XJ11 stock carb vs Dynojet stage 1

[KA1J]

I finally completed my experiment. Well, as completed as any thing ever comes close to getting when it comes to anything mechanical. I rebuilt the carbs in my XJ11 as one of the first things on my to do list. The PO had really messed up this bike and I had many hundreds of hours that were required to undo and repair his damages (including needing new rings & head work). But this post relates to carbs not my rant on the PO...

I rebuilt my original XJ11 carbs replacing the float valve sets, the throttle shaft seals, prolonged carb dipping and extensive squirting carb cleaner through all passageways before and after carb dipping in NAPA dip. Replaced the O rings on the pilot adjustment and made a tool to align the carbs up perfectly when re-attaching the rails. New gaskets and in this carb bank I also installed the Dynojet stage 1 kit. The idea was to replace the throttle shaft seals and all other rubber. I did not replace the diaphragms as they looked to be in as new condition. I made sure the slides dropped freely and polished the inside of the tube to assure as-new operation and cleaned and polished the enrichment plunger/circuit.

The 2nd set of carbs also came from an XJ11 and with these, I did the same replacements and cleaning/polishing as described above with the exception that I bought new stock value Mikuni jets (A PO had upped the main jets from stock #112.5 to #115) - I ordered all stock values so the new mains were #112.5 - I ordered new ones because I've seen first hand how badly carbs work when some PO or PO's goon gets into them and ovals/enlarges things.

I've always run the dynojet carbs and that's what I'm familiar with & never been on another XJ11 and always wondered how well the bike works with stock carbs. My best MPG with the Dynojet kit carbs has been 34 US MPG and the bike is always ready to go at the slightest touch of the throttle. (I'm preaching to the choir here as we all have XS11 or XJ11 bikes and we all know how well they run). My hope was to get maybe better MPG and not see any difference in power loss.

I carbtuned and colortuned with the "new" stock carbs till everything was to me, perfect and I replaced the caps, hooked up the vacuum lines and seated the tank around 11PM to take it out for a operational & MPG check. I took a 40 mile trip on I-95 holding around 65 MPH and noticed some sense of surging and a loss of low end drivability but when on the highway it seemed better I gassed up and found I got 35 MPG. What was missing was the immediate raw power I had before. Got back home and was disappointed in that it didn't respond as I expected and all that work for 1 MPG bothered me.

Next morning I was preparing to put the dynojet carbs back in and noticed the fuel line to carbs 3&4 was kinked badly and how any fuel got through is a mystery. I'd done this in the garage and missed it in the low light. So now to take the bike for another test but just to be sure, I re-checked the carb & colortune. All was fine as I'd done them with the tank elevated and it was seating the tank afterward that had kinked the fuel line. Markedly better performance... Idled perfectly, enrichment working perfectly, not the same immediate response to the throttle and it was a bit more subdued but not much more, just enough for me to notice it didn't have the same acceleration. Not that there is a problem with the acceleration with the stock carbs but the low, mid and upper range response is snappier with the dynojets.

So yesterday I took it on a 100 mile ride to Boston. I stayed between 65-70 and gave it a WOT a few times when I was surrounded by M*******s and when I checked the MPG, I got 40.6 MPG. With the Dyhnojet carbs on the same ride under the same conditions I would get between 32-33; so 7 MPG difference.

Bottom line is the stock and completely rebuilt carbs give me markedly better MPG. I feel like I have lost some horsepower; not a lot and nothing that will matter to me in day to day driving. I will miss the low and mid range immediate jump I got at the least turn of the throttle and rarely did I WOT in the upper RPMs so the loss at the upper end would perhaps mean more to someone else.

I do have a home made K&N filter in it and will keep an eye on the plugs to be sure it's not running too lean but the plug check after 100 miles of steady driving looked great, slightly tan across.

If you want max power and really ideal throttle response, the Dynojet kit is worth it.

If you like better MPG & are willing to not have the same growl in exchange, the stock carbs are worth it.

My 2 cents

Gary

[James England]

Dynojets made a huge difference on my XJR.

Same goes for Dyna coils

[Yahman]

I'm running a Dynojet stage 2 with a 4 into 2 Jardin and my mileage was 40.4 mpg last weekend going down I-5 at 65 to 70 mph. Best I have ever seen from my XJ.

Larry

[trbig]

Now, for grins, you should swap the other carbs' slides/diaphragms/needles to the stock carbs. See if you get the response back AND the MPG. Might take some tinkering, but to get the throttle response I like, in 3 different Dynojet kits I've done, I've had to put the needle's circlip on the top slot (Lowering the slide needles).

[KA1J]

Hi James, long time no hear. I still have that rear wheel bearing tucked away nice & safe for whenever I need it & thanks.

Yes, there is a noticeable difference but I find it most notable in subtleties and MPG. Subtleties like I used to start the bike with no enrichment and it would idle fine immediately. Now I need to use the enrichment to do the same and it takes maybe 3/4 mile of riding to where it idles normally without enrichment. The XJ11/XS11 series being such stock muscle bikes, that they are beefcakes right off the showroom floor. With that inherent power adding a bit more oomph isn't necessarily as obvious but the dynojets do add power.

