Solex jetting

Tech tips and how to's

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69roadster
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Solex jetting

Post by 69roadster » Wed Jun 19, 2019 9:53 am

Looking for some starter jets recommendations for my solex u20 . Not much to the engine..40 over solex with B cam. I saw Dean has a kit anyone have any experience with them.

https://www.datsunparts.com/2328

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Gregs672000
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Re: Solex jetting

Post by Gregs672000 » Wed Jun 19, 2019 12:37 pm

As you probably know, there are a few different versions of Mikuni carbs, so we'll need more info. For example, what version of the carbs, what size main venturi, what are your current jets? Dave Premo knows theses carbs and cams well, and he may offer some suggestions (and supplies jets too).

Later versions came with 34mm venturi vs the early with 37s. People often set the accelerator pump in the bottom hole as the Mikinu accelerators tend to over fuel and that will reduce the volume. All engines vary, so while a change can get you closer, and maybe right on, it may be necessary to try a few different mains and airs to dial it in. Also, without a wideband O2 sensor giving you real immediate feedback, you're going to need to read your plugs and make sure you're not lean or rich. If you don't want to buy and install a wideband (requires welding), then another option would be to get the suggested jets, read plugs and make sure you're OK, and go to a dyno tuning shop and do a test pull with their O2 set up to make sure you're good and safe. They will be able to tell you what it's doing at different rpms and which carb system is operating (pilot vs mains), and likely suggest a step or two in either direction for jet changes. I suggest you familiarize yourself with how the carbs work in general via a mikuni manual or off the internet. All this is optional, but worth doing in my opinion. You have installed a system that is more tunable (Mikuni vs SU) but to get the best results ya have to tune IT! :D

To give you an example of why I love having a wideband, yesterday I was out breaking in my new engine and noted a stumble at times. I could immedialty look at the wideband and see it's a lean stumble, and it has to do with my accelerator system needing adjustment (not enough response) as the jets quickly catch up and air to fuel ratios go back to where I want them... There's a lot less guessing about where or what to tune, and I will be able to see my results with each change. After so many years of jetting carbs by reading plugs, this is awesome.

Hope that helps!
:smt006
Last edited by Gregs672000 on Wed Jun 19, 2019 12:48 pm, edited 1 time in total.
Greg Burrows
'67 2000 #588
Tacoma, WA

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bakerjf
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Re: Solex jetting

Post by bakerjf » Wed Jun 19, 2019 12:46 pm

Dave Premo is the authority on Mikuni tuning, and will figure out what you need very quickly.

http://tuning4performance.com/
J. Baker
Cupertino, CA
'69 2000 (Solex)

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theunz
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Re: Solex jetting

Post by theunz » Wed Jun 19, 2019 4:21 pm

As mentioned save yourself some trouble and just contact Dave. He sent me all the jets and gaskets and they were spot on.
__________

Mike M
1969 2000 solex mine since 1972, under resurrection. 1969 Porsche 911s -worth more, but not as valuable!

69roadster
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Re: Solex jetting

Post by 69roadster » Wed Jun 19, 2019 5:27 pm

Thanks, I will contact Dave