Carb issues

[seth1981]

Ok Im needing help. Im not a carb guy but I want to figure this out so I dont have to take it to somebody everytime it need adjusting.

My first issue is pilot jets. I was going to buy a few different sizes and noticed on

http://www.xs650direct.com/products-39.html

The little diagram they have shows two different type of jets. VM22 and bs30. I have a 74tx650 with (from what I can see 74 carbs) but the jets in it look like the vm22 jets they have listed. Now im going directly off the picture. Mine, like the vm22 have the multiple holes on the side. The ones it has for my carbs only have 1 hole. Can those two be swapped out and work I.E. diameter, threads ect? If so and the wrong one was in my bike what issues would that cause?

Ok #2. I just picked up this bike. It had a low end stutter but when I grabbed a handfull of throttle if ran fine. Came with 127.5 main, needle in 2nd (from top) slot I Switched up jets. Cant remember pilot size, 130 main and needle in the middle slot. Went out and ran it and the low end stumble was much better but it sputteret really bad at the top end. When I pulled the carbs after the bigger jets there seemed to be alot of gas in the carb.

Ive tried just about all variations of the jets I have and needle positions and it just switches up from top end sputter to low end sputter. Carbs dont have a leak (just rebuilt) valves, timing chain ect all good to go. Im lost here.

What I do know is it starts fine no matter what I do. So I have that going for me. Mix screw 3/4-1 turn out. I have read and re-read the carb guide on here but its not helping.

I cant for the life of me get the idle to stay. When I start if even after its warm its fine. After I run it its really high.

Ive tried googling flat spot and stumble so I have a better idea of which is which but got nothing. I say sputter because its like the engine is not getting enough fuel and sputtering kind of sounds like a machine gun.

Last thing is wiring isnt the greatest but I keep the batt on a tender so its fully charged but could a bad ground or grounded wire be hurting? I know its not good but I would think if thats going to mess it up it wouldnt be top end one jet size and llow on another size.

Anybody have any suggestions? Altitude about 2300 temp 50-60 deg F.

So there it is. Sorry for the length of this post. Thank you for any help you might have.

 

[figure8]

This is an obvious one, but have you double checked your float height? Not sure on the jets, someone will be of more assistance on that.

 

[seth1981]

I have. There set at 24mm with the gasket.

 

[charlieyam]

#I cant for the life of me get the idle to stay. When I start if even after its warm its fine. After I run it its really high #

One thing that might be worth checking is that your engine ignition is advancing and retarding as it should. The standard XS650 setup is fine when new , but with time the advance /retard springs go weak and this results in poor tickover and an engine that does overrun when rev'd being slow to return to a steady tickover.. best cure is to fit an electronic ignition, preferably one that does away with the mechanical advance system....

 

[5twins]

There's also the fact that the advance and advance rod need to be serviced from time to time, cleaned and lubed. If the ends of the cam that the advance rod turns in get all dried out, the rod can stick and the timing hang in the advanced position. That gives a higher engine speed.

You can't just think you have '74 carbs, you have to I.D. them for certain. The carb year set will determine jetting specs and pilot jet type. Also, the float bowl design is for one type of pilot or the other. Float bowls can be swapped so it's possible the wrong ones are on your carbs. The holes down the sides of the pilot jets are air bleed holes and really don't have much to do with determining what type of pilot jet you have. What does is which end of the jet the metering orifice is located on .....

Then, as I mentioned, there's the float bowl design. The two types of pilots get their air feed from different ends. You must use the right pilot for the bowl design you have and the right bowl design for the carb set year you have .....

 

[seth1981]

I swear I have the wrong jets in there. I'll check it again. Thanks for the picture. I'm going to start from square 1 tonight and recheck everything again tonight. Make sure the timing or something wasn't set wrong. Thanks for the info guys.

Local shop said these CV carbs have a air bypass on the filter side that can be covered up if the filters are slid on to far......just figured I would throw that in in case somebody happens to read this thread having similar issues.

 

[seth1981]

So I do have vm22 pilots and a bs30 bowl. Unless the metering orifice is supposed to be 1.69mm. I have pics if anybody's interested. Possibly a good chunk of my issues?

 

[seth1981]

OK sooooo yeah. Got the right jets and all is well. No stumble anywhere, pulls good, dosnt backfire... Nothing. I'm a happy camper

 

[angus67]

Air bypass....the oval at the top of the carb throat can be blocked by a filter lip, causing a multitude of issues. Those cheap-ass emgo cones are ine, and the k$n's are another. I use shorty uni foams.cant use them in a airbox, they clamp on.

http://www.motorcycle-superstore.co...ID=AvantLink|NA|55963_d3fe7c65&WT.MC_ID=54020

 

[grizld1]

The oval port at the top of the intake bell is not a bypass jet and has nothing to do with air/fuel mixture. It opens the lower diaphragm chamber to atmosphere so that the slide will rise when you goose the throttle and create a low pressure zone in the upper chamber. The trouble with cheap conical pods is that they have internal flanges which can block the small main and pilot air jets, causing a severely rich mixture long before the slides start to rise at around 4K rpm.