Ok, here is the problem. I have the 350 with specs in sig with the computer controlled carb setup off of my 305. When I first start it I usually have to give it gas while starting to get it to fire. After that I have to keep the rpms up for a couple minutes for it to run. When first started it tries to idle 4-500 rpm and with the cam that just doesnt fly so well. It will run pretty good on its own once it hits closed loop, but it tends to idle at about 1100 rpms. If I turn it off and restart it at this point it will still idle good but it will idle closer to 700 rpms which is where I want it.

When it is first started until it hits closed the mixture is off enough it burns your eyes. I was told that this is rich. Is that right? I have the idle mixture screws 7 turns out and havent messed with the idle air bleed yet, but plan to this coming weekend. Could it be because the idle air bleed needs set or do you think it is something else. Also, my high idle is not functional(at least normally. Sometimes it works if it gets real cold), but if it was I believe it would mask this problem real well.

If you have any ideas or need any more information please let me know.

Thanks

Ben

 

Sounds like you need to work on the fast idle speed (associated with the choke) and IAB.

When in open loop, the MCS goes into a pre-set dwell, so the IAB (and idle mixture screw) adjustment is important.

 

How would you suggest I go about this? Should I go ahead and set the iab first, or do I need to mess with other stuff first?

Ben

 

Ok, my idle mixture screws are 7 turns out. I just set the dwell, and it fluctuates, but I have got it so that it goes from somwhere around 47-53 or 54 with the air cleaner on. 50% dwell is equal to the 30 degrees that you reccomended according to the chart with the fluke meter I used. I set the idle at about 750 and did this. I got it set like this and the idle was still at about 750. I turned the car of and went inside for a while. I came back out and started it up and it was trying to idle at 500 again. Well, I went ahead and let it warm up for a couple minutes and the idle came up. After the idle came up I took it out and drove it for a while. After driving a minute or 2 the idle was up to around 1100. It stayed this way the rest of the drive. I parked the car and put it in park and the idle went up to about 1200 and stayed there for a minute. I punched the pedal to the floor real quick and it reved and then started idling at about 750 again. What the heck is going on and how do I fix it?

Thanks

Ben

 

anybody?

 

Momar, I'm having almost the exact same problem as you are. I just got my new engine running, and 355 with the XE268 cam, AFR 190 heads and around 9.6:1 compression.

When I start it after sitting over night, the choke works, and it idles around 2100 rpm for a few minutes. When I tap the gas is goes back to around 800-900. After driving the vehicle any distance, the engine will not idle below 1100. If I shut the car off. Wait a few minutes and turn it back on, it will idle around 500. And like your engine, 500 is too low. But I after I drive it 200 yrds it will idle at 1100.

The last time I got back from driving the car, it was idling high again. So I popped the hood and looked at the carb. The throttle linkage was fully closed. I did notice that when I pulled the vacuum line for the air cleaner off the engine's rpm increased. I'm going to try and track down a possible vacuum leak the next chance I get. I'm thinking once the engine sees load about 2000rpm, a vacuum leak is starting somewhere. Too bad I'll have to wait until next weekend to look at it.

-Dave

 

Well, thats the same cam as I have, however I cant afford the nice heads right now. If you figure out what is causing your problem for sure, let me know.

Anyway, this does sound similar to my problem other than my high idle doesnt work so it idles low even when I first start it for the day. As far as your theory, if it was only seeing a vacuum leak after it was under load w/ some rpms, then how come it doesnt go back to normal when you idle again? Also, what is causing the low idle since the vacuum leak you created made it idle high? These questions are to anyone and not just you, but I just am trying to think through why this is happening.

BTW, I replaced a couple of my vacuum lines yesterday that were a bit on the shady side and saw no difference.

Ben

 

My thinking is that once the engine sees load, a vacuum leak opens up somewhere and doesn't close until after the car is shut off, but that theory sounds worse the more I think about it. I'm also wondering if it may be related to the charcoal canister system. I really have no idea though. If I just had more time with the vehicle I could probably figure this out.

To be honest I've had this "doesn't want to idle below 1000 rpm" for a long time, even before the engine swap. Its the only problem I'm having right now, besides bubbles in my coolant tank.

I have an A/F gage and it consistantly runs in the middle, with a tendency to be on the rich side. When it gets stuck at this 1000 rpm idle, the gage reads about one or two lights into the green, or rich, section. At cruise, it fluctuates more rapidly between lean and rich. I feel that somewhere air or gas is leaking when it shouldn't be. Did you get a chance to try resetting the dwell with the engine completely warm?

