Vstar 1300 engine surge

The typical cause for "governor hunt" is a fouled carburetor. Could also be water in fuel.

Suggest you drain fuel, especially the carburetor fuel bowl, and put in fresh fuel. A fuel system additive such as Sea Foam will likelyl clear minor carburetor fouling.

Measure and add fuel additive per instruction... too much additive will cause high specific gravity and improper air/fuel mixture (poor running or no run).

(which engine. ?????)_
as always check all fuses. and scan the ECU for DTCs. first.
there is no need to fix OBD2 cars like 1980 cars (hard rows to hoe)
it can be 2 problems this......
lets fix the easy one first. idle. (and hope for moving issues to fix for free) it idle car is parked, so is 100% safe tests. (not moving)

so it surges at idle.
questions.?
1: hot or cold or both.?
2: low extreme RPM and high at idle.
400 to 800 RPM? surge.
1000 to 2000. what? numbers tell the tale.

first off, idle is the last thing to work right on any engine.

there are many ways to find what is wrong.
fix idle surge way.
i make sure that the engine holds closed LOOP status.
hot idle, if not , i fix that first.
keep in mind if not in closes loop and lean
all lean engine surge and guess what the ISC will add to the surge
because idle is way too slow, so the ECU open the ISC wider
and wider and its still too slow, so the ECU resets the ISC
this cause a worst hunt (surge)
the ECU adjust spark time and the ISC to get 800 rpm. (spec. look up yours)
so say , i see closed loop failed, OBD2 scan page 1
i look at the O2 sensor an its stuck lean.
if stuck lean and it really is (o2 bad?) then its lean and it will surge
.
examples.
1: i find 02 sensor bad, (only effects idle and light steady cruise)
2: i find fuel pressure at 15PSI , hopeless low .
3: i find all injectors clogged. and lean.
4: with MAF EFI, ( i find maf reading too low, (dirty) causing lean.
5: if MAP car, i find the MAP stuck hard high vacuum causing lean.
not knowing what engine you have or the idle hot surge range,
i can not go farther.

the driving bog tells me,
1: scan the ecu ,get DTCs; do that first.
2: clean MAF if car has one, ask how..
3: check fuel pressure.


my guess is engine is lean. and starving for fuel all the time.
cept WOT.

MAF cars starve for fuel if there are any vacuum leaks.
MAP cars do opposite, they race fast with 100% full power.
MAF is air density EFI
MAP is speed density EFI.
apples and oranges diffr. so what engine.

cold engine idle surge. (problem)
RPM range of surge not stated
300-700 or 800 to 1500? (range is critical to diagnosis)

bad fuel
running summer fuel in winter (running old fuel?)
needs a tune up bad, see the list in the operator guide.
idle speed controller,sticking or EGR valve same. (clean them)
location not stated, so cant guess about local air temps.?
no other symptoms, lack of engine power? etc?
was it ok last week, or better, when was the last time it was OK?
1week, 1year?
surge , causes, on a tuned engine might be:
1: too lean. so lean the ISC can not control idle. rpm low, stalling
2: too rich, flooding, stalling, spark plugs foul (look at them)
3: weak compression in 1 or more cylinders.
4: bad spark.
5: air leaks, in the plenum causing , ISC to lose control.
why high RPM?

especially?
well that means it fails hot too.
and there is a simple tests. for hot surge.
is engine fully hot? 180F and holds solid there?
say rpm is about 800
and you turn on head lights, heater fan and (not AC) and defrost.
the RPM must hold or the ISC is failing.
ISC -= idle speed controls. (all EFI has this function)

you sure your engine isn't surging... you would see it at lower speeds... my motorcycle surges at a certain rpm due to fuel ratio's at the one speed ( running lean )... so what i am saying is, could it be that the engine surge only shows itself at a certain ground speed.

or is it because of a hydro system pressure relief valve ???

Sounds like vapor lock. Is your fuel line touching your cyclinder head or nearly touching?

Surging is usually a fuel problem. To prove it, put the bike in one gear lower than the top gear. You didn't say what year or model bike you have. If it's a five speed, put the transmission in fourth gear. Do a full throttle roll-on acceleration with the transmission in that gear on a long uphill grade. If the engine RPM's climbs suddenly and drastically without the speed of the bike doing the same, it's a clutch slipping problem. More than likely, you are feeling the surge due to a lean fuel air mixture. This makes it very difficult to maintain a steady cruising speed in all gears.

Good Luck
Steve

Surging is usually caused by a too lean mixture. It depends on what speed this occurs. If it's at a speed of about 30-40 mph, the slow speed mixture is lean and you either need to increase the size of the slow jet to the next richer size or enrichen the idle mixture just a bit. Of course the later procedure messes up your idle mixture and is a "patch" for a too lean slow jet. If it's doing this at high speed, you could have a too small main jet or either of the two jets are not completly open and are partially obstruced. Also the high speed surge could be caused by the float level set to low. I would be more specific but you didn't tell me what year or model bike it was nor the type of carb on the engine.

Good Luck
Steve

It sounds like your bike's fuel-air mixture is too lean. Lean fuel-air mixtures causes the engine to spit back through the intake and surge at the speeds you're talking about. You cannot maintain a steady speed at about 40 mph. I'm sorry but I know nothing about fuel injection systems. I suggest that you take your bike to a shop that has a dynometer and an exhaust gas analyzer. They can run your engine up through the complete rpm range and check the fuel-air mixture throughout the range. They should be able to make the changes necessary to get your bike running correctly.

Good Luck
Steve

Surging engines in lawn mowers are usually related to a lean fuel/air mixture. With today's environmental concerns, the carburetors on these engines are set with a very lean mixture (to reduce air pollution). Furthermore, they usually put limiter caps on the carburetors where you cannot easily adjust the mix to get the engine to run better.

If there are adjustment screws on the carburetor, try turning the high speed adjustment screw a bit counter-clockwise (if the limiter cap will allow it). This will enrich the fuel/air mix a bit and might help the engine run a bit better.