Slant Six Forum :: RPM diagnosis

Quote:

Blocking that hole will increase vacuum and make idle richer, good place for carb cleaner too. After hole is blocked see if it will idle slower then,may need mixture adjustment.

Thanks for the help and the pictures. I have a 1945 but the holes are the same. I was able to get it to idle at 650, it will actually idle now with the blade 100% closed @ 400. Idle enrichment is out about 8 turns for the best idle. Runs and drives wonderfully. It's great until I look over at the vacuum guage or smell the rich mixture. I have zero vacuum at 650 rpm and just a twitch of the needle while cranking. I tried multiple guages at multiple ports and even held a paper towel above the carb hoping the carb would at least try to suck in the paper towel. No luck, it's actually got no vacuum. Thoughts.

Author:	matv91 [ Tue Apr 21, 2020 7:38 pm ]
Post subject:	Re: RPM diagnosis
Where black arrow is air leak or clogged up.

Author:	matv91 [ Tue Apr 21, 2020 7:42 pm ]
Post subject:	Re: RPM diagnosis

Author:	matv91 [ Tue Apr 21, 2020 7:47 pm ]
Post subject:	Re: RPM diagnosis
tighten up those 3 screws at bottom up,but not much.Where that arrow is ,that screw tends to strip.

Author:	davidrad [ Thu Apr 23, 2020 7:39 pm ]
Post subject:	Re: RPM diagnosis
I have a 1945 carb that is NOS. I haven't had a good enough tune yet to diagnose changing anything. I did blow out those two holes. I also put the vacuum guage on and started turning the enrichment needle eft until the idle evened out and got the highest vacuum. Then I turned the hot idle screw down to 650 and it's great. It runs great but I was shocked to see that I have zero vacuum at idle in the manifold. I also went back and counted how many turns the idle enrichment needle is out and it's 11 turns. Something in that carb is just wrong. Or my engine is just done. The vacuum advance is on ported vacuum btw.

Author:	davidrad [ Fri Apr 24, 2020 11:15 pm ]
Post subject:	Re: RPM diagnosis
Quote: Blocking that hole will increase vacuum and make idle richer, good place for carb cleaner too. After hole is blocked see if it will idle slower then,may need mixture adjustment. Thanks for the help and the pictures. I have a 1945 but the holes are the same. I was able to get it to idle at 650, it will actually idle now with the blade 100% closed @ 400. Idle enrichment is out about 8 turns for the best idle. Runs and drives wonderfully. It's great until I look over at the vacuum guage or smell the rich mixture. I have zero vacuum at 650 rpm and just a twitch of the needle while cranking. I tried multiple guages at multiple ports and even held a paper towel above the carb hoping the carb would at least try to suck in the paper towel. No luck, it's actually got no vacuum. Thoughts.

Slant Six Forum https://www.slantsix.org/forum/

RPM diagnosis https://www.slantsix.org/forum/viewtopic.php?t=64784	Page 2 of 2

Author:	volaredon [ Sat Apr 25, 2020 7:05 am ]
Post subject:	Re: RPM diagnosis
Quote: Quote: Blocking that hole will increase vacuum and make idle richer, good place for carb cleaner too. After hole is blocked see if it will idle slower then,may need mixture adjustment. Thanks for the help and the pictures. I have a 1945 but the holes are the same. I was able to get it to idle at 650, it will actually idle now with the blade 100% closed @ 400. Idle enrichment is out about 8 turns for the best idle. Runs and drives wonderfully. It's great until I look over at the vacuum guage or smell the rich mixture. I have zero vacuum at 650 rpm and just a twitch of the needle while cranking. I tried multiple guages at multiple ports and even held a paper towel above the carb hoping the carb would at least try to suck in the paper towel. No luck, it's actually got no vacuum. Thoughts. 8 TURNS?? That is over 4 times where it should be... rarely when everything else is right, do I have an idle mixture screw much over 2 turns out..... something definitely is not right.

Author:	slantzilla [ Sat Apr 25, 2020 9:40 am ]
Post subject:	Re: RPM diagnosis
Where is the initial timing when it's at 600 rpm? With the idle screw 8 turns out it shouldn't run at all. You seem to have multiple issues going on.

Author:	GregCon [ Sat Apr 25, 2020 6:01 pm ]
Post subject:	Re: RPM diagnosis
Maybe your kickdown linkage is hanging up and keeping the throttle open a bit. It's quite hard to get a Slant to 3000RPM with just a vacuum leak. Have you checked the PCV hose/valve? It'd take a hole that big to ever get close to 3000RPM. I don't think it's possible for any Slant to ever have no vacuum at a 650RPM idle. A Slant Six produce vacuum like a Hoover. Maybe your gauge is bad.

Author:	wjajr [ Mon Apr 27, 2020 6:52 am ]
Post subject:	Re: RPM diagnosis
Seams like throttle plate is not fully closing for whatever reason, be it hanging up on sides of throat, or linkage/cable binding somewhere between gas peddle and throttle shaft. I agree with Josh, idle circuit is plugged, and engine is running off of transition circuit. Remove carburetor, clean all internal passages, blow every passage out with compressed air. While carb is on bench, make sure throttle plates can seat without sticking closed, or hanging up in a cracked open position. Adjust throttle stop such that throttle plates just contact throat, and not bind. Play with choke by setting it and working the throttle feeling for binding. Place a force on throttle shaft as it would be exerted by its return spring, and feel for binding while rotating throttle shaft. Is the throttle shaft loose or sloppy due to egged out holes in base of carb? Idle air adjustment screw, starting by gently seating it, should be turned out close to 1.5 turns. End mixture adjustment should be no more than (+ or -) an 1/8 turn from the initial 1.5 setting. Do you have one of the porous cast aluminum intake manifolds? If you have a cast iron intake manifold is it warped or cracked not able to seal? Have you checked valve lash setting?

Page 2 of 2	All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/