2004 Polaris ProX 800 tuneup

2004 Polaris ProX 800 tuneup
This particular ProX800 is owned by Dave Mitchell (AKA Shylock44), a
good pal of Tim Bender who was anxious to perk up the performance of his
sled.
Sean Ray had the opportunity to dyno tweak and tune his Dad’s XC800 last
year. At close to 150 HP it ran 100 ¼ mile asphalt runs (mid tens) on 93
octane pump gas with no problem, and has proven similarly reliable on the
lakes and trails this winter. Sean was eager to try the same setup on the
ProX.
The ProX engine now has a detonation sensor that causes the ECU to retard
timing when it detects knock. If it works, this should be a great benefit for
performance sledders whose greatest challenge is usually achieving the
greatest HP for the longest WOT time on the lowest octane gas.
We suspected that it was the deto sensor that gave us fits when certifying the
ProX800 for the AmSnow Shootout. There may have been some slight high
frequency vibration from the dyno that “sounded” like deto to the ECU.
Since then I have added additional elastic media to the dyno shaft system to
further protect engines from their own torsional vibrations. This may be the
reason that this ProX engine ran flawlessly on the dyno for two days while
we did this step by step tuneup. Here is the baseline test data on a 35 degree
F day, obviously much better than our Shootout sled fared in similar
atmospheric conditions.
test c, 04 ProX800, stock baseline, stock 450 main jets
EngSpd
STPTrq
STPPwr
BSFC
Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio scfm
6200
77.4
91.4
0.78
72.2
10.9
6300
77.5
92.9
0.77
72.1
11.1
6400
78.9
96.2
0.77
74.5
10.7
6500
81.1
100.3
0.78
78.5
10.3
6600
82.8
104.1
0.76
80.1
10.5
6700
82.5
105.3
0.76
80.2
10.6
6800
82.6
107.1
0.77
83.5
10.5
6900
82.9
108.9
0.83
91.2
9.7
7000
83.6
111.4
0.85
94.9
9.4
7100
84.7
114.4
0.93
106.7
8.6
7200
83.3
114.2
0.91
103.1
8.9
7300
83.1
115.5
0.87
100.6
9.2
AirTmp
degF
172
174
175
177
183
186
192
194
195
200
201
202
AirDen
lb/cft
35
0.079
35
0.079
35
0.079
35
0.079
35
0.079
35
0.079
35
0.079
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
7400
7500
7600
7700
7800
7900
8000
83.4
89.6
88.5
87.4
86.1
85.8
77.8
117.5
128.1
128.1
128.2
127.9
129.1
118.5
0.82
0.74
0.72
0.65
0.73
0.84
0.89
97.3
95.7
93.5
84.3
93.6
109.2
107.1
9.6
10.1
10.5
11.6
10.6
9.1
9.3
203
211
214
214
217
217
218
36
36
36
36
35
36
34
0.079
0.079
0.079
0.079
0.079
0.079
0.079
Sean then removed the 450 main jets and installed 410s to lean out the
engine about 10% (Mikuni hex main jet numbers are approximately
proportional to fuel flow). This raised the power peak a bit due to the hotter
exhaust gas (ProX owners have reported that the stock pipe needs to be
smoking hot for best performance). The float bowls are properly vented to
the airbox, but below the shelf. For reference, we measured airbox
restriction and saw 9” of negative water pressure in the airbox at the venturi
inlets and inside the float bowls.
