Let's play a game... What's wrong with my engine

[jser12]

Okay so I have done a little research but I give up and maybe you guys can give me some insight

 

Background - Rebuilt L20b, Mild Cam, Head gone through, Weber 32/36 Carb, NGK bpr6es plugs, new El Dizzy

Problem - Plugs are running rich and there is a popping through the carb around 2500 RPMs when accelerating.  Now my idle is rough because I am not able to adjust the mixture screw (its stuck/ stripped).  There are no leaks or anything on the intake

 

Do you guys think this is an issue with my carb? If so what and why?  or do you think this is a problem with my timing?

I do have a side draft that is going on in a couple weeks... should I just ride it out until I ditch my weber?

Sorry if I don't reply, its about bedtime on this side of the U.S.


 

[wayno]

Okay so I have done a little research but I give up and maybe you guys can give me some insight

 

Background - Rebuilt L20b, Mild Cam, Head gone through, Weber 32/36 Carb, NGK bpr6es plugs, new El Dizzy

 

Problem - Plugs are running rich and there is a popping through the carb around 2500 RPMs when accelerating.  Now my idle is rough because I am not able to adjust the mixture screw (its stuck/ stripped).  There are no leaks or anything on the intake

 

Do you guys think this is an issue with my carb? If so what and why?  or do you think this is a problem with my timing?

 

I do have a side draft that is going on in a couple weeks... should I just ride it out until I ditch my weber?

Sorry if I don't reply, its about bedtime on this side of the U.S.

 

 

 

 

Is this an L20b?

Are you sure your cam is timed correctly?

[flatcat19]

If it's popping-your timing is off.

 

Cam-timing?

Dizzy installed correctly?

[datzenmike]

Valve or valves set too tight.

Burnt or bent valve not closing.

[jser12]

Dizzy is installed correctly, I remember because it took forever to set it properly.

The cam and lashes are installed according to the sheet the build shop sent me back.

I'll have to check to see if the valves are set to tight later.

Thanks for the help guys.

[datzenmike]

A badly seated valve, maybe too tight, damaged seat, bent or burned, I've seen valves with splits across the face... anything that prevents them sealing can allow the explosion in the cylinder to escape into the intake and explode the fuel/air there. Usually a popping sound and not much power. The engine is usually spinning fast enough that it very quickly sucks in more gas and air for the other cylinders and keeps going until that cylinder hits again.

 

 

Forgot to mention last night to check your wires. 1342 in counter clockwise direction.

[jser12]

But its strange because the car ran for almost a month after the rebuild before this problem arose.  And if it is a badly seated valve, why would i only be getting this hiccup around 2500 RPMs?

[datzenmike]

2500 at a steady speed or when floored?

[Mannyvig]

What's the distributor timing set at?

[jser12]

2500 when accelerating
When im at 2500 cruising, it's smooth as silk

[datzenmike]

I'll have to check to see if the valves are set to tight later.

Thanks for the help guys.

.

 

 

 

 

If it is indeed popping out through the carb when accelerating then the combustion chamber is some how leaking into the intake and setting it off.

 

Valve not closed all the way... too tight a clearance is the most likely and an easy check and fix.

 

Blown head gasket between cylinders.

 

Spark jumping from one wire to another or across the inside of the cap or rotor to a cylinder with an intake valve open.

[jser12]

Thanks mike. You kick ass.

[datzenmike]

Just an opinion based on comments about what is wrong. It's possible that the popping..... might.... be something else mistaken for backfiring through the carb? If you take the air filter off and rev it quickly at full throttle through that 2,500 problem area, is it indeed popping out the carb? 

[jser12]

yea, after further investigation I have determined that it is the carb

[datzenmike]

Ignition... move the wires, check the inside of the cap for carbon tracks. They look like a spider web or crack on the plastic surface. 

 

Valve lash... just check that all rockers can be wiggled, showing there is some play, when the cylinder is at TDC valves closed. Look also for a dislodged and jammed lash pad that is holding an intake open.