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#1:  TCI Rebuild (SOLVED) Author: 83500toy Post Posted: Sat May 29, 2010 5:33 pm

Ok I've had a fun past couple days trying to figure this out. The bike starts up fine normally. While i'm riding if I am below 4k the tach works but it putters along. Anything about 4k the tach drops to zero and I get very very very poor accel. From what I've read its doing the same thing as a bunch of peoples. Everything I have read said TCI so far. What I've done so far.

1. Checked all grounds
2. Cleaned all connectors made for sure had good connection by back probing the connectors and checking resistance.
3. Checked ignition coils. Replaced both spark wires because front had really high resistance.
4. Checked petcock and fuel. Both good.
5. Checked battery voltage-12.8

The only thing else I know to do is get or rebuild the TCI. If anyone knows of the parts I will need it would be great.

#2:   Author: grazingazer Post Posted: Sat May 29, 2010 5:50 pm

have you checked the resistance on the pickups...have you tried disconnecting the tach [could be shorting out]...have you checked the rear plug [# 1 cylinder for fouling]

#3:  Re: TCI Rebuild Author: 83500toy Post Posted: Sat May 29, 2010 6:18 pm

You mean the primary side of the coils? if so then Yes, No, Yes

The Tach shorting out wouldn't cause the bike to run irregular, at least I wouldn't think so by the wiring diagrams I have seen.
The plugs looked alright. Rear one was a bit heated but nothing past normal.

#4:   Author: grazingazer Post Posted: Sat May 29, 2010 6:45 pm

think again...the tach shorting out will ground the coil orange primary wire going to the #1 cylinder affectively killing the cylinder when it should fire...i try not to give bad information...the pickups send a voltage signal from their position around the fly wheel to the tci which signals it to open the ground on the primary ignition system and fire the plugs...if the shorting tach causes the ground to be permanent the plug on # 1 [the rear] cylinder will not fire [qed]

#5:  Re: TCI Rebuild Author: 83500toy Post Posted: Sat May 29, 2010 10:00 pm

That would be good if I thats where I was having problems. My front is where I'm having the back fire and everything from.

And how the the tach not working after 4k be a short? I would continuously not have a tach. I'm pretty sure 99% that that is not my problem. I maybe young but I'm surly not dumb. I will check it tomorrow to be 100% sure.
Thank you for the info though.

#6:   Author: grazingazer Post Posted: Sat May 29, 2010 10:20 pm

the needle position could be causing a short...the tach dropping to 0 means that you have lost the pulsing ground signal on the primary ground from the tci to the coil controlling the rear [#1] cylinder and read by the tachometer...a short in the tach might explain it...you have nothing to lose by disconnecting the tach sensor wire from the orange primary wire to check...it's not uncommon...nobody said you're dumb but you may not know as much as you think you do...if you don't want my help i'll stop giving it...just say so no problem...there are other things i could be doing and other people i could be trying to help

#7:   Author: club_c Post Posted: Sat May 29, 2010 11:38 pm

toyboy, you were asking for help. As graz says no one thinks you're dumb just because you're young, but we've been working on these old girls for a while now and have seen odd things pop up on 25+ year old electrics and carbs. You see graz's 12000+ posts? That's here, in this forum, on old Viragos. Just nod your head and say ok, and then check it. If that's not it, come back and we'll give you more to check. There are no shortcuts on diagnosis.

#8:   Author: jayvee43 Post Posted: Sun May 30, 2010 7:28 am

Club_c Says; There are no shortcuts on diagnosis.


Well said Club_C

#9:  Re: TCI Rebuild Author: 83500toy Post Posted: Sun May 30, 2010 10:38 am

Ok I disconnected the orange wire from the Tach and ran it and i'm still getting misfire from the FRONT cylinder. I happen to leave my graphing multimeter at school this weekend and my sh!tty little multimeter I have here won't cut it on the pickup.


O and just a little info from my past. I spent 3 years in the Navy being an Electronics tech specializing in soldering where I obtained my bachelor's degree in electronics engineering. I am currently enrolled in Wyo-tech where I have already completed the electronics side of the courses. I know what I'm doing (mostly)

But thank you gentlemen for your mocking.


