Help me with a fast idle issue.. Up-dated

[LastDeadLast]

Help me with a fast idle issue.. Updated

I'm trying to diagnose a fast idle problem. My carbs have been rebuilt and I've got the timing set at 8 degrees ATDC (I have a Mallory dizzy without the vacuum advance). Anything over 900rpms and my engine diesels badly. So my first inclination was to lower the idle speed, only the idle screws are backed out completely. So I'm thinking that I need to take a close look at the way I've got all my vacuum/emission lines set up. I've made quick diagram that details how I've got things plumed. Is this correct?

I'm pretty sure that I don't have any vacuum leaks. Since I've got the Mallory, the vacuum plug on the bottom of Carb 3 is plugged.

Please see attached file for the diagram.

 

[Guest]

Re: Help me with a fast idle issue..

Hey Shannon.
Since we have similar setups, I will share with you the way I did the vacumns. First off, I have my gas tank vented through a filter and down to the bottom of the frame. I don't have a carbon cannister. Neither do I have a PCV valve. I used the three large vacumn posts on the front side of the ZS carbs to pull the vacumn from my valve cover through an oil separator (Goodparts). The oil fumes tend to get separated out and drip back into a fitting I had welded in the pan. I only use the intake vacumn to activate my brake servo. The other small outlet on the intake vacumn port is blocked off. I feel that I am getting enough negative pressure on my crank to prevent too much pressure and the resultant leaks. I considered using the intake vacumn to help vent my crank but felt there may be a bit much sucking going on, even with a PCV valve, although Richard Good markets one that he maintains will negate this. What I have works for me. Too, I idle at 1000 rpm, even with the GP2 cam and increased compression and I have my timing set at 8 degrees BTDC. No vacumn advance, all centrifugal.

Bill

 

[RomanH]

Re: Help me with a fast idle issue..

Hi Shannon,
In that diagram that you posted you show the PCV tied into the vacuum supply line for the brake servo. Is that a correct illustration of your setup? Have you driven the car this way?
Do your brakes feel like they function properly?
I am no expert but it is my understanding that the vacuum supply line for the brake servo should be only hooked up to the brake servo and not trying to supply vacuum to anything else.
You may try and remove the PCV Tee from the servo hose and connect it to the blue hose in your diagram which terminate at the carburetors. On my stock '74 the pcv is connected to the carb ports which are located before the throttle plates. This is done, I believe, to prevent an unwanted introduction of fresh air into the fuel/air charge thus leaning out the mixture. The fresh air can be drawn into the engine case from any number of places (small leaks in gaskets, oil cap etc)and then almost immediately be drawn into the intake as per your drawing. If you have it connected to the carbs that air can now be accounted for and the mixture adjusted accordingly to compensate. Also, if you have the lines connected in the manner you show I think your brakes might be weak. Moving air takes the path of least resistance and in the setup you show all of the air drawn into the intake will most likely come from the engine case and you will not have adequate vacuum at the servo.
One more observation. Please use a good quality hose specifically designed for use on the brake booster (but you already know this). The only reason I add that is the DPO of my car used a regular fuel line and it can not hold up to the high vacuum without collapsing. When this happens the brakes feel almost non-existant and the car becomes difficult to stop.
Keep us posted on your progress.
Roman

 

[piman]

Re: Help me with a fast idle issue..

Hello Shannon,

although probably not the cause of the high idle; you have a non standard distributor but set very retarded (8 deg ATDC), what is your total advance? I suspect that you will need a lot more advance for the car to run well.

Do a double check of the throttle synchronisation, if you can get a reasonable idle speed (600 - 700 is good)with the carburettors independant of each other then there is a synchronisation problem the way they are presently set up.
(Don't forget the choke idle speed screws also)

Alec

 

[swift6]

Re: Help me with a fast idle issue..

Hi Shannon,
I have to agree with Roman here. The line to the brake servo should be uninterupted. The valve cover line should plug into the lines going into the carbs that also attach to the charcoal canister. In my tri-carb set up, R.G. supplied a four way connector for just that purpose.

If you have more than fumes coming out of the valve cover then there are other issues. The cast aluminum valve covers are not baffled like the factory steel covers. With the tri-carbs, I had a lot of oil being pulled out of the valve cover and through the carbs. That is one of the reasons that R.G. came up with his oil seperator set up. It was never an issue for me with the twin carbs.

/ubbthreads/images/graemlins/cheers.gif

 

[LastDeadLast]

Re: Help me with a fast idle issue..