Well, enough rambling for me. Hopefully somebody has some ideas.

-Dave

 

I did reset the dwell with it completely warmed up and it is still doing the same. Is your charcoal canister system stock? I removed mine and rerouted and my lines. What kind of carb are you running?

Ben

 

That sounds a whole bunch like a mechanical binding/sticking of the throttle mechanism. Could be on/in the carb (including fast idle cam), could be one of the throttle cables.

 

Well, it wont normally go down when I punch it like that but it has once or twice. Also, what is causing the low idle when first started then? My high idle isnt working so I guess something to do with it might be sticking. When I first got the motor together and going a couple weeks ago the high idle would work when it was really cold(well under 30) but now it is not getting that cold and it wont high idle at all.

Ben

 

I'm running the stock cc Q-jet and my canister is stock. I had some problems with my throttle sticking a while ago, but I just added another return spring. I've also had the throttle shafts rebushed. Like yours, mine will sometimes drop if I rev it fast and other times it wont. The last time that my engine was stuck idling high, I popped the hood and looked at the carb. The throttle was completely close and resting against the idle set screw. I even tried to close it more by hand and it was fully closed. The choke was completely open and the fast idle cam was rotated out of the way. Even snapping the throttle by hand didn't bring the rpm's down. Also, the idle solenoid on the driver's side of the carb was fully retracted.

It really isn't that big of a problem, just more of a nusance. I'm sure it's something very simple that we are overlooking.

-Dave

 

I will have to look at it some more, but I would doubt my throttle was sticking I soaked the base in carb cleaner for a couple days before I put it back together, and it seemed real free.

Ben

 

Mine does that. Sounds like something sticking or binding. Examine the idle speed screw on the carb and see if there is ANY gap between the screw and the throttle linkages when its running fast. When its running fast, try backing the idle speed screw out and see if the idle drops as the screw is being backed out. If the idle speed remains the same, then there is something binding or sticking.

I've tracked mine to a worn throttle shaft bushing.

 

Well, actually, I think my problem might just be a sticking throttle linkage. I noticed it goes down to the correct idle if I slip my foot off of the side of the pedal and let it snap closed. I checked for excessive throttle shaft play before I put it together and it seemed fine. I am going to try some wd40 on the shaft and linkage, and then maybe a stiffer return spring if that doesnt help.

Ben

 

Ok, well, I figured out part of the problem. I found that the silinoid was holding it open for some reason. Anyway, I unplugged it and I still have the problem with it trying to idle at 4-500 rpm until it warms up. I reset the idle but did it while it is warmed up and it still idles around 500 when I first start it. The motor can still be hot and it will still idle at about 400-500 when I start it unless I just shut it of within the last minute or 2. What do you think I should do? I could try setting the idle screw when it is idling real low, but I would bet that I am going to end up idling over 1000 when it warms up. Any ideas?

Ben

 

Also, should the high idle work only like the first time you start the car for the day when the motor is completely cold, or should it work anytime the car has sat for a little while(how long?)? Also, what would be causing that silinoid to open the throttle like that? I have another 1 or 2 of them off of other carbs if you think it is the part its self, but I dont know why it would just decide to open the throttle. I would think it was the computer doing it.

Thanks

Ben

 

If i am right, the high idle works with the choke, and when the choke fully opens it kicks off the fast idle cam. So I guess if the car sits long enough to cool down so when you start the car and it closes the choke it will kick in the fast idle cam

 

well, my high idle doesnt work at all.

Ben

 

Well, one of my friends dads looked at it today and said that my choke was way out of adjustment. He said that there was too much tension on it. So do I have to drill out those rivits to adjust it? That should fix my high idle, because it works when it gets real cold(20 degrees or lower) but not above that. That should fix my high idle problem. I disconnected that silenoid and now I have the idle set to where it is about 750 when I first start the car but goes up to about 900 to 1000 when it warms up. This way at least it is not hitting 1200, and it runs good when I start it. I may adjust it down a little and see if I can find a happy medium of startup idle speed and closed loop idle speed. I would rather get this fixed the right way, but I dont know what that is. I would still appreciate it if anyone has any other ideas. Once I get my choke set right it should fix the problem for the first time I start it up for the day, but I dont know about after that. How long should the motor have to set before it gets cool enough for the high idle to kick in if properly set?

Thanks

Ben

 

Drill out the rivets and replace with screws. Be careful, that metal is easy to strip out.

 

will it already be threaded or do I have to tap it or what?

