'90 Fuel Pump Voltage

My '90 has been on consignment the past few months at Logan's Valley Motorcycle's in Mesa (ahem... if anyone's interested in buying it I'll cut ya a super deal right now!). The last guy that came down to take a look at it was seriously interested and ready to buy it, but when he took it out for a test run, she fell on her face... hard.

It doesn't seem to want to accelerate beyond 5k rpm's in any gear. The relay is brand new. The filter is clean. The pump is operational. The carbs are clean. She ran perfect not too long ago, and electrically she's a peach.

The only thing that I can think of after talking with Jesse & Adam in the shop is that the pump is getting 10.5 V instead of nominal voltage. I'm not sure what the voltage going into the pump is supposed to be, but if it's supposed to be higher - she ain't deliverin'. The guys tested the pump out of the bike on a 12V battery and it pumped the proper cfm's. I suggested testing it at 10.5V and see where it's pumping at with the lower voltage, because if it's below standard with the lower voltage then we either have a faulty pump or something sucking juice before it gets to the pump.

Ideas?

I haven't searched the forums on this yet, as I've just got back to the office from visiting the shop and I wanted to get this out to ya's before I left.

 

Gummed up carburators? I replaced my 22 yr old fuel pump just out of peace of mind (I do get things at 10% ova dealer cost) old one still worked ok.

Is your battery fully charged? Check it before you start bike, it should at least be 12.50 - 12.60 being the best...

If I had to hazard a guess, its carburators...clean and test ride...thats my two cents :vtr2:

 

As I stated, the carbs are clean. It starts and idles just fine. It just stutters at 5k rpms.

The battery is on a tender and fully charged. That's where my concern is right now is that I don't know what the voltage going into the fuel pump on this thing. Should it have 12+V coming in, or is the 10.5V that is read coming into it normal? And if it's not, what could be draining it?

The shop is going to see about getting a power supply with an adjustable voltage output and see if the problem might be that the fuel pump just isn't putting out enough to keep the bowls full enough at mid throttle.

 

The pump should be applied with 12+ volts. Even if it's below that it should work ok down to about 11ish. If your only getting 10.5 at the pump. Then my questions would be what are you getting out of the RR or at the battery. The bike shouldn't just bog out when given throttle because there should be enough fuel in the bowls if it runs right prior to. I would suspect you have 10.5 going to coils, CDI etc and that's why the bike is dogging down. Have them check the voltage at idle and at 5k and see what it is.

 

Why sell the newer, better bike and keep the older, slightly less competant '86 ??

Wouldn't cost anything to try a pump relay bypass wire as a test. Is there a jetkit in the '90 ??

 

I'm pretty sure the carbs are stock. The bike will undergo more testing as soon as they get a variable power supply. The R/R is brand new, and replaced the cheapy that I put in it last year when it had lots of electrical issues.... which brings me to squirrel's Q:

I'm not sure what you mean by 'less competant' when comparing my '86 to this '90 when I've dumped more into this one than the '86.

Replaced on the '86:
- Fuel Pump & Relay
- Battery
- Water Pump
- Radiator Cap
- Carb Rebuild
- Carb Boots
- Spark Plugs & Wires
- Tires
- Chain & Sprockets
Purchase Price: $1,000
Total Repairs: Around $1,800
Total Cost: $2,800
Total Mileage Given: over 23,000 (56k on odometer)
Current issues: None

Replaced on the '90:
- Reg/Rectifier (twice)
- Battery
- Starter
- Fuel Relay
- Thermostat
- Carb Rebuild
- Right Mirror
- Brake Lever
- Right Foot Peg
- Turn Signal
- Front Tire Cowl
Purchase Price: $2,500
Total Repairs $2,200
Total Cost: $4,700
Total Mileage Given: 1,200 (20k on odometer)
Current Problems: Fuel Delivery/Sluggish at 5k rpm - Poss Voltage Issue


Yup, I can totally see why I'd stick with the newer model. Besides, I don't look as good in Red as i do on the RWB :tongue: