Air Fuel Mixture at Altitude

[BradenEP1968]

Hey everyone, I'm heading to Big Bear next week and wondered if I'll need to make any adjustments to the carbs? My Manx has a basically stock 1600 in it with duel EMPI carbs. Elevation at Big Bear is 6,700 feet, here in Phoenix its about 1,100. I'm guessing I'll need to lean out the mixture to compensate for the thinner air. Not to familiar with these kinds of adjustments as I have only just got everything together and running so it will big a test of everything while I'm up there. Just trying to get prepared if I need to make any adjustments so any advice would be appreciated.

Thanks

[jsturtlebuggy]

What kind of Empi dual carbs do you have?
You may want to install the next step down in idle jet size.

[BradenEP1968]

I'm not to sure, they look like the HPMX carbs. The "D" series have a vacuum port on them and mine do not. I don't have any jets for them. do you happen to know how can I tell for sure.

[BradenEP1968]

I think I figured it out, did some research on Google this morning and came up with this. Now I just need to come up with some Jets. Looks like the EMPI carbs are 40 HPMX

[jsturtlebuggy]

The Empi Hpmx carbs are copies of Weber IDF and use the same jets as them.
Depending on were you live you should be able to find jets for them at places that sell VW parts.
Shops such as Pierce Manifolds in Gilroy, Ca sell Weber parts and jets, CB Performance in Farmersville, Ca sell Weber parts to.
If you are in Southern California there are many shops that sell jets.
The idle jets are the small one by the fuel inlet valve.
The jets have numbers printed on them. You will see numbers such as 50,55 on the idle jets.
This measurement is in millimeters.

[BradenEP1968]

Thank you Joseph, I really appreciate the feedback. There's only place that I am aware of that sells parts for VW's near me Tempe, AZ. I'll hit them up today and see if they have jets.
The idle jet size currently installed are #60, based on the research I did those carbs came from EMPI with 53's so I'm thinking I will for sure need to drop the size for altitude in Big Bear.
I also found these two YouTube videos that are pretty detailed:
https://youtu.be/9nJK_hhhgk0
On this second video skip to 13 minutes and he starts walking through the tuning with a running motor.
https://youtu.be/PL2eVLOfiT4

Thanks again, will you be going to the event in Big Bear?

[jsturtlebuggy]

I will be at Big Bear. It sound like it is going to be a large turnout for the 25th anniversary event.
I have a Orange Metalflake Manx Kick Out with a Tan top. I tried to add picture, but for some reason this new hosting site will not allow me to open my album.

.60 idle jets are large for a 1600cc engine. I have a 1776cc back up engine that has .50 idle jets for where I live at 220ft above sea level
My 2200cc engine in buggy is using .55 idle jets here at home.

[BradenEP1968]

I picked up some 55's and 50's, do you think I should install the 50's before I get up there? I wasn't able to come up with a carb sink tool yet so little apprehensive to be guessing about that.

Here is my 64 Manx, it's pretty complete and I've tried to keep it period correct. It's about 95% garage build by myself.

[jsturtlebuggy]

Nice Manx you have there. Yes could try the smaller idle jets at home to see if it makes any difference in the way it runs.
With the idle air/fuel adjustment screws should be about a 1-1/2 turns out on the average. If your turning them out more, it means idle jets are to small.

[BradenEP1968]

Thanks again for the help. I feel like I'm heading up there prepared now. I was not able to come up with a EMPI carb sink tool so I'm now a bit hesitant to mess with it but if I have issues I'll be ready.

Looks for me on up in Big Bear, my front lic plate is Daffy Duck.