The Stovebolt Site Forums The Shop Area Engine Shop runs at high RPMS

if i hold the starter and the trucks fires off i can get it to run at 2000 to 4000 rpms but let it drop to 1500 or less it backfires and dies. also the electronic tach is jumpy and does not hold steady. i have a 235 with a pertronix ign. any suggestion, i have been trying for 2 weeks to figure this out. HELP!!!!!!!!!!!! RON

Have ya called Pertronix yet? They might know how to diagnose the problem. At least narrow it down to exclude thier product.

i called pertronix and they offered suggestion on how to test it, i am not enough of a mechanic to do it. i have another mystery, i am seeing antifreeze on the lip of the valve cover coming thru the bolts. could that mean a blown head gasket or a more serious problem? it gets stranger and stranger.

The antifreeze could be leaking from the top hose and dripping down to the head or valve cover bolts. What did pertronix say to test/ how? Someone here could guide you thru it.

WE b OLD,
How did this problem start, all of a sudden one morning or slowly over a period of time? Why are you focusing on the ignition..because of the tach fluctuations! When you start it, how do you get it off idle to the high rpms you state it will only run on. These are clues to the problem.

Stuart.

it got worse over time about 2 months. i use the starter to get it up to rpms. then it will run fine except for the tach flutter. antifreeze only on pass. side if dripping from hose there is a gap in the cover flange where it would run down the front of the block. pertronix talked about resistance and when he asked if it had a resister i got lost from there. 8 volts on neg. side and 6 on positive. also suggested a ground from the coil. there is also a pudddle of antifreeze on the floor but i can't move the truck to check it out.

why cant you move the truck?Fred

We b OLD,
I wouldn't think an electronic problem (the Pertronix) would take 2 months to gradually develope. Electronic items usually just crap out instantly...in the middle of the night on a lonely road. The coolant leak is interesting, but the valve cover area is too high for a typical head gasket failure. Why don't you put a timing light on it and make sure you have fire as it tries to die. Even as it fizzles out you should have timing light output if the ignition is working properly. A compression check would be next. I had an old 216 with a blown head gasket and it did some of the things you describe, especially the backfires. A blow between ajoining cylinders and the water jacket is very possible. The carburetor has a high speed circuit and and low speed/idle circuit, when the idle circuit is plugged, the engine will run, but only at higher speeds. Remember, this problem has developed gradually so it isn't a sudden failure of a component but rather a condition that is getting worse.

Stuart.

also make sure you dont have any water in the oil, check to see if any water is coming out of the tail-pipe,,, if you dont have a blown head gasket, seems like it is in the dist or cam shaft,, but I know very little about old trucks,, I just drive em..Fred

ME TO!!!!!!!! JOKER> but now i can't even do that. i am about ready to give up and take it some where. the antifreeze came from the lower radiator hose and the high rpms and the fan slung it up there.i really believe it is not the electrical because it will start and run obove 2000 rpms. it may be the idle circuit as atomarc suggested. i may just order another new (rebuilt) carb from auto zone this is an orginal and i overhauled it 15 years ago. i ran the battery down trying to start it so i am recharging it now. you can see what kind of day i am having i hooked the charger up backwards. ????????????? ron

Ron,
What is it they say at Home Depot? "you can do it, we can help". Don't give up, there are literally thousands of folks on this site to help you. Out think the truck, you'll feel good when you overcome this little bump in the road of brusied knuckles.
As far as Joker is concerned, all you have to do is look at redryder and you know he can work on this old iron quite well.

Stuart.

Well, sometimes I just think about the most stupid thing it could be, and get lucky..
How about that maybe you have a leak in the lower radiator hose and the fan threw some coolant in a sparking thing..Like somehow getting inside the dizzy cap, coil wires or something like that...After all, the higher the RPM's, the faster the spark and would not be as effected with the moisture as it would at a lower RPM...
I think I would be looking for the wrong thing being wet..
Oh Well, I think I'll make a list of something I shouldn't forget..Whatever that might be..
Good Luck, Steve

Shooper,
That is a very good theory...good form!


Stuart.

shooper, that is a very good thought, man , I just thought you did nothing but tinker and drink beer,,just kidding,, your thought makes a lot of sense,, a lot of times it can be somthing simple,

stuart, thanks, I can do some stuff but I can also spend a lot of money other-wise,, trying to get cletis to be my mech for nothing but that dawg wont hunt with him

I've had two vehicles in the past that had the same sort of symptoms.. you had to start 'em with your foot to the floor and run 'em above the 1500RPM mark.. they simply wouldn't idle.. but at a higher RPM they seemed to run smooth and well.

