Another carb tuning question, Problem solved!! Options

[Cevan]

So I’m entering the wonderful world of carb tuning. (Please save all the FI comments. I couldn’t afford aftermarket FI and I’m using a cam not compatible with stock FI.) The engine is a recently built 2056.

I’ve sync’d the carbs using my STE meter. I adjusted the idle mixture screws per Aircooled.net’s website. It doesn’t appear to make a huge difference when I go from one turn out to all the way in, or from one turn out to two turns out. I adjusted them so that the engine ran the smoothest.

The engine seems to idles nice. So I go for the first drive. After puttering down my long driveway in 1st gear, I pull out onto the road and it goes nicely through 4th gear, maybe at half throttle. At some point (maybe ½ to 1 mile into the drive) it starts to get boggy on acceleration. Definitely a change, so I head back home.

This morning I started it back up. It’s still boggy, pretty much from 2000-4000. If I go WOT, it bogs worse. If I slowly increase the speed, it bogs less. And it smells like it’s running rich, like unburnt fuel (I did check for fuel leaks). I tried adjusting the idle screws some more. It seemed like I got it to run a little faster at idle. The engine revs fine with no load on it. I checked the carb balance again and went for another spin. Still boggy. Still smells like it’s running rich. For the next drive I need to pay more attention to any carb or exhaust popping.

I’m trying to diagnosis this problem in a logical order. I’ve already checked the dwell, timing and valves. The carbs were just rebuilt. The floats are set per the Redine website.

My plan is to pull a spark plug from either side and inspect them for signs of it running rich or lean. I’m also going to clean the idle jets as maybe something clogged the jets during the first drive. I’m also going to install a fuel pressure gauge so a passenger can see it while I drive (just in case it’s running lean), although the fuel pump is new.

If none of this helps, should I try a different size idle jet? I have 50s already. Any other suggestions?

Here’s the current setup:

Weber 40mm IDFs
Idles 55
Main 130
Air 200
Emulsion F11
Vents 32mm

[r_towle]

Chris,

Did it ever run ok? think that one through.
If so, it may be something simple that changed...something you changed or overlooked.

Rich

[jmill]

BTW I used to set mine at 11mm. I parked on a steep driveway. 10mm was too high and flooded me out on start up. The easiest way to set it is upside down like the picture.

[Cevan]

Chris,

Did it ever run ok? think that one through.
If so, it may be something simple that changed...something you changed or overlooked.

Rich

This is the engine I just built so it's only got 4 short drives on it, plus the cam break in.

[Cevan]

BTW I used to set mine at 11mm. I parked on a steep driveway. 10mm was too high and flooded me out on start up. The easiest way to set it is upside down like the picture.

When you set these up, the ball is not supposed to be compressed into the valve, right?

If mine are not adjusted correctly, could this be the cause of my issue?

I think I will pull the carbs and check the float levels.

[Cevan]

So the float was good on the first carb (11mm and 32mm). Pulled the second and I noticed the main jet stacks were completely loose (I turned them out one turn and they came out). (IMG:style_emoticons/default/blink.gif)

Not good, huh?

[Cevan]

Success!!! The loose main jet stacks on one of the carbs was the problem. I just took it for a 10 mile rip. It pulls way harder than the stock 2.0. Holy shit!!! (IMG:style_emoticons/default/piratenanner.gif)

There doesn't appear to be any hesitationat any rpm so I think my jetting may be good. I just re-synchonized the carbs and adjusted the idle to 750. My timing was at 27 degrees and I upped it to 29. I'm going to let it cool down, pull the top and then take it for anther spin. (IMG:style_emoticons/default/driving.gif)

Thanks for everyone's help.

[Cevan]

I think my rings are seated. I went for another spin this afternoon. About 35 miles total today. I had my friend in his mid-engined, targa top, two-seater follow me around some nice twisty sides roads for about 10 miles. (IMG:style_emoticons/default/driving.gif)

[VaccaRabite]

(IMG:style_emoticons/default/smilie_pokal.gif)
Nice! The 2056 is a great motor for these cars. It's really moves them. I am glad that your issue was an easy one to fix. Now go put abot 1000 miles on it to finish the break in. Watch oil temps and head temps especially on the freeway going uphill. You may still have tuning to do.

Zach

[jmill]

Sweet. I'm glad it was something easy. Beautiful engine you have there. Enjoy the heck out of it. Mine will be up on jackstands at least another year.

[Van]

Chris, let me know if you ever want to dyno tune the car... (IMG:style_emoticons/default/smile.gif) I, you know, keep one around for just such occasions.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.ephotomotion.com-8571-1274730658.1.jpg)

[Jake Raby]

Most carb issues are actually ignition issues. Optimization is key.


This post has been edited by Jake Raby: May 24 2010, 03:57 PM

[Cevan]

Most carb issues are actually ignition issues. Optimization is key.

With my L-jet dizzy, I can really only change the timing for a particular rpm. It has about 23 degrees total advance, per my adjustable timing light. I've got it at 30 degrees BTDC. I'm just now sure how far I can advance the timing.


Below 3000, it seems like the engine lugs until it hits about 3200 rpms. I'm not sure if I should experiment with 52 and 57 idle jets.

I still don't know where the power drops off. I've got about 100 miles on it now. Any reason I can't crank it up to 5500 rpms?

[Cevan]

Chris, let me know if you ever want to dyno tune the car... (IMG:style_emoticons/default/smile.gif) I, you know, keep one around for just such occasions.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.ephotomotion.com-8571-1274730658.1.jpg)

I'll PM you my address. I'll be around on Saturday. (IMG:style_emoticons/default/biggrin.gif)