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Fri Sep 17, 2021 6:11 am

Dear Members,

My friend and I just completed a 2276cc engine with Engle cam FK8 and 40X35.5 heads. I decided to go with EMPI 44 HPMX since they don't have 48 size and I can't afford the Weber 48. It came with 0.135 main jets, 0.055 idle jets, 0.200 air jets, 0.055 exhaust pump jets, and 0.050 accelerated pump jets. The engine choked at 50mph and ran very poor performance above that. So we decided to change the main jets to 0.160 and idle jets to 0.70. The engine runs great after that with timing about 10 before TDC at idle and around 30 full advance 3500rpm. It seems to us that the engine is running a little rich as we can see sometime black smoke comes from exhaust. We are wondering should I lower the main jets to like from 0.160 to 0.155 or down more to 0.150 and the same with idle jets from 0.070to 0.065 or down to 0.060?? The car can peel tires on first gear and runs pretty good to me. Appreciate any comments you may have. Thank you.

Fri Sep 17, 2021 6:13 am

Sorry, the setup is a dual carbs.

Fri Sep 17, 2021 6:34 am

Sounds like you went from to small jetting to to big.... Think you change in jetting size was to radical...

Idle jets might be to big.... Go back to your .055's and see if it helps.... Most idle jetting stays in the .055 to .060 range... Idle jets only give good fuel mixture below 3000 or so RPM.... Above that carbs pretty much run on mains... With to big of idle jets you are dumping a lot of fuel into engine you probably don't need...

Fri Sep 17, 2021 7:13 am

Why would you jump so far in one step like that :shock:

Fri Sep 17, 2021 8:45 am

What size venturis?

Yes, you are now way too rich in both the idle and mains.

Fri Sep 17, 2021 10:10 am

I have 32mm venturis. I will go back to .055 idle jets and retest it. Thank you all for great comments.

Fri Sep 17, 2021 10:29 am

You are way big on both your main and idles.

Read this:
https://www.aircooled.net/vw-carburetors-jetting-102/

Also, did you set your floats and verify fuel pressure first:
https://www.youtube.com/watch?v=54uPwTZ3DJw

And did you verify that the jets were sized correctly:
https://vwparts.aircooled.net/SearchResults.asp?Search=jet+gauge&x=0&y=0

Fri Sep 17, 2021 12:58 pm

155 mains and 60 idles

Fri Sep 17, 2021 4:07 pm

I don´t think I have ever seen an ACVW with 44´s that needed 60 idle jets unless the engine was very low compression, like 8-1 with an FK8 or something like that.
But, it is very float height dependant. Set float heght to 12 mm for starters.
Reinstall the 55 idles, keep the 155´s (which are probably too small, especially if there´s some grunt in the engine, Increase main air to 220 and see what happens. Its not unusual to be in the 165-175 main and 210-220 main air range on nippy 2275´s. (For me at least)
Sometimes you need to go down in main air again to control the AFR @ wot, but 220 is a good starting point.
Wrt main jet sizes. Remember, there are two reasons to why an engine with IDF´s needs/wants large jets. 1, if it is low compression and/or inefficient for whatever reason. And 2, if it really makes power.

Wed Jul 06, 2022 4:11 pm

Dear Members,

I am back in the same scenario again. The current setup carbs is .160 main jets, .200 air jets, and .55 idle jets. Sometime the engine choke when I hit the gas lightly. If I hit the gas pedal hard then there is no problem. There is a little of black smoke in the tail pipes (may be running a little rich?). Below is a chart that I found and I think the main jets and air there are too low. Appreciate any comments.

I saw a segment on TV for Iron Resurrection and they had a Ghia on it with 1915cc engine and dual carbs. Man, that car ran like madness. I would love to have that. One thing, they reset the float even they bought it brand new carbs. Should I reset my float? And how?

Wed Jul 06, 2022 7:40 pm

I always clean and set the floats on a new/new to me set of carbs.

