Today's Conundrum

[SaxMan]

A couple of weeks ago, I was driving Baby Blue when the motor began running rough inexplicably. I figured something got out of whack with the carbs or it was from the change in temperature. I've been tweaking the carbs, but the motor still runs very rough in the 1000 - 2000 rpm, starts to find itself again between 2000 - 2500, and then is as smooth as a baby's butt from 2500 to as far as I'm willing to push the motor (usually 4500 max). I also find myself losing power more quickly under load, like hill climbs, and once the revs fall into the 2000 rpm range, Baby Blue turns into "The Engine that Could", and even sounds like the engine is saying "I think I can...I think I can..."

I thought some of the roughness was from mixing the carbs overly lean, but richening the mixture hasn't had any affect. Richening the mixture gave me slightly better acceleration and bit better hill climb power, but not a significant difference and no change to the low end rough running. It almost feels like a cylinder is dropping at low rpms.

I'm thinking something else may be in play besides the carbs? Maybe a bad plug or plug wire, or perhaps the engine's timing is off? Any thoughts?

 

[Trevor Jessie]

Things you can check :
Check the oil in the rocker cover and see if there are any signs of water (white frothy oil).
When it is dark out, let the car idle and look around under the hood and see if you see any arcing.
Check the color of each plug after driving down the street, but do not let it idle too long before shutting it off.
Borrow a compression gauge and check the compression of each cylinder.

 

[AN5Sprite]

Have you had a look at the points and checked the timing since you got the car?

 

[SaxMan]

I'm running a Pentronix ignition system, so no points, but I haven't checked the timing since I first got the car. I was hoping to make it to spring and do a full tune up (as well as purchase all the various items needed, such as a timing light), but it sounds like I may have to bite the bullet a bit sooner.

The one thing I have noticed is that I've been losing small amounts of coolant for no apparent reason: No leaks on the ground, no smell and no white smoke in the tailpipe, but enough that the reservoir beneath the radiator cap drops by an inch or so after about a month, which has been only about 200 miles of driving right now (plus idle time adjusting carbs). I'm thinking possible early head gasket leak?

My bigger fear is that this and the various other issues cropping up are early indications of the 1275 getting ready to throw in the towel. I do know the engine has never been rebuilt. The odometer currently reads 8,000 miles, so we know it's gone at least 100,000 miles, although I think 208,000 is probably the more realistic number given that this car is 45 years old. Heck, for all we know, 308,000 miles is certainly in the realm of possibility. From reading these forums, I know that engine failure is certainly not nearly as catastrophic than it is with other types in terms of replacing or rebuilding the motor from both a mechanical and financial standpoint. I guess I'll just keep an eye on things and see how they develop.

 

[Bayless]

One thing to always remember. "90% of all carb problems are electrical." They do not just suddenly start not working right. The advice given above by Steve and Trevor is spot on.

 

[nomad]

When were the valve adjustment checked last? Closed up clearances = valve's leaking= equals rough running and if you go very far that way a guaranteed head rebuild.

Kurt.

 

[aeronca65t]

All excellent advice above.

Check valve adjustment, look for arcing plug wires or coil (as Trevor suggests, look at engine running in a dark place to spot any arcing).

Also look for cracked rotor or cap. If in doubt, change them (not too expensive).

Check resistance on spark plug wires with an ohm meter....they should all be about the same.

One of the easiest things is to put 4 new spark plugs......old plugs can get partly fouled and will still run but with weak low end performance. I never bother to clean old plugs. It's generally not worth it.

If things are still not right you can do a compression test. If all reading are within 15% you're probably OK.

If that's OK, then look more closely at carbs (see picture below):

Unscrew 3 screws in float chamber cover (the thing under #16) of each carb, remove fuel line and carefully lift up the float chamber cover. Do not damage float mechanism(#12, 14, 15). Look in float chamber for any sediment. If it's really dirty, remove the 2 screws of the piston damper cover (the thing behind #1 in the picture). Pull straight up. The piston and needle are inside it and may come with it. Be sure they don't drop out as you are removing it and don't bend needle (#6). Use a can of WD-40 with "straw" and blow into hole at bottom of float chamber. Clear spray should blow out of jet (#9). You can also blow WD-40 into jet and spray should come out at bottom of float chamber. Watch your eyes! If not...there may be dirt in there which can cause problems like your's. Sometimes these cars end up running on one carb (poorly, of course) because the other carb has a clogged jet.

It's always useful to change the fuel filter if things are dirty. Your fuel pump is probably OK (since the car runs better at higher speeds).

By the way, my '73 currently has only 19,500 miles on it and it was a mess when I got it. It would have been better if it had 100,000+ miles and had at least seen some use. Sitting around is no good for these cars.

 

[Jim_Gruber]

Nial
you've very succinctly covered carb cleaning and trouble shooting. This portion of your note will go into my Spridget Tech notes. Thanks.

 

[DanLewis]

SaxMan,

When you were tweaking the carbs, by any chance did you remove them and/or the intake manifold? I recently had a problem where the car ran really rough below about 1500 rpm. It turned out that there was a small vacuum leak in the manifold gasket when I had reassembled the intake system. Apparently at higher rpms there was enough air rushing through the normal channels of the intake system to pull fuel properly from the carb. At low rpms, however, the vacuum leak reduced the vacuum enough that fuel delivery was compromised - particularly to the one cylinder near the leak. When I finally took the manifold off, there was an obvious opening in the manifold gasket near one of the intake ports. I replaced the gasket and the problem was gone.

