The Stovebolt Site Forums The Shop Area Engine Shop Rough running - diagnosis

Wanted to thank everyone here. Finally ran out of excuses NOT to start my truck's engine after a year in my garage and very sporadic progress. Definitely the biggest mechanical accomplishment of my life...but it wouldn't have happened without the great folks on this site.

It fired right up and ran, albeit poorly, but I am still way more excited than discouraged. Just didn't have time to tinker. You can see it was rather dark.

See video below. Try to ignore the smoke. That is PB Blaster on the exhaust. Fire extinguisher was by my side. JW Lives

Here's a pic of the garden hose cooling system HRL and others helped me devise. JW on life support

So...on to the next evolution.

It did run kind of roughly. Not sure how good the sound is in the video. I would describe it as a "miss." The longest period it ran without dying was probably 4-5 minutes. It would smooth out and sound pretty good for a few seconds and then go back to stumbling.

And when it died...it usually did so with sort of a "backfire" through the carb. Not a loud pop or bang, just a good sharp "puff" sound.

For background, before I started, all of the following were done:

* Timing set with flywheel mark and distributor
* Verified firing order
* Pulled valve cover to see that valves all moved up and down and "seemed" to have some clearance room to close fully. (you can hear some valve noise in the video, I had not done a proper adjustment)
* Complete fuel system rebuild: Tank, lines, filters, etc.
* Carb kit
* Plugs, wires, points, cap, rotor, coil, etc.
* Idle mixture screw set at 1.5 turns out

So, here are some ideas I have on potential causes and fixes...would like some expert opinion on which ones to try first or in which order. Based on what little you can hear in the video and the symptoms I describe.

* Adjust mixture screw another out another half to full turn.
* I'm fairly certain there are exhaust leaks - how much might these contribute to symptoms, and what's the best way to troubleshoot
* Compression test - I didn't do one thinking a cold test on an engine that sat for many years might not be accurate.
* A more scientific cold valve adjustment.
* Check vacuum advance function (need help with this one)
* Verify spark at each cylinder
* Some sort of carb function check (again, not sure where to begin).
* The vacuum leak check with propane or starting fluid

Vacuum advance check is simple: when you rev engine the entire distributor should turn or attach vacuum pump to vacuum advance an see if it holds vacuum.

Quick carb check: look into throat and look for a squirt of gas when the accelerator is pushed.

Nice vids DADS50, and nice truck you have created for your Dad!

JW51, congratulations! It's always nice to get them running and sounds like you're on the right path for tuning it in. I've found the best thing you can do is drive them. Some things work themselves out and the ones that don't become more easy to resolve.

Congrats!

Based only on your video it sounds like some tuning is in order. Get the points, timing, valves, vacuum up to spec THEN see what you have.


Next get it to stop and steer and go for a ride!!

It already stops. That was actually step one. Had a mechanic do that so I could safely put in the garage. Have a steep driveway that would have made it impossible. U-Joints seem pretty rough, other than that...I think a SHORT drive is not too impossible of a dream.

Won't have much time until this weekend to play with it more. Now that the carb has had fuel in it...I can see exactly what folks mean about their leaky Rochesters. Guess I will have to live with that for a little while.

Having had another day to think about it...I think step one is going to be some adjustment to the idle mixture screw. In hindsight, it was quite a ways out before I took it all the way in to set back at 1.5 turns.

Going to attempt a second startup tonight. Having said that, I have some questions about my Rochester Carb and where I should go from here.

* The manifold is pretty clearly damp from fuel leakage/seeping. I'm unsure how much of that occurred during my test run a few nights ago, and how much since it has sat since then.

* The level in the glass bowl filter in front of the carb has dropped. Don't understand the carb function well enough to understand...other than some gas leaking into the carb after shut off....and then the filter media wicking up the rest down to its current level. Perhaps a clue to folks who know what they're doing.

* Having searched the archives, it seems float level setting and/or needle valve debris are the common culprits for causing Rochester leakage. (in addition to the casting warpage)

Any thoughts on what to try first? The guy who did the brakes for me, did the carb kit about a year ago.

Congrats on the 1st run.
Are you sure it's gas on the carb? These carbs will collect quite a bit of condensation when running cold.
Do a finger smell test to see.

If it is gas it could be the float setting, loose fuel line or the dreaded warped casting.

Sometimes fuel will leak down to the fuel pump when sitting. There are valves in the pump that are supposed to stop it but some will leak anyways.

I wouldn't worry too much at this point. Get the engine running smooth 1st. Check/double check points and plugs settings, all wires are good and tight, get the idle to 450-500 rpm and if you have a vacuum gauge adjust the fuel/air setting on the carb to the highest vacuum setting (16 - 21) and set the timing BB directly on the arrow at 450-500 rpm.
That should atleast smooth it out at kidel and low speeds.

