help with the throttle

my bike runs great but if i hit the throttle hard or about medium it stalls around 2 and half rpms and stays that way a while then it will speed up really fast but if i increase the throttle slow it will speed up with no stall is my carbs out of sync and also i have my air breather boots off any help would be great

 

It is because the airbox boots are off. The carbs are lean and the opening of the throttle is sending a rush of air into the carbs and there isn't enough fuel to compensate. Reduce the air by reinstalling the boots and the problem should go away. Besides it is not good to run the bike without soem type of air filtration. You are asking for trouble due to particals that could damage your valves or a lean mixture that could lead to overheating and damage much more.

 

thank you blue ill put the boots back on today and that should fix the problem also i have no exhaust and i was wondering if there should be some type of back pressure in the exhaust system i know little about motorcycles and some cars do need back pressure to keep a smooth idle what your opinion some or no back pressure thanks again for the help

 

No exhaust at all or no mufflers? Either is not good.

What model XJ have you got?

Yes these bikes need a good exhaust system. The CV type carbs will not work properly without back pressure. Your bike will be running very lean; you will also probably be damaging your valves.

Get a standard 4 into 2 exhaust system on there ASAP. That way the bike should not need to be modified in the carbs.

If you get a 4 into 1 aftermarket exhaust or after market 4 into 2 mufflers then you might need some re-jetting, most likely a bigger pilot jet, maybe a raised needle or aftermarket main jet and needle. Depends on the exhaust system.

 

I've got a 1981 xj650 and i have no mufflers got the exhaust tubes that run under the bike where they connect to the mufflers but i don't have the mufflers would it harm the bike to put on some straight pipes or should I bite the bullet and pay a load of cash for some oem or 4 to 1 exhaust thanks

 

Have a four to one exhaust stock air box and boots. Idles fine after several tries but immediately stalls when throttle is engaged (never past 2k). I have never modified to air pods. Anu thoughts?

 

Another reason these bikes will seem to stall and then blast off is a sticky throttle shaft and/or linkage and binding throttle cable.

 

ronmaxim81:

Let's see the "Tale of The Plugs".
Pull the Plugs
Line-'em-up: 1, 2, 3 & 4
Photo. Well lit and in-focus. Business ends of the Plugs.

The PILOT Mixture Screws regulate Mixture for Idle.
If your Bike Idles OK ...
You must adjust the Pilot Mixture Screws to provide Supplemental Richness.
Supplemental Richness is NEEDED during the BRIEF TIME referred to as:
"Off Idle"
At the moment you Turn the Throttle Grip and Open the Throottles, ...
A very short duration of Fresh Air Rushes into the Combustion Chambers.
About 8 -to- 11 "Rapid Eye-blinks" of FRESH Air rushes in.

If the Pilot Mixture contains Supplemental Richness ...
The Bike accelerates as it should.

If the Pilot Mixture hasn't enough Supplemental Richness, ... we call that LEAN and the Bike will Cough, Backfire or Stall.

If the Pilot Mixture has too much Richness ...
The Bike Boggs-out and runs rough.

Connect the Air Box Boots.
Test for Air Leaks.

 

Before we even get there: And this applies to both of the posts regarding the problem--

IN ORDER: (Assuming carbs have already been cleaned and serviced)

-valve clearance check and adjust

-compression test (not so much necessary as a way to know if you're wasting your time.)

-carbs bench synced; mixture screws set at 2.5 turns to start

-float levels verified/adjusted using the "clear tube" method and fuel

-carbs back on bike, running vacuum sync (YICS blocked if applicable)

-ColorTune or plug chops/plug reading to fine-tune mixtures.

Skip over anything? If you did you'll be at this a while.

Want it fixed and running right, no more screwing around except maybe rejetting for a pipe? Go back and do all the steps, in order, and don't leave anything out.

Valves first.

Trust me guys, I learned the hard way. You can too, or not.

 

RickCoMatic:
I pulled the plugs and replaced them all. Carbs cleaned top to bottom. I pulled them out to make sure nothing obstructing jets. Throttle still stalls engine when applied. I'm a little troubled about accessing the pilot screws, do I really have to drill the caps out?

 

UPDATE: I'm loosing my mind here.

Finally, re-installed carbs (again), cleaned hat to bowl. Started her up then there was a knocking, no idea where that came from, slap?, in addition, #2 header is now cold. I'm no expert by any stretch of the imagination but I'm thinking this is a bad sign? Please advice.

 

What plugs did you put in?
What did the old plugs look like?
Did you "break apart" the carbs or just take the cap and bowl off and clean the insides? Did you take out the jets and clean the emulsion tube?
Clunk test?
How is your air filter? New? Dirty? Missing?
Is this a new development or did you get the bike this way?

If you tried to run it without all the parts back together, it won't run right. So put those boots back on if you haven't already.

It's debatable, but I wouldn't go messing with the pilot caps right now. It is hard to clean them without taking the screws out though.

