PDA

View Full Version : exhaust overheating



rdmullings
07-30-2000, 10:25 AM
I have rebuilt the 307 and the original 2 speed tranny in my 69 chevy 108. But I purchased a rebuilt carb from parts store. The number was not on original carb. I think they made a guess and gave me a carb from a six cylinder. I have severe overheating of exhaust manifolds which renders my van useless because the starter gets to hot to work after a short drive. If anyone can get me the number off of an original 307 carberator I will hopefully fix the problem. Or if you know that this could be another problem please let me know. Thanks

------------------
need help

rdmullings
07-30-2000, 10:34 AM
Sorry I posted wrong e-mail address it s rd_mullings@twu514.org not com

------------------
need help

Duane 70gmc
07-30-2000, 01:21 PM
I have a 70 108 with a 307 and a 2bbl. I'll check the stamping numbers on the carb and post them tonight.
Van On Dudes

------------------
Duane
Proud owner of a 1970 GMC 108" V-8 Vintage Van
Any ?
Email:
dkh7d108@hotmail.com
VCVC Rules

JD
07-30-2000, 07:41 PM
HI...I JUST LOOKED AT MY 69 108" 307 AUTO. AND THE NUMBER ON MINE IS #7029125..IM ASSUMING THIS IS ORIGINAL CARB..IVE OWNED IT FOR 4 YEARS..I HOPE THIS HELPS..........JD
MIGHT BE RUNNING TO LEAN(LATE NIGHT) OR YOU MAY HAVE A PLUGGED EXHAUST...HOW DID IT RUN BEFORE? HOW DOES IT RUN NOW,BEFORE THE EXHAUST MANIFOLDS "GLOW"?? MIGHT WANT TO RECHECK YOUR TIMING........

[This message has been edited by JD (edited July 30, 2000).]

[This message has been edited by JD (edited August 07, 2000).]

painterchris
07-30-2000, 09:44 PM
Have you thoroughly checked your exhaust? There is a thermostatically controlled flapper in the exhaust manifolds. The purpose of this flapper is to recirculate hot exhaust back up into the motor and help it warm up faster. Problem is, they become locked up after a while. If they lock up in the OPEN position, like mine, it's no problem. It just takes a little longer for the engine to warm up because the exhaust isn't recirculating. However, if the lock up in the closed position, the flappers act as a major exhaust pipe blockage, causing all kinds of problems. This may not be your problem, but it's worth checking out.
Later,
Andy.

rdmullings
07-31-2000, 12:17 PM
<BLOCKQUOTE>quote:</font><HR>Originally posted by JD:
HI...I JUST LOOKED AT MY 69 108" 307 AUTO. AND THE NUMBER ON MINE IS #7029125..IM ASSUMING THIS IS ORIGINAL CARB..IVE OWNED IT FOR 4 YEARS..I HOPE THIS HELPS..........JD
MIGHT BE RUNNING TO RICH(TO MUCH FUEL) OR YOU MAY HAVE A PLUGGED EXHAUST...HOW DID IT RUN BEFORE? HOW DOES IT RUN NOW,BEFORE THE EXHAUST MANIFOLDS "GLOW"?? MIGHT WANT TO RECHECK YOUR TIMING........

[This message has been edited by JD (edited July 30, 2000).]<HR></BLOCKQUOTE>



------------------
need help

Vanner68
08-01-2000, 08:19 PM
just to help clear things up: i doubt you got a 6 cylinder carb cuz they are 1 bbl carbs and won't bolt up! sounds like you are runnin lean or the above mentioned exhaust flapper door is stuck.

rdmullings
08-02-2000, 08:37 AM
You guys were right the numbers match and it is not the carburator I don't think. I went to a well known Carb shop here and asked them. They said I could be running lean but they did not think that I could be so far off on the carb that I would be running cherry red or orange exhaust. I had the flappers on the exhaust cut off during the overhaul and a glass pack added. So I don't think that is the problem. One older Mechanic there said that if the valves were to tight it would cause the exhaust to run red, he suggested that I loosen each valve until I hear it clatter and then tighten it one half turn. I did set the timing myself and then had a mechanic check it because I also thought that was the problem. Thanks for this forum I don,t feel like I am just guessing by asking you guys about it. Please give me your input on this.

Vanner68
08-02-2000, 03:21 PM
OK, let's review: you have the right carb, no exhaust backpressure, and glowing exhaust manifolds. I think we have a combination of problems here. How does the engine sound when it's running? Is it popping in the exhaust? You may have a tight valve problem, or if the heads are still original, bad valve seats. With leaded gas no longer available, the valve seats will wear and the valves will no longer seal properly. If the heads are not cracked, you can have hardened seats installed. A lean mixture from the carb will increase this problem. You may also have a vacuum leak, which will lean out your mixture and no amount of knob fiddling will change it. Squirt a little WD-40 around the base of the carb with the engine running and listen for an increase in RPM's. If no change, Squirt it along the gasket at the intake and head. One more thing, did you hook up your vacuum advance? It is easy to forget when you are in a hurry to get your van running!

