Engine Doesn't Idle Smooth

[StarDiero75]

Howdy Guys,

I'm slowly tuning the carb right. Ive gone up to 60 jets and it seems to have helped, but it seems that when I cruise at 60-70, the power valve wants to open. As of now, the idle vacuum is about 16-17 inches. I say that b/c it likes to waver.... it has wavered ever since I put the new head on (2V converted head). It did not used to waver. I am pretty sure it is not supposed to waver. My old timer neighbor says it should be solid, as I agree. With a Schneider 256H cam, .420 lift, 112 lobe sep, should this be the case? And should the engine not want to run super smooth at idle? And what kind of idle should it be smooth at? I've played with it and it seems to like to idle at around 850-900 with a AFR of 11.5ish. Something is not right. When I try to run it in the 12.5-13, she vibrates in the car. I have checked time and time again for vacuum leaks. I don't know what to do.

The vacuum will hold steady, then magically drop an inch or 2, then come back up, and repeat, but its not consistent. Could this also be ignition related? If I didn't have enough voltage going to the DUI, could this happen? Its either the Distributor, the Carb, or the head. One of the 3.

Thanks,
Ryan

 

[Econoline]

I was running a 56 or 58 iirc in my 1100 on my 170. It's hard to believe you'd need twin 60's in a 200, but I may not understand how that works out. I remember when I had a 1.08 2100 I was going to install on my 250 it had 45's in there and I thought that would be close, but I never ran it b/c I decided to go fuel injected. 60 sounds way to large to me. There are calculations you can run to get you in the ballpark. I think that ballpark is going to be somewhere in the 40-50 zone for your 200. For example a 289 with a 2100 might run 45's.

People seem to get confused on the what a lean or rich condition does at the carb. A lean carb can run like a bat out of hell(why is h e l l still a problem on this forum? Really?!), but it can kill your engine in the short run or long of it. Too much fuel and she'll puke, stumble and stink.

Edit: The jets in my 2100 might have been 48's now that think about it. I still think you got too much jet. I don't recall how the idle system works on those carbs though or if thte main jest would affect it if the butterflys are in the right range, I.e. not opened to far at idle.

 

[bubba22349]

A DUI needs a full 12 volts going to it. With the engine vacuum droping a couple points and coming back again this would indacat a leaky valve or a plug gap that's too narrow. What rating of economizer valve are you using? Good lucl

 

[wsa111]

Did i recurve your DUI?? What initial advance are you running??
Are you running the vacuum advance to manifold or ported??

 

[StarDiero75]

A DUI needs a full 12 volts going to it. With the engine vacuum droping a couple points and coming back again this would indacat a leaky valve or a plug gap that's too narrow. What rating of economizer valve are you using? Good lucl

Well I checked the voltage and it was good. I ran a line directly to the battery and it ran the same so its not that. I increased the gap to .050" from .045". The car runs the same. I'm thinking its a leaky valve from when I broke the motor in and the pipes got cherry. My money is on an exhaust valve. Am I better off just replacing all the valves and having the seats redone, or just replacing the exhaust valves and calling it good?

I'm not sure on the economizer. Its whatever the stock one comes with a rebuild kit, particularly the Mikes Carb Kit. I do not believe it says.

Currently the plugs look darker than they should so I went back down. I remember 54s running particularly well so I went back to those for the time being b/c my gas mileage has been tanking haha.

 

[StarDiero75]

Did i recurve your DUI?? What initial advance are you running??
Are you running the vacuum advance to manifold or ported??

Yup, that was me. I was running 18, but retarded it back to 16. I think I'll bring her back up again to 18 after I get the valves checked out.
I am running ported. My old timer hot rod neighbor insists i run ported, not vacuum. The car can run manifold vacuum, it does as it should when its hooked up. I don't think that'll fix the fluctuation.

Also, a .050" gap should be good right?

 

[StarDiero75]

I was running a 56 or 58 iirc in my 1100 on my 170. It's hard to believe you'd need twin 60's in a 200, but I may not understand how that works out. I remember when I had a 1.08 2100 I was going to install on my 250 it had 45's in there and I thought that would be close, but I never ran it b/c I decided to go fuel injected. 60 sounds way to large to me. There are calculations you can run to get you in the ballpark. I think that ballpark is going to be somewhere in the 40-50 zone for your 200. For example a 289 with a 2100 might run 45's.

People seem to get confused on the what a lean or rich condition does at the carb. A lean carb can run like a bat out of heck(why is h e l l still a problem on this forum? Really?!), but it can kill your engine in the short run or long of it. Too much fuel and she'll puke, stumble and stink.

Edit: The jets in my 2100 might have been 48's now that think about it. I still think you got too much jet. I don't recall how the idle system works on those carbs though or if thte main jest would affect it if the butterflys are in the right range, I.e. not opened to far at idle.

