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Mixture screws do nothing, replaced carb, still nothing.
1972 Cutlass 442 (clone) with olds 455, TH400, MSD distributor and box, no vacuum advance, Edelbrock 1411 750cfm and performer intake. I think it has an aftermarket cam, but I don't know what it is, and headers, compression at cylinders is 170. Engine probably has had other work done to it. It's a guess, but I believe the car was setup for drag racing at one point in its life.
I'm at a loss on what to do next and could use some advice on where to go from here.
Car was running very rich and getting 4mpg. Tried adjusting mixture screws and they had no effect on vacuum, unless they were fully closed. Idle screw did effect idle. Vacuum seemed low at about 13-14.
I rebuilt the carb and adjusted floats. No change.
I replaced the carb with a refurbished carb (old one was a 600cfm and too small anyways), the same issues exist: Bad mpg and mixture screws do nothing. The new carb is a Edelbrock 1411 750 cfm.
I checked timing, it was about 10 degree after TDC. I adjusted it drastically to maybe 30 BTDC (I don't have timing tape on balancer, so I'm guessing). The engine seemed to respond well and vacuum pressure went up to about 18. The mixture screws still had no effect and now the idle screw didn't work either.
I brought the timing back to a more reasonable 10 BTDC, pressure went down to 14-15, and now idle screw works but still mixture screws do not. I think my MPG is still bad as well.
I adjusted my fuel pressure regulator, dropped it down from 6 to 3, that didn't seem to have any effect on engine at idle. I brought it up to 4 thinking 3 is probably too low and test drove it. Engine seemed fine under WOT. Still no effect on the mixture screws and car smells heavily of unburnt gas.
I checked all vacuum lines, they all held pressure.
I don't think the issue is with the carburetor. I suspect there is something else that is causing the carburetor not to work properly. The carb could be clogged, or needing adjustment internally. I plan to take this one apart soon enough and check. It seems odd that both carbs would have the same problem though.
UPDATE: Starting at post #48
Here is a recap of the conversation:
- I need to find true TDC. Will do this eventually, lots of things in the way that are blocking me from getting to the balancer. I did put my finger over the #1 spark plug hole while a friend bumped the engine. The 0 mark on balancer looked to be aligned with the 0 mark on tab..
- I did a compression test and gapped my sparkplugs. They were pregapped at .035, but they were very off. I gapped them to .040.
- The engine will now not start unless my timing is advanced to roughly 40+ BFTD. Once the engine is started I can lower the timing to about 20, but if I leave it idling, the car dies after about 5 minutes. Then I have to rotate the distributor back to 40ish degrees to get the engine to start. I did mark my distributor before I started tinkering with timing, so I do know where it was originally. Putting it back to this mark, the engine will not start.
- I replaced the sparkplugs. and gapped them at .040.
- I have double checked firing order and understand the rotation is counterclockwise.
- Checked butterfly valves and throttle blades, they seem correct.
- Adjusted carburetor floats and used air to blow out everything. It was very clean
- If the timing is very advanced I can get the car started and it seems to idle well. If I put it in drive though, the rpms drop and the car pulsates from 600 - 900 rpm like the engine is gasping.
Engine is close to stalling when turning the mixture screws almost all the way in. I didn't want to force the screws to tightly, so didn't take it all the way closed.
You might want to watch this video to understand how the Edelbrock/Carter carb works. The screws on the front only change the mixture at idle and have nothing to do with cruising mixture(where your mpg is affected)
Thank you, I have watched a number of his videos and he does a good job at explaining things.
But, I'm not saying the mixture screws are the cause of my bad MPG or vice versa. With my admittedly limited knowledge, it seems like whatever the problem is could be causing the both symptoms.
I've seen mention that the timing could cause similar issues, so I've adjust that. Or a vacuum leak, or too high fuel pressure could also cause similar issues, so I've adjusted those as well.
I'm unsure as to what next I should try.
The VERY first thing to do is to perform a proper tune-up. In this EXACT order:
(1) Establish Dwell
(2) Set timing
(3) Adjust A/F mixture (use a vacuum gauge)
The VERY first thing to do is to perform a proper tune-up. In this EXACT order:
(1) Establish Dwell
(2) Set timing
(3) Adjust A/F mixture (use a vacuum gauge)
Did I mention EXACT order?
Done that.
1) HEI distributor, no Dwell to screw with (or am I mistaken?)
2) Set timing, set it to 8, like the sticker in my engine bay said, set it to (maybe) 30 just to see. Vacuum went way up as did RPM. Retarded it maybe 10 degrees ATDC, rpm and vacuum went way down. Then tried every setting timing to everything in between. Tried step 3 after every different timing setting, same results.
3) Adjusted mixture, screws had no effect. Used a gauge, no change unless screws were all the way in.
Done that.
