Weber selection and initial jet tuning

[siteunseen]

maybe I'll hang on to mine. I'd like to hear them someday.

[Zedyone_kenobi]

Well at any given RPM, a smaller choke will mean a higher velocity air stream to carry the fuel, so it will help everywhere to an extent.  

One thing you should check, and this will seem weird at first is the manifold you are running.  And more specifically the temperature of that manifold.  A manifold must be a proper temperature to keep the fuel from pooling inside of it. Now this is a secondary effect for sure, but having an engine at proper temperature is vital.  Manufacturers go through great lenghts to ensure the manifold is up to temp quickly for this reason.   What temp thermostat are you running?  I recommend a 180-190. 

 

Probably not your cause, but manifold temperature is not insignificant.

[blodi]

Pump jets arrived the other night finally. I had a chance to install them and basically...not much change. Still a bit of a flat spot in the transition. I think you guys may be spot on with the choke size being too large so my next step may be going to 34mm chokes. 

 

[gundee]

Just a a note on my experience. When I purchased my Mikuni's it had 36mm chokes. It was just not driveable on the street.

Like you I tried everything. Then I went to 34mm chokes and it was like night and day. All problems gone. It was only then I could

start the fine tuning. If you had a track car running WOT 90% of the time you would be OK as you have it.

[blodi]

I ordered 34mm chokes and they arrived yesterday. I installed them last night. Haven't had a chance to drive the car yet though. I'll have to re-sync the carbs as I had to remove the air bleeds to put in the new chokes. I will report back though! I was surprised just how much smaller the 34 looks compared to the 36. 

[240260280]

R^2

[blodi]

Drove the Z in today. Flat spot is totally gone with the 34's ! I'll monitor my wideband for a while and see if tweaks are needed, but, overall the car seems to run really well! 

 

[240260280]

...and they lived happily ever after.

-- The End --

[gundee]

On 5/19/2017 at 7:56 AM, blodi said:

Drove the Z in today. Flat spot is totally gone with the 34's ! I'll monitor my wideband for a while and see if tweaks are needed, but, overall the car seems to run really well! 

 

That is really good to hear. Confirms my experience as I stated above. In my case I am not running as much compression or as big a cam as you are.

If I could I would even try 32 chokes on mine, but 34mm is the smallest size that will go into my set up.

When I did buy my Mikuni set up, the chokes were stamped 34. However the guy I got them from said they were actually bored out to 36mm.

If he had not told me that I would have never known and thought I had 34mm chokes installed. I never ever would have got that thing to run right.

Goes to show you can never assume anything.

[blodi]

Took a log of a 3rd gear pull with the innovate today. The RPM sensor was off but I marked the pull...basically 3k-7k....what do you guys make of this? 

AFR6117 by blodi, on Flickr

Current setup:

34mm chokes,

155 mains,

185 air

F16 emulsion,  

65F9 idle

45 pump,

00 exhaust

Edited June 2, 2017 by blodi

[sweatybetty]

3 questions.  how do your plugs look after that pull? what is the ideal afr? and what kind of rpm sensor are you using?

[blodi]

1. Plugs look good overall, light tan. Carbon on the outer portion.  I can take a pic and post later. 

2. I think the ideal is 12.5-13.0 from what I've read at WOT?

3. Just using the Innovate pickup that works with the LM-2 that clamps on one of the spark plug wires. 

I can try again to get a better reading with the rpm...but just started doing logs yesterday and today. 

Overall, the car runs great and pulls hard. But just in the "fine tuning" now I guess.  Seems to go a bit too rich up top...is that the air corrector based on what I've seen in this chart I found?: