The Stovebolt Site Forums The Parking Lot Big Bolts hard starting gmc 302

I'm looking for ideas to get this thing running.

The truck hadn't been run in many years. I put in new plugs and wires. It already had new points, cap and rotor on it.

It started and ran after I put a new starter on it, but there was alot of smoke coming up from the exhaust manifold/exhaust manifold area. I wasn't able to get out of the cab while it was running to be able to locate the exact source or make any adjustments.

I dismantled the carb to clean it out, did that and found that the accelerator pump was installed to where the rubber plunger would not pump, never did.

After re-installing the carb it was as hard as ever to start. I used a whole can of starting fluid to get it to run one time, but the idle was too high.

I adjusted the point gap again, replaced the coil, and put a stiffer spring on the throttle return without any success.

I'm now thinking vacuum leaks, but the only line that comes off the intake goes to the valve cover. What is going on there? I don't see any cracks in the intake, but don't know where they are most likely to crack or leak.

I choke it and pump the pedal and get a significant amount of gas down the carb but only an infrequent pop and with the choke off it isn't better. I've thought possibly the spark is weak. My boys tell me they see a spark but not all the time and that is hooking a spark plug directly to the coil. Are solid core spark plug wires a must?

The truck was used as a fire truck and only used a few thousand miles since 1970 and only 500 since 1990. I found a mouse chewed log book under the seat that documented the mileage and date when gas was purchased.

Before I get really serious like checking compression and removing manifolds, I thought I'd check with anyone hear for something I might be overlooking.

I did cut off the muffler just in case it was plugged.

Thanks

double check the carb Float level and choke operation...

Have one of your boys crank while you check the spark. You shouldn't have to connect spark plug directly to the coil to see spark. If you Don't see a spark when it is properly hooked up, double check your points. Since you have spark at coil you might try replacing the condenser, I have had them fail after sitting for long periods of time. Improper timing can cause hard starting also.

I have tried to have my boys hit the starter button but the starter never meshes. They just don't get it. When it doesn't mesh they push harder. I can't take it!!!

I'll replace the condenser. Would that give a weak or unreliable spark? I thought it wouldn't spark at all if it was bad. If I have spark at the plug connected to the coil wouldn't the condenser be working?

The timing may be off. I guess I could do a static timing check but I haven't done that before and I'm afraid I could make it worse. If I could get it running again I would put a timing light on it.

What about spark plug wires, do they need to be solid core?

The choke closes and the accelerator pump squirts. The jets on the holley are low in the bowl. It does get gas. After the next start try, I'll see if the spark plugs get wet.

I've looked at the points many times and they do spark when I open them. I'll gap them again. I gapped them at 22 then re-gapped them to 16 to see if there was any difference, but found none.

I thought the throttle may not have been closing tight so I put a heavier spring on the return. There was no improvement.

It is 12 neg ground so I have the neg coil terminal going to the distributor. I thought that was right, but I'm questioning everything now.

Thanks

What happened to the old gas when it was sitting? Reason I ask is because the old gas turns to varnish. The motor will run fine the first time started in years, but that varnish sets in on the valves and causes them to stick when the engine cools down.

My guess is you have a few stuck valves and bent pushrods. Pull the valve cover off and have the engine cranked over to make sure there is movement in all of the rockers.

If you have a few bent pushrods, you can straighten them with a hammer and throw them back in. Those GMC motors were rugged as all "H -E- double hockeysticks. About the only things known to kill them is bad gas and high heel shoes!
John

I had the same problem with my 261 a few weeks ago. I hope your solution is as simple. I rebuilt/cleaned the carb about two-years prior, so that was the LAST thing that i looked for trouble. I checked my fuel filter,and it was fine. I then opted to tear the carb apart,and lo and behold, even with a brand-new tank,and blown-out fuel-lines,I had just enough sediment built-up in the jet area,to starve the engine. I gave the carb another good cleaning,and that did the trick. Hope this helps. Good Luck. B.T.W.-I've only heard and seen 6v pos.ground systems. I'm 99.9% sure your system is 12v neg. ground. What year is your truck/302?

