engine rpm drops with brake
Pro
Joined: Apr 2006
Posts: 647
Likes: 22
From: Norwalk CT and Boynton Beach FL
You say that with the car in neutral and ideling, when you pull off the vacuum advance hose the engine quits. This sounds like a carbuerator problem and/or a fuel mixture problem.
First, the mixture is too lean --- back out each of the two carb screws in the front of the carb two full turns. Then get some gumout (or any carbuerator cleaner) and run it through the carb as close to full strength as possible to clean out the jets, etc. See if this doesn't end the problem. If not, you may need to rebuild the carb --- my guess is that your problems are carb problems.
How many miles do you have on this engine? Is it the stock 350? How many carbs are on the engine --- just one 4-barrel I hope.
First, the mixture is too lean --- back out each of the two carb screws in the front of the carb two full turns. Then get some gumout (or any carbuerator cleaner) and run it through the carb as close to full strength as possible to clean out the jets, etc. See if this doesn't end the problem. If not, you may need to rebuild the carb --- my guess is that your problems are carb problems.
How many miles do you have on this engine? Is it the stock 350? How many carbs are on the engine --- just one 4-barrel I hope.
Pro
Joined: Apr 2006
Posts: 647
Likes: 22
From: Norwalk CT and Boynton Beach FL
Tthe weather was bad, whole day of rain, so I could do some more testing.
I have turned some screws on the carburator, mxture, idle speed and have some readings.
I have no idea how I can post them here, so I made a site with the explanation.
Could you check my testing and give me some feed back so that I have an idea what to do next. To be sure, I'll recheck all the vacuum hoses.
http://users.skynet.be/fa604708/vacuum-tuning.htm
I have turned some screws on the carburator, mxture, idle speed and have some readings.
I have no idea how I can post them here, so I made a site with the explanation.
Could you check my testing and give me some feed back so that I have an idea what to do next. To be sure, I'll recheck all the vacuum hoses.
http://users.skynet.be/fa604708/vacuum-tuning.htm
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
After looking at these pictures, your vacuum seems low --- what engine is in this car? Is it stock or does it have an aggressive cam? How many miles on the engine? If it's not the carb, then it might be a valve problem. How long have you had this car and how long did it run fine before this problem cropped up?
I was thinking his vacuum looked low too. I'm pretty sure he has an un-found leak somewhere that may make it hard to diagnose properly.
Burning Brakes
Joined: Sep 2004
Posts: 1,167
Likes: 2
From: Ft.Worth Texas
Well, I dont know if you still have the problem but if you do I would check, as somebody already said, the vac hose going to the tranny modulator valve may have a hole somewhere. Check modulator hose by plugging where it connects at motor. Or most likely the brake booster. Pull out the big vac hose going to it and plug the hose. Start motor and see if you still have the problem.
Check for leaks at intake by lightly spraying starting fluid around gasket surfaces and carb base while motor is running. If rpm increases you have found a leak. Try tightning the bolts
Check for leaks at intake by lightly spraying starting fluid around gasket surfaces and carb base while motor is running. If rpm increases you have found a leak. Try tightning the bolts
Last edited by David Ey; Dec 30, 2006 at 02:13 PM.
Thread Starter
Intermediate
Joined: Aug 2006
Posts: 26
Likes: 0
From: Weerde
You say that with the car in neutral and ideling, when you pull off the vacuum advance hose the engine quits. This sounds like a carbuerator problem and/or a fuel mixture problem.
First, the mixture is too lean --- back out each of the two carb screws in the front of the carb two full turns. Then get some gumout (or any carbuerator cleaner) and run it through the carb as close to full strength as possible to clean out the jets, etc. See if this doesn't end the problem. If not, you may need to rebuild the carb --- my guess is that your problems are carb problems.
How many miles do you have on this engine? Is it the stock 350? How many carbs are on the engine --- just one 4-barrel I hope.
First, the mixture is too lean --- back out each of the two carb screws in the front of the carb two full turns. Then get some gumout (or any carbuerator cleaner) and run it through the carb as close to full strength as possible to clean out the jets, etc. See if this doesn't end the problem. If not, you may need to rebuild the carb --- my guess is that your problems are carb problems.
How many miles do you have on this engine? Is it the stock 350? How many carbs are on the engine --- just one 4-barrel I hope.
