. You may have also read about the "normal" situation of the MFI cars blowing a cloud of black smoke on the first run through the gears. What I believe is that the early cars run rich unless very hot when perfectly set up, and even richer when imperfectly set up - as is the case with almost all cars with miles on them since throttle body rebuilds and check measure adjust routines run. And especially with the micro-switch disconnected - just run a couple tanks of gas through it with fresh oil - if you dare - and smell the oil tank. You'll have a hard time telling it from the gas tank.

Second: the thermostat: if you are going to run the thermostat, my experience has been you need to get all heat possible to it, because the thermostat won't push the mixture rod until it's good and hot. The mixture rod is "suspended" between two springs - on one end, the internal spring in the pump, on the other, the stack of bimetal washers in the thermostat. The thermostat compresses the internal spring on the mix rod with rising temp and leans the engine. It's important to know that the mix is VERY sensitive to displacement of the mix rod. Twenty thousandths of an inch makes a difference. So any crud in the thermostat that causes friction when the rod moves thru the bushing into the pump or slight temp changes on the bimetal stack in the thermostat will cause substantial mix changes. I've installed one of the manual cold start levers to replace the thermostat just so I can try to get the thing leaned out around town, because unless I dog it, it stays rich. LM1 in the garage waiting to go on, then I'll know more.

Any of the other MFI guys know (FOR SURE) if the mix rod has an internal stop that it's supposed to hit when hot and tuned right?

Sorry for length, hope it helps.

[chan1408]

Anthony - try this thread: MFI thermostat spacers from 6-25-04. That should help you, and answered my question about the stop. There is one.

good luck - keep at it.

Chip

['71 911E Coupe]

Originally Posted by milt

The throttle bodies can get worn to the point that the butterflies don't seat well no matter what you do. Mine were like that and my air by-pass screws were screwed all the way in, yet enough air got past the butterflies that the car idled. Not well, mind you. It's impossible to tune the system properly when this condition exists, if it does.

Over time, the ridge formed by the hammering of the butterfly from the intake reversion (I used the wrong term in my previous post) can be fatal to the stacks. The only way to repair them is to bore them larger.

Thank you for the info! So I guess this is pretty normal since most of these cars have the original stacks on them. I guess I'll just have to wait a few years till I get them rebuilt, or get new ones.

['71 911E Coupe]

Originally Posted by chan1408

Hi Anthony,

I'm also a 71E owner (9111200687) w/ the MFI. Some points to agree/disagree with above.

First - oil dilution: If you've read the MFI early car posts for long, either here or at the Early 911S forum, you've heard from some knowledgable folks about oil dilution, and even breaking rods from it. You may have also read about the "normal" situation of the MFI cars blowing a cloud of black smoke on the first run through the gears. What I believe is that the early cars run rich unless very hot when perfectly set up, and even richer when imperfectly set up - as is the case with almost all cars with miles on them since throttle body rebuilds and check measure adjust routines run. And especially with the micro-switch disconnected - just run a couple tanks of gas through it with fresh oil - if you dare - and smell the oil tank. You'll have a hard time telling it from the gas tank.

Second: the thermostat: if you are going to run the thermostat, my experience has been you need to get all heat possible to it, because the thermostat won't push the mixture rod until it's good and hot. The mixture rod is "suspended" between two springs - on one end, the internal spring in the pump, on the other, the stack of bimetal washers in the thermostat. The thermostat compresses the internal spring on the mix rod with rising temp and leans the engine. It's important to know that the mix is VERY sensitive to displacement of the mix rod. Twenty thousandths of an inch makes a difference. So any crud in the thermostat that causes friction when the rod moves thru the bushing into the pump or slight temp changes on the bimetal stack in the thermostat will cause substantial mix changes. I've installed one of the manual cold start levers to replace the thermostat just so I can try to get the thing leaned out around town, because unless I dog it, it stays rich. LM1 in the garage waiting to go on, then I'll know more.

