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> Jensen Healey & Jensen GT Tech > Carburetors > what else is there left to do? just the strombergs I guess

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what else is there left to do? just the strombergs I guess  Rate Topic 
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 Posted: 06-01-2007 06:03 pm
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flatlanderep
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Hi everyone,
First off, thanks to everyone who helped me through the Pertronix distributor install.
But now I have a new set of questions. Please bear with me here.
New pertronix distributor is in, new plugs, new wires, new Pertronix coil. Timing is set to 12 ^ BTDC. Plugs gapped to .035.
I can't remember if the Jensen was hesitating before the new dizzy install. But anyway, the car has major hesitation, stumbling, flatspot during light acceleration. Especially during 3rd gear.
So I understand that most suspected carb problems are actually ignition problems, but all the ignition stuff is up to spec. (oh yeah the ballast resistor is bypassed as well - just wired the two wires together).
I suspect it's the carbs because the previous owner stated that he adjusted the carbs by adjusting only one screw (the idle screw) on the rear carb. So they have to be out of sync for sure.
Does it sound like I'm on the right track if my next step is to sync the Strombergs up?
I'm going to buy the tool off JC Whitney that someone posted on here a while back.

Oh yeah no vacuum leaks, the one that was on the original distributor is t'eed up.

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 Posted: 06-02-2007 05:50 am
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Mark Rosenbaum
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Presuming that the Pertronix coil is the type that works without a ballast resistor, that your valves are sealing and your compression is good, and that the cam timing is correct, the carbs are about all that's left.

Unfortunately, you may find that tuning the carbs is not sufficient to get the car into perfect running order.  Like all other carburetors, Strombergs are subject to wear, and eventually one reaches the point where parts replacements are essential.  The difference in performance between a car using well-worn Strombergs, and completely overhauled ones, can be surprising.

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 Posted: 06-06-2007 03:49 pm
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flatlanderep
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Do you know where I can get the mixture adjuster tool?
Will this work? http://www.motorcarsltd.com/item.wws?sku=IN100586

With the engine warm, I tested the pistons in both carbs by lifting the piston a tiny bit. On the rear one, the RPM's raised and stayed that way, as if the piston got stuck. So I guess the mixture is too rich in the rear?
Could this be causing the hesitation under throttle that I've been plagued with?
And is the fix adjusting the mixture?

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 Posted: 06-06-2007 04:50 pm
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Mark Rosenbaum
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Yes, that looks like the right tool.  Delta Motorsports also sells them, and the Club Store may also handle them.

IIRC, raising a vacuum valve and having the engine speed increase does indeed indicate a slightly rich mixture.  But the original engine speed should be restored within a few seconds once the vacuum valve is released and returns to its initial position.  If the vacuum valve itself does not so return, that carburetor has a mechanical problem that must be addressed before proceeding further.

The hesitation you report may be due to misadjusted carbs, to an insufficiency of the proper oil in the dampers, to a missing or defective damper, to insufficient fuel delivery to the carburetors, to a low float setting in one or both carbs, to debris in the fuel inlet or float bowl, or to some combination thereof.  Unfortunately, the only way to determine the cause(s) is to examine every possibility and correct any and all defects found.

 

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 Posted: 06-06-2007 07:07 pm
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flatlanderep
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Mark - By vacuum valve, you are referring to the actual piston correct?
If so, what measures need to be taken if the piston does not return to its normal position after a given amount of time?

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 Posted: 06-06-2007 09:10 pm
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Mark Rosenbaum
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Yes, the vacuum valve (AKA air valve) is the piston-like part.  It has a steel tube that slides up and down inside a mating steel tube in the upper carb casting (the dome or cover).  Normally these two tubes fit together with very little clearance.  When these two parts are assembled separate from the rest of the carburetor, then suspended so the lower part can fall free, it should take a goodly portion of second, to perhaps a second and a half, for complete separation to occur.  (Caution: if you try this with the vacuum valve as the lower part, be certain to catch it before the mixture needle makes contact with anything!)

Free movement of the vacuum valve can be resisted by even tiny burrs or spots of rust on / in either steel tube, or by a bent vacuum valve tube, damaged or corroded damper mechanism or tube passageway, dirty or congealed damper oil, overly stiff or improperly installed rubber diaphragm, bent or incorrectly installed mixture needle or needle adjuster mechanism, an incorrect or missing piston return spring, and possibly a few other things I've forgotten.  Quite often, proper assembly of the parts, or just a moment's application of emory cloth or a small file, will be sufficient to eliminate the problem.

 

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