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dynojet kit?

  • Thread starter Thread starter thrashin88
  • Start date Start date
T

thrashin88

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hey everyone, i got a 1980 gs 750 that was chopped into a hardtail and the stock airbox wont fit anymore so i have to run pods. it also had the stock exhaust chopped off and straight pipes welded on. so basically i was gonna order the dynajet stage 3 kit today and i was just wondering how hard it is to install yourself. im pretty good at mechanical things and i know where all the jets/needles are in the carbs but i dont wanna get in over my head and ive heard if i dont get the kit ill be in for a rough ride trying to get the thing running again. also will i run into problems with backpressure with the straight pipes? ive heard you can get baffles that pound in but i dont know much about exhaust stuff. any help??
 
A rejet is simple. The hard part is getting the right one. From what you've mentioned...a stage 3 should be about right.

On a side note: When things are hacked up by a PO or someone else, getting the exact correct jetting may be difficult as there are no specific specs for jetting a hacked exhaust and pod combo. You may need to get a good feel of the bike and play with plug chops to get it dialed in correctly.
 
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Get the Dynojet ket
Install the biggest main jet in the kit
Tap in the main air jet corrector
Drill the slide
Put the e-clip on the new needle at three notches from the bottom. You may have to go up to four up but first start rich and work your way down.

Before I'd do any of this though I'd adjust the valves, split all the carb bodies, dip them and install new o-rings in the carbs.

If you don't feel confortable doing all this I will do it for you.
 
i can do that, the only thing im unsure of is the valve adjustments if anyone knows where a how to page is?? i have a manual for a 79 gs850 or something like that, im sure theyre similar enough to figure it out. anyways, im gonna order the dynojet stage 3 kit today and we'll see how it goes. i do have 2 questions though.

1. will i need to do a carb sync after installing the kit or not (not much of a carb expert as you can tell). if not, is there anything im gonna need to do to get it running right or should it be good with the kit and some fine tuning?

2. what do i do with the hoses? as of now theres the 2 vent hoses inbetween carbs 1and2 and 3and4, theres the fuel and skinny vaccum line that go into the petcock, and theres 1 hose coming from the top of the engine. i got the bike in parts and its not easy figuring out what goes where when i wasnt the one who took it apart...

also where can i get o-rings? is that something a shop around town would sell or would i have to order em?

thanks again for the help
 
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You can use Number drill to go up incrementally in jet sizes. The only problem is once you drill, you can't go back.

http://www.affordablegokarts.com/Drilling Main Jets.php

There is a good reference list if you scroll down between the size of number drill and jet sizes.


JET SIZE MM INCHES NUMBERED DRILL BIT JET SIZE WHEN DRILLED
#66 .66mm .02598" #71
#68 .68mm .02677"
#70 .70mm .02756" #70 @ .0280" 71.12 jet
#72 .72mm .02835" #69 @ .0292" 74.2 jet
#79 .79mm .0312" 1/32" @ .0312" 79.2 jet
#80 .80mm .03150" #68 @ .0310" 78.7 jet
#83 .83mm .03268" #66 @ .033" 83.8 jet
#89 .89mm .035" #65 @ .035" 89 jet
#91.5 .915mm .036" #64 @ .036" 91.5 jet
#96.5 .965mm .038" #62 @ .038" 96.5 jet
#101.5 1.015mm .040" #60 101.5 jet
#105 1.05mm .0415" #59 @ 1.06mm 106 jet
#110 1.10mm .043" #57 @ 1.11mm 111 jet
#115 1.15mm .0455"
#120 1.20mm .047" #56 @ 1.19mm 119 jet
#125 1.25mm .049"
#130 1.30mm .051" #55 @ 1.33mm 133 jet
#135 1.35mm .053"
#140 1.40mm .055" #54 @ 1.40mm 140 jet
 
Have you not gotten your welcome kit from BikeCliff yet? His page has howto's on valve adjustment - and all sorts of other useful things!

http://members.dslextreme.com/users/bikecliff/

You can get o-rings from Robert Barr:

http://www.cycleorings.com

Don't forget the O-rings for your intakes, if it needs them! Sounds like your bike has seen some pretty major modifications. Are you sure the carbs are stock?

Plus you'll need float bowl gaskets and pilot plugs. I got those from z1enterprises.com myself. Not sure if your bike is shim adjust for the valves or if you're lucky enough to have adjusters. If it's the former z1 also has pretty good prices on shims, and you can pick up a shim tool if you don't already have one for $15. Of course you'll need some good feeler gauges, and a metric micrometer or digital caliper is awfully handy for those shims where the printed size has rubbed off.

BikeCliff's site I think also has a little nugget on the vent hoses.
 
An '80 750 doesn't have intake gasket o-rings, just rubber boots between the carbs and engine. These should be nice and squishy with no cracks.
And you also have tappet valve adjusters. Easy to do. Here's Cliff's site.....don't forget the valve cover gasket. 16 valve 750. Wait until you get the carbs apart to see what you need.:)

http://members.dslextreme.com/users/bikecliff/
 
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