Fuel spark delivery question

[Robert8096]

I have a 69 truck with a 283 and have a nagging problem where the truck runs fine up till about 50 mph. After that it will start bucking and acts like it is not getting spark or too much or not enough fuel. I can back off and it will continue for a few min and then go back to running normal. Did a compression check and all are 150 to 153 PSI. Vacuum gauge reads a steady 19hg and responds correctly when working the throttle. It was an original point type ignition and I have changed it to HEI, replaced the wires and plugs. I replaced the 4 barrel carb with a known good one and my problem still exists.

Things that have got me saying WTF:

I looked for a fuel filter between the fuel pump and tank and there does not seem to be one. Is this the norm for the old girl? I have one between the pump and carb and I am seeing a little bit of rust in that one but nothing major. Is there a sock on the end of the pickup tube in the tank? I ask this because LMC shows no sock but CPA shows a sock on their sending unit. I also see that there is a difference between the 6 and 8 pickup units for the tank. Is this because of fuel line size and if so will that make a difference in running a stock 283 in a truck that was an originally a six?


When I changed the plugs I came across what is in the pictures below and see no reason for it. There was nothing wrong with the threads of the plug hole as I replaced the plug and had no issues. The extra piece looks to be a compression tester attachment. Any ideas on this PO install?

Thanks
Robert

[68gmsee]

I think the pics show an anti fouling adapter used when the rings or the valve guides are shot. I've tried them and they work like crap! Get rid of them.

RE: fuel delivery. Things I would check .

I would check the fuel pump for proper delivery. Disconnect from carb and place in a plastic container. Have someone crank the engine and check to see how the pump works. Should be a strong stream of gas as the engine turns.

Check filter inside the carb. Maybe remove the top and clean inside.

Check and/or replace the sock in the tank -it should have one unless it was removed like I did. I installed a filter before the fuel pump instead.

[cdowns]

yes by all means get rid of those antifoulers//then i'd check the timing starting at physically setting the number one cylinder at TDC by using a piston stop to get TDCexact and check that the marks on the balancer match the pointer

[Robert8096]

Plug looked fine and a compression check of that cylinder was 150 PSI. Have not done a leakdown test but I am going to do one.

No filter in the carb it's an Elderbrock 650 version and the Holley carb that was on there to begin with did not have one. Two different carbs same symptoms.

Going to drop by the autoparts store on the way home today and pick up a fuel pump (35.00) and rig some kind of filter before the pump since I don't see one between the tank and pump. Then this weekend I am going to pull the tank and check it out and if it has rust issues. I am going to try to find a decent tank for a decent price, if I don't then I am going to contact Fuelcell Guy and get him to build me a tank for the bed.

Timing checks out, I installed a HEI unit, new plugs and wires last weekend and set the timing. I had the same symptoms with the old points unit.

Thanks for the info.

[68gmsee]

Since the compression is good and the plugs look fine, a leakdown test is good, however, it may not show wear on the valve guides. Sometimes a good indicator is smoke when you first start it after it sits for a while.

[cdowns]

filter b4 the pump not good idea

[Robert8096]

I have not noticed any smoke on startup and it does not use any oil, but it could be valve guides because I don't think the heads have been re-done to use our crappy unleaded gas. I miss those days of high octane leaded gas.

Originally Posted by cdowns

filter b4 the pump not good idea

Please elaborate.

[68gmsee]

Re: filter before the pump.

The reason I use one before the pump is because the truck sat for almost 5 years and the tank had a lot of rust sediment. The sock was totally plugged and I decided that took the place of the sock.

I've been running a filter before the pump for almost 10 years and change it every 4-6 months or 2k-3K miles. I also have the one inside the carb that I replace at the same time.

[mr48chev]

Originally Posted by cdowns

filter b4 the pump not good idea

Why would you think that or make such a suggestion?

I've run a filter before the pump on every vehicle I've put together for the past 30 years. It has saved countless fuel pumps.

When I do that I still run the filter at the carb also.

I'm very particular where I buy my gas and the local stations I buy from are fairly new. But sometimes when I am on a road trip I may not have a choice in gas stations and that is usually when I have had problems. Or the lost or left off for some reason or gas cap that seems to be a great attractor for dirt

.

[So.Cal.Super]

"Quoted from Longhorn Man
A filter should be on the pressurized part of the fuel line. If it is on the vacuum side, then this lowers the boiling point... which boiling fuel is called vapor lock, and can lead to walking home. Putting the filter on the vacuum side also increases the work the pump is needed to do."

I read this after I put a very nice very expensive filter on my truck at the same time I replaced my fuel pump. I only run premium gas from good stations and I started to notice at W.O.T. between second and third my truck would buck and jump. well I put 2 + 2 together with what I read and after I got 5 I said ok this can happen to me. I still let it go because I wasn't that worried about it. then it started happening at lower speeds and I still let it go. Then one day I went to pull out of my driveway and it died. Its not fun to try and push one of these back in the driveway by yourself.

After pouring some gas in the carb to start it and back it up in the drive way.
I started trouble shooting and came to find out as soon as I bypassed my pretty fuel filter she fired up and ran like normal.

Yes I have heard the stories of I have ran them with no problem, Sadly I am not one of them.

Hope you find the problem Robert.

(If you run an electric pump I don't think this is a problem.)