Dynojet explanation please!

leakypetcock · Apr 18, 2013

So I recently bought a nice 1997 Triumph Trophy 3. It runs great, looks great and rides nice. The problem? The previous owner installed a set of "Oh my god what was that?" loud D&D pipes and a corresponding Dynojet kit. I ordered a set of stock pipes from Ebay to kill the dB level and pulled the carbs to lean it out to match. The factory jets (which he gave me) are 120 on the outside carbs and 125 on the center. The Dynojet install instructions call for 124's with aftermarket exhaust, 120's for stock exhaust and it also comes with a set of 116's in the kit. I put the 120's in but can't figure out why you would replace the factory jets with the same size and even smaller in the center carb to get more performance. The pipes haven't arrived yet so I haven't ridden the bike yet so I don't know how it's going to run. Should I go with the 120's? Install the 116's?
The kit also has needles, emulsion tubes and calls for some auxiliary slide lift holes which have all been installed.
Please someone explain what this kit is going to do for my bike!

ChromeSux · Apr 18, 2013

DJ jets numbers are not the same as stock numbers, for instance, a DJ 120, may be the same as a stock 125.

If you had two same number jets, 1 DJ, 1 stock, the DJ will have a slightly larger hole.
Somewhere i saw a chart that had the DJ to stock conversion.

anotherguy · Apr 19, 2013

As far as jet numbers what he said. What the jet kit will do for the bike (if tuned correctly) is smooth out the fuel curve,improve response and providing the fuel delivery was insufficient (rare) up top increase power. Take your time and tune from the bottom to the top,i.e. pilot jet to main. DynoJet kits tend to rely heavily on the needle for low-mid delivery so in rare occasions to get it clean from bottom to top you'll need to increase pilot a size and drop the needle a click.

Have fun.

scapegoat · Apr 19, 2013

Check the needles for groves for wear or stepping. DJ kits are notoriously crappy DAHIK as opposed to the coated stock quality needles. The kits typically tell installers to drill the hole in the center of the slide larger,usually 1/8 in size. I had a 97 myself and cant recall different size jets in the center carb. The bike was hugely affected by air box mods also. You'll find 2 snorkles and only one open. The one thats open I put a Uni filter sock on as a pre filter because the stocker is a PITA to get at.

Bronco638 · Apr 19, 2013

You might want to send a PM to inmate 'motolab' and point him in the direction of this thread. Derek can help you decipher the DJ jet sizes and might be able to assist in getting you back to stock (or a properly running set up).

wos · Apr 19, 2013

found this on another site, cant confirm the accuracy

Keihin* Dynojet* Mikuni
92 92 85
95 94 87.5
98 96 90
100 98 92.5
102 100 -
105 102 95
108 104 97.5
110 106 100
112 108 -
115 110 102.5
118 112 105
120 114 107.5
122 116 -
125 118 110
130 122 115
132 124 -
135 126 117.5
138 128 120
140 130 122.5
142 132 -
145 134 125
148 136 127.5
150 138 130
152 140 -
155 142 132.5
158 144 135
160 146 137.5
162 148 -
165 150 140
168 152 142.5
170 154 145
172 156 -
175 158 147.5
178 160 150
180 162 152.5
182 164 -
185 166 155
188 168 157.5
190 170 160
192 172 -
195 174 162.5
198 176 165
200 178 167.5
202 180 -
205 182 170
208 184 172.5
210 186 175
212 188 -
215 190 177.5
218 192 180
220 194 182.5
222 196 -
225 198 185
228 200 187.5

motolab · Apr 19, 2013

PM recieved.

Are you sure the main jets are not 125 on the outside and 120 in the center as original? In any case the sizes sound like the carbs are Mikuni BST36 rather than the later Keihin CVK36. Can you confirm?

Regards,

Derek

leakypetcock · Apr 19, 2013

Yes, they are Mikuni's. You are probably correct in the outside/inside sizes. One of them is scratched on the surface and I can't read what it says.
The bike ran great with the big 124's and obnoxious pipes but I want to quiet it down to a respectable sport-tourer and make it run right with the stock pipes. I fired it up after putting the 120's in and it seemed to have a crisp throttle but I haven't ridden it yet. This bike is so loud that I can't stand to ride it and I don't want to assault my neighbors with the noise.
Hopefully the stock mufflers will be here today. My intention is to put them on, take it for a ride and see how the butt-dyno feels. If it's good then I'll put a few miles on it, check the valve clearances and sync the carbs.
If not, let the tuning begin.

Beezer · Apr 19, 2013

heres a better copy of WOS's chart.... can't guarantee the accuracy but I know for sure the jets are different

 [FONT=&quot]Carb Jet Size Cross Reference:Keihin/DynoJet/Mikuni[/FONT][FONT=&quot] [/FONT]

[FONT=&quot] <hr style="color:#DDDDDD" align="center" noshade="" size="1" width="100%"> [/FONT]
[FONT=&quot]Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92-----------86.3
0.0360---- 95----------- 94-----------88.1
0.0370---- 97.5--------- 96-----------90.0
0.0380---- 100---------- 98-----------91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5 [/FONT]

motolab · Apr 19, 2013

leakypetcock said: ↑

Yes, they are Mikuni's.
Click to expand...

How many miles are there on the carburetors?

