Manky Monkey Motors

hi all,as the time on my virago 750 trike project is approaching the point when i need to be thinking a head on how to modify my exhaust system to fit back on once the rear frame is bolted in place,i would appreciate any input and advice on the subject of carb rejeting, as a total numb Jockey when it comes to carbs  they are something i tend to avoid messing with for fear of not correctly identifying a prob with them in the first place, then tinkering and making the prob worse.    there is proable lots of questions i could ask hear but will try to keep what i would like to know as Short as possible, 1/ when would i need to rejet the carbs, 2/  is it a easy procedure, as it stands at the moment modifying the exhaust system  to fit would not be to difficult and would only need very slight modifying but this would just be the easy way round it for me, ideally i would like to change the compleat system and build my own ,can i do this with out having to rejet the carbs, on the subject of the exhaust system its self is the collector box just simple a baffle or doz this take a part in the flow of gasses out of the system,can i do away with it.     all help is much apriciated cheers guys zak

i ran a kawasaki vn 750 twin without the collecter box and apart from a slight flat spot after decelarating it ran great.

hi trev,your input is much appreciated thank you. zak

Hi, I would suggest you make the modifications you need, IE, airbox and exhaust etc and see how it goes. If you find its running too rich or, more likely too lean then the fun starts. When you get to this point and you have it running post any running problems and I will try to talk you through the setup procedure. Its really not to hard so long as you do things in the correct order. We will cross that bridge if and when required.
Cheers
Andy

hi andy thank you for that

if your just going to modify the exhaust and do away with the collecter box then a stage 1 dynojet kit will eliminate any problems. but when fitting the kit be very careful drilling the carb slides as alot of those viragos were made of plastic ;)

hi toad, thank you for that info its much appreciated. zak

Ive got a non standard exhaust system on my vmax and it did not require any rejetting.

Dont be too worried about the carbs... they may seem really complicated but theres nothing to them really, ive stripped down my carbs twice now, I do one carb at a time (4 in total) as long as you take your time and note where everything goes you wont have a problem, can even take them apart without upsetting the balancing screws, only the mixture screw if it needs to be removed has to be put back the right amount of turns , but thats easy enough as before taking it out, you screw it in completely nothing how many half turns it took, so from being fully in you know how many half turns to undo it.  Not had a problem with them, I just like to clean and polish them etc while trike is off the road.

So personally I wouldnt bother rejetting until you have run it with the new exhaust, if it runs ok and plugs look ok then you saved yourself some time and hassle.

hi vt, thank you for that input I'm starting to feel a lot more confident in going for a total modification of the system,i think my main reason for this is that as you can see in the pic hear of the bike before i started to trike it, and for any one not familiar with the virago system,both pipes run down the same side and as my main rails for my rear frame are coming down the outside of the frame as i am not coming off the swing arm (unless i change my mind again) the top pipe will have to go any way to be able to run the o/s rail from the the mounting point just shown above the top pipe, by being able to  modifying the system Will then allow me to be able to camouflage the box secsion that the rails are  made of n/s and o/s to make the trike more appealing to the eye when the trike is finished. all the best zak

Morning , the exhaust on mines been modified in as much as the collector box was removed , the run of the pipes is still the same though and it ran ok without rejetting . Mine had a stage 1 dyno kit put in to try and cure running problems I've got ( the rear cylinder cuts out at about 3500rpm'ish , it spent about 6 weeks in a garage at the begining of the year and they could'nt cure it ( they only worked on it when they had  spare time though   :-\ ) ... ) .

  ..  Hagar  ..

hi there hagar,i must say i do like the look of your rear frame,and the pipes look good to,i could do with similar pipes and have one each side and mount them to hide the out side rails just to make it more appealing to the eye,glad to hear you was able to do away with the collector box and it still ran ok, all this info from other members makes it a lot easy to make decisions on which way to go with it,so thank you for your input and the pic of your own set up, it is very much appreciated.all the best zak

hi hager. i agree with zak i like the look of your rear end of the trike. one thing though you might want to check on that hand brake position. i was told that you should be able to operate it whilst sitting on the trike

Evening , the end pipes are just cheapy universal bolt ons ( they've got baffles in but you would'nt think so if you heard it  ;D  , I've found a very understanding MOT man ) . This is an old picture .. the trike now sports a disc conversion and the handbrake is now on the left and reachable from a sitting position , not sure when the the "old girl "  was converted but when I got her the hand brake was only on one rear wheel and she had just passed an mot ...  ( never take an mot as proof of build quality , I had to have the rear end stripped and re-welded , the original welder was a crap welder but was an expert with filler and paint  ....  :(  ....  ) .

