1972 Tioga 360 Missing Issue

87Itasca · May 21, 2016, 09:31 PM

Hi all,

A couple friends of mine have a nice little 1972 Tioga with a 360 that they are trying to get back on the road. Last year, they performed a tuneup, and it ran good afterwards. He drove it about 15 miles, with no issues. Camped out overnight, and the next day, he said he had a hard time starting it, then it ran with a bad miss the entire way home. He hasn't messed with it in about 7 months because of this. I am trying to help them get this straight, so that it can get some new rubber, then more issues can be addressed.

We have checked the spark, it is getting spark from the cap through all the wires, through the plugs. On the second cylinder from the pass. rear, it is a dead miss. We did a compression test, and the cylinders on the right bank read 110-95-115-125. The one with low compression is the problematic one. Is that too low to compress the fuel properly?

The plugs are all excessively black, but not enough to seem to foul the plugs. I base this off of seeing the spark jumping from the tip of the plug as the engine is cranking over. I swapped the suspect plug out with another known good one with no success.

I can't imagine I'm not getting air, so I'm thinking either the compression may be the issue, or possibly a fuel delivery issue. It has the original carb, but it has always been my understanding that the carb just dumps the fuel in the intake, and the vacuum from the engine pulls it into each cylinder.

The engine is hard to start, but once it does, it runs and idles as well as it can on 7 cylinders.

Can a carb problem cause a fuel delivery issue to just one cylinder? I wouldn't think so, but I am not well versed on carbs, especially Mopar stuff.

Anything you guys can think of would be really helpful, they love this thing, but are at wits end as to what to do with this issue.

Rickf1985 · May 22, 2016, 11:34 AM

Have you checked for vacuum leaks? How many miles are on it? Possible timing chain jumped? Take distributor cap of and with a wrench turn engine until the rotor starts to turn and then turn engine back the other way and see how far it goes before rotor starts to turn. Should be almost no lag at all, if more than that you may have a bad timing chain. Those compression readings are not all that bad, I have seen worse and run. Did you do the compression test with the throttle held wide open the whole time?

87Itasca · May 22, 2016, 07:03 PM

Hi Rick,

No broken hoses that we could see. Sprayed everything down with some brake cleaner with no real change in engine RPMS.

Would a timing chain only affect one cylinder though? I've never dealt with a sloppy chain before, and am not really aware of what the symptoms are. Do these have phenolic timing gears?

The odometer shows 57,XXX, but when he got it the speedo able was busted. New cable fixed the odometer and speedo. He says he doubts the last owner would have done a lot of driving it with an inoperative speedometer. I can attest to seeing some blowby out the tailpipe when it's running, so I don't really know what the mileage is.

It will, when running, occasionally make a littke 'pop' sound here and there, and it has backfired slightly once or twice when starting, resulting in smoke coming out of the carb.

Rickf1985 · May 23, 2016, 10:14 AM

You may have to pull the valve cover on that side and make sure the rocker arm is on and working and that you do not have a bent pushrod. A timing chain will not usually make just one cylinder miss but with slightly low compression in the one cylinder and valve timing off it could be possible. 50,000 is low for a timing chain failure. Have you checked the plug wire for resistance? I know you are getting spark with the plug out but that does not mean you are getting spark under compression. A bad plug wire will cause this issue.

87Itasca · May 23, 2016, 09:21 PM

I haven't checked the resistance of the wire, but I did swap it out with another wire, and the misfire stayed with the same cylinder.

If the pushrod are working properly, this really gets kind of perplexing.

Rickf1985 · May 24, 2016, 09:11 AM

Have you run a vacuum gauge on it. The readings on the gauge will tell you a lot about what is going on in the engine. Unfortunately it is impossible for me to tell you what the readings are without actually being there to see it.

87Itasca · May 24, 2016, 10:00 AM

No, that's something I need to do, in addition to pulling the valve cover. Maybe this or next weekend. The motorhome isn't close to me, so it's a little trek out there.

Wouldn't a vacuum gauge be really erratic with a misfire anyway? I didn't think it would be much help, which was why I didn't bother bringing the one I had.

M & J · May 24, 2016, 11:13 AM

I googled it, as my gauge came with detailed instructions. There are a wealth of videos and web pages for interpreting vacuum gauge readings. Here's one:

http://www.gregsengine.com/using-a-vacuum-gauge.html

Rickf1985 · May 24, 2016, 12:03 PM

It depends on the reason for the miss. You are also looking for other things at the same time that could be a cause, like the timing chain.

87Itasca · May 30, 2016, 09:52 PM

Hi Rick,

Pulled the valve cover off today while we rolled the engine over. All seems well. The valves are moving as they should be. Pushrods do not seem to be bent, and the rocker arms are not loose.

