Rear cylinders not firing

[brianmac]

has he ruled out the old "throttle cables arcing out the 12V R side coil input lead after wearing thru the insualtion " possibility?

[DWD6955]

I noticed that was an issue on another forum so I made sure it wasn’t a factor on my bike. Appreciate the input

[DWD6955]

I mentioned earlier that all 4 plugs were carbon fouled equally and you mentioned that it was probably due to fuel mix issue. I did change to a Dynojet kit Stage 2 which requires a larger main jet. I installed the DJ 195 jets according to Dynojet recommendations and adjusted the mixture screw out 3 turns as recommended. Do you see any red flags that would contribute to carbon fouled plugs after Dynojet stage 2 mods, Main jet size, mixture screw adjustment?? Please advise!

[DWD6955]

I just realized I did not change the pilot jet as recommended for stage 2 jetting (Dynojet kit). Would that cause excessive carbon buil up on spark plugs? It’s an easy fix but knowing is a comfort. Also what is a recommended main jet size? Stock main jet is 165, stage 2 Dynojet recommendation is 200 & 3 turns out on mix screw. Sounds like a big jump on main jet size considering the cobra slip ons have baffles but I did install Baron xxx air intake as well. It’s big! I’m open to any suggestions.

[roadiemort]

Since most of us use the recommended Barons jet kit and have had great results with the RSC recommended jetting that DaveJ spent time perfecting with AFR readings on his gauge you will be struggling on your own, but you did save $10.00 lol.

[DWD6955]

I must have overlooked that post but would have definitely got the Barons if I knew in advance. I would taken Dave’s recommendation anytime! Actually the yamaha dealer recommended this kit but then again he was just a salesman. Is there by chance that anybody has experience with the Dynojet Kit? Saving $10 wouldn’t be worth the frustration and tuning it on my own must mean that I have to try the different jets in the kit until tuned right?? It’s a pain in the ass removing the carb every time I have to replace the main jet. Would an oversized main jet cause carbon build up on the spark plugs or would the pilot screw adjustment cause it? It’s obviously burning too rich. Just asking in case somebody would know. I don’t claim to be an expert, I learn as I go. I got it running good after installing the re-jet kit, replacing the cracked enricher cover and a new diaphragm but then the rear cylinders stopped firing while idling. Was it the carbon fouled spark plugs that caused no fire on rear cylinder in the first place? May have been but by that time it was too late. Sense all 4 plugs were fouled evenly, as Dave mentioned I may have a fuel delivery issue. Already jumped the gun and bought the ignitor unit or Dyno 3000. This was after I confirmed ignition coil, pick up coil, caps and all wiring continuity was good. As Dave mentioned I failed to check the inputs to the rear coil cylinder first but that will be another bridge I have to cross if I still have no fire after installing Dyno 3000. Learning as I go, paying in the process!!

[davej]

Yes a carbon fouled plug will cause a misfire. did you check for spark at the sparkplug wire? Or you just know the cylinder isn't firing so you are assuming there is no spark? If you are using a 200 main it is to big. I'm gonna change my approach to this issue, You have a dynojet kit, I'm gonna suggest installing a Mikuni 172.5 main jet and a Mikuni 40 pilot jet and put the clip in the 3rd groove on the needle with 1 silver washer and plastic spacer under the clip. Ride it for a few days and pull 1 plug from each cylinder to see how the plugs look. Notice I said "Mikuni" jets

[DWD6955]

I will do that Dave! I already replaced the main jet to a 175 because that’s all that was available in jet kit. I will adjust the needle as stated and see what happens. Will have to purchase a 172.5 Mikuni Jet. Yes, I assumed there was no spark because rear cylinder wasn’t firing so I didn’t test for spark. Mainly because the bike was idling perfect and cut out on my while running, so I assumed it was an electrical issue. Prob jumped way ahead of myself, right? I kinda assumed sense all 4 plugs were fouled equally that the rear plugs were not getting fire for some other reason, like Ignitor Unit. I’ve learned that I should have checked spark and input to the coil prior to assuming the ignitor unit was bad. I can still recover some cost for the Dyno3000 by selling the oem ignitor but at least I can back track to check these other / issues I failed to check.

[davej]

You will like the Dyna 3000 better than the OEM because you can adjust the rev limit to 5000 from the factory 4750. That little bit makes a difference in the way it will run. You can also adjust the timing to 34º instead of the 32º the factory has it set to. The bike will run noticeably different.

[DWD6955]

Dave is there an instance where I would need to advance the timing to 34 deg or is that just a preference? I do appreciate all your advice.

[davej]

it will make the bike more responsive when cranking on the throttle

[DWD6955]

I won’t try it unless I feel I need it, is there anything else that may be effected by advancing to 34 deg? I’ll read up on it but until then feel free to educate me if you don’t mind.

