Ck. the afc (air fuel control or you may also be familiar with the term "aneroid" they are synonimous for our discussion )housing on the top and back of the governor housing, remove the AFC plug that takes the 8mm (5/16" will work in a pinch) hex wrench.
Also remove the afc signal line from the manifold or turbo compressor and use regulated shop air on the back of the afc (say 20 psi max). When adding air does the the afc link/shaft move forward smoothly thru your inspection window? If its sticky or stuck you have found a problem.
I suggest that you may have some sort of throttle linkage limiter to limit road speed. I suppose a governor weight/spring package could limit the speed etc. It may be as simple as the "high idle" limit screw being backed off more than other p-pump applications, which would be like a block under the go pedal.
Here is some commentary on safe methods for uprating the pump/engine output FWIW.
Not sure what your adm policy is on emmisions tampering or maybe its better "to ask forgiveness than permission. . "
The stock pump could likely be Bomb'd (better off modified baby) by several things if tampering doesn't concern you.
The tamper screw in the upper left corner of the afc housing can be removed to allow housing removal. The cam/torq. /fuel plate will be staring at you now.
It could be shifted forward for more fueling at the result of additional emmissions and egt's.
See this site:
http://www.tstproducts.com/INSRUCT98.pdf
This is how you would modify things to keep EGT's in ck. etc. by adding a perf. fuel plate that is calibrated for your engine and pump to safely add some fuel w/out excessive emmisions (nox and particles) and egt's. Simple sliding of the plate (forward) and tampering with the high idle screw can increase power somewhat but not nearly like a perf. fuel plate can. It can also result in soaring EGT's in many pump applications. I'm betting the bus doens't have a pyro and if it did the driver wouldn't likely watch it. . so be forewarned. You like to rebuild B-Series right?
You can also look at the instructions (above) on loosening the star wheel for additional mid-range umph at the cost of extra fuel smoke and also the the pre-boost fueling screw.
I recently went thru a similar complaint with a 230 pump that was added to a Ram, the AFC would intermittantly stick shut, but was difficult to replicate that that was actually the problem. The owner asked us to jerk the pump and send it to the pump shop out of duress and frustration. The pump stand found the problem eventually.
The things previously suggested are also excellent suggestions.
I would also remove the shut down solenoid and wire it up for a test drive and note if solenoid full up equals pump linkage in "full fuel" vs shut down position. You could also zip tie the solenoid up to see if the hold coil on the solenoid allows the solenoid plunger to drop somewhat or slowly across a similated road test (bus route).
Let us know what you find!
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