motor cutting out at highway speeds
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motor cutting out at highway speeds
Posted: June 16 2008 06:58 PM
 
Thomas Yates (aka Tomsmodela) [ View ] [ tpthyates@bellsouth.net ] [ Car Ads ] [ Blogs ]
Brandon, Mississippi
 
My Father-in-law has a 1970 Chevy pickup with a 307 in it with a 4 barrel carb we have replaced everything in the fuel system. The truck runs good until you get up to about 60 to 65 MPH then it acts like it is running out of fuel, as long as you slow down below 60 it runs good. We don't know how many miles are on the motor and we are thinking it is the fuel pump cam lobe is showing wear and not able to pump enough fuel.
 
 
Comments
 
Posted by jdboes  -  06/16/2008 07:20 PM
Take the line loose and start the motor, it will run off the fuel in the carb for a short time. See how long it takes to fill up a coke bottle , about 10 seconds is fine, Filters, carburetor float level, tank screen, restricted fuel line , or even a defective fuel pump can do what your describing. exactly what is just about everything in the fuel system? If you need to check the fuel pump lobe on the cam, you can pull the fuel pump and measure the pushrod movement, it should move the same amount as the cam lobe height. Just measure another cam to compare any wear. Did you check the fuel pressure while this is happening at 60 miles an hour? Just tape the gauge to the wiper and view it through the windshield.
jdboes [ View ] [ Email ] [ Blogs ] [ Car Ads ] silver spring, Maryland
 
Posted by Starfire  -  06/16/2008 07:20 PM
When you say you replaced everything in the fuel system, just exactly what is everything? This candidly sounds a bit like a clogged fuel filter restricting fuel flow to the carburetor.
Starfire [ View ] [ Email ] [ Blogs ] [ Car Ads ] Weimar, Texas
 
Posted by Tomsmodela  -  06/16/2008 07:27 PM
We have repalced everything from the gas tank to the carb. We ran all new steel lines and just used short pieces of rubber to connect to the carb, fuel pump, filter and tank. I have set the floats in the carb and replaced the fuel filter again yesterday. We are thinking about putting in an electric fuel pump, Someone else had said that the vacuum line to the vacuum advanced or the vacuum advanced could make it do this.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
Posted by jdboes  -  06/16/2008 07:40 PM
Starfires right, you could have overlooked the filter in the carb on that model. Your description sound like a fuel related issue however if the car acts like its cutting out at speed a wire in the distributor could have a break in it and only break contact when the vacuum advance moves, disconnecting the vacuum line to the distributor can help identify this.
jdboes [ View ] [ Email ] [ Blogs ] [ Car Ads ] silver spring, Maryland
 
Posted by bigdude  -  06/16/2008 07:34 PM
Make sure your vent for the tank is working if it has one or the cap. Vacuum advance wont do that you still get advance out of dist.
resident know it all [ View ] [ Email ] [ Blogs ] [ Car Ads ] Three Rivers, Michigan Charter Member since January 2004
 
Posted by Tomsmodela  -  06/16/2008 07:51 PM
jdboes-The carb doesn't have a filter in the fuel inlet of the carb. I will check the Dist. I was thinking of doing a tune up to the dist. anyway.

Big dude- The new tank is vented and is working.

Thanks for your advice.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
Posted by jdboes  -  06/16/2008 08:08 PM
If you look at the wires in the distributor be sure to give them a gentle tug, usually the insulation is holding the wire together even if the copper is broken internally. Is the car cutting out like you turned off the key or is it falling flat? The wiring to the distributor will usually cause the car to cut out at least momentaraly as if the key was turned off. As I read your description I would favor this being a fuel related issue. I only mentioned the ignition wiring issue as a response to your previous advice regarding the distributor vacuum line
jdboes [ View ] [ Email ] [ Blogs ] [ Car Ads ] silver spring, Maryland
 
Posted by 1carguy  -  06/16/2008 09:14 PM
Install an electric fuel pump.
1carguy [ View ] [ Email ] [ Blogs ] [ Car Ads ] Pleasanton, California
 
Posted by amswuod1  -  06/16/2008 09:17 PM
Among the many other shade tree test procedures, try removing the distributor vacuum hose at the carb. Suck on it and see if you get fuel. If so the distributor vacuum diaphram is kaput, so I've been told....

