1972 351c 2v, intermediate start/rough running

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boilermaster

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Jasay,
As simple as your points type distributor seems, there is an awful lot that that has to happen inside there to give you good spark intensity and correct base timing, vacuum advance and mechanical advance.
Carcrazy73 suggests checking the points plate assembly and I agree that it needs to be looked into.
Also don't overlook the little ground wire going from the points plate to the distributor case, can and will cause loss of spark.
The points plate has to be lubricated too at the little plastic tabs, at its pivot point and also at the attachment point to the vacuum advance can.
any sticking at any of these places and your timing could be way off.
you can get a new points plate from rock auto for 18 bucks.
I will suggest trying this, When the engine is running well, check your base timing with the vacuum advance hose off and plugged and record the figure, when it acts up, go back and re-check and see if the numbers are the same or different.
If you have a handheld vacuum pump, that would make things a lot easier to determine if the vacuum advance is sticking.
A word to the wise here, if you decide to replace the points plate, make sure you can safely remove the 2 attachment screws from the vacuum can first, they have an awful tendency to be frozen in the housing.
 
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It sounds like you need to focus on why fuel is entering the intake when it shouldn’t. I would pull the carb off, take the top off, and see what’s in the float bowl. If it’s completely clean, see if any of the fuel exit points are clogged. Check to make sure the fasteners that hold the base on are tights, general fastener tightness test. I would also check the fuel inlet needle; I had one that had a defective tip that wouldn’t always seat and it took a rebuild to find and fix it. Unless it’s obvious, finding how the fuel is leaking in may be frustrating.
 

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Boiler, the point plate likely does need removed and cleaned. And also like the others have said, I’ll have to get the carb off and check it over to diagnose the fuel leak. It’s a very subtle leak, just running down the side, had a hard time telling if was 100% coming from boosters, it was just in that general area. Hoping I’ll have an update before the end of the weekend. And unfortunately, I’m the only one i know that’s running a carb like mine, so I don’t have another one i could try testing with.
 

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boilermaster

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Jaysay,
Couple of things here about the level of the float bowl going down.
Yes, it can be fuel percolation, that can be a very real situation, but don't mistake percolation for evaporation, especially with today's fuels, do you have summer blend or winter blend ? , ethanol blend or not ?.
How is the check valve in the fuel pump ? , just as ethanol can have an effect on your needle & seat, the same is true for the check valve inside your fuel pump.
When you take a look at where the fuel filter is attached on the float bowl, you can easily see how the float bowl can be draining back thru the fuel pump.
low float levels after sitting just a short time are commonplace with today's fuels and old mechanical fuel pumps.
 

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Yes, the fuel line connects to the bottom of the float bowl, but then it makes a 90° bend up to the float valve. The lowest it can drain back through the fuel pump is the needle seat, which is about halfway up the float bowl. A bad power bowl, or a porous casting, will completely drain the bowl. 2100 inside.jpg
 

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The other thing about draining back through the fuel pump is both check valves in the fuel pump would have to be leaking/not seating.
 

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Here's a problem that I have just encountered once.

In the mid '70s our neighbor's son had a Land Cruiser and he wanted a Chevy small block in it. They also had a '66 F250 4x4 with a 300 c.i. straight 6 engine. I knew a guy that was going through a divorce and needed some money in a hurry and he had a '56 Chevy Nomad that was in really nice condition with a low mileage small block, that I got so cheap I was almost embarrassed. So, in exchange for the F250 I installed the small block in the Land Cruiser and sold the rolling chassis Nomad to a rich guy from Reno for more than I paid for the complete car. I also supplied the adapter for the engine to L.C. transmission, exhaust, and so on.

The F250 needed a front driveshaft (the old one was damaged by a rock), which was easy, and the engine wasn't running right. On a light acceleration it would stumble. Drove me nuts, rebuilt the carburetor, new points, plug, etc, no vacuum leaks, still had the stumble. I found that when the vacuum advance was disconnected the stumble went away, the vacuum advance worked properly, no leaks. I put vacuum on the advance several times and watched it work, the breaker plate moved like it should. Finally, I noticed that when the breaker plate moved the open points would almost close. Turned out to be the bushing in the pivot on the breaker plate was egg shaped. Sold the F250 for a nice profit.

