XJ750 Running fine but general issues.

that's kind of low.
Im getting 36 mpg on a set of carbs and still have to dial them in just bench sync and mixture screws set to 3 turns have only set idle.

of course riding style affects fuel consumption too
mix screws at 4-3/4 turns more fuel. until you resolve the rich running your fuel mpg will be low

you sync to carb 3 not 4

you are approching the point where you need to look at size of your pilot jet

fix the wobble or slow the f down

 

Fix the wobble.
Check the headstock bearings, tire pressure, tire wear, and rear shocks.

 

Also I just checked the picture from before how the jet should look in the carb, I don't think my carb I have on it actually has the correct jets in it. They look more rounded compared to the picture previously shown.

 

got a pic or 2 of the carbs? get used to taking photos as you work.

 

They could be the correct jets, but damaged.
+1 on pics

 

The jet size that was in it was size 110, I swapped in 120. What is the correct size?

 

The jet size that was in it was size 110, I swapped in 120. What is the correct size?

 

http://xjbikes.wikidot.com/carb-specs

Years & Models: 1981-3 XJ750 Maxim, Midnight Maxim, and Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 15R00 (Maxim, Midnight Maxim)
Carb Model ID: 5G200 (Seca)
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #80
Pilot AIR Jet Size: #225

check them all while your in there.

 

Alright thanks! I took a video and will upload it to YouTube as a private video to show you guys the issue I'm having now. The fuel jet is 120 now, but it still spots and sputters at under 2k rpm, like it has no power. It acts like it wants to die but will eventually get up and going once you get past 2k with tricky throttle control.

 

I guess I should also add real fast that it has a brand new sealed battery, it's an everstart from Walmart.

 

2k rpm is when your carbs running off of the pilot jets.

 

So that indicated something wrong with the main jets? Should I just order a rebuild kit to rule out and issues?

 

I'm not trying to hide information, but some of the pilot jets are chewed to hell where the P.O. had tried to take them off using the incorrect size flathead and destroyed some of the brass, one of them I have to use locking pliers because it's so smoothed I cannot get it out otherwise, and most on the spare carb he gave me are like that too... But the primary jets looked fine, maybe ever so slightly showing signs of careless screwing.

 

your bike runs off of the pilot jet circuit to 2 to 3k rpm and that's when mains kick in.

 

Well so here is another update, the bike is actually running good now but rather quirky. When it is cold the bike will spot and sputter at 1-3k rpm but after 20 or so minutes of riding and getting it warmed up good it runs nearly perfectly, the sputtering goes almost completely away! It will ever so slightly do it every once in awhile. The newest thing that confuses me is that when riding out the rpm the bike stays high rpm between gears, but it will slowly drop while the bike continues to accelerate. It feels like the power keeps climbing but the rpm is dropping, almost like it is running very lean and then fuel starts flowing better after afew seconds.

 

Im just wanting to know, you said you had the idle mix screws out 4 3/4 turns correct ? Im wondering are the idle mix screws are doing anything anymore, sounds to me that the hole is wide open?

 

once bike is fully warmed up set the idle

if you are out 5 turns it would be time to go up a size in the pilots.
you may have a vacuum leak in the mixture screw threads.
also if your jets are that mangled you could have a leak under the head of jet allowing fuel to be sucked up the threads of the jet

so carbs aside for a second.

what is the idle voltage output at battery? and up to 2k rpm?

 

Given the description, I'd just pull the carbs, tear them down for cleaning and replace the messed up jets and seals.

 

after rereading the whole thread. I would agree with k-moe replace the jets with new ones due to mangled and value unknown.

did you ever check the shim clearances? I see where it was suggested but you did not reply.

lost spark in plug 1 then plugs swapped it all fixed itself. make sure your plug wire ends are clean and tight. something happened when you swapped plugs.

after shims resync the carbs

 

Alright, thanks everyone. I have the next two days off so I'll have some more time to fiddle with it and I'll be able to get back after that. I'm just going to bite the bullet and buy the 50 dollar rebuild kit from eBay that comes with an assortment of replacement parts and different jet sizes. I'll check the shims and will make sure I'm getting voltage tomorrow or the following day. I really appreciate the help so far from everyone replying, I'm at work with no service at the moment so can't give too much info but here is a reply to the questions asked:

1. Idle mixture screws are out 4 full revolutions from soft bottom, any more and it starts to run poorly, and less and it sputters worse.

2. I'll check the voltage readout soon.

3. I'm just going to buy the full rebuild kit, any suggestions or should I just get the eBay one?

4. Will check shims soon.

Thanks again!

 

That ebay kit isnt going to contain the most vital parts of the carb rebuild that you need. Yes it will have some jets in it and a few other things but you really need throttle shaft seals and fuel tube o rings. Yes you still need jets, needles, seats, bowl gaskets, etc but there much more to doing the job properly than just a few jets. When we suggest doing an in the church of clean overhaul you have to read the thread and follow it religiously. I have been through 3 sets of carbs on 3 bikes and I can tell you that the first set took the longest and had to come off again to make right what I didnt get right the first time. By the 3rd set they turned out pretty freakin nice. Minus the fact that I tried to use o rings instead of actual throttle shaft seals which did lead to them being pulled again for replacement of those. However, if I had taken my own advice and replaced those with the proper seals the first time I would have had no issues and the bike is running great. Just my 2 cents. And while you have the carbs off, broken apart into 4 separate bodies, soaking in carb dip, that's the most convenient time to pull the valve cover to measure and correct valve clearances

 

+1 on the ebay stuff, normally those kits are underwhelming to day the least! When it comes to the carbs spend the $$ and get the good stuff. IMHO

 

The Ebay kit will have an abundance of parts that will not fit correctly.

 

Alright! I'll go to the thread for the taking carb to church and follow it.

 

Dont mean to sound like I'm on a soap box but even I didnt really get it until I had done it. Wasn't very long until I realized exactly what the other more knowledgeable members were getting at. Do it right the first time and be done with it for quite some time. Granted there's room for error in most things but due diligence pays off.

 

I have been swamped as usual but I decided to take some pictures to show you guys what I'm dealing with. First two are of the spare carb I have I'm using for parts, the condition of those pilot jets are near identical of the same inside the carb currently minus the really destroyed one on the left end. And the jet in my finger is the 110 main jet which I had 4 of installed before taking the 4 120 jets from the spare and swapping them in.