What made you go to fuel injection? A Sniper? How do you like the injection? I am considering it after I figure this problem out. I kept thinking around 50 should be right. 60s make the thing run like a pig. I gotta figure this out here soon, its driving me up the wall.
I don't believe the main jets kick in yet. I got the idle turned lower now, about 700-750 and its not running any leaner. My Weber was like that though.

Whatever my issue is, I'm assuming its definitely vacuum related. Whether it be valves or something. My money is on valves. Thats tye only thing it could be in my mind at this point

 

[B RON CO]

Hi, just a few things pop into my mind.
The power valve should not open until the vacuum drops below @8" Hg. That would be like winging the throttle or heavy load conditions.
The vacuum gauge could be indicating a sticky valve.
My guess is that the jets are too big.
And the initial timing is too advanced. As you know, as you retard the timing the idle will lower itself. Listen to Bill about timing. But make sure there is 0 vacuum at the ported source at idle.
If you have an IR temp gun you can shoot each exhaust port. Rich exhaust ports will be cooler and lean ports will be hotter.
I wonder if you have a rocker arm too tight. That would give you a vacuum issue. Maybe a weak or broken valve spring.
I don't have a feeling about your cam, or if you checked the cam timing when you put it together.
Good luck

 

[Econoline]

The thing about using manifold vacuum is that it will allow you to turn the idle screw out further as you bring the initial timing up b/c timing is bringing the idle up and, in particular, the vacuum advance is being actuated at idle on manifold source and raising the timing further yet. Initial timing set @ 18* with manifold vacuum to the carb you might see 22-28* at idle. Both high timing and using manifold vacuum will help keep you out of the main fuel circuit at idle. So long as detonation and pinging aren't a problem. I'd like to see what happens if you hook up the carb to manifold vacuum and set the timing with vacuum connected to 18. You may have to finagle and readjust as you dial in the idle speed and timing as they are intrinsically tied along with the effect of the vacuum advance.

I'm going fuel injected b/c I've come to loath carburetors on "modern" fuel. I'm a technical type of person and I understand the metrics of computer control better than knowing whats going on with the fuel at the pump. One and done. My Chinese YFA is chugging along and will get me where I want to go just fine and peppy even, but it will evaporate it's bowl, so will your 2100 at any shut down. I'm just done with it. Air pressure change, re-tune, weather change re-tune. You want to drive to the mountains isn't bad b/c it just get's richer. But if you lived up there and want to go downhill, it's a problem. You ever notice in some weather your carb just runs tits? But the weather around here changes all the damned time.

 

[chad]

"...weather round here changes all the damned time...."
stooopid oceans !
Well...he lives by'em too :rolflmao:

 

[B RON CO]

Hi, I would go over the basic stuff, stuff that is off and you will never be able to set the carb.
Have you done a compression test? Have you removed one spark plug wire at a time to look for a bad cylinder? If there is no difference in the idle when you remove the plug wire try a different wire or plug in that cylinder. What plugs are you running? No cracks or carbon in the distributor cap. These are basic diagnostic tests you probably have done before. I doubt you will find an Allen machine or other diagnostic scope to analyze the ignition system. Good luck

 

[StarDiero75]

Hi, I would go over the basic stuff, stuff that is off and you will never be able to set the carb.
Have you done a compression test? Have you removed one spark plug wire at a time to look for a bad cylinder? If there is no difference in the idle when you remove the plug wire try a different wire or plug in that cylinder. What plugs are you running? No cracks or carbon in the distributor cap. These are basic diagnostic tests you probably have done before. I doubt you will find an Allen machine or other diagnostic scope to analyze the ignition system. Good luck

I have not done a compression test but it did the same before and after replacing the rings and rod bearings. Last time I did one was right before the rering. She was approx 160-175. Hatch marks were good on the bore and rehoned it before new rings. She got new plugs. I have yanked wires before and it makes the car run really bad no matter which. The pistons were cleaned spotless but they weren't bad before.

I'm using autolite 45s. I have run 46s and that doesn't do anything.

This motor runs erratically. When I started the car she runs about 13-14 inches, when warmed up about 16-17.

When i put her all together the first time in march, (new head, cam, dizzy, carb, headers), apparently when i got her running I had the dizzy one tooth off and back some, so she ran really retarded. when I checked the timing i don't know how it was running but she was several degrees ATDC. Ultimately running the car for 20 mins at 2000rpm turned the pipes cherry red hot. It has run funny ever since.

My money is on a warped exhaust valve. Bubba just reassured me that and I didn't want to yank the head again but my machinist is gonna pressure test it all and get her back to me.

I'll update what the news is in a few days after the shop calls me back

Ryan

 

[Econoline]

A leak down test will tell you if there's any valve issue and on which cylinder. You already know you have good compression but it never hurts to test again other than wasting time if you don't think you blew a ring land due to to much timing and a detonation issue. And the valve job is very recent as well. Nothing like knowing for sure if you've got the time. I think you've got a carb/fuel problem. What's your ignition system?