Last edited by 83500toy on Mon May 31, 2010 12:48 am; edited 1 time in total

#10:   Author: grazingazer Post Posted: Sun May 30, 2010 11:03 am

you have not been mocked sir...you gave little if any information concerning your qualifications prior to this in your initial post...nor did you mention any backfiring until your third post...none of the information i gave you is incorrect...i hope it may help at some future time...if you don't have a manual i suggest that you get one...it will verify that the information that you have been given is true and correct...the tach signal emenates from the rear cylinder not the front...since you referenced the tach dropping to 0 that suggested a problem emanating from that source...backfiring through the carb may be a vacuum leak and not necessarily an electronics issue...backfiring through the exhaust may be a fuel supply issue and not necessarily an electronics issue...my qualifications include 40 + years as a professional internal combustion engine repair and diagnostic technician in the civilian world

#11:  Re: TCI Rebuild Author: eddiethetech Post Posted: Sun May 30, 2010 3:05 pm

Toy, first, thank you for your service.
Next, though you are posting in the 500 forum, and though your sig seems to indicate your bike, it is forum courtesy as well as a rule that sigs be included. You have your sig set up, so just check the box to include on all posts.
Regarding your problem, the TCI is split between spark control up to 3500 rpm and above 3500. If the problem is not right at 3500, the issue is most likely elsewhere. Even if it is right at 3500, it may be a false positive. Have you checked the float level for the offending cylinder? I know that fuel starvation shouldn't cause the tach to punk out, but again, not every indicator points to the root cause of a problem. Does the cylinder drop in every gear at the same point, and does it happen under both hard and gradual acceleration?
Finally, and I would say the most important thing; it seems that even with your qualifications this problem has you stumped, and there's nothing wrong or even unusual about such things. So since you're asking the board for assistance which is willingly provided, hence our existence, it is inappropriate to get in a pissing match with the guys who are trying to help you. There are millions of miles and hours of experience here, offered for free. With your background you ought to understand the propriety of demonstrating proper respect.

#12:  Re: TCI Rebuild Author: 83500toy Post Posted: Mon May 31, 2010 12:47 am

ok the bike putters and back fires from the front cylinder during all RPM ranges in any gear and is most notable during acceleration but also pops and back fires during decel. The front plug was a little wet (not oil soaked) but has not been firing at its proper spark, when I check it Friday. Which is why I changed the wires because the front cylinder wire had 88k ohms of resistance and the rear one had 4k ohms. That didn't help that much.

I'm not trying to say I know everything. I know there are very very smart people on these forums that have been around the bikes for years. I have read many pages because I hate asking questions that have already been answered. I hope the information provided above gives some insight into the problem.

#13:   Author: lance Post Posted: Mon May 31, 2010 1:20 am

http://www.youtube.com/watch?v=hvS2Xyt94so&feature=related

Similar sounding issues...
allthough not 'one cylinder' specific... (I don't think)
the Tacho did act strangely.
Turned out to be bad ignition switch ???
2 cnts spent..


Last edited by lance on Mon May 31, 2010 2:14 am; edited 1 time in total

#14:   Author: club_c Post Posted: Mon May 31, 2010 1:33 am

the tach picks up it's signal from the rear cylinder so something is not right there if the tach is dropping off.

The front cylinder definately sounds carb related, as in 'lean'. That will indicate a vacuum/air leak. Have you confirmed no vac leaks at the intake of the front carb? Have you had the carbs apart?

#15:   Author: grazingazer Post Posted: Mon May 31, 2010 8:40 am

it could well be that you have a gas fouled [due to the previous high resistance in the wire] plug that is breaking down under compression conditions...a fouling plug can and will present the symptoms that you are experiencing...i'd try changing to a platinum tip [requires less voltage] resistor spark plug...i use autolite ap63 with great success...please disregard without rancor if you have already swapped plugs
but todays gasoline additives can leave deposits on plugs that even beadblasting can't remove and internal shorts in the plugs can exist and not be visible without proper diagnostic equipment

#16:  Re: TCI Rebuild Author: 83500toy Post Posted: Mon May 31, 2010 11:27 am

When I broke the bike down while I was painting it i checked the carbs to see how clean they were. Both seemed really clean. I did not pull them off though. I have checked the petcock on prime and it doesn't affect the performance.

I can go check for vac leaks. And i'll check the wires running to and the ignition switch itself. Seems odd but why not haha.

#17:   Author: grazingazer Post Posted: Mon May 31, 2010 11:35 am

another good test would be to swap the front plug with the rear see if the rear starts backfiring...that way you don't buy a plug unless you need it

#18:  Re: TCI Rebuild Author: 83500toy Post Posted: Mon May 31, 2010 12:12 pm

I just found it! Its the ignition switch. I took it off and jumped the wires to together and started the bike. No puttering no back firing and the tach is acting fine. I'm going to replace that and hopefully that is the end of things!

Thank you Lance for your 2 cents. Money well spent!

#19:  Re: TCI Rebuild Author: eddiethetech Post Posted: Mon May 31, 2010 2:22 pm

Congrats, it's good to hear you solved your problem. Final step is to edit your first post and add (SOLVED) to the thread title.

#20:   Author: club_c Post Posted: Mon May 31, 2010 5:01 pm

You may be able to disassemble/repair the ign switch. The 920's came apart...
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