test f, 04 ProX800, jet down to 410 mains
EngSpd STPTrq STPPwr
BSFC Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph lb/hr
Ratio
scfm
6200
77.8
91.9
0.71
65.6
12.1
6300
78.4
94.1
0.77
73.1
10.9
6400
79.6
97.1
0.73
71.2
11.4
6500
82.2
101.7
0.71
71.6
11.5
6600
82.7
103.9
0.68
71.2
11.9
6700
84.4
107.6
0.71
75.4
11.4
6800
85.8
111.2
0.68
76.6
11.4
6900
87.8
115.4
0.68
79.5
11.4
7000
88.4
117.9
0.68
80.3
11.3
7100
87.7
118.6
0.69
82.2
11.1
7200
88.4
121.2
0.67
81.5
11.5
7300
88.7
123.3
0.71
86.8
10.9
7400
89.1
125.6
0.82
103.9
9.3
7500
88.7
126.7
0.78
99.9
9.7
7600
89.2
129.1
0.74
96.9
10.2
7700
89.9
131.8
0.68
90.2
11.1
7800
89.9
133.5
0.59
79.4
12.6
7900
90.1
135.4
0.73
99.8
10.1
8000
85.1
129.7
0.75
97.8
10.3
8100
52.2
80.5
1.18
95.8
9.9
AirTmp
degF
174
174
177
180
185
188
191
198
199
199
205
206
210
212
215
217
218
221
220
207
AirDen
lb/cft
34
0.079
35
0.079
35
0.079
35
0.079
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
35
0.079
35
0.079
35
0.079
35
0.079
35
0.079
37
0.078
37
0.078
36
0.079
36
0.079
36
0.079
Next, we removed the shelf from the airbox. This had a dramatic effect on
airflow CFM, but it also enrichened the A/F ratio (the opposite of what we
might expect if the float bowls were originally vented above the shelf).
test h, 04 ProX800, remove shelf from inside airbox
EngSpd
STPTrq STPPwr
BSFC Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio
scfm
6200
78.3
92.4
0.71
65.2
12.9
6300
78.9
94.6
0.69
65.9
12.8
6400
81.5
99.3
0.72
71.5
12.1
6500
82.4
101.9
0.69
70.6
12.5
6600
84.9
106.6
0.68
72.8
12.4
6700
85.8
109.5
0.68
75.4
12.2
6800
87.7
113.6
0.67
76.6
12.2
6900
89.7
117.9
0.67
79.3
12.1
7000
90.8
121.1
0.69
84.1
11.6
7100
89.5
120.9
0.69
84.1
11.7
7200
89.5
122.6
0.68
83.8
11.8
7300
92.9
129.2
0.66
86.3
11.7
7400
92.2
130.1
0.66
86.2
11.8
7500
91.5
130.7
0.77
101.5
10.2
7600
91.9
133.1
0.74
98.7
10.6
7700
91.9
134.8
0.76
103.6
10.1
7800
93.2
138.5
0.69
95.9
11.1
7900
91.1
137.1
0.73
100.6
10.6
8000
84.7
128.9
0.78
101.4
10.6
AirTmp
degF
184
185
189
192
197
200
204
209
212
215
215
220
223
225
228
230
232
233
235
AirDen
lb/cft
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
36
0.079
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
37
0.078
32
0.079
Since jetting was still too conservative for us, especially in light of the deto
sensor that ultimately needed to be tested, we dropped to 390 mains which
gave us low .60’s BSFC in 35-40 degreeF air in the dyno room (use Mikuni
Slide rule to correlated this 92 octane spec to other conditions).
test I, 04 ProX800, jet down again to 390 mj
EngSpd
STPTrq STPPwr
BSFC Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio
scfm
6200
78.1
92.2
0.71
64.4
13.1
6300
78.9
94.7
0.68
64.7
12.9
6400
80.9
98.6
0.68
67.7
12.5
6500
83.4
103.2
0.71
72.5
12.1
6600
84.2
105.8
0.71
74.5
11.9
6700
86.1
109.8
0.68
74.8
12.2
6800
87.4
113.1
0.68
77.7
11.9
6900
91.2
119.8
0.65
78.2
12.2
7000
90.9
121.1
0.66
79.7
12.1
7100
90.6
122.4
0.66
81.1
12.1
7200
91.4
125.2
0.67
84.2
11.7
7300
92.9
129.2
0.63
81.7
12.2
AirTmp
degF
183
182
185
190
194
199
202
208
209
212
215
218
AirDen
lb/cft
38
0.078
38
0.078
38
0.078
37
0.078
37
0.078
38
0.078
39
0.078
39
0.078
39
0.078
39
0.078
39
0.078
39
0.078
7400
7500
7600
7700
7800
7900
8000
8100
93.3
94.8
94.3
96.1
95.8
95.5
93.5
85.2
131.5
135.4
136.5
141.1
142.3
143.6
142.4
131.5
0.63
0.72
0.66
0.63
0.63
0.61
0.63
0.65
82.5
98.1
90.5
89.1
89.9
88.2
89.8
85.6
12.2
10.4
11.4
11.8
11.8
12.1
11.9
12.5
219
223
225
229
231
232
234
233
40
40
40
40
39
39
39
38
0.078
0.078
0.078
0.078
0.078
0.078
0.078
0.078
Sean next installed a set of Vforce 3 reeds that had the plastic inserts
matching the oval stock carb boots. Though Sean had seen about 1 HP from
these reeds on his Dad's XC800, we were disappointed to see the reeds have
insignificant effect on airflow and HP on this engine with the stock pipe in
place. We would leave the Vforce reeds in for now.
