The Stovebolt Site Forums The Shop Area Engine Shop Yeah, it's RICH, but why the Choke?!!!

Brand new rebuild on a stock 216, top to bottom. Just installed in truck and fired up for the first time. Carter W-1 carb is a newer professional rebuild (shortly before engine was torn apart, 3 years ago.).

Engine requires full time partial choke to run, at idle & high idle. After first warm-up, plugs were uniformly sooty (dry fouled). Smelled rich as well. Replaced plugs (finally got new AC R45s).

So I get that the engine is running RICH. Thursday, will pull carb and check float first and foremost.

Here's the question: Why does this engine NEED the partial choke to run?! The whole point of the choke, in my mind, is to reduce airflow/increase vacuum in the venturi to draw MORE fuel for starting. But THIS engine doesn't NEED more fuel - it's already OVER-RICH. (At idle, looking down the carb throat, I can see fuel percolating out of the jet in the center - not out the idle port.) Needing choke to run doesn't make sense to me. The two things - Running Rich and needing Choke to run - work against each other in my mind.

Here's my only idea:
The choke is providing increased air velocity which is helping atomize the excess fuel that is entering the manifold?!! Otherwise, the raw fuel wouldn't burn and it would flood?

Somebody School me . . .

-Michael

I think you have a vacuum leak and the engine actually is running lean at idle or you have a idle port plugged. The choke is confusing the issue. I'd check thoroughly for a leak, make sure your intake manifold and carb are properly torqued down. Joe

Perhaps you have a small vacuum leak that results in the need for the richer mixture provided by the partial choke?

check the throttel shaft 0n the carb base.could be worn and sucking vaccum.just a shot in the dark.the brass shafts wears out and becomes sloppy

to check the shafts spray some starting fluid or carb cleaner on the shafts and see if there is a change in the idle speed.

Doesn't sound like your idle system can be working if you have enough airflow through the carb to have started the main system. The throttle would have to open a fair way to have fuel coming out of the emulsion tube unless the float level is way too high IMO.

Would be worth checking that there aren't any blockages in the idle system drillings and the jet too.

Stuart.

I'd make sure I had fresh fuel in the tank before I did any thing. If your trying to start it on old fuel that can cause tons of problems now days.
Denny Graham
Sandwich, IL

If it sat for 3 years with stale gas in the carb, you probably need to go through the carb again.

Well done, as usual, stovebolters - thank you.

Yeah, it occurred to me today that maybe the reason it needs choke, is because the idle circuit is clogged totally, so the only way it would get gas is through the main circuit. Good thought, Stuart.

Denny, yep, I agree - I'm becoming increasingly nervous about fuel these days, what with the seeming decrease in overall quality, and the complications of ethanol. Seems like the future is bleak for vintage vehicles as far as fuel is concerned. Regardless, this was on brand new fuel, so that shouldn't be the culprit.

Crenwelge, yeah, I'm hoping it doesn't need everything again. We'll see tomorrow when I open it up.

Joe, tClederman, Dan-pa, and We b, to be sure I understand the thinking here: Vacuum leak is causing too much air into the manifold, so the engine requires the extra fuel to balance out the mixture, right? Wouldn't this result in different results than dry, powdery soot on the plugs?

Either way, a vacuum leak test (with propane torch) is on the agenda for tomorrow, after the carb is removed and inspected.

I'll post the results.

-Michael

Update for history, posterity, whatever:

Did a vacuum leak test. Used just the acetylene from a torch set-up. Hand-held propane didn't raise the rpms when held at the airhorn. Acetylene worked perfectly. Very obvious rise in rpm when held above carb. Good news is, no vacuum leaks in evidence anywhere.

Warmed up the engine and readjusted the valves. Only helped running a little. Still couldn't get the idle speed down or smooth running.

Swapped to a 180 degree stat. Probably not the culprit, but I wanted it to run at 180, not 160.

REBUILT A SPARE CARTER W-1 CARB I had, using a kit from The Carburetor shop, CarbKing's place. He was very helpful on the phone. Put the new carb on, truck started up with very little choke, ran smooth at high idle, and got the idle down to 500 rpm or so, with NO CHOKE!!!

Runs VERY smoothly, temp pegged at 178, doesn't hesitate when I stomp on it. HUGE difference. This time, anyway, it seems the carb WAS the culprit!

Bought two kits, may rebuild the original carb, see if I can figure out why it wasn't happy. Float level was close-enough. I suspect a plugged idle circuit somewhere, maybe a clogged "equalization" line (tube at top of airhorn ).

Thanks to everyone for the support!

-Michael

Michael -

First, glad its working, our older vehicles are supposed to be fun!

As to the issue you corrected, my "SWAG" is as follows:

Remember the conversation we had concerning the idle tube and how it seals? For those who weren't listening to that conversation , Carter stated to ALWAYS replace the idle tube when rebuilding a W-1. This for several reasons (one, Carter wanted to sell idle tubes); but also because reusing an original idle tube WITHOUT MODIFICATION would give issues. The reason is that the upper end of the idle tube is inserted into a tapered passage. When the tube is rotated (because of the screw plug), the tube is compressed and forms a seal. Reusing the old tube without modification will not form the seal. However, the old tube may be reused if the rebuilder reforms the outer diameter of the upper end of the tube. This may be done by CAREFULLY rolling the point of an icepick inside the upper end of the tube. This will expand the outer diameter, so the tube can again seal when inserted in the tapered passageway. And no damage will be done to the calibration, as the calibration is in the bottom of the tube.

And always remember the ABC's of carburetion: (A)lways (B)uy (C)arter

Jon.

Jon,

I think I get it now. I'm just not too keen on shoving an icepick into my carb!!!

I'll probably try what you say when I rebuild my spare carb. It will be "forensic mechanichism", as I perform the carberator "post-mortem". Heck, I might even get one of those headband lights to wear, and put a lab-coat on!

As for the rebuilt one, think I'll live with it for a while, even though it seems to be gently dribbling onto the throttle plate at idle. It will be nice when that has become the biggest issue I have to worry about with the truck!!!

Thanks again, Jon. Y'er a prince!

-Michael

Hey guys,

Rather than start a whole new thread here I want to chime in on this one. My '50 is acting the exact same way as Michaels was before his rebuild. I've got a 216 cid with a Rochester one barrel. So after reading this entire thread I'm convinced that I too need to rebuild my carb. I've NEVER worked on one before but I'm handy with the tools.

Two questions......

1. Should I invest in buying a Carter carb (new or used)?

2. If I keep the Rochester where should I buy the rebuild kit?
Does anyone have a reorder # and I'll try at NAPA. Anyone
have a good DVD on rebuilding carbs they could loan me??

Thanks!

Spot

Spot,

Fyi, check out CarbKing's post on the Carter: HERE

If you can find rebuild instructions like those, then go for it! I had a spare carb to give me confidence in tearing into one. The step-by-step instructions helped loads. That, and a parts list and diagram did the job. Check out THIS: Identifying and keeping all the parts straight was the hardest part. A drawer-organizer (parts tray) helps.

Also, I think maybe the service manual will walk you through a rebuild as well?

-Michael

Thanks Michael. I just didn't want to sink money in a rebuild of the Rochester if I should spend the money on buying a Carter.

Spot

ooh , I just know I'm going to have this problem when I put my carb on !!