After the carb rebuild the truck runs great...until it gets hot. After a lengthy drive I am noticing almost like a miss or stumble when starting from a stop. It's smooth as glass until it gets really hot. Also runs fine once moving.
I pulled the plugs and cleaned them. They were a little oily/sooty. Re-adjusted the carbs and synched them last night. Haven't had a chance to test it.
Any ideas where to look if I didn't get it?
Slight miss when engine is hot
Moderator: TechMOGogy
Slight miss when engine is hot
1973 712M
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
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Todd from what you are stating something sounds amiss like mixture or richness.
Is there anyone in town who can do a two gas analization for you?
Perhaps that badge and uniform can pull a string or two!
I look after our local "Old Bill" for keeping an eye on the shop in the small hours with a regular pat on the back phone a call to pub' relations after observing patrol night time actvities on our surveillance systems.
A good starting point is about 3.00% CO and 245ppm HC's at idle and a good engine shouild be giving about 2.00% at 2500r/m with HC's in the 200/300 range. O2 should be around 9.5 or better.
If you see a high HC figure at idle suspect over advance, a vaccum leak, or miss firing. If high HC's at revs suspect a heavy vac leak , missfiring or really excessive advance.
Hope that helps
Cheers Dennis
Is there anyone in town who can do a two gas analization for you?
Perhaps that badge and uniform can pull a string or two!
I look after our local "Old Bill" for keeping an eye on the shop in the small hours with a regular pat on the back phone a call to pub' relations after observing patrol night time actvities on our surveillance systems.
A good starting point is about 3.00% CO and 245ppm HC's at idle and a good engine shouild be giving about 2.00% at 2500r/m with HC's in the 200/300 range. O2 should be around 9.5 or better.
If you see a high HC figure at idle suspect over advance, a vaccum leak, or miss firing. If high HC's at revs suspect a heavy vac leak , missfiring or really excessive advance.
Hope that helps
Cheers Dennis
OOOps no customer bashing now
I'll try to locate someone with an analyzer. There is a guy in town that specializes in classic and or racing Porches. He offered to give them (carbs) a look see after the racing season when he's not quite so busy.
I need to replace the idle adjustment screws too. Mine are scored up pretty bad from being tightened in too much apparently. I'm sure that won't help. I do have a bit of play in the rear carb throttle shaft, that I guess I better fix while I'm at it.
I need to replace the idle adjustment screws too. Mine are scored up pretty bad from being tightened in too much apparently. I'm sure that won't help. I do have a bit of play in the rear carb throttle shaft, that I guess I better fix while I'm at it.
1973 712M
On a side note, anyone ever heard of the Colortune system for adjusting mixture? Wonder if it would work on Pinz's?
http://www.carbtune.com/colortune.html
http://www.carbtune.com/colortune.html
1973 712M
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Colortune enquiries have come up on this forum before.
In short yes they work to certain extent and have appealed to the "weekend warrior" mechanic you wanted to adjust his carburetor mixtures etc without the aid of an analyzer.
Very popular in the 1970's with the UK Mini crowd the product has lost its appeal of late as cars have become more complex and less owners are inclined to fiddle with an injected/computerized car.
Dennis
In short yes they work to certain extent and have appealed to the "weekend warrior" mechanic you wanted to adjust his carburetor mixtures etc without the aid of an analyzer.
Very popular in the 1970's with the UK Mini crowd the product has lost its appeal of late as cars have become more complex and less owners are inclined to fiddle with an injected/computerized car.
Dennis
OOOps no customer bashing now
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Gents
Colortune or not, you really cannot beat an analyser for engine diagnostics.
Here's an example.
We have a well neglected Pinz in the shop which has needed a bunch of carb work including rebuilds etc. Having got it all back together it ran up OK, but I had to give the slow running jets an abnormal amount of "backout" to get a decent idle. Usually 3/4 of a turn should do it. This little bugger needed two turns!
A glance at the "zorst" showed a rich mixture to make it run.
So sniffing the tail pipe I get 3.30% CO and 1450HC's.
That tells me we have a very high level of unburnt fuel coming out as HC's
Really I have fudged the truck to run with a decent idle but I am polluting!
Now high HC's are caused by a lean mix or in this case a vaccum leak OR over advanced ign. A strobe check showed 7dgBTDC @ idle so the timing was good.
So I tell the apprentice "rip off all the carbs", 'tin covers", and "the manifolds".
He looked at me with dismay since we had spend a couple of hours installing and tuning???? The carburetors.
Having got the manifolds off we check for cracks, non found, but looking at the gaskets we see one at # 2 port is gasket has collapsed, (been so for a while) since the pulsation of the engine had caused the material to polish the head and gasket mating surfaces.
I havn't fixed it yet, but I am confident with new gaskets and hoses the truck will run with about 2.00%co and about 350hc's.
I have given you blokes a real life treatise on fixing carburetors, so just in case you have overhauled the instruments and don't get satisfactory results look further,like the manifolds etc.
Dennis
Colortune or not, you really cannot beat an analyser for engine diagnostics.
Here's an example.
We have a well neglected Pinz in the shop which has needed a bunch of carb work including rebuilds etc. Having got it all back together it ran up OK, but I had to give the slow running jets an abnormal amount of "backout" to get a decent idle. Usually 3/4 of a turn should do it. This little bugger needed two turns!
A glance at the "zorst" showed a rich mixture to make it run.
So sniffing the tail pipe I get 3.30% CO and 1450HC's.
That tells me we have a very high level of unburnt fuel coming out as HC's
Really I have fudged the truck to run with a decent idle but I am polluting!