My premise with this "experiment" is that most people who add dynojets do so not on a new and perfectly running carb but on a carb bank that already could stand a rebuild and then they either add the new jetting/needles/enlarge the slide orifice and re-install & simply ride on or, they rebuild/clean the carb at the same time and then add the dynojets during the rebuild. What I did was to thoroughly redo the original carb and add the dynojet mods without ever first having a pristine original set of carbs on it. The only carbs I had known on this bike were freshly and totally rebuilt and had the dynojet kit.

In the first instance adding the dynojets with or without thoroughly cleaning the carb & replacing the wear parts would make a positive difference but the unknown is how pristine those carbs were before the dynojets were added. My assumption is people were used to the performance of their carbs and wanted more. Maybe, if they would have rebuilt their carbs completely, they would have noticed an obvious performance gain? Maybe their original jets were buggered by a PO or themselves while trying to clean the jets and enlarging accidentally or on purpose the holes in the soft brass. Both the dynojets in carb bank one and the new mikuni jets in carb bank two were virgin.

So my assumption is that most people adding dynojets do so on a carb that already could stand a rebuild to pristine state and that some of the performance gain is from the rebuild itself, not the dynojets per se. Or... another way do do this (& if you only had one carb bank to work with) would be to completely rebuild the carbs to pristine with new stock jets and then run it awhile to get used to it and then do the dynojet mod and ride again the same day to observe any differences. I'm guessing most people don't do this and instead do it all at the same time & observe that difference which doesn't isolate how much difference there is from a complete rebuild & then, from the addition of Dynojets to that pristine rebuild.

I just rode the bike after letting it cool completely from yesterday and it required the enrichment to start instantly and the enrichment was used at 1/3 travel for maybe 3/4 mile and then I turned off. When I came to a stop light after turning off the enrichment, the idle was a tad below what it was another 2 miles down the road, but when I hit the main road and gave it WOT, there was a momentary hesitation and then its balls kicked in and it was very much like its old dynojet carbs self.

The Dynojets do make you run richer in all ways so that explains the lack of need for the enrichment circuit; with the Dynojet carbs in it I would not had to have used the enrichment circuit, it would have idled beautifully from the get-go and the acceleration would have been what I was used to within 1/4 mile. Now I have to operate it by the owners manual guidelines to make it run right but I think the acceleration after proper warm up is to pick a number, 95% of what it was.

Still to early to make a final decision but the 7 more MPG at today's gasoline prices on the interstate trip to me, easily makes up for a 5% loss in acceleration. I need to check out the difference around town & on country roads; if the MPG comes close to the same as before then I may well go back to the dynojets because I like the instant power as much as anybody.

Gary

[KA1J]

LOL, I see I type slower than people answering my post.

Let's do the time warp again...

Gary

[KA1J]

Now, for grins, you should swap the other carbs' slides/diaphragms/needles to the stock carbs. See if you get the response back AND the MPG. Might take some tinkering, but to get the throttle response I like, in 3 different Dynojet kits I've done, I've had to put the needle's circlip on the top slot (Lowering the slide needles).

Heyya TR,

What do you get for MPG? I can certainly move the slides et al over without removing the carbs, just lift the tank & remove... & interesting about lowering the needle, I was thinking about that as an option. As I recall, the suggested setting (which I used) was the 2nd slot so there is indeed another slot to lower the needles. Also, I really liked the dynojet needles, much longer and a more slender taper than stock. FWIW, I have a set of needles from an old XS (brass float era) I think... they had options for different settings, maybe not... it's been awhile...

Yahman, that's excellent MPG with stage 2. I know different kits allowed different settings but for the XJ11 there was only the stage 1 & stage 3 option. What do you usually get for MPG? & I do have your YICS eliminator installed.

Think I mentioned this in a different post but my Maxim-X was getting a best of 34 MPG. When the one emulsion tube was replaced and new pilot jets were put in all four carbs the max MPG immediately went to 48 MPG. That was all the proof I needed to know how important intact jets are in our bikes.

More about the Maxim-X/XJ11 in a separate thread.

Gary

[trbig]

I get 33-34 at best with the stage 2. Sounds like I might order some jets. I was thinking my XJ kits had a stage 1 and 2 option. No stage 3? Whichever, I went with the larger option because of the pod filters.

Looks like I may order a few new jets and see if my MPG goes up. A 7mpg jump would pay for the jets before too long.

Oh.. and moving that clip up one will get rid of that just off idle stumble. Mine did the same thing until I went to the last notch.

[KA1J]

TR,

I did get a 7 MPG jump in Highway MPG but I removed the carbs with the dynojet stage 1 and replaced them with a set of carbs with new stock Mikuni jets and pilot needle assemblies (needle, spring, spacer & o-ring). So I didn't get that change with the Dynojet kit.

As it is now, my bike with this "virgin" carb would not beat yours in a 1/4 mile race, with the dynojet kit, you will have more acceleration in all gears than I do. I'd be right close on your tail but without a doubt the dynojet kit gives you more power than the stock carbs provide.

