Choke Adjustment?

[chris103549]

First post! I'm a new 720 owner and having an issue I'm hoping someone can help me out with.

 

Basically when I start it up cold (not actually cold out, just not a warmed up engine), it idles like complete trash for about 4-5 minutes. It feels and smells like it's running incredibly rich. The exhaust smells like fuel and the engine feels like it's running on 2 cylinders. I would describe it as a very choppy, chuggy, missing idle. This gradually improves over 4-5 minutes and then it runs absolutely fine.

 

Am I correct in thinking this could be the automatic choke? If so, any tips for how I should go about adjusting or diagnosing this? 

 

Thanks!

 

 

[datzenmike]

Nice looking '83!

 

 

Carburetors are different from EFI. Yes the choke forces a rich condition and it is very normal to smell unburned gas when it is on. I believe the choke is adjusted and set at the factory and may be riveted in place and not adjustable by the owner.

 

 

 

 

This one has three screws that can be loosened and the choke turned richer or leaner. You'll have to look at yours.

 

If you drive short distances the choke is on more than off and this over rich condition can carbon up the spark plugs. Adjusting the choke may not help as it is doing it's job. You could remove the plugs and clean and gap them.

 

Other things that contribute to poor idle during warm up are...

 

Valve lash needs to be checked and set

Plugs, wires, distributor cap and rotor worn out and in need of replacement. Not saying to replace then just replace if worn or old.

Ignition timing checked. Should be 3 degrees BTDC.

Check the both the ignition and the exhaust side plugs are firing. If one side not firing replace the first fuse on the left side of the fuse box.

[chris103549]

Thanks so much for all this great info. I will attack the simple stuff first and see how that goes.

[Charlie69]

If someone installed a Weber DGEV 32/36 on it the choke adjust the same as Mikes information above.  The choke housing on the Weber can be black or white in color.

[chris103549]

It's definitely not a weber.

 

I pulled the distributor cap and it wasn't looking so great. Replaced it and didn't see much improvement. I did confirm both sides of plugs are firing. Next I'll pull the plugs and see how they look.

 

I'm going slow here but making my way through the easy stuff.

[datzenmike]

Just because...

 

[Charlie69]

Did you replace the rotor with the cap?  I buy the cap and rotor as a set for all of my NAPS Z Engines.  I have had problems in the past with different manufacturers parts not working together like the should.  Different designs.

Edited May 21, 2021 by Charlie69

[chris103549]

Update... I have been messing with the mixture/idle screws trying to find a balance and things haven't improved much. However, I pulled the air filter off and looked down the carb and noticed that only one side is spraying fuel... I'm assuming both sides should be, correct?!

 

 

[Charlie69]

Weber should be both sides.

[chris103549]

Mine is stock.. 

[datzenmike]

Then only the primary side because only the primary side is opening.

 

Best idle should be done after the valve lash had been checked and set and the ignition timing checked and set. Idle must be at 800 or lower or mechanical advance may creep in. If you can't get that low, set the idle mixture first then set the timing then confirm the mixture wasn't affected by the timing adjustment...

 

IDLE MIXTURE

Set the idle as low as possible on a thoroughly warmed up engine. Turn mixture screw in and out and find the best smoothest and fastest idle. There may be as much as a half a turn where there isn't much change, just set roughly in the middle. Turn idle down and repeat mixture adjustment as many times as needed till you cannot improve the idle quality and the idle is 750-850.