Bob D.
Cleverly disguised as a responsible adult. [ View ] [ Email ] [ Blogs ] [ Car Ads ] Union, Kentucky Charter Member since July 2006
 
Posted by hotrodgene  -  06/16/2008 10:22 PM
I had a motor home that would run great to 6o mph and then would actual loose speed as long as accl. was down and when I lifted accl.it ran fine.Problem was filter in gas tank.
Gene Riffe [ View ] [ Email ] [ Blogs ] [ Car Ads ] Saint Petersburg, Florida
 
Posted by protruck69orange  -  06/17/2008 09:09 AM
run your truck at 40 mph floor board it, hold it to the floor till it starts acting up,if the motor quits running,let up on gas wait a few seconds put it bach on the floor it shouid run for a few seconds and quit again.it should be screen in fuel tank,replace it.
protruck69orange [ View ] [ Email ] [ Blogs ] [ Car Ads ] kountze, Texas
 
Posted by JAWS  -  06/17/2008 09:50 AM
What kind of ignition system do you have?
An electrical headache can make a great car a pain [ View ] [ Email ] [ Blogs ] [ Car Ads ] Boise, Idaho Charter Member since August 2004
 
Posted by brian41chevy  -  06/17/2008 10:12 AM
Does your exhaust system have any restrictions in it? I've had this happen on cars before and have found a collapsed exhaust pipe or a plugged catalytic convertor. Since your truck should not have a convertor on it I would look at the exhaust pipes.
There is a fine line between hobby and mental illness [ View ] [ Email ] [ Blogs ] [ Car Ads ] New Lenox, Illinois Charter Member since November 2004
 
Posted by Starfire  -  06/17/2008 10:49 AM
The real problem may be it's a 40 year old engine of unknown mileage. In 1969-70 production the 307 wasn't all that great an engine to start with. Had one in a station wagon and the only phrase that adequately described it is "IT SUCKED." Real Dealer service bay queen! I didn't want to bring this up, but if the Distributor doesn't have major problems it just could be there are serious valve train issues that only show up so far at sustained RPMs above 1,800 or so rpms. Any misfiring or backfiring associated with the nature of the symptom? Of course it might also be a timing chain stretched to the point a tooth or two may have been jumped.
Starfire [ View ] [ Email ] [ Blogs ] [ Car Ads ] Weimar, Texas
 
Posted by Tomsmodela  -  06/17/2008 07:14 PM
hotrodgene and protruck69orange- It's a new tank but I will try it and see, it could have gotten trash from a gas station.

jaws- It has an HEI system in it.

brain41chevy- the exhaust is all new duals with no cat. We changed the exhaust and it is still doing it.

starfire- we are going to rebuilt the distributor and see how that works also. It has not back fired or misfired.


I will keep you posted on what happens.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
Posted by jdboes  -  06/17/2008 08:58 PM
I'm still favoring a fuel issue, have you check the presure while it's acting up yet?
jdboes [ View ] [ Email ] [ Blogs ] [ Car Ads ] silver spring, Maryland
 
Posted by Tomsmodela  -  06/17/2008 09:17 PM
jdboes- I will be checking the fuel pressure. My father-in-law lives 2 1/2 hours north of me so I'm going to check everything everyone has suggested when I go up there. He will be checking some of it this weekend, he has limited access to the tools needed to check everything.


I'll let you know what happens.

Thanks.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
Posted by Italianguy63  -  06/18/2008 05:37 PM
Could be a weak coil in the HEI. Check the ignition part out also. MC
Speed is about how fast do you want to spend! [ View ] [ Email ] [ Blogs ] [ Car Ads ] Bartow, Florida
 
Posted by dixie  -  06/18/2008 09:13 PM
Man them must b some kinda dist in them kentucky cars never seen a gas powered one. hey Tomsmodels better stay away from the big muddy are u want have to worry.
jim grace [ View ] [ Email ] [ Blogs ] [ Car Ads ] dade city, Florida Charter Member since January 2006
 
Posted by Tomsmodela  -  07/19/2008 03:09 PM
well everyone just got done taking the fuel tank out and checked the screen and the tank very clean, we also cleaned out all the fuel lines and replaced everything in the distributer(cap, rotor, ignition mod. vacuum advance and coil) and new plugs and wires, so checked pressure and have to put on an electric fuel pump need some suggestions on which brand is the best to use.

I know it needs to be 4 to 7 psi. but would like to know the best to use for longevity the one I ran in my 31 had to be replaced about every year. Need one with better performance than putting a new one on every year.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
Posted by jdboes  -  07/21/2008 08:58 PM
WHAT WAS THE PRESURE? CAN YOU USE A STOCK MECHANICAL PUMP?
jdboes [ View ] [ Email ] [ Blogs ] [ Car Ads ] silver spring, Maryland
 
Posted by Tomsmodela  -  07/23/2008 08:23 PM
The presure was just below 4psi at 60MPH and at idle, it has a stock mech. pump on it, it looks like the cam lobe has worn down.
Tomsmodela [ View ] [ Email ] [ Blogs ] [ Car Ads ] Brandon, Mississippi
 
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