 

[StarDiero75]

A leak down test will tell you if there's any valve issue and on which cylinder. You already know you have good compression but it never hurts to test again other than wasting time if you don't think you blew a ring land due to to much timing and a detonation issue. And the valve job is very recent as well. Nothing like knowing for sure if you've got the time. I think you've got a carb/fuel problem. What's your ignition system?

I really don't think its a carb issue. So I did put a 2100 carb on it that I had put on my original head with the 2-1 adapter. That carb wouldn't drive down the road for crap, but it would at least keep a consistent idle. I did have that one at one point and it did the same.

I have never heard this motor detonate since i put the new custom curved DUI from Bill in it. It used to with the HEI occasionally when I floored it with the weber. The rings didn't look damaged and the pistons looked fine when I just replaced the rings. It runs the same since replacing them.

I've wanted it to bad to be a carb issue but I'm just not seeing it. I've messed with this thing too long and its always done the same thing.

Here's something, should the part of the exhaust valve that contacts the seat be dark or should it be cleanish? I remember when I redid the valve seals that some of the exhaust valves were dark around the seat contact area while a few were not.

 

[bubba22349]

The valve should always be clean and shiny on its area of seat contact as well as the seat itself. So looks like you are not getting a good enough seal on any of those dis colored exhaust valves. You maybe able to hand lap them with valve grinding compound how're ever in your case since the engine ran retarded for quite while and likely overheating them I would suggest a fresh 3 angle valve job with back cutting. You can also test your valve seal on a head that's off the engine by leveling the head upside down then poor fuel into the chamber and watch if you see any fuel start seeping into the exhaust or intake ports the head needs atleast a valve job. I think you will able to see much better tuning results after the valve job. Best of luck

 

[wsa111]

If you have some burned valves. Now is the time to install the SI valves from Matt vintage inlines.

 

[StarDiero75]

If you have some burned valves. Now is the time to install the SI valves from Matt vintage inlines.

Worst part is I already had them. I think they're out of stock as of now

 

[StarDiero75]

The valve should always be clean and shiny on its area of seat contact as well as the seat itself. So looks like you are not getting a good enough seal on any of those dis colored exhaust valves. You maybe able to hand lap them with valve grinding compound how're ever in your case since the engine ran retarded for quite while and likely overheating them I would suggest a fresh 3 angle valve job with back cutting. You can also test your valve seal on a head that's off the engine by leveling the head upside down then poor fuel into the chamber and watch if you see any fuel start seeping into the exhaust or intake ports the head needs atleast a valve job. I think you will able to see much better tuning results after the valve job. Best of luck

As of now, I dropped the head off at the shop, told him what happened and he said he'd vacuum test everything. Head and chambers. I'm pretty sure the exhaust valves are all shot. The intakes are good if I remember but I'll find out after he tells me. If VI is unable to get me new valves since mine are the VI port flow stainless, who makes a replacement 1.5" exhaust valve for this? Doesn't chevy have a 1.5" valve with the same stem diameter?

Yes I'll do the 3 angle and the back cuts. Are those recommended on the exhaust or just the 3 angle? I've heard back cuts on exhaust valves for a daily is unnecessary. Thats at least what I interpreted from the Handbook

 

[StarDiero75]

The valve should always be clean and shiny on its area of seat contact as well as the seat itself. So looks like you are not getting a good enough seal on any of those dis colored exhaust valves. You maybe able to hand lap them with valve grinding compound how're ever in your case since the engine ran retarded for quite while and likely overheating them I would suggest a fresh 3 angle valve job with back cutting. You can also test your valve seal on a head that's off the engine by leveling the head upside down then poor fuel into the chamber and watch if you see any fuel start seeping into the exhaust or intake ports the head needs atleast a valve job. I think you will able to see much better tuning results after the valve job. Best of luck

As of now, I dropped the head off at the shop, told him what happened and he said he'd vacuum test everything. Head and chambers. I'm pretty sure the exhaust valves are all shot. The intakes are good if I remember but I'll find out after he tells me. If VI is unable to get me new valves since mine are the VI port flow stainless, who makes a replacement 1.5" exhaust valve for this? Doesn't chevy have a 1.5" valve with the same stem diameter?

Yes I'll do the 3 angle and the back cuts. Are those recommended on the exhaust or just the 3 angle? I've heard back cuts on exhaust valves for a daily is unnecessary. Thats at least what I interpreted from the Handbook

 

[wsa111]

No back cut required on pro-flow valves, just a slight cut to ensure a perfect seal to the seat. The seat gets a 3 angle cut, but yours are already done.
The only mod which you can do on an exhaust valve is just remove the sharp edge at the top of the valve. Make is slightly rounded. Small gain if you want to do it.
SI Valves in CA can make you valves if Matt can't get them. Their #800-564-8258 or 805-582-0085.