:: Yamaha Virago XV Forums That Rock!!! Tech Help Carb jet kit question (SOLVED)

#1:  Carb jet kit question (SOLVED) Author: ghostdad Post Posted: Wed Mar 31, 2010 10:20 am

Where is a good place to but a carb jet kit? My bike is running extremely rich, the P.O said he drilled out the jets. I have no idea how much he drilled them, so the only thing I can imagine is that could be the problem now is he overdrilled them. So i think my best bet is to put stock jets back into it and hopefully fix my problem.

One other thing that is baffeling me is, I have the pilot screw / mixture screw turned all the way in on the back cylinder and it still runs rich? Shouldn't that pilot screw cut off the fuel and starve the cylinder? Is it possible the P.O put the pilot screws into the wrong carb? I'm pretty sure I have read on here they are carb specific. Am I correct? I kept the parts for each carb seperate and marked.

The bike runs strong but the plugs are black and sooty. They are not wet just sooty, I have checked and eliminated the petcock from being the problem. I did this by checking and marking the fuel level before giving up for the night and checking it in the morning and the fuel level did not change. Then I popped the carbs off so I could check the rear cylinder carb holder and it was dry, so the petcock is not leaking into the cylinder.
I also removed the intake boots thinking that maybe something was plugged and blocking air flow which would cause a rich condition. There was no change in how it ran.

So am I missing something here? I have checked and eliminated everything except the pilot screw being in the wrong carb. ( becuase i just thought of it as I was typing this thread.) LOL I'll get back to you on the results. Any other suggestions?

Last edited by ghostdad on Fri May 07, 2010 7:51 am; edited 1 time in total

#2:   Author: funkamongus Post Posted: Wed Mar 31, 2010 11:19 am

Are the right jets and needles in the right carb? They ARE side specific on the 920.. Did you remove MCV? Did you gain access to your mixture screws? I bought two kits, Ill go look up where I bought em and as much info as I can get, it was a good kit.

#3:   Author: funkamongus Post Posted: Wed Mar 31, 2010 11:23 am part number 18-2578 is the 1982 xv920J kit. With ALL the goodies. cost me about 30 to the door. I got two. So, 60ish for the both. They worked great, and the did good business with me. I can recommend them.

Its saying on the website that no part number was found with that number.. so, email them at . They were very good about communication, so it wont take long to get you hooked up.

#4:   Author: Xumi Post Posted: Wed Mar 31, 2010 5:18 pm

I'd guess it's the drilled jets too, especially if both plugs are sooty.

#5:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed Mar 31, 2010 6:18 pm

I am not sure if the right needle and jets are in the right carb. I put things back where they came out, the P.o might have mixed them up. I switched the pilot screws to the opposite carb and now it is running real rough but still running rich even with them turned all the way in to soft seat. The MCV is removed and the vacuum lines at the carb boots are capped. How can I tell if they are in the right carb?
Thanks Funk I am waiting a reply from SCI on the carb kits.

#6:   Author: Xumi Post Posted: Wed Mar 31, 2010 6:25 pm

Read the numbers on the jets. The smaller jet should be to the front - not sure about the needles (although I do know they are different).

The mix screws are not side specific, just jets and needles.

Not all the fuel for the idle circuit comes through the air/fuel mix screws. It's definitely possible to be rich even with them seated.

Another possibility would be the choke circuit, as it bypasses the air/fuel mix screws.

#7:   Author: funkamongus Post Posted: Wed Mar 31, 2010 6:27 pm

the man jet and the needle, and the pilots for that matter, all have numbers pressed in to the tops of them or on the side, in the case of the needle.. I dont know how good your eyes are,, I need some really good glasses to make out what numbers were on them until I got where I could see them plainly... theyr'e on there!! PS did you find the air passages in the frame and the elbows in the rear of the carb?? Blow out the frame,, I understand you can, if there is a problem with the filters in the elbows, cut them open, replace filter material, and rtv back together?? If you need to do that, let me know, I'll find the article, Im sure Im not explaining it right..

#8:  what mixture screw? Author: ghostdad Post Posted: Wed Mar 31, 2010 8:19 pm

funkamongus wrote (View Post): Are the right jets and needles in the right carb? They ARE side specific on the 920.. Did you remove MCV? Did you gain access to your mixture screws? I bought two kits, Ill go look up where I bought em and as much info as I can get, it was a good kit.

Where is this mixture screw? The only adjustable screw I have is the pilot jet on the bottom of the carb. I have heard reference to this but haven't been able to figure out where it is. A picture and or a good description would be helpfull. I have looked all over the carbs for cap that is blocking it but cannot locate it.

#9:   Author: funkamongus Post Posted: Wed Mar 31, 2010 8:32 pm
Yeah, the pilot on the bottom...

#10:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed Mar 31, 2010 9:17 pm

Thanks Funk, now i know we are talking about the same thing. Correct me if I am wrong here, I just checked the jets in the top of the carb under the float tube? I just watched a you-tube video on cleaning carbs on a 750. I believe the 750 and 920 are basicly the same right. Well in the video he said the smaller jet goes to the side and the large jet is in the middle. Is this correct? My carbs are wrong if this is correct. I will change them tomorrow and test to see if that helps.

#11:  Re: Carb jet kit question Author: ghostdad Post Posted: Thu Apr 01, 2010 5:08 pm

Is the rear cylinder the #1 cylinder?

#12:   Author: funkamongus Post Posted: Thu Apr 01, 2010 5:16 pm

yes on #1 cylinder,, and yes, main jet is in center and pilot (smaller one 41, is off to the side. Theres your problem!!

#13:  Re: Carb jet kit question Author: ghostdad Post Posted: Thu Apr 01, 2010 5:27 pm

Thanks Funk for the qick reply... Here is my current issue, I checked the needles and it appears that the P>O put them in the wrong carb. So I switched them and now it seems to only be running on the rear cyclinder, which is still running rich. Are the jets themselves side specific? If so then when I order new jets are they numbered accordingly?

#14:   Author: funkamongus Post Posted: Thu Apr 01, 2010 5:35 pm

yes and yes..the pilots will be 41s... in both.. the rear or #1 cyl, gets the Y25 needle and 126 main jet,, your #2 or front cyl gets, Y24 needle and 128 main. Your pilots will be about 2 and 1/2 out from soft seat to get you started... Once all is good and it will run, plan your next day out. Set Valve lash first, while engine is cold. Warm up engine really well and put it on stand with fan on motor.. Adjust mixture and sync carbs as per knowledge base article,
and You should be golden!!

#15:   Author: funkamongus Post Posted: Thu Apr 01, 2010 5:37 pm

A lot of folks still say to drill out the pilot jets, I would try what you got when you know its right, and see...

#16:  Re: Carb jet kit question Author: ghostdad Post Posted: Thu Apr 01, 2010 8:43 pm

The P.O said he drilled out the jets and I think that is the cause of my rich condition. I have new jet kits ordered ( thanks Funk for the link ), once I get those I am almost positive I can eliminate that problem.

Thanks for everyones help I will let you know the results once I receive the new jets and get them installed.


p.s. I must say I think I can keep up with the best of em, removing and installing the carbs now...LOL

#17:  Re: Carb jet kit question / update.. Author: ghostdad Post Posted: Sun Apr 25, 2010 10:29 am

Alright I finally had time to install the new jet kit, and the results are good!! Now I have a vacuum leak on the front cylinder, the intake boot is leaking. Looks like the P.O in his ultimate wisdom shoved a small screw driver or something similer through the side of it where the carbs mounts. So is there any way of repairing this at least temporarily so I can finish getting the carbs dialed in?
Anyone know of a good source for the intake boots? Thanks Funk for the link for the jet kits, S.C.I. is a good place to do business.