Now high HC's are caused by a lean mix or in this case a vaccum leak OR over advanced ign. A strobe check showed 7dgBTDC @ idle so the timing was good.
So I tell the apprentice "rip off all the carbs", 'tin covers", and "the manifolds".
He looked at me with dismay since we had spend a couple of hours installing and tuning???? The carburetors.
Having got the manifolds off we check for cracks, non found, but looking at the gaskets we see one at # 2 port is gasket has collapsed, (been so for a while) since the pulsation of the engine had caused the material to polish the head and gasket mating surfaces.
I havn't fixed it yet, but I am confident with new gaskets and hoses the truck will run with about 2.00%co and about 350hc's.
I have given you blokes a real life treatise on fixing carburetors, so just in case you have overhauled the instruments and don't get satisfactory results look further,like the manifolds etc.
Dennis
OOOps no customer bashing now
Sure wish there was a reasonably priced analyzer for us "Shade Tree" types.
Dennis, would the loose fitting throttle shaft cause a vacuum leak like this?
I did notice the back carb (with the loose shaft) with the throttle stop screwed out completely, it still registers higher than the front carb screwed in a few turns. This gives me a smooth idle of about 800RPM. Reading on the synch guage for the rear is about 10, 8 for the front. This was as close as I could get them without the idle being well above 1200 RPM.
I did replace both the carb to manifold gaskets, pulled the tins and checked for leaks/cracks. Only thing I noticed was the loose throttle shaft.
Dennis, would the loose fitting throttle shaft cause a vacuum leak like this?
I did notice the back carb (with the loose shaft) with the throttle stop screwed out completely, it still registers higher than the front carb screwed in a few turns. This gives me a smooth idle of about 800RPM. Reading on the synch guage for the rear is about 10, 8 for the front. This was as close as I could get them without the idle being well above 1200 RPM.
I did replace both the carb to manifold gaskets, pulled the tins and checked for leaks/cracks. Only thing I noticed was the loose throttle shaft.
1973 712M
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Todd
If I can get my hands on this I might even offer my old 2 gas to the forum.
This is available from the "Hallowed Isles".
www.kanesupport.co.uk/desk/scangas/
Nice video too.
Can't wait to call my Bro who is in the trade in Gloucester to bag me one.
Cheers Dennis
I will answer your forum comment in due course, I am too engrossed in this tool to do anything at the moment.
D
If I can get my hands on this I might even offer my old 2 gas to the forum.
This is available from the "Hallowed Isles".
www.kanesupport.co.uk/desk/scangas/
Nice video too.
Can't wait to call my Bro who is in the trade in Gloucester to bag me one.
Cheers Dennis
I will answer your forum comment in due course, I am too engrossed in this tool to do anything at the moment.
D
OOOps no customer bashing now
That is nice. Bet it has a "nice" price too.lindenengineering wrote:Todd
If I can get my hands on this I might even offer my old 2 gas to the forum.
This is available from the "Hallowed Isles".
www.kanesupport.co.uk/desk/scangas/
Nice video too.
Can't wait to call my Bro who is in the trade in Gloucester to bag me one.
Cheers Dennis
I will answer your forum comment in due course, I am too engrossed in this tool to do anything at the moment.
D
1973 712M
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Todd
Thanks for the link. My missus bought the thing for me, I have just discovered.
To be specific the throttle shaft can affect vacuum levels if worn to excess.
I can imagine from what you are stating that getting a balance is a challenge. Usually I strike for 9.75 on those rotary balancers (which you apppear to have). If the engine runs lumpy/erratic I then adjust the mixture to get a nice tickover then "sniff the exhaust" with the analyser to get the best mixture and o2 levels I can. Once running nicely then run up to 1700 to 2200 and re-read the gases, then let it return to idle watching the HC's rise up then return to where they were originally.
Using a vaccum guage hooked to the stub on the manifold should show 14 to 16" of HG if you have the tune and valve clearances set right.
Hope that helps
Dennis
Thanks for the link. My missus bought the thing for me, I have just discovered.
To be specific the throttle shaft can affect vacuum levels if worn to excess.
I can imagine from what you are stating that getting a balance is a challenge. Usually I strike for 9.75 on those rotary balancers (which you apppear to have). If the engine runs lumpy/erratic I then adjust the mixture to get a nice tickover then "sniff the exhaust" with the analyser to get the best mixture and o2 levels I can. Once running nicely then run up to 1700 to 2200 and re-read the gases, then let it return to idle watching the HC's rise up then return to where they were originally.
Using a vaccum guage hooked to the stub on the manifold should show 14 to 16" of HG if you have the tune and valve clearances set right.
Hope that helps
Dennis
OOOps no customer bashing now
-
lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Excellent. Certainly looks like a great tool. Let us know how it works.
On the issue I am having. I had originally set my timing some months ago at the cold setting. It seemed to run fine. Anyway, I decided to check it while the engine was good and hot. Set it the static way with a circuit tester to exactly find out where the contact point was. Turns out hot the engine was WAAAAAAY advanced. Manual says 1-2mm before the mark when warm. It was probably 10X that much!! I can't believe it ran at all.
Haven't road tested yet, we'll see I guess.
On the issue I am having. I had originally set my timing some months ago at the cold setting. It seemed to run fine. Anyway, I decided to check it while the engine was good and hot. Set it the static way with a circuit tester to exactly find out where the contact point was. Turns out hot the engine was WAAAAAAY advanced. Manual says 1-2mm before the mark when warm. It was probably 10X that much!! I can't believe it ran at all.
Haven't road tested yet, we'll see I guess.
1973 712M