Another problem. Poor running poor gas mileage.

[Milton]

About a month ago I replaced my Gil coils for Nology, no problems - I think. New spark plugs. Sealed the rims and went with Shinko 705s. Replaced the 18 tooth front sprocket for a 17 and a new unsealed chain (bad bad idea).

Anyway several weeks ago my ignition pickup sensor went south as, related in another post, got that fixed and thought my problems were over. So a week ago Saturday I took a ride after the p/u sensor was replaced and the bike ran fine or so I thought. Toward the end of the day, coming home via the freeway, I noticed when I would accelerate there would be a little hesitation or lurch. I attributed this to chain slap as the unsealed chain was wearing like crazy (dumb dumb idea).

Yesterday morning I filed up before my ride and noticed my mileage had dropped from around 45-50 mpg, depending on my style, to 34 mpg. I just attributed it to the new 17 tooth sprocket, which raised my rpm by 500 at 70 mph. The bike continued to hesitate and lurch all day but nothing real noticeable or worrisome. After lunch we took a back road to Cripple Creek, CO. Dirt for most of it so I really couldn't feel how the bike was running. When we got to CC, and on pavement, I noticed it was running pretty crappy. Leaving CC there is a 3.5 mile long hill before the road reaches flat ground and a down-grade. I could barely maintain 40 mph coming up the hill; it was just chugging and cutting out. Once on the flat I could get it up to normal road speed but could not easily accelerate. Pulling in the clutch and giving it gas I couldn't get it past 6500 rpm.

Anyway made it home okay, but I had to stop for gas and I was shocked (low gas warning light had come on) to fill up 6.505 gallons at 160 miles for 25 miles per gallon. My friend was following me and said that he could smell the over richness of my exhaust. So now the million dollar question from a thousand mile diagnosis, any ideas as to what might be going on? I'm thinking that I might have a stuck float, but I'm not sure. The carbs are going to be my first attempt at a fix. The carbs, by the way, are Keihin's.

Thanks.

Milton S.

[Mustang]

possible causes in order are :

1. crap in the float bowls keeping 1 or more needle valves open (this will make it run excessively rich and would be what my moneys on )

2. a hung up needle in the slide causing excessive richness in midrange

3 . possible choke circuit malfunction but doubtful this is it .

pull the carbs and give them a good cleaning and while they are off the bike clean or replace the airfilter .

[BruKen]

Something similar happened to me first time I cleaned and rebuilt the carbs. I had not put the "washers" that sit between the slide needle assembly and the vacuum diaphragm back in the correct sequence. The needle washer gradually wound its way up the spring drawing the needle with it. As a result I got the symptoms you mention including a gradual worsening of the performance until it all but died which isn't as easily explained by a sticky float.It's an easy mistake to make so if you have stripped the carbs recently you may wish to check this. If you haven't, when you do, don't make my mistake.

[Milton]

So I've finally torn into the bike to determine what the problem is and it is a bit more serious than I thought. 4 of my 6 intakes have zero (< .04 mm) clearance. Is it possible to re-shim them, as I'm a cheap bastard, or is a valve job/new head necessary? Bike has 54 k miles but was running strong until this.

The last time I adjusted the valves the intake shims were of an average range (although I no longer have the sizes). How should I size the new shims for the zero clearance valves, will (current size - correct clearance = new size) work?

Thanks.

[Mustang]

go 1 size extra on the ones that are  zero
eg. if you have a 2.75 and figure you need a 2.65 go with a 2.6 ,trust me you'll need it and possibly smaller

[Milton]

Mustang, you da man. Thanks for your help with this and other problems in the past. Your advice is much appreciated.

Milton S.

[JetdocX]

What year?  If it's a 98, you probably have the dreaded valve recession.  Ask me how I know.

[Persson]

What year?  If it's a 98, you probably have the dreaded valve recession.  Ask me how I know.

How do you know..?
I have a 98, how will I know, and is there anyway to stay ahead of this?

Thanks,
Karl

[Mustang]

some do some don't ...it's a crap shoot
alot depends on how hard the motor is run for long periods of time .

you spend all day on the interstate highways doing 6k rpm you WILL pound the valves in the head .

i have a 98 that I swear I should have replaced the head on 2 years ago due to running out of shim sizes for the #1 cylinder but it's still hanging in there so far with plenty of life left in her at 70,000 miles

I have another 98 that is only different by 100 in the vin# and it's pushing 50,000 miles and still has lot's of adjustment left in the shim sizes ,so my feeling is it's more how the motors are used / abused than a year specific problem

the only way you will know whats happening is to check the clearances often and see how they are doing

[JetdocX]

Locate a used head if you can right now.  You'll need it.  PM me for the alternative problem solver.  It's a bit more expensive, but the guy knows what he's doing.

[Milton]

Yes its a 98.