#18:   Author: funkamongus Post Posted: Sun Apr 25, 2010 10:53 am

Lots of folks "paint" the boots with 3m liquid electrical tape. If its really bad,, you can glue a section of tire tube over the whole thing. Or, If it were me. Id just try to find some new. Let me see if they're available new.. yes,, bout 70 bucks per.. find your part number,, yes they are side specific, put that part number into google.. Here, I found the boot,, its number 1 on the air cleaner parts page. Its the boot for the REAR cylinders carb.

part number is 10L-13586-01-00 . when put into google, it brings up a page where I compared and found this.

if you need the right one, do the same with this number.
10L-13596-01-00 (right carb boot)

#19:   Author: Xumi Post Posted: Mon Apr 26, 2010 2:56 am

Youch, that's a price!

Try this - $55 for a Pair, and shipping is reasonable too... less than half the price, and it's always much better to replace them as a pair, as you don't want to have the other one getting rubber rot in a few years from age.

That's about the lowest I've seen so far, including fleabay. About the best price anywhere for float needles/seats too (and I'm using a set of their float needles/seats, and they are to date, perfect).

#20:   Author: coalstoves Post Posted: Mon Apr 26, 2010 3:04 am

I dont order from places like that, a cheesy generic websight no address no phone and a hotmail email addy . They just might be fine but those are some red flags a savy internet shopper should look for.

Look up georgefix on ebay lots an lots of folks here buy from him and I've never noticed a complaint .

Last edited by coalstoves on Tue Apr 27, 2010 2:14 pm; edited 1 time in total

#21:   Author: Xumi Post Posted: Mon Apr 26, 2010 3:20 am

That's absolutely your prerogative, coalstoves, and I for one won't judge you for it.

But in fairness to the vendor in question:

I have used them before, and had no problems with them. They shipped on time, and the parts came in as they were supposed to, and have worked perfectly.

They charged exactly the correct amount to my credit card, and no issues with over or repeat or unknown charges (plus I have credit monitoring service, and no flags in the 6 months since I bought from them.

Also in their favor, is that their order page is SSL certified with a real cert provider (equifax)- I'm in the web development business, have helped businesses get SSL certified, and it's impossible to forge a verified SSL certificate.

Personally, I'll trade the cheap website for cheaper parts.

I have no favorites for vendors... I will go with any of them that will provide a good part at a good price, and ship it when they say they will.. At least for the order I placed with them, they met all 3 of those criteria.

Just my $.02 - Take it for what it's worth.


Correction - SSL certifications can be forged if someone has enough firepower to create an MD5 attack and some cash to buy some real SSL certs from older providers and attack them for several weeks to determine the CA key....- at least older ones that use MD5 encryption.

Equifax is Not one of the vulnerable, as they use SHA-2 encryption, which to date has not been cracked in the SSL market.

Sorry if I confused anyone.

#22:  Re: Carb jet kit question / Update Author: ghostdad Post Posted: Mon Apr 26, 2010 8:34 pm

Ok, I used 3M liquid electrical stuff to seal up the vacuum leaks on the boot. I sprayed carb cleaner all around both boots and have no indication of any leak but it doesn't come down to idle very quickly and it is back firing through the exhaust. What has me confused is that back firing through the exhaust is usually a sign of a rich condition. Right? But the plugs are firing good and if anything may be a bit lean.
Also the way it slowly comes back to idle isn't that usually a sign of a vacuum leak? I will be ordering new boots but trying to get things in tune but these contradicting signs have me at a loss. Anyone have any suggestions?

#23:   Author: funkamongus Post Posted: Mon Apr 26, 2010 8:52 pm

Well.. I would do a valve adustment, set my mix and do a sync on the carbs. Then, I would see where I was at. May be so out of sync that it sounds like a vac leak. we talked already about removal of you MCV right? Cap off the front two vac ports on the front carb holder. The rear carb holder has one port to the petcock, leave that.

