Decisions, decisions. . .(also posted in General Lounge)

Hey guys, In the past 4 months, I've dropped over $1K trying to get rid of a "missing" problem when I give the bike 1/3-3/4 throttle; not sever, but it doesn't run like sewing machine as it used to. Did a leak down test (compression is 110 in all 4 cylinder), and it seemed to be fine; changed out the spark advance computer for a new one, changed out the coils, adjusted the valves and rejetted the carbs. . . No joy! Mechanic is "guessing" that it might need a valve job, and I'm kinda going, "Well, do I cut my losses and jump on a new FJR, or do I try this last thing. . ." I have to admit that most of my riding is done around town, and the Seca is wonderful for both town & the road, and gets a consistent 50-55 mpg I've had it since it was brand new, and it still rings my chimes; I love the bike! I know that the FJR is about 100 lbs. heavier, and is a bigger bike, and I'm only 5'7", and it just seems "Big!" to me, but I'm really missing a well running bike. I have until 5/4 to jump on what I think is a pretty good deal on an FJR: $15K out the door, and I might be able to the Y.E.S. thrown in, for that. The price of a valve job (? Haven't gotten a quote on that, it being Sunday!) would certainly be a lot cheaper, but I'd be pretty bummed to invest more money and NOT have it cure the problem, so I'm really in a quandry. Anybody want to throw in some thoughts that might help?

 

emulsion tubes clean, slide needles ok and seated, rubber diaphragms good,
springs on top of diaphragms good, slides go "clunk", air jets correct
prime-on -res makes any difference? what happens at full throttle ? idle?
what did the old plugs look like? gapped right?
what kind of bike is it? how many miles?

 

I assume you have a 550?

110 is on the low side for compression. Should be above 140. What is it wet?

Why did you re-jet? Have you made changes to the intake or exhaust system?

Tried a good carburetor cleaning, especially the emulsion tubes? Check for wear of the needle jets and jet needles?

Are the carb holders cracked and leaking?

If your mechanic needs to "guess" about a valve job it's time for a new mechanic.

 

Sorry guys, it's an '81 XJR 750 Seca with 18,000 miles. The carbs were rebuilt, along with new jets (factory specs), the boots on both sides of the carbs are new, because I was hoping that that was the problem. At full throttle, she gets up and hauls! No throttle, she runs smooth. New plugs are gapped correctly, and don't have enough miles on them yet to have really colored. I hadn't thought about checking whether it would change the way it ran, with the petcock in different positions, but I'll give that a try and get back to you (as soon as it quits raining!). The bike is absolutely stock, just like it came off the showroom floor (except for 1 small ding on the right hand side of the tank where the air valve for the left fork dimpled it. . .Bad design!) And I'll ask the mechanic about the emulsion tubes; I didn't know about them. And, yes, when he said he "guessed" it might need a valve job, I also thought. . . "Hmmmmmm. . ." But this guy has a great reputation around town, and there are not a whole lot of mc mechanics around, and the shops refuse to work on anything over 8 yrs. old!

Thanks for the help and suggestions, and keep 'em coming as they occur to you!