If it won't smooth out then I'd go on to troubleshooting the carb.
At this point you could have several adjustments effecting it.

Good luck
Dave

Yeah, it's gas.

If your carburetor body is actually warped,that will cause enough of a vacuum leak,to display the symptoms you mention. There are a couple of instructional video's on youtube,about the Rochester Bs',and how to "true" the halves,to alleviate the warp.By using a vacuum gauge,you'll find out if you have a (vacuum) leak in a hurry. you will get a poor reading,at best,or the needle will fluctuate,and not stay steady. I couldn't get a "good' reading,using the vacuum port on the firewall,either. I had to plumb into the intake,at the base of the carburetor.That fuel drop at the bottom of your linkage MAY be a torn accelerator pump leather.

Leaky carb aside, did some more running/testing today. Moved the mixture screw out another half turn before I started. Engine ran quite a bit smoother today, actually.

But....

* It will NOT run smoothly (or at all) at a slow idle, but sounds pretty decent at a fast idle.
* It will ONLY run at partial choke, even when warmed up.
* If I even touch the throttle, it will die almost immediately.

Got myself a vacuum gauge today. Will get some readings tomorrow. But thought the detectives here might be able to offer a rough diagnosis with those symptoms.

My baseless theory is vacuum leak at the intake.

Sounds like the float level is set too low...Should be 1-9/32.

Was typing my post when you typed yours. Check out the additional symptoms and see what you think.

Looking at the shop manual. Can I just pull the top half of the carb to do the float adjustment? Or is it best to remove the entire carb from the manifold first?

just pull the top 1/2. Make sure you pull the top 1/2 straight-up,so you don't bend the accelerator pump. now is a good time to check the leather plunger on the pump,as well. It shouldn't have any tears or cracks. If it does,then it's time for a rebuild kit. They cost about $15.00,and take a novice about a 1/2 hour to rebuild. if your carb. is excessively dirty,it'll take a little longer. just make sure everything is CLEAN and DRY,before re-assembly. one EASY,Fatal mistake,is mixing up the check balls. If you install the small one in the accelerator pump,it will not work. Then the ball gets jammed in the orifice and will not come out! Been There-Done That! . Only option is to find another carburetor,and rebuild it. Hope this elps!

I will pull the top half today and at least do the float check thing. Not sur I have a real precise way to check that measurement, will have to get creative.

Before I do that gonna run some more to get some vac gauge readings and look for vac leaks if necessary.

Couldn't find a YouTube video on truing the two halves of a Rochester. If you have a link, please share. Already got a couple feelers out to source a rebuildable Carter or zenith. Probably a little premature on that...

If in your search for a carb you come across a Carter YF787s give it a try. Good carb and easy to rebuild. (216)
walker rebuild kits available at places like autozone.



Use the tuning procedure in the Shop manual . It a good starting point .

It's kind of a dance between advancing the distributor, setting the idle and mixture screw.

Here's a good video you might want to watch. Good luck with the B' , which sometimes seems to stand for something else.

Ran the truck for a while with the vac gauge hooked up a little bit ago.

Pretty steady reading in the 14-16 in range without much bounce or wiggle....when it's running smoothly at fast idle with partial choke. If I back off the idle speed or try to push the choke all the way in....vac gets bouncier, lower, and the engine eventually dies. Sometimes with a backfire.

From looking at this chart ...I guess my next move is advancing the timing?

Got some questions on the vac gauge timing procedure. Looked at several archived threads and there seems to be some variations on this.

1) Understand that I'm to loosen the distributor clamp and rotate the body while running to achieve max vacuum. At what RPM should I do this? Some old posts suggest 500 and others 2000.

2) Should I disconnect the vacuum advance before I try this? And if so, I assume I should plug it somehow?

2) See my aforementioned issues with rough running and having to run higher rpms and part choke. Can I make a rough timing adjustment before starting? And what would be the best way to do that?

1. At recommended idle RPM

2. No

2 (3). Rough timing would be to line up the timing mark on the flywheel to the pointer on the clutch housing (checking that #1 cylinder is on compression/firing stroke and/or checking #1 cylinder valves are both closed (if you have the valve cover off)).

Nice catch on my question numbering

I've done the timing ball - verify rotor at #1 - valves closed thing. I was wondering, given the vac gauge readings I got today, if I could fudge the timing a little advanced before I start up again.

What do higher than normal compression readings suggest?

Quick recap: Late 235. Starts easy. Runs ok at fast idle part choked. Try to slow the idle or push the choke in and it will stumble and die with a backfire through the carb. Also have a leaky Rochester B, FWIW.

