86' XJ 700XS Maxim X diaphragm dilemma?

My brother bought this bike and brought it to 2 different shops in the Minneapolis area and neither could fix it right. I'm pretty sure the diaphragms are shot because it's very hard to start and when it does, it races at high RPM. The last shop did a valve shim and new head gasket job on it raising the compression making it run a bit better for a while. They also cleaned the carbs and flow matched them. Now it races when started. I did some investigating of the problem and found stiff carb diaphragms are the likely cause. Looking them up, I found that new ones cost around $300.00 each, that's x 4. That is as much as he paid for the bike used. That last round of service cost him $1749.00 which I though was a huge rip off, but putting $1200.00 more in 4 small diaphragms is insane. There has to be a fix for this that one of you guys knows. Is there an aftermarket EFI kit available to replace these aged non-servicable carbs or what? he's had it for three years now and hasn't been able to ride it. The rest of the bike is in very good condition. The guy he bought it from said it was all gone through when he purchased it and it ran great ? Were these bikes problem prone or what?

Your experience and knowledge here is desperately needed, Thanks guys.

 

Sounds more like a vacuum leak to me, the likely culprit being the throttle shaft seals.
These carbs are not non-serviceable. Click on the XJ 4Ever logo in the upper right hand corner.

 

Also stop taking it to a shop. You saw first hand what happens when you do. When they "cleaned" the cabs how did they "clean" them? If they dipped them that's probably when the seals went bye-bye.

 

the only time my bike ever sees a shop is for annual inspection.

search for "the church of clean" and "the whole nine yards" on here. you'll see just how serviceable these carbs are.

 

You can't trust anyone but yourself on refurbishing carbs. I know it's a bit of a challenge for some, however there are a lot of tips on this site that will help you along. Sounds like you have a major vacuum leak that you should check out before you go taking it apart though.

As far as the diaphragms go, I redid my X carbs with these replacements and they didn't cost much at all:
http://jbmindustries.com/Yamaha650.html

And you'll want this part#: Mikuni M-70 Found on this page:
http://jbmindustries.com/Dimensions.html

Tony

 

"flow matched them."

Whatever that means. Sounds to me like NOT a "running vacuum sync."

The above *edit* and below* advice is right on. I highly doubt it's "stiff diaphragms." More likely a case of "carbs need to be properly serviced and adjusted."

Based on all the obvious "bunk" the shop told you, I'd go back and check the valve clearances. It doesn't take much doing to CHECK them, and then you'll know if the shop did that right.

 

Racing at idle has nothing to do with a torn diaphragm. Check throttle shaft seals also you say races when you start it. If they are ripped it is not gonna race they control the amount of fuel the butterflies ask for. Usually if they are ripped acceleration will be sluggish because no vac pulling the slides up. They need to sync the carbs properly. Grab a can of starting fluid start it spray it around everything carbs intakes ect see if it changes. Also the bike does not have pods on it does it. My maxim x had them when i got it and was terrible starting when cold with them. I tried a pvc intake i had and it started much better after. Something else that makes them hard starting is a low float level. Also i do not doubt anyone else s work but if someone was in a hurry it could happen. You said it ran better for a while i wonder after they set the carbs they might not have tightened the nut on the adjusters all the way they can be a pain to get to. Also make sure the fast idle cam is free and working properly.

 

See if those Mikuni's will pass a "Clunk Test" before blaming Throttle Shaft Seals.

To make High rpm's, ... the Plant NEEDS Main Jet supplied Fuel..

I'd swap my 900 for an Max-X!

If I had an X-Bike, I'd Scrub and POLISH the Diaphragm Piston Bores.
I'd be sure those Diaphragm Pistons open without the least bit of resistance and slam-shut when you close the Throttles.




Review the Clunk Test by using the Link provided in my signature area.

 

Yes, I meant vacuum synced, and they were after they did a head gasket job, and valve adjustment job. I had them do leak down and compression tests before and after and had them list them on the paperwork. It did initially blow coolant out of rad. cap. Some of the valves had no lash at all. What they did there was effective bring up compression a good deal. I can list the B&A compression specs., once I find them.

 

According to my brother, it had to run with the choke left on somewhat. I did tell him to brig it back, especially after all those dollars spent. He didn't want to hassle with it. I told him that was bad call. They did however install 4 new rubber plenum adapters between the cars and the intake. After what you guys have said and what I've read on this sight about these carbs. they seem very finicky. I wonder if there is a complete rebuild kit with all new seals reasonably priced to get these things running right again. I owned 2 82' Suzuki GS 650GLZs for years and never had any problems with the Mikuni carbs. What a great bike that was, I could do wheelies for a block or so and did so frequently. I will have to reread all the work shop papers he sent me and post some of that info for your opinions. I personally live in Duluth, MN, my brother is in Minneapolis so I as a automotive technician am trying to help him out by looking for and posting on this site. I've personally worked in power equipment, auto motive repair, and fleet service. I bet I've rebuilt at least 1000 carbs in my day, all different types, but only one cycle set from a Honda 1000 cafe style bike. They worked perfectly when I was through. I wonder if there is a cost effective place where these carbs can be sent out to be done right since I don't live exactly near him (165) miles away. Here's the article I read on this site:

file:///Users/timothymccarthy/Desktop/XJBikes.com%20%E2%80%BA%20Forums%20%E2%80%BA%20XJBikes%20Marketplace%20%E2%80%BA%20XJ4Ever%20-%20Supporting%20Vendor%20%E2%80%BA%20XJ%20PARTS%20CATALOG,%20SECTION.html

Scroll down to "From our experience". That seemed to some up a lot of concerns about this situation and this bike. Years ago, I had wanted this bike but couldn't afford it. I still have the Original yamaha literature in mint condition though. I'll have to catch up on the paperwork, as I said and see what I can post in addition.

 

You can get all of the necessary parts from XJ4Ever. Click logo/link in site banner, upper right or PM member chacal.

 

The racing is from the choke being partially on Some bikes will idle 3k 3500 with the choke on. Sounds like he needs to send you the carbs and they need rebuilt. Rust in the tank? If its the same place that shimmed the valves i would check them again. The only way to make sure its right is to do it yourself.

 

Were they carbs particularly problem prone?

Will other more reliable carbs sets work on this bike, also is there an aftermarket EFI system available for these bikes that would eliminate the problems all together?

 

Administrator:

I am note getting any instant notifications in my email. I went into the user section and changed that and still no luck? Also my links don't show up ready to be clicked on for direct routing?

 

I sent you a pm, I do carbs and I am in the minneapolis area. If your brother needs help with his I can help him. Did a set for a guy just this spring

 

Not really. Except yours are a quarter-century old, and as such need service. I wouldn't call needing maintenance after so many years "problem prone" by any stretch. They were plenty reliable when everything was new, you can't expect them to still perform that way without some remediation.

People have adapted various forms of EFI, but there is no ready-made, bolt on kit. Remember the age of the bike.

 

The carbs have been gone over by two shops and the guy that sold it to him, although to what extent I'm not sure.

These days it seems EFI is available for most any engine with some kind of model adaptation. Bikes, I'm not sure, that's why I asked on this forum.

 

Of course you can EFI it. I couldn't tell you where to start though but I can say you probably need some deep pockets.