[DWD6955]

The good news is the bike fired up instantly on front and rear cylinders. Sounds great! I haven’t determined the cause because I’m dumb and learned a lot. Jumped way ahead of necessary steps in the troubleshooting process. May have been as simple as fouled plugs from carbon build up. Sucks! Will never know but I have the new Dyno3000, hopefully the correct jet size and may need to find tune the carb. Looking forward to the test ride tomorrow. 75 deg tomorrow…yah! Thanks again you’all!

[davej]

It should run fine on the 175 main jet in this colder weather but you will probably want to make some adjustments in the warmer weather. My guess is the jetting was way off and the carbon fouled plugs was what gave the misfire.

[DWD6955]

I am pleased to say that the bike runs better than when I bought it. The throttle response is unbelievable, more power and absolutely zero backfire from exhaust or carburetor. I couldn’t ask for a better turn out. The only difference is that it takes choke each time to start up, warm or cold, or a little throttle without choke and a very tiny slight miss. The miss is only noticeable to me most likely. I realize I’m not gonna get a perfect bike and I’m happy with results. Sounds better than a Harley in my opinion.

[davej]

these bikes are cold blooded and you will always need to use the choke. cold start should be pull choke, start bike, wait about 5 seconds or until it stumbles and then push in the choke only enough to get rid of the stumble. ride off and in about 2 miles you can push the choke in all the way. The choke will also need to be pulled after about a half hr shut off. Then pull the choke start the bike push the choke back in all the way and ride.

what pilot jet did you end up using? (brand and size)

I also forgot to tell you that you can cut a hole in the battery box right over the spot that the Dyna 3000 dip switches are to access the switches instead of removing the module to access them. This make it very easy to change things like the timing to try a different setting. Just remove the battery and the switches are right there.

[DWD6955]

Hey Dave, I did cut the hole in the battery box, seen that on your previous posts. Currently I have the Dynatek 175 main and 37.5 pilot jet. Still have needle set on 4th notch with no half spacers. Pms is set 3 turns out. I’m waiting on part Mikuni 172.5 jet to be delivered. Not sure if I need to make any changes, the slight miss seems to have gone away but I do smell a little raw gas from exhaust when idling. Not as bad as it was before switching from main 200 to 175. It never road better but I’m sure some tweaking is needed. After start up and the bike warms up on idle, without any choke, I notice a little black smoke coming from exhaust when I first give it some throttle to check throttle response. But the smoke goes away after a couple rotations of the throttle. Do you think by turning in pms a half turn would eliminate smoke? Absolutely zero back firing from exhaust or intake. That includes when riding, shifting and decelerating. I am really impressed with this Dyno3000. Initially the deceleration back firing in exhaust was partially caused by a crack in the enrichner cover. I replaced cover and diaphragm. What do you think? Any further adjustments that you would recommend?

[DWD6955]

Also, I’ve ordered an easy adjustment pms screw, when I remove the original pms screw will fuel drain from the float bowl? Im going to attempt this without removing carb from the bike sense I have access to the screw. I’ll make sure the fuel is shut off but will the bowl fuel drain out through that port? I’ll have a catch bowl just in case, just want to be ready. The bowl drain screw is on the back of the carb so I don’t want to pull the carb off to drain the bowl. I’m looking for a float bowl drain valve but not sure if it’s available for the BSR40.

[davej]

the float bowl drain is the tube on the bottom of the bowl and the screw next to it. If you are using the 37.5 pilot from the Dyna kit it flows the same amount of fuel as the stock Mikuni 35 pilot. I would buy the 40 mikuni pilot and install it and then put the screw at 2 1/2 turns out. The extended screw may change the pilot adjustment. I have heard the it has a taper different than the stock pilot.
If you have replaced the float bowl screws with Allen head screws you can remove the bowl without removing the carb to change jets.

[DWD6955]

Very good. I doubt I will replace pms screw then. Unfortunately I haven’t replaced float bowl screws with Allen head screws yet. But I will and get the pilot Mikuni 40 jet. Thanks Dave.

[DWD6955]

Will the pms adjustment possibly eliminate the black smoke from exhaust? Or the Mikuni 40 pilot jet? Or both? Either way I will make the changes when parts arrive. Without the pms easy screw replacement though.

[brianmac]

overthinking almost everything. a good mechanic can remove float bowl to rejet(not move needle clips tho) with carb in place, as long as there are hex bolts on carb bowl. . the PMS screw has a fine tip, a spring , and an O ring, which is super easy to either lose, destroy, or have 2 in place of one. not sure if a washer is in there, its hard to see, let alone access, getting the bowl and float off might help, carb . always work in a clean area, with nothing on floor to lose stuff in, and use white cloth under all carb work so u can see shit that drops,.

