trackin xv750

evening project. hopefully this works out alright.
 

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so this weekend I got all the wiring finished up, and got the solenoid in.. my brother and I decided it was time for a cruise down the road. I also am currently running the stock jetting in the front (122) and a 128 main in the rear (+6) due to the short length pipe in the rear.. have to say I was really happy to zip down the road. however.. I started giving it some gas, around half throttle and the bike fell flat on its face.. wondering if I need to continue to raise the jetting on that rear cylinder.
 
doing some looking around online and only seeing the hitachi main jets sold up to 134.. anyone know where I can get different sizes? does anything think ill need to go larger than 134? seems like a big jump from the stock for a shortened pipe and more open exhaust... then again.. im a total amateur at carbs..
 
well last night I pulled the carbs once again and I drilled out the rear cylinder with a number 53 drill bit, figured why not, whats the worse that can happen.. buttoned it all back up and down the road, still falling on its face! got back and the plug is still a chalky whiteish color, I attached pictures of both. the front is a bronzeish color which looks ok. so I spoke with rich last night and im basically going to pick up a #50, #47, #45 bits and start drilling. I have plenty of jets laying around now that ive become a collector of virago parts. guess we'll see..
 

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bit sizes I have to work with.. seems ridiculous, but this bike is ridiculous so why not.

#53 0.059 1.511 = 150 main (currently)
#52 0.064 1.613 = 160 main
#51 0.067 1.702 = 170 main
#50 0.070 1.778 = 180 main
 
Not sure if this will help you but I've found the following guide lines for jet sizes.
2 sizes up for pods.
2 sizes up for less restrictive muffler.
1 size up for every 8 inches of pipe taken off.
1 size up for every pipe split from the rest. (eg, 4 into 1 changed to 4 into 2 = 1 jet size)

Just a guide for starting.

Love the build btw.
 
MJPriceisright said:
doing some looking around online and only seeing the hitachi main jets sold up to 134.. anyone know where I can get different sizes? does anything think ill need to go larger than 134? seems like a big jump from the stock for a shortened pipe and more open exhaust... then again.. im a total amateur at carbs..

I'm always a bit reluctant to dive in on things like that ........."oh he must be a knowitall". I WAS about to throw my 2 pennarth in as it happens !

However ............................... without doubt the problem IS the major difference in primary pipe lengths.

Basically the velocity of the gasses in the front pipe are pulling the gasses along from the rear pipe and effectively the rear carb can't keep up ! That's putting it in very crude terms, obviously a bit more techie than that.

You CAN get away with a slight mis-match in lengths, and actually if the pipes were seperate there wouldn't be so much of a problem - or if the intake was common. On 4 bangers and V8s with a common inlet chamber for all 4 / 8 inlets - the fuel delivery is not so critical IF the exhaust primaries are of differing lengths - sometimes due to packaging it's unnavoidable.

I would suggest bringing the rear pipe up and over the clutch housing to join the front pipe closer to the front head. It will still look the biz [ maybe better ! ] and will reduce, if not solve the jetting problem.

Feel free to contact me anytime.
 
so to bring this thread up to date, I continued to up the main jet with zero success, bike actually started running worse as I got bigger and bigger.. so I have gone back to pretty much stock jetting.. 122 in the front, 128 in the rear (shorter exhaust pipe) and ive placed two washers under each needle. bike still falls on its face right directly at 50% throttle.. starting to think I have some type of electrical problem going on, its too consistent right at that point... Richard and I spoke on the phone and I need to get a good working battery in the bike, Ive just been using a small Suzuki motorcycle battery that is old, and have been jumping the bike with a jump box to get it started.. I also need to get some new plugs in there as well.. it feels like a fouled plug at that 50% throttle point.
 
beachcomber said:
You CAN get away with a slight mis-match in lengths, and actually if the pipes were seperate there wouldn't be so much of a problem - or if the intake was common. On 4 bangers and V8s with a common inlet chamber for all 4 / 8 inlets - the fuel delivery is not so critical IF the exhaust primaries are of differing lengths - sometimes due to packaging it's unnavoidable.

