Can't get over 40km/hr

So I took my 81 Xj 650 Maxim out for the first time the other night and I believe it was going into all gears but I couldn't seem to get it to go over 40, it also stalled out twice and the second time I couldn't get it to run until it sat for a bit then it fired as normal. I was talking to a friend and he mentioned that my intake boots being all kinds of cracked would possibly effect the vaccum which in turn would cause the inability to accelerate fully. Is that possible? I have taken the boots off and am gonna attempt an rvt and heat shrink repair to get me through the season as new boots for the 81 specifically are $500. Any insight on repair technique would also be appreciated. Thanks. I apologize if I left any info out

 

Yes vacuum leaks will cause problems.

 

Since you've already pulled the boots and carbs, are the carbs clean? With the carbs off and petcock on, do you get a steady stream of fuel from the tank? What do your plugs look like in each cylinder?

 

Save $150 with Len. Part HCP23081N

 

I haven't pulled the carbs apart yet, I will be doing that but I was told when I got it Carbs had been rebuilt and re-jetted and next to no km's were put on the bike after that so I presume they are clean. I haven't checked the fuel flow or plugs , I will do that when I get home tomorrow and report back.

 

that part number must be for newer than 81 the one I have is 4H7-13586-02-00 and for whatever reason the pre 82 models are stupid expensive, 82 and 83 I can find for 50-80 per set of 4 I have hunted and only found the 81 model at 90-100 per boot.

 

We can't compare part numbers here. The number is Len's part number for aftermarket boots:

HCP23081N Aftermarket rubber BARE INTAKE MANIFOLDS SET, complete set of 4 intake manifolds (2 left and 2 right). Does not include any accessory items (gaskets, bolts, etc.) ---- manifolds only. Fits all non-YICS XJ650 engines: 1980-81 XJ650 Maxim, XJ650 Midnight Maxim, and 1982 XJ650RJ Seca models, and all 1980-81 XJ650 Euro models. Set of 4:

 

my apologies, I didn't realize he had his own part numbers or that aftermarket were avail, does he have a website?

 

You can click on the XJ4Ever link at the top right corner of the page, or visit his website here: https://www.xj4ever.com/

 

Get constant good fuel flow, carbs are clean, but plugs are black. Got it back together and it starts and runs. I feel like I messed up putting the throttle cable back though, how much turn should the throttle have?, mine is like a quarter inch but I can rev it up without issue. I think it may be running lean though as it dies once warmed up and with the choke in off position at low idle but will sit there and idle at anything over 2000rpm.

 

Sounds like your throttle cable might be an issue. If you can only turn it a 1/4", something is wrong and that may explain your 40 mph limit if you can't open the throttle up.

With the carbs off, you can see how much throw is required to fully open the butterflies. Can you replicate that with the throttle twist?

Do you have any info on what jets are in the carbs now, or why somebody decided to change them?

Post a few photos of your setup if you can. Somebody might spot something that you haven't described.

 

The throttle wasn't that way before I took it apart, at least I didn't remember it being like that, I only rode it once. I was afraid of that, now I have to disassemble it again

The reason they changed the jets was to compensate for the air pods that are on there, at least thats what i'm guessing based on what a mechanic told me about having to upgrade jets to compensate for the pods.

the best pictures I can get assembled.

 

Your fuel line should not be like that. You want it as direct to the carburettors as possible. Run it in front of the link bar that holds the carburettors together. It might not be the cause just mentioning it anyway.

 

Ok, I have to change that line anyway. Thank you. More like the line I drew? Is it a big deal if it's shorter than the vacuum hose?

 

Add to this, that you only have short movement on throttle, I think you have a number of issues...
Firstly, have you connected the throttle cable to the throttle not the choke?
Secondly, pull the carbs and put the original jets back in there, in their right places. Then try to detect where it’s lean (guaranteed it will be because of your “pod” filters - more likely you need a different needle, springs, main jets).
The fuel line okay okoky is not good either.
Never ever trust sellers on eBay or Amazon selling jet kits - why do you yanks do it? You have a US supplier in @chacal who sells the correct stuff?
Lastly, don’t worry about your boots for now, they’re not your issue.
Let us know how you get on?

 

Is the throttle the centre of the carbs or the right hand side?, I hooked the throttle cable to the centre and the choke to the outside, as mentioned I had normal throttle before I initially removed the carbs. I trusted nothing, I got the bike as it was and was told the motor and carbs had been rebuilt and when he fired it it sat there and ran, the jets I mentioned are a guess based off a mechanic telling me that usually when the pods are put on, the jets are replaced. I only drove it once and had the speed issue. I got it for roughly $500 so i'm ok investing some money into it before I call it a lost cause. It fires and runs and feels like all the gears engage.