As it is after 22:00 I cannot start the engine (noise isn' t permitted after 10 o'clock PM)
it is the orginial engine, one Rochester 4MC, next week (next year) i'll try the gumout
Thread Starter
Intermediate
Joined: Aug 2006
Posts: 26
Likes: 0
From: Weerde
After looking at these pictures, your vacuum seems low --- what engine is in this car? Is it stock or does it have an aggressive cam? How many miles on the engine? If it's not the carb, then it might be a valve problem. How long have you had this car and how long did it run fine before this problem cropped up?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
My Dad's from Germany. Never met his parents from what I understand, but my Grandparents, the ones that adopted him, traveled there a lot. I always wanted to visit Germany, learn German, and drive German sports cars and get a Rot as a pet. Hmm...seeing a pattern?
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Thread Starter
Intermediate
Joined: Aug 2006
Posts: 26
Likes: 0
From: Weerde
Well, I dont know if you still have the problem but if you do I would check, as somebody already said, the vac hose going to the tranny modulator valve may have a hole somewhere. Check modulator hose by plugging where it connects at motor. Or most likely the brake booster. Pull out the big vac hose going to it and plug the hose. Start motor and see if you still have the problem.
Check for leaks at intake by lightly spraying starting fluid around gasket surfaces and carb base while motor is running. If rpm increases you have found a leak. Try tightning the bolts
Check for leaks at intake by lightly spraying starting fluid around gasket surfaces and carb base while motor is running. If rpm increases you have found a leak. Try tightning the bolts
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
I think the big problem is your system vacuum should be in the area of 15. Never lower than 10. That indicates a problem in itself.
Thread Starter
Intermediate
Joined: Aug 2006
Posts: 26
Likes: 0
From: Weerde
vacuum confirmed problem
I've done some more testing by reading the threads above.
I think the vacuum problem is the one that's the most important for the moment. As longs as this one isn't solved, looking for other solutions is, in my eyes, a waste of time.
I've described my testing in the url hereunder, and I think I come to the conclusion that the carburator needs to get off, and has to receive a new seal. But before I do this job, which is totaly new for me, I would be shure that this is the thing to do. And if it is difficult, is there a step-by-step explanation how to do it? The only explanation I have is the one in Haynes. IF this is the good one, I'll manage my way throught it.
At the same time I'll change the seals from the valve covers which are pulverised. I think a lot of the seals may be damaged due to the 5 year non activity (the car was in a garage for 5 years without driving it).
http://users.skynet.be/fa604708/vacu...ke-booster.htm
I think the vacuum problem is the one that's the most important for the moment. As longs as this one isn't solved, looking for other solutions is, in my eyes, a waste of time.
I've described my testing in the url hereunder, and I think I come to the conclusion that the carburator needs to get off, and has to receive a new seal. But before I do this job, which is totaly new for me, I would be shure that this is the thing to do. And if it is difficult, is there a step-by-step explanation how to do it? The only explanation I have is the one in Haynes. IF this is the good one, I'll manage my way throught it.
At the same time I'll change the seals from the valve covers which are pulverised. I think a lot of the seals may be damaged due to the 5 year non activity (the car was in a garage for 5 years without driving it).
http://users.skynet.be/fa604708/vacu...ke-booster.htm
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Taking the carb off is very easy, if you go slow and step by step. Take pics of it from all sides before you remove it and document the linkages, washers, pins, and everything else before bagging them. Makes puttin it all back on much faster.
Thread Starter
Intermediate
Joined: Aug 2006
Posts: 26
Likes: 0
From: Weerde
a happy man
HI
some feed back
as you know I changed the hoses which were having vacuum problems. I sealed the hoses which I did not need anymore (cannister and lights).
I found a broken valve cover seal, I changed the pcv valve gommet.
I take off the carburator and found a broken seal too.
I rebuild everything, started the engine and drove off for the rest of the afternone.
For your info, I'm building my own small corvette site with the experience of my problems. which can be seen at the above mentionned url
THANKS!! and again thanks to all of you who helped me.
one of these you will find all the pictures of my problems
meanwhile you can see the car after my afternoon drive
http://users.skynet.be/fa604708/corvette/corvette.htm
some feed back
as you know I changed the hoses which were having vacuum problems. I sealed the hoses which I did not need anymore (cannister and lights).
I found a broken valve cover seal, I changed the pcv valve gommet.
I take off the carburator and found a broken seal too.
I rebuild everything, started the engine and drove off for the rest of the afternone.
For your info, I'm building my own small corvette site with the experience of my problems. which can be seen at the above mentionned url
THANKS!! and again thanks to all of you who helped me.
one of these you will find all the pictures of my problems
meanwhile you can see the car after my afternoon drive
http://users.skynet.be/fa604708/corvette/corvette.htm
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
