XJ 750 will not decelerate

Hi everyone,

When I got my bike it only ran at half choke. I pulled the carbs and bench synced them. I pulled the carbs and bench synced them. I know it is heresy to not check the valve spacing and simply do a mediocre attempt at syncing the carbs, but it worked and the bike starts up perfectly every time now and idles real nice with no choke. I will do the valve check once I am sure I have read enough on here to be confident about what I am doing. Unfortunately by solving one problem many others have arisen, probably from not doing the job right the first time. Thus, I come to you with multiple questions. First, every time I start the bike, I get hear three or four tics. If I am sitting on the bike, the tick corresponds with a slight tremor that I can detect with my butt cheeks, is this pre det or something that is expected from a 20 year old bike warming up? My main concern is that after warming up and driving for a few minutes the bike will not decelerate. Even more worrisome, it will begin to accelerate by its self in neutral when I am at a red light. I imagine that some part of the carb is sticking. Am I mistaken? When I cleaned the carbs all the parts seemed to be working well? Any tests you suggest? The carb to intake manifold rubber is in good condition so I don’t think that I am sucking in extra air from there, should I be checking other places?
My last question is about an appropriate carb syncing tool. My manual refers to a specific tool, is it necessary? My friend has a standard carb syncing tool with metal tubes that screw into the carbs, I was wondering if there were specific parts I could by that would fit the XJ or if I have to spring for a specific tool.
I have already gotten great advice from this forum and I appreciate any one reading through this short novel. I respect this bike and I want to do my best to make sure I am not wrecking it. Thanks for any help.

 

Quit making excuses and check the valve clearances.

How to: http://xjbikes.com/Forums/viewtopic/t=14827.html
Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

Then properly service the carbs, wet-set the floats and THEN bench sync them. Then you'll be able to do your running vac sync and get decent results.

If you want somebody to validate the shortcuts you're trying to take, ain't happenin' here. Especially when you already know better. Shortcuts don't work; all you're doing is prolonging the agony.

And valves come first. From the factory manuals:



Or screw with it forever or until you decide to do it right.

It's up to you. It won't work the way you're going about it.

From re-reading your post, I suspect you aren't working with a service manual. If that's the case, stop right now and get one before proceeding.

 

hey bigfitz,

that was stern, but you are right. I know that short cuts will not work. Thanks for posting the links, it really takes the intimidation out of the process. I actually do have a manual which makes me a real numb nut. I have seen that picture with the red circle quite a bit on this forum haha. What does "wet set" the floats mean? again thanks for taking the time to answer.

 

froggy, Here is the link to wet setting your floats.....

http://www.xj4ever.com/setting%20fuel%20levels.pdf

Heed Fitz's advice......follow his steps...& you will be rewarded in the end....

Anything short of that......you are just setting yourself up for failure.....or re-doing all over again...

 

I didn't mean to be overly stern, but right in your posting you made it clear that you know what needs to be done but for some reason seem unwilling to get after it.

And then you start talking about trying to sync carbs that you know need further attention and that you know can't be done properly without the valves in spec. All of which amounts to simply getting nowhere when you already know what needs to be done to get results.

I was just trying to get you to move from tinkering fruitlessly to actually getting something done.

In regard to vacuum synchronizing tools, if you have access to a four-stick manometer, all the better, that will eventually be quite handy. The "special tool" likely being referred to is a YICS block-off tool, used to isolate the carbs from each other during the vac sync process. There are DIY alternatives to buying the tool.

Which manual are you using?

 

I am using the XJ 750 R genuine yamaha service manual. I was wondering were I could get the gasket (and the shims) you use in your first valve adjustment post. The prior owner just used gasket sealer so I might as well spring for the gasket for the reassembly. Another question: The carbs have paper gaskets and I think that those are contributing to my troubles. Are there any rubber gaskets for the carbs, or does every one use paper gaskets?

Thanks for the help.

 

For parts, we pretty much all turn to XJ4Ever. PM member chacal or send an email to "info AT xj4ever DOT com" with what you need and he'll get back to you with a quote right away.

In regard to that valve cover gasket. The valve cover bolts have stop collars on them that prevent overtightening. What actually presses the cover against the gasket/head are the rubber/metal composite "donuts" on the valve cover bolts. If you replace only the gasket and not the donuts, the new gasket will leak. The upside is, the gasket and donuts can be re-used for numerous subsequent valve clearance checks. (You need to do this every 5000 miles remember.)

I think there may be rubber gaskets available for the Hitachis but I doubt that paper float bowl gaskets are your problem unless they're cracked and broken.

In your factory manual is a whole chapter entitled "carburetion" I do believe. Did you follow the procedure given in the book to fully disassemble and clean the carbs?

One thing the book won't tell you about are the pilot mixture screws. That's because they were "factory sealed" to meet EPA regs; but unfortunately they need to come out and be cleaned, have their passages flushed and their tiny o-rings replaced, etc.

There are two very good "how-to" pieces on getting your carbs properly cleaned up; see: http://xjbikes.com/Forums/viewtopic/t=14692.html and http://xjbikes.com/Forums/viewtopic/t=2908.html

Somebody already posted the "wet setting floats" link for you, that's beaucoup important, and a much better explanation than the manuals.

One more important recommendation: In all of my factory books, Chapter 2 is called "Periodic Inspections and Adjustments." Take a quiet moment, sit down and carefully read this entire chapter all the way through. Study it. Read it again until you understand everything that it's talking about. I'm not being flippant, I'm being serious. That section, which is actually the "Maintenance" section, will teach you a LOT about your bike and how to take care of it.

Then; once you've studied "Periodic Inspections and Adjustments" and understand what all of the procedures are about:

Go do it to your bike. Front to back; perform every single procedure and don't skip anything. Along the way, clean and inspect every single part. Refurbish, repair, or replace any that are unserviceable. When you're done, you'll not only have a reliable bike that's' ready to be ridden and enjoyed, you will know pretty much everything you need to in order to keep it that way.

Along the way, ask questions. The only drawback to the factory manual is that Yamaha expects you're already a trained motorcycle mechanic so a lot of things are simply mentioned since it's assumed you already know those basics (like wheel bearing replacement, for instance.)

And that's why we're here. Ask questions.

 

Thank you very much Bigfitz. I'll do that and read through all of the awesome how to on the forum. I really appreciate the detailed responses.

 

Acceleration of the Engine requires FUEL and AIR.

If the Engine runs-up on its own, ... you need to investigate where the Fuel and Air is coming from.

Likely sources:

• Manifold cracks or leaks at the Manifold -to- Head Joint.
• Stuck Linkage
• Diaphragm Piston stiction.

Touch the Sync Screws with a Long Screwdriver to see if the Linkage sticks.

Replacing Manifold-to-Head Rubber Seals and Gaskets presents a serious risk of possibly Breaking-off a Seized Manifold Cap Screw.

The Cap Screw "acts" as if its turning when in actuality it is TWISTING until it snaps.

Be careful.
Breaking-off a Manifold Fastener is a common issue often requiring the Head to be removed and repaired.