INTAKE SYSTEMS - All Group K 650 kits utilize single carb intake systems only. All '86 - '90 650cc engines were supplied stock with a "remote fuel pump" 28mm Keihin carb, while all '91-'93 650 engines were supplied with the newer model "integral pump" 38mm Keihin carb. Group K throat bores both of these carbs for use in their respective SLEEPER kits with the standard intake manifold and flame arrestor case. This throat boring is an extremely easy and cost effective way to increase intake ability without significantly affecting fuel consumption.
HAMMER KIT INTAKES - It's our position that the carburetor that can provide the best fuel mixing, at all throttle positions, is the carb that will provide the best overall acceleration and throttle response. Dual 38 carbs are commonly used on modified race boats because they can offer better overall throttle response than a heavily modified 44 Mikuni carb. 38 duals offer better response because the smaller 38 carbs can mix the fuel with the incoming air much more efficiently at partial throttle openings, not because they have greater volume abilities.
The 42 Keihin carb, used on all Group K Hammer kits, offers better overall fuel mixing and throttle response than any large throat single carb we have tested. This 42mm carb bolts directly onto the stock '91-'93 650 intake manifold where it works in concert with the small intake runners of the Group K modified '91-'93 650 manifold to provide throttle response and acceleration that no 44 Mikuni and few dual carb setups will match. The single 42mm Keihin carb has no troublesome linkage, and it features easy "two screw" mixture tuning. Your stock '91-'93 intake manifold must be bored slightly to accommodate the larger 42mm carb throat diameter. (the early 28mm type manifold will not accommodate the 42mm carb)
In our tests, the popular K & N flame arrestor replacements performed well as long as they were perfectly dry. However when they became even a little wet, they offered very restricted air intake ability until they were removed and allowed to dry out. For our Hammer kits we recommend the stock Kawasaki '91-'93 flame arrestor case and element. The intake mesh of the stock arrestor is so well guarded in the engine compartment that it is exposed to very little water spray. Whatever spray it may be exposed to will not clog the all stainless steel screen element in any way. The opening on the stock flame arrestor also matches perfectly to the throat opening of the new 42 Kiehin carb.
We have tested several dual carb kits on the 650 engines. Surprisingly they offered only slight increases in overall performance (about 1 mph). All the duals we tested proved to be very difficult to tune and synchronize. That, along with the high price tag, make them a very poor value. Stock '89-'93 Kaw. reed petals have consistently outlasted and out performed all the aftermarket reeds we've tested.