#24:   Author: slowpoke Post Posted: Mon Apr 26, 2010 9:12 pm

Stupid question, but have you checked the routing of your throttle cable? It could be binding and causing the slow return to idle.

#25:  Re: Carb jet kit question Author: ghostdad Post Posted: Mon Apr 26, 2010 9:13 pm

Yes Funk the MCV is removed the valves are adjusted. I was thinking about checking the synch but ran out of motivation tonight, I will try that tomorrow. I had the carbs synched before but maybe with the vacuum leaks i had maybe it is way off now.

#26:   Author: funkamongus Post Posted: Mon Apr 26, 2010 9:25 pm

Could be. Could be the cable routing like Pokey says.. how is your breathing situation? The molded air lines going through the frame could be blown out, if you have a compressor, might have bugs in there,, there is a calm air inlet for each carb too, the little plastic elbow, check those for air flow, too.. I understand they can be cut open and the filter material replaced and glued back together. Make sure your mixture is good. Float level right. Air filter clean, make sure your battery is fully up to snuff, adding an additional ground wouldnt hurt, things get weird with a weird ground... Cant think of anything else, off the top of my head, that can act like a vac leak... Could be just like you said, you compensated for a vac leak with your sync settings,, now that you may have fixed the leak, the vac settings have changed..

#27:  Re: Carb jet kit question Author: ghostdad Post Posted: Mon Apr 26, 2010 10:40 pm

Ok, the throttle snaps back emidiatly, so that is not the issue, all the air tubes are clear and air flows freely, float level is set and fuel level is correct about 1 or 2 mm below the top of the bowl, air filter is good, battery is good, original ground is good but also added another ground and fastened it to the frame behind the battery box. So I think I have the basics covered, I will synch the carbs and try and adjust mixture tomorrow and see what I come up with. I'll keep you posted as to the results.
Thanks for all the suggestions and help..

#28:   Author: funkamongus Post Posted: Mon Apr 26, 2010 10:48 pm

RIGHT ON!! Cant be too far away then! Let us know!

#29:   Author: Xumi Post Posted: Tue Apr 27, 2010 12:52 am

Sounds like you're on the road to getting it fixed, ghost.

And lean running can definitely cause backfires and hunting idle - two of the most common symptoms, in fact. Backfires could be caused by lean (especially on deceleration or through the carbs) or by rich conditions.

#30:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed Apr 28, 2010 3:21 pm

Ok here are the current symptoms, while letting the bike sit and idle to warm it up for synching the idle will suddenly start to climb and it won't come back down. It does it on it's own without even touching the throttle, if I shut off it will start right back up and idle good for a few minutes and start to rev on it's own again. I checked for vacuum leaks using carb cleaner and get no idication of said leak. The carb synch is very close at idle and is at dead zero at 3 to 4K rpm's. At idle the the front carb is pulling slightly harder than the rear, the idle stop screw is missing on the rear carb so as soon as get a new screw/bolt for it it will solve that issue.

When the bike is idling it pops through the exhaust but if I unplug the vacuum port on the rear cylinder the popping stops. It will still start to rev on it's own but without popping. I have the mixture screw turned into about 1/2 turn from soft seat with out any difference in how it runs.

Is there something I missed in the carb to allow extra fuel to bypass the idle curcuit and cause what appears to be a rich condition?

#31:   Author: Xumi Post Posted: Wed Apr 28, 2010 3:36 pm

Definitely a Lean condition, unless you have a strong fuel smell from the exhaust... not rich. Floating/climbing idle is usually lean, and so is popping.

Most likely when you are pulling the vacuum line, you are killing that cylinder - the popping is most likely the only activity in that cylinder.

Put your idle/mix screws at 3 turns out from soft seat and see what happens.

