New build pic, looking for jetting/timing recommendation Options

[consolidated]

The 914 Spec series or "H2R Challenge" is starting next week but I feel the car may not be making optimum power. It has dual 40 IDF Webers with stock 155mm main jets, I'm in Austin, Texas 450' elevation.

Any carb and timing tuning advice would be very much appreciated. The motor is s stock 1.7L, rebuilt with new pistons, rings, bearings, crankshaft, seats etc. Compression is good.

How much timing advance is optimal for these motors?

Thanks!

[Randal]

The 914 Spec series or "H2R Challenge" is starting next week but I feel the car may not be making optimum power. It has dual 40 IDF Webers with stock 155mm main jets, I'm in Austin, Texas 450' elevation.

Any carb and timing tuning advice would be very much appreciated. The motor is s stock 1.7L, rebuilt with new pistons, rings, bearings, crankshaft, seats etc. Compression is good.

How much timing advance is optimal for these motors?

Thanks!

Nice build. That is a very clean car.

Call up Bontempi and ask him about the best settings for a 1.7 race motor.

FYI most tuners would want the motor on the dyno to figure out what works, but the folks I know are out here, i.e., a long ways from Austin. Get your car on a chassis dyno with a good air cooled tuner and you'll find the right power combination. Anything less, unfortunately, won't get you what you want.

[consolidated]

Thanks Randal. We're hoping for some fun and close racing.

[Woody]

Are you required to run the stock camshaft?

[consolidated]

Are you required to run the stock camshaft?

We are.

[Borderline]

155 mains sound pretty rich for Weber 40's and 1.7L. I was running 135's on my 1911cc motor with weber 40"s FWIW

edit: The question I forgot to ask is what venturi size are you running...makes a difference!

[consolidated]

155 mains sound pretty rich for Weber 40's and 1.7L. I was running 135's on my 1911cc motor with weber 40"s FWIW

edit: The question I forgot to ask is what venturi size are you running...makes a difference!

Main venturi is 28mm. The plugs look lean, hmmmm. We had too much advance however, backing that off this week.

[Woody]

What day does the series start? I may come up to watch.

[consolidated]

What day does the series start? I may come up to watch.

Race one is 10am this Saturday, race 2 around 1pm. We draw cards for starting positions, second race is reverse finishing order of race 1 but running the track backwards.

If you car is close to spec let me know if your interested in running with us.

[Woody]

I am running a cam in mine, its also a 2056.

[jmill]

What ET are you using along with AC jet size. If your using the F11 with an AC jet over 2.00 it'll lean your mixture up at higher velocity. I've never been a fan of the F11 and prefer the F7.

[consolidated]

What ET are you using along with AC jet size. If your using the F11 with an AC jet over 2.00 it'll lean your mixture up at higher velocity. I've never been a fan of the F11 and prefer the F7.

I'll find out. We ran a A/F ratio gauge and it's definitely rich, we're going to test smaller than a 115 main.

[jmill]

What's your redline? I ask because 28 vents seem a tad small for a 1700cc race engine that spends most of it's life in the upper RPM range.

[vitis]

What airs are you running? I know if Jake was on this thread he would be telling you that you need to have a weather station and keep track of your CHTs and EGTs to know the best setup for the particular conditions. I would think 155 mains would be o.k. but I think we would normally run 205 airs with that. We only have a 1795 engine with 40 IDFs and 28 mm venturis.

Milt

[consolidated]

Here's what they have, what they came with stock:
Main venturi 28mm
Aux venturi 4.5mm
Main jet 115mm
Air corrector jet 200mm
Emulsion tube F11
Idle jet .5mm
Pump jet .5mm
Needle valve 1.75mm

[jmill]

If you stick with the F11 and 28 vents your 115 mains are in the ballpark. You say you are rich on your A/F ratio gauge. At what RPM are you reading this, 3K to redline or above 4K? If your rich above 4K try stepping up your AC jet size. What's your mixture like at transition from idles to mains?

Are you reading the A/F ratio in the driveway or under load?

[consolidated]

If you stick with the F11 and 28 vents your 115 mains are in the ballpark. You say you are rich on your A/F ratio gauge. At what RPM are you reading this, 3K to redline or above 4K? If your rich above 4K try stepping up your AC jet size. What's your mixture like at transition from idles to mains?

Are you reading the A/F ratio in the driveway or under load?

It's lean at idle, rich from 4K rpm to redline. I doesn't pull well around 3K rpms, doesn't like to cleanly rev at that engine speed. Thanks John.

[jmill]

Sounds like lean transition issues. That's why I'm not a fan of the F11. It was designed for a leaner transition. You can get it to work. You can step up your idles and/or main jets to richen up your transition. You'll then have to step up your AC jets above 2.00 to lean your mixture up at higher RPM.

I prefer the F7 because it is designed to give a richer transition. Most don't want to spend the $80 for the new ET's and then more $ on jets. $80 will buy a bunch of jets to get the F11 to work.

On a side note you need to check your float level. I've had them set too low right out of the box. That would also cause a lean transition.

[consolidated]

Sounds like lean transition issues. That's why I'm not a fan of the F11. It was designed for a leaner transition. You can get it to work. You can step up your idles and/or main jets to richen up your transition. You'll then have to step up your AC jets above 2.00 to lean your mixture up at higher RPM.

I prefer the F7 because it is designed to give a richer transition. Most don't want to spend the $80 for the new ET's and then more $ on jets. $80 will buy a bunch of jets to get the F11 to work.

On a side note you need to check your float level. I've had them set too low right out of the box. That would also cause a lean transition.

Fantastic feedback. I'm a carb idiot, which idle/main jets and AC jets do you recommend I try? More than one is fine we'll order and try them out, my car is the likely beta for the others. Thanks for the float level tip!

[jmill]

Jetting advice is difficult to give without hearing your engine run, knowing how rich or lean it is and knowing exactly where it stumbles. I can run with the little info I have and give a possible range.

Idle = .50 - .55
Main = 1.20 - 1.25
A/C = 2.10 (maybe 2.20 depending on how rich you were)

Buy the Weber Tech manual. I think CB has it for $13. Read it a bunch of times and you'll no longer consider yourself a carb idiot.