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 Post subject: b20 Irregular Idle
PostPosted: Tue Dec 31, 2013 5:35 pm 
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Joined: Thu Mar 31, 2011 9:15 pm
Posts: 67
Location: Lethbridge
Happy New Years everybody.
So the idle is a bit fast but steady until I shut it off for a few minutes getting gas or whatever. When I start back up it wants to stall and stays slow until I run at some RPM steady for a while.
Info - B20 in a 67 122, SU's, new plugs. wires and air filter as of last fall. Plugs are all burning nice except for #2 which is somewhat leaner than the others. Idle screws seem to affect speed about equally so I think they are even... New points, condenser, dist cap and rotor a couple years ago. They look clean to me. I recently cleaned and reset gap to the middle value, set timing to 10 deg btc. Looked steady at idle but kind of jumped around a bit at revs near 30 deg. Oh and the timing of the fourth cylinder looked a little more advanced than the first one. I think I read somewhere they are supposed to be identical. This may be related but it runs fairly steady through the RPMs now but one cylinder I'll assume bangs like crazy if I put the pedal down and then I have no hp. To me it seems like I may have a burnt valve but I'm not sure and would that cause the idle issue? I haven't put a gauge on the fuel line but I popped the hose off the other day and fuel sprayed all over the place so it isn't leaking there at least. I appreciate any thoughts.
Ian


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 Post subject: Re: b20 Irregular Idle
PostPosted: Wed Jan 01, 2014 7:57 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 2995
Location: Lethbridge, AB
A few thoughts…fuel for SU's is around 5-7 psi, so it shouldn't spray around everywhere. Check the height of the floats and the condition of the float jets. Stay away from the aftermarket jets - they are crap. You have to do the compression test or better yet, a leak down to test for the burnt valve.

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 Post subject: Re: b20 Irregular Idle
PostPosted: Wed Jan 01, 2014 9:42 pm 
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Joined: Thu Mar 31, 2011 9:15 pm
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Great, I'll look that up tomorrow.


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 Post subject: Re: b20 Irregular Idle
PostPosted: Sat Jan 04, 2014 10:57 am 
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Joined: Thu Mar 31, 2011 9:15 pm
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Location: Lethbridge
The fuel level in the float bowls are even at 1.5" but honestly carbs are over my head and I don't know what I'm looking for. Probably the best thing is just to get them rebuilt. My question today is this. I have four or five spare carbs and do I just grab one out of the box or is it worth taking them apart to look for best parts? My dilemma with that is that I can't have my car off the road at the moment... And where do I find rebuild kits?


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 Post subject: Re: b20 Irregular Idle
PostPosted: Sat Jan 04, 2014 6:15 pm 
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Joined: Thu Mar 31, 2011 9:15 pm
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Location: Lethbridge
Ok compression is front to back, 125,120,120,130. Wet 140,135,142,142
So I guess that means rings are bad?
Fuel pump 3 psi, steady, no leak
Manifold vac is 14
I don't know what that all means.


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 Post subject: Re: b20 Irregular Idle
PostPosted: Sat Jan 04, 2014 11:55 pm 
Somehow completely sideways in 4th

Joined: Thu Nov 10, 2011 11:43 am
Posts: 238
Location: Regina, SK
Just curious - but can you elaborate on this comment some more - "This may be related but it runs fairly steady through the RPMs now but one cylinder I'll assume bangs like crazy if I put the pedal down and then I have no hp."

Not being familiar with B20's or SU's - I would still suggest a possible vacuum leak, or the condenser might not be doing its job very well.

To me your compression looks OK, and all are within 10%. It is showing wear, but it should still run fine.

Could the 3 psi be too low? (Sounds about right for Webers though)

Rabin


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 Post subject: Re: b20 Irregular Idle
PostPosted: Sun Jan 05, 2014 11:12 am 
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Joined: Thu Mar 31, 2011 9:15 pm
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Location: Lethbridge
Well I can accelerate slowly up through rpms and the engine runs smooth enough, but if I step on the gas hard at any rpm the engine bangs. I don't know how else to describe it. Its kind of like trying to drive a cold car too hard and it just doesn't like it. The condenser is only a couple of years old but maybe I should just replace it. Last night I had the air cleaner off and noticed that the piston on the rear carb moved much slower than the front one. I had to lean it up about a full turn before they responded the same, which I don't understand because the plugs were burning the same light tan color. I'll take it for a drive today and see what happens. Maybe the rear cylinders were flooding.


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 Post subject: Re: b20 Irregular Idle
PostPosted: Sun Jan 05, 2014 8:33 pm 
Somehow completely sideways in 4th

Joined: Thu Nov 10, 2011 11:43 am
Posts: 238
Location: Regina, SK
You say it bangs - but do you think it could be backfiring? I find it if backfires through the intake it's more of a cough, but if it's backfiring out the exhaust then it's it's more like a bang or gun shot / fire cracker.

