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  #21 (permalink)  
Old 06-28-2009, 03:59 AM
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Default Too rich....

After testing on a proper situation (autoslalom- between cones on a track) , I found the middle/ transition to be too rich.

To make things better, can the nuts on the acc.pump shafts be turned innwards (from the valve covers towards the carb- body)?

Can the large idling jet (65) be causing this trouble? (Transition holes are fed by this jet ...)

Or can the 0 (closed) acc.pump bleed be part of it?

Also; after reading an older post by JacMac I've found a probalbe cause of two barrels unwilling to be synchronized; twisted shafts!?!

I'll look into things and hopefully things will get even better....
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  #22 (permalink)  
Old 07-03-2009, 02:42 AM
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Quote:
Originally Posted by Caprimaniac View Post
After testing on a proper situation (autoslalom- between cones on a track) , I found the middle/ transition to be too rich.

To make things better, can the nuts on the acc.pump shafts be turned innwards (from the valve covers towards the carb- body)?

Can the large idling jet (65) be causing this trouble? (Transition holes are fed by this jet ...)

Or can the 0 (closed) acc.pump bleed be part of it?

Also; after reading an older post by JacMac I've found a probalbe cause of two barrels unwilling to be synchronized; twisted shafts!?!

I'll look into things and hopefully things will get even better....
Turning the nuts in gives more volume.

Maybe try a 60 idle and a 35 pump bleed, one at a time, idle jet first.

The idle/transition/main circuit all need to overlap and provide a smooth blending A/F of mid to high 13s, the accelerator pump should then provide the minimum to prevent a stumble at any rate of throttle opening, any more is too much, then the engine recovers from being overrich, soggy throttle response.
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  #23 (permalink)  
Old 07-14-2009, 07:37 PM
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Just a thought,

How much of a turn is your idle speed screw in? ( On the linkage. ) Not idle jets, but idle speed.

You may have the butterflys open too much bleeding fuel from the main circuit.

This will really screw you up trying to get your idle jet size right and adjusted correctly.

If you ok there, back off your nuts and go a size down on idle jets.

I didn't read every post, but you timing needs to spot on in all of this.
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  #24 (permalink)  
Old 08-11-2009, 12:16 PM
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Default Maybe not too rich?

Hello again.

In answer to a previous post: I run 3,5 PSI fuel pressure.

GAZ: yes; I found out turning the nuts in makes more fuel squeeze out..

FlatTyler also has a point. Actually, I have been turning the idle speed screw more in since I have opened the idle jets more to keep it steady at 1000 rpm at idle. I will look into this....

I kept the 65 idle jets and also added 165 main jets bercause I got this conflicting idea: Maybe it's too lean?

the "too rich" theory came up when I discovered the plugs were sooty.

After more testing at idle & full throttle, I found the plugs to be light tan..

But the problem persists: At around 4500 the engine misfires or are a little unwilling when the pedal is kept steady or pressed in gently.

If I floor the pedal in 1.,2. and 3. it revs happily up to 7000+ in one go without hesitation.

Hopefully my pals broadband lamda will be available in a couple of days...
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Old 08-11-2009, 12:57 PM
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Part throttle, cruise is administered by the emulsion tubes.
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  #26 (permalink)  
Old 08-14-2009, 01:02 AM
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Default After sun comes rain

Or after boilings comes ice.

Did a couple of hours with broadbandmeter last night. A/R abaout 11.5 at full throttle. Too rich, I know.

Did some reading and found a formula: Main venturi *4= main jet size= 160
I did put in 165, so that's a fit.

But then: Air corr.= main jet + 60 = 225... I have 190 (drilled to 200...)

Will try to change to 135 mains; fits the formula. Will get a set of 225 or 230 later to go with 165.

Also:
Went autocrossing last weekend. Bubbling sound and hestiation at around 4000- 4500.
Drove to pit & parked. Had a feeling of boiling gas in the float chambers (as I previously have experienced.) But no; THE CARBS WERE ICE COLD.

Same happened last night; after going through 2. and 3. to 7500 rpm, the engine stalled in 4. @ 4000 rpm.

After parking, again, carbs icecold...

Conditions: Humid (rainy), 52 F (11 deg. C). At autocross it was not that cold, but same humidity. Have a large front scoop and "double hood" with a closed chamber surrounding the air horns of the carbs.

And, in addition to the icing this happend: After 1 hour of highway speed (60 mph) my gastank went empty! Wow! I cannot see going up +030 in a mainjet can cause this, but....

Can someone confirm: Can carb icing be the cause of the hesitation in 4. at around 4000 rpm?
I will try some alcohol in the tank to see if that helps. Any other ideas?

Also: Sudden explosion in gas consumption. Can icing conditions be the reason?
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  #27 (permalink)  
Old 09-25-2009, 12:10 AM
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A short roundup;

Did autocross last weekend- personal best 6 sconds better than the last one. Contributions were new Toyo R888 E/DOT- slicks and 5 weekends curcuit- racing in a row.

