Topic: q-jet tuning
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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Vince Vette,after weeks of investigation of trans swapping I have found swapping T350/400 with a 200 R 4 is a better choice.The 200 R 4 is the same length as both 350/400 and will sit perfectly in place without cutting drive shaft and other changes..Using a 700R4 entails to much cutting including drive shaft..Good luck in whatever you do..
Sal C nosal
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I'm probably dealing with some other issue affecting my difficulty getting a good start and transition to idle. I got a vacuum gage and hooked it up to a manifold vacuum port. Started the car. It kicked on OK and kicked off the high idle nicely. Then went to a very low after about 30 or 40 seconds. By very low I mean it would quit if put into gear. Then after a long period like that, perhaps another 40 to 60 seconds it settled in at 800 RPM in park. During this entire time the vacuum gage was fluctuating rapidly over a range of 3 to 4 in Hg. I've posted two photos one of the 600 and the other of the 800 RPM readings.
So, where do we start trouble shooting this?
As it once looked and hopefully will again
PS - I do hear a slight knock, but not sure if it's real. Does not sound like a lifter. I had a stuck lifter in the past and it was much more obvious.
|UPDATED|10/21/2017 2:50:59 PM (AZT)|/UPDATED|
|UPDATED|10/21/2017 2:50:59 PM (AZT)|/UPDATED|
As it once looked and hopefully will again
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.
2023 Accelerate Yellow HTC Stingray
Was your vacuum gauge hooked directly to manifold vacuum and not one of the carburetor modified ports? The vacuum at idle should be much higher than that and steady.
1973 L-82 4 spd
It was hooked to a three way manifold vacuum port. One hooked into a metal line (not the power brakes). I believe the one I was hooked into went to the cruise xducer - but that is laying in drawer so the other end of the line is plugged.
|UPDATED|10/21/2017 3:49:12 PM (AZT)|/UPDATED|
So I swapped the gage over to a rear port on the base of the carb. This feeds into a couple different lines off a tee. I teed the gage line into that so I could keep whatever else they ran going as the vac advance ties into it. This source had some fluctuation also, but a lot less. The reading though was the about the same. I also ran the throttle up a couple times. I noticed when I opened it quickly the pressure dropped to 10" before rising. I ran up to between 2000 and 2500 RPM (by ear). I held about 20" but when I let it drop at first it rose up to 21 or 22".
Note, this engine is 37 years old with a little over 90,000 miles. It sat for the last 13 years being started or once or twice per year.
|UPDATED|10/21/2017 3:49:12 PM (AZT)|/UPDATED|
As it once looked and hopefully will again
It looks like a valve adjustment is in order.Looks like possibly too loose of the rockers..As have been mentioned the VAC gauge should be at a minimum of 14 in.vac and steady,no flocculation and may stop the "clacking"noise.
Sal C NOSAL
Could well be. I replaced the valve seals back around 2000. Replaced the rockers with compcam roller tip rockers - didn't want to deal with higher covers roller rockers would have required as it was all I could accomplish to fit the covers under the air injector hoses (which have gotten lost somewhere since then). The rockers had a slight bump in ratio to 1.52 from 1.50. Their geometry pushed tips rocker tips off center so I did change out the pushrods to something a little longer longer I believe.
As far as adjusting them I followed the shop manual which was rotate the engine until a given cylinder was top dead center and then you could adjust intake cyl X and exhaust cyl Y, etc. Per the manual the adjust was tighten until zero lash and then loosen a certain amount. This was obviously all done statically. One thing I do recall was the compcam stud nuts were so damned tight I thought I would snap the studs so I used the stock nuts instead.
Any thoughts on all of that.
As it once looked and hopefully will again
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.
2023 Accelerate Yellow HTC Stingray
I've found the best way to adjust hydraulic lifters is the engine running method. Just loosen the lifter until the engine starts to run rough and then tighten 3/4 turn. Be sure to use the oil stoppers on the rockers to prevent a mess.
This method can highlight a bad cylinder.
If this doesn't help, then need to do a compression check and a leakdown test.
|UPDATED|10/21/2017 10:08:34 PM (AZT)|/UPDATED|
|UPDATED|10/21/2017 10:08:34 PM (AZT)|/UPDATED|
1973 L-82 4 spd
No luck with the valve readjustment. Set at 3/4 turn past zero lash. '80 shop manual says 1 turn which is what I adjusted them to last time. So I backed off a little as the manual makes no allowance for the different cam in the L82 and my recollection is a cam with more overlap ought to be backed off a little. I admit I didn't feel like spraying oil around so I didn't adjust them running. Anyway, a couple hours spent and no change.
|UPDATED|10/29/2017 3:20:35 PM (AZT)|/UPDATED|
|UPDATED|10/29/2017 3:20:35 PM (AZT)|/UPDATED|
As it once looked and hopefully will again
Vince, Sorry to hear your adjustment did solve the problem.May I make a suggestion?? with cap on distributor,mark the base (where cap meets dist.) with a very bright marker below each spark plug post.Remove #1 plug and have someone "bump" starter until you are at top dead center #1(air should push thumb off spark plug hole).Remove cap and note position of rotor..It should be pointed at mark on base of distributor.Now you are ready to adjust valves at TPC #1..Do your adjustments as you did before.Get to zero lash then 3/4 turn.Rotate crank to next in firing order(#8),and continue on forward. Good Luck... Sal C
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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