I'll do that, but the 1st time it started it seemed to run ok, but it was a hard start, with considerable ether. I cleaned the carb because no gas would come out of the accelerator pump. That is when I found the acc. pump problem. I took the spark plugs out and turned over the engine by hand by pushing the flywheel, before I put on a new starter. That was before the 1st start attempt. It turned very easy and smooth. I thought I'd feel something if there was a valve stuck.

I've been running it out of a gas can with an electric fuel pump with fresh gas. There probably was a small amount of bad gas in the carb to begin with, it did not run very long.

Willy, It is a 53 that was converted to 12 volt.

I have checked for spark and couldn't see anything, thought the coil went bad, put on another used one still nothing, put on another and got some spark, but no start. I think its time to put on a new coil, and condenser. That will eliminate that question mark.

I have given it a good healthy shot of ether before and not even gotten a pop out of it. That made me look hard at the ignition system again but I have not found anything bad. I do have spark but maybe it is only occasional. Usually I eventually find the reason, for a problem like this but I've been after this for quite some time and frustrated to say the least. I appreciate the ideas. I'll see if a brand new coil and condenser makes any difference.

Thanks

Did you check to see if your distributor gear may be worn? Just a thought. You may also want to check your advance. If by chance you do have a vacuum leak, this may throw your timing off enough that it will make starting difficult,if not impossible. Good Luck!

k9trucker,

If it has been converted to 12 volts...did anyone install a ballast resistor for the coil?

Most 12 volt GM coils require a resistor in the hot lead to the positive terminal on the coil.

Also, check that the hot lead from switch goes to the "+" on the coil and the "-" lead goes to the distributor.

My Big Bolt 302 was wired wrong when I got it.

Place a "see through" fuel filter in the fuel line between the fuel pump and carb.

Having such low miles that thing should fly and start easily.

I realize it can be frustrating, but in the end it will be worth it;)

Oh yeah, my preference is to use solid core copper plug wires. Not the carbon core most auto parts stores try to sell.

Try and find American made distributor parts, points, rotor, condenser.

Check the wire connections from the coil to the distributor.

I had a bad condenser right out of the box. The other one I had, the lead wire was broken internally.

Good Luck
GMCPic

Willy is right...

a worn distributor gear or bad shaft bushing will drive you crazy.

Although with the low mileage that is probably not it.

GMCPic

If you had antique fuel in it, then it is all sucked up into the fuel system, so make sure the lines are clear, bent pushrods are likely, so make sure to check them as was stated. Probably not a good idea to use ether to try to start it, it should start on gasoline.

I got the truck without an ignition switch only a hot lead from the battery with a knife switch on the battery cable. It had a hot lead running directly to the coil. I put a toggle switch on that coil wire but there is no ballast resistor unless it is built into the coil. I thought it would start without the resistor but maybe limit the life of the coil without one. Maybe this is the problem, no resistor equals bad condenser or coil. Do coils come with the resistor built in? I'm calling napa to see what they got.

There is no vacuum advance on the distributor. While this is a GMC 450 it was built for the military. It looks civvy but has the military ID on the dash and a 302 without a fuel pump on the engine. Is the timing set differently on this engine?

The only vacuum used is for a line to the valve cover. Is this an early PCV setup?

No resisitor means pitted and or fried points. Remove the points and inspect for abnormal wear.

Years ago when I had my first gmc with a 270 6, the ignition switch would cut out on me. The Catholic school I went to did not teach us how to hotwire a truck, so I took an aligator clip from the battery to the the coil to ensure the engine wouldn't cut out while driving.

I made it 25 miles to work the next morning no problem. The truck wouldn't start to get home. I pulled the points and filed them down flat with some emmery cloth, gapped them with a matchstick and drove home the 25 miles. I made it home, and had to repeat the process for the next few days untill I learned I could take the hot lead to the ignition resistor. Within a week or 2, I had recieved a new switch to swap out the worn out one with.

New points are being produced in questionable places. A Pertronics Flamethrower ignitor will eliminate the points, and the need for a resistor. IMHO the Pertronics pointless ignition retrofit is worth every penny. It is also possible to modify an HEI distributor to work on the 302, or simply purchase one from the restoration parts suppliers.

