Dynojet kit installation

[Anonymous]

It was recommended to me awhile back on this forum to get a Dynojet kit to straighten out the carb glitch on my recently purchased GS1100E. My bike has a 4 into 1 exhaust system of unknown brand and it had a bad mid range sputter and miss which I attributed to the exhaust being changed without the carb being re jetted.

I received the proper kit from Dynojet and when I started to install it I noticed the stock airbox plenum was cracked and leaking and the spring that holds the filter in place was broken and the filter was just kind of rattling around. I decided to replace it with pods. I ordered a set of pod filters, not K&N, some other brand that was cheap. I decided to go with the instuctions for a stage 3 kit since I was using the pods and running a "high performance" 4 into 1 exhaust. I installed the 138 main jets, which is what the instructions called for, and set up the dynojet needles with the clip in the middle position, as per dynojet's instructions.

Fired the bike up and it would barely run above an idle. It seems the "high performance" exhaust wasn't so high performance after all. I pulled the baffle and it was obvious why, it was extremely restricted, I have seen lawn mower mufflers with more flow capacity. Out came the cutting torch and welder and I made a baffle out of a 10 inch piece of 2' O.D. (1 7/8" I.D.) exhaust pipe from the auto parts store. This worked much better, the bike breathes much better and actually seems quieter. But it still had a major mid range problem and at full throttle it would just flatten out and start missing.

Pulled the carbs off again and replaced the mains with the leaner 132s from the kit. This helped but not much. I pulled the carbs again and moved the clip down one notch on the needle in order to richen up the midrange. Again, this helped. I knew I was still too lean on the midrange but I wasn't certain which way to go on the mains. I put a piece of duct tape on each filter in order to block off about a quarter or third of the airflow. It ran worse at full throttle and high rpms, indicating that the mains were still too big.

The first rule when tinkering with carburretors is to only change one thing at a time. But I was getting tired of pulling the carbs so I decided to take a chance. I raised the needles another notch to richen up the mid range and replaced the main jets with the leaner stage 1 114s. Bingo! It now pulls smoothly from idle to wide open without a glitch.

The dynojet kits do work but they still take some experimenting sometimes to get things right.

[Detman101]

Wow, nice write up.
Thank you. This will help others greatly.
Wish I had the opportunity to see this when I was installing mine.

Dm of mD

[Anonymous]

I have a 83 1100E with a Supertrapp 4 into 1, K&N pods and a Dynojet jet kit in it and ended up using the DJ138 mains. It pulls great up top but I think it's still might be on the lean side of things. I think the DJ114 mains supply less fuel that the stock (110 or 112.5 Mikunis) jets do so I'm surprised with pods it's running well at full throttle. Have you had it wide open yet? I had to raise my needles to the 2nd highest position and add a shim under the clip to get my mid range sorted out. I also have my a/f screws turned 4 turns out and still find the bottom end a little on the lean side. One of these days I'll get around to trying a larger pilot jet to see if that helps some. Although it's running pretty much near perfect right now, it's still quite slow to warm up on the cold days.

[Anonymous]

I was also surprised that the richer mains weren't needed. The 138s, or even the 132s, were WAY too rich. I suspect that the exhaust system I am using isn't all that good. Yes, I have had it at full throttle, over 100 mph in 4th gear at which point a high speed weave set in that is a little un nerving.

My needles also ended up in the second highest position without the spacer, if I go back into the carbs I will try them with the spacer under them, I think my midrange is probably still a little lean although it runs well.

I still need to tinker with the air/fuel mixture screws.

[Keith Winter]

Great stuff on this subject,good to know. I have never bought a Dynojet kit(yet) but I do know that jetting a carb is affected by how high above sea level (14.7psi) you are running the bike at. Is there nothing in the kit about this?? I rejetted my bike and because I live 4000ft above sea level, but my rideing will sometimes take me down to sea level, I am a little rich at home but just right at sea level. The difference for me is about 2lbs per square inch in air pressure, weather dependent of course. I'm not sure but it might have some bearing on the settings.

[Mr. Jiggles]

I think that the bottom line is the color of your plugs. You don't want it running too lean or risk burning up your valves.

[Keith Winter]

The color of your plugs is the final word on what your F/a mix is that's for sure. I was just wondering if in the kit it had any data about the height above sea level thing. Every book I own, and I have quite a bunch of em, both 2 cycle and 4cycle performance for both street and raceing all have data, graphs, calculations ect, ect, on jet sizing and barometric pressure seem's to play an important role as a starting point, combined with the other mod's that the engine has as well. I'm probably boreing everyone, but I was just curious if these jet kit's had anything in there about it. It's not a whole lot of fun removing these carb's over and over again to make jet changes and with the amount this topic comes up if it saved some trial and error time it might be worth even having a page or section devoted to the subject. We have one on stators, maybe we could have one on jetting as well?

[Mikael]

Hi Guys !

I installed a Dynojet stage 3 on my GS1150 with a 4-1 pipe and pods.

