Rejet when switching to DynaCoils?!?

[conquest87tsi]

Last season I added pod filters. I had originally used 140 mains, stock idle jets, diahpram needle raised to last notch, and floats at 24mm. The bike ran well through the entire range. With a nice tan plug. I installed dynacoils this winter and synced the bike and all was good. Was finally able to test ride last week and the bike fell on it's face over 5500to rpm. I swapped in fresh plugs and went out to ride in the 5500-8000 range. The plugs were white after 15min flogging. I have ordered the next 3 sizes up. Has anyone noticed this difference after dynas? I am guessing I am getting a more complete combustion now and need more fuel. I did find I got much worse fuel mileage. I used to get in the high 30'sl fuel economy. Now I can't get 90miles out of a tank. This is a special, and I did discover that the #1Iand 3 floats had a leak. 1 was leaking from the whole one side. Was able to solder #3 and had some spares. Found my oil level had greatly increased. So I may be carrying 1/2-1l of fuel in my crankcase.

[bikerphil]

I'd try putting the needles back to the center clip position first. 99% of the time, the bike will run best with them in the center. That needle height is what controls the fuel in the RPM range you are having problems with. Your 140 mains are probably big enough, shouldn't need anything bigger than 145.

[WMarshy]

I'd start with an oil change to be safe.

Are you still running the 140's? Sounds like you neet to jet up one size on the main maybe two after some miles and a plug chop. The needle controls midrange only and doesnt have much influence at 8000 rpm. What exhaust are you running?

Since you added some weight (solder) to number 3 float I would recommend checking float height with clear pvc hose hooked to the bowl drains to see it they are all at the same level. The solder might not affect the float height very much but if your looking for something to do on a rainy day it worth a look.

[conquest87tsi]

The 140s are currently installed. Before last weekend I had test rode and found the bike was running lean, so I had moved the needle from the second to last to the last notch and raised the float height from 25mm to 24mm and it did help quite a bit. However it is still very apparent that I need to move up on the mains. Once they come in I am going to start with 145's and go from there.

[motoman]

The 140s are currently installed. Before last weekend I had test rode and found the bike was running lean, so I had moved the needle from the second to last to the last notch and raised the float height from 25mm to 24mm and it did help quite a bit. However it is still very apparent that I need to move up on the mains. Once they come in I am going to start with 145's and go from there.

..........Hmmmm.......looks like you made two changes at once. One change at a time and test or it's gonna come back and bite you leaving you scratching your head as to what change had the effect, and what change if any to do next.

[TADracer]

I have said it a hundred times before....establish a baseline BEFORE you do any changes. Even with the pods and the Dynas, the stock jetting, timing, etc. is a good baseline to start. Go for the carbs last since they are only reacting to what the motor wants.

My SF has a number of mods, porting, 4-1 header, pods, Dyna coils, etc. and with the stock Mikunis I never had to go over a 142 main and a 42 pilot jet.

Sometimes with carb jetting less is more. Go back to stock and make one change at a time to find the sweet spot.

[conquest87tsi]

Well, I know this is a super old post, but it’s my own so I hope you forgive me. The ‘79 XS1100 special sat for a little over a year while I was on a deployment. I cleaned the carbs and rebuilt the calipers to ride it to the acreage I bought, where it sat for another three years while I worked on tractors and pickups. I finally had time to get her running again and it seems I’m pretty much back to where I was 7 years ago haha. When I tore into the carbs this time, it had 145 mains and the diaphragm needle was at the second from richest. I moved the needle to the center when cleaning the carbs. I set the floats at 24mm. I got them synced and it ran great without a load. On Sunday I took it for a ride and it started stumbling at 6,500rpm. I then put 147.5 mains in it, even though I feel like that is too rich. I just took it for a ride and it still stumbles starting around 6,500rpm, but it doesn’t seem as bad as with the 145 mains. I ran it up to 8,000rpm this time without feeling like I was going to grenade something. I’m starting to wonder if I am going down the wrong path with fuel changes. I adjusted valves years back. I remember having to do it twice for some reason, but I am pretty confident I got that right the second time anyway. I don’t expect an issue there to only effect 6,500rpm and above anyway. I only rode about 4 miles as it’s in the 50s here, but the plugs are actually really clean. I can’t imagine having to increase my mains again. Since it seems I started having troubles when the dynas were installed, I could swap in the original coils, but I don’t see any 1&4 or 2&3 correlation in the plugs. I do remember repairing the timing advance wires years ago. I could take a look at that.

Any ideas fellas? Any help is appreciated. I feel like an XS newb again after not touching this thing for so long.

[jetmechmarty]

I very recently put Dyna coils on my XS11. I was getting awful gas mileage. Replacing the stock coils with Dynas made no difference. None. I found the issue with my carburetors, repaired, and I’m good. My jetting is stock. Dyna coils. Jarring 4 into 1. 40 mpg.

[Schming]

Any ideas fellas? Any help is appreciated. I feel like an XS newb again after not touching this thing for so long.

A few posts up Tadracer gives some good advice.
I suggest put the stock 137.5 mains back in and make sure they're genuine Mikuni.

All my bikes have K&N air filters and the exhausts are opened up some with all stock jetting. I've adjusted the pilot screws to compensate and plugs are the right color and bike runs great.

[bikerphil]

Could try no air filter for a short ride to see if it will then exceed 6.5K. May be restricted air flow. If you have the factory air box, just remove the lower half.

[motoman]

As Schming stated, make sure any main jets used are Genuine Mikuni having the curly looking insignia stamped into them! Since Mikuni uses a certain flow rating to determine sizing. For example: a 110 K&L main jet is bout equivalent to a 115-117.5Mikuni main jet sizing. Mikuni manufacturing has a copy write patent on ALL their carb. components and cannot be exactly copied by law. Same goes for RD jets. RD main jets are a bit closer to correct sizing, but still oversized as per sizing stamped into them. So, IMO THAT would be a good start solving bikes running issue. BTW, same goes for pilot jetting sizes, which WILL definitely affect overall fuel drawing ability through all RPM ranges at some point.

[motoman]

To add, would like to know the NAME result of your main jets used at this time.

[Radioguylogs]

Emulsion Tubes?

Don't know if it helps, but I had the same issue with each of my XS750s (same carbs as you well know).

They would miss and stumble when I got to 6500-7000 RPM.

In both cases, there was aluminum/brass oxide caked up around the emulsion tubes in the carbs, above the Main jets.

I removed the emulsion tubes and gave them a through cleaning and the problems went away.

I had drained the fuel bowls each winter on these bikes. Eventually I concluded it was not necessarily better to drain the fuel bowls in winter.

[conquest87tsi]

Thanks for the reply’s guys.

All of the main gets I have used are from Mikuni packaging. I do also have 45 pilot jets installed. I’ll have to verify the make of them as I don’t remember. The bike has pod filters with 4-5” silicone hose velocity stacks. The exhaust is 2-1 V&H. I believe I may have a stock air box at my Dads that I could throw back in if I need to start fresh with stock jetting and such. It may be what needs to happen. I actually am very meticulous when cleaning the carbs. I take everything apart and soak the bodies and components in pinesol overnight, then scrub everything upon reassembly. I cleaned all of the emulsion tube holes out with copper wire before reassembling. If you guys think it makes sense to go back to stock, I think it’s time to do so. I’ve obviously struggled to get the high rpm range tuning for some time.

[bikerphil]

Don't know which pod filters you have, but some of the cheaper ones can be restrictive. I would try a short run with them off.