1) HEI distributor, no Dwell to screw with (or am I mistaken?)
2) Set timing, set it to 8, like the sticker in my engine bay said, set it to (maybe) 30 just to see. Vacuum went way up as did RPM. Retarded it maybe 10 degrees ATDC, rpm and vacuum went way down. Then tried every setting timing to everything in between. Tried step 3 after every different timing setting, same results.
3) Adjusted mixture, screws had no effect. Used a gauge, no change unless screws were all the way in.
I question whether you did it correctly. Here's what I read and it does not bode well for performing a PROPER tune-up. You stated:
I checked timing, it was about 10 degree after TDC. I adjusted it drastically to maybe 30 BTDC (I don't have timing tape on balancer, so I'm guessing).
Guessing at your timing is not what I'd consider performing a proper tune-up.
I am guessing that it was at 30 degrees. As I said, I don't have a timing tape so that is just a guess. I only took it to this extreme as a test. It's not really important as the the exact degree it was at. What is important is that I then tested it at both extremes and tried many degrees in between.
if I didn't make that part clear, my apologies. I will go back and edit my original post to make it more clear.
This is NOT to take away from FIRST performing a proper tune-up - this means you MUST set the timing correctly. If you cannot set the timing correctly, there is no amount of fiddling with the carburetor which will assist in troubleshooting an issue. With that said, have you read this? I know you removed the 1406 you had on there and evidently installed a 1411. Again, the timing must be correct FIRST, no guessing it has to be dialed in. Don't be looking for what the vacuum gauge reads, what happens to the RPM, set the timing correctly then move forward.
Norm is correct, but even more fundamental than that is knowing what is inside the engine. If you don't know the specs on the cam, you have no idea whether you can even get an acceptable idle. You also don't know if the cam was degreed properly when it was installed or if the timing mark on the balancer is accurate. Trying to tweak timing and idle mixture without at least first confirming these variables is like polishing a turd.
Norm is correct, but even more fundamental than that is knowing what is inside the engine. If you don't know the specs on the cam, you have no idea whether you can even get an acceptable idle. You also don't know if the cam was degreed properly when it was installed or if the timing mark on the balancer is accurate. Trying to tweak timing and idle mixture without at least first confirming these variables is like polishing a turd.
Thank you Joe, I do not know anything about the cam and I get that it does effect timing. I wish the previous owner had included some info on this, but hey oh well.
I adjusted the timing at many different degrees and then tried the mixture screws. Am I incorrect in thinking that if it was close, within 10 degrees, that It would have been close enough that IF timing is why the mixture screws have no effect, that they would then at least have some effect on the engine?
I'm not trying to argue the importance of correct timing. I just am looking for what avenues to explore that could be causing these symptoms. Could a vacuum leak also cause these symptoms?
Go on ebay and buy an dial back timing light, I bought a very nice chrome plated old craftsman for 40.00 bucks a couple years ago. Easy to use so you get accurate timing info. You can find top dead center fairly close with your finger on the number one cylinder hole, plug removed then once the compression blows your finger out of the hole you can rock back and forth with a cheap wood chopstick..Watch it as you rock it to get as close to tdc as possible, now you can at least see if your balancer is showing the correct timing mark..its not the most scientific but at least you will know if your balancer timing mark is correct..then you can use your dial back timing light to get timing dialed in..one thing done, then eliminates that part of the equation..
Also hei ignitions don’t advance as much as the points dist. So your base/ idle timing should be between 14 and 18 degrees with the vacuum line to the dist. disconnected at idle. Then work from there. Make sure the secondary butterfly's are fully closed. If they are sticking open, your mixture screws will do nothing. Make sure your throttle cable isn’t holding the the throttle plates open either. Best bet set the timing to roughly above recommendations. Disconnect throttle cable from carb and try adjusting mixture. Your throttle cable my be too short and holding the plates open, which will render the mixture screws useless. Good luck
If the throttle blades are open too far the mixture screws won't have much effect on the idle. Take the carb off and look at the throttle plate position from the underside. The transfer slot should just barely be exposed (see picture) if not you are crutching some other problem.
Go on ebay and buy an dial back timing light, I bought a very nice chrome plated old craftsman for 40.00 bucks a couple years ago. Easy to use so you get accurate timing info. You can find top dead center fairly close with your finger on the number one cylinder hole, plug removed then once the compression blows your finger out of the hole you can rock back and forth with a cheap wood chopstick..Watch it as you rock it to get as close to tdc as possible, now you can at least see if your balancer is showing the correct timing mark..its not the most scientific but at least you will know if your balancer timing mark is correct..then you can use your dial back timing light to get timing dialed in..one thing done, then eliminates that part of the equation..
Awesome! I just got got one at harbor freight for $30, probably cheap quality but reviews said it was okay. I've never used the dial back feature, but what you said makes total sense. I'll give that a try. Thank you!
