The Stovebolt Site Forums The Shop Area Engine Shop Adjusting Fuel Mixture + Seafoaming

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here's the thread containing the video of my "inaugural" drive. if you listen kinda closely, you can hear the engine "revving" at cruising speed and then operating smoothly at acceleration. i'm guessing this is a bad fuel mix and was wondering if anybody had any tips for adjusting the mixture at the carb?
idle is smooth as butter, by the way.


also, i have a pint of seafoam and would like pointers on getting it into the engine. i know i can put it in the oil and the fuel, but on a previous vehicle i was able to suck it up into a vacuum line on the intake manifold and don't see how to do it on this chevy. tips?

What carb on what motor?

it's a carter (yf?).. it was stamped "carter" and from searching, carter yf seems to be the common replacement for the rochester.

216 ci, btw

Any smoke when at idle?

nope, no noticeable smoke at idle.

100 views and no inputs? anybody at all?

Perhaps a vacuum leak?? Take some carb cleaner and spray it around the intake ports, carb base, and see if the idle changes doing that. Its the first thing I'd do. May as well check the wiper vacuum line for a leak to?

Yes a vacuum leak will cause what you are describing. Look at all the usual suspects and plug the wiper line just for the test. I had a vacuum wiper motor cause all sorts of evil stuff in the past. Went with electric to get away from it.
1, Carb base
2, Intake manifold: 3 places
3, Intake valve adjustment. Surprise!
4, Exhaust valve adjustment. Surprise #2!
5, Float level, if too low it will lean out and starve under load.
6, Vacuum advance, if it leaks you will have trouble.
This will give you a good start. fix one problem at a time. Keeps the stress level down a bit. Also look at the air filter. If it is blocking the air flow you will have more trouble. Enjoy!

vacuum leak; hadn't thought of that, thank you. i also didn't realize the windshield wipers operated off of engine vacuum.

hopefully it's not valve timing, i haven't looked into how difficult it is to adjust valve timing on these engines, but i hope i don't have to be that intrusive so soon.

Just get rid of it now then...
find something you'll be more comfortable cleaning up and playing on rather than working on...
Unless you have money to burn having others work on these trucks, ESPECIALLY old and unrestored ones, need work before they will play. Deep down dirty work

You'd want to learn how to adjust the ignition timing and valve lash. There is no real need to concern yourself with valve timing, which might refer to installing the cam gear correctly relative to the crank gear.

Where do you live in SE VA? Might there be a car/truck club nearby? See if you can join a club and find someone who has done his/her own mechanical work - they might help you in person.

Presumably, you have bought a reproduction Shop Manual and Operator's Manual?

right now is not the time for me to be doing an engine rebuild, not that i can't because i have before, i'm just not in a place to do that right now.
the reason i'm having issues with this truck is because the engineering principles from 60 years ago are much different than what is common in cars from 20 years ago (what i'm use to working on).

besides, i didn't go through the trouble of getting this truck driving again just to sell it because i hit a rough patch

If you do not have one, buy a vacuum tester .

Use it to adjust ignition timing and fuel mixture. Connect the vacuum gauge/meter/tester to the vacuum-wiper port on the intake manifold. Another explanation for using a vacuum gauge for tuning.

thanks! to answer your previous question, yes i have the shop manual, the factory assembly manual and the two smaller books on rebuilding the trans and differential. i was all about the literature when i first got the truck

Pulling covers and adjusting valves is just routine maintenance on the 60 year old tech...
But thats the spirit

valve lash adjustment procedure

He are some general tips that may help,

Idle quality does not effect driving quality. Once the throttle is opened, even a little bit, the carb switches from idle circuit to drive circuit. Full throttle is also different. So you can have one with out the other. I would start with a carb rebuild if you already haven't done it. These are very simple to rebuild. They need to be super clean and have clean fresh fuel. So clean it again if it still acts funny.

Modern fuel goes bad a lot faster then old fuel used to. Don't store it to long!

Valve adjustment usually will not effect driving much unless its way off. If all the rocker arms sound about the same, then the adjustment is probably pretty close. If you hear one clatter more then the others, its time to read up on valve adjustment. Its a good idea to check them and set them once you know how. Being to tight will hold a valve open, you will hear a "pop" either in the carb or tail pipe, depends on which valve is held open. To loose and you can hear them clatter much louder then normal. Dirty oil will muffle them some.

Timing, vacuum advance, points gap, plug wires, and spark plugs, all should be checked as they will effect drive more then anything thing else. Vacuum advance should be working and can be checked really easy, just watch the distributor house for rotation as you rev the engine and let off. Throw in some new plugs if there is any question about them, same with wires and cap. File the points and set the gap. Setting time will easy with a light, its nothing different then what you are used to.

Read your manual or check out this one,
http://chevy.oldcarmanualproject.com/engine/56etu/index.htm

Plug all but the vacuum advance line including PVC if it has one. Install a vacuum gauge at the manifold or below the throttle blade. Above throttle blades is what is know as ported vacuum ( only has vacuum when the throttle is open). You want full time vacuum, I would expect you to see 18 to 20 inches at idle, possibly more. This is where valve adjustment will be seen. Smooth steady needle, great, jumping around or low vacuum, valves timing is late. As the clearance in the rocker arm to valve stem gets looser, the valve opens less and at a later time then designed for. The cam is always turning, as it turns it pushes the valve open, if the gap is to big, you loose a large number of degrees of rotation before the valve opens. In effect, a large valve stem gap makes the cam smaller in both valve lift and the amount of duration the valves are open. The valves also close sooner causing even less duration.

Using the vacuum gauge while setting the timing helps, try to set for the maximum vacuum, still able to crank easy, and not ping under a heavy load (pulling a hill in high gear). Its a little trial and error. Todays fuel are still better then they used to be so you can get by with more timing then the manuals call for, more is better then less, just don't go to far. As long as it fires right up without trying to kick back, you will be good to go. Again, read the manual I posted above, 4 degrees at idle is not much, bump it up to 6 or even 8 and see how it runs. More timing helps keep the engine cooler.

Joe

Forgot to add,

Seafoam and like cleaners work pretty good, you can just poor it down the carb at high idle or feed it through a vacuum line. A good quality fuel clean would help also. Don't expect a total tune up from a can, you are still going to to put in some time there!

Hows the oil look? Does your engine have a oil filter? Don't go adding oil cleaners unless you are willing to pull the pan, you can make it worse with cleaners since most don't have a filter. The crap all settles at the bottom of the pan, unless you dig it out, the cleaners just loosen and circulate it back through. Fuel is kinda of the same way, be prepared to change filters often if using a fuel system cleaner. Fuel differs from oil as you have the ability to catch the impurities in a filter.

I have seen the top end engine cleaners where you dump them end and shut off the engine. It coats and cleans while setting. Then you go run it fairly hard to blow it out. A high idle and a cup of water works really good an heavy carbon build up. Slowly poor it in while running at high idle. The water turns to steam and washes the carbon out, don't drown it or you can have a tough time restarting. It will let you know how much to poor in. You can also use a vacuum hose to feed water in, meter it down and go for a long heavy footed drive. Pull a long hill in a higher gear to really work the engine while feeding in water, the higher heat will steam clean the tops of the pistons.

Joe

I have found that having the timing advanced to much can give you a surge at highway speeds. I've found that if I back it down a bit all is well.

In the good old days they just poured water into the carb.. all it will do is turn to steam and hopefully clean up some carbon... it doesn't fix anything. Plus the uneven distribution of the Siamese intake and distance from the 1 and 6 intakes from the 3 and 4 intakes means its not an even distribution.

If you think about it.. why would you want to clean your cylinders while it running where the junk can score the cylinders and damage a valve seat? Nothing you pour into an engine will fix it.

If you want to.. as noted, set a high idle and pour into the carb.. hope for the best.

There is a special tool for setting the valve lash... its a combo wrench and screwdrier... allows you to adjust the lash with one hand and hold the feeler with another. Its the easiest way to do it. Remember the motor MUST be running and normalized (oil at steady temp for 20 minutes).

thanks for all the responses, guys. a couple weeks ago, there was sediment settled inches deep in the oil filter housing so i wiped it clean, which lead me to doing the same for the oil pan while replacing the rear main seal. put in a new oil filter and fresh new oil. so i'm right there with you about the gunk settled in the oil pan. all these responses help, thanks again; i've got a lot of diagnostics to run

Here's another link to interpreting a vacuum gauge Click the scenarios about half way down the page do a nice job of explaining what's what...

That link is good, but on a 4 or 6 you will notice a slight bounce at idle (around 18-20inches/vacuum). My L134 bounces about 1-2inches.

Harbor Fright sells a very good vacuum gauge. Large and easy to read. Also comes with several tips for whatever hole you have available.

Glad to help, sounds like you don't need much anyway. Keep at it and you will figure it out.

Joe

pfarber -

Is this the HF vac gauge that you mentioned?
> Fuel Pump and Vacuum Tester

Thanks,

- Lonnie

...click...
a video of making idle adjustment and adjusting the mixture screw on a carter.

you can see the needle bounce when my idle was set to low at the begining.

Lonnie, I have a vacuum gauge if you want to borrow it.

That is the gauge: use it to adjust ignition timing and carburetor mixture. It is also used to measure fuel pump pressure; and, it is quite useful for many other automotive testing/diagnosis purposes.

HF will most likely have it on sale for as low as $9.99, but you can now buy it with their readily available 20% off coupon.

Thanks Wayne,

But for $15 minus 20% coupon, I'll buy one and play with it. Then I'll call you and ask how to use it!!

Should be easy enough with Gus's video and Tim's links.

- Lonnie

Lonnie,

When they were on sale, I bought an extra one - one for my shop and one in my "road trip" box.