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Throttle valve butterfly leaking air????

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dbnoaol Avatar
dbnoaol doug bowers
milford, ohio, USA   USA
Gentlemen I need your help....again..

67 Sprite 1275 HS2 carbs
pictured is the throttle valve butterfly from both sides with a light behind it- notice the leakage...is this a normal amount?
These are new, the shafts are new, the bushings are new.
I have read about being certain to install them in the proper direction- there are comments everywhere about the butterfly having a beveled edge and this bevel should go toward the fuel jet.
My butterfly has no such bevel!

whats the problem? cant idle below 1500-1800 rpm...anything lower and the engine gets erratic and the tach jumps all over the place. Runs decent at higher rpms but after a few minutes under load smells gassy as all get out-
no smoke, nice grey ash on plugs, so mixture seems good.

So everything i read says air leak...everything has been tested time and time again for leaks using the WD40 method- carbs are balanced, needles AN new, every gasket is new, the thick black rubber insulator blocks are new, the intake manifold has no leaks whatsoever...the only thing left is the throttle valves by my logic. they are new, the bushings are new, the shafts are new.
The timing is 10 BTDC (@1000rpm best i can tell), the dizzy is new Pertronix, electronic. (previous owner had the drive dogs 180 out of place- fixed that...but it did not improve my idle issue.)
running 87 octane fuel with lead additive....

so my questions is this- do the gaps shown around the butterfly seem acceptable (normal?) or is this VB garbage part????
if normal, what do you suggest?

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jmac Avatar
jmac Silver Member Jere McSparran
Greenup, IL, USA   USA
1978 MG Midget "Therapy"
1978 MG Midget "(SOLD)"
You are right, it should seal completely. You should not be able to see that much light around it. It looks like your butterfly is in backwards. But that still would account for all that light on the sides.
The holes in the disc are big enough for you to move the disc around a little. Try loosening the screws and while the screws are loose try to get it to close. If that doesn't work you should try to remove them and turn them over and try it again.



JMac
JMAC Engine Shop
http://www.jmacengineshop.com

refisk Avatar
refisk Rick Fisk
Frankenmuth, Michigan, USA   USA
Doug,

Those butterflys are bad. There should definitely be a bevel on the top and bottom edge and when installed you should not be able to see light, especially on the sides next to the shaft.



Edited 1 time(s). Last edit at 2017-07-16 12:31 PM by refisk.

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dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
That's why your idle won't come down. Hard to tell from the photos, but I think you may have the throttle discs in backwards. They should be installed so that the tapered/beveled edges come in to seal against the carb body...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

Speedracer Avatar
Speedracer Platinum Member Hap Waldrop
Greenville, SC, USA   USA
1967 MG MGB Racecar "The Biscuit"
Call Joe Curto and get two new butterflies, www.joeccurto.com , Look at one in there when you take them out, I never saw a butterfly for these carbs that was not beveled, and they have to be positioned right to close completely when assembled, which they never really do in normal operation, due to the idle screw setting. I think you will find they are beveled, but in backwards and now possibly damaged, so best to start with new, they are not expensive.



Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com


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dbnoaol Avatar
dbnoaol doug bowers
milford, ohio, USA   USA
Thanks guys for the confirmation of my suspicion.
I removed the old Victoria British junk ( they did have a bevel and were in correctly) and replaced with new from Moss- much tighter fit, especially around the sides, I can still see a tiny bit of light top and bottom, but so so much less.

on another point with the butterflies- it seems the tighter you set the screws on them, the tighter the shaft becomes to move, so i loosened them up to where the return spring could pull them back shut with no issue...logic tells me this makes sense...do you agree?

next issue is confusing static timing information and setting the dizzy with a test light:

some info says set to TDC, some say 4'BTDC.
Then rotate dizzy anti-clockwise until the light is off, then back slightly back until light comes back on- tighten down there.
my question- with this done, should my rotor button be ON the post for cylinder #1, or just past it heading to cyl #3?

then tweak until idle speed gets established set to 10 BTDC @ 1000rpm.

it seems previous owner had some things out of wack here- dizzy was 180 out...I questioned his firing order wiring of plug leads- i now have corrected the order to 1-3-4-2

but again, what I am asking is, with the engine at TDC- will the rotor be contacting cyl 1 post or be moving just past it on to the next.


and for clarification: I have installed Pertronix electronic ignition, no points- so, is 12v present ( test light on) when the rotor is in contact with plug wire post, or when it is off of it?

66jalopy Avatar
66jalopy Silver Member Phillip Jolliffe
Lake City, FL, USA   USA
Did you get the split screws on those butterflies? If they are not tight enough they can vibrate out and the engine swallows them, not good.

Speedracer Avatar
Speedracer Platinum Member Hap Waldrop
Greenville, SC, USA   USA
1967 MG MGB Racecar "The Biscuit"
Loctite the throttle plate screws.



Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com


Member Services:
MG/ Triumph Performance Street/Race Engines - Cylinder Head Porting - Modified SU HS Carbs - DIY Engine Rebuild Kits With Free Tech Advice - Alloy wheels for British Sport Cars,and others
Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
Hi Doug,

x2 on what Hap and Phillip said: loc tite those screws!
I am not sure why fully tightening them would make your shaft hard to turn, unless the slot is deformed and rubs the carb body? I think it would be wise to study the reason why, just to make sure that there is not an issue that will cause trouble later!


To answer your other questions: the points are closed most of the time, and the distributor cam opens them at the right time (opening the points allows the field in the coil to collapse, creating the high energy spark current).

So, you want the light to go out at the right time.

What you are trying to do when setting static timing is just get it close enough to run, so the exact angle isn't too super critical. Say you are aiming for 10deg BTDC, you want the light to go out just before the #1 piston reaches TDC on its compression stroke.


By the way, If your distributor drive gear is installed 180deg out, the engine will run fine if the distributor is also installed 180deg out too. The gear can be removed and rotated and reinstalled, if that is an issue with your engine.

As far as whether the rotor's pointer should be just approaching the post or just leaving the post, IIRC it is just approaching the post. But, going back to my earlier statement: the static timing isn't too critical as long as the engine will start. Some folks just simply set it to 0TDC, turn the starter with the distributor clamp loose and their hand on the cap and rotate it while the starter is cranking until the engine fires up. Then, once the engine is running, scootch the distributor forward or backward for the smoothest idle and that's your initial timing.

Ultimately, the numbers in the book are only useful for perfectly stock motors in new condition. The best timing for your engine will be whatever makes it run the best (smooth idle, no pinking under load and total, max advance at top RPM doesn't go above 30 or 34degrees).


hope this is helpful,
Norm

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Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
oops, forgot to add: regarding the amount of light getting around the closed throttle disc, once you've adjusted them to minimize it, make sure it is the same in both carbs.

The most key thing (after getting them both adjusted on the shaft to close as much as possible) is that they match (for best balance). As long as you've got those two things, and you know the screws won't fall out later, then you are all set with that step.


N

dbnoaol Avatar
dbnoaol doug bowers
milford, ohio, USA   USA
OK- throttle valve issues have all been corrected with your help...thank you all!.....back to my original situation...

timing: still fighting this after replacing the distributor having found the old one cracked at the base where the clamp tightens it down, the clamp bolt bent..... also found the distributor drive 180 out.

so, new distributor and clamp- drive dog corrected so that the larger half of the offset is up.

now with the car at #1 cylinder TDC...this is the position of my rotor (6 o'clock position)...something about that does not look right...shouldn't it be about the 1'oclock position?
opinions?

before i dove into this, the engine ran, but crappy...firing on about 2 cylinders, very gassy smelling and fouling plugs left and right...i chalk that all up to the 180 out of phase distributor and butterfly issues...now trying to make it right and find myself second guessing everything about the alignment of this engine.

this car came to me in boxes, half reassembled by the previous owner- but an engine that did start and run...halfway. I've rebuilt everything , replaced every hydraulic line, rubber boot, interior, paint ect ect...saving the final tweaking of the engine for last...now I'm wondering if the timing marks on the timing chain sprockets are properly aligned, or were just thrown together.....hopefully its something more simple than that..

any suggestions/insight much appreciated

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dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
I suspect that your distributor drive gear down in the block is not properly oriented, and part of your problem may be in not properly identifying "firing position" for cylinder number 1. Just putting the number 1 piston at the top of its travel and aligning the timing marks on the timing cover and balancer is not sufficient to putting cylinder number 1 in firing position. This piston may be at the top of its compression stroke or at the top of its exhaust stroke. It needs to be at the top of its compression stroke in order to be ready for spark.

The way to do this is to remove the rocker cover, turn the engine in normal direction of rotation, which is clockwise when viewed from the front of the car, until the second valve from the front, which is the intake valve for cylinder number 1, opens (valve spring compressed) then closes., Then continue turning until the next time the timing marks on the timing cover and balancer align. This will put cylinder number 1 in firing position, at the top of its compression stroke, ready for spark. It is only now that the distributor drive gear, down in the block, should be installed with the slots at the 2 and 8 o'clock position and the larger segment offset.

If you have done all of this, it's possible that the drive dog, which is the small round part on the bottom of the distributor rotor shaft, is installed incorrectly. To confirm this condition, you might momentarily install an original distributor to see if the rotor falls into the same orientation...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

dbnoaol Avatar
dbnoaol doug bowers
milford, ohio, USA   USA
That was it. The dist gear drive drive was out of position a bit.
So now I'm idling at 1000rpm at 10 BTDC...a little rough, so I'll keep tweaking, but all you guys advice lead me right to the handful of issues i was encountering.
Thanks for the responses.

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
smileys with beer

Dick

In reply to # 3557155 by dbnoaol That was it. The dist gear drive drive was out of position a bit.
So now I'm idling at 1000rpm at 10 BTDC...a little rough, so I'll keep tweaking, but all you guys advice lead me right to the handful of issues i was encountering.
Thanks for the responses.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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