I followed the Dynojet recommendation as I set the idle screws 2,5 turns out and
the clips in third groove on the needles. However, I left the DM175 main jets in the
box, in favour of size 140 standard Mikuni jets. The bike ran quite good with this
combination, although there was some hesitation at part time throttle. WOT was ok.
The plugs did however indicate a rich conditions.

So, I lowered the needles 1/2-groove and changed to 135 mains jet. I was quite
surprised to find out that part throttle hesitation problem got much worse, and WOT
was also a bit stumbling.

So, carbs off again. I have now changed back to 140 mains and I have raised the
needles one full groove, (=1/2-groove over first setting). I have not done any test
driving yet, due to bad weather, but I did start her up and I found the throttle respons
to be very, very nice.

All things considered, maybe these carbs need to be set on the rich side to work out
with pods and a pipe. Actually richer than the plugs indicate. Or ?

/ Mikael

[Detman101]

I don't know michael....dynojet has issues.
I have an 81 GS750L with pods and MAC 4into1 pipe and their settings are WAY too rich!

I am using DJ132 mains and I have my needles on the #4 Groove from the top. The darn thing runs great at mid-range and WOT but I can't set the idle mixture screws. The dynojet recommendations of 4 turns out is WAY too much. Instant flood and smoke coming out the exhaust.
I have my screws set at 1.25 turns out and it's still rich smelling at idle.
Plus the #2 cylinder runs rich at idle no matter what I do. Even if I turn the screw for it all the way in (then it runs lean at anything else).

All in all, from my horrible experience I don't think dynojet knows what they are recommending or doing. Following their kits instructions I get about 9 miles to the gallon/25 miles to the tank and wind up smelling like gas everyday.

In another month I'm looking into another jet kit from a different manufacturer if possible.


Dm of mD

[Mikael]

I so totally agree.

From my experience the recommendation from Dynojet is way too rich. That is
why I tossed the DM175?s, (which would equal approx. 164 in Mikuni jets),
for the 140 mains. When I think about it Dynojet recommends 3,5-4,0 turns
out on the idel mixture screws, not 2,5 as I said. (I was wrong, sorry.)

No, what I was speculating about in my previous message, is that plug reading
might actually misguide you in some cases. Plugs said go leaner, and testing said
for me to enrichen the fuel delivery.

/ Mikael

[Detman101]

Yeah, see that is the same reason I can't figure out how to set my idle mixture screws. The plugs show rich but all the symptoms show that I'm lean!?!?!

I don't know how the hell the pros read these things. I think I need to jet get an exhaust gas analyzer or something and do it that way.
All this plug reading and crap is for the birds.



Dm of mD

[Keith Winter]

Put the carbs on take em off put em on take em off, I did the same thing but at least it's less painfull with the pod filter's. I could be wrong, but does'nt Dynojet have stage 1, 2, and 3 kit's? I thought stage 1 was for stock bike(pipe's, aircleaner, ect) stage 2 is for pod's and pipe's and stage 3 is for bike's with mod's such as cam's, head's, compression and other engine mod's. If you got the stage 3 kit but put it into a stage 2 bike would'nt the direction's be wrong?? If you where jetting your bike for mod's that are not there, I don't know if it would run very good.
Here's a thought about the #2 cylinder, and it's only a thought, but is #2 carb the one that the vacuum come's from for your fuel valve? Maybe if you know that the float height, pilot screw, idle air mix screw, carb sync, and everything else is ok, I would turn the fuel valve to prime, disconnect the vacuum line, plug it with a bolt or something and then try the idle mix adjustments again, maybe it could be that,maybe.

[Detman101]

Doesn't apply to me sadly.
My #2 vacuum port is plugged off. I have a pingle valve.
Simple on and off...no vacuum diaphragm to worry about hehe.

What I capped it off with was one of those little rubber caps you put on the ends of bolts. Maybe I can lean out the #2 cylinder by poking a few holes in it or something. Cause originally didn't the #2 cylinder pull air in through that opening? Cause when the first diaphragm on my stock petcock went kablooey it sure as hell sucked in fuel from that hole.

Dm of mD

[Keith Winter]

I would have to go out and look at my bike but I'm pretty sure it is #2 carb that supply's the vacuum for the fuel valve. And if everything is working right in the valve it stays a vacuum so long as the bike is running. I don't think it would suck air, that would then be a leak, but it could suck gas if the diaphram had a hole or tear in it. But you have fixed that problem already. I don't think pokeing a hole in the rubber cap is to good an idea as you would then have a vacuum leak. There is one other thing, though I'm sure I'm wrong, is both your float bowl vent tubes clear? Those vents are to keep atmospheric pressure equal inside the bowl to that outside the bowl thereby allowing correct flow of fuel in and up the main jet tube, I'm not good at explaining things but thats close to what happens anyway! If that's ok I'd have another look at float level.

[Detman101]

Yep, they're clear. I have a stage-3 kit in my carbs so there are no hoses on my carb vents. They point down/forward and have no hoses on them as per the dynojet instructions.


Dm of mD