Any of the other MFI guys know (FOR SURE) if the mix rod has an internal stop that it's supposed to hit when hot and tuned right?

Sorry for length, hope it helps.

Chip,

All of that does help. Thank you! As for Oil dilution, it doesn't appear for me to have much of that. Wouldn't the oil on the dipstick be really loose too? I did put Lucas Oil Stabizer in it too, that stuff is like a jelly. But Still, I don't think I have too much of that. My car seems to blow some blue smoke (oil) when you first start it up. But I ran the car for over an hour today and that goes away after like 10 minutes. But the car does not blow that much black smoke, it just smells really nasty and you can tell the car runs rich.

As for the therostat, I had that off the car when I first got it. I cleaned the whole thing up and reinstalled it. I have hot air going to it, but I need to get the proper hose. I guess it's working, but like you said something like a LM1 would tell you for sure. I'll have to get one, one of these days. I also need to check the the micro-switch is activating the RPM transducer(right, isnt that what it works with?) But if it wasn't, like you said, I think I would have much oil dilution, I'll know when I change the oil in a few months for sure.



So today, I ran the car, and it ran great, no stalling, and I did what you guys said about the idle stop screws. I lowered them down till they just touch the plate, but I still have to go back and doube check them. I also took air flow measurements at 3000 RPM. It ranged from 13-16 kg/hr. So I had to adjust them to the average using the air bypass screws, correct?

I'll report back here after I do the next thing.
Thanks guys!

[Zeke]

Air by-pass screws are to balance the system, yes. The butterfly stops are there only to keep the butterflies ever so slightly off the walls of the stacks. One reason for this is that they can stick. I suspect another is so they don't constantly rub in a groove as previously mentioned. The proper stop adjustment is covered in the CMA. I can't recall for sure, but it's something like one half turn off of stuck closed.

['71 911E Coupe]

Originally Posted by milt

Air by-pass screws are to balance the system, yes. The butterfly stops are there only to keep the butterflies ever so slightly off the walls of the stacks. One reason for this is that they can stick. I suspect another is so they don't constantly rub in a groove as previously mentioned. The proper stop adjustment is covered in the CMA. I can't recall for sure, but it's something like one half turn off of stuck closed.

Yea, that must have been why mine would stick before I would start the car up when it is cold. And I also don't want to ruin the shafts or the thottle bodies anymore as they are, until I can get the rebuilt. I'll take a look in CMA to double check on both of these adjustments.

Thanks!!!!! I'll report back soon.

['71 911E Coupe]

Okay guys,

I drove the car on Saturday after I put a new set of Dunlop tires on it. It rides much nicer now.
The car pulled very strong and ran like a charm. Was very powerful. Did not have any type of backfiring or hissing what-so-ever.

But the car did stall once, when I was going up a small hill in 3rd gear after I pulled out onto this road. It sounded like the engine stopped getting fuel. So I pulled off to the side of the road and it started right back up, and I pulled away with no problems. Didn't have any problems after that getting it home.

But when I first pulled out of my street there is a small hill that you have to go up, and it was fine on that one.

Could the electric fuel pump may of cut-out? Maybe I need a new fuel filter on it too.....I better check.

But any other ideas, and like I said besides from that the car had a really good day.

I've been readign the Open Heart Surgery MFI Thread too...and am wondering if my pump needs these adjustments too to get everything as good as it can be.

Thanks!

['71 911E Coupe]

Got some more info:

I just ran the car and did a CO test on it..just to see what it was at.

I was susprised to see that it was above 7% at idle. I did not do a part load test....I'm also thinking about getting a LM-1. But, isn't this way too high. I turned the main rack screw a little lean and then did a test again and when I would rev the engine, it would backfire slightly, so I put it back to where I first had it and it was fine.

The car did stall 2 times though...once just out of the blue, and another after I had it above 4000 RPM for a few seconds. I still sounded like it was running out of fuel....gonna check the filter next.

Any thoughts? Thanks.