MikesXS Electronic Ignition Kit

I’m digging in my old 78 past which was set up with UNI pods and fairly loud open mufflers here .@ work tho.
77 is jetted differently.
My 78E was running well one size up on main and one size up on pilot.
Needle took a few tries.
The 4,000 stumble was resolved .

Well, moving the clip to position 2 did NOT help... much worse! Back to the drawing board... maybe I'll try the clip at position 5.

Did you ride it yet,to see how it acts under load?

Yes, These tests are all under load... Ridng!

Ok, so with the needle clip in position 5, the '77 XS runs significantly better! There is no longer a stutter at about 4000 rpm, and the throttle response is basically smooth through the RPM's. Not sure if this means I should change my mains and re-adjust. I need to read the Carb Guide page 21 more tonight and see if I can improve it tomorrow! The Carb Guide seems to suggest trying the next main size down (in my case this would be 130) and adjusting the needles for it... and see if it pulls any better or worse.

Here's how it is sounding at the end of today!

https://photos.app.goo.gl/H3wdnctx8WJnUH2x5

rbirkey said:

Ok, so with the needle clip in position 5, the '77 XS runs significantly better! There is no longer a stutter at about 4000 rpm, and the throttle response is basically smooth through the RPM's. Not sure if this means I should change my mains and re-adjust. I need to read the Carb Guide page 21 more tonight and see if I can improve it tomorrow! The Carb Guide seems to suggest trying the next main size down (in my case this would be 130) and adjusting the needles for it... and see if it pulls any better or worse.

Click to expand...

I'm not the carb expert here, but I think you got it backwards. You had to go full rich with the needle. That would suggest you need to go up one the main and (probably) back to the center on the needle.

The bike is sounding good! You’re making progress. By the way that exhaust sounds throaty!

Videos are really cool ! Much better than the first now.
Great Looking bike too !
Good going

Yup - I think that Jim is right on this.

BTW - have you identified the year of the carbs? It is clear that they are BS38s - but the details of the carburetor changed from year to year (regardless of what year the bike actually was built) and if someone has swapped a set of say....’76 carbs onto that bike, then you’d need to use the ‘76 tuning specifications to get it to run properly.

As far as I know, the year of the engine doesn't matter at all - it is the year of the carbs that counts in terms of the proper adjustments.

My ‘76 XS650C had a float needle leak and I had a set of ‘78 carbs that I had bought as spare, so I swapped them on. I had been told that they had come off a running 1975 XS650B. When I started the bike, there was a lot of popping and especially on deceleration. It turned out that these 1978 carbs had been tuned using the 1975 settings - and that made them very lean. All I did was change the air screw setting to the ‘78 setting (see the carb guide chart) and my bike began to run perfectly.

There is a handy-dandy carb identification guide in the Carb Guide - all you need to do is remove an air filter and look at the configuration of holes in the carb intake bell. The number of holes tells the tale about the year of those carbs and thus, how to adjust them.

MaxPete... I have verified these are the "M" carbs standard for the 1977 XS650D... thanks!

Today, I have tried a couple of things to see if I can improve the tuning. I changed the 127.5 mains to 126 mains and left the needle on the 5th clip setting. I did not run as well under load.. increased stutters at 4-5K RPM. So, I put the needles on the 4th setting and that was even worse. Next, I went back to the 127.5 mains (which I am pretty confident is the correct main), and put the needle clip on position 5 and added a single shim. This did not help with the 4-5K stutters. I am next going to try putting the clip on the 3rd or middle position with the 127.5 mains.

The air needle is set at 1.5 turns out, plus or minus a 1/8 turn, while I am test riding with each set up.

I am SO CLOSE I can feel it... there is one last setting somewhere to get rid of that higher RPM stutter.

Hi, I'm back!

I am still trying to get this 1977 Yamaha XS650D running well at higher RPM's. It bogs down around 45 MPH or 3000 RPM. It idles and runs well below that. I've tried everything I can think of including:

• Check Cam Chain Tension - Good according to manual
• Check Timing - seems to be right. The timing mark is on "Ignite" at idle, and moves forward to "Advance" when throttle applied as in the video
• Check Carb sync - seems to be equal
• Check Plugs - seem to be gapped correct and to appear clean - no oil or wetness
• I've increased and decreased the main jets, and it seems to make little or no difference. They were at 127.5 this morning and I've increased them to 130... no perceived change.
• The idle jets are at 27.5
• Needle is stock with E clip on 5th slot from the top end
• Air screws are 1.5 turns out
• I am using Uni Pod Filters
• I have the Yamaha Performance mufflers

Here is a video running the throttle up to 5000 RPM

https://photos.app.goo.gl/Ui9kgvR8jprdU1RdA

Any suggestions?

