Did a compression test today..

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Did a compression test today..

Postby marco_1978_spyder » Tue Jun 01, 2010 8:56 am

Well I got through a compression test today... Here's the results.

The first number is the first result the needle would jump to / the second is the max reading after about 8 seconds of cranking.

All plugs removed, and primaries held open. in PSI.

Odd Cyl bank: ...... Even
1 )130 / 190 ....... 2 )138 / 205
3 )112 / 195 ........4 )135 / 211
5 )130 / 194 ........6 )133 / 200
7 )140 /190 ........8 ) 120 / 200

All Plugs looked good, despite how smokey the exhaust has been at idle the past few days.

I think I have some valve guides that are going.
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
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Re: Did a compression test today..

Postby Len » Wed Jun 02, 2010 3:16 am

the comp test look ok ! plus or minus 10 to 20 % balance is good. When is it smoking ? On start up ? Decel ? all the time? Hot cold ?
Len
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Re: Did a compression test today..

Postby 72 SS PNL » Wed Jun 02, 2010 3:33 am

you read the first and fourth , not the 8th

also all plugs need to be out of the motor , and either a good batt or good batt with charger on it

but the compression is good , sounds like like its time for the heads to be redone
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Re: Did a compression test today..

Postby marco_1978_spyder » Wed Jun 02, 2010 8:11 am

Len, it smokes at Idle only. Not down the road. It's not fully blue, and its light. Seems like a mix of light oil and gas.

All plugs seems like nothings burning at all. A little black soot at the end of the threads, white /tan insulator, normal looking electrode. (500 miles on plugs)

Paul, all the plugs were out. and the throttle held open. On the 4th crank the cyl's were all around 180-190.

So yeah ,looks like compression is within reason. So either I have a bad intake gasket (hoping) or time to get the heads redone.

Wish I knew. If I tear into the motor now, and find out the intake gasket was just fine, that means that the motor will be torn down untill I can find a deal on heads.

Although I do have a spare running-when-pulled 305...Hmmm...

I wont swap the heads because the ones on my red spyder are better ones from an '84 305HO.
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
Featuring special guests; Carl Beraytor and Ray D'atore

My Red spyder now has a youtube channel please Like and Subscribe!!!
https://www.youtube.com/channel/UCOzzSR ... ISuing7KLA
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Re: Did a compression test today..

Postby cosvega76 » Wed Jun 02, 2010 9:18 am

If you don't want to tear into it, I would recommend putting some positive valve seals on it. Look for some on a late-'80s small block. If you have a choice, get the orange seals instead of the black. They fit on the top of the valve guide, shouldn't require any machining. You can change them with the heads on the car, just need the tool to compress the valve spring that fits on the rocker arm stud and the air fitting for the spark plug hole.

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Re: Did a compression test today..

Postby marco_1978_spyder » Wed Jun 02, 2010 9:50 pm

I have to go through my carb again, its acting all screwed up.

I've made to many small tweakes and now its all messed up. I also found that the bowl screws had loosened up, maybe causeing some internal leakage.

Most Importantly: I was able to turn the idle screws in all the way without the car stalling. It actually seemed to clear the exhaust up.

So I know that means gas is leaking in from somewhere other than the idle circuit...

I dont think its a blown PV since its new and I've never popped through the carb. Though I will check it.

I'm pulling the carb on Friday, and readjusting where the throttle blades sit. Then rechecking the rest of my rebuild..It ran nice for a while, so I think I've just got something adjusted out to far.

I may also pull the base off and see if I need to clear any passages that may still be clogged.

So it looks like now I need to get the carb back into shape, then resume the search for the idle bucking gremlin.
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
Featuring special guests; Carl Beraytor and Ray D'atore

My Red spyder now has a youtube channel please Like and Subscribe!!!
https://www.youtube.com/channel/UCOzzSR ... ISuing7KLA
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Re: Did a compression test today..

Postby Len » Thu Jun 03, 2010 3:15 am

Hello marco .
If your just blowing blue at idle and know where else ! Have had some one follow you to see if the blue shows else where ? If you can do so . If not ck the breather and pvc sytem .As those systems could allow for oil to enter into the combustion
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Re: Did a compression test today..

Postby 72 SS PNL » Thu Jun 03, 2010 3:40 am

blue = oil

white = moisture/coolant

black = rich
first and best car owned 72 GT(changed to SS) panel wagon

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Re: Did a compression test today..

Postby marco_1978_spyder » Thu Jun 03, 2010 7:42 am

72 SS PNL wrote:blue = oil

white = moisture/coolant

black = rich


Yep, I know that. The smoke is blue-ISH. But not thick obvious blue like oil burning. It burns your eyes and smells like a rich mixture, and leaves a black stain on the grass. It aslo responds to the idle mixture screws, so I think its just fuel.
My eyes have been known to get light gray / blue confused

I suspect that 1 my oil needs to be changed from being diluted with extra fuel. Its probably thinned out and seeping past seals easier. Maybe oil's in the cyl is also being burned from the extra fuel washing the cyl clean.

None of the plugs looked that bad though...

