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1972 Chevy C-10 with 250 L-6

Hello, recently I changed out an enigne in my truck I am using a 250 from a

77 Nova. I notice when cruising at highway speeds for a few minutes the engine cuts out sporadically and almost rhythmically then backfires until I let off the gas a bit and let it settle out and then it runs fine until awhile later and it does it again. Only at highway speed though??? Around town it works great. Here's what I've done: Readjusted the valves/timing Checked the fuel lines and filter

The only thing that confuses me are the fuel tank vent lines that run in the top of the cab. where do they go from there and why cant I blow back into them. Do they have chack valves of some sort? My fuel tank is full too. I have not tried blowing air back into the tank through the pump suction line yet. Could it be a stuck float in the MONOJEY Carb? and would it have anything to do with switvhing from points and condenser equipped engine to an HEI style ignition?

Any help would be greatly appreciated.

Chad

Reply to
Chad Hamann
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your not getting enough fuel!

try running at hwy speeds with the Gas tank cap lossened . u also could have a Carb filter that is pugging up..

Chad Hamann wrote:

Reply to
no one

That and I was thinking that the needle might not be out of the seat enough or the seat inlet hole might be to small.

Reply to
Shades

Yes, changing from points system to HEI system is causing the problem. I had the same thing happen to me on my 69 Chevy truck. Its a simple fix. You will need to run from the fuse box a 10-12 guage wire, from the "ignition" point in the fuse block, out to the ignition coil.(most trucks have a breakout spade to connect to) You want the voltage to cut off when the ignition switch is turned off. Don't reuse the wire old wire. It is a resistor wire that takes the 12 volts down to

9 volts so the points won't burn up.
Reply to
jdpolk

I missed that part of the post...I apologize. JD is right. running 9V to an HEI isn't gonna work to good! Do as he said and all should be peachy...with that aspect at least!

Reply to
Shades

peachy...with

Reply to
Chad Hamann

You checked the fuel filter, did you replace it?

Reply to
Commentator

I am going to agree with the need to repower the coil. long enough running under powered the coil will take a dump. It is assumed you have installed a new rotor(don't get cheap on these, the coil can burn through a cheap one in a heart beat). Is the vacuum advance working properly? Timing light can help check that, or a vacuum pump hooked up with the cap off and watch for advance linkage to move. have you checked fuel pump pressure? Have you checked fuel pump volume? Check the fuel line feeding the pump in the area around the motor mount. It also sounds like the ignition module could be going bad too.

Whitelightning

Reply to
Whitelightning

Reply to
Chad Hamann

Reply to
Chad Hamann

Your running out of Gas to the CARB

Do u have rubber hose on the Suction side of the fuel pump? if so is it Collapsing ? Fuel tank Cap NOT VENTED ? Take it off

Accertation pump in the CARB has gone BAD Turn off the Engine. Key off , look inside the Carb Throat and pump the Gas.. GAS should Stream into the CARB

!

Reply to
no one

Reply to
Chad Hamann

Reply to
Chad Hamann

A resistance wire by design only allows a limited amount of voltage through...in the case of a point ignition system, it only allows

9volts...though I have seen them with as little as 6-7volts.

Reply to
Shades

Reply to
Chad Hamann

Have you opened the carb and checked the float adjustment? Check and adjust.

Main jet(s) clear? Remove and clean.

Fuel pump working up to snuff? .Check and replace if necessary.

Vacuum in the tank? Remove the radiator cap and drive. Remove the sending unit and check the inlet for blockage

Kinked fuel line from the tank to the carb? Replace if so.

When you swapped over to HEI, did you replace the spark plugs with HEI compatible plugs?

Just a few ideas...lemme know how they pan out!

Reply to
Shades

rhythmically

Reply to
Chad Hamann

Reply to
Chad Hamann

distributor bushings

the shaft is wobbling at high speeds

had one once that was only running on 4 cylinders, the bushings were so sloppy that the points weren't opening for 2 cylinders

swap out distributor before you go further

Reply to
TranSurgeon

Does it do it ANY other time? Hard on the throttle accelerating? Cruising just under 45? Have you checked the valves? Like TranSurgeon said, have you checked the distributor for bad bushings? You didn't answer if you had the points plugs or swapped HEI plugs in? How's the exhaust?

Did it only start cutting out after you put the HEI in?

Reply to
Shades

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