Aftermarket carb

So as i understand. The stock carbs on the xj's are really sensitive?

So arent there any "new" carbs that you could buy for it and maybe have it working more smoothly?

Couldt find anything searching around so maybe im asking a rookie question

Much love
Proar

 

1. the stock carbs are not sensitive, they just require thoroughness when being serviced. Once serviced they are dead-reliable and provide excellent fueling characteristics.

2. New carbs will set you back at least $1000 US (for brand-new), and won't make the engine run any better than properly serviced stock carbs. Used carbs will have to be serviced, and then you'll have to mess around with jetting for a few weeks/months. This is not out of the question to do, but is (in my opinion) not the easiest path to take.

So, what's the issue that you are having with your XJ in the carb department?

 

well not a problem. but like many others i want to switch to pods. but as i read it this is a bad idea.

 

Yup......BAD IDEA

 

It is.
If you really want to have pods then you will need carbs with cable operated slides, or a fuel injection system. Bout will require fabrication and futzing to work, and neither will make the machine run any better that it does with the CV carbs (though cold startup will be a bit better with fuel injection).
If you want to ride this summer just get your carbs in order.

 

rookie question. but arent "all" carbs cable operated?

 

No

 

The thottle plates on the CV carbs we have are cable operated, but the slides are not. They are controlled by airflow. Alter the airflow and you alter fueling. Alter the airflow in an uncontrolable manner (as with pods) and you get crap fueling.

Carbs that have the slides operated directly by the throttle cable(s) can have alterations made to the airflow without altering fueling characteristics as much, but they also have other tradeoffs in terms of fueling (mainly with fuel economy and the tendancy to bog when suddenly bringing the throttle wide open).

Then there are carbs that are operated by other means...many other means, most of which aren't used much anymore.

 

Please don' t put pods on a stock airbox will allow the bike to run soooo much better.

 

ok where can i find a stock airbox for my 82 xj 750 maxim

 

eBay or port up in the For Sale/Wanted section.

 

I have a 1982 yamaha xj650 maxim. It’s my project bike. I’m a mechanic and I would even say change the carbs out for a smoother ride all around. If you go on Murray’s carbs you can find one for you’re bike. I got duel carbs. They come pre synced and pre jetted ready to slap on the bike and ride right away. Takes a whole 20mins to set up on the bike it’s well worth it. I noticed after I put them on it was smooth asf starts up right away. Adds about 5-10 more Hp. Take a look let me know.

 

Devil's advocate: I bought a parts bike (1982 750 Maxim, avatar photo) that the PO had sold the carbs and airbox (also the wiring harness) so I was forced to buy some carbs. I thought why not, ebay 4 x 34mm knock-off Keihin PWK flat slides. Really cheap at about $110.00 for 4 new carbs. Made a 4 into 1 cable pull and they fit very well. I did have to clearance the #1 carb float bowl drain plug not too difficult however. Installed them (they fit the stock boots perfectly) and fired up immediately, I was totally surprised, I'm now getting the idle and jetting just right although it pulls like a freeking train and the throttle response is amazing no lag or delay at all. My two test rides have been without air filters but I have foam individual filters. They look way cool and are actually much lighter than the stock carburetors by about 3# which is good for 1/2 hp. I had never ridden a XJ750 Maxim before and I'm very impressed by how quick the bike feels. Not the best close up shot of the carburetors but..
Cheers, 50gary

 

How did you manage the 4-1 conversion?

 

They make a 4/1 cable pull. Mine works very well, happy and simple. If there's a downside it's that it's not pull to open and pull to close
like a lot of modern high performance bike have. I could maybe take a close picture of the throttle pulls.
Cheers, 50gary

 

Very cool, i didnt realize you did that. I looked into mikuni carbs for my xj650 and the cost was 3k for a push/pull setup. I came close to buying them but then the pandemic hit. I am still rocking the factory carb and 3k richers.

 

For the carb kit from Murray’s carbs for a 82 yamaha xj650 maxim its $950 for the kit with the quick turn throttle

 

Does anyone know were to get different size jets for the stock carbs for an '83 XJ750MK? The parts list from Yamaha does not list alternate sizes for low speed or mains.
At some point smoothbores would be nice, but they are pricey.
For now the stock carbs, whatever brand they are, will have to do.

 

Jets R US has a variety of jet sizes .

 

A full stock carb rebuild kit and a set of carb synch gauges is much cheaper than switching carbs . I have rebuilt six sets of these carbs , not hard at all .

 

info@xj4ever.com

 

hi, what did you use for the 4 throttle cables? how's your top end power.. im currently experimenting on one of my 650. tnxs!

 

The 4/1 cable pull is a simple aluminum cylinder about 3/4" diameter x 4" length (19m x 100m) commercially available. I'll try to get a picture posted later today.
Cheers, 50gary

 

Curious where you got the throttle cable from, is it one of the DIY kits or premade? I am doing exactly the same thing on an XJ550 Maxim with 28mm carbs and I found a Motion Pro 1969 Honda CB750 4-1 throttle cable that I use which is basically identical to the cable that you have. I'm also trying to connect my carbs to the stock airbox and I was able to make boots from a rubber pipe coupler. However it already ran too rich and that made it even worse so smaller jets are on the way

 

Thanks for the info. Going to order some larger idle jets soon.

 

Motion Pro sound about right, I got my setup from a drag race guy, very helpful fellow. I'm now working on my gas miser Pit bike 140cc Lifan
clone motor 12.5 bhp 4 speed I'll use one of the 28mm PWK clone carburetors should be close to your 550 four cylinder. 140cc vs 137.5cc.
I spoke with a Honda Grom rider (125cc) and he says he gets 120+ MPH on Rec gas.
I'd like to know your jetting for the 550 when you get it right?
Cheers, 50gary

 

I'll definitely post some updates once I get jetting etc figured out. 28mm carb sounds about right for a 140cc, I have a similar 28mm on a 180cc 4 stroke scooter and it works pretty well

 

Where did you get $950 from? I have an '83 Maxim 650 and they're quoting me $675.

 

Is there a specific rebuild kit you like to buy? I can't seem to find a kit that includes everything to do the entire set and the interconnecting pieces.

 

http://www.xj4ever.com/

Email the man himself and you will be able to get all the parts you need. The right parts for the right carbs and shipped fast.

 

Xj4ever has everything you will need the aftermarket butterfly seals are around 39$ the hast tome I ordered them , he has the gaskets and needle and seats ( I personally bought the solid brass needles with ethonol fuel these are better than the vitron needles if bike sits for a while but they are not cheap ) the other item I bought from Len with cool factor is Allen head fuel bowl drain screws.

 

I find the allen head bowl drain screws from Len are more than a cool factor. They make draining it much easier. Especially if over the years you didn't know the stock drain screws weren't Philips, but JIS, and they were stripped from using a Philips... As me how I know....

 

I order those as standard fare for Hitachi rebuild kits. I only install the Deluxe complete rebuild kits, with metal tip needles and the hex drive drain screws.....mikuni rebuild kits only come with rubber tip needles though.....