Hooked the vacuum gauge up to an unused port at the base of the carb, and we got an average reading of 12-14 in. hg. The rings are definitely worn, when the throttle is punched it goes all the way down to zero and rebounds to 21-22-ish before returning to 12-14. The reading is fairly steady, I would think light fluctuations would be due to the misfire, but perhaps not.

Unfortunately it stalled, and we were unable to restart it before wearing the battery down. It has a bad habit of backfiring out of the carb pretty regularly when cranking. Almost started a fire more than one.

I'm fairly confident the timing is too far advanced, but I don't think that would affect the dead miss on just one cylinder. Could be wrong through.

Adjusting timing is one thing I've never really learned. Not sure if it's just as simple as disconnecting/plugging the advance hose, and rotating the dizzy slightly while it's idling, or if I need a timing light and a bunch of other stuff.

turbinebronze · May 30, 2016, 11:15 PM

You might want to try a leak down test. A leaking valve could cause the problem (hard to think it would happen over night..)
I wanted to throw the spark plugs under the bus, (especially Champions) but I read you moved them around.
(my 2 cents, Craig)

Rickf1985 · May 31, 2016, 09:16 AM

Well, the carb is not an ideal place to tap for vacuum unless you know for sure it is manifold vacuum but let's assume it is. That is a real low reading. You are telling me now that you do not have any idea if the timing is right or not?! Well, Yes, you need a timing light to set it and the vacuum advance has to be off and plugged. You basically have to do a complete tune up before you can diagnose the problem. But if you set the timing with a light and it is correct and the vacuum is still that low and you have consistent carb backfires and you have verified that the accelerator pump is working, I would venture you have a timing chain issue. Bad rings will not cause backfires. If the timing chain jumped a link then the cam timing will be retarded and the intake valves will be staying open to late and ignition will be firing back through the still closing valve. You should be able to check a loose chain by cranking the engine with a wrench in one direction while watching the rotor in the distributor, stop turning in that direction and go the other way, the rotor should turn almost instantly. If you turn the crank and the rotor lags behind by more than a couple degrees then the chain is bad.

87Itasca · June 02, 2016, 09:40 AM

I'm just providing information as it's provided to me.

He didn't mess with the actual timing with a timing light, he was tweaking the distributor slightly.

I suspect a faulty accelerator pump as well, it is very hard starting, if you use a spritz of starting fluid in each barrel, it pretty much fires right up. Once it was running, it would only surface as a fuel delivery problem under moderate throttle, correct?

Was going to check the chain, but it was raining heavily on Memorial Day, and I wasn't going to get in a puddle of water and crank the engine back and forth.

Rickf1985 · June 02, 2016, 10:04 AM

You can look down the carb with it not running and hit the throttle all the way and you should see a solid stream of gas on the two primary barrels. If it is just a little or a short squirt then the pump is bad. It will bog and backfire if you hit the gas fast but if you ease onto the gas slowly it will be fine. Another thing to check is one good backfire can blow the gasket out from under the carburetor base so you may have a vacuum leak under the carb base which could be giving you both the backfiring and the low vacuum reading.

87Itasca · June 05, 2016, 08:41 PM

Hi Rick,

I should have known better than to ASSume. Never checked the wire routing because he said he replaced them one at a time, and (to my understanding) the issue popped up after the fact.

Turns out, #6 and #8 were crossed. Good grief.

Question though, is there a procedure for adjusting the timing at the distributor without using a timing light? What I did was get the engine hot, disconnect the vacuum advance, and tweak it until I got a vacuum reading of around 18. The rings are worn, so I figured 20-21 in/hg would be too advanced. Then I hooked the distributor advance back up. The engine e sounds noticeably better now, and the idle sounds about right also.

Rickf1985 · June 05, 2016, 11:07 PM

You can set the timing with a vacuum gauge, if the dogbox is not that hard to get off or you can stand driving with it off set the timing to the best vacuum and see if it pings under normal driving when it is up to normal operating temp. If it pings back it up 2 degrees and try again, if it still pings then back it 2 more degrees. You get the point. Once you get it where you want it then button it up but be prepared to have to back it up just a bit more somewhere down the road. It always seem to run good until you get a full load in it and are going somewhere. If it kicks back on the starter at anytime then it is too far advanced.

87Itasca · June 06, 2016, 08:09 AM

Hi Rick,

Sounds like the best plan of attack then. Do you do this when driving with the vacuum advance hooked up, or capped off?

Rickf1985 · June 06, 2016, 10:48 AM

When driving you have everything set up as you would normally. If you are not using a timing light then you really do not know how far you are changing it anyway so really all you have to do is stop, tap it back a hair and try again until you get it where you want it. Doing it that way you do not have to disconnect anything, you don't even have to shut it off. Leave the lockdown bolt tight enough that the distributor will not move on its own but you can still move it with a tap from a hammer or screwdriver handle. Hammer handle! Not the hammer head!!! You can buy a decent inductive timing light for 30 or 40 bucks.