Remove the top of the carb and stand it vertically, with the float hanging from the pivot shaft.
Measure the distance from the top to the float. Make sure that the gasket is in place when you measure.

There is a little metal tab on the float that contacts the fuel shutoff valve in the carb top.
When adjusting your float level. Bend the tab closer to the valve to lower the float level.
If you need more float height bend the tab away from the valve.

I usually set my Weber (or whatever clone IDF) at 10.4mm. I have a cheap 3/8" extension that works as a tool for setting the float level.
Just slip the tool between the float and carb top. If the float blocks the tool from slipping between the float and the top, make an adjustment as described above.
Ideally you want the float to just touch the measuring tool when the float height is set correctly.

That's the way I set them. Others will have their own method of setting the floats.

YMMV!

Thu Jul 07, 2022 5:20 am

kdnguyen61 wrote: I have 32mm venturis. I will go back to .055 idle jets and retest it. Thank you all for great comments.

you need 36s in there at least

Thu Jul 07, 2022 11:38 am

Slow 1200 wrote: kdnguyen61 wrote: I have 32mm venturis. I will go back to .055 idle jets and retest it. Thank you all for great comments.

you need 36s in there at least
I agree. But 36 is plenty. the engine wohnt pull more than about just shy of 160 anyway, unless the heads are really good.

Mon Jul 11, 2022 8:40 am

Path forward for me I am thinking is:

1) Reset float
2) Change out to 36mm venturis
3) Change out main jets to .150 or should I change to .140? Engine compression is 9.5:1. Heads have 40X35.5 heavy duty springs
4) Keep air and idle jets the same.

Is that sounds good?

Mon Jul 11, 2022 9:29 am

Please tell us more details about the engine. Exactly which 40X35 heads. What exhaust system. What ratio rockers. Maybe a few pics.

Wed Jul 13, 2022 2:15 pm

It is a 2276cc engine with Engle cam FK8. It also has:

82mm chromoly stroker crank
9.5 compression ratio
31mm HP lifters

The heads are:

GTV-2 Dual Port Air-cooled VW Cylinder Head 94mm Bore
Intake Valve 40mm Stainless Steel
Exhaust Valve 35.5mm Stainless Steel
Combustion Chamber 56cc
Cylinder Head Material: Aluminum Alloy
Spark Plug Hole: 12mm 3/4" Reach
Dual Hi-Rev Valve Springs
Chromoly Retainers
Hardened Valve Stem Keepers

Wed Jul 13, 2022 2:18 pm

It also has performance super Hi-Ratio Rocker Arm Shaft Kits 1.25 ratio and running with EMPI 4 tips Monza exhaust system.

Wed Jul 13, 2022 5:17 pm

Quote: The engine choked at 50mph and ran very poor performance above that. Quote: running with EMPI 4 tips Monza exhaust system.
Oh my... You're blowing so much combustion exhaust volume out the larger exhaust valves at mid-range rpms and higher; but the gas volume is being significantly restricted by the small pipe diameter of that exhaust... You should ideally have a real header that uses 1.5" diameter pipes. Are you also using stock-type heater boxes? If so, that's another restriction in the exhaust flow.

Wed Jul 13, 2022 5:32 pm

FK 8 requires a 1:4 ratio Rocker

Wed Jul 13, 2022 7:37 pm

Rome wrote: Quote: The engine choked at 50mph and ran very poor performance above that. Quote: running with EMPI 4 tips Monza exhaust system.
Oh my... You're blowing so much combustion exhaust volume out the larger exhaust valves at mid-range rpms and higher; but the gas volume is being significantly restricted by the small pipe diameter of that exhaust... You should ideally have a real header that uses 1.5" diameter pipes. Are you also using stock-type heater boxes? If so, that's another restriction in the exhaust flow.

That was my thought and why I ask him what exhaust.

I'd suggest 1 5/8" exhaust.
36mm venturies
55 idle - 150main - 200 air - F-11 emulsion tubes as a starting point.