Hot Rods !!!Please Help Me With My Stumbly 283!!!

This is what my fear is. I know the engine needs to be gone through. I have another to hopefully rebuild this winter. I am just trying to get through the season. How do you determine that the cam has flattened? Is this something a compression test will tell you?

I am new to all of this so please bear with me!

 

From what Cactus has said it's a tip in stumble or hesitation. A flat cam is going to cause a misfire. Sometimes a hesitation can be mistaken for a misfire or vice versa, but he said it ran fine other than the stumble.

 

A real bad flat lobe on the cam can be seen turning over the motor with the valve covers off the flat lob will not raise the rocker arm up as far as the others, there fore not opening the valve as much, you can pull the intake and lifters and visually inspect the cam lobes looking down the lifter boars.
Re adjusting that rocker arm can limp you by for a while, until the lobe is completely flat.
We ran the 2gc carbs in the circle track cars for 15 years, the 2gc carbs have an issue with the power valve sticking if the bowl sits dry, causing random stumbling on acceleration, real pain in the arse to fiquire out,
working the valve open and close a few times before you put the carb back together and adding a little fuel to the bowl if its going to be awhile before its ran helps.

 

After new plugs, tightening loose ground to trans, ball in acc. pump, shortening PV spring, and trying it out, still the same! Poop!

Had a ticky rocker, see vid:



I adjusted that out and got rid of the miss/popping ( it would seem.)

I bought a new timing light just for Unkl Ian that is the dial back type. It also shows dwell which is at 35deg. The book says it should be 30deg but I assume Bubba set it to what he thought it should be for my application? I'll have to get ahold of him to verify.

I haven't checked total timing yet. It seems to idling best at about 18 deg initial? My balancer could have slipped though I did find tdc the other night and it seemed to jive. This is why I have been using the vac gauge instead.

"professional"

 

It sounds to me like you are most likely haveing a carberator problem. You no doubt have already run the valves more than once so I am got going to say that you have one tight as I normally would.

I have an exceptionaly good book on Rochester carbs over here. I don't have much in the line of transporation here these days but you are sure welcome to cruise over and borrow the book. it may have some insite that we are missing on your carbs.

 

Thanks for the offer Ben. I may have to drag You over here as well as the book!

 

I've been dicking with this thing all day. The miss is back at idle and higher rpm as well. I adjusted the valves, again. I am doing this hot/running loosening them till they tick, then tightening a 1/4- 1/2 turn?

Anyway, I finally did my first compression check, don't laugh- remember I'm new and have never done this stuff before.

The numbers are as follows:
1 -140
2 -130
3 -137
4 -125
5 -127
6 -140
7 -127
8 -130

Seems like an acceptable range for an old worn out engine, or not?

 

cactus, your doing good, heres a few important things to do and check. With all of the plugs out, have someone turn the crankshaft back and forth slowly, while you observe the rotor of the distributor. This will be a indication of timing chain slop or play. The rotor should move in conjunction with the crankshaft. Now heres something else to help you learn and diagnose your mill. Squirt a little oil down the cylinders that had the lowest compression and take the test again. For a old worn out mill with no known history, the readings aren't all that bad. The oil test will help you learn and diagnose. Also, when you adjust the valves with the engine running, back them off until they clatter and go just a little more. Now tighten them slowly until they quiet down/ stop ticking, and then 1/2 turn tighter. One other thing, when you do the compression test, you should hold the throttle wide open and the choke should be open as well. Disconnect the fuel line so you dont fill the crankcase with fuel. TR

 

Heres two other things to check. Look at the inside of the distributor cap real good for cracks or carbon tracking between posts. Then next time you have it running, you need to get it somewhere that its real dark, or just late at night outside. Now start it up and look for sparking down the length of each plug wire. In fact if you dont know the history of the wires, I would replace them. The ticky rocker deal, have you been using a ZDDP additive or oil with adequate amounts of Zinc and Phosphorus? Chances are if not you could have a lobe going flat. TR

 

I will try all this, thanks. I ran it in the dark last night looking for any arcing. The plug wires are all brand new. This is a car I built, well still building (link in signature line) so everything is new or gone through (except the engine, ha!)
The dizzy, cap, everything is all new. New coil(s), ballast resister supplied with distributer, etc.

I did the crankshaft rotor thing last night as well and had about 5 deg. backlash.

The oil I have been using does have the ZDDP. 30 or 40 wt Valvoline racing oil I think. I will have to look to be sure on the weight.

 

My chevy truck stumbled at low speeds and it turned out my timing chain had stretched and jumped a couple teeth, I replaced it and it quit the stumbling, so i think its your timing chain.

 

I hope this is not the case. I have checked for slack and the dots were aligned when I had the timing chain cover off last winter to inspect, paint and replace gaskets?

 

If you had the timing chain cover off and looked at the chain then I would say its ok, Have you checked your Points in the distributor?