test L, 04 ProX800, install Vforce 3 reeds
EngSpd STPTrq STPPwr
BSFC Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph lb/hr
Ratio
scfm
6200
76.7
90.5
0.66
60.6
13.6
6300
77.6
93.1
0.64
60.5
13.7
6400
81.1
98.7
0.66
65.2
13.1
6500
80.4
99.5
0.67
66.7
12.9
6600
83.9
105.4
0.65
68.7
12.9
6700
83.9
107.1
0.65
69.7
12.9
6800
86.6
112.1
0.67
75.2
12.3
6900
86.6
113.7
0.64
73.8
12.6
7000
87.7
116.8
0.63
74.4
12.7
7100
89.1
120.4
0.63
77.1
12.5
7200
88.6
121.4
0.64
78.7
12.3
7300
92.1
127.9
0.67
86.9
11.4
7400
92.2
129.9
0.63
83.1
12.1
7500
93.7
133.8
0.71
96.2
10.6
7600
93.1
134.6
0.61
81.3
12.6
7700
93.4
137.1
0.62
85.2
12.1
7800
95.1
141.2
0.66
94.4
11.1
7900
95.1
143.1
0.64
92.7
11.5
8000
94.5
143.9
0.59
85.5
12.5
8100
93.1
143.4
0.62
89.7
11.9
8200
59.4
92.8
0.91
85.1
11.9
AirTmp
degF
180
181
187
188
193
196
202
204
206
210
211
216
219
222
224
225
228
232
234
233
222
AirDen
lb/cft
35
0.079
35
0.079
35
0.079
35
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
34
0.079
35
0.079
33
0.079
33
0.079
34
0.079
33
0.079
Changing the static ignition timing in the ProX requires lifting the engine
out of the sled to gain access to the flywheel area. I said: “Sean are you sure
you want to spend an hour of F’ing around to add about one more HP?”
Sean said “Yup” [that’s one reason Tim Bender hires Sean to be sort of a
Team Industries/ Polaris “sled chief” at major snow-cross events when Sean
has time to help out] . We removed the dyno shaft, removed motor mounts
etc and jacked the engine up above the bulkhead. After pulling the flywheel,
Sean was able to move the stator plate (with slotted attaching holes) @1/8”
counter clockwise, all the way to the stops. After reinstalling the engine we
were rewarded with extra torque and HP throughout the powerband. Time
well spent.