#32:   Author: grazingazer Post Posted: Wed Apr 28, 2010 5:14 pm

check the o-rings on the pilot screws

#33:   Author: funkamongus Post Posted: Wed Apr 28, 2010 5:55 pm

and THAT is why GG is da man. I bet thats exactly what it is. I hope to know as much, one day, as he's forgotten. Right on, GG.

#34:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed Apr 28, 2010 8:24 pm

Xumi - it is a rich condition and strong smell of gas in exhaust. The popping has got to be because of a rich condition and when I unplug the vacuum line on the rear cylinder it leans it out enough to run decent. If I pull the vacuum cap on the front cylinder it dies probably because it is then too lean.

GG - the o-rings are brand new along with the pilot screw, they came with jet kit I bought. I started out with them set at 2.5 turns from soft seat and have tighten the the pilot screw on the rear cylinder so now it about a half turn out from soft seat. I will check them tomorrow to verify but would be surprised if they are bad already.

I pulled and checked the plugs - front is fine, the rear plug is black but not wet. (it is firing consistently)

#35:   Author: funkamongus Post Posted: Wed Apr 28, 2010 8:40 pm

Hmmmmm..... an enigma.....
lack of Air in??? air filter? calm air inlet?? intake manifolds?? hmm has anyone drilled the pilot jets? Air jets nice and clean inside the carbs?? Carb Diaphragm ok?

#36:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed Apr 28, 2010 8:55 pm

air filter is good, air inlets are clean, all passenges in the carb are clean - sparayed out with carb cleaner and compressed air, the intake manifold would only lean out the mixture if they were bad not cause a rich condition.. Right?
As far as the pilot jets being drilled - I don't know. Is there anyway to tell?

#37:   Author: funkamongus Post Posted: Wed Apr 28, 2010 9:14 pm

"Manifold..." unless something is plugging it up!!! HAHAHA Maybe a small cat or something stuck in your manifold!! Hmm. Did you check that it has the right jets and needles in the correct carb? (they are probably side specific) you installed your carb kits right?!?!
We'll get down to it,, it can only be so many things, right?!?!?!?

#38:   Author: funkamongus Post Posted: Wed Apr 28, 2010 9:14 pm

checked your float level?

#39:   Author: grazingazer Post Posted: Wed Apr 28, 2010 9:24 pm

i'm assuming that you're working with hitachi carbs and have set your float levels correctly and did not leave out the washer that goes around the main metering jet and checked the petcock vacuum line for the presence of gasoline...that might suggest that your trouble lies in having developed a weak spark [which can be caused by something as simple as a loose battery connection] why not stop pulling your hair and check for a hot blue or blue/white spark...lots of times spark issues immitate carburetor it's worth a look and it'll save you from becoming fixated...goes without saying make sure there's no fuel around when you test the spark

#40:   Author: Xumi Post Posted: Thu Apr 29, 2010 1:31 am

Ah - rich it is - sorry about that ... and if I'm covering things you've already tried - sorry there too, just want to make sure you've looked at all angles.

Four possibilities:

Too much fuel?
Too little air?
Not enough spark?
Fuel going through wrong path?

Too much fuel:
Check for drilled jets - look for drill scratches with magnifying glass, or with a set of hobby drill bits, finding the largest one that will fit down the hole, and the size of that bit.

Float height checked with clear tube = 1-2mm below carb/bowl flange.

Too Little air:
Have you tried with the air intake boots disconnected?

Fuel down wrong path:
Disconnect petcock vacuum lines, plug them (a screw will do), and put the petcock on prime. If problem is gone, then issue is with petcocks leaking fuel into vacuum line.

Choke circuit? If fuel is getting through there with choke off, will cause rich running.

As GG said, visually inspect for bright blue or white spark when grounded against engine, make sure carbs are dry.

