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Message started by chzeckmate on 07/15/15 at 19:34:06

Title: Drastic gas mileage drop
Post by chzeckmate on 07/15/15 at 19:34:06

For the last two tanks of gas I've had a serious reduction in mpg. It's roughly 35% reduction. I've also noticed oil consumption has increased as well. Roughly 100 ml for every 200 miles. Aside from that everything seems fine mechanically and with the exception of the seat spacer mod, I haven't done anything to the bike and my riding habits haven't changed. Same daily commute as usual. Anyone have any ideas?

Title: Re: Drastic gas mileage drop
Post by Neilap on 07/15/15 at 19:46:45

I may be no good for this particularly. But I had a 1991 mustang LX 2.3 and the same thing happened except it went to burning literally 4qts every 800 miles. turned out it popped an exhaust valve and once it was fixed, all mentionable power, fuel economy and oil consumption returned to normal. it was de-restricted (no a/c, power steering or smog control) and got roughly 40mpg. it dropped down to 22-24. Maybe this could help.

Title: Re: Drastic gas mileage drop
Post by stewmills on 07/15/15 at 19:47:01

Someone stealing your gas and oil?

Title: Re: Drastic gas mileage drop
Post by verslagen1 on 07/15/15 at 20:13:09

do you use the choke?

ever left it on for the whole commute?

Title: Re: Drastic gas mileage drop
Post by chzeckmate on 07/15/15 at 20:15:05

2D060A0F0213630 wrote:

...turned out it popped an exhaust valve and once it was fixed, all mentionable power, fuel economy and oil consumption returned to normal..

I appreciate the thought, but I've had no noticeable change in performance at all.

47405143595D585847340 wrote:

Someone stealing your gas and oil?

It's funny that you mentioned that because the third from the last tank is where this actually began and when I switched to reserve in the morning I actually considered that some a-hole might have drained it during the night. I pulled into the gas station straight away and sure enough it took exactly 2 gallons. Very unlikely that someone would drain it to exactly the reserve capacity. I was mad as hell until I realized that wasn't it.

Title: Re: Drastic gas mileage drop
Post by chzeckmate on 07/15/15 at 20:17:19

647760617E7375777C23120 wrote:

do you use the choke?

ever left it on for the whole commute?

I don't have to use the choke at all. When it was cooler here half choke was needed in the morning but since it warmed up I've never needed it. That's good thinking though.

Title: Re: Drastic gas mileage drop
Post by stewmills on 07/15/15 at 20:23:06

are you using the raptor or stock petcock?

Title: Re: Drastic gas mileage drop
Post by chzeckmate on 07/15/15 at 20:26:00

I'm still waiting for my raptor...so for now I'm still using the stock petcock.

Oh, I forgot to mention one thing. I sometimes smell raw fuel. I have been attributing that to the cap vent and the sweltering heat here though.

Title: Re: Drastic gas mileage drop
Post by stewmills on 07/15/15 at 20:31:43

well that should eliminate fuel just leaking from below the petcock when the engine is off. however, it could be leaking when running which could be a fire hazard.

sure all of your fuel lines and petcock are not leaking?

i smell fuel too, briefly when i am cranking up and moving the bike around, but not a ginormous amount as if i have a leak.

Title: Re: Drastic gas mileage drop
Post by verslagen1 on 07/15/15 at 20:36:35

you need to test your petcock, there's a thread in the tech section.

Title: Re: Drastic gas mileage drop
Post by chzeckmate on 07/15/15 at 20:59:36

313627352F2B2E2E31420 wrote:

That's what I'm getting too. Occasionally I do smell it when I'm sitting at a light but not a crazy overwhelming smell. Certainly more than any of my other bikes though.

706374756A6761636837060 wrote:

you need to test your petcock, there's a thread in the tech section.

Agreed. I hadn't gotten to that because I'm replacing it with the raptor petcock anyway to make removing the tank easier. The functional benefits of the raptor are just a bonus to me. When I want the tank off, I just want the thing off...don't want to wrestle with it. Do you really think the petcock could be responsible for a 35% drop in fuel economy? Wouldn't I smell it in the oil if it was the case?

Title: Re: Drastic gas mileage drop
Post by verslagen1 on 07/15/15 at 21:14:29

013E383F22250D4B0 wrote:

Hell yes, if you do nothing else pull the vac line and check for gas.
your diaphragm probably has a hole in it.

Title: Re: Drastic gas mileage drop
Post by jcstokes on 07/16/15 at 00:12:08

Excess petrol into the carburettor isn't making its way into your oil and diluting it? perhaps check your oil window after the bike has been standing all night.

Title: Re: Drastic gas mileage drop
Post by Dave on 07/16/15 at 03:51:03

Problems with the stock vacuum petcock occur frequently....that is why we promote the use of the manual Raptor petcock.

Check the oil level.....when the bike is not running the gasoline may be running past a bad diaphragm in the vacuum petcock and diluting the oil with fuel. When the bike is running the fuel can be going into the running engine and making the engine run too rich.

Do the petcock test.....at a minimum pull the vacuum line and see if there is any fuel in it - there shouldn't be. Plug the vacuum port, plug the vacuum line, switch the petcock to "PRIME" and see if the bike runs normal again.

Title: Re: Drastic gas mileage drop
Post by chzeckmate on 07/22/15 at 18:27:37

Follow up: You guys were correct. Bad diaphram. The raptor will fix it. I can't get to it now but I'll try to do the transplant this weekend. Thanks!