Question..Does this truck have the seat fuel tank or saddle tanks.

Check the fuel lines for cracks..especially if it has the seat tank, check the fuel line under the truck where fuel shut off is. Also, check fuel lines to fuel pump for cracks. It may be sucking air in a bad fuel line.

Mine had a bad fuel line on the fuel shut-off valve under the seat tank, but did not leak fuel when not running, but sucked air when trying to start.

If it was running before, it should not be a timing issue. These things will start when out of time, just no power or fires back through the carb.

My practice when approaching one of these old GMC is to first, check fuel line and tank for bad fuel and leak in fuel lines. Disconnect fuel line at carb add a short piece of hose to fuel line put other end of hose into a coke can or plastic bottle. Then crank engine over a few times to see what come out. Do what is necessary to correct any problems replace fuel line into carb.

I automatically replace the battery to 12volts negative ground regardless of what is in there. Buy a new resistor, coil, rotor & distributor cap, points and condenser. I even carry a spare distributor that is rebuilt just in case.

I carry roles of automotive Red 10 & 12 gauge wire, clean all battery cables inspect them and replace what is necessary. Run new Red 10 gauge wire from starter to amp meter then Red 10 gauge from amp meter to switch, then new 12 gauge wire from switch to resistor, then 12 or 14 gauge wire from resistor to "+" terminal on coil, 14 gauge from "-" terminal on coil to distributor. check that insulator in distributor is okay and replace point and condenser, replace rotor with new and cap as new, make sure plug wire are copper core and no cracks or bad plug wires.

I have several GMC L6 engines to deal with, (2) 228s, (2) 248s, (1) 270 and (1) 302 the latest. I've had Chevy 216s and 235s.

The procedure is time consuming, but it is easier than spending a lot of time trouble shooting problems. The cost is less then $100.00 at my local NAPA store.

I always put a see-through fuel filter between the fuel pump and carb to catch any water, crud or rust flakes and I can see what is happening and fuel color.

It is about 2 to 3 hours work, but well spent time in the long run.

The only exception is if the person I am buying from gets into the vehicle and starts it for me. ...

I have also learned to replace the 2 rubber flex fuel lines with new ones. They are cheap, a pain to replace but worth it.

The valve from valve cover to intake manifold is an early type of PVC, but not for smog control.

It is part of the vacuum system for windshield wipers and in some cases Hydro-vac Brakes and Vacuum shift rear axle. It does help the engine to suck up crankcase fumes/vapors.

I hope some of the information helps.

Good luck again and happy motoring.


GMCPic

Thanks for all your good advice, I'm hopeful to get some time this weekend to follow up on it.

GMCPic, I wish I had started as you do with a new truck. I think this truck has not run right for 40 years. That was why so little miles were put on it. The last fire dept owners burned up the starter trying to get it to run so they just towed it around if it got in the way, and it sat for years.

It has the saddle tanks but I haven't even looked in them. I've hooked up an electric fuel pump straight to the carb and pumped clean gas out of a can through a filter to it.

Does that PCV valve need to be checked, cleaned or replaced? I think it is the only thing vacuum on the truck. The truck has a compressor for the brakes and the wipers also use that air. The advance is mechanical no vacuum there either. The only line coming off the intake or carb is the one going to the valve cover.

I'm feeling confident that when I replace the ignition parts with the correct recommended ones the truck will run.

I'm alittle worried about bent pushrods. Is my assumption correct that I would have felt resistance when I turned the engine over by hand if they were going to be bent at startup?

Thanks again

Usually...;) unless the timing gear is bad and it has jumped timing it is not likely to bend a push rod.

You've eliminated the fuel issue.

So my guess is you are on the right track with the distributor/ignition problem.

Sounds like you have full on air brakes, that is a whole new issue.

But lets get you running first.

NAPA has always been good to me.

Take the PVC valve and soak it in carburetor cleaner, let it sit over night, then wash it out with water and blow dry... Even dirty it should not prevent the engine from starting. Just run a little rough.

You should be able to blow air in one direction only and it is slightly spring loaded.

If you have to wash/clean out any compressed air lines, I use denatured alcohol. Then blow dry air (air that has passed though a moisture separator) through the lines. A later task.