Thanks,

Randy

You might try a test run with the filters removed. Those short UNIs with the capped ends don't flow very well, not much better, if any better, than the stock airbox. It's very strange that you have to set the needles at their highest, richest position. With larger than stock mains and pilots, the bike should run awful like that. The jet sizes and needle setting (one step leaner than stock) I recommended follow the normal guidelines for how you rejet any of the 650 carbs for mods. You increase the pilots one or two, increase the mains one up to as much as four, and usually have to lean the needles a step because of the larger mains. Yours isn't fitting into these normal guidelines at all. Have you checked your needles to insure they are the correct 4M1 stock needles for your year carb set? And you are assembling the slide and needle correctly - needle w/ clip dropped in the slide first with the thick plastic disc on top? The last thing you could do is closely examine your needle jet. It should be a Z-8 and be a snug slip fit into the carb body if it's sealing o-ring is good. Maybe it's worn out or something. If the carbs were really gummed up and sat that way for a while, the jet can be eaten away inside making it larger and richer.

Thanks for your reply. I did some further testing and trying options today:

• Installed the original 4M1 needles, instead of using the new ones (marked as Y55-S but claims to be the same as 4M1) I got in the MikesXS carb rebuild kit (a kit by Keyster).
• Moved the E-clip to the 2nd slot down from the top, which I inferred from your note as being the "lean the needles a step" comment. I've never been clear on which direction the e-clip is supposed to move to be leaner. I had been moving it the other direction.
• I switched back to the 127.5 mains
• Pilot jets the same
• Checked timing again - seems OK
• Removed the UNI pods
• Re-balanced carbs (very small re-adjustment)
• FYI - I have already replaced all the gaskets and seals and needle jets, float valves, float height in the carbs as part of a complete rebuild kit.

All of this has actually made it run worse. It now sputters, has less power, and cuts out at an even lower RPM. Can't get going more than 30-35 MPH. It's really frustrating as I can't seem to find this engine's sweet spot.

I'm assuming that the idle jet is OK since it starts, idles and runs well at low RPM's. I assume that I still need to find the correct combo of main and needle setting. Any suggestions?

Don't assume, inspect. You might start by checking fuel level with a sight tube.

Hi grizld1 - thanks for the note. I am not familiar with what you are suggesting. Can you supply more info or point me in a direction for additional resources? Are you talking about fuel level in the gas tank, or in the carbs... or both? I'm not sure what the connection would be with "fuel level" and what I am experiencing. Sorry if this request is too novice for you.

This gives a lot of faith in the quality and accuracy of the kit....

gggGary said:

This gives a lot of faith in the quality and accuracy of the kit....
View attachment 146732

Click to expand...

Indeed. The point Gary is making is that the "TX" designation was only used for the <I think> '73 and '74 models while the 1976 and on-wards bikes were all labelled "XS650" (with suffix letters that indicated the year and whether the bike was one of the "cruiser" styled models). So, a '75 was an XS650B, the '76 was a "C", etc.

Anyhow - many people have found the those aftermarket generic carb kits contain lots of parts - many of which are either out of spec or simply not applicable to the captioned model. The other thing is that with these old bikes having been built for so many years in such large numbers, there has been a great deal of parts swapping around from one to another. You might have a 1977 registered bike, and the carbs might look like 1977 carbs, but some of the parts in them may simply not be correct for that bike. The parts will all fit - because the carbs are all Mikuni BS38s - but they will not function properly together.

The one other issue which I don't think you have mentioned is the float bowl fuel level - as pointed out by Grizld1.

I have simply checked mine statically and that has always worked fine but you can check it while running. You will need a bayonette fitting that can thread into the bottom of each the float bowl (thus, you'll need two) and a short piece of tubing to run up the side of the carb as a "sight glass". That will confirm the float bowl fuel level while the bike is running (it should be just about level with the joint between the bowl and carb body if I recall correctly). There are photos on the Forum of this set-up (I know that Mailman has done it and posted a photo). Perhaps your float level is set a bit too low and the engine is running lean at higher RPMs - which could account for the "miss".

From the video you posted, it sounds pretty good - until you get that miss at 5,000+RPM. I'm sure you are close - but keep searching because it certainly sounds like something is just a bit off. 2M's suggestion on the air filters is definitely a possibility - these bikes seem to be fairly sensitive to intake irregularities.

Cheers,

Pete

Yes, some of these things have been mentioned in this thread before about the MikesXS and aftermarket carb rebuild kits. However, the needles I am currently using are the originals as far as I can tell, and the jets were purchased through Niche Cycles and are Mikuni. The carbs appear to be the correct ones for this year bike. Only the gaskets, float valves and air mix screws are from the kit at this point. The float heights were adjusted when I did the rebuild and one was definitely off. I will look for and try the float bowl measurement... Thanks!

Re. sight tube fuel level inspection, gggGary offered the idea of drilling out a 6x1.0 mm. grease zerk for use as a float bowl inspection plug, and commercial inspection plugs are also available. Level the bike, attach a piece of clear tubing to the zerk (or barb on a ready-made plug), hold the line beside the carburetor, and open the petcock. Fuel should rise no higher than the car body flange and no lower than 2 mm.below it. For more, use the search window, it actually works well here!