Projects 1956 straight six idles but won’t rev

Hello. I have a 1948 Chevy 3100 with a 1956 straight six. It’s was running fine then all of a sudden died. The truck will start with gas pedal pressed to the floor and idles when pedal
is released. However, it will not rev when I press the gas pedal and it dies with gas poured down carb. I changed fuel line, spark plugs, rebuilt carb, changed points, changed gas and checked timing. I even tried spraying a touch of starter fluid with it idling and it dies. The pedal linkage to the carb is good. I can’t figure out why when given gas, there is no change in the revs of engine. Any help would be appreciated. Thanks.

 

Plugged exhaust?

 

thanks trollst but the exhaust is good.

 

If starting fluid won’t light it off, maybe weak spark? Coil or condenser issue maybe?

 

Hook up a vacuum Gauge and see what it tells you

Vacuum leak

bad / weak spark

burnt valve

carb ? Dirty / worn etc ?

 

Put a good used Delco-Remy condenser in it

 

Thanks budget. I did change the spark plugs, points, and condenser. It does start but it won’t rev. I changed the coil about a year ago but perhaps it went bad. Not sure why is will run at idle but not rev if it’s the coil but I’m just learning here.

Vandenplas, thanks. I did just clean and rebuild the carb. I can see that it adds fuel when the gas pedal
is pressed but I can’t seem to get it to rev, it dies if too much fuel is added. Maybe it’s a weak spark (bad coil?), would that cause the issue? I haven’t hooked up a vacuum gauge so I will try that. I did pull the valve cover and had one valve stuck closed. I was able to free it up and everything seems to work fine. Not sure how to check for a burnt valve though or what symptoms that would cause. Any thoughts would be greatly appreciated as I have been working on it for the past three weekends and nothing.

 

Thanks 302GMC. I did just put in a new condenser but maybe it’s a bad one. A coil was my next guess but I’m tired of throwing parts at this one so wanted to check in with the experts here to get some thoughts. Would a bad condenser cause the no rev?

 

Is there any fuel spilling from the carb? You said you rebuilt the carb. There might be a chance that the kit you bought was an old kit with rubber parts that are destroyed by the ethanol in the gas. I'm just throwing that out there. It happened to me when I rebuilt two carbs with old kits.

 

Thanks 52. No fuel spilling from the carb. My first carb rebuild so may need to redo, but I was very thorough and everything seemed good. I did the carb first thinking that was it but it didn’t change things. I would think if it was a carb issue, the gas down the carb trick would give me a little rev but still nothing. I could be off on that thought though.

 

How did you fix a stuck closed valve?

 

Hey Greybeard, I put a small thin flat screwdriver against the spring and gave a few light taps on the end and the valve popped opened. Didn’t take much force.

 

When you rebuilt the carb how did you adjust the float level? Rochester or carter Carb?
The float level adjusts a tad different on each.

It may be that you have the float level set way too low and the needle valve won't open enough to fill the fuel bowl.
Try this first. Take something that you can carefully pour gas into the float bowl vent tube and pour maybe between 1/4 and half a cup of gas into the vent tube. That will fill the float bowl and should let the engine rev up for 20 seconds or as much as a minute or so. Start the engine and see if you can get it to rev up without dying for several seconds or until the bowl runs out of gas. If it won't rev up it could be inside the carb and if you got a kit with several gaskets between the bowl and the top you could even have the wrong gasket if you didn't match the new gasket to the old gasket.

One more thing to think about, is it getting enough fuel? There is usually a shut off valve under the floor on trucks with seat tanks and that valve may be partially closed. If you take the fuel line off the carb and crank the engine do you get a good shot of gas into a plastic pop bottle held over the end of the line?

Simple things first always when you are trying to figure something out.

 

I'm not going to edit post 13 again but in reference to my comment on more than one gasket for between the top and the bowl. If you use the wrong one it will block off fuel to the main nozzle and possibly the accelerator pump discharge nozzle

 

What did the old plugs look like when you took them out? Maybe you have a weak spark. Rebuilding the carb. didn't change anything. Pull the dist. cap and look to see if you are getting a good spark.

 

Still not understanding this..... If the valve it stuck closed ( in the up position) it would bend a pushrod or break a rocker arm. Are you sure it wasn't stuck open (downward)?

Either way it wouldn't idle very well. Was it popping thru the exhaust or intake?

 

Thanks Mr48. I’ll definitely take your advice and post back. It’s a Carter carb. I adjusted the float with a gauge that came with the rebuild kit but it’s basically parallel with the top (when full). I checked the gaskets when I put them back. They looked the same but I saved the old ones and will double check. I’ll also try filling the float bowl like you suggested but when I changed the gas I emptied the tank and kept the line disconnected. The engine idles for a while before finally dying (wanted to ensure all bad gas was out). I’m guessing the float bowl is filling but I will double check. The strange thing is I can see down the carb and move the accelerator arm and I can see gas pump down the carb but there is no rev and the engine just wants to die. It looks like it’s getting gas but there’s no reaction. I’ve also sprayed starter fluid around the whole carb looking for leaks but again no change in engine rev.