test O, 04 ProX800, advance timing by rolling stator 1/8" to the stops
EngSpd
STPTrq
STPPwr
BSFC
Fuel A
A/F
Air 2 AirTmp
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio scfm
degF
6200
78.1
92.2
0.71
65.4
12.4
178
6300
79.6
95.5
0.69
66.3
12.4
179
6400
81.3
99.1
0.69
68.6
12.1
182
6500
82.6
102.2
0.68
70.7
12.1
186
6600
85.6
107.6
0.66
72.2
12.1
190
6700
86.7
110.6
0.66
73.5
12.1
193
6800
89.4
115.7
0.64
75.1
12.1
199
6900
90.1
118.2
0.63
75.8
12.2
201
7000
92.4
123.2
0.62
76.7
12.3
207
7100
93.3
126.2
0.62
79.2
12.1
208
7200
94.8
129.9
0.62
81.6
11.9
212
7300
96.2
133.7
0.63
85.2
11.5
214
7400
97.3
137.1
0.64
88.3
11.3
219
7500
97.2
138.9
0.65
90.8
11.1
220
7600
97.9
141.6
0.53
76.3
13.3
222
7700
98.8
144.8
0.61
88.4
11.6
225
7800
98.1
145.7
0.64
93.7
11.1
228
7900
96.4
145.1
0.62
91.5
11.5
230
8000
92.1
140.4
0.71
99.7
10.6
231
AirDen
lb/cft
34
0.079
34
0.079
33
0.079
32
0.079
32
0.079
32
0.079
33
0.079
32
0.079
31
0.079
32
0.079
32
0.079
32
0.079
30
0.08
31
0.079
32
0.079
33
0.079
33
0.079
32
0.079
33
0.079
We had ordered aftermarket single pipes from several sources, but after a
month of waiting only the silver ceramic coated Starting Line Products pipe/
can combo was available. While we were at first disappointed that the pipe
would not fit the stock quiet muffler, we were pleased that the SLP muffler
was very quiet, only a few dB louder than stock. Note that the SLP single
added five lb/ft of torque and over six HP while adding significant airflow
CFM to the engine.
test R, 04 ProX800, install SLP single pipe, Ypipe and muffler
EngSpd
STPTrq
STPPwr
BSFC
Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio scfm
6100
77.8
90.4
0.74
67.8
11.9
6200
77.2
91.1
0.73
66.9
12.1
6300
78.1
93.7
0.72
67.9
11.9
6400
82.3
100.2
0.69
70.1
12.1
6500
84.5
104.6
0.68
72.1
12.1
6600
85.8
107.9
0.65
71.1
12.5
6700
88.2
112.5
0.64
73.2
12.4
6800
92.1
119.2
0.64
76.5
12.2
6900
95.4
125.4
0.63
80.2
12.1
7000
97.8
130.4
0.62
81.2
12.2
7100
98.9
133.7
0.62
84.1
12.1
7200
99.9
136.9
0.62
85.6
12.1
7300
101.3
140.8
0.61
85.1
12.4
7400
101.1
142.4
0.64
92.6
11.4
7500
102.7
146.6
0.64
94.5
11.4
7600
102.7
148.5
0.65
96.8
11.2
7700
103.8
152.2
0.59
91.3
12.1
7800
102.6
152.3
0.64
98.3
11.3
7900
99.7
150.1
0.64
97.2
11.4
8000
88.7
135.1
0.69
94.5
11.6
AirTmp
degF
176
176
177
184
191
194
199
205
212
217
221
224
230
232
235
238
240
243
243
239
AirDen
lb/cft
33
0.079
33
0.079
33
0.079
32
0.079
32
0.079
32
0.079
32
0.079
32
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
34
0.079
34
0.079
34
0.079
A late arrival was a new set of Boyeson Rad Valve reed cages which we
installed. Though airflow showed a slight increase at peak compared to
VForce, there was no change in HP, even though fuel flow remained
relatively constant. We first saw this happen in 1991 when Tim Bender
dyno’d the original (then secret) Vmax4 FIII “crate” race engine he received
from Yamaha. The first thing Tim tried (of course he couldn’t leave it alone
even though it was about 50HP stronger than his old Exciter FIII’s) was a set
of reed cages with larger reed windows, designed for a Yamaha 250
motocross bike. Airflow CFM went up, HP went down. ???. So the logical
thing was to try four stock Phazer reed cages which had even smaller reed
windows. Airflow CFM went down a few percent, HP went up a few percent
so that’s what Tim used. The rule is, HP rules.