  ..  Hagar  .. 

evening hagar,it would be nice to see a pic of her as she is now do you have any on hear,do you know what the diameter of tube was used on the rear frame.cheers zak

If you`re unfortunate enough to have Hitachi Carbs then you can`t get a Dyno Jet Kit for them, some later models have Mikuni`s and you can get Dyno kits ok. I`ve only found one supplier of replacement jets for Hitachi and they`re in the states and charge an absolute fortune to ship 2 main jets about the same as the cost of the jets in the first place.
Hagar: your running problem is most probably the cdi box. Does the rev counter play around when the rear cylinder misfires?? There is a man in the states that re cons them for $99 which is better than £350 for a replacement.

hi cabman77,  thanks for your info, being the later model i am fortunate to have the mikuni bst40s, but the mikuni and hitachi,s did appear through out the range of viragos at diffrent years, but well pointed out cabman77

Evening , my old girls got Hitachi Carbs and I picked up a dyno kit for it off ebay from the states for about $40 .


Yep the rev counter dies till you ease off the throttle ... then she picks up and the rev counter kicks in again , I've tried a second hand cdi box ( from an alledged running bike ) and there was no change in the running , when she was in the garage the guy put the original one back on as he said it seemed to run a bit better .

cheers  ..  Hagar  ..   

hi there hagar,well its nice to know that these parts can be found, as I'm a little out of my comfort zone when it comes to the technical side of the carbs can any one tell me exactly how the dynojet kits work and what it doz i think when and if it comes to modifying my exhaust system and i get any probs with the ruining of the trike and a dynojet kit is going to be the answer it would be great to under stand how the kit works for future reference. cheers lads

Evening , no idea how they work but heres a link to the US dynojet site ....

http://www.dynojet.com/jetkits/motorcycle/yamaha.aspx

these are the same fitting instructions I got with my kit  ... ( did'nt pay $85 for my kit though ..   ;D  )

http://www.dynojet.com/pdf/4114.pdf

The only thing I noticed was the throttle response , it cut down on throttle lag ( the power comes on from the 1st mm of throttle twist ) ,  ... made the first couple of times in traffic interesting ...  ;D

..  Hagar  ..

good morning hagar, thank you again for your info, the only price i have found over hear is £80.83 from (tts performance parts) don't know if that's an average price or not as i haven't shopped around yet.  all the best zak

http://homepage.mac.com/ddenowh/TCI/index.html    take a look at this Hagar. Until I saw this I was convinced a CDI unit would either work or it wouldn`t, how wrong was I???? I got lucky and picked one up at an autojumble for a fiver and it worked fine.

Sorry for sidetracking this thread Zakboy

no prob cabman77 your very welcome.

I wonder iof that's just a Virago problem or if it could apply to other bikes?  The lad who bought my Superdream is having similar problems and has just stripped the carbs for the umpteenth time.

hi bikergran thanks for popping in, i think it is a problem that may or may not develop on any bike when you change the origanal exhaust system to a modified system, i have not modified mine as yet but may have to,so its not a problem for me yet,if i do modify it i wont know until i run the bike if its going to be a prob or not, if i do have a prop then the dynojet kit appears to be the answer .all the best zak

Sorry Zak, I was referring to Cabman's post where he said

After looking into this CDI/TCI (there is a difference but we all know what I mean????) problem I would say Bobbi that it could happen to any bike with electronic ignition. It`s basically a problem with the components and standard of soldering. Most standard units use components rated at 85 degrees C and with constant heating up and cooling down the solder gives up the ghost. My bike started this problem after being laid up for a while and a friend bought a Virago that had been stored for a few years and after a week his did the same.

Hagar take a look at this    http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280593638308&ssPageName=ADME:B:SS:GB:1123#vi-desc