 

No just screw some replacment screws in and you will be alright. It does sound like what people have been saying all along. 1st the fast idle cam is set too high. 2nd the choke is too lean. Turn the fast idle screw out a turn, you might hear a small pop if the linkage is binding slightly then adjust the choke a little richer/firmer. The fast idle can takeover your idle setting and give improper/erratic idle if it is out of whack. You may have to adjust your idle once the fast idle is working right.


Also make sure the choke pull off rod is still attached correctly. My rod kept popiing off when I was working on my Qjet that had the same problems your having.

 

I'm not sure you understand how the fast idle works. It is a separate adjustment from the warmed-up idle, on the opposite side of the carb, and adjusted from the rear. It either isn't adjusted properly, or the fast idle cam isn't coming up like it should when the choke is "on".

I seriously doubt the diagnosis of the friend's dad is right. The best time to baseline choke adjustments is when the engine is stone cold, but the choke should come on at least partially when the engine has sat and cooled for an hour, as an example. An original choke thermostat that still has the rivets installed is more likely to have too little tension, but that can be verified by insuring the choke butterfly snaps closed and the fast idle cam comes up when the engine is stone cold and you first move the throttle a little.

I would suggest that you take the carb off, drain the fuel, and sit and play with all the mechanism until you see and understand exactly how they all work. Honestly, that's how I figured them all out. Us trying to explain them remotely will help a little, but you need a clear understanding of it all.

P.S.: The replacement screws of which SSC speaks come in rebuild kits (typically), and are self-tapping.

 

Well, I had the same sort of problem and it started when I installed a 355 eng. I used a set of racing pistons (not a good idea) that required .006" piston to cyl. wall clearance. When I started the eng. cold the eng. sounds like a diesel. It went to high idle ok but little by little the idle slowed way down and it would hardley idle. When the eng. warmed up it idled fine and of course the piston noise was gone. Anyhow I finelly figured out that the piston noise was causeing the "ESC" (knoc sensor) to retard the timing (as much as 20*) which slowed the eng. idle way down. To fix the problem I bought a N.O. coolent temp sensor (closed at 170* open at 145*) and mounted it on the stat housing. I then cut the wire to the knock sensor and wired the coolent sensor in series. Because the coolent sensor is N.O. when the eng. is cold the ESC module can not tell the ECM to tell the EST to retard the timing. I have to keep the ESC system working because I run a 150 shot of nitrous. If for some reason my eng. starts to deto with the button pushed it would save my eng. a world of hurt. This may not have anything to do with your problem but you never know.

Auggie

 

Ok, I actually understand the high idle pretty much, but it is not the main problem that I am asking about. I understand that it is a seperate function, and I have t carbs sitting around to look at so I am not taking this one off unless I need to to fix something. I think that my choke is just not coming on. I know that the high ilde works when it gets below like 20 degrees outside but not above so I think that I just need to adjust the tension not the speed. Also, I have stock pistons, so I dont think that that is my problem.

What I really want to know is why my idle is low when I first start it and raises up. It does this to an extent even with the silenoid unplugged. With it plugged in it has about 3 stages it would start out idleing about 4-500 and then go up to 750(which is where I set it with the motor warmed up) and then when i drive it it goes up to about 1200(which I tracked down to the silenoid). If I unplug it it doesnt go up to 1200, but the idle is still low when I first start it. I have it unplugged right now and have the idle turned up a bit so it is about 700 when it first starts, and then goes up to about 1000 when it warms up, but want to get it so the idle is the same when I start it as when it warms up. It seems to go up when it hits closed loop. It will idle lower again even if I just turn it off for a few minutes and start it back up. It can still be up to temp, but when it hits closed loop again the idle will go back up. Does anyone know what I should look for to fix this?

Thanks for all the help.

Ben

 

In the carb book i have. it tells you how to adjust theIdle speed solenoid .I cant tell you right of hand, something like running a wire from the positive side of the battery to the post and it is suppose to move out. I f you have a carb rebuild book look in that, or I am sure a bunch of guys here can tell you. I put a new one on mine when I rebuilt my carb . I never messed with it , just put it on. a month or so down the road it was doing fine , and then all of a sudden it had a real high idle, and I figured out that was the problem. Put the old one back on and it is still working fine.
I also think if you unplug the solenoid while the battery is hooked up ,it may mess up your solenoid
I hope this helps some

 

If you mean the soleniod in the dr side of carb.You can adjust it by turning the plunger head with a 13MM wrench.I think you set it according to the lable on the plastic cover ahead of the radiator.With your a/c on.