[davej]

I think the combination of the smaller 172.5 main jet and the screw at 2 1/2 turns will take care of it but you still may have to drop the clip to the 3 grove with a silver washer and plastic spacer on it.

[DWD6955]

Very good, will let you know how it turns out after I get parts and install. May not have warm enough weather to ride but at least the starting and pilot section can be checked.

[DWD6955]

Last couple evenings During cooler temps outside I get a little backfire out of the intake on start up with enricher/choke fully open. Once started seems to run fine after warming up. Warms up within 30 seconds. I haven’t received my Mikuni 40 pilot jet yet but would the back firing be caused by a lean condition in the pilot circuit? I still have Dynatek pilot jet 37.5 on the bike. I believe it was mentioned that is the same size that I took off basically…which was the stock pilot jet Mikuni size 35 jet. Or should I try adjusting pms screw? Currently at 3 turns out.

[Lug Nut]

Last couple evenings During cooler temps outside I get a little backfire out of the intake on start up with enricher/choke fully open. Once started seems to run fine after warming up. Warms up within 30 seconds. I haven’t received my Mikuni 40 pilot jet yet but would the back firing be caused by a lean condition in the pilot circuit? I still have Dynatek pilot jet 37.5 on the bike. I believe it was mentioned that is the same size that I took off basically…which was the stock pilot jet Mikuni size 35 jet. Or should I try adjusting pms screw? Currently at 3 turns out.

You're mixing and matching DynaJet and Mikuni jets. Not a good idea. If you want it to run right you need to get a Mikuni pilot a Mikuni Main a Barron's adjustable needle and follow the jetting instructions that have been gone over here. PMS should be two and a half out to start.

Also these bikes hate to run at idle without the air filter. They're very choppy without some restriction.

I wouldn't bother trying to run it or do anything you're just going to mess up your plugs if it's too rich. I'm attaching the chart to show you the difference between dynatech and Mikuni, left to right. You're trying to run your bike at idle with the wrong jetting You might as well buy new spark plugs at this point and put them in also. After you do the jetting that is lol. If you do the following completely it will work just fine. If you insist on mixing up Dynatech and Mikuni and doing it piece by piece you're just creating headaches for yourself.

Barron's jet kit with adjustable needle, take your current dynatech needle and dynatech Jets and put them aside in a safe place until you can throw them away lol.

clip on 4th Grove from blunt end with factory stock positions for washer/spacer
172.5 main jet 40 pilot jet
PMS 2.5 turns out
Hot idle set to 900.rpms with a tach
Fresh plugs.
seafoam in tank
Go ride

Period.

If you do this you will be fine if you keep replacing one jet at a time and mixing and matching your jetting and possibly refiling spark plugs then you will be back on her again...and again...and again.

If you want to reinvent the wheel and use your dynatech kit that would fine also. I have no idea on Earth why you would want to do that though. The Barrons jet kit is about $70 shipped with tax....But if you enjoy pulling your tank pulling your carb pulling spark plugs instead of riding by all means keep using the dynatek jetting parts. You can certainly get close with the dynatech adjustable needle but it's different You can look at the chart and get close with dynatech jets to the Mikuni Jets but it's not perfect.

If you have your stock 1700 CDI and would like to sell it let me know.

[DWD6955]

I’ve been corresponding with DaveJ and have been educated on the Dynojet vs Mikuni jets so yes, I’ve ordered the Mikuni jets and have no intention of mixing jets. It was just a general question about backfiring on start up. Would a lean condition cause a backfire at the air intake on start up regardless of what brand jet is used? As I said, I’ve ordered the right Mikuni jets, not easy to find. Most part suppliers do not tell you if the jets are true Mikuni brand. I actually found Jets r Us which itemizes Mikuni jets only for the BS series carb. From what I understand every bike has different air mix depending on your geographical location and elevation (mine 728’, yours in the area of 4000’) you are at as well, true? You live in Arizona, I live in the central Middle East. I agree there should be a starting point but leaving it alone isn’t in my creed. Call me a perfectionist or anal but in my opinion the better fine tuning the better fuel mileage and performance. Just my opinion! I’ve seen several different opinions on settings that work for that person and their bike even if it’s same bike. I have 53k miles, probably not the same exhaust and air intake some have and the new Dyno3000 CDI, my point….probably a different senerio than others. I do have the original CDI but I can’t say it’s any good or not. If you will take the time to read the entire long ass post you will understand why I’ve come to that conclusion.

[DWD6955]

Lug Nut, do you have a pilot jet conversion chart file? Just for future ref if I want to sell Dynojet kit in the future.

[DWD6955]

My awaiting parts: