Timing issue?

[Gene 64 2dr]

I may have a timing issue here. I a rookie as far as timing go. I’ve read plenty of articles and understand the basics but not quite sure what numbers I should be seeing with my setup.

Back ground: DUI, 268/274 110 cam, 6 to 1 roller tip rockers, Offy 3x1 weber, manual Trans
The cam was originally advanced 4 degrees but has been returned to straight up, ( noticed a very small mark on top of one piston that looked like a valve may have just slightly tap it)

Here are the numbers I get:

Timing @ 900 rpm
12 degrees vac disconnected and plugged
29 degrees vac line connected

Timing@ 3K
31 degrees vac disconnected and plugged
44 degrees vac line connected

Vac@ idle
8”
Vac@ 3.5K
14” (max vac that can be obtained)

Symptoms: when initial timing set @ 12 degrees (14 better) normal driving is great, nice and smooth acceleration to 3K. However if you stand on it at around 3.5K it gets a little rough and around 4K to 5K starts to back fire.

If the timing is set to 10 degrees the acceleration is great and pulls real strong all the way above 5K. At a steady speed however you get a slight bucking that’s not right.

Anybody have any thoughts on this.

Thanks
Gene

 

[rbohm]

8) it sounds like you have a vacuum leak, not a timing issue, until you advance the timing too far which is where you run into a combination of issues, too much timing coupled with a vacuum leak.

 

[First Fox]

Bucking or surging at a constant speed could also be an indication of a fuel problem, generally a lean condition. Your fuel pump/filter in good shape? You may need to jet a bit more on the rich side. If you haven't done so yet, take a good long drive and then pull the plugs and take a close look at them. They can tell you about fuel conditions if you dont have a wideband. There has to be a few articles about reading spark plugs out there and you should probably find one. It would be easier to see pics of what you are looking for than describing it on here.

 

[wsa111]

First of all do you have dished pistons or flat tops.
How may CC's in the combustion chamber.
Can you run a hot cranking compression test so i can pinpoint your combination.
You need to get a A/F ratio check especially on full throttle.
I am trying to see if you have an ignition problem causing the bucking or a fuel mixture & or delivery problem.
Mikes Dui's normally have 12 degrees of mechanical X 2 = 24 + 14 initial will get you close..
Need more info, V/R Bill

 

[Gene 64 2dr]

I did not realize that I left out that bit of information.
I have an AF meter installed and at idle it’s around 13-13.5, at cruise 14, and wide open 12
Pistons flat top 40 over
Head 62cc
6 to 1 roller tip rockers
Cam 268/274 110
Deck height .025
Head gasket .050
All the plugs look like this one:

 

[MPGmustang]

http://www.falcon6handbook.com/compcalculator.asp
whoa... you have 8.3 compresion ratio... that's really low... good thing you got flat tops pistons...

bucking surging can be attributed to irratic timng, broken vacuum canister on dist, or broken spring in dist, and even a happy power valve that can't make up it's mind, or possible lean mixture. there can be other reasons like gremlins under the car messing with the brakes but I'll let other mention them.

 

[FalconSedanDelivery]

Pull the Dist and look at the gear , to see if its wearing alright , unfortunately there are some issues with DUI , if you wait too long it can kill the cam as well , if its fine then its an elimination of a possible source

 

[Gene 64 2dr]

I'll pull the dist tomorrow and give it a look. Already checked the springs and they are ok. I know now that the solution will be a simple one. I do field service work and if a problem takes a while to fix and drives you crazy, the solution is usually very simple.

I know the compresion is on the low side but I wasn't sure what I was going to end up with in the end. You can always machine things down but adding it back is a little hard to do.

As for the gremlins I think I already caught all of them. They are a lot like catching snipes.

Gene

 

[69.5Mav]

Timing @ 900 rpm
12 degrees vac disconnected and plugged

Are you sure that your Balencer has not slipped? Check number one top dead center against the timing mark.

idle it’s around 13-13.5, at cruise 14, and wide open 12

You sound to rich across the board. I like 14.7 at idle, 15 to 17 at cruise and 12.5 wide open. A little rich is not bad but at cruise 14 may be causing your bucking. 15 to 17 will give you your best econimy.

 

[wsa111]

You have to be very cautious of A/F readings.
The 14-1 cruise is a little rich, but should not cause surging. A lean cruise will cause surging.
I like 12.8-13.1 WOT, but let drag strip mph & et be your final choice.
Gene Fiore during his dyno runs the A/F readings read rich & he kept leaning the mixture. He fried #1 piston.
Somewhere along the line he got bad A/F readings.
Remember a dyno doesn't move so always go a little richer on the front cylinders cause liquid fuel will move back during acceration. That is the beauty of fuel injection cause the intake has only air where a carburated engine has air flow as well as fuel flow to be concerned about.
Great idea to check for damper ring movement.
Always mark the outer ring & the hub, then if there is movement you can see it right away. Bill

 

[69.5Mav]

The 14-1 cruise is a little rich, but should not cause surging. A lean cruise will cause surging.

Opinions vary but Toyota recomends 15 to 17 at cruise. However Bill is correct these sixs are notorius for bad fuel distribution so I would recomend caution in approching a very lean cruise with lots of plug checking for over lean condition. But you have a tri-power so fuel distribution should not be a big concer.

Also as you pass the sweet spot milage will drop.

 

[Gene 64 2dr]

I want to thank everyone for all your input.

The dist gears looked good. I put everything back together and tried a few test runs making it a little bit richer. At first it looked good but just when I thought it was all set it started to miss above 3,500. I checked for vac leaks again at cold start up and after warming it up after a few good pull thru the gears, nothing. Not long ago I put in a pcv valve to take care of the oil vapor smell. Before I had two breather filters on top. There were no problems when I put it and I assumed that it wasn’t the problem (you know what happens when you assume)
I pulled the valve, plugged the hose and put back the valve cover breather filters. The idle vac went from 8” to 13” and above 3.5K rpm high end went from 14” to 20”. I adjusted the carbs and made a few test rides, no problems.
I just got back from going to a cruise in that was about 45min from home with both highway and back roads. I cruised both slow, fast and at times ran it pretty hard though the gears without even a hiccup.
I would like to run some kind of pcv valve. I just got one off the shelf that fit and it seemed to work ok. I ran it right off of the intake manifold.
Any suggestions?

Thanks again
Gene

 

[First Fox]

Sounds like you got it licked. I am a bit confused though, what kind of suggestion are looking for? Sound like you have it figured out.

If you are wondering where to plumb the PVC valve, it needs to be plumbed to manifold vacuum via a large port. I am not familiar with the tri-power setup, but there may or may not be one there. You may have to tap a hole and install a fitting. Dont use an existing small fitting for accessory vacuum and cobble it with adapters or anything like that. The line from that goes to the PVC valve which needs to fit tightly in a grommet in the valve cover. The valve cover will also need a breather in another location to allow fresh air to be drawn it. I only mention it because I have seen people trying to "clean up" under the hood and install plugs thus blocking off the breather holes. :roll:

Good work on solving your issue man!

 

[Gene 64 2dr]

The pcv valve I was using was plumbed straight into the manifold with a 3/8” line with a tight grommet and a vent fill cap. The valve I bought must have just been a piece of crap and failed to soon. I was just wondering if there were any recommendations on a good brand to use that’s not a piece of junk.

Gene

 

[bubba22349]

You have the right conection point for the PCV vacuum source but it Would work better if you find another valve cover with the PCV hole (they also have the baffle so it won't pull excessive oil in). the oil fill cap should be vented and be located at the opposite end of the valve cover run the hose vent from your fill cap to your air cleaner and your good to go.

 

[wsa111]

Purchase a pcv valve for the 200 six first of all.
The best place to get vacuum is on the base of the carburetor that holley uses or on the adapter plate below the center carb.
If you tap into the intake log at either end you are inducing a major vacuum leak at that cylinder & it will roughen the idle or in your case with the wrong flow pcv and the wrong place to get a vacuum source.
Bubba described the best place for either a vented oil filler cap & fet fresh filtered air from the air cleaner. Bill

 

[Gene 64 2dr]

Well off to get the right pcv valve. Did not realize there was that much of a difference in them.
I have a CI valve cover so I’m all set there all though it isn’t baffled. The only place to pull a decent vacuum is in the center of the log. There is no adapter plates used in the Offy manifold but I’ve used this spot for vacuum before when wasn’t using a pcv valve and worked ok.
I’m pretty sure I’m all set now.

Again thanks for all the help
Gene

 

[wsa111]

Gene since you have the CI valve cover make sure you get a baffled pcv valve grommet to prevent oil from being sucked into the pcv valve.
I believe spectra makes a baffled grommet.
I even went a step further & put a spacer hose 4" above the grommet & put the pcv valve there.
That keeps the valve away from any oil that even gets past the baffled grommet.
Bill

 

[Gene 64 2dr]

So you think that the oil getting int the valve is what caused it to fail in a short period of time?

 

[wsa111]

Gene, the valve you had was one possibly for a 460 engine which flows twice the air that the correct valve for a 200 does.
You also had it plumbed into the intake log at the wrong spot.
A pcv valve is a controlled vacuum leak which removes blowby from the crankcase. Now you know what to do. Bill