carb question
- Thread starter MikeG
- Start date
Why ? This head was designed to use 930's.
My 70 ran best with them into the smaller intake ports.
Use matching manifolds into the correct heat insulating washers to avoid any possible air dam effect from a mismatch situation.
My 70 ran best with them into the smaller intake ports.
Use matching manifolds into the correct heat insulating washers to avoid any possible air dam effect from a mismatch situation.
MikeG
VIP MEMBER
Because they are brand new, I have them and they were free.
It will work fine. My combat head self destructed and I replaced it with an earlier one with the smaller ports. Used the combat carbs, chamfered the Tufnol heat resistant washers. Bike runs fine, accelerates fine, pulls well. No problems at all.
MikeG
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The manifolds on it are 30MM at carb and 28.5MM at head. I was thinking of chamfering the carb end out a bit so as not to have an abrupt lip there but it's hardly noticeable so maybe not.
Fast Eddie
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Unless you’re gonna put it on a dyno searching for every last BHP, you won’t notice that tiny step.
In fact, you might not notice even on the dyno !
In fact, you might not notice even on the dyno !
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The increased power experienced while testing on a dynamometer has to be attributed to better fuel/air mixing. The stepping, as vell the venturi, will increase air speed and swirl. Swirl consumes energy and allows manifold pressure to increase (i.e., the partial vacuum will be reduced), affecting the volumetric efficiency of the engine. However, because of the improved mixing and higher gas speeds within the combustion chamber at the exhaust stroke, there may still be a positive net outcome.
In the low rpm range, the manifold pressure is higher because of dynamic effects within the combustion chamber. The net gain may turn into a loss because of the increase in manifold pressure along with no improved mixing.
I think the best strategy overall is to have a good carburettor (or injectors!) and even ducts, preventing large swirls. Rather experimenting with venturis, I would have focused on crancase ventilation. Keeping a partial vacuum in the crancase will promote a higher combustion chamber pressure and avoid pumping losses.
- Knut
MikeG
VIP MEMBER
Thats the set I really wanted.....
Fast Eddie
VIP MEMBER
On my old Nourish race bike I found that it produced slightly higher peak power with posh mk2 smoothbore Amals, but actually, it gave a better overall power curve with normal none smoothbore Amals. I have no idea why other than the none smoothbores caused some turbulence or swirl that was accidentally beneficial.
concours
VIP MEMBER
Holley 0-8896-1 1050 CFM Dominator Carburetor
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Shelby-Right
VIP MEMBER
Going to need a real good adapter for this one , 1200cfm, the saving grace will be the Vac secondarys ,I prefer double pumpers.
marshg246
VIP MEMBER
I'm no expert...
I've always thought that smooth let the fuel/air in easier, but turbulent caused the fuel and air to mix better. I was told that by member of Gary Nixon's 1967 Triumph 500 Daytona winning team. Supposedly, they slightly smoothed out the manifolds and then slightly roughed them to get as much well mixed fuel and air into the cylinders as possible.
I've always thought that smooth let the fuel/air in easier, but turbulent caused the fuel and air to mix better. I was told that by member of Gary Nixon's 1967 Triumph 500 Daytona winning team. Supposedly, they slightly smoothed out the manifolds and then slightly roughed them to get as much well mixed fuel and air into the cylinders as possible.
mean gene
VIP MEMBER
Mike just did this with my 750. Flared the intakes to match the carbs, not polished. 3.5 slides #2 needle in the richest clip setting 17 pilot. K&N filter and Baffled reverse megaphones. Runs great, it always ran better the my 850's. Just posted my problems with it not wanting to idle down. Hope to correct this tomorrow.
MikeG
VIP MEMBER
What port sizes are in your head? 30mm or 28.5mm?