Originally Posted by gs72
Also hei ignitions don’t advance as much as the points dist. So your base/ idle timing should be between 14 and 18 degrees with the vacuum line to the dist. disconnected at idle. Then work from there. Make sure the secondary butterfly's are fully closed. If they are sticking open, your mixture screws will do nothing. Make sure your throttle cable isn’t holding the the throttle plates open either. Best bet set the timing to roughly above recommendations. Disconnect throttle cable from carb and try adjusting mixture. Your throttle cable my be too short and holding the plates open, which will render the mixture screws useless. Good luck
Thank you!! I will dig into this today.
Originally Posted by dragline
If the throttle blades are open too far the mixture screws won't have much effect on the idle. Take the carb off and look at the throttle plate position from the underside. The transfer slot should just barely be exposed (see picture) if not you are crutching some other problem.
Ahhh, thank you! I did watch a video on exactly this, but forgot to check it.
You can easily add a timing mark to show 36 degrees. Measure 2 inches to the right of TDC, make a new timing mark, that mark will be 36 degrees.
Disconnect the vacuum advance, plug the vacuum line. Connect your timing light, start the engine. Slowly rev the engine until the timing stops advancing, put your new timing mark at the 0 point on the timing tab. Bingo! You just set the timing at 36 degrees.
You can easily add a timing mark to show 36 degrees. Measure 2 inches to the right of TDC, make a new timing mark, that mark will be 36 degrees.
Disconnect the vacuum advance, plug the vacuum line. Connect your timing light, start the engine. Slowly rev the engine until the timing stops advancing, put your new timing mark at the 0 point on the timing tab. Bingo! You just set the timing at 36 degrees.
Matt, unless I'm wrong, the OPs first post said he doesn't have vacuum advance.
I'm on my phone and a bit distracted, did I miss a post saying my timing should be at 36, or was that just an arbitrary number that just coincides with being 2 inches from tdc?
Total timing is typically around 36º for most engines, and a line 2" from the TDC mark on the balancer is around 36º.
Note that this is total advance and NOT initial advance. Initial advance is simply the total advance minus the mechanical advance, and gives a value that is easy to set during a tune-up.
I'm on my phone and a bit distracted, did I miss a post saying my timing should be at 36, or was that just an arbitrary number that just coincides with being 2 inches from tdc?
Simple math.
Determine the diameter of the balancer. Then figure the circumference (pi times the radius squared if I remember my math correctly) then divide the circumference by 360 (360 degrees in a circle) that’s how many fractions of an inch PER degree. Multiply that number by 36, that how far from TDC you need to measure for your new timing mark.
You can also use this method for marking the balancer every 90* for setting valve lash.
Most engines like 34-36 degrees for best power. Normally, the vacuum advance would add another 15 degrees for best economy at cruise. Since your distributor doesn’t have vacuum advance that’s one less thing to dial in.
The advantage of following Matt’s guidance is beneficial in particular if: (1) the harmonic balancer has slipped; and, (2) you may not be sure the harmonic balancer is of the same OEM size. Either (1) and/or (2) would not be unheard of. Be certain your zero timing mark is established at TDC on the compression stroke. A piece of tissue paper works well to get close (remove #1 cylinder spark plug), once you’re close a chop stick dropped into #1 cylinder works great to dial in top of the piston stroke to set TDC.
Thanks all for the advice! Things got weird and now I'm even more lost then before.
A friend suggested I do a compression test, just because. So I did. I also gapped the sparkplugs that were a bit off, gapped to .040. This may be irrelevant to anything, but my compression was high, all cylinders were right around 170. I'm pretty sure this car must have been used for racing. No vacuum advance on distributor, headers, high compression, lift bars and pretty sure there was a fuel cell in the trunk.
Since doing the compression test, the car won't start. I finally managed to get it running by drastically advancing the timing, to what appears to be about 40 degrees. Car won't start at anything less. Once it got up to operating temperature, I tried lowering the timing. I got it down to about 20 degrees and left it there idling at about 1100rpm for roughly 5 minutes until the car died. The car again wouldn't start until I advanced the timing back to 40. I've repeated this process 3 times. On my last attempt, at about 20 degrees, I put the car into neutral and it instantly died.
I tried to do a quick check of TDC. I put my finger on the #1 sparkplug hole and had a friend bump start the car. the timing mark on the balancer seemed to be inline with the 0 mark on the tab, or at least as close as this hillbilly test could show.
Thanks all for the advice! Things got weird and now I'm even more lost then before.
A friend suggested I do a compression test, just because. So I did. I also gapped the sparkplugs that were a bit off, gapped to .040. This may be irrelevant to anything, but my compression was high, all cylinders were right around 170. I'm pretty sure this car must have been used for racing. No vacuum advance on distributor, headers, high compression, lift bars and pretty sure there was a fuel cell in the trunk.