So, that's one more thing I would check, the breaker plate pivot bushing.
 

Jaysay

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Here in a little bit I’m gunna go out and take the carburetor off an check it over for some of issues that y’all have suggested. While I’m out there i wanted to look over the vacuum advance. I have a quick question on that now since i won’t have signal out there. Right now the way I’m set up, and the diagram shows, is the vacuum advance line goes from the end of the diaphragm, straight to the carburetor. The retard goes to the port on the pvs an when it reaches temp, (220degrees i believe) direct manifold vacuum is activated and it retards timing. As i said awhile back it drops my rpm’s drastically. I don’t see the advantage to this other than emissions. So, my question is if i want to change that, should i get a vacuum T and have the advance go to the carburetor, an also to the pvs, so that when it reaches 220 it advances timing further to speed the cooling system up an then just plug the retard port on the diaphragm? Wanting to make sure it makes sense to do that. Also, at what temp should the pvs disengage the manifold vacuum?
 

Jaysay

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A word to the wise here, if you decide to replace the points plate, make sure you can safely remove the 2 attachment screws from the vacuum can first, they have an awful tendency to be frozen in the housing.
Also, it’s funny you mention that, because I just noticed the other day that someone had already broken off 1 of the screw heads to the vacuum advance lol. I’ll have to remove the distributor an drill it out an retap it. Not much left to grab on to.
 

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Also, it’s funny you mention that, because I just noticed the other day that someone had already broken off 1 of the screw heads to the vacuum advance lol. I’ll have to remove the distributor an drill it out an retap it. Not much left to grab on to.
Jaysay,
You might be able to get it broke free by double nutting that broken screw from the bottom (with the distributor out ), as I recall those screws are quite long.
worth an attempt before drilling.
 

Jaysay

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Jaysay,
You might be able to get it broke free by double nutting that broken screw from the bottom (with the distributor out ), as I recall those screws are quite long.
worth an attempt before drilling.
I like that idea, I’ll give that a try first. And an update from yesterday, i took the carb off took it apart an checked the float which was slightly on the high side, so i adjusted it down. Then checked the power valve which i believe i over tightened because the gasket around it was saturated with fuel and had to peel it off. Replaced an carefully snugged the valve down. Also replaced the Venturi booster gasket just to be safe. Couldn’t find a direct cause of why the fuel was leaking from that area, but it could’ve also been leaking through the power valve. Started up an no signs of leaking anymore. And started up fine 30-45mins later. Gunna work with it a little more today an make sure everything is still good, but may have it solved. I’ll give another, and hopefully the final, update after a few days. Thanks for all the good comments.
 
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I like that idea, I’ll give that a try first. And an update from yesterday, i took the carb off took it apart an checked the float which was slightly on the high side, so i adjusted it down. Then checked the power valve which i believe i over tightened because the gasket around it was saturated with fuel and had to peel it off. Replaced an carefully snugged the valve down. Also replaced the Venturi booster gasket just to be safe. Couldn’t find a direct cause of why the fuel was leaking from that area, but it could’ve also been leaking through the power valve. Started up an no signs of leaking anymore. And started up fine 30-45mins later. Gunna work with it a little more today an make sure everything is still good, but may have it solved. I’ll give another, and hopefully the final, update after a few days. Thanks for all the good comments.
I am glad you seem to have corrected the problem. I have read where leaking Power Valve gaskets are problematic. There is one guy on YouTube that no longer uses the kit gaskets for 2100/2150 Power Valves. Rather, he used a "Viton" O-Ring to provide a better seal for the Power Valve. That YouTube video is at the following link:


I have not used the Viton O-Rings yet, as my Power Valves are working on my 2150 and Holley carburetors at this time. But, with any new carb rebuilds I will be using the Viton O-Rings.
 

Jaysay

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Here is the final update, sometime has passed now, and i believe the issue is solved. Starts right up an runs with no leaks, can fire it up anytime with no problems. Idle RPMs are fluctuating a bit more than it should, so still have to make a couple of adjustments. But overall things look promising, thanks for the assistance, I’ll definitely be coming back to this forum with any future questions.
 
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