Got some vac readings yesterday. Steady 15ish inches when running ok fast idle/ part choke. Slow the idle or push in the choke readings get much more erratic and much lower.

My next move was going to be advancing the timing a bit with the vac gauge hooked up. As well as making sure the float is adjusted and needle is seating.

But I got to wondering if maybe had a more significant issue with the bottom end, so I did a cold compression test tonight. I know cold isn't ideal but had been old by folks here that it's still work doing. Throttle blocked open. All plugs pulled.

Compression, I have. Maybe too much?

First round through I got readings from 130-150. A few spikes up higher that I ignored and reran. Did a second run through where I recorded the high spikes:
CYL - PSI
1 - 140
2 - 140
3 - 160? Redo 140
4 - 150? Redo 145
5 - 170? Redo 160
6 - 150? Redo 150

For what it's worth, #5 had a 140 on my first run.

What are these telling us? Exhaust valves not opening sometimes? Exhaust obstruction close to the manifold? Does this piece of the puzzle explain any of the symptoms while running?

The only valuable information that a cold compression test will give you is whether you have any completely dead cylinders. You indicated that you can get it to run. Why not do a fully warmed up test?

I certainly can. It was running poorly enough that I was just trying to eliminate a few things before I did another run and didn't have time to do a proper warm up last night.

I think you've answered my question. Sounds like I need to basically disregard.

Need to revive this thread. Still need help diagnosing my rough running 235.

After a few months' hiatus (moved to a new place), I'm back to it. Still the same thing, pretty much only runs with part or full choke and a fast idle. Push in the choke or slow the idle much and it stumbles and dies with a big "poof" back through the carb. Still working with the garden hose cooling system.

Made a valiant attempt in January to get her moving under her own power to get on a trailer. Rebuilt the Rochester B but ran out of time before move day didn't get it reinstalled until this week. It doesn't seem to leak anymore, but runs more or less the same. Did a cold valve adjustment at .002 wider than the spec just to eliminate that variable.

Help me vet the following ideas, and choose which path to go down next. I will try things one at a time:

1) I was going to chase vacuum leaks with carb cleaner or whatever, but hate to run it choked for that long. Thoughts?

2) After I gave up tonight, it occurred to me I've never verified the function of the heat riser valve. Should I be able to move by hand from the counterweight side?

3) Can I advance the timing a few degrees with the ball as reference? It's timed right at the ball right now. I know the vac gauge is better, but can't run it well enough to do that right now.

4) Points were replaced a year ago, but not sure about condenser.

5) This was a "barn find." Its quite possible I have some sort of critter obstruction in the exhaust. But how would I check?

6) The B could very well be junk. I've got a Carter YF waiting in the wings to be rebuilt, but want to eliminate and test a few theories before I go there.

IMO:
1. wait till later
2. Yes
3. at least five degrees... do a search for "timing advance" here then look for HRL's advice and 'try' that.
4. The condenser is a go. no go. unit
5. a shop vac and a cigar?
6. don't wait.

Things that come to mind. All are cheap(no money, just time)
1, Put a dwell meter on it. Points that are gaped wrong will not work well. Dwell is fairly stable over a wide range of RPM(might help find a bad spring if the points float at higher RPM)
2, Pull the valve cover. Watch the rockers as you turn the motor over by hand. Reset the valve lash.
3, The "B" is not so bad(opinion). Is it leaking? Is it flooding?
4, Pull the plugs and see if they are wet,( oiled, or fuel). Check the gaps.
5, Undo the exhaust at the manifold. 2 nuts and some care. If the exhaust is plugged you will know.
6. Test the fuel pump. Pull the line at the carb, spin the motor and catch in a clean can.
6, The vacuum advance only works "on demand". At idle there is no vacuum signal to the advance on the dizzy. A movement of the butterfly will get a signal and the whole dizzy will move. Pull the vacuum line from the carb and test the advance unit. Be brave, you can make enough vacuum to move it(soap and water will help clean up the fitting before the "test".) Check the advance unit for leaking( Your tongue will work for this).
Advisory: Do one step at a time. Test and go to the next. It can help narrow down what is the issue and what is not.
The above posts are good ones, follow as best as you can. Let us know what you find and how it goes.

Thanks CASO and Steve for the suggestions.

Comments/questions in no particular order:

1). The engine definitely seems to be running rich. But not sure if I can pin that on the carb when the choke plate is nearly closed anyway

2). The one aspect of the carb rebuild I wasn't quite satisfied with was the power piston. Despite cleaning it and it's bore, seemed not to move all that freely. But I had no context for how it should move, so I went with it. Could this explain my symptoms?

