fuel flow question

'85 700 maxim with inline see through filter. No problems until it hits reserve, which happens so quickly that it usually quits before I can switch it over. Once it stops (for lack of fuel) I can turn it to prime and the gas just does not flow on its own. I had to rebuild the petcock when I first got the bike and it has always behaved this way with me. I can look into the filter and see that no gas is flowing so what I have done is open the gas cap and pressurized the tank by blowing into it. This gets the fuel to flowing for a few seconds and I have to repeat several times to fill the carbs enough to start. Once it starts gas flows freely and it runs fine. I have also blown into one of the vent hoses to get the same effect. I even looked carefully to see if the vent was blocked some when I had the carbs off but that was not the case.

I checked the fuel flow with the tank off and it came out normal when switched to prime but if I connect the line to the carbs I get the same old problem. I can blow through the line and there seems to be no resistance so why am I getting no flow with the tank connected? I don't expect anyone to have an answer as it does not make sense but I am wondering if anyone else has had this happen to them.

 

If you have any high spot in the fuel line it will tend to trap air. When you run out you get air in the line, and there isn't enough weight in the tank when down to reserve to push past the air.

Any high spot in the line will do, including a horizontal filter. Your fuel flow needs to be only downhill from the tank to the carbs.

 

Sounds like a problem with the petcock. Disconnect the fuel line and check for free flow on Prime. When you get it started does it run in both Reserve and Prime? My petcock had a problem with the flat rubber fuel control washer (or whatever the proper name is) on the lever side of the petcock. If it doesn't run on Prime then check it for tears and proper positioning. Also, be sure the fuel line does not turn up and create the air bubble the previous rider mentioned.

 

I do not think I have an air pocket in the line but there is one in the filter because it lays horizontal. It was not an ideal filter choice but was one I already had lying around. I use a metal tube type on my LTD 454 which is maybe 3/4'' thick so maybe I will pick up one of those if my checking shows it is warranted. I could point one that size downhill no problem and it would probably even fit between the carbs.

Right now the bike is over at my daughter's so it may be some time before I get over to check it out. Her hubby mentioned it the other day which got me to thinking so I mentioned it on here. So yeah thanks for giving my brain a jolt. Being shut up with the flu for a couple weeks is not very conducive to good thinking.

 

Thanks. Yeah it will run on any of the 3 settings and the fuel flows freely when the line is unhooked from the filter.

So did you ever figure out why your mileage was so low? I have not done a real check of mine but it seems to be pretty normal and not out of whack mileage wise as yours was.

 

Give the Petc0ck a Vacuum Function test.
Easiest way is to hook-up a Vacuum Line to the Petc0ck and run a Clear Vinyl Hose off the outlet to a gas can.

Place the Vacuum Line to your lips and draw a Vacuum on the Line.
Gas should flow from the Petc0ck when you are drawing on the line.
Stop when Vacuum is not present.

Test the Inline Filter for porosity.
Blow through it.
Be sure the Gas Line doesn't kink.

 

Just a side note, if you put the filter down between the carbs I think you'd have a hell of a time trying to change it.

 

Sounds like a filter issue as well as a petcock issue.

Haven't solved the mileage issue, still about 31 in town and 35 on the road.