In this case, HP is virtually identical—repeating within a few tenths of HP.
test 1b, 04 ProX800, remove Vforce reeds, install Boyeson Rad Valves
EngSpd
STPTrq
STPPwr
BSFC
Fuel A
A/F
Air 2 AirTmp
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio scfm
degF
5700
71.1
77.2
0.75
58.8
12.4
160
5800
71.7
79.1
0.81
64.8
11.4
162
5900
73.1
82.1
0.79
65.6
11.5
164
6000
73.5
84.1
0.79
67.4
11.4
168
AirDen
lb/cft
26
0.08
27
0.08
27
0.08
27
0.08
6100
6200
6300
6400
6500
6600
6700
6800
6900
7000
7100
7200
7300
7400
7500
7600
7700
7800
7900
74.3
77.2
79.4
82.6
84.4
88.6
90.7
91.1
95.2
98.1
99.1
99.8
101.6
102.9
103.6
104.9
103.8
102.5
98.8
86.3
91.1
95.2
100.7
104.4
111.4
115.7
117.9
125.1
130.6
133.9
136.8
141.2
144.9
147.9
151.8
152.1
152.2
148.7
0.76
0.74
0.75
0.72
0.72
0.73
0.71
0.71
0.68
0.68
0.71
0.68
0.67
0.67
0.62
0.62
0.63
0.61
0.64
66.2
68.9
72.4
73.4
76.1
82.6
83.6
84.2
86.1
90.2
95.3
95.2
96.1
98.1
92.7
95.1
97.2
93.4
97.1
11.7
11.5
11.3
11.6
11.5
11.3
11.3
11.4
11.5
11.5
11.1
11.2
11.3
11.3
12.1
11.9
11.8
12.3
11.9
169
174
179
187
191
203
206
209
216
227
231
233
238
241
244
247
250
250
252
27
26
26
26
26
25
25
25
25
25
24
25
25
25
26
27
26
26
26
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
Next, we reinstalled the stock reed cages. This time we saw a very slight
airflow decrease and a very slight, not significant decrease in top end HP if
you look at the overall numbers there. This could only be measured on a
dyno. So probably because of the higher airflow of the SLP exhaust, there
was some gain from the aftermarket reeds, maybe ½ HP average at the crest
of the power curve. Dave opted to stay with the stock reeds.
test 1d, 04 ProX 800, remove Boyeson Rad Valves, reinstall stock OEM reed cages
EngSpd
STPTrq
STPPwr
BSFC
Fuel A
A/F
Air 2 AirTmp
AirDen
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio scfm degF
lb/cft
5700
71.9
78.1
0.74
67.8
11.9
157
30
0.079
5800
72.1
79.5
0.73
66.9
12.1
158
31
0.079
5900
73.1
82.1
0.72
67.9
11.9
161
31
0.079
6000
73.3
83.7
0.69
70.1
12.1
163
31
0.079
6100
75.3
87.4
0.68
72.1
12.1
168
30
0.079
6200
76.1
89.7
0.65
71.1
12.5
170
29
0.08
6300
80.2
96.2
0.64
73.2
12.4
178
29
0.08
6400
82.6
100.6
0.64
76.5
12.2
183
29
0.08
6500
85.9
106.3
0.63
80.2
12.1
190
29
0.08
6600
89.1
112.1
0.62
81.2
12.2
200
30
0.079
6700
90.6
115.5
0.62
84.1
12.1
206
30
0.079
6800
93.2
120.7
0.62
85.6
12.1
209
31
0.079
6900
97.1
127.6
0.59
85.1
12.4
220
31
0.079
7000
98.1
130.6
0.64
92.6
11.4
222
31
0.079
7100
100.1
135.3
0.64
94.5
11.4
228
30
0.079
7200
7300
7400
7500
7600
7700
7800
7900
100.4
101.6
103.8
102.8
103.6
103.9
101.8
98.3
137.6
141.2
146.3
146.9
149.9
152.3
151.2
147.8
0.65
0.6
0.64
0.64
0.69
0.71
0.62
0.76
96.8
91.4
98.3
97.2
94.5
108.3
95.6
113.7
11.2
12.1
11.3
11.4
11.6
10.4
11.9
10.1
230
233
238
239
244
245
248
248
30
31
31
31
30
30
30
30
0.079
0.079
0.079
0.079
0.079
0.079
0.079
0.079
The final change was to lower compression one full point from 12.5 to 11.51 uncorrected. Sean’s idea is that the stock compression is high for a pump
gas engine that’s tuned the way we like them. Plus since his dad is old like
me, pull starting was a challenge especially when Tug Hill Temps drop well
below zero. Sean first tried the reduced compression concept on his Dad’s
XC800, and was able to match the original compression HP with added
timing. He left the squish band stock, and CNC machined the bowls to add
the necessary volume. In this case, the much lower compression only
dropped one HP at peak. Sean’s idea is that the higher compression HP
could be restored with one or two more degrees of timing (in this case
requiring grinding out the slots in the stator). We’re thinking that the same
HP with added timing with lower compression could ultimately result in
lower peak cylinder temp (= less chance of deto). Here’s one full point lower
compression than stock with identical timing.