I know that MJ was concerned about this from the get go - but as the exhaust pipes *are* separate, he should be able to tune for same, no?
 
Rich Ard said:
I know that MJ was concerned about this from the get go - but as the exhaust pipes *are* separate, he should be able to tune for same, no?

NO Rich .........with a Siamese system effectively one pipe works off the other. IOW they interact.

There's no point getting all techie - simple explanation, imagine it is water running through the pipes. The front pipe has more volume and more velocity by the time the second pipe joins it.

The problem would be reduced if the two pipes were completely seperate.
 
I think we're arguing the same point, Beach - MJ has two completely separate exhaust pipes, rather than having gone 2-1. Neither the intake nor the exhaust are joined (in fact, he recently picked up a single carb manifold and decided not to use it as it might cause just such a problem).
 
i need to check the carbs are synced etc tomorrow. today i did however get my new battery in there, as well as some brand new ngk plugs to try and see if that helped.. well it didnt. it runs and idles so well up until half throttle, then cuts out.. so richard told me to try and let the bike sit in neutral, rev it up to half throttle when it starts to cut out, and pull a plug off to see which cylinder is cutting out, and it is definitely the back cylinder. pulled the plug wire while it was cutting out and no change when the wire came off... soooo having that said. i am thinking about getting the carbs off once again, and going threw them myself. the friend who sold them to me cleaned them, but how well? he said he cleaned them "decent" so that im sure doesnt mean he got into those air passageways with the wire or whatever.. so if the air passageway was clogged up, essentially that would refrain from opening the slide up any further than half throttle and thats why it could be cutting out? not enough air to lift the diaphragm up any further? thanks everyone for all the help.. god im so close, i cant wait to ride this bad boy.
 
Rich Ard said:
I think we're arguing the same point, Beach - MJ has two completely separate exhaust pipes, rather than having gone 2-1. Neither the intake nor the exhaust are joined (in fact, he recently picked up a single carb manifold and decided not to use it as it might cause just such a problem).

OOOOOOPPPPS - the sketch I saw way back was Siamese - no ? That'll teach me to keep up with the whole thread. However - disregarding the first part of my response - the second part is still valid
 
well I believe I have found the problem. last night after getting everything cleaned up for the last time.. the bike was still running like shit.. so we popped a test like on the bike, and I have great spark and good flow of light coming from the rear cylinder the whole time, but not the front. you can see breaks in the light on the test light here and there on the front cylinder, and when you rev the bike up, big big gaps in the light causing the bike to shut down. ive checked and double checked my wiring, tested both the coils, switched them completely to see if the problem follows the coils or wires, with no such luck. so once again, back to the TCI module troubles. been doing some reading about troubleshooting and symptoms, and seems pretty similar. keep in mind this is my second module, the first one wouldn't supply any spark to the rear cylinder. so im going to send out my first plastic style module for repair. nice that the repair guy is just over in Illinois, so should have it back mid week next week. so having that said, this should be the last time I have to post bitching about the running like shit symptoms im having.
 
Maritime said:
CDI/TCI etc. when the magic smoke goes, forget about it. Glad you found a repair guy close to home.

right on man, just tired of dealing with this thing, its almost july for Christ sake and I don't have a daily rider yet.. oh well, shipped the tci this morning and should have it back by Wednesday of next week if all goes well and smooth. also picked up a fleebay tail light today, should see that soon as well. all I need now is it finish the front brake, bodywork, and figure out my headlight setup.. oh and go get a license plate..
 

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LOL I know, I hate being without a bike, I went to do my tires on Wed and buggered the valve core on the back tube, said oh well I'll go to the dealer and get a tube tomorrow, no-one in 100 miles had a tube in stock, so I found a valve core repaire kit for 4.00 and I am riding today, but 3 days without a bike sucked. I can't imagine 3+ months or more.
 
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