rdmullings
08-02-2000, 09:22 PM
I do have some slight puffing or popping noise in the exhaust. Vacuum advance is hooked up. but I don't remember checking to see how much vacuum I had. I have checked the base of the carb and the intake manifold gaskets with WD-40 and did not find a leak there. The heads are a question also. I remember asking about the unleaded gas problem when I took them in. The mechanic stated that he had some heads already fixed that he could swap for mine. But it seems as if he ended up working my heads over instead. The problem is I don,t remember and the mechanic is no longer around. I think if I can this weekend I need to see about the vacuum, vacuum advance and possibly reseting the valves and then go from there.

tomschaner
08-02-2000, 09:56 PM
hey dude,i've got a 67 van and you wouldn't believe this but my harmonic balancer shifted causing a major timing problem on my 250 cu in engine.which means the engine timing may line up with the balancer but it is not correct.my mark wound up being about 25 degrees from where it should.you may want to get #1 cyl. on its compression stroke and see were the rotor is pointing.if its no where near #1 position you may have the same problem i encountered a harmonic balancer that let loose.just a mind bogler which people sometimes overlook.especially with probably a original balancer thats 30 some odd years old.good luck.

rdmullings
08-04-2000, 08:45 AM
I am not for sure yet because I have not been able to test it. I might have the problem solved. I took the van to a guy that had helped me with an old 59 Belair that had problems no one could figure out. He said its running lean. When I told him what all I had already done he cmae out and listened to the engine. He pulled the pcv valve and sealed it off with his hand and the engine immedietly improved. I had replaced this valve once since having this problem but it did not make any differance in how it ran so I gave up on the idea. This guy said he does not remember the 69 307 having a pcv valve and that it might have been put on by other owner. My hook up comes off the back and base of carb and hooks to the pcv valve which is in the valve cover next to the driver. Does your 307 have this set up.

68chevyboy
08-04-2000, 12:16 PM
not mine. it was all original and it had a normal intake. at autozone, or any auto parts store they sell pvc blockoff plates that are chrome. mr. gasket co. makes them.

rdmullings
08-07-2000, 10:34 AM
Well that was most of my problem. The van is running and I have already taken two fairly long trips and have no trouble with exhaust overheating. I changed plugs since they were some what fouled out from running to lean to long. It runs like a charm going down the road. But when it is idling it lopes or surges pretty good. It does not die but it is annoying. I want it to be as right as possible. Before I go changing things I thought I would ask you guys what your thoughts are on getting a smooth Idle. Thanks RDM

smiley
08-07-2000, 11:39 AM
Your idle aounds like it may need a timing adjustment, which could also contribute to your previous problem. If the timing is too advanced or retarded, the cylinders aren't firing at the optimum moment. Also, running too far out of time in either direction (advanced or retarded) for an extended period can cause head damage and premature piston wear.

Duane 70gmc
08-07-2000, 07:30 PM
If the PCV valve cured a lot of the problem, then don't forget to reset the idle mixture screws on the carb. If the PCV valve was causing a vacume leak then the idle mixture screws definently should be readjusted.

Duane

------------------
Duane
Proud owner of a 1970 GMC 108" V-8 Vintage Van
Any ?
Email:
dkh7d108@hotmail.com
VCVC Rules

Not a Vette
03-21-2010, 11:19 AM
Thermostatically controlled flapper in the exhaust manifold is broken. There is also an exhaust leak.There is a half solid steel cylindrical part exposed- which position is open? Should I remove this? Symptoms are; hard starting and running poor when cold and back firing when starting. Also sometimes pre-ignites/ spins a couple times after shutting off. Advice would be appreciated, can not find this dohiggy in the Chilton manual.

fustkarr
03-21-2010, 11:38 AM
Check you timing.The heat riser w/not present starting problems, it only affects driveability when the engine is cold.It sounds like its stuck open, providing no "warm-up" help for the engine.Preignition {you don't say hot/cold} isn't a cold engine typical.BTW, does it sound like a coupla ball bearings rolling around the bottom of a coffee can..this is pinging, normally associated w/crummy fuel, lean fuel condition or too much ign timing{spark coming in too early b4 TDC}Does the carb have a antidieseling solinoid? Check this, it may be defective.Also; when you shut the motor off try holding the gas pedal slightly open, this will kill the vacumn of the motor and it will lessen the fuel drawn in upon shut off.
Goodluk, Randy

van-itti
03-21-2010, 06:32 PM
I couldnt get my L-6 to run until I removed all the smog stuff.
Replaced points,cap,rotor - timing dead-on and it would still backfire and run-on.
I removed the pump and plugged up all the intake holes and I havent touched it since...I run mid-range plugs and set the idle at 500. Slightly lower than the 550 factory.
Good gas helps too!!

joyrde
03-22-2010, 10:51 AM
if someone already suggested the folowing, I apologize. .. just way too much reading.

Sounds like either the float is not controlling fuel flow or the needle/seat is not working correctly. Either way fuel would be dunped into the exhause AND oil pan. Both of which can cause a major FIRE or explosion.

Start the van - - take off the air cleaner - -using a flash light (not a drop light!!!) look down the throat of the carb at idle. You should NOT see ANY fuel flowing - - at the most just a very little bit. Anything more than a dribble indicates carb issues.

I am sure someone has said this - - but if the issue was not there before the carb change AND you have not done anything else - - then the carb is the problem.