One was a gunked up carb, the other was a gunked up fuel filter.

with fenton headers and dual carbs can it run on one carb? i just got it started again and plugs are black and previously they were med. brown. i would like to have it running for JAMES DEAN days next weekend in fairmount in. 12 miles away. two big car shows one in fairmount and the other in gas city, in. i hope i havn't overlooked the obvious. i am going to get a new dist. cap and rotor. i am a bit tight and don't like to spend money where not needed. i just put new carb gaskets on and reset the idle screw. doesn't seem to change a thing.????????????????? thanks for the encouragement. i live in a quite subdivision or did til i started this project. RON

I would think that it would run on one,,but.
you might also try running it at night and see if you can see any of the plug wires leaking fire, if it is bad, you can see the glo and may even hear it,however I think that one of your carbs may be acting up...Fred

May also want to check and see if the intake gasket has crept up or down and caused a leak. I have heard of this happening from time to time around here. I read somewhere that you can take an unlit propane torch and move it around the intake while someone cranks it over to see. It will smooth right out if there is a leak.

WE b OLD,
TWO CARBS!!!!!!!!!Geezzz, a minor detail. Did you put a timing light on it yet? See if #1 stays near it's timing mark on the vibration dampner (damper) as you come down in RPM's. I am guessing the Pertronix unit has NO vacuum advance, but still has it's centrifugal advance. This will show you if the timing goes nuts as you drop engine speed and start to die. I think the engine might run on only one of the dual carbs, but would be WAY lean...your plugs say RICH. Is the tailpipe sooty..do you smell heavy unburned gas fumes when you run it? The throttle linkage on some of the dual setups is
sort of funky, is one carb at 1/2 throttle while
the other is on the idle screw. I wish I was nearer to IN so I could help. Sometimes you just want to walk out of the garage and call Mr. Goodwrench! He would probably be 18 years old and have never seen a carburetor. When it backfires, does it do it through the carburetor, complete with flames, or out the tailpipe?

Stuart.

i am about to give up and take it to a guy who has worked on these things for over 30 years. i have tried everything i can alone. i can't keep it running long enough to put a light on it. yes unburnt fuel smell. the linkage is ok. with backfiring i still think it is electrical. THANKS ALL. ron

You might try disconecting the tach from the distributor or coil which ever it is hooked up to. I have had problems with tachs causing problems simular to what you describe before. it wont cost anythingto unhook the tach wire if tyha aint it you can just hook it back up

WE b OLD,
Be sure to report back to us what the heck the problem was. Good luck!

Stuart.

i don't give up easily, the one thing that bothered me was the backfiring, sooooooooooo, the one thing that had been change about the time this all started was i had the timing reset because of pinging by the people who do my major work, he also build race cars and races the so i figured he knew what he was doing. soooooooo i went out and messed with dist. setting first clockwise no start, counter started a little easier, more almost idles still backfires a little, but is better. will order new carb i think that is part of the problem. another question, i had to remove the down tube and no fumes came out but did come out the oil fill in copious amounts, is that a problem, maybe to much back pressure some where, or is it the movement of the truck that will draw it out at speeds? RON

Ron, do you have carter yf or rochester, if you have carter I might be interested in buying it,,, I am not so sure that the carb is your problem,,,I may be nuts but I have never had a carb backfire as you describe, seems like mine have always been electrical but I am no expert, by moving the dist and making it run better may seem to support that it may not be the carb.. good luck and let us know, I know how you feel, it is nerve racking to try and fix somthing and not be able to do it and have to take it to a mech,, I know just enough about these old trucks to be dangerous,,, take care........Fred

Ron,
I would certainly do a compression check before I ordered a carb...you might pull the plugs and line them up on the work bench in order, comparing the electrode color. It is possible to retard the timing SO much that the engine would run in almost any condition.

Stuart.

will do a compression check. one of the guys at work has compression gauge if he can find it.. i have rochesters. i have overheated the starter so it is hard starting and the battery is down, have it on charger. i am pleased that i have gotten this far. one weeks work and it almost idles on its own. baby steps. hope i don't mess it up with further fiddling. the new carb was not adjusted at all as i thought so i check other things on it idle screw not touching had to bend the arm. so much for assuming. ron

Ron,
Good for you...baby steps will accomplish the same things as big steps, it just takes a little longer. In the process of fixing something, you can't assume anything. You have to check each item, prove it is working then move on to the next item, prove it is working etc. Does Marion have a high school with an auto shop? You could take your truck there and maybe the class could use their resources to help find the problem, for FREE. They would have the basic tools and the instructors supervision. Keep at it!

Stuart.

you might even consider taking it somewhere to see what it is and the do the work yourself,, just pay for their time if needed,,,,,,,,Fred