 

Cold pipe is maybe no spark. If you need a hand getting your bike running right give me a shout. Even though it's snowing here as I type this....

 

Plugs standard replacement NGK's
Previous plugs were blacked out...rich?
Aside from not removing the carbs from the rack...it has been completely disassembled, soaked in carb cleaner (minus rubber parts) all ports blown out with air and cleaner
Stock airbox, new filter, boots are on.

She was a garage stored bike Im getting street ready. The knocking noise is unsettling and now not all headers are warming up. She's stopped turning over so I'm worried to start her up again until I know what's going on.

 

Ok, this is confusing, original poster is from 2007, ronmaxim81 has the original intake and didn't mention removing exhaust.

Make sure you can check off everything on Fitz's list. Spec valves and check compression to make sure cylinder 2 isn't cold due to bad valve timing or low compression. Then make sure your carbs are clean (according to many well written threads on this site). You may not be able to "see" blockages that will make a BIG difference.

Then make sure they are bench synced, and pilots are set to the recommended settings. You may not have to drill anything out if that has already been done.

If you do all that and slap 'em on, you might get a racing simply due to the idle being adjust too wide. Shut it down and adjust the idle until you can get it to 950-1050 rpm. Then you can get a running sync and start going through any symptoms.

Also, read carefully, Rick said post pics of your plug, not just change them. They can help determine the actual running condition of the engine.


Where are you in DC? We've got some members in the area that are very knowledgable. Send me a PM.

 

A knock from where? Could be a great many things, exhaust gasket leak, cam chain slapping around, busted valve, etc.

My schedule's a bit busy coming up with the holidays and everything. I'm glad to help though if you need it and I don't charge. I point and teach, you work.

 

Knock seems to be originating from the upper portion left side. It would knock for few seconds, stop, then again while idling. I tapped the throttle and it stalled. Seems more hesitant to start/idle now.

Thanks for the help...I understand the holidays are going to kill everyones time. I'll let you know what I come up with after testing compression.

 

Did you check the valve clearances yet?

 

Biggies, that's on my ongoing list of things to do, thanks...lol

 

Hey fitz, are these non-interference engines?

 

Do it before you do the compression test. An out-of-spec valve can cause you false results on a compression test.

 

Oh, they're "interference" engines all right; get the cam timing wrong and you'll bend a valve or worse.

 

Or have loose/broken/knocked off when fell over cam chain....

sounds like someone needs to remove the valve cover with a quickness.

 

Finally had time to run to Advance to get gauge feelers to check clearances. I'll post my results soon depending on weather.

 

Make sure to post results in MM the specs re in Millimeters as these are metric bikes. Your feelers may or may not have metric markings on them.

 

it can haz metrix

 

Okay, used fleeler gauges and here's what I got...
In order from 1 - 4
Carb side: .076mm for all
Exhaust side: .152mm, .152mm, .127mm, .127mm

 

http://www.xjbikes.com/Forums/viewtopic/t=14827.html

If you didn't read that already, the specs and new shim sizes are in there.

I don't remember which bike you have so please verify the below specs for your bike.

Intake (carb side) .076 mm is tight. Should be .11 - .15. You'll need to change all these. You did pull them out and get the number off the bottom of the shims right?

Your Exhaust side is all tight as well should be .16-.20. I'd probably remeasure a .152 just to be sure. You'd change all those as well.

Also, any compression numbers yet?

 

With all of them tight like that, don't even bother with a compression test until they're in spec. With #3 and #4 that tight on both intake and exhaust you'd probably get wonky numbers from those two anyway.

 

Sad news, had a guy check out my XJ for a tune up to get her street ready. I was told it would be easier to just get another motor instead. Got me what was suppose to be a good deal for one, handed him the cash, and said he was going to glass bead it.

Unfortunately, I haven't heard from him since 08Jan11. sigh.

 

Sorry someone ran off with your cash.

You still have the bike or did they get that too?

Offer still stands to help get it on the road. Just give me a shout. My weekends free up as the weather warms up.

 

You might want to just get your valves in spec and then do a compression test.

If the guy took you money do you still trust his "easier to replace it" diagnosis? I sure wouldn't.

 

Okay, gonna dive back in. Thanks for the suggestions/help, I'll definitely need it. The guy pulled the cam chain off the sprocket, would I have to readjust it or is it a question of having it back on with little to no slack? Then it's off to valve adjusting time. Wish me luck.

 

Good luck.

You'll need to make sure it's in time BEFORE tunring the crank. These are interferance engines and you can bend a valve if it's down in the cylinder at the wrong time. If the chain is off you may need to pull the head and get #1 at TDC before retiming the cams.

Offer to help still stands.

