Engine power question
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
I didn't read all of the posts but My experience tells me that you need to check your timing gears and chain. The easiest way is to remove the distributor cap and use a 1/2" ratchet and 13/16"(?) deep socket to turn the crank a little bit, each direction and if the distributor rotor does not follow the movement very closely, the timing set must be replaced.
Late timing causes low vacuum and poor performance which is always caused by a bad timing set.
Late timing causes low vacuum and poor performance which is always caused by a bad timing set.
Postmaster
Joined: Jan 2009
Posts: 4,584
Likes: 3
From: Chesapeake, Va.
I think what was meant was centrifugal and vacuum advance. You can check the advance by using a timing light with the vacuum disconnected from the diaphram at the distributor and with the timing light on the timing marks, reconnect the vacuum hose. You should be able to see the timing marks advance right then. To check the centrifugal advance shine the timing light on the timing marks and rev the engine with the vacuum disconnected and you should see the marks move if it is working correctly.
Using the toming light and holding the rpms at about 2,000-2,500 rpm you should not see the marks jump around, they should hold dead steady. If they jump around your timing set is worn out.
Thread Starter
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Senior User
Joined: Jan 2012
Posts: 333
Likes: 1
From: Denver, Co
Timing does advance a bit when vacuum is connected to distributor, and when throttle is held steady it does not jump around. At least not enough where i can notice. Could it be that my gas line is to small? So when there is a high demand for gas (quickly jumping on the throttle) that it bogs down til it can get more?
Postmaster
Joined: Jan 2009
Posts: 4,584
Likes: 3
From: Chesapeake, Va.
What carburetor do you have on your truck? It sounds like it is running too lean of main jets as well as possibly the wrong power valve, if it's a Holley.
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Postmaster
Joined: Jan 2009
Posts: 4,584
Likes: 3
From: Chesapeake, Va.
It would need more fuel or bigger mainjets if it's running lean, not more air. If the truck came from a lower elevation or has sat for a long time the carb probably needs a really good cleaning with all of the very small passages cleared. A "Tune-Up" in a bottle will not fix the problem.
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Senior User
Joined: Jan 2012
Posts: 333
Likes: 1
From: Denver, Co
Well when i changed the spark plugs they were all black( rich i believe) After decoding the vin i found the truck cane from San Jose but spent all of its life in the colorado mtns. So i dont believe its a jetting problem.
I only used carb cleaner once about a month ago and this last week i took the carb appart and fully cleaned all the jets. That was when i did plugs and timing. It helped out a bit but i dont know if that was because of the timing plugs or carb. Or all three
I only used carb cleaner once about a month ago and this last week i took the carb appart and fully cleaned all the jets. That was when i did plugs and timing. It helped out a bit but i dont know if that was because of the timing plugs or carb. Or all three
Postmaster
Joined: Jan 2009
Posts: 4,584
Likes: 3
From: Chesapeake, Va.
I suggest that you go through the carb again and use high pressure air through every passage to verify it all is clear. I don't remember if the 2100 has a power valve like a Holley but if it does replace it with a new one just to be sure it's good. If you can borrow a carb that is known to be good or just buy a new one you may fix the problem quicker.
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
What's the altitude where you live? If your plugs are all black they are carbon fouled. So no lean as would haven with a vacuum leak. You may need to open the air/fuel jets more living in the high country, this would give it more "Air to your fuel". Plus you may have a weak coil. As you said you have replaced the plug wires Right? it could be them to... my 2cents orich
PS HOPE YOU WERE NOT NEAR THAT SHOOTING IN YOUR STATE
PS HOPE YOU WERE NOT NEAR THAT SHOOTING IN YOUR STATE
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
Sorry, yes I did mean vacuum and centrifugal advance. As mentioned you can check the centrifugal, or mechanical advance by bring the rpms up and seeing if it advances with the timing light. The only good way to test the vacuum advance is with a hand held vacuum pump. There are specs for your distributor. Somewhere I have an old Motors Manual from around 1975 that has all those distributor specs. They vary from engine to engine and even from different distributor numbers on the same engine size. You should see the vacuum advance start in around 3-5 inches and be all in at maybe 10-11. But also the amount of advance when it's all in is important and can be adjusted using a small allen wrench in through the vacuum port on the advance unit. With the hose connected you should see a total of around 34-36 degrees with the engine at 2500-3000 rpms.
The only adjustable air/fuel jets are for idle mixture and they don't affect mid range much if at all. A rich condition could be the power valve, as mentioned, or too high of float level, or a lazy choke. Every carb kit should come with a new power valve. It is the thing under the bottom of the carb, has a cover with 4 screws.
The only adjustable air/fuel jets are for idle mixture and they don't affect mid range much if at all. A rich condition could be the power valve, as mentioned, or too high of float level, or a lazy choke. Every carb kit should come with a new power valve. It is the thing under the bottom of the carb, has a cover with 4 screws.