Topic: EC carb on modded Intek?

[Kokamo]

Having some issues with a factory Nikki carb that has been modified by EC. From what I see, it has been bored, ported and the main jets removed while an adjustable needle has been fitted to the (metal) bowl. The thing idles good (fairly rich, but not adjustable), always runs fantastic out of the corner under WOT......most of the time but not always around the middle of the strait, it will bang out and start running really bad around 5K (turning a little over 6K)....I know it could be rich or lean, but it won't clear up either way I make a high speed screw adjustment. I pull the plugs and one side looks good, but the other is charcoal. I change plugs just to run a heat or race and it'll run good for 5 laps and then start missing again due to a fouled plug. Pull plugs and the same thing, but on opposite cylinders. I've cleaned the carb and find no obstructions or bad gaskets. I know these carbs and I know what is common gaskets or issues, but I have made sure those issues aren't present.   

So, I figure I should be done with this carb and just upgrade....anyone use the ECH203-1 carb from EC? I see that it has an adjustable idle circuit and I like that part. I also like the ability to change jets, but hate the amount of trouble it would take to make a jet change....especially if it were at the track.

A bit of background....I have been studying and working with carbs for well over 15 years and I know how they work, but I work on stock carbs, not modded or performance units such as this.

A bit about the motor. 93 octane GASOLINE, precision cam, ARC rods, ARC FW, stock model 40 heads, stock air filter system with K&N filter, otherwise completely stock.

Any advice?

Thanks,

~Joe

[PJG56]

You didn't mention anything about valve springs,if you still have stock springs you are floating the valves.
Stock springs will start to float around5k

[Kokamo]

You didn't mention anything about valve springs,if you still have stock springs you are floating the valves.
Stock springs will start to float around5k

You are correct, I failed to mention springs. It does have a set of EC springs on it....singles I might add. However, I kinda ruled floating valves out of the picture because sometimes it will run good....but never consistent.

~Joe

[PJG56]

So you have EC springs and your only running the outter spring?
When does it run ok when its cold?
Warmer it gets worse it gets?

[Kokamo]

So you have EC springs and your only running the outter spring?
When does it run ok when its cold?
Warmer it gets worse it gets?

It starts right up (has no choke) when it's cold and when it's at temp. I don't run it hard or rev it when it's cold but if I were to guess, it wouldn't matter either way.

Yes, just the outer spring. My heads aren't cut to utilize the inner spring. I spoke with George directly before he passed and he told me to just run the outer only or I would have rocker stud failure. It revs higher than it did before after changing the springs and that fixed an earlier issue, but now I have this one.

Suppose I'll go back thru it once more with a fine tooth comb and see if I see any cracks or anything broken. If anything I'll throw on a known good stock carb and see how good it works.

~Joe

[Extreme 40]

I had the same issue with a 33 ci single. Once I went to 104. The problem went away.
Make sure the fuel has no ethanol in it too. Any type of alcohol in fuel will lean it out.
What do your plugs look like after a hard run? Also take a temp check on each cylinder.

[cycloneracer]

Are you running the diodes on the coils? 
Mine did the same thing when I ran without the diodes. 

Sounds like your loosing spark. 

If your running without the diodes get new coils. 

[Kokamo]

I had the same issue with a 33 ci single. Once I went to 104. The problem went away.
Make sure the fuel has no ethanol in it too. Any type of alcohol in fuel will lean it out.
What do your plugs look like after a hard run? Also take a temp check on each cylinder.

Good info. I'm using 94 octane VP fuel....the same ethanol free fuel you get from the hardware store in the metal gallon can you use in your regular mower. Our rules follow USLMRA....pump gas only, but I can't find any ethanol free pumps anywhere near me. The same fuel is running great in my 33ci with no issues.

Plugs directly after a hard run and the motor stopped directly after (no idle time) have a sooty black plug on one cylinder and the other is normal. Check it again after another run and it's the same issue, but on opposite cylinders. Makes absolutely no sense.

I have a Digitron but it won't power on. It has the CHT option and I plan on using it as soon as I can get it back from servicing.

Thank you!

[Kokamo]

Are you running the diodes on the coils? 
Mine did the same thing when I ran without the diodes. 

Sounds like your loosing spark. 

If your running without the diodes get new coils.

This could very well be something I haven't thought of. There are no diodes to speak of. I suppose I will need to look into this and why I should or shouldn't be using them.

Thanks a ton!

~Joe

[cycloneracer]

That's your problem. 

If you've wired the 2 kill wires together without the diodes they are shutting each other off.  It gets worse at high RPMs. 

Get 2 new coils.  Yours  are shot and will never be right. 

The wires used to ground the coils to shut them off are back feeding power to each other.  Doing lots of wild things.

Get the OEM wire loom with the diodes or use 2 seperate kill switches.

[Extreme 40]

Now that is good information