If backfiring I'd be looking at the ignition system again. New condenser, and ensuring the points are in good shape is a must. If the condense is weak - then the points burn up pretty quick...

Rabin


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 Post subject: Re: b20 Irregular Idle
PostPosted: Mon Jan 06, 2014 8:29 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
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Location: Calgary, Ab
If your carb pistons are moving at different rates, you've got a synchronization problem or a mechanical problem. Your front carb could be opening more quickly, your springs could be different/warn/corroded, your pistons could be sticky and dirty, your front carb damper could be filled with different volume or viscosity of fluid, or your rear two cylinders aren't pulling as hard. That final point could be a misadjusted rockers or a worn out camshaft.

Regardless of electrical diagnosis, you need to deal with that at some point. Adjusting rich/lean isn't going to make a difference to how quickly the pistons move, only to the mixture on that pair of cylinders.

If your front piston is only jumping quicker and not further, it could be leaning out in the transition and causing your rapid acceleration backfires, if that's indeed what you're hearing.

Keep moving on the electrical tune-up though - check your points condition and setting, as they need constant adjustment. Maybe time for an upgraded distributor? How warn are your distributor shaft bushings - what kind of play have you got there? What about your advance/retard mechanism?

I'm not a huge fan of wet/dry compression tests as a guide to warn engines - oil is incompressible, so squirting an incompressible fluid into the cylinder will raise the compression ratio and therefore the compression pressure. Keeping the volume of oil small and consistent between cylinders is essential. Having said that, three cylinders jumped 12-15 psi and the fourth jumped 22 psi, so you might have a small problem there. I doubt it's causing you this issue, though...


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 Post subject: Re: b20 Irregular Idle
PostPosted: Mon Jan 06, 2014 3:40 pm 
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Joined: Thu Mar 31, 2011 9:15 pm
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I never thought about the oil on the wet test and I very well may have added more oil on the last cylinder. I'll change out my condenser and have someone check the points for me. The distributor shaft does have a little bit of play, I don't know what's normal there. I've plugged off the vacuum there as I couldn't find any vacuum on the rear carb. I was assuming the mechanical advance is fine as the timing light shows it advancing to 30 deg with an increase in rpm. Dampers are filled to where the plunger has 9/16 of an inch to go. On that note I can't find how much to put in there and I have only used ATF. Thanks for all the input.


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 Post subject: Re: b20 Irregular Idle
PostPosted: Mon Jan 06, 2014 5:35 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 2995
Location: Lethbridge, AB
Just quickly...to fill the dashpots, put in some ATF (or whatever you use) and then cover the top of the plunger (you put it back on the carb - the piston thingy) with a rag and raise the piston up to the top of the stroke. This will push out the excess oil through the hole and you're now set. They should raise in perfect sync when bliping the throttle. Compression numbers seem fine. No shaft wabble on the distributor is about right (if yours wabbles, that's no good).

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Coburn Performance - OCD comes naturally.


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 Post subject: Re: b20 Irregular Idle
PostPosted: Fri Jun 13, 2014 8:49 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 2995
Location: Lethbridge, AB
Just to bump this with some results...here's why we buy leak down gauges people.

Cylinder Leak %
1 60%
2 100%
3 20%
4 100%

It was showing cylinder wear on 1, intake and exhaust valves on 2 and 4. Looks like it's time for a new head.

A leak down gauge works by setting the piston at TDC then putting a given pressure into the cylinder. I use whatever line pressure is at my back air line (around 100 psi). The gauge is attached to the air line and the line pressure is set to zero on the gauge. Then the gauge is attached to the cylinder and the difference between the line pressure and how much pressure the cylinder can hold is measured.

Once connected, you listen to 4 areas for evidence of leaking (it's obvious) - intake valves hiss out the carbs (or intake manifold), exhaust valves hiss out the tail pipe, rings out the oil filler, and block crack or blown head gasket hiss (or bubble) out the radiator.

So Ian's got 2 piston's doing the work and it's a good thing they are out of phase or it would run even worse. Sure cylinder 1 probably has a worn bore or stuck rings or whatever, but the rest all shows leaks out the valves. So it's an easier and cheaper fix than scrapping the engine for a new rebuilt one.

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 Post subject: Re: b20 Irregular Idle
PostPosted: Sun Jun 15, 2014 11:01 pm 
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Joined: Thu Mar 31, 2011 9:15 pm
Posts: 67
Location: Lethbridge
Yeah... Thanks again for helping me out with that. It will be nice to drive again when I have more than one cylinder really working! I didn't know how bad it was until a dubious Craig says, "Well, lets see if it'll start up" [-o<


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