#41:   Author: grazingazer Post Posted: Thu Apr 29, 2010 11:52 am

these bikes do not run well if at all with the air boots disconnected...disconnecting a boot can kill a running cylinder

#42:   Author: Xumi Post Posted: Thu Apr 29, 2010 2:29 pm

Good point, GG - I was thinking of both my other bikes, that will run a little lean, but isn't quite so picky.

#43:   Author: slowpoke Post Posted: Thu Apr 29, 2010 6:08 pm

I'm waiting to find out what it turns out to be. I have a friend of mine's little ninja 250 here that only has 400 miles on it doing the same thing, ran great even after sitting for 5 years in his sister's garage. But it all of the sudden started to run extreamly rich. I have removed the carbs but didn't touch a thing other the the float bowl scwers to remove the float bowls to check for bad floats, petcock doesn't leak, but it will foul out a set of plugs in minutes. When I put in new plugs it will start and run but the idle will climb to above 4000 and only come down for a second after reving it up. and when I shut it off it will not start again due to the plugs being fouled. I am at a loss with this thing.

Last edited by slowpoke on Sun May 02, 2010 6:53 am; edited 1 time in total

#44:  Re: Carb jet kit question Author: ghostdad Post Posted: Sat May 01, 2010 10:34 am

doh ..ok after taking a day off to clear my head. I rechecked everything and after scratching my head for a few minutes cause everything you guys told me to verify checked out good, ie; spark, air flow, float level etc. all good. Then I realized that I had never disassebled and cleaned the choke plunger. Yes I'm an idiot... Unfortunately that isn't the end of my problems, in the process of disassembly of the choke plunger. I had to put a lot of pressure on the wrench to remove the plunger and I tweaked the linkage that controls the carbs.

Now the bike runs a whole lot better but the throttle is stiff and doesn't return to it's stops all the time. Did I just ruin my carbs / linkage? I thought I had the linkage freed up while on the bench but as the bike warmed up the linkage began the bind up and the rear carbs won't automaticly return. Any suggestion?

I just want to say thanks to G.G, Funk, Xumi and everyone else who has had a hand in getting this far.. Thank You. Dave

#45:   Author: Xumi Post Posted: Sun May 02, 2010 4:15 am

Nice Job, Dave - glad to hear the mystery is solved at the very least. Your bike was starting to make me scratch my head too.

Oy - as far as linkage goes, that's a tough call - I know I've had issues similar in the past when I separated carbs and didn't route the linkage correctly on re-assembly.. But never dealt with a bent linkage before.

My best suggestion would be make sure that the linkage is as straight as you can get it and not rubbing against the throttle body or other various parts - get the carbs off the bike and really work the throttle by hand, and Feel for resistance, especially on return. A healthy set of carbs should Snap back to return when off the bike, since the cable resistance is essentially missing.

Also, check cable routing, lubrication, and cable resistance (try rolling on/off throttle with carbs removed - is it smooth and easy all the way through the throttle range in Both directions?)

#46:  Re: Carb jet kit question Author: ghostdad Post Posted: Wed May 05, 2010 8:31 pm

Alright I seem to have the sticky throttle solved. By removing the carbs and looseneing up the top screws and letting everything shift back into place. Now the throttles snap back freely and no longer stick..

Does anyone know the bolt size for the rear carb throttle stop? It was missing when I got the bike and I can't synch the carbs at idle without being able to adjust the rear carb.

One other question, is it possible that the headlight went out while just sitting there? Is there any way to check a headlight? What headlight do I need? And now all of a sudden my blinkers don't work, any suggestions?

Thanks again to all who helped me through my carb issues, your help was priceless.

#47:  Re: Carb jet kit question/ solved Author: coonj3 Post Posted: Mon Jul 05, 2010 11:02 pm

just a question on why remove the mcv valve ? i have the same issue with rich rear cylinder and a lot of back firring out of exhaust on deceleration . very good information on this topic. Tech Help Carb jet kit question (SOLVED)

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