Regards,

Derek

leakypetcock · Apr 19, 2013

46,000 on the bike. Not sure how long the Dynojet has been in there. The carbs looked great when I pulled them off. Clean and clear.

motolab · Apr 19, 2013

leakypetcock said: ↑

46,000 on the bike. Not sure how long the Dynojet has been in there. The carbs looked great when I pulled them off. Clean and clear.
Click to expand...

The first thing I would recommend is to inspect the slide guides & slides. At 46K miles, the slide guides are likely to be completely worn out. See http://www.moto-lab.com/gallery/view?itemid=262, http://www.moto-lab.com/gallery/view?itemid=295, http://www.moto-lab.com/gallery/view?itemid=263, http://www.moto-lab.com/gallery/view?itemid=296, http://www.moto-lab.com/gallery/view?itemid=264 and http://www.moto-lab.com/gallery/view?itemid=297. I recommend replacing the slides if the slide lift hoes have been drilled, and/or if there is vertical grooving on the downstream side.

Regards,

Derek

leakypetcock · Apr 19, 2013

Thanks, hopefully it'll just run OK and I won't have to worry too much about that. Can you share a price on the parts?

Triumphrider · Apr 20, 2013

I have a 1995 Trophy 4 1200, a 95 Daytona Super 3, 95 Speed Triple and 1998 Tiger. I have a lot of experience with carb tuning. The first thing I would do if going to stock mufflers is get rid of the Dynojet kit, emulsion tubes, jets and needles, especially if you have all the stock items and don't plan to race your bike. Don't be concerned about the enlarged vacuum hole in the slides, they will not be an issue. The stock set up is pretty good with the exception of the primary jets being a tad too small (EPA lean). I used a number drill bit one size larger than what will go through the low speed jet by hand to enlarge the low speed jets by about .001". It will be a lot less cold natured on cold starts and run much better. Also set your air bleed screws 2.5 to 3 turns out. You can look up your model stock jet specs on BikeBandit.com web site OEM parts fiche to get a starting point. By the way, you can reduce the sound level of D&D cans by about 40% by installing nozzle restrictors made by Staintune for about $25.00 each.

Cheers, Steve

joexr · Apr 20, 2013

Jets R Us will have stock specs on your bike on their website and what jets are available. Again the drilled slides will be ok.I wouldn't drill your own jets if you've never done this or you'll end up buying new jets anyway. Even with stock pipes it'll still run better than stock with the jet kit setup for stock. I'd go this route , plus you've already got the parts and info. From the factory most bikes are too lean on the bottom so they meet emissions. Your jetkit is your freind , not the devil.

motolab · Apr 20, 2013

Triumphrider said: ↑

Don't be concerned about the enlarged vacuum hole in the slides, they will not be an issue.
Click to expand...

They will absolutely be an issue, as BST carbs have chronic slide guide and therefore emulsion tube wear problems, which in turn cause overly rich mixtures toward the lower end of the rpm range. The larger the lift hole area, the more rapid the wear.

I used a number drill bit one size larger than what will go through the low speed jet by hand to enlarge the low speed jets by about .001".It will be a lot less cold natured on cold starts and run much better.
Click to expand...

I don't recommend drilling jets. They are cheap, so why not just install some that are the right size? That way you can be sure what size they really are and there will be no confusion caused by stamped on sizes not being valid.

Also set your air bleed screws 2.5 to 3 turns out.
Click to expand...

BST36 carbs do not have air bleed screws.

You can look up your model stock jet specs on BikeBandit.com web site OEM parts fiche to get a starting point.
Click to expand...

But don't buy from them, as they don't have stock (meaning long delivery time) and their prices are very high.

By the way, you can reduce the sound level of D&D cans by about 40% by installing nozzle restrictors made by Staintune for about $25.00 each.
Click to expand...

That is sound advice.

Regards,

Derek

motolab · Apr 20, 2013

joexr said: ↑

Again the drilled slides will be ok.
Click to expand...

It's been well documented by myself and many others that they won't.

From the factory most bikes are too lean on the bottom so they meet emissions.
Click to expand...

True.

Your jetkit is your freind , not the devil.
Click to expand...

I would generally not choose a DynoJet kit if there was an option. A drawback with kit needles is that they are in most cases made out of stainless steel, which accelerates emulsion tube wear. In this case, it's not necessary as the stock needles are already adjustable and have a reasonable shape.

Regards,

Derek

joexr · Apr 20, 2013

The size of the vacuum holes has nothing to do with slide wear. And most jetkits are relabeled Dynojet kits anyway.

motolab · Apr 20, 2013

joexr said: ↑

The size of the vacuum holes has nothing to do with slide wear.
Click to expand...

Consider that the slide rises at the beginning of every intake event, and falls at the end of every intake event (i.e. once every 720°). If the lift hole area is increased, the slide's up and down excursion at every intake event will be greater (limited by the stops of course). Unfortunately, more slide travel at every intake event equals more wear.

And most jetkits are relabeled Dynojet kits anyway.
Click to expand...

Factory Pro Jet kits are most certainly not relabeled DynoJet kits.

Regards,

Derek

joexr · Apr 20, 2013

I thought maybe we were misunderstanding each other , but now I know we are not. The slides do NOT open and close with every intake stroke. Wow!

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