Help: No high rpms
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Naperville il
Help: No high rpms
I have a '70 base 350/300 4 spd. I recently replaced the fuel pump and ever since then it seems the motor hates to go above 4000rpm under load. It will spin past 4k but the rate of increase is abysmal. New carb, new fuel line, new fuel pump, fresh gas, new plugs wires and coil. I could always hit red line in no time before the old pump went south. I changed all the other parts before the problem started. Any ideas?
:confused:
:confused:
Intermediate
Joined: Mar 2003
Posts: 29
Likes: 0
From: Boone NC
Re: Help: No high rpms (stock70SB)
Not to be overly simplistic, but it sounds like the fuel pump.
First of all, why did you change it? Did it puke gas out on the floor or just crap out?
Second of all, where did you get the new one and what brand is it? Chain parts store or a good Holley/brand x pump?
Third of all, are you sure you aren't experiencing an ignition breakdown? Do you have points or HEI? If you have HEI, are you sure it isn't getting heat soak into the coil?
Good luck
First of all, why did you change it? Did it puke gas out on the floor or just crap out?
Second of all, where did you get the new one and what brand is it? Chain parts store or a good Holley/brand x pump?
Third of all, are you sure you aren't experiencing an ignition breakdown? Do you have points or HEI? If you have HEI, are you sure it isn't getting heat soak into the coil?
Good luck
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Naperville il
Re: Help: No high rpms (kraventhearcher)
Replaced 'cause the car wouldn't start. Hate to say it, but it's a NAPA part. All recommended brands put out 8psi, stock is 5-6psi. I'd rather not install a regulator under the hood as I'm trying to keep a factory appearance. I have stock points distributor w/ a Mallory electronic conversion kit. If it was bad I'd guess it wouldn't work at all.
I'm going to check the fuel pressure at the carb now that you question the new pump.
:chevy
I'm going to check the fuel pressure at the carb now that you question the new pump.
:chevy
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Help: No high rpms (stock70SB)
couple a things to check:
Air restriction? make a run with out the breather and see if it improves.
Clogged fuel filter? replace with one that doesnt have a check valve in it. Some of the filters do. If yurs does you can remove the spring and plactic valve then put it back in if its not clogged.
Ignition timing too far advanced? retard a few degrees and test drive again.
thats the first things that come to my head and any one of them could cause yur problem
[Modified by Jvette73, 9:29 PM 4/27/2003]
Air restriction? make a run with out the breather and see if it improves.
Clogged fuel filter? replace with one that doesnt have a check valve in it. Some of the filters do. If yurs does you can remove the spring and plactic valve then put it back in if its not clogged.
Ignition timing too far advanced? retard a few degrees and test drive again.
thats the first things that come to my head and any one of them could cause yur problem
[Modified by Jvette73, 9:29 PM 4/27/2003]
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Naperville il
Re: Help: No high rpms (Jvette73)
Ran w/o air filter no difference. Just replaced fuel filter(no ckeck valve) no diff. Changed timing both ways, no diff. I'll try w/o any fuel filter and check pump pressure too. I'm also going to check valve train operation, maybe sticking valve or spring weak or broke.
Thanks for the help.
:steering:
Thanks for the help.
:steering:
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Help: No high rpms (stock70SB)
nother thing to check. play in the dist shaft. It should move up and down a bit but no side to side. Turn the motor till the points are in the open position on the high step off the dist cam. Then grab the dist shaft and attempt to move it back and forth from side to side. Watch the gap in the points while yur doing this. If the shaft is loose you should see the gap changing between the points. If its loose and the point gap is moving it could be messin with yur dwell at higher rpms and causing the problem.
Intermediate
Joined: Feb 2003
Posts: 46
Likes: 0
From: Pompano bch fl
Re: Help: No high rpms (stock70SB)
What type of carb do you have, vaccum or mechanical? Also do you still have the cats in the exhaust? I had a cat go bad and i could rev the motor fine but under load it felt as if I was pulling a house. Good luck
Le Mans Master
Joined: Feb 2002
Posts: 5,722
Likes: 0
Re: Help: No high rpms (stock70SB)
Is it running hot? Does it "bog"? Have you ever replaced your catalyctic converter? I had the same type problem on my FireChicken, and found out it was an old burnt up cat causing all the trouble.
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Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: Naperville il
Re: Help: No high rpms (Jman)
1970, so no cats. No bog just can't spin high r's under load. After checking a hunch, the fuel pump inlet hose is real soft, potentially collapsing under big vacuum. Maybe the cause of the failure of the other pump either running hot or hose is deteriorating on the inside. Just ordered a new one from CC for $9. Hopefully the cause.
Thanks for the suggestions.
Thanks for the suggestions.
