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Long crank time, problem solved.

4083 Views 7 Replies 4 Participants Last post by  Okie
1986 Honda Fourtrax 350. After setting for several days especially in cold weather the engine had to be cranked on and off over several times and finally would hear the fuel pump briefly click few times and it would start. Would not ever start until the fuel pump eventually ran. The fuel pump normally only operates on this model unit when the engine cranks or is running. Choke is operating ok also, just not getting enough fuel pump prime to the carb.

I noticed if I applied 12v to the fuel pump run wire manually for a prime until the fuel pump stopped clicking the cycle would immediately start. I installed a fender mounted primer switch like this one (see ebay number below) fused at 10 amps and works great. Cycle will now set for long time and immediately cold start after getting the manual fuel pump prime.

Note this switch is wired to apply 12v to the pump hot wire only after the normal regular feed wire is disconnected. (no backfeed thru the cycles regular wiring)

ebay number 302323003823
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Hey Okie
Do you have new or old fuel lines? Wonder if your old lines might have cracks that allow pressure drop?
No it has all new lines and the gas tank can be full. It sets on a concrete floor and no leaks of any kind. Runs great once it's pump primed after it's set for several days and all electrical works great. Enough gas evaporates out of the carb that the engine won't fire up until it gets little bit of gas. The manual prime only takes about 5 seconds and the fuel pump automatically stops when it sense back pressure from the carb needle not needing gas. Engine after manually fuel pump primed will start right up after several days of not being operated.
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Those Hondas are equip with 12 volt pulse fuel pumps, as the tank is located to low for gravity feed, nice okie.

i had that same problem with my 86, had a fresh good battery, BUT..... 1st turn on the key (everything else electrical worked fine)....... But, Only One click from the pump ...... Did the same as you, and , many clicks, till she primed! She ran fine after that fix.

tel:302323003823 <<nice weather proof toggle switch
Yep, sure saves the starter and battery by reducing the crank time on mine.

Mine has the heavy duty battery that the previous owner had installed and engine cranks fast but it just don't get a fast enough fuel pump prime from the pulse relay when gas level has dropped in the carb due to evaporation from long resting periods. I seen this no fuel pump run voltage by doing voltage tests at the fuel pump while cranking the engine and just started manually jumping voltage the fuel pump at first just to see if manually priming would get a run. Works great.
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The fuel cannot evaporate out of the bowl of the carb because it is sealed in there by the float needle and seat. Here is what I think is causing the problem on these old machines with diaphragm style fuel pumps:

Diaphragm pumps have two reed valves that act as check valves so the pump can function. Also, when the machine is off, the reed valves hold the fuel in the discharge line and fuel bowl of the carb. Over the years, the reed valves get stiff, curl up, erode, etc., to the point where they don't seal well. This allows fuel to leak from the fuel bowl, through the reed valves and back to the tank when the machine is off. This is the root cause of the problem. With the fuel missing from the bowl and fuel line, the pump has to run for quite a while to restore that fuel during a cold start. This is made even more difficult because the pump isn't operating as efficiently as it would be with good reed valves in place.

The way to repair it is to either install a pump repair kit, which includes a new diaphragm and reed valves, or just buy a new pump. I don't know if either of those are available any more due to the age of the machine, though.
Very good explanation. Your theory might be correct. This machine has a ON-OFF-Reserve switch and I normally just leave the switch ON in normal. I'll try setting the switch to OFF for long term storage (which I should be doing anyway for safety purposes) to see if the fuel is back-draining to the tank. (little bit of seepage back through the needle seat would not be noticeable to reduce the fuel level in the carb bowl just enough that the machine would not immediately get fuel from the bowl)) Since this is a pulse type fuel system the fuel pump does not get a run voltage immediately when the ign switch is turned on. The Engine has to be cranking which eventually operates a pulse relay (which is new) then the pulse relay senses engines cranking and eventually sends pulse voltage (not continuous voltage) to the fuel pump when the engine is cranking. Installing the manual primer reduces the crank time to get a prime after the loss of carb fuel bowl gas and would also be beneficial in reducing the long crank time if the 86 machine ever ran out of gas and had to be switched to the reserve. Reducing the long crank time with the manual prime sure saves the wear and tear on the starter and battery on this machine. (and if battery ever goes dead on this 86 Honda system you are SOL) Has to have battery voltage to get a ignition start when manually cranking. I think maybe the OEM pump is a sealed unit with no rebuild kits ever offered by Honda.(probably due to safety concerns)

A OEM replacement fuel pump part number 16710-HA7-672 is around $120.

I Don't trust the $20 generic replacement fuel pumps.

I did test the fuel pump as supplying (pumping) the rated output per the service manual.
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