Thanks 57fury. It definitely could be the ignition system. I changed the distributor cap last year and just did the plugs, points, and condenser. The only thing left there is the coil. Each plug is getting spark but not sure if it’s strong enough under pressure. There was a lot of soot on the plugs when I changed them.

 

Hey Greybeard. Definitely new at this so maybe I am thinking of it wrong. The spring was stuck compressed down. I thought that was closed but maybe that is open. The push rod was off the rocker arm but luckily not bent. I’m guessing once the spring got stuck in the compressed position the push rod slipped out from the rocker arm. I found that because there was exhaust coming out of the carb and the engine would only start with a plug removed. Once the valve was released the engine started with all plugs in and there was no more exhaust out the carb. Again, new to this so please correct me if I am thinking of this wrong.

 

Makes sense now.... Yes, down is open.

Sounds like this may have set for a while and old fuel is causing the valves to stick.

How did you clean the carb? Just spraying with carb spray won't get all of the little passages cleaned out. It also needs air pressure blown thru the passages to make sure they are clear.

 

Thanks for the clarification on the valves Greybeard. I took the carb apart, soaked it for a few hours in the chem dip stuff, used carb cleaner, sprayed out all the ports and used compressed air to ensure all ports were clear. I then put each piece back together checking that they worked as I went (added gas to check the accelerator pump before I put it back together). I was surprised how few components were in this carb but it’s a simple single barrel carb.

I got the truck with the house. It’s a yard truck used to plow and grade a long dirt driveway. I’ve learned a little each year. I was tuning it up before the winter and that’s when the issues started. It’s been used every year for the last 8 years. Not regularly but I live in Maine so it gets enough action each year.

 

I know you said it’s good but did you verify this, had a bike do the same, cleaned carbs , changed tank , filter, would run but would not accelerate, turned out mice had packed about a pound of canola into exhaust pipe.

 

If (or when) you pull the carb off and apart check the float drop along with float level. If the tang that controls the float drop gets bent it may not drop down the right distance to let enough fuel in and just let a tiny dribble in.
This link shows the correct adjustments for a Carter YF
Carter YF & YFA Adjustments - Mikes Carburetor Parts (carburetor-blog.com)

 

Disconnect the exhaust pipe and see how it runs

 

X3^^^^^

 

I had the same experience with a Chevy straight six that wouldn't rev.
I had just rebuilt and installed the engine... all new tune up parts. But the carburetor was not good. Rebuilt and reinstalled the carburetor.
Same symptom. Still would not rev up. Couldn't figure it out.
Wife came out to check on how I was doing. Not good. She said... Did you change the spark plugs? Silly woman... of course I changed the spark plugs. She said okay well, good luck and went back in the house.
Standing there wondering what next. Thought about what she said. Whatever... I don't know what else to do anyway. Can't hurt to check the spark plugs again I guess.
Well what do you know. My brand new spark plugs were already black and fuzzy as could be from running the engine before I rebuilt the carb. Changed them out and the engine ran like butter. Revved like crazy. 500 HP.
So the obvious question is...
Have you checked your new spark plugs since you rebuilt the carburetor?
Good luck.

 

I know everyone is settled in on the carb but did you make sure the springs in the distributor our good. Just throwing other ideas out there

 

Thank you everyone for the advice. Had work today so when I get home I’ll check it out. The air coming out of the exhaust pipe is strong, however, living in the woods, I would not be surprised if some critters got in there so I will definitely pull the exhaust to see if it makes a difference. I did pull a plug last night and it was all sooted up. Gonna grab a few on my way home, could be a simple fix. I truly appreciate everyone chiming in. I’ll keep everyone posted.

 

"The engine was running fine, and then it died"

"It does start, but won't REV"

If changing the plugs do not solve the issue, try loosening the distributor slightly so that you can manually advance the spark as a test.

If the distributor does not advance, the engine will not rev regardless of the condition of the carburetor.

Jon.

 

Hello Everyone. I wanted to provide an update to this one. I went through all the suggestions here and still couldn’t get the engine to rev. I pulled apart the carb one more time and that’s when I finally noticed there was an “extra” piece sitting between the carb and the manifold. Turns out the truck had a governor on it. I pulled it off, cleaned it up, changed the gaskets, and reinstalled but still no rev. I finally changed out the mounting bolts for shorter ones and pulled the governor all together. I turned the key and without hesitation she started right up. Pressed the gas and she revel’s right up. A little adjustment to the carb, and the truck runs better than ever. Such a simple thing, I can’t believe I didn’t figure it out earlier. Maybe someone suffering from the same problem will use my stupidity to easily figure out their issue and get rid of the governor.

Anyway, thank you everyone for chiming in. I truly appreciate the help and definitely learned tons from all your answers. This is such a great community. Thanks again.

 

Glad you figured it out. Were mostly hot rodder's here....stuff like a governor will be removed automatically!