 

these guys on XJbikes are the pros ronmaxim. I completely rebuilt top-end engine rebuild (new piston and rings across the board) by myself. for me only being 23 years old and hardly any mechanical experience, you yourself can do the same thing. just last sunday I put the cylinder jugs/head/cam chain back together. the valve clearance measurements is the easy part and once you put it back together, you feel like a champ. don't be afraid to ask questions. plus a Haynes manual helps nontheless. best investment you could make if you don't even have that

 

Sorry to hear about the guy ripping you off. He'll get his. It goes without saying at this point, but I know you will be more prudent in the future in terms of giving people cash "up front" for anything.

That said it would be a damn shame if that caused you to give up... I would love to see you follow through regardless, take up iwingameover's offer and get your bike road worthy! XJBikes guys are the pros, and we could always use more XJs on the road.

Best of luck and don't lose hope in humanity and/or the XJ. Everything can be fixed.

 

Thanks guys. I'll let you all know of my progress. iwingameover thanks for the assist, will definitely be in touch.

 

Okay, so I finally, finally, had time to dive into the project again. When I cracked her open. I had a buddy help out with the cam chain, ran tests, and addressed cracked boots and replaced them as well (thank you donor bike). She ran good and strong and revved with no problems. I turned my attention to the seat and how to remount it. The next weekend I cranked her up and she started up like a champ but began to rev high and within seconds cut off as if I hit the switch. What now?! I checked for air leaks, fuel starvation from petcock, clogged tubes. All seem fine. Suggestions?

 

I didn't read back through the whole thread....

Was your choke open or closed? choke open and bike warm will make it rev up.

After that:

Valves in spec?

Carbs clean?

bench synced?

Float Levels set "wet" clear tube?

vac synced?

Idle adjusted?

 

Sure.

In order:

Valves in spec. First. Can't sync if they aren't.
Carbs clean.
Float levels verified using fuel and the "clear tube method."
Bench sync.
--carbs back on bike--
Running vacuum sync.
ColorTune or tweak mixtures based on plug reading/"plug chops."

IN ORDER. Skip any or try to do them out of order and you'll be chasing your tail until you break down and do it right.

 

Must be an echo in here...

 

Oh yea, sorry. Tried so hard to forget the douchebag that ran off with my money that I lost track. In any event...valve specs are as follows:

Intake:
(1).004/y285 (2).004/y285 (3).004/y285 (4).004/y290

Exhaust:
(1).006/y265 (2).006/y255 (3).007/y265 (4).005/y265

Not sure how bad that is but according to the replacement chart I would need:
Intake: 3- 275's, 1- 300

Exhaust: 2- 255's, 1- 245, 1-250

(is this even worth it?) *sigh*

Carbs are coming off again for a thorough cleaning
Have clear tube to check float levels
Have directions on bench syncing
I don't have the dough for a colortune so how do you "tweak" mixtures based on plug readings/plug chops?

 

to quote Yoda... "do or do not there is no try"

They're either in spec or they are not. Your intake would need 3 275's and 1 280 not a 300. Exhaust looks good with your numbers for shim replacement.

On the up side I may have the 3 275's and the 280. I'd have to check which I can't do until tomorrow. Let me know if you want them.

Your carb tuning efforts will be in vain until the valves are fixed. But to do research ahead of time search this site for "tune by ear" Rickcomatic has a great write up on it.

If all else fails give me a shout. I'm a bit busy currently but I can find a weekend hour to get them tuned up for you if you get all the leg work done ahead of time.

 

Nice Yoda drop..lol. Well that's some good news. I'll check if I my "parts" bike might have the shims I need. Otherwise let me know what you want for them, appreciate it. Yea I'm not tearing into the carbs until I get valves in spec..baby steps...lol.

Cool, I'll lookup Rickomatic's post on tuning.

According to Chacals post on valve specs wouldn't this mean I'm within that range (except 4th exhaust shim) or am I missing something here?

650 all x. Turbo:
Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

 

I read them all as MM and dropped one 0 out. Ooops.

If you change the ones that are .11MM to one shim smaller they will then be .16MM too wide. You seem fine for this check.

 

whew, thought I was losing it. Carbs....we meet again.

 

After 3 bleeding knuckles later (yankin carbs off boots) carbs are clean. Needles clear, some crud at the bottom of bowls (boiled) but pretty clean. Figured since I have the carbs out to check diaphragms, slide, etc. Bench synced using paperclip method then mounted back on.

Any good deals on a comp tester? Rental?

 

I do not understand how someone "Pulled the Cam Chain" off its Sprocket???

One TEST is to see IF the Chain does lift off the Center Bridge.

If the Chain was loose enough to be lifted off a Sprocket, ... something wasn't right.

Did he Take the Sprocket off the Cam?
Probably not.
The Tensioner would extend and make it impossible to get back ON without removing the Tensioner and resetting it.
(Auto Tensioners)

 

ron did I miss you talking about the cams off?

I got my compression tester at advance auto parts about $25. Take a spark plug with you and make sure it has the same size adapter.

 

No, I thought when the guy came to check the bike he pulled it off. My neighbor came by and checked the tension on it and said it was fine. I just called him and he said he didn't mount it back on the cam.

I'll check with advance...thanks.