Read and re-read the shop manual. As far as synchronizing the carbs go, it says to, "Mount synchro-tester on one carburettor and adjust, then put it on the other and synchronize by means of the idle mixture control screws..."
Is that a mis-translation? I thought the you used the idle speed adjustment screws to sync them up?
Please, Carb experts try to explain this to me.
Moderator: TechMOGogy
I use both. I adjust idle mixture screws first, all the way in then out 2 1/2, tweak them a lil from there. I try to keep both readings as close as possible and still have a smooth idle. Then i work on making the reading the same for both carbs with the idle speed adjust.
Mike Newton 1973 712M (sold)
I do not like this word "bomb." It is not a bomb. It is a device that is exploding. Jacques le Blanc
I do not like this word "bomb." It is not a bomb. It is a device that is exploding. Jacques le Blanc
carb assistance
Following along with this thought...I have balanced the carbs again.
I have adjusted the plastic ends on the connector rods, the idle mix screws and the idle speed screws. I got the idle smooth and about 950
and balanced to within a hairs difference with the syncro tester.
All this happens in the driveway with the engine warm after driving for about 5 to 10 km around town.
Now the interesting part..when I drive after all this, the idle will go up to 1300 to 1500, setting at a stop. If I give a quick tug on the hand throttle it goes back to about 1000, which is close to the original settings. Sometimes it will not go back to idle speed and just revs high at about 1300 rpm. What gives? What am I doing wrong or is it just an old truck thing?
While inspecting this weekend I noticed the linkage arm between the hand throttle and the carb linkage arms was almost worn through at the spring hole. I had a neighbor weld the hole shut and redrilled it. looks like a new one now. I checked the price for a new one and it was about $145, that is, if I could find one.
Morris
I have adjusted the plastic ends on the connector rods, the idle mix screws and the idle speed screws. I got the idle smooth and about 950
and balanced to within a hairs difference with the syncro tester.
All this happens in the driveway with the engine warm after driving for about 5 to 10 km around town.
Now the interesting part..when I drive after all this, the idle will go up to 1300 to 1500, setting at a stop. If I give a quick tug on the hand throttle it goes back to about 1000, which is close to the original settings. Sometimes it will not go back to idle speed and just revs high at about 1300 rpm. What gives? What am I doing wrong or is it just an old truck thing?
While inspecting this weekend I noticed the linkage arm between the hand throttle and the carb linkage arms was almost worn through at the spring hole. I had a neighbor weld the hole shut and redrilled it. looks like a new one now. I checked the price for a new one and it was about $145, that is, if I could find one.
Morris
Might you have some binding at the swivel post on your #4 cylinder cover? Mine has two plastic bushings, an upper and a lower, if those are missing, perhaps your linkage is binding. Also, is your hand throttle cable lubed?
Mike Newton 1973 712M (sold)
I do not like this word "bomb." It is not a bomb. It is a device that is exploding. Jacques le Blanc
I do not like this word "bomb." It is not a bomb. It is a device that is exploding. Jacques le Blanc
carb assistance
Thanks,
The two bushings are there. They are lubed. I increased the spring tension (by slilghtly moving the dead side of the spring attachment point) to compensate for the possible hang up of the hand throttle. It gives me a tighter foot pedal but that is all.
I am thinking of removing the hand throttle as I do not use it except to return the idle to desired rpm. It is warm here in San Diego and the pinz starts right up, usually first try, but that will change when I move to Washington. I really do not llike taking things off to solve problems as they were installed for a reason, but it is worth doing to see if that is the problem area.
This whole issue is relatively new thing, within the last few months. Previously it was that the rpm would not stay up, especially after a long decent.
Morris
The two bushings are there. They are lubed. I increased the spring tension (by slilghtly moving the dead side of the spring attachment point) to compensate for the possible hang up of the hand throttle. It gives me a tighter foot pedal but that is all.
I am thinking of removing the hand throttle as I do not use it except to return the idle to desired rpm. It is warm here in San Diego and the pinz starts right up, usually first try, but that will change when I move to Washington. I really do not llike taking things off to solve problems as they were installed for a reason, but it is worth doing to see if that is the problem area.
This whole issue is relatively new thing, within the last few months. Previously it was that the rpm would not stay up, especially after a long decent.
Morris
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lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Here's a few tips.
all adjustment has to be done "engine hot". The reason is that if you adjust the idle mixture when partially warm it will race due to improved combustion when hot. This is a bit difficult without a gas analyser, but you may be a bit far out (rich) at 2.5 turns.
Don't discount vaccum leaks into the manifold.
Worn carburetor spindles can cause racing at perceived idle as can lack of free play on the accelerator pump links that hold up the throttle.
Any play in the plastic ball joints can also cause the engine to race since it will cause one of the spindles to be lazy on the return.
Don't negate the diz advance, it may have a lazy set of weights or a worn shaft. This will cause the engine to race at idle after a run since it won't come back to base timing.
Just a few thoughts over a cup of Brook Bond.
Lipton? bah humbug!