 

Your choke cable is hooked up correctly in the photo. Can't see the throttle, but since it's the only one left it's probably in the right spot. There might be something weird going on with the link that connects the cable and the carbs, or there might be something on the throttle twist end where the cable wraps around in a plastic channel. Maybe try pulling it loose at the throttle twist end and see if you can pull it by hand. If it jams up, then investigate the carb end.

With pods, at least your carbs aren't hard to pull. You might want to pull the jets and see if you can find all the numbers on them. Maybe pod filters were added and you still have the original jets?

https://www.xjbikes.com/forums/threads/xj-parts-catalog-section-c-fuel-system.44642/

See the link here for jet info from XJ4EVER for various models.

I'm not a jetting expert, and have not installed pods, but there's dozens of posts on this site describing the difficulty in tuning, although it can be done. There's always the option of finding an airbox!

 

Yeah, thats what a different mechanic was saying to me, he knows mechanics that finally caved and just went back to the stock box. Which i'm not opposed to. I just want it to run and drive so I can practice.

 

If when it boggs/dies on you and you see a bubble in the fuel line, that may be the reason, Here is a pic of how I re routed my fuel line after removing an inline filter. So far all is good.
I also had a problem with my float needles sticking and used different ones. I could tell it was sticking cause when it died, multiple bowls were low. Hooking up a tube to the drain then opening them up would tell me the bowls were not full.
Pic attached is of a full bowl. When my bike was stalling/bogging, multiple bowls were like half of what is in the pic. Tapping on the carb and/or sitting for a while filled them back up.
Clogged filter screen on the carb can cause slow filling bowls also. .

 

Hey Gordie, scanning back through this thread this morning and you've probably got more info bombarded at you than you want. I guess first question is "how much wrenching on your bike do you want to do?". A few basic categories of ancient bike owners:

A) I love working on greasy stuff. I'd prefer to do my own heart surgery after watching a YouTube video.
B) I don't mind doing the work and have the basic skills, but just need experience with these weird two-wheeled contraptions.
C) I'll do all the basic maintenance stuff, but probably want a mechanic to deal with the complicated bits.
D) I just want to ride, damnit!

If you're in the first couple categories, you definitely can solve your issues with some time and patience. I would definitely recommend finding an airbox and some boots. Not that pods won't work...but your resources for help are infinitely greater if you have a stock setup. Next is a deep dive into the carbs. It is very possible that a "quickie" rebuild was performed before you bought the bike. Issues could include bad needles and seats, float/fuel levels not adjusted, carbs not cleaned properly, incorrect jets (a $25 rebuild kit almost certainly will have wrong parts). These carbs can be a little intimidating at first, but they are just pieces of metal. Keep them organized and labeled. Find one of the many posts on this site with good photos of carb innards. Read the "Church of clean" a few dozen times. Look at videos of how these CV (constant velocity) carbs work. Look at the carb body, blow air through the passages to understand where everything goes. Get a Haynes manual. Read it for recreation. Eventually things will really make sense, I promise.

If parts are correct and in good shape, you can clean the carbs for $0. Maybe you'll need bowl gaskets, needles and a few O-rings. Maybe throttle shaft seals. But at least you can make a list and some decisions based on your time and dollars.

After carbs, valve shims will be the next thing that is confusing as hell, and then really easy.

If you are in the latter two categories and just want to economically learn to ride, buy a GSXR or a Rebel for cheap that already runs. Since you've already been pulling carbs, I'm guessing you can make that old Yamaha work! Don't despair. Even taking a few wrong turns provides priceless education.

Heck, go buy that Rebel while you are still working on the Yamaha. No judging here.

 

Haha, well I appreciate the lack of judging. I've seen the rebels, not a bad bike. I basically am between B and C and D at this point. I am not opposed to learning the bike and working on it, tearing things apart is not foreign to me I just need time with it, but at this point I took it to a mechanic because I am basically flying blind not knowing anything about it prior to my having it and our season in Canada is quickly coming to an end and if I have any hopes of getting some seat time I need someone who knows whats what. That being said once it's running and functioning properly I will be learning the ins and outs of it and eventually making it a project, I fully intend on having multiple bikes and would love to make this one a bobber down the line.

 

So anyone that was active on this thread I thank you for all input and also if anyone cares the carbs basically had to be entirely rebuilt, new intake boots, and a new clutch pack. Now it's running wonderfully and easily hits 120km's/hr or roughly 75miles. Now to tackle an oil leak