3). Exhaust flange bolts are seized up. Not sure what else to do besides sawzall the pipe. And I'm willing to do that if necessary.

4). Need to play with the heat riser thing. Any suggestion on freeing if it seems stuck? Hammer?

5). My thought for a quick and dirty timing adjustment. Move the ball to the lower (left) portion of window and get the rotor lined up with #1. That would be a few degrees advanced, no?

6). Should I do the dwell meter before playing with the timing?

For your engine to run correctly, you need to systematically address all of the things that have been mentioned to date. Start with the heat riser, it needs to work. Get the manifold hot, shut the engine off and spray PB Blaster on the shaft from both sides, let it work for a few minutes and see if you can get it to move. If you can't break it free,remove the manifolds. To get the exhaust pipe off use a little bit of heat on the flange nuts to heat them up a little. Spray on PB Blaster and let it work for a while. Use a deep well socket and try and break them loose, if they are still stuck break them off and replace them later. With the manifold off, you can soak the shaft in a solvent or go back and repeatedly work on breaking it loose. When this is repaired and replaced, start the engine and see if that was the problem.

If not, or even if it is the trouble, use your Carter YF, I have found them to be much better than the Rochester B.

Timing, Dwell and Valve adjustment are important but may not be the problem. Remember Dwell affects timing, Timing does not affect Dwell. Always set the dwell first. Follow the tune up procedures strictly from the manual and the this engine should run.

Thanks, Mike. Heat riser seems like a logical first step.

When playing the heat riser game, try tapping it left and right just to get some movement. Don't be stingy with heat or blaster, but also be careful and patient. On one of mine I ended up putting a lot of heat on it, red hot, before I freed it up. Did this with manifold in a vice. Although I have never found one, there are supposed to be shaft replacement kits that have bushings and new shafts.

To do a total complete restoration of the exhaust manifold, you need to separate it from the intake, clean out all the threads, have it surfaced flat, repair the heat riser and replace the bolts and studs. No one of these things is all that hard to do, you just have to be careful not break any cast iron. Follow the manual instructions on reassembly to the block, has to be done in a sequence.

Modest progress this evening:

Heat riser - had to remove oil canister to verify, but it is stuck. If I am interpreting Denny's pictures correctly, it is stuck in the open position. That kind of shoots my theory. I was thinking it was closed and not allowing fuel mix to warm. I will invest in a propane torch tomorrow to see if I can free it.

Exhaust - after much ado, got the exhaust separated from the manifold. Ran it briefly and that doesn't seem to be an issue.

Running symptoms - more or less the same. Did get it to run briefly a couple times without choke. Have to keep a fair amount of throttle applied to achieve that. Still stumbles and dies no matter what. Acts like its flooding.

Carburetion - can I do something radical with the B float setting or drop to prevent the flooding...temporarily?

Also did some inspection of my spare carb. Its a YF 2101s. Took the airhorn off. It's kinda crusty but might be good enough to try if I can verify the accelerator pump function. Also would have to rig up some sort of choke stove.

Need some guidance before I chase the wrong bunny down the wrong hole. Have the day off and need to use my time wisely. Perfect can wait, the goal for today is to get it running acceptably.

How likely is it that either of these is a contributor to my symptoms?

Vac advance- I did the "test" (thought maybe it was some kind of hazing ritual) but can't move the distributor. New vac advance needed. However, can a leaky vac advance contribute to running this poorly? I know there's no advance at idle, wondering more about the vac leak.

Heat riser- still stuck despite heating and penetrating oil. Verified on my parts motor that it is stuck in the "heat on" position. I could swap manifolds, but again, how likely is it to be major contributor?

Also don't have a lot of faith in my carb. Going to look at a couple things there.

Plugged the vac advance port to take that out of equation for a bit. Didn't help.

Partially disassembled the B. Reset the float height and drop. Didn't help. Not crazy about the way the needle moves in the seat. Hangs up when float drops. Is the fuel pump pressure enough to move it down in real world conditions?

Maybe this has been covered already, but have you changed the points and condenser? What brings you to fuel system issues? Trying to help. If it IS fuel system related, start at the gas tank. Make sure that its not stopped up with rust and crud which is very likely. Then check the fuel pump. With the line disconnected at the carb, does it spurt dangerous explosive gasoline all over your hot engine? If it does, and your carb is filling the bowl, go to ignition issues. Lots of guys here happy to help you troubleshoot.

Sounds like you have multiple problems at the same time. This makes trouble shooting a big challenge.
I always do the easier things first.
1)Plugs, points, condenser, spark plug wires (especially the coil one).
2)Set the timing.
3)Compression test.
4)The carb. Least likely to be bad and most difficult to fix, therefore save it for last if needed.
Carl