Engine still hesitates around 2-4000 after I've left the throttle pedal alone for a second or so. Very clean & crisp up the RPM scale.
What made worries was low oil pressure in the tight 180/ 360 deg turns. But that , I hope, will be fixed with twin idle stop screws & idle nonfluctuating @1100 rpm.

Will test at oct. 10. After that: winter & waiting for spring....
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  #28 (permalink)  
Old 10-12-2009, 07:35 PM
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Rune,

I've read about and experienced venturis icing up and restricting the engine.

Could it be that after your blasts to 7500 in 2nd and 3rd that the chokes have iced up,
which would then make the A/F ratio extremely rich and limit the power output?
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  #29 (permalink)  
Old 10-16-2009, 02:11 AM
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Default OK; last roundup!

Hello, Gary.

Yes, icing might have been a possibility. But; before this last autocross I tested if the carbs were synced. They were NOT! I di a synch in may or something- either this was not good enough or it'd wiggled out of sync during summer. I also had to clear one of the idle circuits.

The week before I'd changed back to the old, small jets: 140/ 200 (fuel/ air).

All this made the transition really smooth; hesitation around 3-4000 were gone. Although, I suspect it to be a little too weak at higher RPM.

Wiil get new jets and maybe a set of F14, maybe 15?, emultions tubes next season.

Also: By using 2 x idle stop screws, the got idle better. But, it fluctates. Indeed. First 1000 at cold.... then up to 1200 at warm.... then after driving it's down to 700.... So; any tip on this problem would be appreciated, indeed.

Will clean idel system completely & hopefully it will run on all cylinders with all CO- screws one round out. Right now some of the CO's are random; turn the knob until the cylinder fires.
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  #30 (permalink)  
Old 09-07-2010, 10:39 AM
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Default This is the result

AF on 8000 rpm is 12.5. Also "good" on other rpm's.

No hesitation, but a small "thing " around 3000 rpm (too fat) when bottoming at 2000 (which I seldom do. Acc. pump causing this?).

Idle fine.

Idle jet: .050 screws out by 1/2 turn.

Acc. jet: 45. Nuts all the way out. (Or 3/4, if you take off what I have cut off the threads)

Emulsion tube: F11

Main choke 40,5mm

Main jet: 155

Air corr. jet: 170

This is with a 308 deg. .613 lift solid roller 347 with 40 deg max ignition, Mallory Al6 and no RPM limit (runs out of power at around 8200), K&N air filters (large), medium stacks.

May be refined some, but really happy. Only a rolling- road trip is missing....

Thanks for all tip & trick learnt by people at Club Cobra forums.

Rune
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  #31 (permalink)  
Old 09-07-2010, 11:12 AM
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If you're spining a 347 to 8000 RPM for "ANY" time you better have some deep pockets and a place to store broken spares.
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  #32 (permalink)  
Old 09-19-2010, 12:51 AM
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I know, Rick, I know....

When that is said; Rotating assembly is rated to 1500 Hp/ 8000 rpm. And it's lasted for a couple of years now, without any issues. Oil pressure stays the same, noe need to adjust valves, etc.

Worried about the Comp solid rollers: yes. Will run one more year and then inspect.

Back to the webers: As 12.5 in AF ratio is a bit high for a N/A, I have to try 140 main jets just to check. This might eliminate the off- on throtttle issue and also bring the gas fumes away when criusing at 3000 at the highway.

And there is unburnt fuel leaving the engin; after every run when engine is turned off, it takes 30 seconds before a dull but loud BOUM sound leave the exhaust.... Should have uploaded a sound file- really funny thing.

<rs
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  #33 (permalink)  
Old 09-19-2010, 02:14 AM
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Quote:
Originally Posted by Caprimaniac View Post
I know, Rick, I know....

When that is said; Rotating assembly is rated to 1500 Hp/ 8000 rpm. And it's lasted for a couple of years now, without any issues. Oil pressure stays the same, noe need to adjust valves, etc.

Worried about the Comp solid rollers: yes. Will run one more year and then inspect.

Back to the webers: As 12.5 in AF ratio is a bit high for a N/A, I have to try 140 main jets just to check. This might eliminate the off- on throtttle issue and also bring the gas fumes away when criusing at 3000 at the highway.

And there is unburnt fuel leaving the engin; after every run when engine is turned off, it takes 30 seconds before a dull but loud BOUM sound leave the exhaust.... Should have uploaded a sound file- really funny thing.

<rs
Rune, your engine sounds really tough, would love to hear the "boom" after key off.
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  #34 (permalink)  
Old 09-19-2010, 08:05 AM
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Let's see if I'll record this one day... (Or maybe I'll manage to get rid of this annoying sound very soon?)

RS
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