What I'm seeing at this point is a tad less power but a noticeable increase in MPG. I'll need to see how the MPG is with around town driving and with rural road driving. It may be less of a change with those trials.

From my home in Groton, CT to Providence, RI I was able to see 5 bars on my gas gauge all that way, never before did I see that on this bike with the dynojet carbs.

I do miss the power of the Dynojet carbs. Like the MPG of the "virgin" carbs.

[Yahman]

I was running the stage 3 with a Kerker and 35 mpg was the best it would get with that setup. I changed it to the stage 1 (Your right, I was thinking it was a stage 2 ) and the Jardin last winter.

Larry

[KA1J]

The way companies assign model #'s & selections it's likely they had a stage 2 along the way. I mean, stage 1 & stage 3 but no stage 2? It's seemingly arbitrary numbering but there is a definite difference in the jetting.

I personally really like the way the bike performs with the Dynojets and without them in it, I feel the difference. With that, I also really like the MPG I am getting with this second set of carbs with stock jetting and the new Mikuni jets; I just got back from Boston and stayed in the upper 60's MPH range all the way back, made a couple stops because of rain & needing to pull out the rain gear & let the engine idle while I did that & one side trip off the interstate to get a bite to eat. I checked my mileage and I got 39.7 MPG (Got 40.6 on the way up).

If one has carbs with un-molested jets, ie: jets that nobody used wire or worse to clean them and they weren't buggered by a bad screwdriver application and they are free of obstruction, then I can't see any advantage to having virgin jets installed. Since I have no way to know what the history is to the jets I figured it's a few good six packs worth of change to get new jets so what's the loss in buying new ones?

From that experience with the Maxim-X carbs & the incredible increase in MPG when the buggered emulsion tube was replaced and the pilots were all replaced, I learned a very important truth about the importance of perfect jetting. (Yama calls the emulsion tubes "Main Nozzle"). That emulsion tube was ovaled ever so slightly and my friend who noticed that had a good replacement that he kindly provided me with as they are unobtanium today. I don't know if it was the new pilots that made the big difference or the replaced emulsion tube but I think the emulsion tube was a major part. So...

I think what would be a helpful thing for someone to do here would be to find a drill that is the exact size as the ID of the upper & lower lumens of our emulsion tubes and tell us what that is. What we could then do is stick the shaft end in the tubes and see if they are ovaled somewhat or truly round. Any ovaling from wear from the slide needles then they (and the needles) need to be replaced with another from the type our specific carbs need. I know there are different emulsion tubes depending on which model bike we have. My drill sizes are too limited or I'd do it myself & post it for the XJ carbs.

I'm going to open my carbs every couple of years and give them a good cleaning. I won't need to replace the throttle shaft seals again but a good cleaning of all the tubes and jets are a good maintenance idea and when I clean the jets, I'm not going to use anything metal or hard to clean them, I'll use brush bristles and carb cleaner to keep them un-molested and as-new.

Sure is fun to learn the right things to do and the simplest way of accomplishing that.

That said, I still am not looking forward to replacing the clutch and the fork oil seals (never done them before).... :/

Gary

[Rasputin]

That said, I still am not looking forward to replacing the clutch and the fork oil seals (never done them before).... :/

Gary

If you can do the carb work that you have already done then the rest is simple. Besides you have the best XS11 forum to help you with anything you care to ask about. Fork seals and clutch work are fairly simple compared to carbs. The unforunate part is that while doing fork seals one may decide to do triple tree bearings and all that while you are already that far. Never fear as they are easily dealt with as well.

[KA1J]

If you can do the carb work that you have already done then the rest is simple. Besides you have the best XS11 forum to help you with anything you care to ask about. Fork seals and clutch work are fairly simple compared to carbs. The unforunate part is that while doing fork seals one may decide to do triple tree bearings and all that while you are already that far. Never fear as they are easily dealt with as well.

Oh yes, the help on this forum has allowed me to get this bike running in pretty much as new condition. Last year thanks to the help here, I replaced the rings and I've completely redone the carbs and much more.

I've done forks on a XJ650 Maxim before but I've never done them on a XJ11 and I know there are differences. The worst concern is running into frozen parts or ones buggered by the PO. This bike was brutalized by at least one PO and I have had to spend hours undoing the damage he caused. Same with the issue of the clutch, I don't know what to expect and it would be good to have someone who knows what to do looking over my shoulder. Since that's not happening, I do have to rely on this forum for my answers. I did find one page by someone here on rebuilding the forks so that won't be much difficulty. I remember seeing one for the clutch as well, I'll have to search that one up.

Don't think I need to replace the triple tree bearings, they seem fine in this bike. I replaced the steering bearings with rollers in the 650 but that was my first "major" bit of repair and I had help from a friend who knew what to do and guided me through it.

Imagine how difficult all this would be if there were no internet or XS11 forum. I donated here last year, think it's time to do that again.

Gary

[Rasputin]

Thanks for reminding me about donations. I just made one myself. You will have no problems....we can't help you with, either in knowledge or parts or suppliers so quit worrying and have fun.

[KA1J]

Yes, I just donated $20 which is a pittance compared to the help I've gotten here.

Gary