Dennis
all adjustment has to be done "engine hot". The reason is that if you adjust the idle mixture when partially warm it will race due to improved combustion when hot. This is a bit difficult without a gas analyser, but you may be a bit far out (rich) at 2.5 turns.
Don't discount vaccum leaks into the manifold.
Worn carburetor spindles can cause racing at perceived idle as can lack of free play on the accelerator pump links that hold up the throttle.
Any play in the plastic ball joints can also cause the engine to race since it will cause one of the spindles to be lazy on the return.
Don't negate the diz advance, it may have a lazy set of weights or a worn shaft. This will cause the engine to race at idle after a run since it won't come back to base timing.
Just a few thoughts over a cup of Brook Bond.
Lipton? bah humbug!
Dennis
OOOps no customer bashing now
carb assistance
Thanks Dennis,
Where should I look for the possible manifold leak?
Will a total rebuild on the carbs help to eliminate any of these issues?
I have new plastic ball joint ends on the linkage.
As for the diz advance...petronix. Now where does that put me in the 'spin the wheel of problems'?
Morris
Where should I look for the possible manifold leak?
Will a total rebuild on the carbs help to eliminate any of these issues?
I have new plastic ball joint ends on the linkage.
As for the diz advance...petronix. Now where does that put me in the 'spin the wheel of problems'?
Morris
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Jimm391730
- Posts: 1456
- Joined: Wed Apr 14, 2004 10:58 pm
- Location: Idyllwild, CA
Watch both linkages carefully as you just start to crack the throttle by using the hand control. Probably you have one carb just starting to open before the other, the early one has the shaft linkage a half turn too long. This can keep one carb cracked open unless it is dropped quickly from above idle, slamming both closed, where a gentle closure will keep one just barely open.
Best of luck,
Jim M.
Best of luck,
Jim M.
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lindenengineering
- Posts: 715
- Joined: Sat Apr 17, 2004 6:14 pm
- Location: Golden Colorado USA
- Contact:
Vaccum leaks can exist from external brake servo hose connections including the vent hose to the diz and the restriction (or the lack of it).
The whole induction system is prone to leakage, from worn carburetors, to loose bases and blown out gaskets at the heads. The manifold runners can crack at the bridge fixing lugs and the flanges. The front unit seems particularly prone to that. As a rule I always grasp each carburetor manifold assy and try to rock the thing. Any movement must be investigated.
The distributer on the Pinz is also prone to wear and sticking of the adv unit. The install of a Petronix unit often acentuates this wear. To test the smooth operation of the diz, set the base timing, then rev the engine until full adv is reached by observing the timing gun and the adjustment needed to hold the timing pin on the c/shaft at those revolutions.Then let it (engine) return to idle. It must return to base timing within a degree. If it doesn't sticking or wear are present. A rule of thumb can be determined if the fault is present by starting the engine hot without touching the gas pedal. Rev the engine and let it return to idle. Read or make a mental note of engine speed. Any increase is the degree of wear. If you switch off and then restart the engine will often return to a lower idle (if you don't touch the gas pedal again.
All simple stuff really
Best of luck
Dennis
The whole induction system is prone to leakage, from worn carburetors, to loose bases and blown out gaskets at the heads. The manifold runners can crack at the bridge fixing lugs and the flanges. The front unit seems particularly prone to that. As a rule I always grasp each carburetor manifold assy and try to rock the thing. Any movement must be investigated.
The distributer on the Pinz is also prone to wear and sticking of the adv unit. The install of a Petronix unit often acentuates this wear. To test the smooth operation of the diz, set the base timing, then rev the engine until full adv is reached by observing the timing gun and the adjustment needed to hold the timing pin on the c/shaft at those revolutions.Then let it (engine) return to idle. It must return to base timing within a degree. If it doesn't sticking or wear are present. A rule of thumb can be determined if the fault is present by starting the engine hot without touching the gas pedal. Rev the engine and let it return to idle. Read or make a mental note of engine speed. Any increase is the degree of wear. If you switch off and then restart the engine will often return to a lower idle (if you don't touch the gas pedal again.
All simple stuff really
Best of luck
Dennis
OOOps no customer bashing now
throttle linkage
Thanks to all that gave advice on this one.
Jim,
I looked at the linkage to check for one perhaps being slightly tighter than the other, looking for a simple solution first. It seems as I pulled the hand throttle I noticed that the foot throttle linkage was tight. It was keeping both carbs just a bit open. I popped the plastic end off the ball and loosened it a bit and it seems to have done the trick, at least in the driveway. Before I put it all back together I will take it for a spin and see how it performs in real life.
I hope this works.
Cheers,
Morris
Jim,
I looked at the linkage to check for one perhaps being slightly tighter than the other, looking for a simple solution first. It seems as I pulled the hand throttle I noticed that the foot throttle linkage was tight. It was keeping both carbs just a bit open. I popped the plastic end off the ball and loosened it a bit and it seems to have done the trick, at least in the driveway. Before I put it all back together I will take it for a spin and see how it performs in real life.
I hope this works.
Cheers,
Morris