The Stovebolt Site Forums The Shop Area Engine Shop Hard starting with exhaust pipe removed

I have a 52 1/2 ton with the original 216. I disconnected my exhaust pipe to replace the leaking donut. As soon as I did that, the truck became VERY hard to start. It fires right away, but immediately dies, no matter what I do with the choke or the throttle. Would disconnecting the exhaust pipe have caused this?

Thanks.

Shouldn't. Could part of the throttle linkage have been moved out of place? Perhaps pulling on the butterfly in the carb making it close?

But it should run fine without the exhaust pipe, just be a little loud.

why would the exhaust have anything to do with starting?
is it still disconnected?
"VERY hard to start" meaning it eventually started or hasn't since the exhaust work?
still 6V or converted to 12?
have you checked if it's getting gas?

Bill

It eventually starts. Still 6 volt. I'm pretty sure it's getting gas because when it doesn't start right away, it acts like it's flooded, and I have to wait awhile before it will fire again. But I will verify and also check the throttle linkage.

Check your ground circuit to be sure it's not using the exhaust pipe for a ground. It really shouldn't be if the pipe is using rubber hangers, but you never can tell.

I suspect you are dealing with two different issues, the pipe should have no effect on starting.

Joe

When I redid my exhaust (split manifold and 2.25" pipe) I had to tune my carburetor. Someone even suggested that I'd have to re-jet it. The couple times I started it with no pipes I found it hard to keep running.

It might change the flow a bit...but not too much. It will be very LOUD and that will make you shut it down real fast. Look for any linkage issues while it is out of the way. Check the grounds as has been suggested, and put it back on so the neighbors won't complain.

The improperly installed exhaust on an old truck of mine fell off on the highway and was destroyed. For the next week the truck was very hard to start and acted like it was cold blooded. The mechanic that installed my new exhaust told me the hard starting was due to very low back pressure. After the new exhaust was installed the truck would start right up and run great.

I'm going to be hooking the exhaust pipe back up next Monday. So I guess we'll see if that makes a difference. I was just wondering if I had two separate problems.
I'll let you know how this turns out. Thanks for everyone's opinions.

I drove my truck to the muffler shop with nothing more than a set of fenton headers, it had absolutely no effect on how it started. But then again my truck you just basically stomp the pedal to the floor and let it up and it is running.

On these old trucks the only result of not having the exhaust pipe attached is in the loudness. Should not have any effect on the starting or running of the engine. Mayu run a bit better though if the exhaust system is clogged up.

But it should start with no problem.

I found the problem. The spring that wraps around the choke plate shaft had come loose. So the choke was not closing. As soon as I hooked it back up, it started up just fine.

Thanks again to everyone.

lol...I always get tickled when I read where someone suggests "low back pressure" as the culprit of a problem. That's some funny stuff right there! LMFAO!!

^ Why? If the exhaust is completely off it could very well be an issue. My bike (4-1 header and a 5" exit on a long megaphone) will fire up with the baffle out but it won't stay running unless I give it a bunch of throttle or open the choke quite a bit. Same thing happened with my truck the other weekend when we had the exhaust off. Fired up but only idles for 10sec or so without the throttle and choke pulled. That right there is "low back pressure as the culprit"
However, I do agree that with a proper exhaust system in place, even one that has a sizable leak or decent length pipes but no mufflers, back pressure is rarely an issue.

1. Several posters had problems starting after exhaust removal. Fairly good proof it has something to do with it on some trucks. 2. It's really not fooling anyone to say you knew it was not that after you find out it wasn't. Your occupation is "Duh" in your profile. LMFAO

the only way removing the exhaust should be able to affect anything, is if it is severely restricted to begin with. Or you get the spring all goobered up...

^ I would consider a tiny 1.75" pipe all the way to the back of the vehicle with a big muffler at some point, severely restricted when compared to an open header.

The difference in just starting and continued running depends on how the carburetor is tuned. An unnoticed vac leak could result in a rich tune which could in turn make the truck run in the absence of a proper exhaust. Likewise, a lean tune with no leaks could cause it to stumble and stall when the pipe is removed.
In addition, restricting the exhaust at different points with various types of baffles and/or mufflers can change the back pressure to the point that it can alter the tq/hp characteristics of an engine.

Back pressure is just BS, there is no reason for it. If the guys designing the engine wanted back pressure, they would have plugged the exhaust ports.

Give me a good reason for having any back pressure, or any reason for that matter because I sure can't think of any.

Headers are designed to pull the exhaust out as fast as possible. The exhaust pulse from one cylinder pulls the next one inline out with it due to a vacuum made by speeding exhaust gas. This is why cars with headers run lean, they actually pull fuel out of the cylinders when the valves overlap due to cam timing. Open exhaust manifolds do the same just, just not on the same scale as headers.

Here is a good read on exhaust pipe sizing. If you will note, a 1 1/2" pipe diameter can support approx. 78 hp. A 1 5/8" can support approx. 98 hp, both with in range of a stock 235 engine.

http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/

Joe

If it's non turbo, back pressure doesn't do much. Maybe a couple lb/ft of torque. These old trucks are all carb tuning I think.

Just my opinion: No header, only issue would be cold air on the valve guides. That might cause them to distort. Might. Back pressure? Not an issue. We are not talking about "high performance" here. Back pressure from impulse or shock waves? Come on we got around 3,000 RPM to work with. Look at "megaphone" type motorcycle exhaust systems for a reference. Not gonna be an issue here cause it needs to take the whole exhaust pipe length to matter. Exhaust manifold split works cause you shove all 6 into a bent and restricted cast iron pipe. Check it out, 2 90 degree bends plus a small dump for 2 ports and it gets worse for all the rest. Not a "back pressure" issue for sure. It might go a bit lean, better flow, but that would only happen after it started.