Thanks guys,

I'll change my setup and see what happens.

 

[LastDeadLast]

Re: Help me with a fast idle issue.. Updated

Ok, I took the crankcase ventelation hose and spliced it to the line going to carbon canister and drove the old girl to work this morning. She idled at 700 rpm like a champ. Brake pedal feel is much better too. The best thing of all is that the run-on is gone!

Thanks for all your help!!!

 

[Guest]

Re: Help me with a fast idle issue.. Updated

Shannon, my Chevy Tahoe doesn't idle at 700 rpm. How in the world do you keep it from dying on you at this idle? The best I can get is 1000 and sometimes 1200. Except for the vacumn mis-hookup, you must have that thing balanced and blueprinted. Surely you don't have a lightened flywheel.

Bill

 

[LastDeadLast]

Re: Help me with a fast idle issue.. Updated

Bill,

It is a little slow, but it still runs. My goal is to have it idle at 800-850rpms.

I figure that I've probably got my problem fixed I can re-adjust the carbs to be sync'd the way I want them to be. At least now I have room to advance the timing a little. I'd like to see how it runs at 10 degrees BTDC.

My motor has been balanced, but not blueprinted, and the flywheel has been lightened to 19 pounds. However, I've got my eye on Racetorations steel 10 pounder (without the ring gear). After feeling the difference from my 30 pound OEM flywheel, I'm ready for MORE!!! I highly recommend balancing to any motor rebuild, it usually don't cost more than a couple hundred dollars but is well worth it in terms of longevity.

 

[Guest]

Re: Help me with a fast idle issue.. Updated

Shannon, just as an fyi the steel flywheels are about the same weight as the fidenza aluminium ones, but by the time you are done cost 250-300+ more (the fidenza comes with the ring gear fitted and pinned, the steel doesn't).

I was going to do the steel one, but have been convinced that the aluminium is going to be just as good so that's what I'll be putting on. ymmv of course, Alan.

 

[LastDeadLast]

Re: Help me with a fast idle issue.. Updated

Alana,

I was going to do the alloy flywheel, but I've been told by several knowledgeable people that the flywheel bolts have a tendency to work loose after a time. The steel unit does not suffer from this.

Not having to pull the tranny to periodically torque the flywheel is worth the extra money IMO.

FYI, Ractorations quoted me $567 delivered with the ring gear installed. That's cheaper than TRF and within $40.00 of Moss.

 

[Guest]

Re: Help me with a fast idle issue.. Updated

I felt the same way until the guy selling it to me offered to replace the whole thing with steel including the cost of all the labor if it failed to satisfy in any way. That's on an engine that he knows is being specced for well over 200hp.

If he's that confident, then I figure I'll give it a go. His point about the same flywheels being used on high hp tuner imports was also well made. I know it's the crankshaft flex that's an issue, but I don't intend going over 6200 rpm, so flex is minimised.

btw: don't even think of getting it from one of the big 3. You can get it from Jegs for $325, and a whole bunch of other places for under 400. P/N is 383-172661. $500 is daylight robbery.

https://www.jegs.com/webapp/wcs/stores/se...ategoryId=26355

 

[LastDeadLast]

Re: Help me with a fast idle issue.. Updated

Alan,
Interesting, Ill have to look into that. thanks for the tip!

 

[Guest]

Re: Help me with a fast idle issue.. Updated

As a slightly irrelevant update - the wife's out, so I get to look at car books and watch dodgy uk gangster movies - it's layer cake tonight.

The book was the Kastner Triumph Prep book. Pg 116 has him talking about the problems with crank flex they had. They used an aluminium flywheel from a Porsche to get it to run to 7500rpm for the duration of a race. I figure if it's good enough for him...

He has a real nice bit about nitriding too. I was intending to get the crank done, I just never realised there was more than one type of nitriding.

Totally different and it deserves a seperate thread, but has anyone tried cryo treatment? Does it work or is it snake oil?

 

[LastDeadLast]

Re: Help me with a fast idle issue.. Updated

There's so many things you can do... from what I've learned with working with Ford's and Chevy's, It's how fast you want to go, how much you want to spend.

I think it's important to balance what you spend with what you're going to use the car for. For me.. with the occasional autocross and 98% street duty, I don't need to get very exotic... triple carbs and a lightened flywheel is about good as it gets.... You must be careful though, something thats good for a race isn't neccessarily good for the street. It's only got to stay together long enough to finish the race, then everything gets torn apart and rebuilt.

With that being said... the technology thats available now is amazing!!!!