test 1k, 04 ProX800, reduce compression one point
EngSpd
STPTrq STPPwr
BSFC Fuel A
A/F
Air 2
RPM
Clb-ft
CHp
lb/hph
lb/hr
Ratio
scfm
5700
71.3
77.3
0.75
58.7
12
5800
71.3
78.7
0.77
60.8
11.8
5900
72.1
80.8
0.78
63.3
11.4
6000
73.5
84.1
0.78
65.7
11.3
6100
74.8
86.9
0.75
65.6
11.5
6200
76.6
90.4
0.74
67.2
11.5
6300
77.9
93.5
0.72
68.1
11.6
6400
80.8
98.4
0.72
71.3
11.5
6500
83.6
103.4
0.71
73.8
11.5
6600
87.1
109.5
0.69
76.3
11.6
6700
89.7
114.5
0.71
82.3
11.2
6800
92.1
119.3
0.69
83.1
11.4
6900
94.1
123.6
0.69
86.2
11.4
7000
96.1
128.1
0.69
89.5
11.2
7100
96.3
130.2
0.67
88.3
11.5
7200
97.1
132.9
0.68
91.6
11.3
7300
98.1
136.3
0.67
91.9
11.3
AirTmp
degF
154
156
158
162
165
169
173
179
185
193
201
208
214
219
223
226
228
AirDen
lb/cft
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
33
0.079
32
0.079
32
0.079
33
0.079
32
0.079
32
0.079
33
0.079
33
0.079
34
0.079
7400
7500
7600
7700
7800
7900
8000
101.1
101.7
102.1
102.9
101.9
98.4
93.2
142.4
145.2
147.7
150.8
151.3
147.9
142.1
0.66
0.64
0.63
0.59
0.58
0.58
0.68
95.1
93.4
94.1
90.1
88.7
86.3
97.4
11.3
11.6
11.7
12.4
12.7
13.1
11.6
234
237
240
243
245
248
247
34
34
34
35
35
33
34
0.079
0.079
0.079
0.079
0.079
0.079
0.079
EPILOGUE
The perplexing thing about this ProX800 sled is that if the detonation sensor
works and the ECU protects, why would Polaris provide stock carb
calibration at 10/1 A/F ratio at close to .80 lb/hphr? I shouldn’t complain
because that sort of lazy calibration provides job security at
DynoTechResearch. But guys like Dave Mitchell who’s not a savvy engine
tuner bought this sled for performance riding. Because of this ultraconservative stock setup Dave has been at the back of the pack all season,
but no more thanks to this tuneup and Sean’s clutch setup. Please note that in
some of this test data the fuel flow is not as smooth as it could be, probably
due to some engine harmonics aggravated by the dyno. So we have to
mentally average out fuel flow spikes that have no effect on overall actual
combustion chamber A/F ratio. The dyno measures fuel as it goes into the
sled’s fuel pump, and these small spikes have very momentary effect on
float bowl level and have little effect on what fuel actually travels up the
needle jets into the engine.