'Hope this helps,

Dan

 

[aeronca65t]

Dan reminds me of a very good point. I have noticed over the years that A series engines (1275, etc) will often develop a "loose" manifold after a while (allowing vacuum leaks).

It's worthwhile to check the manifold nuts for tightness.

 

[SaxMan]

Like most things that I've discovered with LBCs is that quite often problems tend to be multi-faceted. I think I have multiple issues in play with Baby Blue, but I figured we'd isolate them one by one. I ran a compression test today. At some point, a p.o. ran a test in the past and wrote the results down on the valve cover. Here are the comparisons. For my purposes, cylinder 1 is the one closet to the firewall:

Cylinder 1: 165 (old) / 150 (today)

Cylinder 2: 150 (old) / 80 (today)

Cylinder 3: 150 (old) / 75 (today)

Cylinder 4: 165 (old) / 150 (today)

Granted there may be disparities between compression testers, but I'd say there is definitely a problem with cylinders 2 & 3!

All four spark plugs were fouled, and cylinder #2's plug had no gap. Cylinder 3 & 4's plugs were almost completely carbon colored, while 1 & 2 had much lighter color, but were equally fouled. All had evidence of oil on the plugs. I did a cursory cleaning of the plugs to see if there was any improvement and because I had no replacement plugs available. Driveability did improve somewhat, but the rough running and lack of power is still apparent.

It's clear based on my previous post about the smokescreen Baby Blue is laying down that I have some valvetrain issues. I'll likely do the "dark room" testing this evening to check for arcing, then it's off to pull the valve cover and see what's going on in the valvetrain.

I think the front carb could probably stand for the inspection that Nial has suggested as well.

On the upside, I did find my coolant leak: The hose clamp from the small hose that goes from reservoir to the main radiator tank has snapped. I'll probably go ahead and replace both clamps and the hose.

 

[Bayless]

Could easily be a break in the head gasket between 2 & 3. But, time for a leakdown test, if you can, to better isolate the actual problem before you start tearing it down too far.

 

[SaxMan]

What is a leakdown test? I kind of catch the gist of what it would be, but how does one go about doing so on an LBC?

Update: The arcing test was negative.

Update 2: Looking at what's involved with the cylinder head, perhaps just checking the rocker clearances would be a good place to start before removing the cylinder head (which is recommended by British Leyland before doing a valve job)?

 

[Jim_Gruber]

Google leak down tester. With a compression tester and a couple if fittings and an air compressor you can build your own leak down tester.

 

[nomad]

I agree that I would check valve clearances first but, after that, low compression in adjoining cylinders sound's suspiciously like a head gasket leak. The cylinders of 2 and 3 have got the water passage between them and i would be more likely to suspect problems between the 3 and 4 or the 1 and 2 which have no water passage and a very thin bit of cast iron between the cylinders. Hope for the best and if there are major problems at lest its a good time of year to be without a LBC!
I built a fitting for leak down testing out of a old spark plug. Didn't need to do the test since applying a little compressed air quickly revealed a valve leak.

Kurt.

 

[AN5Sprite]

When I tried to make a fitting for a leak-down tester, I must have picked the wrong spark plug. The ceramic destroyed every tool I attacked it with! Eventually I gave up and spent the $3 on a store bought fitting. Anyhoo... Like Kurt I'm thinking the low compression on adjoining cylinders is more head gasket than valve related. Hopefully that's all it is and you caught it before any additional damage occurred. Check the clearances but count on pulling the head. Not really a big deal btw. Once you accept that you have to do it, it's not a hard process.

 

[AN5Sprite]

Also, to avoid confusion it's probably best to accept that the #1 cylinder is closest to the radiator and #4 is back toward the firewall.

 

[aeronca65t]

Here's a suggestion before you take things apart:

I'm not sure if you did those compression reading with a fully cold engine (not been run for at least 48 hours).

If not, make sure you do the compression testing with a cold engine and record numbers. It's best to do compression testing with ALL spark plugs out so engine spins over easy.
Then put plugs back in and warm up engine.
Remove all plugs a second time and do a second compression test. Just before you test each cylinder squirt a small amount of motor oil into the spark plug hole (maybe a half teaspoon of oil).

If the compression increases a lot, it is almost always piston rings. If there is little or no change, the problem is almost always valves or head gasket (or, less likely, a cracked head or cracked piston).

The overall effect of testing twice ("cold" and "hot") might be called a "poor man's leak down test" because it can help you figure out where the problem is.

Or, you can buy this leakdown tester from Harbor Freight for under $40 USD. I have one and it works fine. Don't forget that you also need a compressor with this tester.

https://www.harborfreight.com/cylinder-leak-down-tester-94190.html

 

[SaxMan]

Thanks. All good stuff. The compression test was done on a warm engine, per the instruments instructions, but with the remaining spark plugs intact. I'll try the cold compression test, and that Harborfreight leakdown tester looks good.

 

[58Custom]

Sudden low compression of 2 & 3 with no loss of coolant or no coolant contamination with oil suggests head gasket seal loss due to a receding blanking plug.

https://www.britishcarforum.com/bcf/showthread.php?85532-Head-blanking-plug