carbs

[Steve Litzell]

With a single carb feeding "alternate acting" cylinders, there would actually be a constant flow through the carburator. Where one piston stops pulling air, the other piston pulls. But any time you have one carburetor per cylinder that is isolated to one cylinder in induction, then the air flow is only repetitive (on/off). Because of this, it may be necessary to have a bigger jet to ease flow feed of fuel under this condition to keep primed.

Interestingly, a twin cylinder alternate firing arrangement with a single carburator can be much better than a twin carb/ twin cylinder arrangement....unless the two carbs are feeding at once through an interconnected intake path as a progressive stage systematic throttle, which I never seen on an outboard. It might be a good idea though....Ive seen this on old cars with twin carbs.

Don't tell the hundreds of Konig's and Za Quincy motors that for they might not run! Steve

[champ20B]

Don't tell the hundreds of Konig's and Za Quincy motors that for they might not run! Steve

If you mean the "opposed cylinder" pro-outboards, that is reverting back to the one carb per cylinder scenario (even if you have only one carb feeding both cylinders). An opposed twin is like a single cylinder engine as to how it runs in a (on/off) intake cycle regardless, but having one carb per cylinder is likely more efficient here than just one double sized carb shared by both cylinders........ In fact, thinking about the exhaust side, I cant help but to wonder why they don't just use a centered single expansion chamber fed by both cylinders (for a 350 cc as an example). That is a situation where weight could be saved, is cheaper, more practical and would work exactly as well as having two expansion chambers (one per cylinder) on the opposed engines perhaps.

[Fastjeff57]

Another advantage of the two cylinders/ one carb setup is elimination of that standing wave of fuel droplets in FRONT of the carb at certain low rpms. On my triple project, the droplets formed at low idle and extended at least 4 inches in front of the carbs--scary stuff! (I cured that nonsense with a series of equalizing passages between the carbs and reeds.)

On running progressive opening carbs, believe it or not I tried that, on my first external reeds triple project. It worked, but was 'boggy' thanks to an embarrassing screw up on my part (don't ask!) But it did work.

Jeff

[Steve Litzell]

If you mean the "opposed cylinder" pro-outboards, that is reverting back to the one carb per cylinder scenario (even if you have only one carb feeding both cylinders). An opposed twin is like a single cylinder engine as to how it runs in a (on/off) intake cycle regardless, but having one carb per cylinder is likely more efficient here than just one double sized carb shared by both cylinders........ In fact, thinking about the exhaust side, I cant help but to wonder why they don't just use a centered single expansion chamber fed by both cylinders (for a 350 cc as an example). That is a situation where weight could be saved, is cheaper, more practical and would work exactly as well as having two expansion chambers (one per cylinder) on the opposed engines perhaps.

You have never seen a Konig twin nor a Z series Quincy motor. They were alternating fire not like modern motors opposed. As far as exhaust is concerned, You can not get the primary tubes short enough for your idea. You must remember motors run at a very high rate of speed. Even your lawn mower motor and this ON/OFF thing you refer to is not really noticed by the two stroke motor. This of course depends on the intake track from the back of carburetor to crankcase. The wave you refer to is in all engines that reciprocate and many hours are spent to reduce this reversion on Intakes and cam grinds for 4 cycle. In a two stroke the closer the back of the carb is to the transfers, the better to a limit. In a stock type fishing motor, idle quality is more important than performance. Three cylinder motors seem to have more problems with reversion than two's or sixes. That may because of the crank index and the pulses the carbs receive so a balance type valley is used on fishing engines. The three banger Quincy had no problem with this. Most reversion can be slowed down with smaller Carburetors as the velocity in the intake track is higher. BIGGER IS NOT BETTER! even in racing as low velocity intake makes for a doggy motor and very hard to drive.

[smittythewelder]

Steve, they don't need to have seen either of those two rather rare alky motors; any old A/B/C/D Mercury (now all turned into Mods, I guess) has the single-carb-feeding-paired-alternate-firing-cylinders layout.

[champ20B]

You have never seen a Konig twin nor a Z series Quincy motor. They were alternating fire not like modern motors opposed. As far as exhaust is concerned, You can not get the primary tubes short enough for your idea. You must remember motors run at a very high rate of speed. Even your lawn mower motor and this ON/OFF thing you refer to is not really noticed by the two stroke motor. This of course depends on the intake track from the back of carburetor to crankcase. The wave you refer to is in all engines that reciprocate and many hours are spent to reduce this reversion on Intakes and cam grinds for 4 cycle. In a two stroke the closer the back of the carb is to the transfers, the better to a limit. In a stock type fishing motor, idle quality is more important than performance. Three cylinder motors seem to have more problems with reversion than two's or sixes. That may because of the crank index and the pulses the carbs receive so a balance type valley is used on fishing engines. The three banger Quincy had no problem with this. Most reversion can be slowed down with smaller Carburetors as the velocity in the intake track is higher. BIGGER IS NOT BETTER! even in racing as low velocity intake makes for a doggy motor and very hard to drive.

Not to change the subject, but I was wondering if these alternate twin konig and "Z" quincy models were what was used in "B-restricted" later on till the 1980s? I know that a modified alky Yamato 80 set the final 90+mph record in that class in 1986 I think. BTW, you are right about those expansion pipes. I forgot about the leading pipe length as well as the sliding tuning action they need.

[Steve Litzell]

Yes they were the same motor, The 90 mPH Yamato was a kilo record, but the man that owned that thing had it haulin a$$ for quite some time till the Quincy motor came to the class. Steve