Choke needed to run - why?

[ybt502r]

I'm back with my truck - left it with my son for 3 years during an assignment in Indonesia - and have something that I don't remember. In normal driving, it struggles to accelerate and run at high speeds. However, when I pull the choke out, it runs like I recall - good pulling, smooth idle, and able to climb highway overpasses without loosing speed. It's a 5-bearing SIII with an aftermarket Zenith copy for a carb. I used to have an original Zenith but replaced it when gas started flowing from the gaskets and other places (I have a rebuild kit to address that issue at some point).

My question is why does it work so well with the choke (in moderate weather) and seem breathless without it? I'm at sea level (Anchorage), and it's got (I expect) a normal jet. I don't think my son messed with anything while he had it...

[crankin]

1. An air leak around the fuel intake or Carburetor areas. to much air gets into the combustion chamber...

2. Fuel system contamination has resulted in the air and fuel mixture jets inside of the carburetor to become clogged. Clean the Jets and Carb

3. The fuel has an excessive amount of alcohol content.

[ybt502r]

This has been an issue for a couple years (in Wash and Alaska), so I don't think it's the fuel. I gave the whole carb a good cleaning the other weekend (carb cleaner) inside and out; it's pretty shiny since it has only a couple hundred miles at best. So I think an air leak is possible, but I hear nothing (outside of all the other noises) under idle that sounds like air being sucked in. I have had to increase the RPM at idle to make it run smooth, but I basically have to have it at least halfway choked to run smooth and with power. I'll try rebuilding my original Zenith I guess.

[I Leak Oil]

The choke also advaces the throttle linkage if setup right which is probably why you think it runs fine with the choke. Perhaps your base idle is too low or maybe check your timing.

[mearstrae]

Try the old water in a spray bottle trick, spray every area on the intake and carb in its turn, and see if anything you spray down makes the idle jump up.

'95 R.R.C. Lwb
'76 Series III Hybrid 109
'70 Rover 3500S

[artpeck]

From your description it seems like you replaced the carb a few years ago and it was running fine. Then you left the truck for a few years and it only got a few hundred miles on it? If so that would imply it sat a lot which would have resulted in the gas going bad most likely and leaving varnish in the system. That could easily be messing up the fuel air ratio if so. My advice is don't mess with anything else until you have pulled the card and soaked it in carb cleaner to make sure all bad gas, varnish etc is gone. If the only thing that happened between it running well and running poorly was a few hundred miles and a lot of sitting my bet would be a gummed up carb.

Then reinstall and see what you have. If I misread the sequence of event my apologies.

[ybt502r]

It's been mostly sitting, but my son would get it out to run about once a month. He went through a few tanks of gas. It was he who pointed out that he needed to keep the choke on for it to run well. I gave the carb a big hosing with carb cleaner, inside and out, to no real improvement. So I got a carb rebuild kit for the old carb and also a new (aftermarket) carb to try. It's running better (without choke), but now I've got more issues...time for a new thread.

[artpeck]

My experience with the spray on carb cleaner (similar problem) is that until I soak the carb in cleaner literally in a bucket it didn't really get everywhere and clean it. Hope you figure it out.

[martindktm]

Its not complicated...If it need choke its because carb does not deliver the right amount on fuel... Or an air leak... From the intake, the carb, the distributor vacuum, the brake booster vacuum or blown bosster diaphragm or distributor diaphragm...

That is if points are ok, timing, plugs, wires, fuel pump, etc...etc....

But I would start where some told....Clean the carb and the jets inside.

[TedW]

I just had a similar problem - very rough starting and running - liberal and repeated application of Gumout Carb & Choke Cleaner did the trick.