 

If you have one of the thick spacers under your carb, take it off and bolt the carb down without it, just use the gasket. I had this exact same problem when i put a spacer under my carb hoping to solve the hot start problem I was having. Removed the spacer- no more stumbling. Still have the hot start problem though.

 

No spacer.

Thanks everyone. Keep 'em coming. I'm checking everything.

 

I see that you did a compression test. It looked ok for an old engine. A leak down test will tell you even more about the condition of your engine. A lack of cranking compression can be caused by various things. A leak down test will help determing where the loss of compression is going. It kinda sounds like you may have a couple of valves not seating very well.

 

How do I do a leakdown test? Would the valves not seating properly cause the stumble and now miss that I think I didn't realize I had before? I'll assume that #4 and #7 would have the suspect valves?

I am going to run the valve again today the way T R suggested. I keep finding conflicting techniques.

 

Burnt Valve right............?

 

(Shrugging shoulders) I dunno? Is there a way to tell without tearing it down?

 

It COULD be a dead cylinder, but again, that wouldn't be intermittent, it would be a consistent stumble in the idle. Rotor or cap cracked or fouled - heavy carbon buildup, maybe rotor contacts aren't reaching the cap? Even a tiny hairline crack that you can't see will create this kind of issue....could be arcing inside the cap. I hope you find this gremlin...these situations are frustrating as hell.

 

Just a thought sounds like you have tried about every thing but have u checked to see if you have a manafolds leak to the block if Its ok try a little hotter plug another trick drain the gas tank or have it vary low put a couple gal of 110 race fuel in It if that helps work off the octain issue hope that helps some times fixing problems come easyer working from different directions

 

cactus, the leakdown is the best way for determining the condition of an internal combustion engine. Primarily the condition of the way the engine seals within the combustion chamber. It wont tell you the condition of the bearings or crankshaft, just within the combustion area. I did not want to overwhelm you with the leak down while you were doing the compresion test, because that's very good to know also. This in turn is why I asked you previously to add the oil to the low cylinders and see if they come up or not. If they dont, then you definately need to move on to the leak down test. Theres a good chance you might have a issue between one or more of the valves and possibly the valve seats. This could very well explain the popping in the exhaust at idle. A leak down tester will alow you to " listen " for leaks after you apply air pressure from an external sourse to the cylinder. That's how its diffrent from a compression test, which relies on making its own pressure within the cylinder and allowing you to measure that pressure. The leak down will allow you to measure the " loss " of pressure and listen for it. If after applying air pressure to the cylinder and you hear air escaping when you listen into the carb, that could be a indicator of a leaking intake valve and or seat. Hear the leak down the exhaust pipe or header, and you have to look at the exhaust valve and or seat. Hear the sound in the crankcase, and that could be pressure leaking past the rings and cylinder, or even a head gasket. If your handy enough you can even build a leak down tester kit, but buy or build and you will need a air sourse to hook up to the tester and your engine. TR

 

Distributor caps have been known to be cracked even when new. Small hairline cracks are possible and should always be checked for even when new. Even if I buy a new Echlin or MSD cap, it doesn't matter, I bring my GOOD glasses and check for cracks BEFORE I leave the store with it. Just a goos habit to get into, TR

 

A leaking head gasket can also be heard and seen in the cooling system too, , TR

 

I had the same problem with my 283 and it also has 3x2 setup and I also thought it was the carbs - it wasn't. I was setting my timing by ear at half throttle and I had it advanced to far, I put it at factory timing and it runs great.

 

Thanks everyone for all the help and suggestions. It is very much appreciated. I am learning a lot here.

 

Just because the timing chain "dots" line up does not mean there is slack in the chain.
If you are sure there is no slack in the chain then your problem could be worn valve (intake) guides..possibly burnt vavles, creating vacuum leaks, however this condition will usually show up when using a vacuum gauge as a fluctuating needle.

 

Well, I figured since the dots lined up, it had not jumped a tooth. I checked for slack in the chain after it was suggested earlier in the thread. I am leaning toward the carbon build up, burnt valve scenario. Like I said, I have another engine to rebuild this winter. I am just trying to improve drivability for the rest of the season. I am driving it to the HAMB drags this year come hell or high water. I think I will sign up with AAA just to be safe, haha!

Oh, and vac gauge reads steady.

 

I had the same issue with a 283 and they answer for me was play in the timing chain. I replaced the set and the issue went away

 

Tiny update. I threw another 2G on it that I had. It is the same bore as the first one ,
1-3/32". I had measured the jets when I had it apart and they measured out at .042".
That is the same size jet that is in the first carby, but the pump charge is much fatter and the hesitation seems to be gone? ( just running it in the garage right now.) The other thing I noticed when I had it apart was that the air bleed tubes seemed a lot larger.

I still have the occasional pop/ miss out of the tailpipe that I can't seem to tune out with the mix screws or dizzy, so I guess a valve job might be in my future.

Unfortunately, the better performing carb has the fuel boss on the front rather than the side. I may have to mix and match parts to get the desired result.

This has turned into a HAMB Drags thrash of sorts!! Stay tuned! ( get it?, ha!)