Since doing the compression test, the car won't start. I finally managed to get it running by drastically advancing the timing, to what appears to be about 40 degrees. Car won't start at anything less. Once it got up to operating temperature, I tried lowering the timing. I got it down to about 20 degrees and left it there idling at about 1100rpm for roughly 5 minutes until the car died. The car again wouldn't start until I advanced the timing back to 40. I've repeated this process 3 times. On my last attempt, at about 20 degrees, I put the car into neutral and it instantly died.
I tried to do a quick check of TDC. I put my finger on the #1 sparkplug hole and had a friend bump start the car. the timing mark on the balancer seemed to be inline with the 0 mark on the tab, or at least as close as this hillbilly test could show.
When you did your compression test, did you pull all the wires/plugs at the same time, or did you pull one wire and the plug individually, test that cylinder, put the plug back and wire back on, then move to the next cylinder and repeat the process?
The sparkplugs were pregapped at .035, but they were way off when I checked them, then gapped them at .040.
I then put in another set of plugs that were pregapped at .040 and double checked the gap.
Sorry, but you're all over the place. When are you going to find absolute TDC and find the absolute zero timing mark on your harmonic balancer and align that mark exactly at TDC? Until then, you're polishing a turd.
EDIT: BTW, "if" you seriously believe this engine was used for racing...there is a very, very good chance (as I have previously suggested): (1) the harmonic balancer has shifted &/or: (2) it isn't the OEM harmonic balancer.
"I tried to do a quick check of TDC. I put my finger on the #1 sparkplug hole and had a friend bump start the car. the timing mark on the balancer seemed to be inline with the 0 mark on the tab, or at least as close as this hillbilly test could show."
I know this isn't absolutely perfect, but if its only off by a few degrees, It's not going to be the cause of the car not starting unless at 40 degrees.
"I tried to do a quick check of TDC. I put my finger on the #1 sparkplug hole and had a friend bump start the car. the timing mark on the balancer seemed to be inline with the 0 mark on the tab, or at least as close as this hillbilly test could show."
I know this isn't absolutely perfect, but if its only off by a few degrees, It's not going to be the cause of the car not starting unless at 40 degrees.
You fail to understand the significance of a harmonic balancer which may either not be the same size as the OEM harmonic balancer or a harmonic balancer which has shifted. If either one or both cases is true, that timing mark is meaningless.
The correct Oldsmobile firing order? It's different than other GM V-8 engines.
Actually the firing order is 1-8-4-3-6-5-7-2, which is the same as on pretty much every GM V8 of the 1960s and 70s. I'm sure you meant distributor direction of rotation, but that isn't firing order. And for all who ever have a question about the firing order, it's cast right into the intake of just about every Olds engine made.
Well written w/ excellent advice...pay attention to the size of the harmonic balancer, location of the timing mark & the camshaft degree. In particular, note when an engine is used for racing (and you don't know how the cam was degreed), it is important to establish fundamentals (simple math, but you have to do the math).
Actually the firing order is 1-8-4-3-6-5-7-2, which is the same as on pretty much every GM V8 of the 1960s and 70s. I'm sure you meant distributor direction of rotation
Yep, that's what I meant - thanks for the clarification.
I used 1-8-4-3-6-5-7-2 for the firing order and a counterclockwise distributor rotation.
I will confirm TDC when I can. I have a fan shroud in the way, to remove it I have to remove the radiator. The shroud is blocking me from getting to the balancer, I can't get even get my hand in there to wrap something around it to measure. It's more then likely not the original, not much on the car seems to be. The car WAS running at 8 BTDC before I did the compression test and gapped the sparkplugs. Unless the person who broke into my house the other night decided to also swap my balancer while they were at it, I don't think that's the source of my new problem. In a few weeks I will have a couple days to tackle finding true TDC.
I used 1-8-4-3-6-5-7-2 for the firing order and a counterclockwise distributor rotation.
I will confirm TDC when I can. I have a fan shroud in the way, to remove it I have to remove the radiator. The shroud is blocking me from getting to the balancer, I can't get even get my hand in there to wrap something around it to measure. It's more then likely not the original, not much on the car seems to be. The car WAS running at 8 BTDC before I did the compression test and gapped the sparkplugs. Unless the person who broke into my house the other night decided to also swap my balancer while they were at it, I don't think that's the source of my new problem. In a few weeks I will have a couple days to tackle finding true TDC.
If it was running better with the plugs at .035, and ALL you did was change the gap, then why not set them back at .035? At least you'd be back to where you were.
The sparkplugs were pregapped at .035, but they were way off when I checked them, then gapped them at .040.
I then put in another set of plugs that were pregapped at .040 and double checked the gap.