Installing the new ignition parts should..."I HOPE" fix your starting problem...did you fix the starter? Do not use either...pull a couple of plugs and squirt some gas in the spark plug holes then replace spark plugs, then crank over.

I use a long heavy screw-driver to engage the starter from under the hood. So I can watch what if happening.

Oh yeah

The distributor has a mechanical advance internally. You can add a vacuum advance later if you think you need it.

The ignition timing mark is on the flywheel, it can be seen through a hole in the bell housing just above the starter. There is a pointer there also.

A quick way to find timing marks is, pull number one spark plug (with ignition "OFF") place you finger over the spark plug hole and rotate engine until you feel the compression for number one. Then slowly crank it over by hand till you see the marks.

This usually takes several tries to get it right.

Or crawl under the truck pull the flywheel dust cover, rotate the flywheel until you see the marks...I paint mine white.

I hauled the truck to the DMV today to get the title and next week I'm taking my kids camping so the truck will have to go on hold for a bit.

I really wanted to be able to drive it off the trailer, but I ended up pulling the trailer out from under it. Everything went as planned, which was good for a change.

I'm looking forward to putting all the advice given to work. I feel confident I'll get it going. I'll update my progress when I make some.

Thanks to all, but special thanks to GMCPic for all your help.

Bent push rods can be the result of stuck valves.

If the engine turned over freely by hand with the plugs out. It was smooth as butter. Would I not feel the contact or resistance if there was stuck valve? I thought I would feel it.

with the plugs out there would be no compression so you wouldn't feel any thing unusual from that point. if push rod was already bent prior to you aquiring the truck or from when you first got it to start it wouldn't make full contact with rocker arm and you may not feel any resistance. You need to remove valve cover to actually see everythings turning. Wish I was close by you need someone who understands these engines a little bit, to crank while you check things on the engine such as spark. Your Boys are obviuosly enthusiastic but don't yet understand how the stomp starter engagement works.

kb3csw is right about rotating the engine with the plugs out. If the rods were already bent you would not feel anything.

Valves just would not open, or only open marginally.

45 minutes to an hour tops labor.

With plugs out remove valve cover, turn by hand and watch the rocker arm assembly and push rods.

Later...

While the cover is off you can also check you valve lash and verify oil is getting to the top end. When it is running.

You can run the engine with valve cover off.

I really doubt that you have any bent push rods. I have 6 old GMC L6 engines and only time I bent a push rod was when I lost the timing gear. Some timing gears are made of a pressed fiber material...others are aluminum.

You said this is a 1953 Truck...already converted to 12v.

GMCPic

Update....Back from camping and had a few minutes so I put on a resistor, condenser, and a new coil, and happy days, she started immediately, but the idle was too fast so I shut it off and got that slower but it idles a little rough. When it first started it would rev but after a few minutes of idling it won't rev.

The good news is it runs and starts good with no smoke, but I still need to check the timing and pull the jets to see if there is a blockage. The accelerator pump was pumping good when it first started, I'll look at that again too.

The miss wasn't rhythmic so I think it probably is a carb problem and not a valve.

Glad you were able to make some progress.

Yes, I sure felt relieved when it fired. It startled me because it fired on the first rev.
Thanks for yours and everyones support.

I am very glad to hear the results on your labors.

I would have loved to see the look on your face when it started....weeeee.

Good Luck and have fun with your Big Bolt.

I told you it would run...lol

GMCPic

High idle and erratic missing is Often the Sign of a vacuum leak, (well if your mixture is rich enough to support it ) clean plugs, good wires, proper timing clean fuel and plugged vacuum lines, set the valves lash and evaluate the running from there.....can narrow it down to leaking vacuum accessories, carb issues or valve or other compression related issues.

Sorry if I am rehashing things.. I admit to not reading the full thread, Congrats on getting her running, now smooth her out and enjoy!

When you get it running we can go have a drag ran...one 302 against another.

I'll give you half a length head start...lol

GMCPic

Which Carburetor and manifold does yours have?

WW Strongberg 23-223 (4 Bolt Flange)or Holly 660-A1 (3 Bolt Flange)