Im going to change the oil and recheck/ reset the carb.. I'll know more on friday afternoon.
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
Featuring special guests; Carl Beraytor and Ray D'atore

My Red spyder now has a youtube channel please Like and Subscribe!!!
https://www.youtube.com/channel/UCOzzSR ... ISuing7KLA
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Re: Did a compression test today..

Postby marco_1978_spyder » Sun Jun 06, 2010 10:49 am

So...

I pulled the carb off.

I pulled the float bowls and checked things out.

I retightened the rear metering plate. and reassembled, everything else was ok.

I set both throttle plate stops so that the transfer slot looked like a little squares on both primary butterflies and Secondaries. Probably .030 max.
The actual idle speed screw (no not the mixture screwS).. was left backed almost completely out.

I re installed the carb and reset the floats.

Idle speed was @ 1,100.

I used the throttle stop on the secondaries to adjust the idle speed... I brought it down to 700 rpm.

Reset the floats, reset the timing back up to @ 16 advanced . Reset the idle (using secondaries) and floats and timing a few more times.

Finally... the exhaust seemed to clear up and the car would die once again with the idle mixture screws turned all the way in.

So I backed those out for max vacuum which parked around 17hg. And a more steady needle than before.

Engine sounds decent and pulls nicely to 5k. rpm.
-BUT-...The damn Idle bucking...flat spot, and surging in cruise are all still happening!!

Now I want to pull the manifold and do an inspection (Been through the dizzy already)

I'm hoping to find out I have a bad intake gasket seal. But I have the feeling I'm going to tear the manifold off only to find everything looking normal.

I wonder if an aging drivers side engine mount could be a culprit... My theory there is, some of the engines power is being used to lift the engine up an inch or 2, until it falls back under its own weight.
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
Featuring special guests; Carl Beraytor and Ray D'atore

My Red spyder now has a youtube channel please Like and Subscribe!!!
https://www.youtube.com/channel/UCOzzSR ... ISuing7KLA
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Re: Did a compression test today..

Postby Len » Sun Jun 06, 2010 1:37 pm

Marco I am not a holly guru but most carb I have worked on the idle circuit is in the primary's and the scondaries are for the power circuit. The secondary throttle plates should be closed at idle. Your Idle speed and mixture should be done on the primary circuit alone whith the secondary plates closed . when you have hat set the idle . The secondary plates should start to open some where about 1/4 to 1/3 to wot. By using the secondaries to set idle speed you have eliminated some fuel delivery and this may be cousing the stumble.
Do you have another know good carb you can try to see if that one can be adjusted to achieve a good idle ect . Might save you the trouble of removing the intake.
Len
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Re: Did a compression test today..

Postby marco_1978_spyder » Sun Jun 06, 2010 9:11 pm

On a Holley there's an Idle transfer slot that has to be partially uncovered by the butterflies @ about .02 to about .04" for the idle circuit to work properly.

I was following some advice on Holley tuning from another forum as far as using the secondaries to control the idle speed.

I dont have another carb to check, but the old 600 DP I had on there was doing the same thing no matter how I tuned it.

Thanks for the reply
1978 Monza Spyder V8 4speed, posi
1978 Sunbird Formula V6, 5 Speed, Hatchback
1980 Sunbird Hatchback 4cyl, 4spd.
2006 Chevrolet Aveo 5 speed Hatchback
Yes, you can refer to me as Mark
Please visit my blog... http://chevymonza.blogspot.com/ Follow if you like!
Featuring special guests; Carl Beraytor and Ray D'atore

My Red spyder now has a youtube channel please Like and Subscribe!!!
https://www.youtube.com/channel/UCOzzSR ... ISuing7KLA
User avatar
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Re: Did a compression test today..

Postby Len » Mon Jun 07, 2010 3:03 am

Again based on my knowledge of carbs, I am assuming that holley is calling the Idle transfer slots are the little slots in the primaries at the throttle plates ? Theses slots are what allow the fuel to enter the intake. below the throttle plates, the measurements that are supplied are for where the throttle pates should be in comparison to those openings .on a good day! And they also allow fuel to enter on or off idle or under slight acceleration as the plates pass these openings the more fuel is allowed or sucked in . So there fore the the plate position at idle is important.
I am going to suggest that you have the secondary plates closed , adjust the mix screws to 2 turns out from bottom and turn up your idle speed screw to get the car running at a fast idle till hot . Some play here might be involved on Idle speed screw . Once hot and the choke plate is wide open , adjust the idle speed screw to about 900/ 1000 rpm then adjust the mixture screws in one at a time in till a stubble is heard then back out until a stubble is heard and set in the middle take time here and allow the eng to recover, for each one then bring then bring the idle speed screw down to the idle that works for you in gear this should get your idle speed to work./ poss not your choke or power circuit but it might all work .
This is were you have to start as all the rest is based on how this is set as the fuel delivery for the power circuit is based on the idle fuel delivery and off idle transfer to power circuit and acell pump . Or as the the primary throttle plates pass the the transfere ports and the linkage starts to open the the secondary fuel delivery ports to eng vac to allow fuel to be sucked in to the eng via the secondarys and start the acell pump pushing fuel through all fuel delivery ports in a carb. It is a balance of all these but it does all start at the hot idle being set at what it should be .

Len
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