DT-85 running out of fuel problem

This problem continues to plague me. I've eliminated everything from the system that I can. Right now I'm running off a 6 gal portable tank to help troubleshoot the problem. So far, I've rebuilt all the carbs, rebuilt the fuel pump, eliminated the Suzuki fuel line connector by replacing with a straight through double ended fuel barb, and eliminated the water separator filter.

The problem arises after about 4-5 minutes of running. It feels just like I shut the throttle down. If I reach back and pump the bulb up, I can hear the cylinders come back in and I can take off again, that is until the next 4-5 minutes when it repeats.

I don't know why it's running out of gas like this. The motor starts great, takes off great, and runs up to 5500 rpm @WOT. What am I missing ??? Do I need to replace every fuel line on the engine or is it something else ??? I feel it is definitely fuel related, or more properly, lack of fuel.

Thoughts and advice ??????? The engine is a 1986 DT-85

Re: DT-85 running out of fuel problem

If I reach back and pump the bulb up, I can hear the cylinders come back in and I can take off again
Appears there is air getting into the fuel system or just may be the tank is not vented causing the bulb to suck close?. The bulb also could be bad and not holding prime. Have you changed it? Also look closely at the lines at the tank as well as the fitting there. May be a pin hole. Pump up the bulb with the motor off and look closely for a small pin hole with fuel seeping anywhere on the inlet side of the fuel lines from the tank upto the fuel pump.
Does the problem start when you are staying at the 5500 rpms or say 4500 rpms?

When you take it out for a spin again try momentarly pushing in on the ignition switch when it starts to bogg (which will bring the choke closed) , let out on the switch and see if the engime revs back up. If so you definely have a fuel supply problem. The fuel bowl could be empty due to a needle sticking closed not allowing fuel to flow into the bowl....result engine will run out of fuel, pumping up the bulb will sometimes force fuel into the bowl.
Also assume the tank fuel pick up is ok and the tank is not on a sharp incline when on the way

Re: DT-85 running out of fuel problem

Hopalong,

I have a Yamaha which runs perfect at 5500rpm but appears to run out of fuel at lower rpm. You seem to suggest this is a common problem. Can you advise what this could be?

Re: DT-85 running out of fuel problem

after you check all lines for leaks and carb. check fuel pump that is what it sounds like

Re: DT-85 running out of fuel problem

bgbass.1 said:

after you check all lines for leaks and carb. check fuel pump that is what it sounds like

Click to expand...

Fuel pump was rebuilt.

Re: DT-85 running out of fuel problem

ianyoung77 said:

Hopalong,

I have a Yamaha which runs perfect at 5500rpm but appears to run out of fuel at lower rpm. You seem to suggest this is a common problem. Can you advise what this could be?

Click to expand...

I have had the primer bulb perform good at normal cruising rpms and would loose it's prime slowly when I started to idle for awhile and cause the engine to shut off. Pumped the primer back up and I was off and running again.
There other things that may cause this also but the bulb can be the culprit and is inexspensive to replace. I have gone for many years using the same bulb. They do wear out in time. And sometimes a new one can be defective right out of the box...go figure

Re: DT-85 running out of fuel problem

It seems to do it not only at WOT, but also at cruising speed (4200 rpm) and even just maintaining plane at 18 mph. I'm going to have to see if I can find a leak somewhere, although there really isn't many places left for it to be. I wish I could find that small Suzuki fuel line that they use to the carbs in bulk, It looks like they are all individual in the parts fiche.It will cost a small fortune to replace them all individually. I also don't think much of those little spring clamps that they use on the lines either. I'll see if I can find another bulb this weekend. Did you know that Tempo is out of business ??? That's going to make it hard to find stuff like bulbs, etc.

Re: DT-85 running out of fuel problem

The fuel lines on the inlet side of the fuel filter and pump is were it would be sucking air. The fuel line on the outlet of the fuel pump will be pushing/pumping fuel under pressure.

Like suggested, when the engine boggs/stubbles pump the primer bulb and or intermittently push the ignition switch in to choke the carbs and see if the engine gets back into the throttle.If it does there IS a fuel delivery problem etc. That rebuilt pump/diaphram may be weak?? There is an O ring on a part between the pump at the motor side. Did you install the part that the O ring is on facing the way you removed it?

The small orangish fuel lines from the pump to the carbs usually last for years and the spring clamps are adequate to clamp the lines. You're not seeing much pressure in them lines. Of course if the lines are deterioated,leaking etc...replace em.